ENGINE

  ======

  With OpenSSL 0.9.6, a new component was added to support alternative

  cryptography implementations, most commonly for interfacing with external

  crypto devices (eg. accelerator cards). This component is called ENGINE,

  and its presence in OpenSSL 0.9.6 (and subsequent bug-fix releases)

  caused a little confusion as 0.9.6** releases were rolled in two

  versions, a "standard" and an "engine" version. In development for 0.9.7,

  the ENGINE code has been merged into the main branch and will be present

  in the standard releases from 0.9.7 forwards.

  There are currently built-in ENGINE implementations for the following

  crypto devices:

      o Microsoft CryptoAPI

      o VIA Padlock

      o nCipher CHIL

  In addition, dynamic binding to external ENGINE implementations is now

  provided by a special ENGINE called "dynamic". See the "DYNAMIC ENGINE"

  section below for details.

  At this stage, a number of things are still needed and are being worked on:

      1 Integration of EVP support.

      2 Configuration support.

      3 Documentation!

1 With respect to EVP, this relates to support for ciphers and digests in

  the ENGINE model so that alternative implementations of existing

  algorithms/modes (or previously unimplemented ones) can be provided by

  ENGINE implementations.

2 Configuration support currently exists in the ENGINE API itself, in the

  form of "control commands". These allow an application to expose to the

  user/admin the set of commands and parameter types a given ENGINE

  implementation supports, and for an application to directly feed string

  based input to those ENGINEs, in the form of name-value pairs. This is an

  extensible way for ENGINEs to define their own "configuration" mechanisms

  that are specific to a given ENGINE (eg. for a particular hardware

  device) but that should be consistent across *all* OpenSSL-based

  applications when they use that ENGINE. Work is in progress (or at least

  in planning) for supporting these control commands from the CONF (or

  NCONF) code so that applications using OpenSSL's existing configuration

  file format can have ENGINE settings specified in much the same way.

  Presently however, applications must use the ENGINE API itself to provide

  such functionality. To see first hand the types of commands available

  with the various compiled-in ENGINEs (see further down for dynamic

  ENGINEs), use the "engine" openssl utility with full verbosity, ie;

       openssl engine -vvvv

3 Documentation? Volunteers welcome! The source code is reasonably well

  self-documenting, but some summaries and usage instructions are needed -

  moreover, they are needed in the same POD format the existing OpenSSL

  documentation is provided in. Any complete or incomplete contributions

  would help make this happen.

  STABILITY & BUG-REPORTS

  =======================

  What already exists is fairly stable as far as it has been tested, but

  the test base has been a bit small most of the time. For the most part,

  the vendors of the devices these ENGINEs support have contributed to the

  development and/or testing of the implementations, and *usually* (with no

  guarantees) have experience in using the ENGINE support to drive their

  devices from common OpenSSL-based applications. Bugs and/or inexplicable

  behaviour in using a specific ENGINE implementation should be sent to the

  author of that implementation (if it is mentioned in the corresponding C

  file), and in the case of implementations for commercial hardware

  devices, also through whatever vendor support channels are available.  If

  none of this is possible, or the problem seems to be something about the

  ENGINE API itself (ie. not necessarily specific to a particular ENGINE

  implementation) then you should mail complete details to the relevant

  OpenSSL mailing list. For a definition of "complete details", refer to

  the OpenSSL "README" file. As for which list to send it to;

     openssl-users: if you are *using* the ENGINE abstraction, either in an

          pre-compiled application or in your own application code.

     openssl-dev: if you are discussing problems with OpenSSL source code.

  USAGE

  =====

  The default "openssl" ENGINE is always chosen when performing crypto

  operations unless you specify otherwise. You must actively tell the

  openssl utility commands to use anything else through a new command line

  switch called "-engine". Also, if you want to use the ENGINE support in

  your own code to do something similar, you must likewise explicitly

  select the ENGINE implementation you want.

  Depending on the type of hardware, system, and configuration, "settings"

  may need to be applied to an ENGINE for it to function as expected/hoped.

  The recommended way of doing this is for the application to support

  ENGINE "control commands" so that each ENGINE implementation can provide

  whatever configuration primitives it might require and the application

  can allow the user/admin (and thus the hardware vendor's support desk

  also) to provide any such input directly to the ENGINE implementation.

  This way, applications do not need to know anything specific to any

  device, they only need to provide the means to carry such user/admin

  input through to the ENGINE in question. Ie. this connects *you* (and

  your helpdesk) to the specific ENGINE implementation (and device), and

  allows application authors to not get buried in hassle supporting

  arbitrary devices they know (and care) nothing about.

  A new "openssl" utility, "openssl engine", has been added in that allows

  for testing and examination of ENGINE implementations. Basic usage

  instructions are available by specifying the "-?" command line switch.

  DYNAMIC ENGINES

  ===============

  The new "dynamic" ENGINE provides a low-overhead way to support ENGINE

  implementations that aren't pre-compiled and linked into OpenSSL-based

  applications. This could be because existing compiled-in implementations

  have known problems and you wish to use a newer version with an existing

  application. It could equally be because the application (or OpenSSL

  library) you are using simply doesn't have support for the ENGINE you

  wish to use, and the ENGINE provider (eg. hardware vendor) is providing

  you with a self-contained implementation in the form of a shared-library.

  The other use-case for "dynamic" is with applications that wish to

  maintain the smallest foot-print possible and so do not link in various

  ENGINE implementations from OpenSSL, but instead leaves you to provide

  them, if you want them, in the form of "dynamic"-loadable

  shared-libraries. It should be possible for hardware vendors to provide

  their own shared-libraries to support arbitrary hardware to work with

  applications based on OpenSSL 0.9.7 or later. If you're using an

  application based on 0.9.7 (or later) and the support you desire is only

  announced for versions later than the one you need, ask the vendor to

  backport their ENGINE to the version you need.

  How does "dynamic" work?

  ------------------------

    The dynamic ENGINE has a special flag in its implementation such that

    every time application code asks for the 'dynamic' ENGINE, it in fact

    gets its own copy of it. As such, multi-threaded code (or code that

    multiplexes multiple uses of 'dynamic' in a single application in any

    way at all) does not get confused by 'dynamic' being used to do many

    independent things. Other ENGINEs typically don't do this so there is

    only ever 1 ENGINE structure of its type (and reference counts are used

    to keep order). The dynamic ENGINE itself provides absolutely no

    cryptographic functionality, and any attempt to "initialise" the ENGINE

    automatically fails. All it does provide are a few "control commands"

    that can be used to control how it will load an external ENGINE

    implementation from a shared-library. To see these control commands,

    use the command-line;

       openssl engine -vvvv dynamic

    The "SO_PATH" control command should be used to identify the

    shared-library that contains the ENGINE implementation, and "NO_VCHECK"

    might possibly be useful if there is a minor version conflict and you

    (or a vendor helpdesk) is convinced you can safely ignore it.

    "ID" is probably only needed if a shared-library implements

    multiple ENGINEs, but if you know the engine id you expect to be using,

    it doesn't hurt to specify it (and this provides a sanity check if

    nothing else). "LIST_ADD" is only required if you actually wish the

    loaded ENGINE to be discoverable by application code later on using the

    ENGINE's "id". For most applications, this isn't necessary - but some

    application authors may have nifty reasons for using it. The "LOAD"

    command is the only one that takes no parameters and is the command

    that uses the settings from any previous commands to actually *load*

    the shared-library ENGINE implementation. If this command succeeds, the

    (copy of the) 'dynamic' ENGINE will magically morph into the ENGINE

    that has been loaded from the shared-library. As such, any control

    commands supported by the loaded ENGINE could then be executed as per

    normal. Eg. if ENGINE "foo" is implemented in the shared-library

    "libfoo.so" and it supports some special control command "CMD_FOO", the

    following code would load and use it (NB: obviously this code has no

    error checking);

       ENGINE *e = ENGINE_by_id("dynamic");

       ENGINE_ctrl_cmd_string(e, "SO_PATH", "/lib/libfoo.so", 0);

       ENGINE_ctrl_cmd_string(e, "ID", "foo", 0);

       ENGINE_ctrl_cmd_string(e, "LOAD", NULL, 0);

       ENGINE_ctrl_cmd_string(e, "CMD_FOO", "some input data", 0);

    For testing, the "openssl engine" utility can be useful for this sort

    of thing. For example the above code excerpt would achieve much the

    same result as;

       openssl engine dynamic \

                 -pre SO_PATH:/lib/libfoo.so \

                 -pre ID:foo \

                 -pre LOAD \

                 -pre "CMD_FOO:some input data"

    Or to simply see the list of commands supported by the "foo" ENGINE;

       openssl engine -vvvv dynamic \

                 -pre SO_PATH:/lib/libfoo.so \

                 -pre ID:foo \

                 -pre LOAD

    Applications that support the ENGINE API and more specifically, the

    "control commands" mechanism, will provide some way for you to pass

    such commands through to ENGINEs. As such, you would select "dynamic"

    as the ENGINE to use, and the parameters/commands you pass would

    control the *actual* ENGINE used. Each command is actually a name-value

    pair and the value can sometimes be omitted (eg. the "LOAD" command).

    Whilst the syntax demonstrated in "openssl engine" uses a colon to

    separate the command name from the value, applications may provide

    their own syntax for making that separation (eg. a win32 registry

    key-value pair may be used by some applications). The reason for the

    "-pre" syntax in the "openssl engine" utility is that some commands

    might be issued to an ENGINE *after* it has been initialised for use.

    Eg. if an ENGINE implementation requires a smart-card to be inserted

    during initialisation (or a PIN to be typed, or whatever), there may be

    a control command you can issue afterwards to "forget" the smart-card

    so that additional initialisation is no longer possible. In

    applications such as web-servers, where potentially volatile code may

    run on the same host system, this may provide some arguable security

    value. In such a case, the command would be passed to the ENGINE after

    it has been initialised for use, and so the "-post" switch would be

    used instead. Applications may provide a different syntax for

    supporting this distinction, and some may simply not provide it at all

    ("-pre" is almost always what you're after, in reality).

  How do I build a "dynamic" ENGINE?

  ----------------------------------

    This question is trickier - currently OpenSSL bundles various ENGINE

    implementations that are statically built in, and any application that

    calls the "ENGINE_load_builtin_engines()" function will automatically

    have all such ENGINEs available (and occupying memory). Applications

    that don't call that function have no ENGINEs available like that and

    would have to use "dynamic" to load any such ENGINE - but on the other

    hand such applications would only have the memory footprint of any

    ENGINEs explicitly loaded using user/admin provided control commands.

    The main advantage of not statically linking ENGINEs and only using

    "dynamic" for hardware support is that any installation using no

    "external" ENGINE suffers no unnecessary memory footprint from unused

    ENGINEs. Likewise, installations that do require an ENGINE incur the

    overheads from only *that* ENGINE once it has been loaded.

    Sounds good? Maybe, but currently building an ENGINE implementation as

    a shared-library that can be loaded by "dynamic" isn't automated in

    OpenSSL's build process. It can be done manually quite easily however.

    Such a shared-library can either be built with any OpenSSL code it

    needs statically linked in, or it can link dynamically against OpenSSL

    if OpenSSL itself is built as a shared library. The instructions are

    the same in each case, but in the former (statically linked any

    dependencies on OpenSSL) you must ensure OpenSSL is built with

    position-independent code ("PIC"). The default OpenSSL compilation may

    already specify the relevant flags to do this, but you should consult

    with your compiler documentation if you are in any doubt.

    This example will show building the "atalla" ENGINE in the

    crypto/engine/ directory as a shared-library for use via the "dynamic"

    ENGINE.

    1) "cd" to the crypto/engine/ directory of a pre-compiled OpenSSL

       source tree.

    2) Recompile at least one source file so you can see all the compiler

       flags (and syntax) being used to build normally. Eg;

           touch hw_atalla.c ; make

       will rebuild "hw_atalla.o" using all such flags.

    3) Manually enter the same compilation line to compile the

       "hw_atalla.c" file but with the following two changes;

         (a) add "-DENGINE_DYNAMIC_SUPPORT" to the command line switches,

	 (b) change the output file from "hw_atalla.o" to something new,

             eg. "tmp_atalla.o"

    4) Link "tmp_atalla.o" into a shared-library using the top-level

       OpenSSL libraries to resolve any dependencies. The syntax for doing

       this depends heavily on your system/compiler and is a nightmare

       known well to anyone who has worked with shared-library portability

       before. 'gcc' on Linux, for example, would use the following syntax;

          gcc -shared -o dyn_atalla.so tmp_atalla.o -L../.. -lcrypto

    5) Test your shared library using "openssl engine" as explained in the

       previous section. Eg. from the top-level directory, you might try;

          apps/openssl engine -vvvv dynamic \

              -pre SO_PATH:./crypto/engine/dyn_atalla.so -pre LOAD

       If the shared-library loads successfully, you will see both "-pre"

       commands marked as "SUCCESS" and the list of control commands

       displayed (because of "-vvvv") will be the control commands for the

       *atalla* ENGINE (ie. *not* the 'dynamic' ENGINE). You can also add

       the "-t" switch to the utility if you want it to try and initialise

       the atalla ENGINE for use to test any possible hardware/driver

       issues.

  PROBLEMS

  ========

  It seems like the ENGINE part doesn't work too well with CryptoSwift on Win32.

  A quick test done right before the release showed that trying "openssl speed

  -engine cswift" generated errors. If the DSO gets enabled, an attempt is made

  to write at memory address 0x00000002.