This is gpgme.info, produced by makeinfo version 6.3 from gpgme.texi. Copyright © 2002–2008, 2010, 2012–2018 g10 Code GmbH. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. The text of the license can be found in the section entitled “Copying”. This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. INFO-DIR-SECTION GNU Libraries START-INFO-DIR-ENTRY * GPGME: (gpgme). Adding support for cryptography to your program. END-INFO-DIR-ENTRY This file documents the GPGME library. This is Edition 1.12.1-beta100, last updated 3 December 2018, of ‘The ‘GnuPG Made Easy’ Reference Manual’, for Version 1.12.1-beta100. Copyright © 2002–2008, 2010, 2012–2018 g10 Code GmbH. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. The text of the license can be found in the section entitled “Copying”. This document is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.  File: gpgme.info, Node: Top, Next: Introduction, Up: (dir) Main Menu ********* This is Edition 1.12.1-beta100, last updated 3 December 2018, of ‘The ‘GnuPG Made Easy’ Reference Manual’, for Version 1.12.1-beta100 of the GPGME library. * Menu: * Introduction:: How to use this manual. * Preparation:: What you should do before using the library. * Protocols and Engines:: Supported crypto protocols. * Algorithms:: Supported algorithms. * Error Handling:: Error numbers and their meanings. * Exchanging Data:: Passing data to and from GPGME. * Contexts:: Handling GPGME contexts. Appendices * UI Server Protocol:: The GnuPG UI Server Protocol. * Debugging:: How to solve problems. * Deprecated Functions:: Documentation of deprecated functions. * Library Copying:: The GNU Lesser General Public License says how you can copy and share ‘GnuPG Made Easy’. * Copying:: The GNU General Public License says how you can copy and share this manual. Indices * Concept Index:: Index of concepts and programs. * Function and Data Index:: Index of functions, variables and data types. — The Detailed Node Listing — Introduction * Getting Started:: Purpose of the manual, and how to use it. * Features:: Reasons to install and use GPGME. * Overview:: Basic architecture of the GPGME library. Preparation * Header:: What header file you need to include. * Building the Source:: Compiler options to be used. * Largefile Support (LFS):: How to use GPGME with LFS. * Using Automake:: Compiler options to be used the easy way. * Using Libtool:: Avoiding compiler options entirely. * Library Version Check:: Getting and verifying the library version. * Signal Handling:: How GPGME affects signal handling. * Multi-Threading:: How GPGME can be used in an MT environment. Protocols and Engines * Engine Version Check:: Verifying the engine version. * Engine Information:: Obtaining more information about the engines. * Engine Configuration:: Changing the engine configuration. * OpenPGP:: Support for the OpenPGP protocol. * Cryptographic Message Syntax:: Support for the CMS. Algorithms * Public Key Algorithms:: A list of all public key algorithms. * Hash Algorithms:: A list of all hash algorithms. Error Handling * Error Values:: The error value and what it means. * Error Codes:: A list of important error codes. * Error Sources:: A list of important error sources. * Error Strings:: How to get a descriptive string from a value. Exchanging Data * Creating Data Buffers:: Creating new data buffers. * Destroying Data Buffers:: Releasing data buffers. * Manipulating Data Buffers:: Operations on data buffers. Creating Data Buffers * Memory Based Data Buffers:: Creating memory based data buffers. * File Based Data Buffers:: Creating file based data buffers. * Callback Based Data Buffers:: Creating callback based data buffers. Manipulating Data Buffers * Data Buffer I/O Operations:: I/O operations on data buffers. * Data Buffer Meta-Data:: Meta-data manipulation of data buffers. * Data Buffer Convenience:: Convenience function for data buffers. Contexts * Creating Contexts:: Creating new GPGME contexts. * Destroying Contexts:: Releasing GPGME contexts. * Result Management:: Managing the result of crypto operations. * Context Attributes:: Setting properties of a context. * Key Management:: Managing keys with GPGME. * Trust Item Management:: Managing trust items with GPGME. * Crypto Operations:: Using a context for cryptography. * Miscellaneous:: Miscellaneous operations. * Run Control:: Controlling how operations are run. Context Attributes * Protocol Selection:: Selecting the protocol used by a context. * Crypto Engine:: Configuring the crypto engine. * Setting the Sender:: How to tell the engine the sender. * ASCII Armor:: Requesting ASCII armored output. * Text Mode:: Choosing canonical text mode. * Offline Mode:: Choosing offline mode. * Included Certificates:: Including a number of certificates. * Key Listing Mode:: Selecting key listing mode. * Passphrase Callback:: Getting the passphrase from the user. * Progress Meter Callback:: Being informed about the progress. * Status Message Callback:: Status messages received from gpg. * Locale:: Setting the locale of a context. Key Management * Key objects:: Description of the key structures. * Listing Keys:: Browsing the list of available keys. * Information About Keys:: Requesting detailed information about keys. * Manipulating Keys:: Operations on keys. * Generating Keys:: Creating new key pairs. * Signing Keys:: Adding key signatures to public keys. * Exporting Keys:: Retrieving key data from the key ring. * Importing Keys:: Adding keys to the key ring. * Deleting Keys:: Removing keys from the key ring. * Changing Passphrases:: Change the passphrase of a key. * Changing TOFU Data:: Changing data pertaining to TOFU. * Advanced Key Editing:: Advanced key edit operation. Trust Item Management * Listing Trust Items:: Browsing the list of available trust items. * Manipulating Trust Items:: Operations on trust items. Crypto Operations * Decrypt:: Decrypting a ciphertext. * Verify:: Verifying a signature. * Decrypt and Verify:: Decrypting a signed ciphertext. * Sign:: Creating a signature. * Encrypt:: Encrypting a plaintext. Sign * Selecting Signers:: How to choose the keys to sign with. * Creating a Signature:: How to create a signature. * Signature Notation Data:: How to add notation data to a signature. Encrypt * Encrypting a Plaintext:: How to encrypt a plaintext. Miscellaneous * Running other Programs:: Running other Programs. * Using the Assuan protocol:: Using the Assuan protocol. * Checking for updates:: How to check for software updates. Run Control * Waiting For Completion:: Waiting until an operation is completed. * Using External Event Loops:: Advanced control over what happens when. * Cancellation:: How to end pending operations prematurely. Using External Event Loops * I/O Callback Interface:: How I/O callbacks are registered. * Registering I/O Callbacks:: How to use I/O callbacks for a context. * I/O Callback Example:: An example how to use I/O callbacks. * I/O Callback Example GTK+:: How to integrate GPGME in GTK+. * I/O Callback Example GDK:: How to integrate GPGME in GDK. * I/O Callback Example Qt:: How to integrate GPGME in Qt.  File: gpgme.info, Node: Introduction, Next: Preparation, Prev: Top, Up: Top 1 Introduction ************** ‘GnuPG Made Easy’ (GPGME) is a C language library that allows to add support for cryptography to a program. It is designed to make access to public key crypto engines like GnuPG or GpgSM easier for applications. GPGME provides a high-level crypto API for encryption, decryption, signing, signature verification and key management. GPGME uses GnuPG and GpgSM as its backends to support OpenPGP and the Cryptographic Message Syntax (CMS). * Menu: * Getting Started:: Purpose of the manual, and how to use it. * Features:: Reasons to install and use GPGME. * Overview:: Basic architecture of the GPGME library.  File: gpgme.info, Node: Getting Started, Next: Features, Up: Introduction 1.1 Getting Started =================== This manual documents the GPGME library programming interface. All functions and data types provided by the library are explained. The reader is assumed to possess basic knowledge about cryptography in general, and public key cryptography in particular. The underlying cryptographic engines that are used by the library are not explained, but where necessary, special features or requirements by an engine are mentioned as far as they are relevant to GPGME or its users. This manual can be used in several ways. If read from the beginning to the end, it gives a good introduction into the library and how it can be used in an application. Forward references are included where necessary. Later on, the manual can be used as a reference manual to get just the information needed about any particular interface of the library. Experienced programmers might want to start looking at the examples at the end of the manual, and then only read up those parts of the interface which are unclear. The documentation for the language bindings is currently not included in this manual. Those languages bindings follow the general programming model of GPGME but may provide some extra high level abstraction on top of the GPGME style API. For now please see the README files in the ‘lang/’ directory of the source distribution.  File: gpgme.info, Node: Features, Next: Overview, Prev: Getting Started, Up: Introduction 1.2 Features ============ GPGME has a couple of advantages over other libraries doing a similar job, and over implementing support for GnuPG or other crypto engines into your application directly. it’s free software Anybody can use, modify, and redistribute it under the terms of the GNU Lesser General Public License (*note Library Copying::). it’s flexible GPGME provides transparent support for several cryptographic protocols by different engines. Currently, GPGME supports the OpenPGP protocol using GnuPG as the backend, and the Cryptographic Message Syntax using GpgSM as the backend. it’s easy GPGME hides the differences between the protocols and engines from the programmer behind an easy-to-use interface. This way the programmer can focus on the other parts of the program, and still integrate strong cryptography in his application. Once support for GPGME has been added to a program, it is easy to add support for other crypto protocols once GPGME backends provide them. it’s language friendly GPGME comes with languages bindings for several common programming languages: Common Lisp, C++, Python 2, and Python 3.  File: gpgme.info, Node: Overview, Prev: Features, Up: Introduction 1.3 Overview ============ GPGME provides a data abstraction that is used to pass data to the crypto engine, and receive returned data from it. Data can be read from memory or from files, but it can also be provided by a callback function. The actual cryptographic operations are always set within a context. A context provides configuration parameters that define the behaviour of all operations performed within it. Only one operation per context is allowed at any time, but when one operation is finished, you can run the next operation in the same context. There can be more than one context, and all can run different operations at the same time. Furthermore, GPGME has rich key management facilities including listing keys, querying their attributes, generating, importing, exporting and deleting keys, and acquiring information about the trust path. With some precautions, GPGME can be used in a multi-threaded environment, although it is not completely thread safe and thus needs the support of the application.  File: gpgme.info, Node: Preparation, Next: Protocols and Engines, Prev: Introduction, Up: Top 2 Preparation ************* To use GPGME, you have to perform some changes to your sources and the build system. The necessary changes are small and explained in the following sections. At the end of this chapter, it is described how the library is initialized, and how the requirements of the library are verified. * Menu: * Header:: What header file you need to include. * Building the Source:: Compiler options to be used. * Largefile Support (LFS):: How to use GPGME with LFS. * Using Automake:: Compiler options to be used the easy way. * Using Libtool:: Avoiding compiler options entirely. * Library Version Check:: Getting and verifying the library version. * Signal Handling:: How GPGME affects signal handling. * Multi-Threading:: How GPGME can be used in an MT environment.  File: gpgme.info, Node: Header, Next: Building the Source, Up: Preparation 2.1 Header ========== All interfaces (data types and functions) of the library are defined in the header file ‘gpgme.h’. You must include this in all programs using the library, either directly or through some other header file, like this: #include The name space of GPGME is ‘gpgme_*’ for function names and data types and ‘GPGME_*’ for other symbols. Symbols internal to GPGME take the form ‘_gpgme_*’ and ‘_GPGME_*’. Because GPGME makes use of the GPG Error library, using GPGME will also use the ‘GPG_ERR_*’ name space directly, and the ‘gpg_err*’, ‘gpg_str*’, and ‘gpgrt_*’ name space indirectly.  File: gpgme.info, Node: Building the Source, Next: Largefile Support (LFS), Prev: Header, Up: Preparation 2.2 Building the Source ======================= If you want to compile a source file including the ‘gpgme.h’ header file, you must make sure that the compiler can find it in the directory hierarchy. This is accomplished by adding the path to the directory in which the header file is located to the compilers include file search path (via the ‘-I’ option). However, the path to the include file is determined at the time the source is configured. To solve this problem, gpgme ships with a small helper program ‘gpgme-config’ that knows about the path to the include file and other configuration options. The options that need to be added to the compiler invocation at compile time are output by the ‘--cflags’ option to ‘gpgme-config’. The following example shows how it can be used at the command line: gcc -c foo.c `gpgme-config --cflags` Adding the output of ‘gpgme-config --cflags’ to the compiler command line will ensure that the compiler can find the GPGME header file. A similar problem occurs when linking the program with the library. Again, the compiler has to find the library files. For this to work, the path to the library files has to be added to the library search path (via the ‘-L’ option). For this, the option ‘--libs’ to ‘gpgme-config’ can be used. For convenience, this option also outputs all other options that are required to link the program with GPGME (in particular, the ‘-lgpgme’ option). The example shows how to link ‘foo.o’ with the GPGME library to a program ‘foo’. gcc -o foo foo.o `gpgme-config --libs` Of course you can also combine both examples to a single command by specifying both options to ‘gpgme-config’: gcc -o foo foo.c `gpgme-config --cflags --libs` If you need to detect the installed language bindings you can use list them using: gpgme-config --print-lang or test for the availability using gpgme-config --have-lang=python && echo 'Bindings for Pythons available'  File: gpgme.info, Node: Largefile Support (LFS), Next: Using Automake, Prev: Building the Source, Up: Preparation 2.3 Largefile Support (LFS) =========================== GPGME is compiled with largefile support by default, if it is available on the system. This means that GPGME supports files larger than two gigabyte in size, if the underlying operating system can. On some systems, largefile support is already the default. On such systems, nothing special is required. However, some systems provide only support for files up to two gigabyte in size by default. Support for larger file sizes has to be specifically enabled. To make a difficult situation even more complex, such systems provide two different types of largefile support. You can either get all relevant functions replaced with alternatives that are largefile capable, or you can get new functions and data types for largefile support added. Those new functions have the same name as their smallfile counterparts, but with a suffix of 64. An example: The data type ‘off_t’ is 32 bit wide on GNU/Linux PC systems. To address offsets in large files, you can either enable largefile support add-on. Then a new data type ‘off64_t’ is provided, which is 64 bit wide. Or you can replace the existing ‘off_t’ data type with its 64 bit wide counterpart. All occurrences of ‘off_t’ are then automagically replaced. As if matters were not complex enough, there are also two different types of file descriptors in such systems. This is important because if file descriptors are exchanged between programs that use a different maximum file size, certain errors must be produced on some file descriptors to prevent subtle overflow bugs from occurring. As you can see, supporting two different maximum file sizes at the same time is not at all an easy task. However, the maximum file size does matter for GPGME, because some data types it uses in its interfaces are affected by that. For example, the ‘off_t’ data type is used in the ‘gpgme_data_seek’ function, to match its POSIX counterpart. This affects the call-frame of the function, and thus the ABI of the library. Furthermore, file descriptors can be exchanged between GPGME and the application. For you as the user of the library, this means that your program must be compiled in the same file size mode as the library. Luckily, there is absolutely no valid reason for new programs to not enable largefile support by default and just use that. The compatibility modes (small file sizes or dual mode) can be considered an historic artefact, only useful to allow for a transitional period. On POSIX platforms GPGME is compiled using largefile support by default. This means that your application must do the same, at least as far as it is relevant for using the ‘gpgme.h’ header file. All types in this header files refer to their largefile counterparts, if they are different from any default types on the system. On 32 and 64 bit Windows platforms ‘off_t’ is declared as 32 bit signed integer. There is no specific support for LFS in the C library. The recommendation from Microsoft is to use the native interface (‘CreateFile’ et al.) for large files. Released binary versions of GPGME (libgpgme-11.dll) have always been build with a 32 bit ‘off_t’. To avoid an ABI break we stick to this convention for 32 bit Windows by using ‘long’ there. GPGME versions for 64 bit Windows have never been released and thus we are able to use ‘int64_t’ instead of ‘off_t’ there. For easier migration the typedef ‘gpgme_off_t’ has been defined. The reason we cannot use ‘off_t’ directly is that some toolchains (e.g. mingw64) introduce a POSIX compatible hack for ‘off_t’. Some widely used toolkits make use of this hack and in turn GPGME would need to use it also. However, this would introduce an ABI break and existing software making use of libgpgme might suffer from a severe break. Thus with version 1.4.2 we redefined all functions using ‘off_t’ to use ‘gpgme_off_t’ which is defined as explained above. This way we keep the ABI well defined and independent of any toolchain hacks. The bottom line is that LFS support in GPGME is only available on 64 bit versions of Windows. On POSIX platforms you can enable largefile support, if it is different from the default on the system the application is compiled on, by using the Autoconf macro ‘AC_SYS_LARGEFILE’. If you do this, then you don’t need to worry about anything else: It will just work. In this case you might also want to use ‘AC_FUNC_FSEEKO’ to take advantage of some new interfaces, and ‘AC_TYPE_OFF_T’ (just in case). If you do not use Autoconf, you can define the preprocessor symbol ‘_FILE_OFFSET_BITS’ to 64 _before_ including any header files, for example by specifying the option ‘-D_FILE_OFFSET_BITS=64’ on the compiler command line. You will also want to define the preprocessor symbol ‘LARGEFILE_SOURCE’ to 1 in this case, to take advantage of some new interfaces. If you do not want to do either of the above, you probably know enough about the issue to invent your own solution. Just keep in mind that the GPGME header file expects that largefile support is enabled, if it is available. In particular, we do not support dual mode (‘_LARGEFILE64_SOURCE’).  File: gpgme.info, Node: Using Automake, Next: Using Libtool, Prev: Largefile Support (LFS), Up: Preparation 2.4 Using Automake ================== It is much easier if you use GNU Automake instead of writing your own Makefiles. If you do that you do not have to worry about finding and invoking the ‘gpgme-config’ script at all. GPGME provides an extension to Automake that does all the work for you. -- Macro: AM_PATH_GPGME ([MINIMUM-VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) -- Macro: AM_PATH_GPGME_PTH ([MINIMUM-VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) -- Macro: AM_PATH_GPGME_PTHREAD ([MINIMUM-VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) Check whether GPGME (at least version MINIMUM-VERSION, if given) exists on the host system. If it is found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, if given. Additionally, the function defines ‘GPGME_CFLAGS’ to the flags needed for compilation of the program to find the ‘gpgme.h’ header file, and ‘GPGME_LIBS’ to the linker flags needed to link the program to the GPGME library. If the used helper script does not match the target type you are building for a warning is printed and the string ‘libgcrypt’ is appended to the variable ‘gpg_config_script_warn’. ‘AM_PATH_GPGME_PTH’ checks for the version of GPGME that can be used with GNU Pth, and defines ‘GPGME_PTH_CFLAGS’ and ‘GPGME_PTH_LIBS’. ‘AM_PATH_GPGME_PTHREAD’ checks for the version of GPGME that can be used with the native pthread implementation, and defines ‘GPGME_PTHREAD_CFLAGS’ and ‘GPGME_PTHREAD_LIBS’. Since version 1.8.0 this is no longer required to GPGME_PTHREAD as GPGME itself is thread safe. This macro searches for ‘gpgme-config’ along the PATH. If you are cross-compiling, it is useful to set the environment variable ‘SYSROOT’ to the top directory of your target. The macro will then first look for the helper program in the ‘bin’ directory below that top directory. An absolute directory name must be used for ‘SYSROOT’. Finally, if the configure command line option ‘--with-gpgme-prefix’ is used, only its value is used for the top directory below which the helper script is expected. You can use the defined Autoconf variables like this in your ‘Makefile.am’: AM_CPPFLAGS = $(GPGME_CFLAGS) LDADD = $(GPGME_LIBS)  File: gpgme.info, Node: Using Libtool, Next: Library Version Check, Prev: Using Automake, Up: Preparation 2.5 Using Libtool ================= The easiest way is to just use GNU Libtool. If you use libtool, and link to ‘libgpgme.la’, ‘libgpgme-pth.la’ or ‘libgpgme-pthread.la’ respectively, everything will be done automatically by Libtool.  File: gpgme.info, Node: Library Version Check, Next: Signal Handling, Prev: Using Libtool, Up: Preparation 2.6 Library Version Check ========================= -- Function: const char * gpgme_check_version (const char *REQUIRED_VERSION) The function ‘gpgme_check_version’ has four purposes. It can be used to retrieve the version number of the library. In addition it can verify that the version number is higher than a certain required version number. In either case, the function initializes some sub-systems, and for this reason alone it must be invoked early in your program, before you make use of the other functions in GPGME. The last purpose is to run selftests. As a side effect for W32 based systems, the socket layer will get initialized. If REQUIRED_VERSION is ‘NULL’, the function returns a pointer to a statically allocated string containing the version number of the library. If REQUIRED_VERSION is not ‘NULL’, it should point to a string containing a version number, and the function checks that the version of the library is at least as high as the version number provided. In this case, the function returns a pointer to a statically allocated string containing the version number of the library. If REQUIRED_VERSION is not a valid version number, or if the version requirement is not met, the function returns ‘NULL’. If you use a version of a library that is backwards compatible with older releases, but contains additional interfaces which your program uses, this function provides a run-time check if the necessary features are provided by the installed version of the library. If a selftest fails, the function may still succeed. Selftest errors are returned later when invoking ‘gpgme_new’ or ‘gpgme-data_new’, so that a detailed error code can be returned (historically, ‘gpgme_check_version’ does not return a detailed error code). -- Function: int gpgme_set_global_flag (const char *NAME, const char *VALUE) SINCE: 1.4.0 On some systems it is not easy to set environment variables and thus hard to use GPGME’s internal trace facility for debugging. This function has been introduced as an alternative way to enable debugging and for a couple of other rarely used tweaks. It is important to assure that only one thread accesses GPGME functions between a call to this function and after the return from the call to ‘gpgme_check_version’. All currently supported features require that this function is called as early as possible — even before ‘gpgme_check_version’. The features are identified by the following values for NAME: ‘debug’ To enable debugging use the string “debug” for NAME and VALUE identical to the value used with the environment variable ‘GPGME_DEBUG’. ‘disable-gpgconf’ Using this feature with any VALUE disables the detection of the gpgconf program and thus forces GPGME to fallback into the simple OpenPGP only mode. It may be used to force the use of GnuPG-1 on systems which have both GPG versions installed. Note that in general the use of ‘gpgme_set_engine_info’ is a better way to select a specific engine version. ‘gpgconf-name’ ‘gpg-name’ Set the name of the gpgconf respective gpg binary. The defaults are ‘GNU/GnuPG/gpgconf’ and ‘GNU/GnuPG/gpg’. Under Unix the leading directory part is ignored. Under Windows the leading directory part is used as the default installation directory; the ‘.exe’ suffix is added by GPGME. Use forward slashed even under Windows. ‘require-gnupg’ Set the minimum version of the required GnuPG engine. If that version is not met, GPGME fails early instead of trying to use the existent version. The given version must be a string with major, minor, and micro number. Example: "2.1.0". ‘w32-inst-dir’ On Windows GPGME needs to know its installation directory to find its spawn helper. This is in general no problem because a DLL has this information. Some applications however link statically to GPGME and thus GPGME can only figure out the installation directory of this application which may be wrong in certain cases. By supplying an installation directory as value to this flag, GPGME will assume that that directory is the installation directory. This flag has no effect on non-Windows platforms. This function returns ‘0’ on success. In contrast to other functions the non-zero return value on failure does not convey any error code. For setting “debug” the only possible error cause is an out of memory condition; which would exhibit itself later anyway. Thus the return value may be ignored. After initializing GPGME, you should set the locale information to the locale required for your output terminal. This locale information is needed for example for the curses and Gtk pinentry. Here is an example of a complete initialization: #include #include void init_gpgme (void) { /* Initialize the locale environment. */ setlocale (LC_ALL, ""); gpgme_check_version (NULL); gpgme_set_locale (NULL, LC_CTYPE, setlocale (LC_CTYPE, NULL)); #ifdef LC_MESSAGES gpgme_set_locale (NULL, LC_MESSAGES, setlocale (LC_MESSAGES, NULL)); #endif } Note that you are highly recommended to initialize the locale settings like this. GPGME can not do this for you because it would not be thread safe. The conditional on LC_MESSAGES is only necessary for portability to W32 systems.  File: gpgme.info, Node: Signal Handling, Next: Multi-Threading, Prev: Library Version Check, Up: Preparation 2.7 Signal Handling =================== The GPGME library communicates with child processes (the crypto engines). If a child process dies unexpectedly, for example due to a bug, or system problem, a ‘SIGPIPE’ signal will be delivered to the application. The default action is to abort the program. To protect against this, ‘gpgme_check_version’ sets the ‘SIGPIPE’ signal action to ‘SIG_IGN’, which means that the signal will be ignored. GPGME will only do that if the signal action for ‘SIGPIPE’ is ‘SIG_DEF’ at the time ‘gpgme_check_version’ is called. If it is something different, ‘GPGME’ will take no action. This means that if your application does not install any signal handler for ‘SIGPIPE’, you don’t need to take any precautions. If you do install a signal handler for ‘SIGPIPE’, you must be prepared to handle any ‘SIGPIPE’ events that occur due to GPGME writing to a defunct pipe. Furthermore, if your application is multi-threaded, and you install a signal action for ‘SIGPIPE’, you must make sure you do this either before ‘gpgme_check_version’ is called or afterwards.  File: gpgme.info, Node: Multi-Threading, Prev: Signal Handling, Up: Preparation 2.8 Multi-Threading =================== The GPGME library is mostly thread-safe, and can be used in a multi-threaded environment but there are some requirements for multi-threaded use: • The function ‘gpgme_check_version’ must be called before any other function in the library, because it initializes the thread support subsystem in GPGME. To achieve this in multi-threaded programs, you must synchronize the memory with respect to other threads that also want to use GPGME. For this, it is sufficient to call ‘gpgme_check_version’ before creating the other threads using GPGME(1). • Any ‘gpgme_data_t’ and ‘gpgme_ctx_t’ object must only be accessed by one thread at a time. If multiple threads want to deal with the same object, the caller has to make sure that operations on that object are fully synchronized. • Only one thread at any time is allowed to call ‘gpgme_wait’. If multiple threads call this function, the caller must make sure that all invocations are fully synchronized. It is safe to start asynchronous operations while a thread is running in gpgme_wait. • The function ‘gpgme_strerror’ is not thread safe. You have to use ‘gpgme_strerror_r’ instead. ---------- Footnotes ---------- (1) At least this is true for POSIX threads, as ‘pthread_create’ is a function that synchronizes memory with respects to other threads. There are many functions which have this property, a complete list can be found in POSIX, IEEE Std 1003.1-2003, Base Definitions, Issue 6, in the definition of the term “Memory Synchronization”. For other thread packages other, more relaxed or more strict rules may apply.  File: gpgme.info, Node: Protocols and Engines, Next: Algorithms, Prev: Preparation, Up: Top 3 Protocols and Engines *********************** GPGME supports several cryptographic protocols, however, it does not implement them. Rather it uses backends (also called engines) which implement the protocol. GPGME uses inter-process communication to pass data back and forth between the application and the backend, but the details of the communication protocol and invocation of the backend is completely hidden by the interface. All complexity is handled by GPGME. Where an exchange of information between the application and the backend is necessary, GPGME provides the necessary callback function hooks and further interfaces. -- Data type: enum gpgme_protocol_t The ‘gpgme_protocol_t’ type specifies the set of possible protocol values that are supported by GPGME. The following protocols are supported: ‘GPGME_PROTOCOL_OpenPGP’ ‘GPGME_PROTOCOL_OPENPGP’ This specifies the OpenPGP protocol. ‘GPGME_PROTOCOL_CMS’ This specifies the Cryptographic Message Syntax. ‘GPGME_PROTOCOL_GPGCONF’ Under development. Please ask on for help. ‘GPGME_PROTOCOL_ASSUAN’ SINCE: 1.2.0 This specifies the raw Assuan protocol. ‘GPGME_PROTOCOL_G13’ SINCE: 1.3.0 Under development. Please ask on for help. ‘GPGME_PROTOCOL_UISERVER’ Under development. Please ask on for help. ‘GPGME_PROTOCOL_SPAWN’ SINCE: 1.5.0 Special protocol for use with ‘gpgme_op_spawn’. ‘GPGME_PROTOCOL_UNKNOWN’ Reserved for future extension. You may use this to indicate that the used protocol is not known to the application. Currently, GPGME does not accept this value in any operation, though, except for ‘gpgme_get_protocol_name’. -- Function: const char * gpgme_get_protocol_name (gpgme_protocol_t PROTOCOL) The function ‘gpgme_get_protocol_name’ returns a statically allocated string describing the protocol PROTOCOL, or ‘NULL’ if the protocol number is not valid. * Menu: * Engine Version Check:: Verifying the engine version. * Engine Information:: Obtaining more information about the engines. * Engine Configuration:: Changing the engine configuration. * OpenPGP:: Support for the OpenPGP protocol. * Cryptographic Message Syntax:: Support for the CMS. * Assuan:: Support for the raw Assuan protocol.  File: gpgme.info, Node: Engine Version Check, Next: Engine Information, Up: Protocols and Engines 3.1 Engine Version Check ======================== -- Function: const char * gpgme_get_dirinfo (cons char *WHAT) SINCE: 1.5.0 The function ‘gpgme_get_dirinfo’ returns a statically allocated string with the value associated to WHAT. The returned values are the defaults and won’t change even after ‘gpgme_set_engine_info’ has been used to configure a different engine. ‘NULL’ is returned if no value is available. Commonly supported values for WHAT are: ‘homedir’ Return the default home directory. ‘sysconfdir’ Return the name of the system configuration directory ‘bindir’ Return the name of the directory with GnuPG program files. ‘libdir’ Return the name of the directory with GnuPG related library files. ‘libexecdir’ Return the name of the directory with GnuPG helper program files. ‘datadir’ Return the name of the directory with GnuPG shared data. ‘localedir’ Return the name of the directory with GnuPG locale data. ‘agent-socket’ Return the name of the socket to connect to the gpg-agent. ‘agent-ssh-socket’ Return the name of the socket to connect to the ssh-agent component of gpg-agent. ‘dirmngr-socket’ Return the name of the socket to connect to the dirmngr. ‘uiserver-socket’ Return the name of the socket to connect to the user interface server. ‘gpgconf-name’ Return the file name of the engine configuration tool. ‘gpg-name’ Return the file name of the OpenPGP engine. ‘gpgsm-name’ Return the file name of the CMS engine. ‘g13-name’ Return the name of the file container encryption engine. ‘gpg-wks-client-name’ Return the name of the Web Key Service tool. -- Function: gpgme_error_t gpgme_engine_check_version (gpgme_protocol_t PROTOCOL) The function ‘gpgme_engine_check_version’ verifies that the engine implementing the protocol PROTOCOL is installed in the expected path and meets the version requirement of GPGME. This function returns the error code ‘GPG_ERR_NO_ERROR’ if the engine is available and ‘GPG_ERR_INV_ENGINE’ if it is not.  File: gpgme.info, Node: Engine Information, Next: Engine Configuration, Prev: Engine Version Check, Up: Protocols and Engines 3.2 Engine Information ====================== -- Data type: gpgme_engine_info_t The ‘gpgme_engine_info_t’ type specifies a pointer to a structure describing a crypto engine. The structure contains the following elements: ‘gpgme_engine_info_t next’ This is a pointer to the next engine info structure in the linked list, or ‘NULL’ if this is the last element. ‘gpgme_protocol_t protocol’ This is the protocol for which the crypto engine is used. You can convert this to a string with ‘gpgme_get_protocol_name’ for printing. ‘const char *file_name’ This is a string holding the file name of the executable of the crypto engine. Currently, it is never ‘NULL’, but using ‘NULL’ is reserved for future use, so always check before you use it. ‘const char *home_dir’ This is a string holding the directory name of the crypto engine’s configuration directory. If it is ‘NULL’, then the default directory is used. See ‘gpgme_get_dirinfo’ on how to get the default directory. ‘const char *version’ This is a string containing the version number of the crypto engine. It might be ‘NULL’ if the version number can not be determined, for example because the executable doesn’t exist or is invalid. ‘const char *req_version’ This is a string containing the minimum required version number of the crypto engine for GPGME to work correctly. This is the version number that ‘gpgme_engine_check_version’ verifies against. Currently, it is never ‘NULL’, but using ‘NULL’ is reserved for future use, so always check before you use it. -- Function: gpgme_error_t gpgme_get_engine_info (gpgme_engine_info_t *INFO) The function ‘gpgme_get_engine_info’ returns a linked list of engine info structures in INFO. Each info structure describes the defaults of one configured backend. The memory for the info structures is allocated the first time this function is invoked, and must not be freed by the caller. This function returns the error code ‘GPG_ERR_NO_ERROR’ if successful, and a system error if the memory could not be allocated. Here is an example how you can provide more diagnostics if you receive an error message which indicates that the crypto engine is invalid. gpgme_ctx_t ctx; gpgme_error_t err; [...] if (gpgme_err_code (err) == GPG_ERR_INV_ENGINE) { gpgme_engine_info_t info; err = gpgme_get_engine_info (&info); if (!err) { while (info && info->protocol != gpgme_get_protocol (ctx)) info = info->next; if (!info) fprintf (stderr, "GPGME compiled without support for protocol %s", gpgme_get_protocol_name (info->protocol)); else if (info->file_name && !info->version) fprintf (stderr, "Engine %s not installed properly", info->file_name); else if (info->file_name && info->version && info->req_version) fprintf (stderr, "Engine %s version %s installed, " "but at least version %s required", info->file_name, info->version, info->req_version); else fprintf (stderr, "Unknown problem with engine for protocol %s", gpgme_get_protocol_name (info->protocol)); } }  File: gpgme.info, Node: Engine Configuration, Next: OpenPGP, Prev: Engine Information, Up: Protocols and Engines 3.3 Engine Configuration ======================== You can change the configuration of a backend engine, and thus change the executable program and configuration directory to be used. You can make these changes the default or set them for some contexts individually. -- Function: gpgme_error_t gpgme_set_engine_info (gpgme_protocol_t PROTO, const char *FILE_NAME, const char *HOME_DIR) SINCE: 1.1.0 The function ‘gpgme_set_engine_info’ changes the default configuration of the crypto engine implementing the protocol PROTO. FILE_NAME is the file name of the executable program implementing this protocol, and HOME_DIR is the directory name of the configuration directory for this crypto engine. If HOME_DIR is ‘NULL’, the engine’s default will be used. The new defaults are not applied to already created GPGME contexts. This function returns the error code ‘GPG_ERR_NO_ERROR’ if successful, or an error code on failure. The functions ‘gpgme_ctx_get_engine_info’ and ‘gpgme_ctx_set_engine_info’ can be used to change the engine configuration per context. *Note Crypto Engine::.  File: gpgme.info, Node: OpenPGP, Next: Cryptographic Message Syntax, Prev: Engine Configuration, Up: Protocols and Engines 3.4 OpenPGP =========== OpenPGP is implemented by GnuPG, the GNU Privacy Guard. This is the first protocol that was supported by GPGME. The OpenPGP protocol is specified by ‘GPGME_PROTOCOL_OpenPGP’.  File: gpgme.info, Node: Cryptographic Message Syntax, Next: Assuan, Prev: OpenPGP, Up: Protocols and Engines 3.5 Cryptographic Message Syntax ================================ CMS is implemented by GpgSM, the S/MIME implementation for GnuPG. The CMS protocol is specified by ‘GPGME_PROTOCOL_CMS’.  File: gpgme.info, Node: Assuan, Prev: Cryptographic Message Syntax, Up: Protocols and Engines 3.6 Assuan ========== Assuan is the RPC library used by the various GnuPG components. The Assuan protocol allows one to talk to arbitrary Assuan servers using GPGME. *Note Using the Assuan protocol::. The ASSUAN protocol is specified by ‘GPGME_PROTOCOL_ASSUAN’.  File: gpgme.info, Node: Algorithms, Next: Error Handling, Prev: Protocols and Engines, Up: Top 4 Algorithms ************ The crypto backends support a variety of algorithms used in public key cryptography.(1) The following sections list the identifiers used to denote such an algorithm. * Menu: * Public Key Algorithms:: A list of all public key algorithms. * Hash Algorithms:: A list of all hash algorithms. ---------- Footnotes ---------- (1) Some engines also provide symmetric only encryption; see the description of the encryption function on how to use this.  File: gpgme.info, Node: Public Key Algorithms, Next: Hash Algorithms, Up: Algorithms 4.1 Public Key Algorithms ========================= Public key algorithms are used for encryption, decryption, signing and verification of signatures. -- Data type: enum gpgme_pubkey_algo_t The ‘gpgme_pubkey_algo_t’ type specifies the set of all public key algorithms that are supported by GPGME. Possible values are: ‘GPGME_PK_RSA’ This value indicates the RSA (Rivest, Shamir, Adleman) algorithm. ‘GPGME_PK_RSA_E’ Deprecated. This value indicates the RSA (Rivest, Shamir, Adleman) algorithm for encryption and decryption only. ‘GPGME_PK_RSA_S’ Deprecated. This value indicates the RSA (Rivest, Shamir, Adleman) algorithm for signing and verification only. ‘GPGME_PK_DSA’ This value indicates DSA, the Digital Signature Algorithm. ‘GPGME_PK_ELG’ This value indicates ElGamal. ‘GPGME_PK_ELG_E’ This value also indicates ElGamal and is used specifically in GnuPG. ‘GPGME_PK_ECC’ SINCE: 1.5.0 This value is a generic indicator for ellipic curve algorithms. ‘GPGME_PK_ECDSA’ SINCE: 1.3.0 This value indicates ECDSA, the Elliptic Curve Digital Signature Algorithm as defined by FIPS 186-2 and RFC-6637. ‘GPGME_PK_ECDH’ SINCE: 1.3.0 This value indicates ECDH, the Eliptic Curve Diffie-Hellmann encryption algorithm as defined by RFC-6637. ‘GPGME_PK_EDDSA’ SINCE: 1.7.0 This value indicates the EdDSA algorithm. -- Function: const char * gpgme_pubkey_algo_name (gpgme_pubkey_algo_t ALGO) The function ‘gpgme_pubkey_algo_name’ returns a pointer to a statically allocated string containing a description of the public key algorithm ALGO. This string can be used to output the name of the public key algorithm to the user. If ALGO is not a valid public key algorithm, ‘NULL’ is returned. -- Function: char * gpgme_pubkey_algo_string (gpgme_subkey_t KEY) SINCE: 1.7.0 The function ‘gpgme_pubkey_algo_string’ is a convenience function to build and return an algorithm string in the same way GnuPG does (e.g. “rsa2048” or “ed25519”). The caller must free the result using ‘gpgme_free’. On error (e.g. invalid argument or memory exhausted), the function returns NULL and sets ‘ERRNO’.  File: gpgme.info, Node: Hash Algorithms, Prev: Public Key Algorithms, Up: Algorithms 4.2 Hash Algorithms =================== Hash (message digest) algorithms are used to compress a long message to make it suitable for public key cryptography. -- Data type: enum gpgme_hash_algo_t The ‘gpgme_hash_algo_t’ type specifies the set of all hash algorithms that are supported by GPGME. Possible values are: ‘GPGME_MD_MD5’ ‘GPGME_MD_SHA1’ ‘GPGME_MD_RMD160’ ‘GPGME_MD_MD2’ ‘GPGME_MD_TIGER’ ‘GPGME_MD_HAVAL’ ‘GPGME_MD_SHA256’ ‘GPGME_MD_SHA384’ ‘GPGME_MD_SHA512’ ‘GPGME_MD_SHA224’ SINCE: 1.5.0 ‘GPGME_MD_MD4’ ‘GPGME_MD_CRC32’ ‘GPGME_MD_CRC32_RFC1510’ ‘GPGME_MD_CRC24_RFC2440’ -- Function: const char * gpgme_hash_algo_name (gpgme_hash_algo_t ALGO) The function ‘gpgme_hash_algo_name’ returns a pointer to a statically allocated string containing a description of the hash algorithm ALGO. This string can be used to output the name of the hash algorithm to the user. If ALGO is not a valid hash algorithm, ‘NULL’ is returned.  File: gpgme.info, Node: Error Handling, Next: Exchanging Data, Prev: Algorithms, Up: Top 5 Error Handling **************** Many functions in GPGME can return an error if they fail. For this reason, the application should always catch the error condition and take appropriate measures, for example by releasing the resources and passing the error up to the caller, or by displaying a descriptive message to the user and cancelling the operation. Some error values do not indicate a system error or an error in the operation, but the result of an operation that failed properly. For example, if you try to decrypt a tempered message, the decryption will fail. Another error value actually means that the end of a data buffer or list has been reached. The following descriptions explain for many error codes what they mean usually. Some error values have specific meanings if returned by a certain functions. Such cases are described in the documentation of those functions. GPGME uses the ‘libgpg-error’ library. This allows to share the error codes with other components of the GnuPG system, and thus pass error values transparently from the crypto engine, or some helper application of the crypto engine, to the user. This way no information is lost. As a consequence, GPGME does not use its own identifiers for error codes, but uses those provided by ‘libgpg-error’. They usually start with ‘GPG_ERR_’. However, GPGME does provide aliases for the functions defined in libgpg-error, which might be preferred for name space consistency. * Menu: * Error Values:: The error value and what it means. * Error Sources:: A list of important error sources. * Error Codes:: A list of important error codes. * Error Strings:: How to get a descriptive string from a value.  File: gpgme.info, Node: Error Values, Next: Error Sources, Up: Error Handling 5.1 Error Values ================ -- Data type: gpgme_err_code_t The ‘gpgme_err_code_t’ type is an alias for the ‘libgpg-error’ type ‘gpg_err_code_t’. The error code indicates the type of an error, or the reason why an operation failed. A list of important error codes can be found in the next section. -- Data type: gpgme_err_source_t The ‘gpgme_err_source_t’ type is an alias for the ‘libgpg-error’ type ‘gpg_err_source_t’. The error source has not a precisely defined meaning. Sometimes it is the place where the error happened, sometimes it is the place where an error was encoded into an error value. Usually the error source will give an indication to where to look for the problem. This is not always true, but it is attempted to achieve this goal. A list of important error sources can be found in the next section. -- Data type: gpgme_error_t The ‘gpgme_error_t’ type is an alias for the ‘libgpg-error’ type ‘gpg_error_t’. An error value like this has always two components, an error code and an error source. Both together form the error value. Thus, the error value can not be directly compared against an error code, but the accessor functions described below must be used. However, it is guaranteed that only 0 is used to indicate success (‘GPG_ERR_NO_ERROR’), and that in this case all other parts of the error value are set to 0, too. Note that in GPGME, the error source is used purely for diagnostical purposes. Only the error code should be checked to test for a certain outcome of a function. The manual only documents the error code part of an error value. The error source is left unspecified and might be anything. -- Function: static inline gpgme_err_code_t gpgme_err_code (gpgme_error_t ERR) The static inline function ‘gpgme_err_code’ returns the ‘gpgme_err_code_t’ component of the error value ERR. This function must be used to extract the error code from an error value in order to compare it with the ‘GPG_ERR_*’ error code macros. -- Function: static inline gpgme_err_source_t gpgme_err_source (gpgme_error_t ERR) The static inline function ‘gpgme_err_source’ returns the ‘gpgme_err_source_t’ component of the error value ERR. This function must be used to extract the error source from an error value in order to compare it with the ‘GPG_ERR_SOURCE_*’ error source macros. -- Function: static inline gpgme_error_t gpgme_err_make (gpgme_err_source_t SOURCE, gpgme_err_code_t CODE) The static inline function ‘gpgme_err_make’ returns the error value consisting of the error source SOURCE and the error code CODE. This function can be used in callback functions to construct an error value to return it to the library. -- Function: static inline gpgme_error_t gpgme_error (gpgme_err_code_t CODE) The static inline function ‘gpgme_error’ returns the error value consisting of the default error source and the error code CODE. For GPGME applications, the default error source is ‘GPG_ERR_SOURCE_USER_1’. You can define ‘GPGME_ERR_SOURCE_DEFAULT’ before including ‘gpgme.h’ to change this default. This function can be used in callback functions to construct an error value to return it to the library. The ‘libgpg-error’ library provides error codes for all system error numbers it knows about. If ERR is an unknown error number, the error code ‘GPG_ERR_UNKNOWN_ERRNO’ is used. The following functions can be used to construct error values from system errnor numbers. -- Function: gpgme_error_t gpgme_err_make_from_errno (gpgme_err_source_t SOURCE, int ERR) The function ‘gpgme_err_make_from_errno’ is like ‘gpgme_err_make’, but it takes a system error like ‘errno’ instead of a ‘gpgme_err_code_t’ error code. -- Function: gpgme_error_t gpgme_error_from_errno (int ERR) The function ‘gpgme_error_from_errno’ is like ‘gpgme_error’, but it takes a system error like ‘errno’ instead of a ‘gpgme_err_code_t’ error code. Sometimes you might want to map system error numbers to error codes directly, or map an error code representing a system error back to the system error number. The following functions can be used to do that. -- Function: gpgme_err_code_t gpgme_err_code_from_errno (int ERR) The function ‘gpgme_err_code_from_errno’ returns the error code for the system error ERR. If ERR is not a known system error, the function returns ‘GPG_ERR_UNKNOWN_ERRNO’. -- Function: int gpgme_err_code_to_errno (gpgme_err_code_t ERR) The function ‘gpgme_err_code_to_errno’ returns the system error for the error code ERR. If ERR is not an error code representing a system error, or if this system error is not defined on this system, the function returns ‘0’.  File: gpgme.info, Node: Error Sources, Next: Error Codes, Prev: Error Values, Up: Error Handling 5.2 Error Sources ================= The library ‘libgpg-error’ defines an error source for every component of the GnuPG system. The error source part of an error value is not well defined. As such it is mainly useful to improve the diagnostic error message for the user. If the error code part of an error value is ‘0’, the whole error value will be ‘0’. In this case the error source part is of course ‘GPG_ERR_SOURCE_UNKNOWN’. The list of error sources that might occur in applications using GPGME is: ‘GPG_ERR_SOURCE_UNKNOWN’ The error source is not known. The value of this error source is ‘0’. ‘GPG_ERR_SOURCE_GPGME’ The error source is GPGME itself. This is the default for errors that occur in the GPGME library. ‘GPG_ERR_SOURCE_GPG’ The error source is GnuPG, which is the crypto engine used for the OpenPGP protocol. ‘GPG_ERR_SOURCE_GPGSM’ The error source is GPGSM, which is the crypto engine used for the CMS protocol. ‘GPG_ERR_SOURCE_GCRYPT’ The error source is ‘libgcrypt’, which is used by crypto engines to perform cryptographic operations. ‘GPG_ERR_SOURCE_GPGAGENT’ The error source is ‘gpg-agent’, which is used by crypto engines to perform operations with the secret key. ‘GPG_ERR_SOURCE_PINENTRY’ The error source is ‘pinentry’, which is used by ‘gpg-agent’ to query the passphrase to unlock a secret key. ‘GPG_ERR_SOURCE_SCD’ The error source is the SmartCard Daemon, which is used by ‘gpg-agent’ to delegate operations with the secret key to a SmartCard. ‘GPG_ERR_SOURCE_KEYBOX’ The error source is ‘libkbx’, a library used by the crypto engines to manage local keyrings. ‘GPG_ERR_SOURCE_USER_1’ ‘GPG_ERR_SOURCE_USER_2’ ‘GPG_ERR_SOURCE_USER_3’ ‘GPG_ERR_SOURCE_USER_4’ These error sources are not used by any GnuPG component and can be used by other software. For example, applications using GPGME can use them to mark error values coming from callback handlers. Thus ‘GPG_ERR_SOURCE_USER_1’ is the default for errors created with ‘gpgme_error’ and ‘gpgme_error_from_errno’, unless you define ‘GPGME_ERR_SOURCE_DEFAULT’ before including ‘gpgme.h’.  File: gpgme.info, Node: Error Codes, Next: Error Strings, Prev: Error Sources, Up: Error Handling 5.3 Error Codes =============== The library ‘libgpg-error’ defines many error values. Most of them are not used by ‘GPGME’ directly, but might be returned by GPGME because it received them from the crypto engine. The below list only includes such error codes that have a specific meaning in ‘GPGME’, or which are so common that you should know about them. ‘GPG_ERR_EOF’ This value indicates the end of a list, buffer or file. ‘GPG_ERR_NO_ERROR’ This value indicates success. The value of this error code is ‘0’. Also, it is guaranteed that an error value made from the error code ‘0’ will be ‘0’ itself (as a whole). This means that the error source information is lost for this error code, however, as this error code indicates that no error occurred, this is generally not a problem. ‘GPG_ERR_GENERAL’ This value means that something went wrong, but either there is not enough information about the problem to return a more useful error value, or there is no separate error value for this type of problem. ‘GPG_ERR_ENOMEM’ This value means that an out-of-memory condition occurred. ‘GPG_ERR_E...’ System errors are mapped to GPG_ERR_FOO where FOO is the symbol for the system error. ‘GPG_ERR_INV_VALUE’ This value means that some user provided data was out of range. This can also refer to objects. For example, if an empty ‘gpgme_data_t’ object was expected, but one containing data was provided, this error value is returned. ‘GPG_ERR_UNUSABLE_PUBKEY’ This value means that some recipients for a message were invalid. ‘GPG_ERR_UNUSABLE_SECKEY’ This value means that some signers were invalid. ‘GPG_ERR_NO_DATA’ This value means that a ‘gpgme_data_t’ object which was expected to have content was found empty. ‘GPG_ERR_CONFLICT’ This value means that a conflict of some sort occurred. ‘GPG_ERR_NOT_IMPLEMENTED’ This value indicates that the specific function (or operation) is not implemented. This error should never happen. It can only occur if you use certain values or configuration options which do not work, but for which we think that they should work at some later time. ‘GPG_ERR_DECRYPT_FAILED’ This value indicates that a decryption operation was unsuccessful. ‘GPG_ERR_BAD_PASSPHRASE’ This value means that the user did not provide a correct passphrase when requested. ‘GPG_ERR_CANCELED’ This value means that the operation was canceled. ‘GPG_ERR_INV_ENGINE’ This value means that the engine that implements the desired protocol is currently not available. This can either be because the sources were configured to exclude support for this engine, or because the engine is not installed properly. ‘GPG_ERR_AMBIGUOUS_NAME’ This value indicates that a user ID or other specifier did not specify a unique key. ‘GPG_ERR_WRONG_KEY_USAGE’ This value indicates that a key is not used appropriately. ‘GPG_ERR_CERT_REVOKED’ This value indicates that a key signature was revoced. ‘GPG_ERR_CERT_EXPIRED’ This value indicates that a key signature expired. ‘GPG_ERR_NO_CRL_KNOWN’ This value indicates that no certificate revocation list is known for the certificate. ‘GPG_ERR_NO_POLICY_MATCH’ This value indicates that a policy issue occurred. ‘GPG_ERR_NO_SECKEY’ This value indicates that no secret key for the user ID is available. ‘GPG_ERR_MISSING_CERT’ This value indicates that a key could not be imported because the issuer certificate is missing. ‘GPG_ERR_BAD_CERT_CHAIN’ This value indicates that a key could not be imported because its certificate chain is not good, for example it could be too long. ‘GPG_ERR_UNSUPPORTED_ALGORITHM’ This value means a verification failed because the cryptographic algorithm is not supported by the crypto backend. ‘GPG_ERR_BAD_SIGNATURE’ This value means a verification failed because the signature is bad. ‘GPG_ERR_NO_PUBKEY’ This value means a verification failed because the public key is not available. ‘GPG_ERR_USER_1’ ‘GPG_ERR_USER_2’ ‘...’ ‘GPG_ERR_USER_16’ These error codes are not used by any GnuPG component and can be freely used by other software. Applications using GPGME might use them to mark specific errors returned by callback handlers if no suitable error codes (including the system errors) for these errors exist already.  File: gpgme.info, Node: Error Strings, Prev: Error Codes, Up: Error Handling 5.4 Error Strings ================= -- Function: const char * gpgme_strerror (gpgme_error_t ERR) The function ‘gpgme_strerror’ returns a pointer to a statically allocated string containing a description of the error code contained in the error value ERR. This string can be used to output a diagnostic message to the user. This function is not thread safe. Use ‘gpgme_strerror_r’ in multi-threaded programs. -- Function: int gpgme_strerror_r (gpgme_error_t ERR, char *BUF, size_t BUFLEN) The function ‘gpgme_strerror_r’ returns the error string for ERR in the user-supplied buffer BUF of size BUFLEN. This function is, in contrast to ‘gpgme_strerror’, thread-safe if a thread-safe ‘strerror_r’ function is provided by the system. If the function succeeds, 0 is returned and BUF contains the string describing the error. If the buffer was not large enough, ERANGE is returned and BUF contains as much of the beginning of the error string as fits into the buffer. -- Function: const char * gpgme_strsource (gpgme_error_t ERR) The function ‘gpgme_strerror’ returns a pointer to a statically allocated string containing a description of the error source contained in the error value ERR. This string can be used to output a diagnostic message to the user. The following example illustrates the use of ‘gpgme_strerror’: gpgme_ctx_t ctx; gpgme_error_t err = gpgme_new (&ctx); if (err) { fprintf (stderr, "%s: creating GpgME context failed: %s: %s\n", argv[0], gpgme_strsource (err), gpgme_strerror (err)); exit (1); }  File: gpgme.info, Node: Exchanging Data, Next: Contexts, Prev: Error Handling, Up: Top 6 Exchanging Data ***************** A lot of data has to be exchanged between the user and the crypto engine, like plaintext messages, ciphertext, signatures and information about the keys. The technical details about exchanging the data information are completely abstracted by GPGME. The user provides and receives the data via ‘gpgme_data_t’ objects, regardless of the communication protocol between GPGME and the crypto engine in use. -- Data type: gpgme_data_t The ‘gpgme_data_t’ type is a handle for a container for generic data, which is used by GPGME to exchange data with the user. ‘gpgme_data_t’ objects do not provide notifications on events. It is assumed that read and write operations are blocking until data is available. If this is undesirable, the application must ensure that all GPGME data operations always have data available, for example by using memory buffers or files rather than pipes or sockets. This might be relevant, for example, if the external event loop mechanism is used. -- Data type: gpgme_off_t SINCE: 1.4.1 On POSIX platforms the ‘gpgme_off_t’ type is an alias for ‘off_t’; it may be used interchangeable. On Windows platforms ‘gpgme_off_t’ is defined as a long (i.e. 32 bit) for 32 bit Windows and as a 64 bit signed integer for 64 bit Windows. -- Data type: gpgme_ssize_t The ‘gpgme_ssize_t’ type is an alias for ‘ssize_t’. It has only been introduced to overcome portability problems pertaining to the declaration of ‘ssize_t’ by different toolchains. * Menu: * Creating Data Buffers:: Creating new data buffers. * Destroying Data Buffers:: Releasing data buffers. * Manipulating Data Buffers:: Operations on data buffers.  File: gpgme.info, Node: Creating Data Buffers, Next: Destroying Data Buffers, Up: Exchanging Data 6.1 Creating Data Buffers ========================= Data objects can be based on memory, files, or callback functions provided by the user. Not all operations are supported by all objects. * Menu: * Memory Based Data Buffers:: Creating memory based data buffers. * File Based Data Buffers:: Creating file based data buffers. * Callback Based Data Buffers:: Creating callback based data buffers.  File: gpgme.info, Node: Memory Based Data Buffers, Next: File Based Data Buffers, Up: Creating Data Buffers 6.1.1 Memory Based Data Buffers ------------------------------- Memory based data objects store all data in allocated memory. This is convenient, but only practical for an amount of data that is a fraction of the available physical memory. The data has to be copied from its source and to its destination, which can often be avoided by using one of the other data object -- Function: gpgme_error_t gpgme_data_new (gpgme_data_t *DH) The function ‘gpgme_data_new’ creates a new ‘gpgme_data_t’ object and returns a handle for it in DH. The data object is memory based and initially empty. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, ‘GPG_ERR_INV_VALUE’ if DH is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Function: gpgme_error_t gpgme_data_new_from_mem (gpgme_data_t *DH, const char *BUFFER, size_t SIZE, int COPY) The function ‘gpgme_data_new_from_mem’ creates a new ‘gpgme_data_t’ object and fills it with SIZE bytes starting from BUFFER. If COPY is not zero, a private copy of the data is made. If COPY is zero, the data is taken from the specified buffer as needed, and the user has to ensure that the buffer remains valid for the whole life span of the data object. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, ‘GPG_ERR_INV_VALUE’ if DH or BUFFER is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Function: gpgme_error_t gpgme_data_new_from_file (gpgme_data_t *DH, const char *FILENAME, int COPY) The function ‘gpgme_data_new_from_file’ creates a new ‘gpgme_data_t’ object and fills it with the content of the file FILENAME. If COPY is not zero, the whole file is read in at initialization time and the file is not used anymore after that. This is the only mode supported currently. Later, a value of zero for COPY might cause all reads to be delayed until the data is needed, but this is not yet implemented. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, ‘GPG_ERR_INV_VALUE’ if DH or FILENAME is not a valid pointer, ‘GPG_ERR_NOT_IMPLEMENTED’ if CODE is zero, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Function: gpgme_error_t gpgme_data_new_from_filepart (gpgme_data_t *DH, const char *FILENAME, FILE *FP, off_t OFFSET, size_t LENGTH) The function ‘gpgme_data_new_from_filepart’ creates a new ‘gpgme_data_t’ object and fills it with a part of the file specified by FILENAME or FP. Exactly one of FILENAME and FP must be non-zero, the other must be zero. The argument that is not zero specifies the file from which LENGTH bytes are read into the data object, starting from OFFSET. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, ‘GPG_ERR_INV_VALUE’ if DH and exactly one of FILENAME and FP is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if not enough memory is available.  File: gpgme.info, Node: File Based Data Buffers, Next: Callback Based Data Buffers, Prev: Memory Based Data Buffers, Up: Creating Data Buffers 6.1.2 File Based Data Buffers ----------------------------- File based data objects operate directly on file descriptors or streams. Only a small amount of data is stored in core at any time, so the size of the data objects is not limited by GPGME. -- Function: gpgme_error_t gpgme_data_new_from_fd (gpgme_data_t *DH, int FD) The function ‘gpgme_data_new_from_fd’ creates a new ‘gpgme_data_t’ object and uses the file descriptor FD to read from (if used as an input data object) and write to (if used as an output data object). When using the data object as an input buffer, the function might read a bit more from the file descriptor than is actually needed by the crypto engine in the desired operation because of internal buffering. Note that GPGME assumes that the file descriptor is set to blocking mode. Errors during I/O operations, except for EINTR, are usually fatal for crypto operations. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Function: gpgme_error_t gpgme_data_new_from_stream (gpgme_data_t *DH, FILE *STREAM) The function ‘gpgme_data_new_from_stream’ creates a new ‘gpgme_data_t’ object and uses the I/O stream STREAM to read from (if used as an input data object) and write to (if used as an output data object). When using the data object as an input buffer, the function might read a bit more from the stream than is actually needed by the crypto engine in the desired operation because of internal buffering. Note that GPGME assumes that the stream is in blocking mode. Errors during I/O operations, except for EINTR, are usually fatal for crypto operations. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Function: gpgme_error_t gpgme_data_new_from_estream (gpgme_data_t *DH, gpgrt_stream_t STREAM) The function ‘gpgme_data_new_from_estream’ creates a new ‘gpgme_data_t’ object and uses the gpgrt stream STREAM to read from (if used as an input data object) and write to (if used as an output data object). When using the data object as an input buffer, the function might read a bit more from the stream than is actually needed by the crypto engine in the desired operation because of internal buffering. Note that GPGME assumes that the stream is in blocking mode. Errors during I/O operations, except for EINTR, are usually fatal for crypto operations. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, and ‘GPG_ERR_ENOMEM’ if not enough memory is available.  File: gpgme.info, Node: Callback Based Data Buffers, Prev: File Based Data Buffers, Up: Creating Data Buffers 6.1.3 Callback Based Data Buffers --------------------------------- If neither memory nor file based data objects are a good fit for your application, you can implement the functions a data object provides yourself and create a data object from these callback functions. -- Data type: ssize_t (*gpgme_data_read_cb_t) (void *HANDLE, void *BUFFER, size_t SIZE) The ‘gpgme_data_read_cb_t’ type is the type of functions which GPGME calls if it wants to read data from a user-implemented data object. The function should read up to SIZE bytes from the current read position into the space starting at BUFFER. The HANDLE is provided by the user at data object creation time. Note that GPGME assumes that the read blocks until data is available. Errors during I/O operations, except for EINTR, are usually fatal for crypto operations. The function should return the number of bytes read, 0 on EOF, and -1 on error. If an error occurs, ERRNO should be set to describe the type of the error. -- Data type: ssize_t (*gpgme_data_write_cb_t) (void *HANDLE, const void *BUFFER, size_t SIZE) The ‘gpgme_data_write_cb_t’ type is the type of functions which GPGME calls if it wants to write data to a user-implemented data object. The function should write up to SIZE bytes to the current write position from the space starting at BUFFER. The HANDLE is provided by the user at data object creation time. Note that GPGME assumes that the write blocks until data is available. Errors during I/O operations, except for EINTR, are usually fatal for crypto operations. The function should return the number of bytes written, and -1 on error. If an error occurs, ERRNO should be set to describe the type of the error. -- Data type: off_t (*gpgme_data_seek_cb_t) (void *HANDLE, off_t OFFSET, int WHENCE) The ‘gpgme_data_seek_cb_t’ type is the type of functions which GPGME calls if it wants to change the current read/write position in a user-implemented data object, just like the ‘lseek’ function. The function should return the new read/write position, and -1 on error. If an error occurs, ERRNO should be set to describe the type of the error. -- Data type: void (*gpgme_data_release_cb_t) (void *HANDLE) The ‘gpgme_data_release_cb_t’ type is the type of functions which GPGME calls if it wants to destroy a user-implemented data object. The HANDLE is provided by the user at data object creation time. -- Data type: struct gpgme_data_cbs This structure is used to store the data callback interface functions described above. It has the following members: ‘gpgme_data_read_cb_t read’ This is the function called by GPGME to read data from the data object. It is only required for input data object. ‘gpgme_data_write_cb_t write’ This is the function called by GPGME to write data to the data object. It is only required for output data object. ‘gpgme_data_seek_cb_t seek’ This is the function called by GPGME to change the current read/write pointer in the data object (if available). It is optional. ‘gpgme_data_release_cb_t release’ This is the function called by GPGME to release a data object. It is optional. -- Function: gpgme_error_t gpgme_data_new_from_cbs (gpgme_data_t *DH, gpgme_data_cbs_t CBS, void *HANDLE) The function ‘gpgme_data_new_from_cbs’ creates a new ‘gpgme_data_t’ object and uses the user-provided callback functions to operate on the data object. The handle HANDLE is passed as first argument to the callback functions. This can be used to identify this data object. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the data object was successfully created, and ‘GPG_ERR_ENOMEM’ if not enough memory is available.  File: gpgme.info, Node: Destroying Data Buffers, Next: Manipulating Data Buffers, Prev: Creating Data Buffers, Up: Exchanging Data 6.2 Destroying Data Buffers =========================== -- Function: void gpgme_data_release (gpgme_data_t DH) The function ‘gpgme_data_release’ destroys the data object with the handle DH. It releases all associated resources that were not provided by the user in the first place. -- Function: char * gpgme_data_release_and_get_mem (gpgme_data_t DH, size_t *LENGTH) The function ‘gpgme_data_release_and_get_mem’ is like ‘gpgme_data_release’, except that it returns the data buffer and its length that was provided by the object. The user has to release the buffer with ‘gpgme_free’. In case the user provided the data buffer in non-copy mode, a copy will be made for this purpose. In case an error returns, or there is no suitable data buffer that can be returned to the user, the function will return ‘NULL’. In any case, the data object DH is destroyed. -- Function: void gpgme_free (void *BUFFER) SINCE: 1.1.1 The function ‘gpgme_free’ releases the memory returned by ‘gpgme_data_release_and_get_mem’ and ‘gpgme_pubkey_algo_string’. It should be used instead of the system libraries ‘free’ function in case different allocators are used by a program. This is often the case if gpgme is used under Windows as a DLL.  File: gpgme.info, Node: Manipulating Data Buffers, Prev: Destroying Data Buffers, Up: Exchanging Data 6.3 Manipulating Data Buffers ============================= Data buffers contain data and meta-data. The following operations can be used to manipulate both. * Menu: * Data Buffer I/O Operations:: I/O operations on data buffers. * Data Buffer Meta-Data:: Meta-data manipulation of data buffers. * Data Buffer Convenience:: Convenience function for data buffers.  File: gpgme.info, Node: Data Buffer I/O Operations, Next: Data Buffer Meta-Data, Up: Manipulating Data Buffers 6.3.1 Data Buffer I/O Operations -------------------------------- -- Function: ssize_t gpgme_data_read (gpgme_data_t DH, void *BUFFER, size_t LENGTH) The function ‘gpgme_data_read’ reads up to LENGTH bytes from the data object with the handle DH into the space starting at BUFFER. If no error occurs, the actual amount read is returned. If the end of the data object is reached, the function returns 0. In all other cases, the function returns -1 and sets ERRNO. -- Function: ssize_t gpgme_data_write (gpgme_data_t DH, const void *BUFFER, size_t SIZE) The function ‘gpgme_data_write’ writes up to SIZE bytes starting from BUFFER into the data object with the handle DH at the current write position. The function returns the number of bytes actually written, or -1 if an error occurs. If an error occurs, ERRNO is set. -- Function: off_t gpgme_data_seek (gpgme_data_t DH, off_t OFFSET, int WHENCE) The function ‘gpgme_data_seek’ changes the current read/write position. The WHENCE argument specifies how the OFFSET should be interpreted. It must be one of the following symbolic constants: ‘SEEK_SET’ Specifies that OFFSET is a count of characters from the beginning of the data object. ‘SEEK_CUR’ Specifies that OFFSET is a count of characters from the current file position. This count may be positive or negative. ‘SEEK_END’ Specifies that OFFSET is a count of characters from the end of the data object. A negative count specifies a position within the current extent of the data object; a positive count specifies a position past the current end. If you set the position past the current end, and actually write data, you will extend the data object with zeros up to that position. If successful, the function returns the resulting file position, measured in bytes from the beginning of the data object. You can use this feature together with ‘SEEK_CUR’ to read the current read/write position. If the function fails, -1 is returned and ERRNO is set.  File: gpgme.info, Node: Data Buffer Meta-Data, Next: Data Buffer Convenience, Prev: Data Buffer I/O Operations, Up: Manipulating Data Buffers 6.3.2 Data Buffer Meta-Data --------------------------- -- Function: char * gpgme_data_get_file_name (gpgme_data_t DH) SINCE: 1.1.0 The function ‘gpgme_data_get_file_name’ returns a pointer to a string containing the file name associated with the data object. The file name will be stored in the output when encrypting or signing the data and will be returned to the user when decrypting or verifying the output data. If no error occurs, the string containing the file name is returned. Otherwise, ‘NULL’ will be returned. -- Function: gpgme_error_t gpgme_data_set_file_name (gpgme_data_t DH, const char *FILE_NAME) SINCE: 1.1.0 The function ‘gpgme_data_set_file_name’ sets the file name associated with the data object. The file name will be stored in the output when encrypting or signing the data and will be returned to the user when decrypting or verifying the output data. The function returns the error code ‘GPG_ERR_INV_VALUE’ if DH is not a valid pointer and ‘GPG_ERR_ENOMEM’ if not enough memory is available. -- Data type: enum gpgme_data_encoding_t The ‘gpgme_data_encoding_t’ type specifies the encoding of a ‘gpgme_data_t’ object. For input data objects, the encoding is useful to give the backend a hint on the type of data. For output data objects, the encoding can specify the output data format on certain operations. Please note that not all backends support all encodings on all operations. The following data types are available: ‘GPGME_DATA_ENCODING_NONE’ This specifies that the encoding is not known. This is the default for a new data object. The backend will try its best to detect the encoding automatically. ‘GPGME_DATA_ENCODING_BINARY’ This specifies that the data is encoding in binary form; i.e. there is no special encoding. ‘GPGME_DATA_ENCODING_BASE64’ This specifies that the data is encoded using the Base-64 encoding scheme as used by MIME and other protocols. ‘GPGME_DATA_ENCODING_ARMOR’ This specifies that the data is encoded in an armored form as used by OpenPGP and PEM. ‘GPGME_DATA_ENCODING_MIME’ SINCE: 1.7.0 This specifies that the data is encoded as a MIME part. ‘GPGME_DATA_ENCODING_URL’ SINCE: 1.2.0 The data is a list of linefeed delimited URLs. This is only useful with ‘gpgme_op_import’. ‘GPGME_DATA_ENCODING_URL0’ SINCE: 1.2.0 The data is a list of binary zero delimited URLs. This is only useful with ‘gpgme_op_import’. ‘GPGME_DATA_ENCODING_URLESC’ SINCE: 1.2.0 The data is a list of linefeed delimited URLs with all control and space characters percent escaped. This mode is is not yet implemented. -- Function: gpgme_data_encoding_t gpgme_data_get_encoding (gpgme_data_t DH) The function ‘gpgme_data_get_encoding’ returns the encoding of the data object with the handle DH. If DH is not a valid pointer (e.g. ‘NULL’) ‘GPGME_DATA_ENCODING_NONE’ is returned. -- Function: gpgme_error_t gpgme_data_set_encoding (gpgme_data_t DH, gpgme_data_encoding_t ENC) The function ‘gpgme_data_set_encoding’ changes the encoding of the data object with the handle DH to ENC. -- Function: gpgme_error_t gpgme_data_set_flag (gpgme_data_t DH, const char *NAME, const char *VALUE) SINCE: 1.7.0 Some minor properties of the data object can be controlled with flags set by this function. The properties are identified by the following values for NAME: ‘size-hint’ The value is a decimal number with the length gpgme shall assume for this data object. This is useful if the data is provided by callbacks or via file descriptors but the applications knows the total size of the data. If this is set the OpenPGP engine may use this to decide on buffer allocation strategies and to provide a total value for its progress information. This function returns ‘0’ on success.  File: gpgme.info, Node: Data Buffer Convenience, Prev: Data Buffer Meta-Data, Up: Manipulating Data Buffers 6.3.3 Data Buffer Convenience Functions --------------------------------------- -- Data type: enum gpgme_data_type_t SINCE: 1.4.3 The ‘gpgme_data_type_t’ type is used to return the detected type of the content of a data buffer. ‘GPGME_DATA_TYPE_INVALID’ This is returned by ‘gpgme_data_identify’ if it was not possible to identify the data. Reasons for this might be a non-seekable stream or a memory problem. The value is 0. ‘GPGME_DATA_TYPE_UNKNOWN’ The type of the data is not known. ‘GPGME_DATA_TYPE_PGP_SIGNED’ The data is an OpenPGP signed message. This may be a binary signature, a detached one or a cleartext signature. ‘GPGME_DATA_TYPE_PGP_ENCRYPTED’ SINCE: 1.7.0 The data is an OpenPGP encrypted message. ‘GPGME_DATA_TYPE_PGP_SIGNATURE’ SINCE: 1.7.0 The data is an OpenPGP detached signature. ‘GPGME_DATA_TYPE_PGP_OTHER’ This is a generic OpenPGP message. In most cases this will be encrypted data. ‘GPGME_DATA_TYPE_PGP_KEY’ This is an OpenPGP key (private or public). ‘GPGME_DATA_TYPE_CMS_SIGNED’ This is a CMS signed message. ‘GPGME_DATA_TYPE_CMS_ENCRYPTED’ This is a CMS encrypted (enveloped data) message. ‘GPGME_DATA_TYPE_CMS_OTHER’ This is used for other CMS message types. ‘GPGME_DATA_TYPE_X509_CERT’ The data is a X.509 certificate ‘GPGME_DATA_TYPE_PKCS12’ The data is a PKCS#12 message. This is commonly used to exchange private keys for X.509. -- Function: gpgme_data_type_t gpgme_data_identify (gpgme_data_t DH) SINCE: 1.4.3 The function ‘gpgme_data_identify’ returns the type of the data with the handle DH. If it is not possible to perform the identification, the function returns zero (‘GPGME_DATA_TYPE_INVALID’). Note that depending on how the data object has been created the identification may not be possible or the data object may change its internal state (file pointer moved). For file or memory based data object, the state should not change.  File: gpgme.info, Node: Contexts, Next: UI Server Protocol, Prev: Exchanging Data, Up: Top 7 Contexts ********** All cryptographic operations in GPGME are performed within a context, which contains the internal state of the operation as well as configuration parameters. By using several contexts you can run several cryptographic operations in parallel, with different configuration. -- Data type: gpgme_ctx_t The ‘gpgme_ctx_t’ type is a handle for a GPGME context, which is used to hold the configuration, status and result of cryptographic operations. * Menu: * Creating Contexts:: Creating new GPGME contexts. * Destroying Contexts:: Releasing GPGME contexts. * Result Management:: Managing the result of crypto operations. * Context Attributes:: Setting properties of a context. * Key Management:: Managing keys with GPGME. * Trust Item Management:: Managing trust items with GPGME. * Crypto Operations:: Using a context for cryptography. * Miscellaneous:: Miscellaneous operations * Run Control:: Controlling how operations are run.  File: gpgme.info, Node: Creating Contexts, Next: Destroying Contexts, Up: Contexts 7.1 Creating Contexts ===================== -- Function: gpgme_error_t gpgme_new (gpgme_ctx_t *CTX) The function ‘gpgme_new’ creates a new ‘gpgme_ctx_t’ object and returns a handle for it in CTX. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the context was successfully created, ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if not enough memory is available. Also, it returns ‘GPG_ERR_NOT_OPERATIONAL’ if ‘gpgme_check_version’ was not called to initialize GPGME, and ‘GPG_ERR_SELFTEST_FAILED’ if a selftest failed. Currently, the only selftest is for Windows MingW32 targets to see if ‘-mms-bitfields’ was used (as required).  File: gpgme.info, Node: Destroying Contexts, Next: Result Management, Prev: Creating Contexts, Up: Contexts 7.2 Destroying Contexts ======================= -- Function: void gpgme_release (gpgme_ctx_t CTX) The function ‘gpgme_release’ destroys the context with the handle CTX and releases all associated resources.  File: gpgme.info, Node: Result Management, Next: Context Attributes, Prev: Destroying Contexts, Up: Contexts 7.3 Result Management ===================== The detailed result of an operation is returned in operation-specific structures such as ‘gpgme_decrypt_result_t’. The corresponding retrieval functions such as ‘gpgme_op_decrypt_result’ provide static access to the results after an operation completes. Those structures shall be considered read-only and an application must not allocate such a structure on its own. The following interfaces make it possible to detach a result structure from its associated context and give it a lifetime beyond that of the current operation or context. -- Function: void gpgme_result_ref (void *RESULT) SINCE: 1.2.0 The function ‘gpgme_result_ref’ acquires an additional reference for the result RESULT, which may be of any type ‘gpgme_*_result_t’. As long as the user holds a reference, the result structure is guaranteed to be valid and unmodified. -- Function: void gpgme_result_unref (void *RESULT) SINCE: 1.2.0 The function ‘gpgme_result_unref’ releases a reference for the result RESULT. If this was the last reference, the result structure will be destroyed and all resources associated to it will be released. Note that a context may hold its own references to result structures, typically until the context is destroyed or the next operation is started. In fact, these references are accessed through the ‘gpgme_op_*_result’ functions.  File: gpgme.info, Node: Context Attributes, Next: Key Management, Prev: Result Management, Up: Contexts 7.4 Context Attributes ====================== * Menu: * Protocol Selection:: Selecting the protocol used by a context. * Crypto Engine:: Configuring the crypto engine. * Setting the Sender:: How to tell the engine the sender. * ASCII Armor:: Requesting ASCII armored output. * Text Mode:: Choosing canonical text mode. * Offline Mode:: Choosing offline mode. * Pinentry Mode:: Choosing the pinentry mode. * Included Certificates:: Including a number of certificates. * Key Listing Mode:: Selecting key listing mode. * Passphrase Callback:: Getting the passphrase from the user. * Progress Meter Callback:: Being informed about the progress. * Status Message Callback:: Status messages received from gpg. * Context Flags:: Additional flags for a context. * Locale:: Setting the locale of a context. * Additional Logs:: Additional logs of a context.  File: gpgme.info, Node: Protocol Selection, Next: Crypto Engine, Up: Context Attributes 7.4.1 Protocol Selection ------------------------ -- Function: gpgme_error_t gpgme_set_protocol (gpgme_ctx_t CTX, gpgme_protocol_t PROTO) The function ‘gpgme_set_protocol’ sets the protocol used within the context CTX to PROTO. All crypto operations will be performed by the crypto engine configured for that protocol. *Note Protocols and Engines::. Setting the protocol with ‘gpgme_set_protocol’ does intentionally not check if the crypto engine for that protocol is available and installed correctly. *Note Engine Version Check::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the protocol could be set successfully, and ‘GPG_ERR_INV_VALUE’ if PROTOCOL is not a valid protocol. -- Function: gpgme_protocol_t gpgme_get_protocol (gpgme_ctx_t CTX) The function ‘gpgme_get_protocol’ retrieves the protocol currently use with the context CTX.  File: gpgme.info, Node: Crypto Engine, Next: Setting the Sender, Prev: Protocol Selection, Up: Context Attributes 7.4.2 Crypto Engine ------------------- The following functions can be used to set and retrieve the configuration of the crypto engines of a specific context. The default can also be retrieved without any particular context. *Note Engine Information::. The default can also be changed globally. *Note Engine Configuration::. -- Function: gpgme_engine_info_t gpgme_ctx_get_engine_info (gpgme_ctx_t CTX) SINCE: 1.1.0 The function ‘gpgme_ctx_get_engine_info’ returns a linked list of engine info structures. Each info structure describes the configuration of one configured backend, as used by the context CTX. The result is valid until the next invocation of ‘gpgme_ctx_set_engine_info’ for this particular context. This function can not fail. -- Function: gpgme_error_t gpgme_ctx_set_engine_info (gpgme_ctx_t CTX, gpgme_protocol_t PROTO, const char *FILE_NAME, const char *HOME_DIR) SINCE: 1.1.0 The function ‘gpgme_ctx_set_engine_info’ changes the configuration of the crypto engine implementing the protocol PROTO for the context CTX. FILE_NAME is the file name of the executable program implementing this protocol, and HOME_DIR is the directory name of the configuration directory for this crypto engine. If HOME_DIR is ‘NULL’, the engine’s default will be used. Currently this function must be used before starting the first crypto operation. It is unspecified if and when the changes will take effect if the function is called after starting the first operation on the context CTX. This function returns the error code ‘GPG_ERR_NO_ERROR’ if successful, or an error code on failure.  File: gpgme.info, Node: Setting the Sender, Next: ASCII Armor, Prev: Crypto Engine, Up: Context Attributes 7.4.3 How to tell the engine the sender. ---------------------------------------- Some engines can make use of the sender’s address, for example to figure out the best user id in certain trust models. For verification and signing of mails, it is thus suggested to let the engine know the sender ("From:") address. GPGME provides two functions to accomplish that. Note that the esoteric use of multiple "From:" addresses is not supported. -- Function: gpgme_error_t gpgme_set_sender (gpgme_ctx_t CTX, int ADDRESS) SINCE: 1.8.0 The function ‘gpgme_set_sender’ specifies the sender address for use in sign and verify operations. ADDRESS is expected to be the “addr-spec” part of an address but my also be a complete mailbox address, in which case this function extracts the “addr-spec” from it. Using ‘NULL’ for ADDRESS clears the sender address. The function returns 0 on success or an error code on failure. The most likely failure is that no valid “addr-spec” was found in ADDRESS. -- Function: const char * gpgme_get_sender (gpgme_ctx_t CTX) SINCE: 1.8.0 The function ‘gpgme_get_sender’ returns the current sender address from the context, or NULL if none was set. The returned value is valid as long as the CTX is valid and ‘gpgme_set_sender’ has not been called again.  File: gpgme.info, Node: ASCII Armor, Next: Text Mode, Prev: Setting the Sender, Up: Context Attributes 7.4.4 ASCII Armor ----------------- -- Function: void gpgme_set_armor (gpgme_ctx_t CTX, int YES) The function ‘gpgme_set_armor’ specifies if the output should be ASCII armored. By default, output is not ASCII armored. ASCII armored output is disabled if YES is zero, and enabled otherwise. -- Function: int gpgme_get_armor (gpgme_ctx_t CTX) The function ‘gpgme_get_armor’ returns 1 if the output is ASCII armored, and ‘0’ if it is not, or if CTX is not a valid pointer.  File: gpgme.info, Node: Text Mode, Next: Offline Mode, Prev: ASCII Armor, Up: Context Attributes 7.4.5 Text Mode --------------- -- Function: void gpgme_set_textmode (gpgme_ctx_t CTX, int YES) The function ‘gpgme_set_textmode’ specifies if canonical text mode should be used. By default, text mode is not used. Text mode is for example used for the RFC2015 signatures; note that the updated RFC 3156 mandates that the mail user agent does some preparations so that text mode is not needed anymore. This option is only relevant to the OpenPGP crypto engine, and ignored by all other engines. Canonical text mode is disabled if YES is zero, and enabled otherwise. -- Function: int gpgme_get_textmode (gpgme_ctx_t CTX) The function ‘gpgme_get_textmode’ returns 1 if canonical text mode is enabled, and ‘0’ if it is not, or if CTX is not a valid pointer.  File: gpgme.info, Node: Offline Mode, Next: Pinentry Mode, Prev: Text Mode, Up: Context Attributes 7.4.6 Offline Mode ------------------ -- Function: void gpgme_set_offline (gpgme_ctx_t CTX, int YES) SINCE: 1.6.0 The function ‘gpgme_set_offline’ specifies if offline mode should be used. Offline mode is disabled if YES is zero, and enabled otherwise. By default, offline mode is disabled. The details of the offline mode depend on the used protocol and its backend engine. It may eventually be extended to be more stricter and for example completely disable the use of Dirmngr for any engine. For the CMS protocol the offline mode specifies whether Dirmngr shall be used to do additional validation that might require connecting external services (e.g. CRL / OCSP checks). Here the offline mode only affects the keylist mode ‘GPGME_KEYLIST_MODE_VALIDATE’. For the OpenPGP protocol offline mode entirely disables the use of the Dirmngr and will thus guarantee that no network connections are done as part of an operation on this context. It has only an effect with GnuPG versions 2.1.23 or later. For all other protocols the offline mode is currently ignored. -- Function: int gpgme_get_offline (gpgme_ctx_t CTX) SINCE: 1.6.0 The function ‘gpgme_get_offline’ returns 1 if offline mode is enabled, and ‘0’ if it is not, or if CTX is not a valid pointer.  File: gpgme.info, Node: Pinentry Mode, Next: Included Certificates, Prev: Offline Mode, Up: Context Attributes 7.4.7 Pinentry Mode ------------------- -- Function: gpgme_error_t gpgme_set_pinentry_mode (gpgme_ctx_t CTX, gpgme_pinentry_mode_t MODE) SINCE: 1.4.0 The function ‘gpgme_set_pinentry_mode’ specifies the pinentry mode to be used. For GnuPG >= 2.1 this option is required to be set to ‘GPGME_PINENTRY_MODE_LOOPBACK’ to enable the passphrase callback mechanism in GPGME through ‘gpgme_set_passphrase_cb’. -- Function: gpgme_pinentry_mode_t gpgme_get_pinentry_mode (gpgme_ctx_t CTX) SINCE: 1.4.0 The function ‘gpgme_get_pinenty_mode’ returns the mode set for the context. -- Data type: enum gpgme_pinentry_mode_t SINCE: 1.4.0 The ‘gpgme_minentry_mode_t’ type specifies the set of possible pinentry modes that are supported by GPGME if GnuPG >= 2.1 is used. The following modes are supported: ‘GPGME_PINENTRY_MODE_DEFAULT’ SINCE: 1.4.0 Use the default of the agent, which is ask. ‘GPGME_PINENTRY_MODE_ASK’ SINCE: 1.4.0 Force the use of the Pinentry. ‘GPGME_PINENTRY_MODE_CANCEL’ SINCE: 1.4.0 Emulate use of Pinentry’s cancel button. ‘GPGME_PINENTRY_MODE_ERROR’ SINCE: 1.4.0 Return a Pinentry error ‘No Pinentry’. ‘GPGME_PINENTRY_MODE_LOOPBACK’ SINCE: 1.4.0 Redirect Pinentry queries to the caller. This enables the use of ‘gpgme_set_passphrase_cb’ because pinentry queries are redirected to gpgme. Note: For 2.1.0 - 2.1.12 this mode requires ‘allow-loopback-pinentry’ to be enabled in the ‘gpg-agent.conf’ or an agent started with that option.  File: gpgme.info, Node: Included Certificates, Next: Key Listing Mode, Prev: Pinentry Mode, Up: Context Attributes 7.4.8 Included Certificates --------------------------- -- Function: void gpgme_set_include_certs (gpgme_ctx_t CTX, int NR_OF_CERTS) The function ‘gpgme_set_include_certs’ specifies how many certificates should be included in an S/MIME signed message. By default, only the sender’s certificate is included. The possible values of NR_OF_CERTS are: ‘GPGME_INCLUDE_CERTS_DEFAULT’ SINCE: 1.0.3 Fall back to the default of the crypto backend. This is the default for GPGME. ‘-2’ Include all certificates except the root certificate. ‘-1’ Include all certificates. ‘0’ Include no certificates. ‘1’ Include the sender’s certificate only. ‘n’ Include the first n certificates of the certificates path, starting from the sender’s certificate. The number ‘n’ must be positive. Values of NR_OF_CERTS smaller than -2 are undefined. This option is only relevant to the CMS crypto engine, and ignored by all other engines. -- Function: int gpgme_get_include_certs (gpgme_ctx_t CTX) The function ‘gpgme_get_include_certs’ returns the number of certificates to include into an S/MIME signed message.  File: gpgme.info, Node: Key Listing Mode, Next: Passphrase Callback, Prev: Included Certificates, Up: Context Attributes 7.4.9 Key Listing Mode ---------------------- -- Function: gpgme_error_t gpgme_set_keylist_mode (gpgme_ctx_t CTX, gpgme_keylist_mode_t MODE) The function ‘gpgme_set_keylist_mode’ changes the default behaviour of the key listing functions. The value in MODE is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_KEYLIST_MODE_LOCAL’ The ‘GPGME_KEYLIST_MODE_LOCAL’ symbol specifies that the local keyring should be searched for keys in the keylisting operation. This is the default. Using only this option results in a ‘--list-keys’. ‘GPGME_KEYLIST_MODE_EXTERN’ The ‘GPGME_KEYLIST_MODE_EXTERN’ symbol specifies that an external source should be searched for keys in the keylisting operation. The type of external source is dependent on the crypto engine used and whether it is combined with ‘GPGME_KEYLIST_MODE_LOCAL’. For example, it can be a remote keyserver or LDAP certificate server. Using only this option results in a ‘--search-keys’ for ‘GPGME_PROTOCOL_OpenPGP’ and something similar to ‘--list-external-keys’ for ‘GPGME_PROTOCOL_CMS’. ‘GPGME_KEYLIST_MODE_LOCATE’ This is a shortcut for the combination of ‘GPGME_KEYLIST_MODE_LOCAL’ and ‘GPGME_KEYLIST_MODE_EXTERN’, which results in a ‘--locate-keys’ for ‘GPGME_PROTOCOL_OpenPGP’. ‘GPGME_KEYLIST_MODE_SIGS’ The ‘GPGME_KEYLIST_MODE_SIGS’ symbol specifies that the key signatures should be included in the listed keys. ‘GPGME_KEYLIST_MODE_SIG_NOTATIONS’ SINCE: 1.1.1 The ‘GPGME_KEYLIST_MODE_SIG_NOTATIONS’ symbol specifies that the signature notations on key signatures should be included in the listed keys. This only works if ‘GPGME_KEYLIST_MODE_SIGS’ is also enabled. ‘GPGME_KEYLIST_MODE_WITH_TOFU’ SINCE: 1.7.0 The ‘GPGME_KEYLIST_MODE_WITH_TOFU’ symbol specifies that information pertaining to the TOFU trust model should be included in the listed keys. ‘GPGME_KEYLIST_MODE_WITH_SECRET’ SINCE: 1.5.1 The ‘GPGME_KEYLIST_MODE_WITH_SECRET’ returns information about the presence of a corresponding secret key in a public key listing. A public key listing with this mode is slower than a standard listing but can be used instead of a second run to list the secret keys. This is only supported for GnuPG versions >= 2.1. ‘GPGME_KEYLIST_MODE_EPHEMERAL’ SINCE: 1.2.0 The ‘GPGME_KEYLIST_MODE_EPHEMERAL’ symbol specifies that keys flagged as ephemeral are included in the listing. ‘GPGME_KEYLIST_MODE_VALIDATE’ SINCE: 0.4.5 The ‘GPGME_KEYLIST_MODE_VALIDATE’ symbol specifies that the backend should do key or certificate validation and not just get the validity information from an internal cache. This might be an expensive operation and is in general not useful. Currently only implemented for the S/MIME backend and ignored for other backends. At least one of ‘GPGME_KEYLIST_MODE_LOCAL’ and ‘GPGME_KEYLIST_MODE_EXTERN’ must be specified. For future binary compatibility, you should get the current mode with ‘gpgme_get_keylist_mode’ and modify it by setting or clearing the appropriate bits, and then using that calculated value in the ‘gpgme_set_keylisting_mode’ operation. This will leave all other bits in the mode value intact (in particular those that are not used in the current version of the library). The function returns the error code ‘GPG_ERR_NO_ERROR’ if the mode could be set correctly, and ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer or MODE is not a valid mode. -- Function: gpgme_keylist_mode_t gpgme_get_keylist_mode (gpgme_ctx_t CTX) The function ‘gpgme_get_keylist_mode’ returns the current key listing mode of the context CTX. This value can then be modified and used in a subsequent ‘gpgme_set_keylist_mode’ operation to only affect the desired bits (and leave all others intact). The function returns 0 if CTX is not a valid pointer, and the current mode otherwise. Note that 0 is not a valid mode value.  File: gpgme.info, Node: Passphrase Callback, Next: Progress Meter Callback, Prev: Key Listing Mode, Up: Context Attributes 7.4.10 Passphrase Callback -------------------------- -- Data type: gpgme_error_t (*gpgme_passphrase_cb_t)(void *HOOK, const char *UID_HINT, const char *PASSPHRASE_INFO, int PREV_WAS_BAD, int FD) The ‘gpgme_passphrase_cb_t’ type is the type of functions usable as passphrase callback function. The argument UID_HINT might contain a string that gives an indication for which user ID the passphrase is required. If this is not available, or not applicable (in the case of symmetric encryption, for example), UID_HINT will be ‘NULL’. The argument PASSPHRASE_INFO, if not ‘NULL’, will give further information about the context in which the passphrase is required. This information is engine and operation specific. If this is the repeated attempt to get the passphrase, because previous attempts failed, then PREV_WAS_BAD is 1, otherwise it will be 0. The user must write the passphrase, followed by a newline character, to the file descriptor FD. The function ‘gpgme_io_writen’ should be used for the write operation. Note that if the user returns 0 to indicate success, the user must at least write a newline character before returning from the callback. If an error occurs, return the corresponding ‘gpgme_error_t’ value. You can use the error code ‘GPG_ERR_CANCELED’ to abort the operation. Otherwise, return ‘0’. Note: The passphrase_cb only works with GnuPG 1.x and 2.1.x and not with the 2.0.x series. See ‘gpgme_set_pinentry_mode’ for more details on 2.1.x usage. -- Function: void gpgme_set_passphrase_cb (gpgme_ctx_t CTX, gpgme_passphrase_cb_t PASSFUNC, void *HOOK_VALUE) The function ‘gpgme_set_passphrase_cb’ sets the function that is used when a passphrase needs to be provided by the user to PASSFUNC. The function PASSFUNC needs to implemented by the user, and whenever it is called, it is called with its first argument being HOOK_VALUE. By default, no passphrase callback function is set. Not all crypto engines require this callback to retrieve the passphrase. It is better if the engine retrieves the passphrase from a trusted agent (a daemon process), rather than having each user to implement their own passphrase query. Some engines do not even support an external passphrase callback at all, in this case the error code ‘GPG_ERR_NOT_SUPPORTED’ is returned. For GnuPG >= 2.1 the pinentry mode has to be set to ‘GPGME_PINENTRY_MODE_LOOPBACK’ to enable the passphrase callback. See ‘gpgme_set_pinentry_mode’. The user can disable the use of a passphrase callback function by calling ‘gpgme_set_passphrase_cb’ with PASSFUNC being ‘NULL’. -- Function: void gpgme_get_passphrase_cb (gpgme_ctx_t CTX, gpgme_passphrase_cb_t *PASSFUNC, void **HOOK_VALUE) The function ‘gpgme_get_passphrase_cb’ returns the function that is used when a passphrase needs to be provided by the user in *PASSFUNC, and the first argument for this function in *HOOK_VALUE. If no passphrase callback is set, or CTX is not a valid pointer, ‘NULL’ is returned in both variables. PASSFUNC or HOOK_VALUE can be ‘NULL’. In this case, the corresponding value will not be returned.  File: gpgme.info, Node: Progress Meter Callback, Next: Status Message Callback, Prev: Passphrase Callback, Up: Context Attributes 7.4.11 Progress Meter Callback ------------------------------ -- Data type: void (*gpgme_progress_cb_t)(void *HOOK, const char *WHAT, int TYPE, int CURRENT, int TOTAL) The ‘gpgme_progress_cb_t’ type is the type of functions usable as progress callback function. The arguments are specific to the crypto engine. More information about the progress information returned from the GnuPG engine can be found in the GnuPG source code in the file ‘doc/DETAILS’ in the section PROGRESS. -- Function: void gpgme_set_progress_cb (gpgme_ctx_t CTX, gpgme_progress_cb_t PROGFUNC, void *HOOK_VALUE) The function ‘gpgme_set_progress_cb’ sets the function that is used when progress information about a cryptographic operation is available. The function PROGFUNC needs to implemented by the user, and whenever it is called, it is called with its first argument being HOOK_VALUE. By default, no progress callback function is set. Setting a callback function allows an interactive program to display progress information about a long operation to the user. The user can disable the use of a progress callback function by calling ‘gpgme_set_progress_cb’ with PROGFUNC being ‘NULL’. -- Function: void gpgme_get_progress_cb (gpgme_ctx_t CTX, gpgme_progress_cb_t *PROGFUNC, void **HOOK_VALUE) The function ‘gpgme_get_progress_cb’ returns the function that is used to inform the user about the progress made in *PROGFUNC, and the first argument for this function in *HOOK_VALUE. If no progress callback is set, or CTX is not a valid pointer, ‘NULL’ is returned in both variables. PROGFUNC or HOOK_VALUE can be ‘NULL’. In this case, the corresponding value will not be returned.  File: gpgme.info, Node: Status Message Callback, Next: Context Flags, Prev: Progress Meter Callback, Up: Context Attributes 7.4.12 Status Message Callback ------------------------------ -- Data type: gpgme_error_t (*gpgme_status_cb_t)(void *HOOK, const char *KEYWORD, const char *ARGS) The ‘gpgme_status_cb_t’ type is the type of function usable as a status message callback function. The argument KEYWORD is the name of the status message while the ARGS argument contains any arguments for the status message. If an error occurs, return the corresponding ‘gpgme_error_t’ value. Otherwise, return ‘0’. -- Function: void gpgme_set_status_cb (gpgme_ctx_t CTX, gpgme_status_cb_t STATUSFUNC, void *HOOK_VALUE) SINCE: 1.6.0 The function ‘gpgme_set_status_cb’ sets the function that is used when a status message is received from gpg to STATUSFUNC. The function STATUSFUNC needs to be implemented by the user, and whenever it is called, it is called with its first argument being HOOK_VALUE. By default, no status message callback function is set. The user can disable the use of a status message callback function by calling ‘gpgme_set_status_cb’ with STATUSFUNC being ‘NULL’. -- Function: void gpgme_get_status_cb (gpgme_ctx_t CTX, gpgme_status_cb_t *STATUSFUNC, void **HOOK_VALUE) SINCE: 1.6.0 The function ‘gpgme_get_status_cb’ returns the function that is used to process status messages from gpg in *STATUSFUNC, and the first argument for this function in *HOOK_VALUE. If no status message callback is set, or CTX is not a valid pointer, ‘NULL’ is returned in both variables.  File: gpgme.info, Node: Context Flags, Next: Locale, Prev: Status Message Callback, Up: Context Attributes 7.4.13 Context Flags -------------------- -- Function: gpgme_error_t gpgme_set_ctx_flag (gpgme_ctx_t CTX, const char *NAME, const char *VALUE) SINCE: 1.7.0 Some minor properties of the context can be controlled with flags set by this function. The properties are identified by the following values for NAME: ‘"redraw"’ This flag is normally not changed by the caller because GPGME sets and clears it automatically: The flag is cleared before an operation and set if an operation noticed that the engine has launched a Pinentry. A Curses based application may use this information to redraw the screen; for example: err = gpgme_op_keylist_start (ctx, "foo@example.org", 0); while (!err) { err = gpgme_op_keylist_next (ctx, &key); if (err) break; show_key (key); gpgme_key_release (key); } if ((s = gpgme_get_ctx_flag (ctx, "redraw")) && *s) redraw_screen (); gpgme_release (ctx); ‘"full-status"’ Using a VALUE of "1" the status callback set by gpgme_set_status_cb returns all status lines with the exception of PROGRESS lines. With the default of "0" the status callback is only called in certain situations. ‘"raw-description"’ Setting the VALUE to "1" returns human readable strings in a raw format. For example the non breaking space characters ("~") will not be removed from the ‘description’ field of the ‘gpgme_tofu_info_t’ object. ‘"export-session-key"’ Using a VALUE of "1" specifies that the context should try to export the symmetric session key when decrypting data. By default, or when using an empty string or "0" for VALUE, session keys are not exported. ‘"override-session-key"’ The string given in VALUE is passed to the GnuPG engine to override the session key for decryption. The format of that session key is specific to GnuPG and can be retrieved during a decrypt operation when the context flag "export-session-key" is enabled. Please be aware that using this feature with GnuPG < 2.1.16 will leak the session key on many platforms via ps(1). ‘"auto-key-retrieve"’ Setting the VALUE to "1" asks the backend to automatically retrieve a key for signature verification if possible. Note that this option makes a "web bug" like behavior possible. Keyserver or Web Key Directory operators can see which keys you request, so by sending you a message signed by a brand new key (which you naturally will not have on your local keyring), the operator can tell both your IP address and the time when you verified the signature. ‘"request-origin"’ The string given in VALUE is passed to the GnuPG engines to request restrictions based on the origin of the request. Valid values are documented in the GnuPG manual and the gpg man page under the option ‘--request-origin’. Requires at least GnuPG 2.2.6 to have an effect. ‘"no-symkey-cache"’ For OpenPGP disable the passphrase cache used for symmetrical en- and decryption. This cache is based on the message specific salt value. Requires at least GnuPG 2.2.7 to have an effect. ‘"ignore-mdc-error"’ This flag passes the option ‘--ignore-mdc-error’ to gpg. This can be used to force decryption of a message which failed due to a missing integrity check. This flag must be used with great caution and only if it is a known non-corrupted old message and the decryption result of the former try had the decryption result flag ‘legacy_cipher_nomdc’ set. For failsafe reasons this flag is reset after each operation. ‘"auto-key-locate"’ The string given in VALUE is passed to gpg. This can be used to change the behavior of a ‘GPGME_KEYLIST_MODE_LOCATE’ keylisting. Valid values are documented in the GnuPG manual and the gpg man page under the option ‘--auto-key-locate’. Requires at least GnuPG 2.1.18. Note: Keys retrieved through ‘auto-key-locate’ are automatically imported in the keyring. ‘trust-model’ SINCE: 1.11.2 Change the trust-model for all GnuPG engine operations. An empty string sets the trust-model back to the users default. If the trust-model is not supported by GnuPG the behavior is undefined and will likely cause all operations to fail. Example: "tofu+pgp". This options should be used carefully with a strict version requirement. In some versions of GnuPG setting the trust-model changes the default trust-model for future operations. A change in the trust-model also can have unintended side effects, like rebuilding the trust-db. This function returns ‘0’ on success. -- Function: const char * gpgme_get_ctx_flag (gpgme_ctx_t CTX, const char *NAME) SINCE: 1.8.0 The value of flags settable by ‘gpgme_set_ctx_flag’ can be retrieved by this function. If NAME is unknown the function returns ‘NULL’. For boolean flags an empty string is returned for False and the string "1" is returned for True; either atoi(3) or a test for an empty string can be used to get the boolean value.  File: gpgme.info, Node: Locale, Next: Additional Logs, Prev: Context Flags, Up: Context Attributes 7.4.14 Locale ------------- A locale setting can be associated with a context. This locale is passed to the crypto engine, and used for applications like the PIN entry, which is displayed to the user when entering a passphrase is required. The default locale is used to initialize the locale setting of all contexts created afterwards. -- Function: gpgme_error_t gpgme_set_locale (gpgme_ctx_t CTX, int CATEGORY, const char *VALUE) SINCE: 0.4.3 The function ‘gpgme_set_locale’ sets the locale of the context CTX, or the default locale if CTX is a null pointer. The locale settings that should be changed are specified by CATEGORY. Supported categories are ‘LC_CTYPE’, ‘LC_MESSAGES’, and ‘LC_ALL’, which is a wildcard you can use if you want to change all the categories at once. The value to be used for the locale setting is VALUE, which will be copied to GPGME’s internal data structures. VALUE can be a null pointer, which disables setting the locale, and will make PIN entry and other applications use their default setting, which is usually not what you want. Note that the settings are only used if the application runs on a text terminal, and that the settings should fit the configuration of the output terminal. Normally, it is sufficient to initialize the default value at startup. The function returns an error if not enough memory is available.  File: gpgme.info, Node: Additional Logs, Prev: Locale, Up: Context Attributes 7.4.15 Additional Logs ---------------------- Additional logs can be associated with a context. These logs are engine specific and can be be obtained with ‘gpgme_op_getauditlog’. -- Function: gpgme_error_t gpgme_op_getauditlog (gpgme_ctx_t CTX, gpgme_data_t OUTPUT, unsigned int FLAGS) SINCE: 1.1.1 The function ‘gpgme_op_getauditlog’ is used to obtain additional logs as specified by FLAGS into the OUTPUT data. If The function returns the error code ‘GPG_ERR_NO_ERROR’ if a log could be queried from the engine, and ‘GPG_ERR_NOT_IMPLEMENTED’ if the log specified in FLAGS is not available for this engine. If no log is available ‘GPG_ERR_NO_DATA’ is returned. The value in FLAGS is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_AUDITLOG_DIAG’ SINCE: 1.11.2 Obtain diagnostic output which would be written to ‘stderr’ in interactive use of the engine. This can be used to provide additional diagnostic information in case of errors in other operations. Note: If log-file has been set in the configuration the log will be empty and ‘GPG_ERR_NO_DATA’ will be returned. Implemented for: ‘GPGME_PROTOCOL_OpenPGP’ ‘GPGME_AUDITLOG_DEFAULT’ SINCE: 1.11.2 This flag has the value 0 for compatibility reasons. Obtains additional information from the engine by issuing the ‘GETAUDITLOG’ command. For ‘GPGME_PROTOCOL_CMS’ this provides additional information about the X509 certificate chain. Implemented for: ‘GPGME_PROTOCOL_CMS’ ‘GPGME_AUDITLOG_HTML’ SINCE: 1.1.1 Same as ‘GPGME_AUDITLOG_DEFAULT’ but in HTML. Implemented for: ‘GPGME_PROTOCOL_CMS’ -- Function: gpgme_error_t gpgme_op_getauditlog_start (gpgme_ctx_t CTX, gpgme_data_t OUTPUT, unsigned int FLAGS) SINCE: 1.1.1 This is the asynchronous variant of ‘gpgme_op_getauditlog’.  File: gpgme.info, Node: Key Management, Next: Trust Item Management, Prev: Context Attributes, Up: Contexts 7.5 Key Management ================== Some of the cryptographic operations require that recipients or signers are specified. This is always done by specifying the respective keys that should be used for the operation. The following section describes how such keys can be selected and manipulated. * Menu: * Key objects:: Description of the key structures. * Listing Keys:: Browsing the list of available keys. * Information About Keys:: Requesting detailed information about keys. * Manipulating Keys:: Operations on keys. * Generating Keys:: Creating new key pairs. * Signing Keys:: Adding key signatures to public keys. * Exporting Keys:: Retrieving key data from the key ring. * Importing Keys:: Adding keys to the key ring. * Deleting Keys:: Removing keys from the key ring. * Changing Passphrases:: Change the passphrase of a key. * Changing TOFU Data:: Changing data pertaining to TOFU. * Advanced Key Editing:: Advanced key edit operation.  File: gpgme.info, Node: Key objects, Next: Listing Keys, Up: Key Management 7.5.1 Key objects ----------------- The keys are represented in GPGME by structures which may only be read by the application but never be allocated or changed. They are valid as long as the key object itself is valid. -- Data type: gpgme_key_t The ‘gpgme_key_t’ type is a pointer to a key object. It has the following members: ‘gpgme_keylist_mode_t keylist_mode’ SINCE: 0.9.0 The keylist mode that was active when the key was retrieved. ‘unsigned int revoked : 1’ This is true if the key is revoked. ‘unsigned int expired : 1’ This is true if the key is expired. ‘unsigned int disabled : 1’ This is true if the key is disabled. ‘unsigned int invalid : 1’ This is true if the key is invalid. This might have several reasons, for a example for the S/MIME backend, it will be set during key listings if the key could not be validated due to missing certificates or unmatched policies. ‘unsigned int can_encrypt : 1’ This is true if the key (ie one of its subkeys) can be used for encryption. ‘unsigned int can_sign : 1’ This is true if the key (ie one of its subkeys) can be used to create data signatures. ‘unsigned int can_certify : 1’ This is true if the key (ie one of its subkeys) can be used to create key certificates. ‘unsigned int can_authenticate : 1’ SINCE: 0.4.5 This is true if the key (ie one of its subkeys) can be used for authentication. ‘unsigned int is_qualified : 1’ SINCE: 1.1.0 This is true if the key can be used for qualified signatures according to local government regulations. ‘unsigned int secret : 1’ This is true if the key is a secret key. Note, that this will always be true even if the corresponding subkey flag may be false (offline/stub keys). This is only set if a listing of secret keys has been requested or if ‘GPGME_KEYLIST_MODE_WITH_SECRET’ is active. ‘unsigned int origin : 5’ SINCE: 1.8.0 Reserved for the origin of this key. ‘gpgme_protocol_t protocol’ This is the protocol supported by this key. ‘char *issuer_serial’ If ‘protocol’ is ‘GPGME_PROTOCOL_CMS’, then this is the issuer serial. ‘char *issuer_name’ If ‘protocol’ is ‘GPGME_PROTOCOL_CMS’, then this is the issuer name. ‘char *chain_id’ If ‘protocol’ is ‘GPGME_PROTOCOL_CMS’, then this is the chain ID, which can be used to built the certificate chain. ‘gpgme_validity_t owner_trust’ If ‘protocol’ is ‘GPGME_PROTOCOL_OpenPGP’, then this is the owner trust. ‘gpgme_subkey_t subkeys’ This is a linked list with the subkeys of the key. The first subkey in the list is the primary key and usually available. ‘gpgme_user_id_t uids’ This is a linked list with the user IDs of the key. The first user ID in the list is the main (or primary) user ID. ‘char *fpr’ SINCE: 1.7.0 This field gives the fingerprint of the primary key. Note that this is a copy of the fingerprint of the first subkey. For an incomplete key (for example from a verification result) a subkey may be missing but this field may be set nevertheless. ‘unsigned long last_update’ SINCE: 1.8.0 Reserved for the time of the last update of this key. -- Data type: gpgme_subkey_t SINCE: 1.5.0 The ‘gpgme_subkey_t’ type is a pointer to a subkey structure. Subkeys are one component of a ‘gpgme_key_t’ object. In fact, subkeys are those parts that contains the real information about the individual cryptographic keys that belong to the same key object. One ‘gpgme_key_t’ can contain several subkeys. The first subkey in the linked list is also called the primary key. The subkey structure has the following members: ‘gpgme_subkey_t next’ This is a pointer to the next subkey structure in the linked list, or ‘NULL’ if this is the last element. ‘unsigned int revoked : 1’ This is true if the subkey is revoked. ‘unsigned int expired : 1’ This is true if the subkey is expired. ‘unsigned int disabled : 1’ This is true if the subkey is disabled. ‘unsigned int invalid : 1’ This is true if the subkey is invalid. ‘unsigned int can_encrypt : 1’ This is true if the subkey can be used for encryption. ‘unsigned int can_sign : 1’ This is true if the subkey can be used to create data signatures. ‘unsigned int can_certify : 1’ This is true if the subkey can be used to create key certificates. ‘unsigned int can_authenticate : 1’ SINCE: 0.4.5 This is true if the subkey can be used for authentication. ‘unsigned int is_qualified : 1’ SINCE: 1.1.0 This is true if the subkey can be used for qualified signatures according to local government regulations. ‘unsigned int is_de_vs : 1’ SINCE: 1.8.0 This is true if the subkey complies with the rules for classified information in Germany at the restricted level (VS-NfD). This are currently RSA keys of at least 2048 bits or ECDH/ECDSA keys using a Brainpool curve. ‘unsigned int secret : 1’ This is true if the subkey is a secret key. Note that it will be false if the key is actually a stub key; i.e. a secret key operation is currently not possible (offline-key). This is only set if a listing of secret keys has been requested or if ‘GPGME_KEYLIST_MODE_WITH_SECRET’ is active. ‘gpgme_pubkey_algo_t pubkey_algo’ This is the public key algorithm supported by this subkey. ‘unsigned int length’ This is the length of the subkey (in bits). ‘char *keyid’ This is the key ID of the subkey in hexadecimal digits. ‘char *fpr’ This is the fingerprint of the subkey in hexadecimal digits, if available. ‘char *keygrip’ SINCE: 1.7.0 The keygrip of the subkey in hex digit form or ‘NULL’ if not availabale. ‘long int timestamp’ This is the creation timestamp of the subkey. This is -1 if the timestamp is invalid, and 0 if it is not available. ‘long int expires’ This is the expiration timestamp of the subkey, or 0 if the subkey does not expire. ‘unsigned int is_cardkey : 1’ SINCE: 1.2.0 True if the secret key is stored on a smart card. ‘char *card_number’ SINCE: 1.2.0 The serial number of a smart card holding this key or ‘NULL’. ‘char *curve’ For ECC algorithms the name of the curve. -- Data type: gpgme_user_id_t A user ID is a component of a ‘gpgme_key_t’ object. One key can have many user IDs. The first one in the list is the main (or primary) user ID. The user ID structure has the following members. ‘gpgme_user_id_t next’ This is a pointer to the next user ID structure in the linked list, or ‘NULL’ if this is the last element. ‘unsigned int revoked : 1’ This is true if the user ID is revoked. ‘unsigned int invalid : 1’ This is true if the user ID is invalid. ‘gpgme_validity_t validity’ This specifies the validity of the user ID. ‘char *uid’ This is the user ID string. ‘char *name’ This is the name component of ‘uid’, if available. ‘char *comment’ This is the comment component of ‘uid’, if available. ‘char *email’ This is the email component of ‘uid’, if available. ‘char *address;’ The mail address (addr-spec from RFC-5322) of the user ID string. This is general the same as the ‘email’ part of this structure but might be slightly different. If no mail address is available ‘NULL’ is stored. ‘gpgme_tofu_info_t tofu’ SINCE: 1.7.0 If not ‘NULL’ information from the TOFU database pertaining to this user id. ‘gpgme_key_sig_t signatures’ This is a linked list with the signatures on this user ID. ‘unsigned int origin : 5’ SINCE: 1.8.0 Reserved for the origin of this user ID. ‘unsigned long last_update’ SINCE: 1.8.0 Reserved for the time of the last update of this user ID. -- Data type: gpgme_tofu_info_t SINCE: 1.7.0 The ‘gpgme_tofu_info_t’ type is a pointer to a tofu info structure. Tofu info structures are one component of a ‘gpgme_user_id_t’ object, and provide information from the TOFU database pertaining to the user ID. The tofu info structure has the following members: ‘gpgme_key_sig_t next’ This is a pointer to the next tofu info structure in the linked list, or ‘NULL’ if this is the last element. ‘unsigned int validity : 3’ This is the TOFU validity. It can have the following values: ‘0’ The value ‘0’ indicates a conflict. ‘1’ The value ‘1’ indicates a key without history. ‘2’ The value ‘2’ indicates a key with too little history. ‘3’ The value ‘3’ indicates a key with enough history for basic trust. ‘4’ The value ‘4’ indicates a key with a lot of history. ‘unsigned int policy : 4’ This is the TOFU policy, see ‘gpgme_tofu_policy_t’. ‘unsigned short signcount’ This is the number of signatures seen for this binding (or ‘USHRT_MAX’ if there are more than that). ‘unsigned short encrcount’ This is the number of encryptions done with this binding (or ‘USHRT_MAX’ if there are more than that). ‘unsigned long signfirst’ Number of seconds since Epoch when the first signature was seen with this binding. ‘unsigned long signlast’ Number of seconds since Epoch when the last signature was seen with this binding. ‘unsigned long encrfirst’ Number of seconds since Epoch when the first encryption was done with this binding. ‘unsigned long encrlast’ Number of seconds since Epoch when the last encryption was done with this binding. ‘char *description’ A human-readable string summarizing the TOFU data (or NULL). -- Data type: gpgme_key_sig_t The ‘gpgme_key_sig_t’ type is a pointer to a key signature structure. Key signatures are one component of a ‘gpgme_key_t’ object, and validate user IDs on the key in the OpenPGP protocol. The signatures on a key are only available if the key was retrieved via a listing operation with the ‘GPGME_KEYLIST_MODE_SIGS’ mode enabled, because it can be expensive to retrieve all signatures of a key. The signature notations on a key signature are only available if the key was retrieved via a listing operation with the ‘GPGME_KEYLIST_MODE_SIG_NOTATIONS’ mode enabled, because it can be expensive to retrieve all signature notations. The key signature structure has the following members: ‘gpgme_key_sig_t next’ This is a pointer to the next key signature structure in the linked list, or ‘NULL’ if this is the last element. ‘unsigned int revoked : 1’ This is true if the key signature is a revocation signature. ‘unsigned int expired : 1’ This is true if the key signature is expired. ‘unsigned int invalid : 1’ This is true if the key signature is invalid. ‘unsigned int exportable : 1’ This is true if the key signature is exportable. ‘gpgme_pubkey_algo_t pubkey_algo’ This is the public key algorithm used to create the signature. ‘char *keyid’ This is the key ID of the key (in hexadecimal digits) used to create the signature. ‘long int timestamp’ This is the creation timestamp of the key signature. This is -1 if the timestamp is invalid, and 0 if it is not available. ‘long int expires’ This is the expiration timestamp of the key signature, or 0 if the key signature does not expire. ‘gpgme_error_t status’ This is the status of the signature and has the same meaning as the member of the same name in a ‘gpgme_signature_t’ object. ‘unsigned int sig_class’ This specifies the signature class of the key signature. The meaning is specific to the crypto engine. ‘char *uid’ This is the main user ID of the key used to create the signature. ‘char *name’ This is the name component of ‘uid’, if available. ‘char *comment’ This is the comment component of ‘uid’, if available. ‘char *email’ This is the email component of ‘uid’, if available. ‘gpgme_sig_notation_t notations’ This is a linked list with the notation data and policy URLs.  File: gpgme.info, Node: Listing Keys, Next: Information About Keys, Prev: Key objects, Up: Key Management 7.5.2 Listing Keys ------------------ -- Function: gpgme_error_t gpgme_op_keylist_start (gpgme_ctx_t CTX, const char *PATTERN, int SECRET_ONLY) The function ‘gpgme_op_keylist_start’ initiates a key listing operation inside the context CTX. It sets everything up so that subsequent invocations of ‘gpgme_op_keylist_next’ return the keys in the list. If PATTERN is ‘NULL’, all available keys are returned. Otherwise, PATTERN contains an engine specific expression that is used to limit the list to all keys matching the pattern. Note that the total length of the pattern is restricted to an engine-specific maximum (a couple of hundred characters are usually accepted). The pattern should be used to restrict the search to a certain common name or user, not to list many specific keys at once by listing their fingerprints or key IDs. If SECRET_ONLY is not ‘0’, the list is restricted to secret keys only. The context will be busy until either all keys are received (and ‘gpgme_op_keylist_next’ returns ‘GPG_ERR_EOF’), or ‘gpgme_op_keylist_end’ is called to finish the operation. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_keylist_ext_start (gpgme_ctx_t CTX, const char *PATTERN[], int SECRET_ONLY, int RESERVED) The function ‘gpgme_op_keylist_ext_start’ initiates an extended key listing operation inside the context CTX. It sets everything up so that subsequent invocations of ‘gpgme_op_keylist_next’ return the keys in the list. If PATTERN or *PATTERN is ‘NULL’, all available keys are returned. Otherwise, PATTERN is a ‘NULL’ terminated array of strings that are used to limit the list to all keys matching at least one of the patterns verbatim. Note that the total length of all patterns is restricted to an engine-specific maximum (the exact limit also depends on the number of patterns and amount of quoting required, but a couple of hundred characters are usually accepted). Patterns should be used to restrict the search to a certain common name or user, not to list many specific keys at once by listing their fingerprints or key IDs. If SECRET_ONLY is not ‘0’, the list is restricted to secret keys only. The value of RESERVED must be ‘0’. The context will be busy until either all keys are received (and ‘gpgme_op_keylist_next’ returns ‘GPG_ERR_EOF’), or ‘gpgme_op_keylist_end’ is called to finish the operation. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_keylist_from_data_start (gpgme_ctx_t CTX, gpgme_data_t DATA, int RESERVED) SINCE: 1.8.0 The function ‘gpgme_op_keylist_from_data_start’ initiates a key listing operation inside the context CTX. In contrast to the other key listing operation the keys are read from the supplied DATA and not from the local key database. The keys are also not imported into the local key database. The function sets everything up so that subsequent invocations of ‘gpgme_op_keylist_next’ return the keys from DATA. The value of RESERVED must be ‘0’. This function requires at least GnuPG version 2.1.14 and currently works only with OpenPGP keys. The context will be busy until either all keys are received (and ‘gpgme_op_keylist_next’ returns ‘GPG_ERR_EOF’), or ‘gpgme_op_keylist_end’ is called to finish the operation. While the context is busy DATA may not be released. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_keylist_next (gpgme_ctx_t CTX, gpgme_key_t *R_KEY) The function ‘gpgme_op_keylist_next’ returns the next key in the list created by a previous ‘gpgme_op_keylist_start’ operation in the context CTX. The key will have one reference for the user. *Note Manipulating Keys::. This is the only way to get at ‘gpgme_key_t’ objects in GPGME. If the last key in the list has already been returned, ‘gpgme_op_keylist_next’ returns ‘GPG_ERR_EOF’. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX or R_KEY is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if there is not enough memory for the operation. -- Function: gpgme_error_t gpgme_op_keylist_end (gpgme_ctx_t CTX) The function ‘gpgme_op_keylist_end’ ends a pending key list operation in the context CTX. After the operation completed successfully, the result of the key listing operation can be retrieved with ‘gpgme_op_keylist_result’. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if at some time during the operation there was not enough memory available. The following example illustrates how all keys containing a certain string (‘g10code’) can be listed with their key ID and the name and email address of the main user ID: gpgme_ctx_t ctx; gpgme_key_t key; gpgme_error_t err = gpgme_new (&ctx); if (!err) { err = gpgme_op_keylist_start (ctx, "g10code", 0); while (!err) { err = gpgme_op_keylist_next (ctx, &key); if (err) break; printf ("%s:", key->subkeys->keyid); if (key->uids && key->uids->name) printf (" %s", key->uids->name); if (key->uids && key->uids->email) printf (" <%s>", key->uids->email); putchar ('\n'); gpgme_key_release (key); } gpgme_release (ctx); } if (gpg_err_code (err) != GPG_ERR_EOF) { fprintf (stderr, "can not list keys: %s\n", gpgme_strerror (err)); exit (1); } -- Data type: gpgme_keylist_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_keylist_*’ operation. After successfully ending a key listing operation, you can retrieve the pointer to the result with ‘gpgme_op_keylist_result’. The structure contains the following member: ‘unsigned int truncated : 1’ This is true if the crypto backend had to truncate the result, and less than the desired keys could be listed. -- Function: gpgme_keylist_result_t gpgme_op_keylist_result (gpgme_ctx_t CTX) The function ‘gpgme_op_keylist_result’ returns a ‘gpgme_keylist_result_t’ pointer to a structure holding the result of a ‘gpgme_op_keylist_*’ operation. The pointer is only valid if the last operation on the context was a key listing operation, and if this operation finished successfully. The returned pointer is only valid until the next operation is started on the context. In a simple program, for which a blocking operation is acceptable, the following function can be used to retrieve a single key. -- Function: gpgme_error_t gpgme_get_key (gpgme_ctx_t CTX, const char *FPR, gpgme_key_t *R_KEY, int SECRET) The function ‘gpgme_get_key’ gets the key with the fingerprint (or key ID) FPR from the crypto backend and return it in R_KEY. If SECRET is true, get the secret key. The currently active keylist mode is used to retrieve the key. The key will have one reference for the user. If the key is not found in the keyring, ‘gpgme_get_key’ returns the error code ‘GPG_ERR_EOF’ and *R_KEY will be set to ‘NULL’. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX or R_KEY is not a valid pointer or FPR is not a fingerprint or key ID, ‘GPG_ERR_AMBIGUOUS_NAME’ if the key ID was not a unique specifier for a key, and ‘GPG_ERR_ENOMEM’ if at some time during the operation there was not enough memory available.  File: gpgme.info, Node: Information About Keys, Next: Manipulating Keys, Prev: Listing Keys, Up: Key Management 7.5.3 Information About Keys ---------------------------- Please see the beginning of this section for more information about ‘gpgme_key_t’ objects. -- Data type: gpgme_validity_t The ‘gpgme_validity_t’ type is used to specify the validity of a user ID in a key. The following validities are defined: ‘GPGME_VALIDITY_UNKNOWN’ The user ID is of unknown validity. The string representation of this validity is “?”. ‘GPGME_VALIDITY_UNDEFINED’ The validity of the user ID is undefined. The string representation of this validity is “q”. ‘GPGME_VALIDITY_NEVER’ The user ID is never valid. The string representation of this validity is “n”. ‘GPGME_VALIDITY_MARGINAL’ The user ID is marginally valid. The string representation of this validity is “m”. ‘GPGME_VALIDITY_FULL’ The user ID is fully valid. The string representation of this validity is “f”. ‘GPGME_VALIDITY_ULTIMATE’ The user ID is ultimately valid. The string representation of this validity is “u”.  File: gpgme.info, Node: Manipulating Keys, Next: Generating Keys, Prev: Information About Keys, Up: Key Management 7.5.4 Manipulating Keys ----------------------- -- Function: void gpgme_key_ref (gpgme_key_t KEY) The function ‘gpgme_key_ref’ acquires an additional reference for the key KEY. -- Function: void gpgme_key_unref (gpgme_key_t KEY) The function ‘gpgme_key_unref’ releases a reference for the key KEY. If this was the last reference, the key will be destroyed and all resources associated to it will be released.  File: gpgme.info, Node: Generating Keys, Next: Signing Keys, Prev: Manipulating Keys, Up: Key Management 7.5.5 Generating Keys --------------------- GPGME provides a set of functions to create public key pairs. Most of these functions require the use of GnuPG 2.1 and later; for older GnuPG versions the ‘gpgme_op_genkey’ function can be used. Existing code which wants to update to the new functions or new code which shall supports older GnuPG versions may try the new functions first and provide a fallback to the old function if the error code ‘GPG_ERR_NOT_SUPPORTED’ is received. -- Function: gpgme_error_t gpgme_op_createkey (gpgme_ctx_t CTX, const char *USERID, const char *ALGO, unsigned long RESERVED, unsigned long EXPIRES, gpgme_key_t EXTRAKEY, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_createkey’ generates a new key for the procotol active in the context CTX. As of now this function does only work for OpenPGP and requires at least version 2.1.13 of GnuPG. USERID is commonly the mail address associated with the key. GPGME does not require a specific syntax but if more than a mail address is given, RFC-822 style format is suggested. The value is expected to be in UTF-8 encoding (i.e. no IDN encoding for mail addresses). This is a required parameter. ALGO specifies the algorithm for the new key (actually a keypair of public and private key). For a list of supported algorithms, see the GnuPG manual. If ALGO is ‘NULL’ or the string "default", the key is generated using the default algorithm of the engine. If the string "future-default" is used the engine may use an algorithm which is planned to be the default in a future release of the engine; however existing implementation of the protocol may not be able to already handle such future algorithms. For the OpenPGP protocol, the specification of a default algorithm, without requesting a non-default usage via FLAGS, triggers the creation of a primary key plus a secondary key (subkey). RESERVED must be set to zero. EXPIRES specifies the expiration time in seconds. If you supply 0, a reasonable expiration time is chosen. Use the flag ‘GPGME_CREATE_NOEXPIRE’ to create keys that do not expire. Note that this parameter takes an unsigned long value and not a ‘time_t’ to avoid problems on systems which use a signed 32 bit ‘time_t’. Note further that the OpenPGP protocol uses 32 bit values for timestamps and thus can only encode dates up to the year 2106. EXTRAKEY is currently not used and must be set to ‘NULL’. A future version of GPGME may use this parameter to create X.509 keys. FLAGS can be set to the bit-wise OR of the following flags: ‘GPGME_CREATE_SIGN’ ‘GPGME_CREATE_ENCR’ ‘GPGME_CREATE_CERT’ ‘GPGME_CREATE_AUTH’ SINCE: 1.7.0 Do not create the key with the default capabilities (key usage) of the requested algorithm but use those explicitly given by these flags: “signing”, “encryption”, “certification”, or “authentication”. The allowed combinations depend on the algorithm. If any of these flags are set and a default algorithm has been selected only one key is created in the case of the OpenPGP protocol. ‘GPGME_CREATE_NOPASSWD’ SINCE: 1.7.0 Request generation of the key without password protection. ‘GPGME_CREATE_SELFSIGNED’ SINCE: 1.7.0 For an X.509 key do not create a CSR but a self-signed certificate. This has not yet been implemented. ‘GPGME_CREATE_NOSTORE’ SINCE: 1.7.0 Do not store the created key in the local key database. This has not yet been implemented. ‘GPGME_CREATE_WANTPUB’ ‘GPGME_CREATE_WANTSEC’ SINCE: 1.7.0 Return the public or secret key as part of the result structure. This has not yet been implemented. ‘GPGME_CREATE_FORCE’ SINCE: 1.7.0 The engine does not allow the creation of a key with a user ID already existing in the local key database. This flag can be used to override this check. ‘GPGME_CREATE_NOEXPIRE’ SINCE: 1.8.0 Request generation of keys that do not expire. After the operation completed successfully, information about the created key can be retrieved with ‘gpgme_op_genkey_result’. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_createkey_start (gpgme_ctx_t CTX, const char *USERID, const char *ALGO, unsigned long RESERVED, unsigned long EXPIRES, gpgme_key_t EXTRAKEY, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_createkey_start’ initiates a ‘gpgme_op_createkey’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. -- Function: gpgme_error_t gpgme_op_createsubkey (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *ALGO, unsigned long RESERVED, unsigned long EXPIRES, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_createsubkey’ creates and adds a new subkey to the primary OpenPGP key given by KEY. The only allowed protocol in CTX is ‘GPGME_PROTOCOL_OPENPGP’. Subkeys (aka secondary keys) are a concept in the OpenPGP protocol to bind several keys to a primary key. As of now this function requires at least version 2.1.13 of GnuPG. KEY specifies the key to operate on. ALGO specifies the algorithm for the new subkey. For a list of supported algorithms, see the GnuPG manual. If ALGO is ‘NULL’ or the string "default", the subkey is generated using the default algorithm for an encryption subkey of the engine. If the string "future-default" is used the engine may use an encryption algorithm which is planned to be the default in a future release of the engine; however existing implementation of the protocol may not be able to already handle such future algorithms. RESERVED must be set to zero. EXPIRES specifies the expiration time in seconds. If you supply 0, a reasonable expiration time is chosen. Use the flag ‘GPGME_CREATE_NOEXPIRE’ to create keys that do not expire. Note that this parameter takes an unsigned long value and not a ‘time_t’ to avoid problems on systems which use a signed 32 bit ‘time_t’. Note further that the OpenPGP protocol uses 32 bit values for timestamps and thus can only encode dates up to the year 2106. FLAGS takes the same values as described above for ‘gpgme_op_createkey’. After the operation completed successfully, information about the created key can be retrieved with ‘gpgme_op_genkey_result’. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_createsubkey_start (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *ALGO, unsigned long RESERVED, unsigned long EXPIRES, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_createsubkey_start’ initiates a ‘gpgme_op_createsubkey’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. -- Function: gpgme_error_t gpgme_op_adduid (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_adduid’ adds a new user ID to the OpenPGP key given by KEY. Adding additional user IDs after key creation is a feature of the OpenPGP protocol and thus the protocol for the context CTX must be set to OpenPGP. As of now this function requires at least version 2.1.13 of GnuPG. KEY specifies the key to operate on. USERID is the user ID to add to the key. A user ID is commonly the mail address to be associated with the key. GPGME does not require a specific syntax but if more than a mail address is given, RFC-822 style format is suggested. The value is expected to be in UTF-8 encoding (i.e. no IDN encoding for mail addresses). This is a required parameter. FLAGS are currently not used and must be set to zero. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_adduid_start (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_adduid_start’ initiates a ‘gpgme_op_adduid’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. -- Function: gpgme_error_t gpgme_op_revuid (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_revuid’ revokes a user ID from the OpenPGP key given by KEY. Revoking user IDs after key creation is a feature of the OpenPGP protocol and thus the protocol for the context CTX must be set to OpenPGP. As of now this function requires at least version 2.1.13 of GnuPG. KEY specifies the key to operate on. USERID is the user ID to be revoked from the key. The user ID must be given verbatim because the engine does an exact and case sensitive match. Thus the ‘uid’ field from the user ID object (‘gpgme_user_id_t’) is to be used. This is a required parameter. FLAGS are currently not used and must be set to zero. Note that the engine won’t allow to revoke the last valid user ID. To change a user ID is better to first add the new user ID, then revoke the old one, and finally publish the key. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_revuid_start (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_revuid_start’ initiates a ‘gpgme_op_revuid’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. -- Function: gpgme_error_t gpgme_op_set_ui_flag (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, cons char * NAME, cons char * VALUE); SINCE: 1.8.0 The function ‘gpgme_op_set_uid_flag’ is used to set flags on a user ID from the OpenPGP key given by KEY. Setting flags on user IDs after key creation is a feature of the OpenPGP protocol and thus the protocol for the context CTX must be set to OpenPGP. KEY specifies the key to operate on. This parameters is required. USERID is the user ID of the key to be manipulated. This user ID must be given verbatim because the engine does an exact and case sensitive match. Thus the ‘uid’ field from the user ID object (‘gpgme_user_id_t’) is to be used. This is a required parameter. NAME names the flag which is to be changed. The only currently supported flag is: ‘primary’ This sets the primary key flag on the given user ID. All other primary key flag on other user IDs are removed. VALUE must be given as NULL. For technical reasons this functions bumps the creation timestamp of all affected self-signatures up by one second. At least GnuPG version 2.1.20 is required. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_set_uid_flag_start (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, cons char * NAME, cons char * VALUE); SINCE: 1.8.0 The function ‘gpgme_op_set_uid_flag_start’ initiates a ‘gpgme_op_set_uid_flag’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. -- Function: gpgme_error_t gpgme_op_genkey (gpgme_ctx_t CTX, const char *PARMS, gpgme_data_t PUBLIC, gpgme_data_t SECRET) The function ‘gpgme_op_genkey’ generates a new key pair in the context CTX. The meaning of PUBLIC and SECRET depends on the crypto backend. GPG does not support PUBLIC and SECRET, they should be ‘NULL’. GnuPG will generate a key pair and add it to the standard key ring. The fingerprint of the generated key is available with ‘gpgme_op_genkey_result’. GpgSM requires PUBLIC to be a writable data object. GpgSM will generate a secret key (which will be stored by ‘gpg-agent’, and return a certificate request in PUBLIC, which then needs to be signed by the certification authority and imported before it can be used. GpgSM does not make the fingerprint available. The argument PARMS specifies parameters for the key in an string that looks something like XML. The details about the format of PARMS are specific to the crypto engine used by CTX. The first line of the parameters must be ‘’ and the last line must be ‘’. Every line in between the first and last lines is treated as a Header: Value pair. In particular, no XML escaping is necessary if you need to include the characters ‘<’, ‘>’, or ‘&’. Here is an example for GnuPG as the crypto engine (all parameters of OpenPGP key generation are documented in the GPG manual): Key-Type: default Subkey-Type: default Name-Real: Joe Tester Name-Comment: with stupid passphrase Name-Email: joe@foo.bar Expire-Date: 0 Passphrase: abc Here is an example for GpgSM as the crypto engine (all parameters of OpenPGP key generation are documented in the GPGSM manual): Key-Type: RSA Key-Length: 1024 Name-DN: C=de,O=g10 code,OU=Testlab,CN=Joe 2 Tester Name-Email: joe@foo.bar Strings should be given in UTF-8 encoding. The only format supported for now is “internal”. The content of the ‘GnupgKeyParms’ container is passed verbatim to the crypto backend. Control statements are not allowed. After the operation completed successfully, the result can be retrieved with ‘gpgme_op_genkey_result’. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, ‘GPG_ERR_INV_VALUE’ if PARMS is not a well-formed string (e.g. does not have the expected tag-like headers and footers), ‘GPG_ERR_NOT_SUPPORTED’ if PUBLIC or SECRET is not valid, and ‘GPG_ERR_GENERAL’ if no key was created by the backend. -- Function: gpgme_error_t gpgme_op_genkey_start (gpgme_ctx_t CTX, const char *PARMS, gpgme_data_t PUBLIC, gpgme_data_t SECRET) The function ‘gpgme_op_genkey_start’ initiates a ‘gpgme_op_genkey’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, ‘GPG_ERR_INV_VALUE’ if PARMS is not a valid XML string, and ‘GPG_ERR_NOT_SUPPORTED’ if PUBLIC or SECRET is not ‘NULL’. -- Data type: gpgme_genkey_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_genkey’ operation. After successfully generating a key, you can retrieve the pointer to the result with ‘gpgme_op_genkey_result’. The structure contains the following members: ‘unsigned int primary : 1’ This flag is set to 1 if a primary key was created and to 0 if not. ‘unsigned int sub : 1’ This flag is set to 1 if a subkey was created and to 0 if not. ‘unsigned int uid : 1’ This flag is set to 1 if a user ID was created and to 0 if not. ‘char *fpr’ This is the fingerprint of the key that was created. If both a primary and a subkey were generated, the fingerprint of the primary key will be returned. If the crypto engine does not provide the fingerprint, ‘fpr’ will be a null pointer. ‘gpgme_data_t pubkey’ SINCE: 1.7.0 This will eventually be used to return the public key. It is currently not used. ‘gpgme_data_t seckey’ SINCE: 1.7.0 This will eventually be used to return the secret key. It is currently not used. -- Function: gpgme_genkey_result_t gpgme_op_genkey_result (gpgme_ctx_t CTX) The function ‘gpgme_op_genkey_result’ returns a ‘gpgme_genkey_result_t’ pointer to a structure holding the result of a ‘gpgme_op_genkey’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_genkey’ or ‘gpgme_op_genkey_start’ operation, and if this operation finished successfully. The returned pointer is only valid until the next operation is started on the context.  File: gpgme.info, Node: Signing Keys, Next: Exporting Keys, Prev: Generating Keys, Up: Key Management 7.5.6 Signing Keys ------------------ Key signatures are a unique concept of the OpenPGP protocol. They can be used to certify the validity of a key and are used to create the Web-of-Trust (WoT). Instead of using the ‘gpgme_op_interact’ function along with a finite state machine, GPGME provides a convenient function to create key signatures when using modern GnuPG versions. -- Function: gpgme_error_t gpgme_op_keysign (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned long EXPIRES, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_keysign’ adds a new key signature to the public key KEY. This function requires at least version 2.1.12 of GnuPG. CTX is the usual context which describes the protocol to use (which must be OpenPGP) and has also the list of signer keys to be used for the signature. The common case is to use the default key for signing other keys. If another key or more than one key shall be used for a key signature, ‘gpgme_signers_add’ can be used. *Note Selecting Signers::. KEY specifies the key to operate on. USERID selects the user ID or user IDs to be signed. If USERID is set to ‘NULL’ all valid user IDs are signed. The user ID must be given verbatim because the engine does an exact and case sensitive match. Thus the ‘uid’ field from the user ID object (‘gpgme_user_id_t’) is to be used. To select more than one user ID put them all into one string separated by linefeeds characters (‘\n’) and set the flag ‘GPGME_KEYSIGN_LFSEP’. EXPIRES specifies the expiration time of the new signature in seconds. The common case is to use 0 to not set an expiration date. However, if the configuration of the engine defines a default expiration for key signatures, that is still used unless the flag ‘GPGME_KEYSIGN_NOEXPIRE’ is used. Note that this parameter takes an unsigned long value and not a ‘time_t’ to avoid problems on systems which use a signed 32 bit ‘time_t’. Note further that the OpenPGP protocol uses 32 bit values for timestamps and thus can only encode dates up to the year 2106. FLAGS can be set to the bit-wise OR of the following flags: ‘GPGME_KEYSIGN_LOCAL’ SINCE: 1.7.0 Instead of creating an exportable key signature, create a key signature which is is marked as non-exportable. ‘GPGME_KEYSIGN_LFSEP’ SINCE: 1.7.0 Although linefeeds are uncommon in user IDs this flag is required to explicitly declare that USERID may contain several linefeed separated user IDs. ‘GPGME_KEYSIGN_NOEXPIRE’ Force the creation of a key signature without an expiration date. This overrides EXPIRE and any local configuration of the engine. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_keysign_start (gpgme_ctx_t CTX, gpgme_key_t KEY, const char *USERID, unsigned long EXPIRES, unsigned int FLAGS); SINCE: 1.7.0 The function ‘gpgme_op_keysign_start’ initiates a ‘gpgme_op_keysign’ operation; see there for details. It must be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::.  File: gpgme.info, Node: Exporting Keys, Next: Importing Keys, Prev: Signing Keys, Up: Key Management 7.5.7 Exporting Keys -------------------- Exporting keys means the same as running ‘gpg’ with the command ‘--export’. However, a mode flag can be used to change the way the export works. The available mode flags are described below, they may be or-ed together. ‘GPGME_EXPORT_MODE_EXTERN’ If this bit is set, the output is send directly to the default keyserver. This is currently only allowed for OpenPGP keys. It is good practise to not send more than a few dozens key to a keyserver at one time. Using this flag requires that the KEYDATA argument of the export function is set to ‘NULL’. ‘GPGME_EXPORT_MODE_MINIMAL’ SINCE: 1.3.1 If this bit is set, the smallest possible key is exported. For OpenPGP keys it removes all signatures except for the latest self-signatures. For X.509 keys it has no effect. ‘GPGME_EXPORT_MODE_SECRET’ SINCE: 1.6.0 Instead of exporting the public key, the secret key is exported. This may not be combined with ‘GPGME_EXPORT_MODE_EXTERN’. For X.509 the export format is PKCS#8. ‘GPGME_EXPORT_MODE_RAW’ SINCE: 1.6.0 If this flag is used with ‘GPGME_EXPORT_MODE_SECRET’ for an X.509 key the export format will be changed to PKCS#1. This flag may not be used with OpenPGP. ‘GPGME_EXPORT_MODE_PKCS12’ SINCE: 1.6.0 If this flag is used with ‘GPGME_EXPORT_MODE_SECRET’ for an X.509 key the export format will be changed to PKCS#12 which also includes the certificate. This flag may not be used with OpenPGP. ‘GPGME_EXPORT_MODE_NOUID’ SINCE: 1.12.0 - experimental Do not export user ids. Works only with certain gpg version. -- Function: gpgme_error_t gpgme_op_export (gpgme_ctx_t CTX, const char *PATTERN, gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) The function ‘gpgme_op_export’ extracts public keys and returns them in the data buffer KEYDATA. The output format of the key data returned is determined by the ASCII armor attribute set for the context CTX, or, if that is not set, by the encoding specified for KEYDATA. If PATTERN is ‘NULL’, all available keys are returned. Otherwise, PATTERN contains an engine specific expression that is used to limit the list to all keys matching the pattern. MODE is usually 0; other values are described above. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation completed successfully, ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_export_start (gpgme_ctx_t CTX, const char *PATTERN, gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) The function ‘gpgme_op_export_start’ initiates a ‘gpgme_op_export’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer. -- Function: gpgme_error_t gpgme_op_export_ext (gpgme_ctx_t CTX, const char *PATTERN[], gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) The function ‘gpgme_op_export’ extracts public keys and returns them in the data buffer KEYDATA. The output format of the key data returned is determined by the ASCII armor attribute set for the context CTX, or, if that is not set, by the encoding specified for KEYDATA. If PATTERN or *PATTERN is ‘NULL’, all available keys are returned. Otherwise, PATTERN is a ‘NULL’ terminated array of strings that are used to limit the list to all keys matching at least one of the patterns verbatim. MODE is usually 0; other values are described above. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation completed successfully, ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_export_ext_start (gpgme_ctx_t CTX, const char *PATTERN[], gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) The function ‘gpgme_op_export_ext_start’ initiates a ‘gpgme_op_export_ext’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer. -- Function: gpgme_error_t gpgme_op_export_keys (gpgme_ctx_t CTX, gpgme_key_t keys[], gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) SINCE: 1.2.0 The function ‘gpgme_op_export_keys’ extracts public keys and returns them in the data buffer KEYDATA. The output format of the key data returned is determined by the ASCII armor attribute set for the context CTX, or, if that is not set, by the encoding specified for KEYDATA. The keys to export are taken form the ‘NULL’ terminated array KEYS. Only keys of the currently selected protocol of CTX which do have a fingerprint set are considered for export. Other keys specified by the KEYS are ignored. In particular OpenPGP keys retrieved via an external key listing are not included. MODE is usually 0; other values are described above. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation completed successfully, ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer, ‘GPG_ERR_NO_DATA’ if no useful keys are in KEYS and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_export_keys_start (gpgme_ctx_t CTX, gpgme_key_t KEYS[], gpgme_export_mode_t MODE, gpgme_data_t KEYDATA) SINCE: 1.2.0 The function ‘gpgme_op_export_keys_start’ initiates a ‘gpgme_op_export_ext’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if KEYDATA is not a valid empty data buffer, ‘GPG_ERR_NO_DATA’ if no useful keys are in KEYS and passes through any errors that are reported by the crypto engine support routines.  File: gpgme.info, Node: Importing Keys, Next: Deleting Keys, Prev: Exporting Keys, Up: Key Management 7.5.8 Importing Keys -------------------- Importing keys means the same as running ‘gpg’ with the command ‘--import’. -- Function: gpgme_error_t gpgme_op_import (gpgme_ctx_t CTX, gpgme_data_t KEYDATA) The function ‘gpgme_op_import’ adds the keys in the data buffer KEYDATA to the key ring of the crypto engine used by CTX. The format of KEYDATA can be ASCII armored, for example, but the details are specific to the crypto engine. After the operation completed successfully, the result can be retrieved with ‘gpgme_op_import_result’. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the import was completed successfully, ‘GPG_ERR_INV_VALUE’ if KEYDATA if CTX or KEYDATA is not a valid pointer, and ‘GPG_ERR_NO_DATA’ if KEYDATA is an empty data buffer. -- Function: gpgme_error_t gpgme_op_import_start (gpgme_ctx_t CTX, gpgme_data_t KEYDATA) The function ‘gpgme_op_import_start’ initiates a ‘gpgme_op_import’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the import could be started successfully, ‘GPG_ERR_INV_VALUE’ if CTX or KEYDATA is not a valid pointer, and ‘GPG_ERR_NO_DATA’ if KEYDATA is an empty data buffer. -- Function: gpgme_error_t gpgme_op_import_keys (gpgme_ctx_t CTX, gpgme_key_t *KEYS) SINCE: 1.2.0 The function ‘gpgme_op_import_keys’ adds the keys described by the ‘NULL’ terminated array KEYS to the key ring of the crypto engine used by CTX. It is used to actually import and make keys permanent which have been retrieved from an external source (i.e. using ‘GPGME_KEYLIST_MODE_EXTERN’) earlier. The external keylisting must have been made with the same context configuration (in particular the same home directory). (1) Note that for OpenPGP this may require another access to the keyserver over the network. Only keys of the currently selected protocol of CTX are considered for import. Other keys specified by the KEYS are ignored. As of now all considered keys must have been retrieved using the same method, i.e. the used key listing mode must be identical. After the operation completed successfully, the result can be retrieved with ‘gpgme_op_import_result’. To move keys from one home directory to another, export and import the keydata using ‘gpgme_op_export’ and ‘gpgme_op_import’. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the import was completed successfully, ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, ‘GPG_ERR_CONFLICT’ if the key listing mode does not match, and ‘GPG_ERR_NO_DATA’ if no keys are considered for export. -- Function: gpgme_error_t gpgme_op_import_keys_start (gpgme_ctx_t CTX, gpgme_key_t *KEYS) SINCE: 1.2.0 The function ‘gpgme_op_import_keys_start’ initiates a ‘gpgme_op_import_keys’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the import was completed successfully, ‘GPG_ERR_INV_VALUE’ if KEYDATA if CTX or KEYDATA is not a valid pointer, ‘GPG_ERR_CONFLICT’ if the key listing mode does not match, and ‘GPG_ERR_NO_DATA’ if no keys are considered for export. -- Data type: gpgme_import_status_t This is a pointer to a structure used to store a part of the result of a ‘gpgme_op_import’ operation. For each considered key one status is added that contains information about the result of the import. The structure contains the following members: ‘gpgme_import_status_t next’ This is a pointer to the next status structure in the linked list, or ‘NULL’ if this is the last element. ‘char *fpr’ This is the fingerprint of the key that was considered. ‘gpgme_error_t result’ If the import was not successful, this is the error value that caused the import to fail. Otherwise the error code is ‘GPG_ERR_NO_ERROR’. ‘unsigned int status’ This is a bit-wise OR of the following flags that give more information about what part of the key was imported. If the key was already known, this might be 0. ‘GPGME_IMPORT_NEW’ The key was new. ‘GPGME_IMPORT_UID’ The key contained new user IDs. ‘GPGME_IMPORT_SIG’ The key contained new signatures. ‘GPGME_IMPORT_SUBKEY’ The key contained new sub keys. ‘GPGME_IMPORT_SECRET’ The key contained a secret key. -- Data type: gpgme_import_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_import’ operation. After a successful import operation, you can retrieve the pointer to the result with ‘gpgme_op_import_result’. The structure contains the following members: ‘int considered’ The total number of considered keys. ‘int no_user_id’ The number of keys without user ID. ‘int imported’ The total number of imported keys. ‘int imported_rsa’ The number of imported RSA keys. ‘int unchanged’ The number of unchanged keys. ‘int new_user_ids’ The number of new user IDs. ‘int new_sub_keys’ The number of new sub keys. ‘int new_signatures’ The number of new signatures. ‘int new_revocations’ The number of new revocations. ‘int secret_read’ The total number of secret keys read. ‘int secret_imported’ The number of imported secret keys. ‘int secret_unchanged’ The number of unchanged secret keys. ‘int not_imported’ The number of keys not imported. ‘gpgme_import_status_t imports’ A list of gpgme_import_status_t objects which contain more information about the keys for which an import was attempted. ‘int skipped_v3_keys’ For security reasons modern versions of GnuPG do not anymore support v3 keys (created with PGP 2.x) and ignores them on import. This counter provides the number of such skipped v3 keys. -- Function: gpgme_import_result_t gpgme_op_import_result (gpgme_ctx_t CTX) The function ‘gpgme_op_import_result’ returns a ‘gpgme_import_result_t’ pointer to a structure holding the result of a ‘gpgme_op_import’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_import’ or ‘gpgme_op_import_start’ operation, and if this operation finished successfully. The returned pointer is only valid until the next operation is started on the context. ---------- Footnotes ---------- (1) Thus it is a replacement for the usual workaround of exporting and then importing a key to make an X.509 key permanent.  File: gpgme.info, Node: Deleting Keys, Next: Changing Passphrases, Prev: Importing Keys, Up: Key Management 7.5.9 Deleting Keys ------------------- -- Function: gpgme_error_t gpgme_op_delete_ext (gpgme_ctx_t CTX, const gpgme_key_t KEY, unsigned int FLAGS) SINCE: 1.9.1 The function ‘gpgme_op_delete_ext’ deletes the key KEY from the key ring of the crypto engine used by CTX. FLAGS can be set to the bit-wise OR of the following flags: ‘GPGME_DELETE_ALLOW_SECRET’ SINCE: 1.9.1 If not set, only public keys are deleted. If set, secret keys are deleted as well, if that is supported. ‘GPGME_DELETE_FORCE’ SINCE: 1.9.1 If set, the user is not asked to confirm the deletion. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the key was deleted successfully, ‘GPG_ERR_INV_VALUE’ if CTX or KEY is not a valid pointer, ‘GPG_ERR_NO_PUBKEY’ if KEY could not be found in the keyring, ‘GPG_ERR_AMBIGUOUS_NAME’ if the key was not specified unambiguously, and ‘GPG_ERR_CONFLICT’ if the secret key for KEY is available, but ALLOW_SECRET is zero. -- Function: gpgme_error_t gpgme_op_delete_ext_start (gpgme_ctx_t CTX, const gpgme_key_t KEY, unsigned int FLAGS) SINCE: 1.9.1 The function ‘gpgme_op_delete_ext_start’ initiates a ‘gpgme_op_delete’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation was started successfully, and ‘GPG_ERR_INV_VALUE’ if CTX or KEY is not a valid pointer. The following functions allow only to use one particular flag. -- Function: gpgme_error_t gpgme_op_delete (gpgme_ctx_t CTX, const gpgme_key_t KEY, int ALLOW_SECRET) Similar to ‘gpgme_op_delete_ext’, but only the flag ‘GPGME_DELETE_ALLOW_SECRET’ can be provided. -- Function: gpgme_error_t gpgme_op_delete_start (gpgme_ctx_t CTX, const gpgme_key_t KEY, int ALLOW_SECRET) Similar to ‘gpgme_op_delete_ext_start’, but only the flag ‘GPGME_DELETE_ALLOW_SECRET’ can be provided.  File: gpgme.info, Node: Changing Passphrases, Next: Changing TOFU Data, Prev: Deleting Keys, Up: Key Management 7.5.10 Changing Passphrases --------------------------- -- Function: gpgme_error_t gpgme_op_passwd (gpgme_ctx_t CTX, const gpgme_key_t KEY, unsigned int FLAGS) SINCE: 1.3.0 The function ‘gpgme_op_passwd’ changes the passphrase of the private key associated with KEY. The only allowed value for FLAGS is ‘0’. The backend engine will usually popup a window to ask for the old and the new passphrase. Thus this function is not useful in a server application (where passphrases are not required anyway). Note that old ‘gpg’ engines (before version 2.0.15) do not support this command and will silently ignore it. -- Function: gpgme_error_t gpgme_op_passwd_start (gpgme_ctx_t CTX, const gpgme_key_t KEY, unsigned int FLAGS) SINCE: 1.3.0 The function ‘gpgme_op_passwd_start’ initiates a ‘gpgme_op_passwd’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns ‘0’ if the operation was started successfully, and an error code if one of the arguments is not valid or the oepration could not be started.  File: gpgme.info, Node: Changing TOFU Data, Next: Advanced Key Editing, Prev: Changing Passphrases, Up: Key Management 7.5.11 Changing TOFU Data ------------------------- The OpenPGP engine features a Trust-On-First-Use (TOFU) key validation model. For resolving conflicts it is necessary to declare the policy for a key. See the GnuPG manual for details on the TOFU implementation. -- Data type: enum gpgme_tofu_policy_t SINCE: 1.7.0 The ‘gpgme_tofu_policy_t’ type specifies the set of possible policy values that are supported by GPGME: ‘GPGME_TOFU_POLICY_AUTO’ Set the policy to “auto”. ‘GPGME_TOFU_POLICY_GOOD’ Set the policy to “good”. ‘GPGME_TOFU_POLICY_BAD’ Set the policy to “bad”. ‘GPGME_TOFU_POLICY_ASK’ Set the policy to “ask”. ‘GPGME_TOFU_POLICY_UNKNOWN’ Set the policy to “unknown”. To change the policy for a key the following functions can be used: -- Function: gpgme_error_t gpgme_op_tofu_policy (gpgme_ctx_t CTX, const gpgme_key_t KEY, gpgme_tofu_policy_t POLICY) SINCE: 1.7.0 The function ‘gpgme_op_tofu_policy’ changes the TOFU policy of KEY. The valid values for POLICY are listed above. As of now this function does only work for OpenPGP and requires at least version 2.1.10 of GnuPG. The function returns zero on success, ‘GPG_ERR_NOT_SUPPORTED’ if the engine does not support the command, or a bunch of other error codes. -- Function: gpgme_error_t gpgme_op_tofu_policy_start (gpgme_ctx_t CTX, const gpgme_key_t KEY, gpgme_tofu_policy_t POLICY) SINCE: 1.7.0 The function ‘gpgme_op_tofu_policy_start’ initiates a ‘gpgme_op_tofu_policy’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns ‘0’ if the operation was started successfully, and an error code if one of the arguments is not valid or the oepration could not be started.  File: gpgme.info, Node: Advanced Key Editing, Prev: Changing TOFU Data, Up: Key Management 7.5.12 Advanced Key Editing --------------------------- -- Data type: gpgme_error_t (*gpgme_interact_cb_t) (void *HANDLE, const char *STATUS, const char *ARGS, int FD) SINCE: 1.7.0 The ‘gpgme_interact_cb_t’ type is the type of functions which GPGME calls if it a key interact operation is on-going. The status keyword STATUS and the argument line ARGS are passed through by GPGME from the crypto engine. An empty string represents EOF. The file descriptor FD is -1 for normal status messages. If STATUS indicates a command rather than a status message, the response to the command should be written to FD. The HANDLE is provided by the user at start of operation. The function should return ‘GPG_ERR_FALSE’ if it did not handle the status code, ‘0’ for success, or any other error value. -- Function: gpgme_error_t gpgme_op_interact (gpgme_ctx_t CTX, gpgme_key_t KEY, unsigned int FLAGS, gpgme_interact_cb_t FNC, void *HANDLE, gpgme_data_t OUT) SINCE: 1.7.0 The function ‘gpgme_op_interact’ processes the key KEY interactively, using the interact callback function FNC with the handle HANDLE. The callback is invoked for every status and command request from the crypto engine. The output of the crypto engine is written to the data object OUT. Note that the protocol between the callback function and the crypto engine is specific to the crypto engine and no further support in implementing this protocol correctly is provided by GPGME. FLAGS modifies the behaviour of the function; the only defined bit value is: ‘GPGME_INTERACT_CARD’ SINCE: 1.7.0 This is used for smartcard based keys and uses gpg’s ‘--card-edit’ command. The function returns ‘0’ if the edit operation completes successfully, ‘GPG_ERR_INV_VALUE’ if CTX or KEY is not a valid pointer, and any error returned by the crypto engine or the edit callback handler. -- Function: gpgme_error_t gpgme_op_interact_start (gpgme_ctx_t CTX, gpgme_key_t KEY, unsigned int FLAGS, gpgme_interact_cb_t FNC, void *HANDLE, gpgme_data_t OUT) SINCE: 1.7.0 The function ‘gpgme_op_interact_start’ initiates a ‘gpgme_op_interact’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns ‘0’ if the operation was started successfully, and ‘GPG_ERR_INV_VALUE’ if CTX or KEY is not a valid pointer.  File: gpgme.info, Node: Trust Item Management, Next: Crypto Operations, Prev: Key Management, Up: Contexts 7.6 Trust Item Management ========================= *Caution:* The trust items interface is experimental. -- Data type: gpgme_trust_item_t The ‘gpgme_trust_item_t’ type is a pointer to a trust item object. It has the following members: ‘char *keyid’ This is a string describing the key to which this trust items belongs. ‘int type’ This is the type of the trust item. A value of 1 refers to a key, a value of 2 refers to a user ID. ‘int level’ This is the trust level. ‘char *owner_trust’ The owner trust if ‘type’ is 1. ‘char *validity’ The calculated validity. ‘char *name’ The user name if ‘type’ is 2. * Menu: * Listing Trust Items:: Browsing the list of available trust items. * Manipulating Trust Items:: Operations on trust items.  File: gpgme.info, Node: Listing Trust Items, Next: Manipulating Trust Items, Up: Trust Item Management 7.6.1 Listing Trust Items ------------------------- -- Function: gpgme_error_t gpgme_op_trustlist_start (gpgme_ctx_t CTX, const char *PATTERN, int MAX_LEVEL) The function ‘gpgme_op_trustlist_start’ initiates a trust item listing operation inside the context CTX. It sets everything up so that subsequent invocations of ‘gpgme_op_trustlist_next’ return the trust items in the list. The string PATTERN contains an engine specific expression that is used to limit the list to all trust items matching the pattern. It can not be the empty string. The argument MAX_LEVEL is currently ignored. The context will be busy until either all trust items are received (and ‘gpgme_op_trustlist_next’ returns ‘GPG_ERR_EOF’), or ‘gpgme_op_trustlist_end’ is called to finish the operation. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_trustlist_next (gpgme_ctx_t CTX, gpgme_trust_item_t *R_ITEM) The function ‘gpgme_op_trustlist_next’ returns the next trust item in the list created by a previous ‘gpgme_op_trustlist_start’ operation in the context CTX. The trust item can be destroyed with ‘gpgme_trust_item_release’. *Note Manipulating Trust Items::. This is the only way to get at ‘gpgme_trust_item_t’ objects in GPGME. If the last trust item in the list has already been returned, ‘gpgme_op_trustlist_next’ returns ‘GPG_ERR_EOF’. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX or R_ITEM is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if there is not enough memory for the operation. -- Function: gpgme_error_t gpgme_op_trustlist_end (gpgme_ctx_t CTX) The function ‘gpgme_op_trustlist_end’ ends a pending trust list operation in the context CTX. The function returns the error code ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, and ‘GPG_ERR_ENOMEM’ if at some time during the operation there was not enough memory available.  File: gpgme.info, Node: Manipulating Trust Items, Prev: Listing Trust Items, Up: Trust Item Management 7.6.2 Manipulating Trust Items ------------------------------ -- Function: void gpgme_trust_item_ref (gpgme_trust_item_t ITEM) The function ‘gpgme_trust_item_ref’ acquires an additional reference for the trust item ITEM. -- Function: void gpgme_trust_item_unref (gpgme_trust_item_t ITEM) The function ‘gpgme_trust_item_unref’ releases a reference for the trust item ITEM. If this was the last reference, the trust item will be destroyed and all resources associated to it will be released.  File: gpgme.info, Node: Crypto Operations, Next: Miscellaneous, Prev: Trust Item Management, Up: Contexts 7.7 Crypto Operations ===================== Sometimes, the result of a crypto operation returns a list of invalid keys encountered in processing the request. The following structure is used to hold information about such a key. -- Data type: gpgme_invalid_key_t This is a pointer to a structure used to store a part of the result of a crypto operation which takes user IDs as one input parameter. The structure contains the following members: ‘gpgme_invalid_key_t next’ This is a pointer to the next invalid key structure in the linked list, or ‘NULL’ if this is the last element. ‘char *fpr’ The fingerprint or key ID of the invalid key encountered. ‘gpgme_error_t reason’ An error code describing the reason why the key was found invalid. * Menu: * Decrypt:: Decrypting a ciphertext. * Verify:: Verifying a signature. * Decrypt and Verify:: Decrypting a signed ciphertext. * Sign:: Creating a signature. * Encrypt:: Encrypting a plaintext.  File: gpgme.info, Node: Decrypt, Next: Verify, Up: Crypto Operations 7.7.1 Decrypt ------------- -- Function: gpgme_error_t gpgme_op_decrypt (gpgme_ctx_t CTX, gpgme_data_t CIPHER, gpgme_data_t PLAIN) The function ‘gpgme_op_decrypt’ decrypts the ciphertext in the data object CIPHER and stores it into the data object PLAIN. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the ciphertext could be decrypted successfully, ‘GPG_ERR_INV_VALUE’ if CTX, CIPHER or PLAIN is not a valid pointer, ‘GPG_ERR_NO_DATA’ if CIPHER does not contain any data to decrypt, ‘GPG_ERR_DECRYPT_FAILED’ if CIPHER is not a valid cipher text, ‘GPG_ERR_BAD_PASSPHRASE’ if the passphrase for the secret key could not be retrieved, and passes through some errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_decrypt_start (gpgme_ctx_t CTX, gpgme_data_t CIPHER, gpgme_data_t PLAIN) The function ‘gpgme_op_decrypt_start’ initiates a ‘gpgme_op_decrypt’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if CIPHER or PLAIN is not a valid pointer. -- Function: gpgme_error_t gpgme_op_decrypt_ext ( gpgme_ctx_t CTX, gpgme_decrypt_flags_t FLAGS, gpgme_data_t CIPHER, gpgme_data_t PLAIN) SINCE: 1.8.0 The function ‘gpgme_op_decrypt_ext’ is the same as ‘gpgme_op_decrypt’ but has an additional argument FLAGS. If FLAGS is 0 both function behave identically. The value in FLAGS is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_DECRYPT_VERIFY’ SINCE: 1.8.0 The ‘GPGME_DECRYPT_VERIFY’ symbol specifies that this function shall exactly act as ‘gpgme_op_decrypt_verify’. ‘GPGME_DECRYPT_UNWRAP’ SINCE: 1.8.0 The ‘GPGME_DECRYPT_UNWRAP’ symbol specifies that the output shall be an OpenPGP message with only the encryption layer removed. This requires GnuPG 2.1.12 and works only for OpenPGP. This is the counterpart to ‘GPGME_ENCRYPT_WRAP’. The function returns the error codes as described for ‘gpgme_op_decrypt’ respective ‘gpgme_op_encrypt’. -- Function: gpgme_error_t gpgme_op_decrypt_ext_start ( gpgme_ctx_t CTX, gpgme_decrypt_flags_t FLAGS, gpgme_data_t CIPHER, gpgme_data_t PLAIN) SINCE: 1.8.0 The function ‘gpgme_op_decrypt_ext_start’ initiates a ‘gpgme_op_decrypt_ext’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if CIPHER or PLAIN is not a valid pointer. -- Data type: gpgme_recipient_t SINCE: 1.1.0 This is a pointer to a structure used to store information about the recipient of an encrypted text which is decrypted in a ‘gpgme_op_decrypt’ operation. This information (except for the status field) is even available before the operation finished successfully, for example in a passphrase callback. The structure contains the following members: ‘gpgme_recipient_t next’ This is a pointer to the next recipient structure in the linked list, or ‘NULL’ if this is the last element. ‘gpgme_pubkey_algo_t’ The public key algorithm used in the encryption. ‘char *keyid’ This is the key ID of the key (in hexadecimal digits) used as recipient. ‘gpgme_error_t status’ This is an error number with the error code GPG_ERR_NO_SECKEY if the secret key for this recipient is not available, and 0 otherwise. -- Data type: gpgme_decrypt_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_decrypt’ operation. After successfully decrypting data, you can retrieve the pointer to the result with ‘gpgme_op_decrypt_result’. As with all result structures, it this structure shall be considered read-only and an application must not allocate such a strucure on its own. The structure contains the following members: ‘char *unsupported_algorithm’ If an unsupported algorithm was encountered, this string describes the algorithm that is not supported. ‘unsigned int wrong_key_usage : 1’ SINCE: 0.9.0 This is true if the key was not used according to its policy. ‘unsigned int legacy_cipher_nomdc : 1’ SINCE: 1.11.2 The message was made by a legacy algorithm without any integrity protection. This might be an old but legitimate message. ‘unsigned int is_mime : 1;’ SINCE: 1.11.0 The message claims that the content is a MIME object. ‘unsigned int is_de_vs : 1;’ SINCE: 1.10.0 The message was encrypted in a VS-NfD compliant way. This is a specification in Germany for a restricted communication level. ‘gpgme_recipient_t recipients’ SINCE: 1.1.0 This is a linked list of recipients to which this message was encrypted. ‘char *file_name’ This is the filename of the original plaintext message file if it is known, otherwise this is a null pointer. ‘char *session_key’ SINCE: 1.8.0 A textual representation (nul-terminated string) of the session key used in symmetric encryption of the message, if the context has been set to export session keys (see ‘gpgme_set_ctx_flag, "export-session-key"’), and a session key was available for the most recent decryption operation. Otherwise, this is a null pointer. You must not try to access this member of the struct unless ‘gpgme_set_ctx_flag (ctx, "export-session-key")’ returns success or ‘gpgme_get_ctx_flag (ctx, "export-session-key")’ returns true (non-empty string). ‘char *symkey_algo’ SINCE: 1.11.0 A string with the symmetric encryption algorithm and mode using the format ".". Note that the deprecated non-MDC encryption mode of OpenPGP is given as "PGPCFB". -- Function: gpgme_decrypt_result_t gpgme_op_decrypt_result (gpgme_ctx_t CTX) The function ‘gpgme_op_decrypt_result’ returns a ‘gpgme_decrypt_result_t’ pointer to a structure holding the result of a ‘gpgme_op_decrypt’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_decrypt’ or ‘gpgme_op_decrypt_start’ operation. If the operation failed this might be a ‘NULL’ pointer. The returned pointer is only valid until the next operation is started on the context.  File: gpgme.info, Node: Verify, Next: Decrypt and Verify, Prev: Decrypt, Up: Crypto Operations 7.7.2 Verify ------------ -- Function: gpgme_error_t gpgme_op_verify (gpgme_ctx_t CTX, gpgme_data_t SIG, gpgme_data_t SIGNED_TEXT, gpgme_data_t PLAIN) The function ‘gpgme_op_verify’ verifies that the signature in the data object SIG is a valid signature. If SIG is a detached signature, then the signed text should be provided in SIGNED_TEXT and PLAIN should be a null pointer. Otherwise, if SIG is a normal (or cleartext) signature, SIGNED_TEXT should be a null pointer and PLAIN should be a writable data object that will contain the plaintext after successful verification. The results of the individual signature verifications can be retrieved with ‘gpgme_op_verify_result’. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be completed successfully, ‘GPG_ERR_INV_VALUE’ if CTX, SIG or PLAIN is not a valid pointer, ‘GPG_ERR_NO_DATA’ if SIG does not contain any data to verify, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_verify_start (gpgme_ctx_t CTX, gpgme_data_t SIG, gpgme_data_t SIGNED_TEXT, gpgme_data_t PLAIN) The function ‘gpgme_op_verify_start’ initiates a ‘gpgme_op_verify’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, ‘GPG_ERR_INV_VALUE’ if CTX, SIG or PLAIN is not a valid pointer, and ‘GPG_ERR_NO_DATA’ if SIG or PLAIN does not contain any data to verify. -- Data type: gpgme_sig_notation_t This is a pointer to a structure used to store a part of the result of a ‘gpgme_op_verify’ operation. The structure contains the following members: ‘gpgme_sig_notation_t next’ This is a pointer to the next new signature notation structure in the linked list, or ‘NULL’ if this is the last element. ‘char *name’ The name of the notation field. If this is ‘NULL’, then the member ‘value’ will contain a policy URL. ‘int name_len’ The length of the ‘name’ field. For strings the length is counted without the trailing binary zero. ‘char *value’ The value of the notation field. If ‘name’ is ‘NULL’, then this is a policy URL. ‘int value_len’ The length of the ‘value’ field. For strings the length is counted without the trailing binary zero. ‘gpgme_sig_notation_flags_t flags’ The accumulated flags field. This field contains the flags associated with the notation data in an accumulated form which can be used as an argument to the function ‘gpgme_sig_notation_add’. The value ‘flags’ is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_SIG_NOTATION_HUMAN_READABLE’ SINCE: 1.1.0 The ‘GPGME_SIG_NOTATION_HUMAN_READABLE’ symbol specifies that the notation data is in human readable form ‘GPGME_SIG_NOTATION_CRITICAL’ SINCE: 1.1.0 The ‘GPGME_SIG_NOTATION_CRITICAL’ symbol specifies that the notation data is critical. ‘unsigned int human_readable : 1’ This is true if the ‘GPGME_SIG_NOTATION_HUMAN_READABLE’ flag is set and false otherwise. This flag is only valid for notation data, not for policy URLs. ‘unsigned int critical : 1’ This is true if the ‘GPGME_SIG_NOTATION_CRITICAL’ flag is set and false otherwise. This flag is valid for notation data and policy URLs. -- Data type: gpgme_signature_t This is a pointer to a structure used to store a part of the result of a ‘gpgme_op_verify’ operation. The structure contains the following members: ‘gpgme_signature_t next’ This is a pointer to the next new signature structure in the linked list, or ‘NULL’ if this is the last element. ‘gpgme_sigsum_t summary’ This is a bit vector giving a summary of the signature status. It provides an easy interface to a defined semantic of the signature status. Checking just one bit is sufficient to see whether a signature is valid without any restrictions. This means that you can check for GPGME_SIGSUM_VALID like this: if ((sig.summary & GPGME_SIGSUM_VALID)) { ..do stuff if valid.. } else { ..do stuff if not fully valid.. } The defined bits are: ‘GPGME_SIGSUM_VALID’ The signature is fully valid. ‘GPGME_SIGSUM_GREEN’ The signature is good but one might want to display some extra information. Check the other bits. ‘GPGME_SIGSUM_RED’ The signature is bad. It might be useful to check other bits and display more information, i.e. a revoked certificate might not render a signature invalid when the message was received prior to the cause for the revocation. ‘GPGME_SIGSUM_KEY_REVOKED’ The key or at least one certificate has been revoked. ‘GPGME_SIGSUM_KEY_EXPIRED’ The key or one of the certificates has expired. It is probably a good idea to display the date of the expiration. ‘GPGME_SIGSUM_SIG_EXPIRED’ The signature has expired. ‘GPGME_SIGSUM_KEY_MISSING’ Can’t verify due to a missing key or certificate. ‘GPGME_SIGSUM_CRL_MISSING’ The CRL (or an equivalent mechanism) is not available. ‘GPGME_SIGSUM_CRL_TOO_OLD’ Available CRL is too old. ‘GPGME_SIGSUM_BAD_POLICY’ A policy requirement was not met. ‘GPGME_SIGSUM_SYS_ERROR’ A system error occurred. ‘GPGME_SIGSUM_TOFU_CONFLICT’ A TOFU conflict was detected. ‘char *fpr’ This is the fingerprint or key ID of the signature. ‘gpgme_error_t status’ This is the status of the signature. In particular, the following status codes are of interest: ‘GPG_ERR_NO_ERROR’ This status indicates that the signature is valid. For the combined result this status means that all signatures are valid. ‘GPG_ERR_SIG_EXPIRED’ This status indicates that the signature is valid but expired. For the combined result this status means that all signatures are valid and expired. ‘GPG_ERR_KEY_EXPIRED’ This status indicates that the signature is valid but the key used to verify the signature has expired. For the combined result this status means that all signatures are valid and all keys are expired. ‘GPG_ERR_CERT_REVOKED’ This status indicates that the signature is valid but the key used to verify the signature has been revoked. For the combined result this status means that all signatures are valid and all keys are revoked. ‘GPG_ERR_BAD_SIGNATURE’ This status indicates that the signature is invalid. For the combined result this status means that all signatures are invalid. ‘GPG_ERR_NO_PUBKEY’ This status indicates that the signature could not be verified due to a missing key. For the combined result this status means that all signatures could not be checked due to missing keys. ‘GPG_ERR_GENERAL’ This status indicates that there was some other error which prevented the signature verification. ‘gpgme_sig_notation_t notations’ This is a linked list with the notation data and policy URLs. ‘unsigned long timestamp’ The creation timestamp of this signature. ‘unsigned long exp_timestamp’ The expiration timestamp of this signature, or 0 if the signature does not expire. ‘unsigned int wrong_key_usage : 1’ This is true if the key was not used according to its policy. ‘unsigned int pka_trust : 2’ This is set to the trust information gained by means of the PKA system. Values are: ‘0’ No PKA information available or verification not possible. ‘1’ PKA verification failed. ‘2’ PKA verification succeeded. ‘3’ Reserved for future use. Depending on the configuration of the engine, this metric may also be reflected by the validity of the signature. ‘unsigned int chain_model : 1’ SINCE: 1.1.6 This is true if the validity of the signature has been checked using the chain model. In the chain model the time the signature has been created must be within the validity period of the certificate and the time the certificate itself has been created must be within the validity period of the issuing certificate. In contrast the default validation model checks the validity of signature as well at the entire certificate chain at the current time. ‘gpgme_validity_t validity’ The validity of the signature. ‘gpgme_error_t validity_reason’ If a signature is not valid, this provides a reason why. ‘gpgme_pubkey_algo_t’ The public key algorithm used to create this signature. ‘gpgme_hash_algo_t’ The hash algorithm used to create this signature. ‘char *pka_address’ The mailbox from the PKA information or ‘NULL’. ‘gpgme_key_t key’ SINCE: 1.7.0 An object describing the key used to create the signature. This key object may be incomplete in that it only conveys information availabale directly with a signature. It may also be ‘NULL’ if such information is not readily available. -- Data type: gpgme_verify_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_verify’ operation. After verifying a signature, you can retrieve the pointer to the result with ‘gpgme_op_verify_result’. If the operation failed this might be a ‘NULL’ pointer. The structure contains the following member: ‘gpgme_signature_t signatures’ A linked list with information about all signatures for which a verification was attempted. ‘char *file_name’ This is the filename of the original plaintext message file if it is known, otherwise this is a null pointer. Warning: The filename is not covered by the signature. ‘unsigned int is_mime : 1;’ SINCE: 1.11.0 The message claims that the content is a MIME object. Warning: This flag is not covered by the signature. -- Function: gpgme_verify_result_t gpgme_op_verify_result (gpgme_ctx_t CTX) The function ‘gpgme_op_verify_result’ returns a ‘gpgme_verify_result_t’ pointer to a structure holding the result of a ‘gpgme_op_verify’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_verify’, ‘gpgme_op_verify_start’, ‘gpgme_op_decrypt_verify’ or ‘gpgme_op_decrypt_verify_start’ operation, and if this operation finished successfully (for ‘gpgme_op_decrypt_verify’ and ‘gpgme_op_decrypt_verify_start’, the error code ‘GPG_ERR_NO_DATA’ counts as successful in this context). The returned pointer is only valid until the next operation is started on the context.  File: gpgme.info, Node: Decrypt and Verify, Next: Sign, Prev: Verify, Up: Crypto Operations 7.7.3 Decrypt and Verify ------------------------ -- Function: gpgme_error_t gpgme_op_decrypt_verify (gpgme_ctx_t CTX, gpgme_data_t CIPHER, gpgme_data_t PLAIN) The function ‘gpgme_op_decrypt_verify’ decrypts the ciphertext in the data object CIPHER and stores it into the data object PLAIN. If CIPHER contains signatures, they will be verified. After the operation completed, ‘gpgme_op_decrypt_result’ and ‘gpgme_op_verify_result’ can be used to retrieve more information about the signatures. If the error code ‘GPG_ERR_NO_DATA’ is returned, CIPHER does not contain any data to decrypt. However, it might still be signed. The information about detected signatures is available with ‘gpgme_op_verify_result’ in this case. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the ciphertext could be decrypted successfully, ‘GPG_ERR_INV_VALUE’ if CTX, CIPHER or PLAIN is not a valid pointer, ‘GPG_ERR_NO_DATA’ if CIPHER does not contain any data to decrypt, ‘GPG_ERR_DECRYPT_FAILED’ if CIPHER is not a valid cipher text, ‘GPG_ERR_BAD_PASSPHRASE’ if the passphrase for the secret key could not be retrieved, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_decrypt_verify_start (gpgme_ctx_t CTX, gpgme_data_t CIPHER, gpgme_data_t PLAIN) The function ‘gpgme_op_decrypt_verify_start’ initiates a ‘gpgme_op_decrypt_verify’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, ‘GPG_ERR_INV_VALUE’ if CTX, CIPHER, PLAIN or R_STAT is not a valid pointer, and ‘GPG_ERR_NO_DATA’ if CIPHER does not contain any data to decrypt. When processing mails it is sometimes useful to extract the actual mail address (the “addr-spec”) from a string. GPGME provides this helper function which uses the same semantics as the internal functions in GPGME and GnuPG: -- Function: char * gpgme_addrspec_from_uid (const char *UID) SINCE: 1.7.1 Return the mail address (called “addr-spec” in RFC-5322) from the string UID which is assumed to be a user id (called “address” in RFC-5322). All plain ASCII characters (i.e. those with bit 7 cleared) in the result are converted to lowercase. Caller must free the result using ‘gpgme_free’. Returns ‘NULL’ if no valid address was found (in which case ‘ERRNO’ is set to ‘EINVAL’) or for other errors.  File: gpgme.info, Node: Sign, Next: Encrypt, Prev: Decrypt and Verify, Up: Crypto Operations 7.7.4 Sign ---------- A signature can contain signatures by one or more keys. The set of keys used to create a signatures is contained in a context, and is applied to all following signing operations in this context (until the set is changed). * Menu: * Selecting Signers:: How to choose the keys to sign with. * Creating a Signature:: How to create a signature. * Signature Notation Data:: How to add notation data to a signature.  File: gpgme.info, Node: Selecting Signers, Next: Creating a Signature, Up: Sign 7.7.4.1 Selecting Signers ......................... The key or the keys used to create a signature are stored in the context. The following functions can be used to manipulate this list. If no signer has been set into the context a default key is used for signing. -- Function: void gpgme_signers_clear (gpgme_ctx_t CTX) The function ‘gpgme_signers_clear’ releases a reference for each key on the signers list and removes the list of signers from the context CTX. Every context starts with an empty list. -- Function: gpgme_error_t gpgme_signers_add (gpgme_ctx_t CTX, const gpgme_key_t KEY) The function ‘gpgme_signers_add’ adds the key KEY to the list of signers in the context CTX. Calling this function acquires an additional reference for the key. -- Function: unsigned int gpgme_signers_count (const gpgme_ctx_t CTX) SINCE: 1.4.3 The function ‘gpgme_signers_count’ returns the number of signer keys in the context CTX. -- Function: gpgme_key_t gpgme_signers_enum (const gpgme_ctx_t CTX, int SEQ) The function ‘gpgme_signers_enum’ returns the SEQth key in the list of signers in the context CTX. An additional reference is acquired for the user. If SEQ is out of range, ‘NULL’ is returned.  File: gpgme.info, Node: Creating a Signature, Next: Signature Notation Data, Prev: Selecting Signers, Up: Sign 7.7.4.2 Creating a Signature ............................ -- Data type: enum gpgme_sig_mode_t The ‘gpgme_sig_mode_t’ type is used to specify the desired type of a signature. The following modes are available: ‘GPGME_SIG_MODE_NORMAL’ A normal signature is made, the output includes the plaintext and the signature. ‘GPGME_SIG_MODE_DETACH’ A detached signature is made. ‘GPGME_SIG_MODE_CLEAR’ A clear text signature is made. The ASCII armor and text mode settings of the context are ignored. -- Function: gpgme_error_t gpgme_op_sign (gpgme_ctx_t CTX, gpgme_data_t PLAIN, gpgme_data_t SIG, gpgme_sig_mode_t MODE) The function ‘gpgme_op_sign’ creates a signature for the text in the data object PLAIN and returns it in the data object SIG. The type of the signature created is determined by the ASCII armor (or, if that is not set, by the encoding specified for SIG), the text mode attributes set for the context CTX and the requested signature mode MODE. After the operation completed successfully, the result can be retrieved with ‘gpgme_op_sign_result’. If an S/MIME signed message is created using the CMS crypto engine, the number of certificates to include in the message can be specified with ‘gpgme_set_include_certs’. *Note Included Certificates::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the signature could be created successfully, ‘GPG_ERR_INV_VALUE’ if CTX, PLAIN or SIG is not a valid pointer, ‘GPG_ERR_NO_DATA’ if the signature could not be created, ‘GPG_ERR_BAD_PASSPHRASE’ if the passphrase for the secret key could not be retrieved, ‘GPG_ERR_UNUSABLE_SECKEY’ if there are invalid signers, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_sign_start (gpgme_ctx_t CTX, gpgme_data_t PLAIN, gpgme_data_t SIG, gpgme_sig_mode_t MODE) The function ‘gpgme_op_sign_start’ initiates a ‘gpgme_op_sign’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if CTX, PLAIN or SIG is not a valid pointer. -- Data type: gpgme_new_signature_t This is a pointer to a structure used to store a part of the result of a ‘gpgme_op_sign’ operation. The structure contains the following members: ‘gpgme_new_signature_t next’ This is a pointer to the next new signature structure in the linked list, or ‘NULL’ if this is the last element. ‘gpgme_sig_mode_t type’ The type of this signature. ‘gpgme_pubkey_algo_t pubkey_algo’ The public key algorithm used to create this signature. ‘gpgme_hash_algo_t hash_algo’ The hash algorithm used to create this signature. ‘unsigned int sig_class’ The signature class of this signature. ‘long int timestamp’ The creation timestamp of this signature. ‘char *fpr’ The fingerprint of the key which was used to create this signature. -- Data type: gpgme_sign_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_sign’ operation. After successfully generating a signature, you can retrieve the pointer to the result with ‘gpgme_op_sign_result’. The structure contains the following members: ‘gpgme_invalid_key_t invalid_signers’ A linked list with information about all invalid keys for which a signature could not be created. ‘gpgme_new_signature_t signatures’ A linked list with information about all signatures created. -- Function: gpgme_sign_result_t gpgme_op_sign_result (gpgme_ctx_t CTX) The function ‘gpgme_op_sign_result’ returns a ‘gpgme_sign_result_t’ pointer to a structure holding the result of a ‘gpgme_op_sign’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_sign’, ‘gpgme_op_sign_start’, ‘gpgme_op_encrypt_sign’ or ‘gpgme_op_encrypt_sign_start’ operation. If that operation failed, the function might return a ‘NULL’ pointer. The returned pointer is only valid until the next operation is started on the context.  File: gpgme.info, Node: Signature Notation Data, Prev: Creating a Signature, Up: Sign 7.7.4.3 Signature Notation Data ............................... Using the following functions, you can attach arbitrary notation data to a signature. This information is then available to the user when the signature is verified. -- Function: void gpgme_sig_notation_clear (gpgme_ctx_t CTX) SINCE: 1.1.0 The function ‘gpgme_sig_notation_clear’ removes the notation data from the context CTX. Subsequent signing operations from this context will not include any notation data. Every context starts with an empty notation data list. -- Function: gpgme_error_t gpgme_sig_notation_add (gpgme_ctx_t CTX, const char *NAME, const char *VALUE, gpgme_sig_notation_flags_t FLAGS) SINCE: 1.1.0 The function ‘gpgme_sig_notation_add’ adds the notation data with the name NAME and the value VALUE to the context CTX. Subsequent signing operations will include this notation data, as well as any other notation data that was added since the creation of the context or the last ‘gpgme_sig_notation_clear’ operation. The arguments NAME and VALUE must be ‘NUL’-terminated strings in human-readable form. The flag ‘GPGME_SIG_NOTATION_HUMAN_READABLE’ is implied (non-human-readable notation data is currently not supported). The strings must be in UTF-8 encoding. If NAME is ‘NULL’, then VALUE should be a policy URL. The function ‘gpgme_sig_notation_add’ returns the error code ‘GPG_ERR_NO_ERROR’ if the notation data could be added successfully, ‘GPG_ERR_INV_VALUE’ if CTX is not a valid pointer, or if NAME, VALUE and FLAGS are an invalid combination. The function also passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_sig_notation_t gpgme_sig_notation_get (const gpgme_ctx_t CTX) SINCE: 1.1.0 The function ‘gpgme_sig_notation_get’ returns the linked list of notation data structures that are contained in the context CTX. If CTX is not a valid pointer, or there is no notation data added for this context, ‘NULL’ is returned.  File: gpgme.info, Node: Encrypt, Prev: Sign, Up: Crypto Operations 7.7.5 Encrypt ------------- One plaintext can be encrypted for several recipients at the same time. The list of recipients is created independently of any context, and then passed to the encryption operation. * Menu: * Encrypting a Plaintext:: How to encrypt a plaintext.  File: gpgme.info, Node: Encrypting a Plaintext, Up: Encrypt 7.7.5.1 Encrypting a Plaintext .............................. -- Function: gpgme_error_t gpgme_op_encrypt (gpgme_ctx_t CTX, gpgme_key_t RECP[], gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) The function ‘gpgme_op_encrypt’ encrypts the plaintext in the data object PLAIN for the recipients RECP and stores the ciphertext in the data object CIPHER. The type of the ciphertext created is determined by the ASCII armor (or, if that is not set, by the encoding specified for CIPHER) and the text mode attributes set for the context CTX. RECP must be a ‘NULL’-terminated array of keys. The user must keep references for all keys during the whole duration of the call (but see ‘gpgme_op_encrypt_start’ for the requirements with the asynchronous variant). The value in FLAGS is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_ENCRYPT_ALWAYS_TRUST’ The ‘GPGME_ENCRYPT_ALWAYS_TRUST’ symbol specifies that all the recipients in RECP should be trusted, even if the keys do not have a high enough validity in the keyring. This flag should be used with care; in general it is not a good idea to use any untrusted keys. ‘GPGME_ENCRYPT_NO_ENCRYPT_TO’ SINCE: 1.2.0 The ‘GPGME_ENCRYPT_NO_ENCRYPT_TO’ symbol specifies that no default or hidden default recipients as configured in the crypto backend should be included. This can be useful for managing different user profiles. ‘GPGME_ENCRYPT_NO_COMPRESS’ SINCE: 1.5.0 The ‘GPGME_ENCRYPT_NO_COMPRESS’ symbol specifies that the plaintext shall not be compressed before it is encrypted. This is in some cases useful if the length of the encrypted message may reveal information about the plaintext. ‘GPGME_ENCRYPT_PREPARE’ ‘GPGME_ENCRYPT_EXPECT_SIGN’ The ‘GPGME_ENCRYPT_PREPARE’ symbol is used with the UI Server protocol to prepare an encryption (i.e. sending the ‘PREP_ENCRYPT’ command). With the ‘GPGME_ENCRYPT_EXPECT_SIGN’ symbol the UI Server is advised to also expect a sign command. ‘GPGME_ENCRYPT_SYMMETRIC’ SINCE: 1.7.0 The ‘GPGME_ENCRYPT_SYMMETRIC’ symbol specifies that the output should be additionally encrypted symmetrically even if recipients are provided. This feature is only supported for the OpenPGP crypto engine. ‘GPGME_ENCRYPT_THROW_KEYIDS’ SINCE: 1.8.0 The ‘GPGME_ENCRYPT_THROW_KEYIDS’ symbols requests that the identifiers for the decrption keys are not included in the ciphertext. On the receiving side, the use of this flag may slow down the decryption process because all available secret keys must be tried. This flag is only honored for OpenPGP encryption. ‘GPGME_ENCRYPT_WRAP’ SINCE: 1.8.0 The ‘GPGME_ENCRYPT_WRAP’ symbol specifies that the input is an OpenPGP message and not a plain data. This is the counterpart to ‘GPGME_DECRYPT_UNWRAP’. ‘GPGME_ENCRYPT_WANT_ADDRESS’ SINCE: 1.11.0 The ‘GPGME_ENCRYPT_WANT_ADDRESS’ symbol requests that all supplied keys or key specifications include a syntactically valid mail address. If this is not the case the operation is not even tried and the error code ‘GPG_ERR_INV_USER_ID’ is returned. Only the address part of the key specification is conveyed to the backend. As of now the key must be specified using the RECPSTRING argument of the extended encrypt functions. This feature is currently only supported for the OpenPGP crypto engine. If ‘GPG_ERR_UNUSABLE_PUBKEY’ is returned, some recipients in RECP are invalid, but not all. In this case the plaintext might be encrypted for all valid recipients and returned in CIPHER (if this happens depends on the crypto engine). More information about the invalid recipients is available with ‘gpgme_op_encrypt_result’. If RECP is ‘NULL’, symmetric rather than public key encryption is performed. Symmetrically encrypted cipher text can be deciphered with ‘gpgme_op_decrypt’. Note that in this case the crypto backend needs to retrieve a passphrase from the user. Symmetric encryption is currently only supported for the OpenPGP crypto backend. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the ciphertext could be created successfully, ‘GPG_ERR_INV_VALUE’ if CTX, RECP, PLAIN or CIPHER is not a valid pointer, ‘GPG_ERR_UNUSABLE_PUBKEY’ if RECP contains some invalid recipients, ‘GPG_ERR_BAD_PASSPHRASE’ if the passphrase for the symmetric key could not be retrieved, and passes through any errors that are reported by the crypto engine support routines. -- Function: gpgme_error_t gpgme_op_encrypt_start (gpgme_ctx_t CTX, gpgme_key_t RECP[], gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) The function ‘gpgme_op_encrypt_start’ initiates a ‘gpgme_op_encrypt’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. References to the keys only need to be held for the duration of this call. The user can release its references to the keys after this function returns, even if the operation is not yet finished. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, ‘GPG_ERR_INV_VALUE’ if CTX, RSET, PLAIN or CIPHER is not a valid pointer, and ‘GPG_ERR_UNUSABLE_PUBKEY’ if RSET does not contain any valid recipients. -- Function: gpgme_error_t gpgme_op_encrypt_ext (gpgme_ctx_t CTX, gpgme_key_t RECP[], const char *RECPSTRING, gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) SINCE: 1.11.0 This is an extended version of ‘gpgme_op_encrypt’ with RECPSTRING as additional parameter. If RECP is NULL and RECPSTRING is not NULL, the latter is expected to be a linefeed delimited string with the set of key specifications. In contrast to RECP the keys are given directly as strings and there is no need to first create key objects. Leading and trailing white space is remove from each line in RECPSTRING. The keys are then passed verbatim to the backend engine. For the OpenPGP backend several special keywords are supported to modify the operation. These keywords are given instead of a key specification. The currently supported keywords are: ‘--hidden’ ‘--no-hidden’ These keywords toggle between normal and hidden recipients for all following key specifications. When a hidden recipient is requested the gpg option ‘-R’ (or ‘-F’ in file mode) is used instead of ‘-r’ (‘-f’ in file mode). ‘--file’ ‘--no-file’ These keywords toggle between regular and file mode for all following key specification. In file mode the option ‘-f’ or ‘-F’ is passed to gpg. At least GnuPG version 2.1.14 is required to handle these options. The ‘GPGME_ENCRYPT_WANT_ADDRESS’ flag is ignored in file mode. ‘--’ This keyword disables all keyword detection up to the end of the string. All keywords are treated as verbatim arguments. To create a RECPSTRING it is often useful to employ a strconcat style function. For example this function creates a string to encrypt to two keys: char * xbuild_recpstring (const char *key1, const char *key2) { char *result = gpgrt_strconcat ("--\n", key1, "\n", key2, NULL); if (!result) { perror ("strconcat failed"); exit (2); } return result; } Note the use of the double dash here; unless you want to specify a keyword, it is a good idea to avoid any possible trouble with key specifications starting with a double dash. The used strconcat function is available in Libgpg-error 1.28 and later; Libgpg-error (aka Gpgrt) is a dependency of GPGME. The number of arguments to ‘gpgrt_strconcat’ is limited to 47 but that should always be sufficient. In case a larger and non-fixed number of keys are to be supplied the following code can be used: char * xbuild_long_recpstring (void) { gpgrt_stream_t memfp; const char *s; void *result; memfp = gpgrt_fopenmem (0, "w+b"); if (!memfp) { perror ("fopenmem failed"); exit (2); } gpgrt_fputs ("--", memfp); while ((s = get_next_keyspec ())) { gpgrt_fputc ('\n', memfp); gpgrt_fputs (s, memfp); } gpgrt_fputc (0, memfp); if (gpgrt_ferror (memfp)) { perror ("writing to memstream failed"); exit (2); } if (gpgrt_fclose_snatch (memfp, &result, NULL)) { perror ("fclose_snatch failed"); exit (2); } return result; } In this example ‘get_next_keyspec’ is expected to return the next key to be added to the string. Please take care: Encrypting to a large number of recipients is often questionable due to security reasons and also for the technicality that all keys are currently passed on the command line to ‘gpg’ which has as a platform specific length limitation. -- Function: gpgme_error_t gpgme_op_encrypt_ext_start (gpgme_ctx_t CTX, gpgme_key_t RECP[], const char *RECPSTRING, gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) SINCE: 1.11.0 This is an extended version of ‘gpgme_op_encrypt_start’ with RECPSTRING as additional parameter. If RECP is NULL and RECPSTRING is not NULL, the latter is expected to be a linefeed delimited string with the set of key specifications. In contrast to RECP the keys are given directly as strings and there is no need to first create key objects. The keys are passed verbatim to the backend engine. -- Data type: gpgme_encrypt_result_t This is a pointer to a structure used to store the result of a ‘gpgme_op_encrypt’ operation. After successfully encrypting data, you can retrieve the pointer to the result with ‘gpgme_op_encrypt_result’. The structure contains the following members: ‘gpgme_invalid_key_t invalid_recipients’ A linked list with information about all invalid keys for which the data could not be encrypted. -- Function: gpgme_encrypt_result_t gpgme_op_encrypt_result (gpgme_ctx_t CTX) The function ‘gpgme_op_encrypt_result’ returns a ‘gpgme_encrypt_result_t’ pointer to a structure holding the result of a ‘gpgme_op_encrypt’ operation. The pointer is only valid if the last operation on the context was a ‘gpgme_op_encrypt’, ‘gpgme_op_encrypt_start’, ‘gpgme_op_sign’ or ‘gpgme_op_sign_start’ operation. If this operation failed, this might be a ‘NULL’ pointer. The returned pointer is only valid until the next operation is started on the context. -- Function: gpgme_error_t gpgme_op_encrypt_sign (gpgme_ctx_t CTX, gpgme_key_t RECP[], gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) The function ‘gpgme_op_encrypt_sign’ does a combined encrypt and sign operation. It is used like ‘gpgme_op_encrypt’, but the ciphertext also contains signatures for the signers listed in CTX. The combined encrypt and sign operation is currently only available for the OpenPGP crypto engine. -- Function: gpgme_error_t gpgme_op_encrypt_sign_start (gpgme_ctx_t CTX, gpgme_key_t RECP[], gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) The function ‘gpgme_op_encrypt_sign_start’ initiates a ‘gpgme_op_encrypt_sign’ operation. It can be completed by calling ‘gpgme_wait’ on the context. *Note Waiting For Completion::. The function returns the error code ‘GPG_ERR_NO_ERROR’ if the operation could be started successfully, and ‘GPG_ERR_INV_VALUE’ if CTX, RSET, PLAIN or CIPHER is not a valid pointer. -- Function: gpgme_error_t gpgme_op_encrypt_sign_ext (gpgme_ctx_t CTX, gpgme_key_t RECP[], const char *RECPSTRING, gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) SINCE: 1.11.0 This is an extended version of ‘gpgme_op_encrypt_sign’ with RECPSTRING as additional parameter. If RECP is NULL and RECPSTRING is not NULL, the latter is expected to be a linefeed delimited string with the set of key specifications. In contrast to RECP the keys are given directly as strings and there is no need to first create the key objects. The keys are passed verbatim to the backend engine. -- Function: gpgme_error_t gpgme_op_encrypt_sign_ext_start (gpgme_ctx_t CTX, gpgme_key_t RECP[], const char *RECPSTRING, gpgme_encrypt_flags_t FLAGS, gpgme_data_t PLAIN, gpgme_data_t CIPHER) SINCE: 1.11.0 This is an extended version of ‘gpgme_op_encrypt_sign_start’ with RECPSTRING as additional parameter. If RECP is NULL and RECPSTRING is not NULL, the latter is expected to be a linefeed delimited string with the set of key specifications. In contrast to RECP the keys are given directly as strings and there is no need to first create the key objects. The keys are passed verbatim to the backend engine.  File: gpgme.info, Node: Miscellaneous, Next: Run Control, Prev: Crypto Operations, Up: Contexts 7.8 Miscellaneous operations ============================ Here are some support functions which are sometimes useful. * Menu: * Running other Programs:: Running other Programs * Using the Assuan protocol:: Using the Assuan protocol * Checking for updates:: How to check for software updates  File: gpgme.info, Node: Running other Programs, Next: Using the Assuan protocol, Up: Miscellaneous 7.8.1 Running other Programs ---------------------------- GPGME features an internal subsystem to run the actual backend engines. Along with data abstraction object this subsystem can be used to run arbitrary simple programs which even need not be related to cryptographic features. It may for example be used to run tools which are part of the GnuPG system but are not directly accessible with the GPGME API. -- Function: gpgme_error_t gpgme_op_spawn (gpgme_ctx_t CTX, const char *FILE, const char *ARGV[], gpgme_data_t DATAIN, gpgme_data_t DATAOUT, gpgme_data_t DATAERR, unsigned int FLAGS) SINCE: 1.5.0 The function ‘gpgme_op_spawn’ runs the program FILE with the arguments taken from the NULL terminated array ARGV. If no arguments are required ARGV may be given as ‘NULL’. In the latter case or if ‘argv[0]’ is the empty string, GPGME uses the basename of FILE for ‘argv[0]’. The file descriptors ‘stdin’, ‘stdout’, and ‘stderr’ are connected to the data objects DATAIN, DATAOUT, and DATAERR. If NULL is passed for one of these data objects the corresponding file descriptor is connected to ‘/dev/null’. The value in FLAGS is a bitwise-or combination of one or multiple of the following bit values: ‘GPGME_SPAWN_DETACHED’ SINCE: 1.5.0 Under Windows this flag inhibits the allocation of a new console for the program. This is useful for a GUI application which needs to call a command line helper tool. ‘GPGME_SPAWN_ALLOW_SET_FG’ SINCE: 1.5.0 Under Windows this flag allows the called program to put itself into the foreground. -- Function: gpgme_error_t gpgme_op_spawn_start (gpgme_ctx_t CTX, const char *FILE, const char *ARGV[], gpgme_data_t DATAIN, gpgme_data_t DATAOUT, gpgme_data_t DATAERR, unsigned int FLAGS) SINCE: 1.5.0 This is the asynchronous variant of ‘gpgme_op_spawn’.  File: gpgme.info, Node: Using the Assuan protocol, Next: Checking for updates, Prev: Running other Programs, Up: Miscellaneous 7.8.2 Using the Assuan protocol ------------------------------- The Assuan protocol can be used to talk to arbitrary Assuan servers. By default it is connected to the GnuPG agent, but it may be connected to arbitrary servers by using ‘gpgme_ctx_set_engine_info’, passing the location of the servers socket as FILE_NAME argument, and an empty string as HOME_DIR argument. The Assuan protocol functions use three kinds of callbacks to transfer data: -- Data type: gpgme_error_t (*gpgme_assuan_data_cb_t) (void *OPAQUE, const void *DATA, size_t DATALEN) SINCE: 1.2.0 This callback receives any data sent by the server. OPAQUE is the pointer passed to ‘gpgme_op_assuan_transact_start’, DATA of length DATALEN refers to the data sent. -- Data type: gpgme_error_t (*gpgme_assuan_inquire_cb_t) (void *OPAQUE, const char *NAME, const char *ARGS, gpgme_data_t *R_DATA) SINCE: 1.2.0 This callback is used to provide additional data to the Assuan server. OPAQUE is the pointer passed to ‘gpgme_op_assuan_transact_start’, NAME and ARGS specify what kind of data the server requested, and R_DATA is used to return the actual data. Note: Returning data is currently not implemented in GPGME. -- Data type: gpgme_error_t (*gpgme_assuan_status_cb_t) (void *OPAQUE, const char *STATUS, const char *ARGS) SINCE: 1.2.0 This callback receives any status lines sent by the server. OPAQUE is the pointer passed to ‘gpgme_op_assuan_transact_start’, STATUS and ARGS denote the status update sent. -- Function: gpgme_error_t gpgme_op_assuan_transact_start (gpgme_ctx_t CTX, const char *COMMAND, gpgme_assuan_data_cb_t DATA_CB, void * DATA_CB_VALUE, gpgme_assuan_inquire_cb_t INQUIRE_CB, void * INQUIRE_CB_VALUE, gpgme_assuan_status_cb_t STATUS_CB, void * STATUS_CB_VALUE) SINCE: 1.2.0 Send the Assuan COMMAND and return results via the callbacks. Any callback may be ‘NULL’. The result of the operation may be retrieved using ‘gpgme_wait_ext’. Asynchronous variant. -- Function: gpgme_error_t gpgme_op_assuan_transact_ext (gpgme_ctx_t CTX, const char *COMMAND, gpgme_assuan_data_cb_t DATA_CB, void * DATA_CB_VALUE, gpgme_assuan_inquire_cb_t INQUIRE_CB, void * INQUIRE_CB_VALUE, gpgme_assuan_status_cb_t STATUS_CB, void * STATUS_CB_VALUE, gpgme_error_t *OP_ERR) Send the Assuan COMMAND and return results via the callbacks. The result of the operation is returned in OP_ERR. Synchronous variant.  File: gpgme.info, Node: Checking for updates, Prev: Using the Assuan protocol, Up: Miscellaneous 7.8.3 How to check for software updates --------------------------------------- The GnuPG Project operates a server to query the current versions of software packages related to GnuPG. GPGME can be used to access this online database and check whether a new version of a software package is available. -- Data type: gpgme_query_swdb_result_t SINCE: 1.8.0 This is a pointer to a structure used to store the result of a ‘gpgme_op_query_swdb’ operation. After success full call to that function, you can retrieve the pointer to the result with ‘gpgme_op_query_swdb_result’. The structure contains the following member: ‘name’ This is the name of the package. ‘iversion’ The currently installed version or an empty string. This value is either a copy of the argument given to ‘gpgme_op_query_swdb’ or the version of the installed software as figured out by GPGME or GnuPG. ‘created’ This gives the date the file with the list of version numbers has originally be created by the GnuPG project. ‘retrieved’ This gives the date the file was downloaded. ‘warning’ If this flag is set either an error has occurred or some of the information in this structure are not properly set. For example if the version number of the installed software could not be figured out, the ‘update’ flag may not reflect a required update status. ‘update’ If this flag is set an update of the software is available. ‘urgent’ If this flag is set an available update is important. ‘noinfo’ If this flag is set, no valid information could be retrieved. ‘unknown’ If this flag is set the given ‘name’ is not known. ‘tooold’ If this flag is set the available information is not fresh enough. ‘error’ If this flag is set some other error has occurred. ‘version’ The version string of the latest released version. ‘reldate’ The release date of the latest released version. -- Function: gpgme_error_t gpgme_op_query_swdb (gpgme_ctx_t CTX, const char *NAME, const char *IVERSION, gpgme_data_t RESERVED) SINCE: 1.8.0 Query the software version database for software package NAME and check against the installed version given by IVERSION. If IVERSION is given as ‘NULL’ a check is only done if GPGME can figure out the version by itself (for example when using "gpgme" or "gnupg"). If ‘NULL’ is used for NAME the current gpgme version is checked. RESERVED must be set to 0. -- Function: gpgme_query_swdb_result_t gpgme_op_query_swdb_result (gpgme_ctx_t CTX) SINCE: 1.8.0 The function ‘gpgme_op_query_swdb_result’ returns a ‘gpgme_query_swdb_result_t’ pointer to a structure holding the result of a ‘gpgme_op_query_swdb’ operation. The pointer is only valid if the last operation on the context was a successful call to ‘gpgme_op_query_swdb’. If that call failed, the result might be a ‘NULL’ pointer. The returned pointer is only valid until the next operation is started on the context CTX. Here is an example on how to check whether GnuPG is current: #include int main (void) { gpg_error_t err; gpgme_ctx_t ctx; gpgme_query_swdb_result_t result; gpgme_check_version (NULL); err = gpgme_new (&ctx); if (err) fprintf (stderr, "error creating context: %s\n", gpg_strerror (err)); else { gpgme_set_protocol (ctx, GPGME_PROTOCOL_GPGCONF); err = gpgme_op_query_swdb (ctx, "gnupg", NULL, 0); if (err) fprintf (stderr, "error querying swdb: %s\n", gpg_strerror (err)); else { result = gpgme_op_query_swdb_result (ctx); if (!result) fprintf (stderr, "error querying swdb\n"); if (!result->warning && !result->update) printf ("GnuPG version %s is current\n", result->iversion); else if (!result->warning && result->update) printf ("GnuPG version %s can be updated to %s\n", result->iversion, result->version); else fprintf (stderr, "error finding the update status\n"); } gpgme_release (ctx); } return 0; }  File: gpgme.info, Node: Run Control, Prev: Miscellaneous, Up: Contexts 7.9 Run Control =============== GPGME supports running operations synchronously and asynchronously. You can use asynchronous operation to set up a context up to initiating the desired operation, but delay performing it to a later point. Furthermore, you can use an external event loop to control exactly when GPGME runs. This ensures that GPGME only runs when necessary and also prevents it from blocking for a long time. * Menu: * Waiting For Completion:: Waiting until an operation is completed. * Using External Event Loops:: Advanced control over what happens when. * Cancellation:: How to end pending operations prematurely.  File: gpgme.info, Node: Waiting For Completion, Next: Using External Event Loops, Up: Run Control 7.9.1 Waiting For Completion ---------------------------- -- Function: gpgme_ctx_t gpgme_wait (gpgme_ctx_t CTX, gpgme_error_t *STATUS, int HANG) The function ‘gpgme_wait’ continues the pending operation within the context CTX. In particular, it ensures the data exchange between GPGME and the crypto backend and watches over the run time status of the backend process. If HANG is true, the function does not return until the operation is completed or cancelled. Otherwise the function will not block for a long time. The error status of the finished operation is returned in STATUS if ‘gpgme_wait’ does not return ‘NULL’. The CTX argument can be ‘NULL’. In that case, ‘gpgme_wait’ waits for any context to complete its operation. ‘gpgme_wait’ can be used only in conjunction with any context that has a pending operation initiated with one of the ‘gpgme_op_*_start’ functions except ‘gpgme_op_keylist_start’ and ‘gpgme_op_trustlist_start’ (for which you should use the corresponding ‘gpgme_op_*_next’ functions). If CTX is ‘NULL’, all of such contexts are waited upon and possibly returned. Synchronous operations running in parallel, as well as key and trust item list operations, do not affect ‘gpgme_wait’. In a multi-threaded environment, only one thread should ever call ‘gpgme_wait’ at any time, regardless of whether CTX is specified or not. This means that all calls to this function should be fully synchronized by locking primitives. It is safe to start asynchronous operations while a thread is running in ‘gpgme_wait’. The function returns the CTX of the context which has finished the operation. If HANG is false, and the timeout expires, ‘NULL’ is returned and ‘*status’ will be set to 0. If an error occurs, ‘NULL’ is returned and the error is returned in ‘*status’.  File: gpgme.info, Node: Using External Event Loops, Next: Cancellation, Prev: Waiting For Completion, Up: Run Control 7.9.2 Using External Event Loops -------------------------------- GPGME hides the complexity of the communication between the library and the crypto engine. The price of this convenience is that the calling thread can block arbitrary long waiting for the data returned by the crypto engine. In single-threaded programs, in particular if they are interactive, this is an unwanted side-effect. OTOH, if ‘gpgme_wait’ is used without the HANG option being enabled, it might be called unnecessarily often, wasting CPU time that could be used otherwise. The I/O callback interface described in this section lets the user take control over what happens when. GPGME will provide the user with the file descriptors that should be monitored, and the callback functions that should be invoked when a file descriptor is ready for reading or writing. It is then the user’s responsibility to decide when to check the file descriptors and when to invoke the callback functions. Usually this is done in an event loop, that also checks for events in other parts of the program. If the callback functions are only called when the file descriptors are ready, GPGME will never block. This gives the user more control over the program flow, and allows to perform other tasks when GPGME would block otherwise. By using this advanced mechanism, GPGME can be integrated smoothly into GUI toolkits like GTK+ even for single-threaded programs. * Menu: * I/O Callback Interface:: How I/O callbacks are registered. * Registering I/O Callbacks:: How to use I/O callbacks for a context. * I/O Callback Example:: An example how to use I/O callbacks. * I/O Callback Example GTK+:: How to use GPGME with GTK+. * I/O Callback Example GDK:: How to use GPGME with GDK. * I/O Callback Example Qt:: How to use GPGME with Qt.  File: gpgme.info, Node: I/O Callback Interface, Next: Registering I/O Callbacks, Up: Using External Event Loops 7.9.2.1 I/O Callback Interface .............................. -- Data type: gpgme_error_t (*gpgme_io_cb_t) (void *DATA, int FD) The ‘gpgme_io_cb_t’ type is the type of functions which GPGME wants to register as I/O callback handlers using the ‘gpgme_register_io_cb_t’ functions provided by the user. DATA and FD are provided by GPGME when the I/O callback handler is registered, and should be passed through to the handler when it is invoked by the user because it noticed activity on the file descriptor FD. The callback handler always returns ‘0’, but you should consider the return value to be reserved for later use. -- Data type: gpgme_error_t (*gpgme_register_io_cb_t) (void *DATA, int FD, int DIR, gpgme_io_cb_t FNC, void *FNC_DATA, void **TAG) The ‘gpgme_register_io_cb_t’ type is the type of functions which can be called by GPGME to register an I/O callback function FNC for the file descriptor FD with the user. FNC_DATA should be passed as the first argument to FNC when the handler is invoked (the second argument should be FD). If DIR is 0, FNC should be called by the user when FD is ready for writing. If DIR is 1, FNC should be called when FD is ready for reading. DATA was provided by the user when registering the ‘gpgme_register_io_cb_t’ function with GPGME and will always be passed as the first argument when registering a callback function. For example, the user can use this to determine the event loop to which the file descriptor should be added. GPGME will call this function when a crypto operation is initiated in a context for which the user has registered I/O callback handler functions with ‘gpgme_set_io_cbs’. It can also call this function when it is in an I/O callback handler for a file descriptor associated to this context. The user should return a unique handle in TAG identifying this I/O callback registration, which will be passed to the ‘gpgme_register_io_cb_t’ function without interpretation when the file descriptor should not be monitored anymore. -- Data type: void (*gpgme_remove_io_cb_t) (void *TAG) The ‘gpgme_remove_io_cb_t’ type is the type of functions which can be called by GPGME to remove an I/O callback handler that was registered before. TAG is the handle that was returned by the ‘gpgme_register_io_cb_t’ for this I/O callback. GPGME can call this function when a crypto operation is in an I/O callback. It will also call this function when the context is destroyed while an operation is pending. -- Data type: enum gpgme_event_io_t The ‘gpgme_event_io_t’ type specifies the type of an event that is reported to the user by GPGME as a consequence of an I/O operation. The following events are defined: ‘GPGME_EVENT_START’ The operation is fully initialized now, and you can start to run the registered I/O callback handlers now. Note that registered I/O callback handlers must not be run before this event is signalled. TYPE_DATA is ‘NULL’ and reserved for later use. ‘GPGME_EVENT_DONE’ The operation is finished, the last I/O callback for this operation was removed. The accompanying TYPE_DATA points to a ‘struct gpgme_io_event_done_data’ variable that contains the status of the operation that finished. This event is signalled after the last I/O callback has been removed. ‘GPGME_EVENT_NEXT_KEY’ In a ‘gpgme_op_keylist_start’ operation, the next key was received from the crypto engine. The accompanying TYPE_DATA is a ‘gpgme_key_t’ variable that contains the key with one reference for the user. ‘GPGME_EVENT_NEXT_TRUSTITEM’ In a ‘gpgme_op_trustlist_start’ operation, the next trust item was received from the crypto engine. The accompanying TYPE_DATA is a ‘gpgme_trust_item_t’ variable that contains the trust item with one reference for the user. -- Data type: void (*gpgme_event_io_cb_t) (void *DATA, gpgme_event_io_t TYPE, void *TYPE_DATA) The ‘gpgme_event_io_cb_t’ type is the type of functions which can be called by GPGME to signal an event for an operation running in a context which has I/O callback functions registered by the user. DATA was provided by the user when registering the ‘gpgme_event_io_cb_t’ function with GPGME and will always be passed as the first argument when registering a callback function. For example, the user can use this to determine the context in which this event has occurred. TYPE will specify the type of event that has occurred. TYPE_DATA specifies the event further, as described in the above list of possible ‘gpgme_event_io_t’ types. GPGME can call this function in an I/O callback handler.  File: gpgme.info, Node: Registering I/O Callbacks, Next: I/O Callback Example, Prev: I/O Callback Interface, Up: Using External Event Loops 7.9.2.2 Registering I/O Callbacks ................................. -- Data type: struct gpgme_io_cbs This structure is used to store the I/O callback interface functions described in the previous section. It has the following members: ‘gpgme_register_io_cb_t add’ This is the function called by GPGME to register an I/O callback handler. It must be specified. ‘void *add_priv’ This is passed as the first argument to the ‘add’ function when it is called by GPGME. For example, it can be used to determine the event loop to which the file descriptor should be added. ‘gpgme_remove_io_cb_t remove’ This is the function called by GPGME to remove an I/O callback handler. It must be specified. ‘gpgme_event_io_cb_t event’ This is the function called by GPGME to signal an event for an operation. It must be specified, because at least the start event must be processed. ‘void *event_priv’ This is passed as the first argument to the ‘event’ function when it is called by GPGME. For example, it can be used to determine the context in which the event has occurred. -- Function: void gpgme_set_io_cbs (gpgme_ctx_t CTX, struct gpgme_io_cbs *IO_CBS) The function ‘gpgme_set_io_cbs’ enables the I/O callback interface for the context CTX. The I/O callback functions are specified by IO_CBS. If IO_CBS->‘add’ is ‘NULL’, the I/O callback interface is disabled for the context, and normal operation is restored. -- Function: void gpgme_get_io_cbs (gpgme_ctx_t CTX, struct gpgme_io_cbs *IO_CBS) The function ‘gpgme_get_io_cbs’ returns the I/O callback functions set with ‘gpgme_set_io_cbs’ in IO_CBS.  File: gpgme.info, Node: I/O Callback Example, Next: I/O Callback Example GTK+, Prev: Registering I/O Callbacks, Up: Using External Event Loops 7.9.2.3 I/O Callback Example ............................ To actually use an external event loop, you have to implement the I/O callback functions that are used by GPGME to register and unregister file descriptors. Furthermore, you have to actually monitor these file descriptors for activity and call the appropriate I/O callbacks. The following example illustrates how to do that. The example uses locking to show in which way the callbacks and the event loop can run concurrently. For the event loop, we use a fixed array. For a real-world implementation, you should use a dynamically sized structure because the number of file descriptors needed for a crypto operation in GPGME is not predictable. #include #include #include #include #include #include /* The following structure holds the result of a crypto operation. */ struct op_result { int done; gpgme_error_t err; }; /* The following structure holds the data associated with one I/O callback. */ struct one_fd { int fd; int dir; gpgme_io_cb_t fnc; void *fnc_data; void *loop; }; struct event_loop { pthread_mutex_t lock; #define MAX_FDS 32 /* Unused slots are marked with FD being -1. */ struct one_fd fds[MAX_FDS]; }; The following functions implement the I/O callback interface. gpgme_error_t add_io_cb (void *data, int fd, int dir, gpgme_io_cb_t fnc, void *fnc_data, void **r_tag) { struct event_loop *loop = data; struct one_fd *fds = loop->fds; int i; pthread_mutex_lock (&loop->lock); for (i = 0; i < MAX_FDS; i++) { if (fds[i].fd == -1) { fds[i].fd = fd; fds[i].dir = dir; fds[i].fnc = fnc; fds[i].fnc_data = fnc_data; fds[i].loop = loop; break; } } pthread_mutex_unlock (&loop->lock); if (i == MAX_FDS) return gpg_error (GPG_ERR_GENERAL); *r_tag = &fds[i]; return 0; } void remove_io_cb (void *tag) { struct one_fd *fd = tag; struct event_loop *loop = fd->loop; pthread_mutex_lock (&loop->lock); fd->fd = -1; pthread_mutex_unlock (&loop->lock); } void event_io_cb (void *data, gpgme_event_io_t type, void *type_data) { struct op_result *result = data; /* We don't support list operations here. */ if (type == GPGME_EVENT_DONE) { result->done = 1; result->err = *type_data; } } The final missing piece is the event loop, which will be presented next. We only support waiting for the success of a single operation. int do_select (struct event_loop *loop) { fd_set rfds; fd_set wfds; int i, n; int any = 0; struct timeval tv; struct one_fd *fdlist = loop->fds; pthread_mutex_lock (&loop->lock); FD_ZERO (&rfds); FD_ZERO (&wfds); for (i = 0; i < MAX_FDS; i++) if (fdlist[i].fd != -1) FD_SET (fdlist[i].fd, fdlist[i].dir ? &rfds : &wfds); pthread_mutex_unlock (&loop->lock); tv.tv_sec = 0; tv.tv_usec = 1000; do { n = select (FD_SETSIZE, &rfds, &wfds, NULL, &tv); } while (n < 0 && errno == EINTR); if (n < 0) return n; /* Error or timeout. */ pthread_mutex_lock (&loop->lock); for (i = 0; i < MAX_FDS && n; i++) { if (fdlist[i].fd != -1) { if (FD_ISSET (fdlist[i].fd, fdlist[i].dir ? &rfds : &wfds)) { assert (n); n--; any = 1; /* The I/O callback handler can register/remove callbacks, so we have to unlock the file descriptor list. */ pthread_mutex_unlock (&loop->lock); (*fdlist[i].fnc) (fdlist[i].fnc_data, fdlist[i].fd); pthread_mutex_lock (&loop->lock); } } } pthread_mutex_unlock (&loop->lock); return any; } void wait_for_op (struct event_loop *loop, struct op_result *result) { int ret; do { ret = do_select (loop); } while (ret >= 0 && !result->done); } The main function shows how to put it all together. int main (int argc, char *argv[]) { struct event_loop loop; struct op_result result; gpgme_ctx_t ctx; gpgme_error_t err; gpgme_data_t sig, text; int i; pthread_mutexattr_t attr; struct gpgme_io_cbs io_cbs = { add_io_cb, &loop, remove_io_cb, event_io_cb, &result }; init_gpgme (); /* Initialize the loop structure. */ /* The mutex must be recursive, since remove_io_cb (which acquires a lock) can be called while holding a lock acquired in do_select. */ pthread_mutexattr_init (&attr); pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init (&loop.lock, &attr); pthread_mutexattr_destroy (&attr); for (i = 0; i < MAX_FDS; i++) loop.fds[i].fd = -1; /* Initialize the result structure. */ result.done = 0; err = gpgme_data_new_from_file (&sig, "signature", 1); if (!err) err = gpgme_data_new_from_file (&text, "text", 1); if (!err) err = gpgme_new (&ctx); if (!err) { gpgme_set_io_cbs (ctx, &io_cbs); err = gpgme_op_verify_start (ctx, sig, text, NULL); } if (err) { fprintf (stderr, "gpgme error: %s: %s\n", gpgme_strsource (err), gpgme_strerror (err)); exit (1); } wait_for_op (&loop, &result); if (!result.done) { fprintf (stderr, "select error\n"); exit (1); } if (!result.err) { fprintf (stderr, "verification failed: %s: %s\n", gpgme_strsource (result.err), gpgme_strerror (result.err)); exit (1); } /* Evaluate verify result. */ ... return 0; }  File: gpgme.info, Node: I/O Callback Example GTK+, Next: I/O Callback Example GDK, Prev: I/O Callback Example, Up: Using External Event Loops 7.9.2.4 I/O Callback Example GTK+ ................................. The I/O callback interface can be used to integrate GPGME with the GTK+ event loop. The following code snippets shows how this can be done using the appropriate register and remove I/O callback functions. In this example, the private data of the register I/O callback function is unused. The event notifications is missing because it does not require any GTK+ specific setup. #include struct my_gpgme_io_cb { gpgme_io_cb_t fnc; void *fnc_data; guint input_handler_id }; void my_gpgme_io_cb (gpointer data, gint source, GdkInputCondition condition) { struct my_gpgme_io_cb *iocb = data; (*(iocb->fnc)) (iocb->data, source); } void my_gpgme_remove_io_cb (void *data) { struct my_gpgme_io_cb *iocb = data; gtk_input_remove (data->input_handler_id); } void my_gpgme_register_io_callback (void *data, int fd, int dir, gpgme_io_cb_t fnc, void *fnc_data, void **tag) { struct my_gpgme_io_cb *iocb = g_malloc (sizeof (struct my_gpgme_io_cb)); iocb->fnc = fnc; iocb->data = fnc_data; iocb->input_handler_id = gtk_input_add_full (fd, dir ? GDK_INPUT_READ : GDK_INPUT_WRITE, my_gpgme_io_callback, 0, iocb, NULL); *tag = iocb; return 0; }  File: gpgme.info, Node: I/O Callback Example GDK, Next: I/O Callback Example Qt, Prev: I/O Callback Example GTK+, Up: Using External Event Loops 7.9.2.5 I/O Callback Example GDK ................................ The I/O callback interface can also be used to integrate GPGME with the GDK event loop. The following code snippets shows how this can be done using the appropriate register and remove I/O callback functions. In this example, the private data of the register I/O callback function is unused. The event notifications is missing because it does not require any GDK specific setup. It is very similar to the GTK+ example in the previous section. #include struct my_gpgme_io_cb { gpgme_io_cb_t fnc; void *fnc_data; gint tag; }; void my_gpgme_io_cb (gpointer data, gint source, GdkInputCondition condition) { struct my_gpgme_io_cb *iocb = data; (*(iocb->fnc)) (iocb->data, source); } void my_gpgme_remove_io_cb (void *data) { struct my_gpgme_io_cb *iocb = data; gdk_input_remove (data->tag); } void my_gpgme_register_io_callback (void *data, int fd, int dir, gpgme_io_cb_t fnc, void *fnc_data, void **tag) { struct my_gpgme_io_cb *iocb = g_malloc (sizeof (struct my_gpgme_io_cb)); iocb->fnc = fnc; iocb->data = fnc_data; iocb->tag = gtk_input_add_full (fd, dir ? GDK_INPUT_READ : GDK_INPUT_WRITE, my_gpgme_io_callback, iocb, NULL); *tag = iocb; return 0; }  File: gpgme.info, Node: I/O Callback Example Qt, Prev: I/O Callback Example GDK, Up: Using External Event Loops 7.9.2.6 I/O Callback Example Qt ............................... The I/O callback interface can also be used to integrate GPGME with the Qt event loop. The following code snippets show how this can be done using the appropriate register and remove I/O callback functions. In this example, the private data of the register I/O callback function is unused. The event notifications is missing because it does not require any Qt specific setup. #include #include struct IOCB { IOCB( GpgmeIOCb f, void * d, QSocketNotifier * n ) : func( f ), data( d ), notifier( n ) {} GpgmeIOCb func; void * data; QSocketNotifier * notifier; } class MyApp : public QApplication { // ... static void registerGpgmeIOCallback( void * data, int fd, int dir, GpgmeIOCb func, void * func_data, void ** tag ) { QSocketNotifier * n = new QSocketNotifier( fd, dir ? QSocketNotifier::Read : QSocketNotifier::Write ); connect( n, SIGNAL(activated(int)), qApp, SLOT(slotGpgmeIOCallback(int)) ); qApp->mIOCBs.push_back( IOCB( func, func_data, n ) ); *tag = (void*)n; } static void removeGpgmeIOCallback( void * tag ) { if ( !tag ) return; QSocketNotifier * n = static_cast( tag ); for ( QValueList::iterator it = qApp->mIOCBs.begin() ; it != qApp->mIOCBs.end() ; ++it ) if ( it->notifier == n ) { delete it->notifier; qApp->mIOCBs.erase( it ); return; } } public slots: void slotGpgmeIOCallback( int fd ) { for ( QValueList::const_iterator it = mIOCBs.begin() ; it != mIOCBs.end() ; ++it ) if ( it->notifier && it->notifier->socket() == fd ) (*(it->func)) ( it->func_data, fd ); } // ... private: QValueList mIOCBs; // ... };  File: gpgme.info, Node: Cancellation, Prev: Using External Event Loops, Up: Run Control 7.9.3 Cancellation ------------------ Sometimes you do not want to wait for an operation to finish. GPGME provides two different functions to achieve that. The function ‘gpgme_cancel’ takes effect immediately. When it returns, the operation is effectively canceled. However, it has some limitations and can not be used with synchronous operations. In contrast, the function ‘gpgme_cancel_async’ can be used with any context and from any thread, but it is not guaranteed to take effect immediately. Instead, cancellation occurs at the next possible time (typically the next time I/O occurs in the target context). -- Function: gpgme_ctx_t gpgme_cancel (gpgme_ctx_t CTX) SINCE: 0.4.5 The function ‘gpgme_cancel’ attempts to cancel a pending operation in the context CTX. This only works if you use the global event loop or your own event loop. If you use the global event loop, you must not call ‘gpgme_wait’ during cancellation. After successful cancellation, you can call ‘gpgme_wait’ (optionally waiting on CTX), and the context CTX will appear as if it had finished with the error code ‘GPG_ERR_CANCEL’. If you use an external event loop, you must ensure that no I/O callbacks are invoked for this context (for example by halting the event loop). On successful cancellation, all registered I/O callbacks for this context will be unregistered, and a ‘GPGME_EVENT_DONE’ event with the error code ‘GPG_ERR_CANCEL’ will be signalled. The function returns an error code if the cancellation failed (in this case the state of CTX is not modified). -- Function: gpgme_ctx_t gpgme_cancel_async (gpgme_ctx_t CTX) SINCE: 1.1.7 The function ‘gpgme_cancel_async’ attempts to cancel a pending operation in the context CTX. This can be called by any thread at any time after starting an operation on the context, but will not take effect immediately. The actual cancellation happens at the next time GPGME processes I/O in that context. The function returns an error code if the cancellation failed (in this case the state of CTX is not modified).  File: gpgme.info, Node: UI Server Protocol, Next: Debugging, Prev: Contexts, Up: Top Appendix A The GnuPG UI Server Protocol *************************************** This section specifies the protocol used between clients and a User Interface Server (UI server). This protocol helps to build a system where all cryptographic operations are done by a server and the server is responsible for all dialogs. Although GPGME has no direct support for this protocol it is believed that servers will utilize the GPGME library; thus having the specification included in this manual is an appropriate choice. This protocol should be referenced as ‘The GnuPG UI Server Protocol’. A server needs to implement these commands:(1) * Menu: * UI Server Encrypt:: Encrypt a message. * UI Server Sign:: Sign a message. * UI Server Decrypt:: Decrypt a message. * UI Server Verify:: Verify a message. * UI Server Set Input Files:: Specifying the input files to operate on. * UI Server Sign/Encrypt Files:: Encrypting and signing files. * UI Server Verify/Decrypt Files:: Decrypting and verifying files. * UI Server Import/Export Keys:: Managing certificates. * UI Server Checksum Files:: Create and verify checksums for files. * Miscellaneous UI Server Commands:: Commands not related to a specific operation. ---------- Footnotes ---------- (1) In all examples we assume that the connection has already been established; see the Assuan manual for details.  File: gpgme.info, Node: UI Server Encrypt, Next: UI Server Sign, Up: UI Server Protocol A.1 UI Server: Encrypt a Message ================================ Before encryption can be done the recipients must be set using the command: -- Command: RECIPIENT STRING Set the recipient for the encryption. STRING is an RFC-2822 recipient name ("mailbox" as per section 3.4). This command may or may not check the recipient for validity right away; if it does not all recipients are expected to be checked at the time of the ‘ENCRYPT’ command. All ‘RECIPIENT’ commands are cumulative until a successful ‘ENCRYPT’ command or until a ‘RESET’ command. Linefeeds are obviously not allowed in STRING and should be folded into spaces (which are equivalent). To tell the server the source and destination of the data, the next two commands are to be used: -- Command: INPUT FD=N Set the file descriptor for the message to be encrypted to N. The message send to the server is binary encoded. GpgOL is a Windows only program, thus N is not a libc file descriptor but a regular system handle. Given that the Assuan connection works over a socket, it is not possible to use regular inheritance to make the file descriptor available to the server. Thus ‘DuplicateHandle’ needs to be used to duplicate a handle to the server process. This is the reason that the server needs to implement the ‘GETINFO pid’ command. Sending this command a second time replaces the file descriptor set by the last one. -- Command: OUTPUT FD=N [--binary] Set the file descriptor to be used for the output (i.e. the encrypted message) to N. If the option ‘--binary’ is given the output shall be in binary format; if not given, the output for OpenPGP needs to be ASCII armored and for CMS Base-64 encoded. For details on the file descriptor, see the ‘INPUT’ command. The setting of the recipients, the data source and destination may happen in any order, even intermixed. If this has been done the actual encryption operation is called using: -- Command: ENCRYPT --protocol=NAME This command reads the plaintext from the file descriptor set by the ‘INPUT’ command, encrypts it and writes the ciphertext to the file descriptor set by the ‘OUTPUT’ command. The server may (and should) overlap reading and writing. The recipients used for the encryption are all the recipients set so far. If any recipient is not usable the server should take appropriate measures to notify the user about the problem and may cancel the operation by returning an error code. The used file descriptors are void after this command; the recipient list is only cleared if the server returns success. Because GpgOL uses a streaming mode of operation the server is not allowed to auto select the protocol and must obey to the mandatory PROTOCOL parameter: ‘OpenPGP’ Use the OpenPGP protocol (RFC-2440). ‘CMS’ Use the CMS (PKCS#7) protocol (RFC-3852). To support automagically selection of the protocol depending on the selected keys, the server MAY implement the command: -- Command: PREP_ENCRYPT [--protocol=NAME] [--expect-sign] This commands considers all recipients set so far and decides whether it is able to take input and start the actual encryption. This is kind of a dry-run ‘ENCRYPT’ without requiring or using the input and output file descriptors. The server shall cache the result of any user selection to avoid asking this again when the actual ‘ENCRYPT’ command is send. The ‘--protocol’ option is optional; if it is not given, the server should allow the user to select the protocol to be used based on the recipients given or by any other means. If ‘--expect-sign’ is given the server should expect that the message will also be signed and use this hint to present a unified recipient and signer selection dialog if possible and desired. A selected signer should then be cached for the expected SIGN command (which is expected in the same session but possible on another connection). If this command is given again before a successful ‘ENCRYPT’ command, the second one takes effect. Before sending the OK response the server shall tell the client the protocol to be used (either the one given by the argument or the one selected by the user) by means of a status line: -- Status line: PROTOCOL NAME Advise the client to use the protocol NAME for the ‘ENCRYPT’ command. The valid protocol names are listed under the description of the ‘ENCRYPT’ command. The server shall emit exactly one PROTOCOL status line. Here is an example of a complete encryption sequence; client lines are indicated by a C:, server responses by C:: C: RESET S: OK C: RECIPIENT foo@example.net S: OK C: RECIPIENT bar@example.com S: OK C: PREP_ENCRYPT S: S PROTOCOL OpenPGP S: OK C: INPUT FD=17 S: OK C: OUTPUT FD=18 S: OK C: ENCRYPT S: OK  File: gpgme.info, Node: UI Server Sign, Next: UI Server Decrypt, Prev: UI Server Encrypt, Up: UI Server Protocol A.2 UI Server: Sign a Message ============================= The server needs to implement opaque signing as well as detached signing. Due to the nature of OpenPGP messages it is always required to send the entire message to the server; sending just the hash is not possible. The following two commands are required to set the input and output file descriptors: -- Command: INPUT FD=N Set the file descriptor for the message to be signed to N. The message send to the server is binary encoded. For details on the file descriptor, see the description of ‘INPUT’ in the ‘ENCRYPT’ section. -- Command: OUTPUT FD=N [--binary] Set the file descriptor to be used for the output. The output is either the complete signed message or in case of a detached signature just that detached signature. If the option ‘--binary’ is given the output shall be in binary format; if not given, the output for OpenPGP needs to be ASCII armored and for CMS Base-64 encoded. For details on the file descriptor, see the ‘INPUT’ command. To allow the server the selection of a non-default signing key the client may optionally use the ‘SENDER’ command, see *note command SENDER::. The signing operation is then initiated by: -- Command: SIGN --protocol=NAME [--detached] Sign the data set with the ‘INPUT’ command and write it to the sink set by OUTPUT. NAME is the signing protocol used for the message. For a description of the allowed protocols see the ‘ENCRYPT’ command. With option ‘--detached’ given, a detached signature is created; this is actually the usual way the command is used. The client expects the server to send at least this status information before the final OK response: -- Status line: MICALG STRING The STRING represents the hash algorithm used to create the signature. It is used with RFC-1847 style signature messages and defined by PGP/MIME (RFC-3156) and S/MIME (RFC-3851). The GPGME library has a supporting function ‘gpgme_hash_algo_name’ to return the algorithm name as a string. This string needs to be lowercased and for OpenPGP prefixed with "‘pgp-’".  File: gpgme.info, Node: UI Server Decrypt, Next: UI Server Verify, Prev: UI Server Sign, Up: UI Server Protocol A.3 UI Server: Decrypt a Message ================================ Decryption may include the verification of OpenPGP messages. This is due to the often used combined signing/encryption modus of OpenPGP. The client may pass an option to the server to inhibit the signature verification. The following two commands are required to set the input and output file descriptors: -- Command: INPUT FD=N Set the file descriptor for the message to be decrypted to N. The message send to the server is either binary encoded or — in the case of OpenPGP — ASCII armored. For details on the file descriptor, see the description of ‘INPUT’ in the ‘ENCRYPT’ section. -- Command: OUTPUT FD=N Set the file descriptor to be used for the output. The output is binary encoded. For details on the file descriptor, see the description of ‘INPUT’ in the ‘ENCRYPT’ section. The decryption is started with the command: -- Command: DECRYPT --protocol=NAME [--no-verify] [--export-session-key] NAME is the encryption protocol used for the message. For a description of the allowed protocols see the ‘ENCRYPT’ command. This argument is mandatory. If the option ‘--no-verify’ is given, the server should not try to verify a signature, in case the input data is an OpenPGP combined message. If the option ‘--export-session-key’ is given and the underlying engine knows how to export the session key, it will appear on a status line