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 Windows targets can be classified as "native", ones that use Windows API
 directly, and "hosted" which rely on POSIX-compatible layer. "Native"
 targets are VC-* (where "VC" stems from abbreviating Microsoft Visual C
 compiler) and mingw[64]. "Hosted" platforms are Cygwin and MSYS[2]. Even
 though the latter is not directly supported by OpenSSL Team, it's #1
 popular choice for building MinGW targets. In the nutshell MinGW builds
 are always cross-compiled. On Linux and Cygwin they look exactly as such
 and require --cross-compile-prefix option. While on MSYS[2] it's solved
 rather by placing gcc that produces "MinGW binary" code 1st on $PATH.
 This is customarily source of confusion. "Hosted" applications "live" in
 emulated file system name space with POSIX-y root, mount points, /dev
 and even /proc. Confusion is intensified by the fact that MSYS2 shell
 (or rather emulated execve(2) call) examines the binary it's about to
 start, and if it's found *not* to be linked with MSYS2 POSIX-y thing,
 command line arguments that look like file names get translated from
 emulated name space to "native". For example '/c/some/where' becomes
 'c:\some\where', '/dev/null' - 'nul'. This creates an illusion that
 there is no difference between MSYS2 shell and "MinGW binary", but
 there is. Just keep in mind that "MinGW binary" "experiences" Windows
 system in exactly same way as one produced by VC, and in its essence
 is indistinguishable from the latter. (Which by the way is why
 it's referred to in quotes here, as "MinGW binary", it's just as
 "native" as it can get.)

 Visual C++ builds, a.k.a. VC-*

 Requirement details

 In addition to the requirements and instructions listed in INSTALL,
 these are required as well:

 - Perl. We recommend ActiveState Perl, available from Another viable alternative
   appears to be Strawberry Perl,
   You also need the perl module Text::Template, available on CPAN.
   Please read NOTES.PERL for more information.

 - Microsoft Visual C compiler. Since we can't test them all, there is
   unavoidable uncertainty about which versions are supported. Latest
   version along with couple of previous are certainly supported. On
   the other hand oldest one is known not to work. Everything between
   falls into best-effort category.

 - Netwide Assembler, a.k.a. NASM, available from,
   is required. Note that NASM is the only supported assembler. Even
   though Microsoft provided assembler is NOT supported, contemporary
   64-bit version is exercised through continuous integration of
   VC-WIN64A-masm target.

 Installation directories

 The default installation directories are derived from environment

 For VC-WIN32, the following defaults are use:

     PREFIX:      %ProgramFiles(86)%\OpenSSL
     OPENSSLDIR:  %CommonProgramFiles(86)%\SSL

 For VC-WIN64, the following defaults are use:

     PREFIX:      %ProgramW6432%\OpenSSL
     OPENSSLDIR:  %CommonProgramW6432%\SSL

 Should those environment variables not exist (on a pure Win32
 installation for examples), these fallbacks are used:

     PREFIX:      %ProgramFiles%\OpenSSL
     OPENSSLDIR:  %CommonProgramFiles%\SSL

 ALSO NOTE that those directories are usually write protected, even if
 your account is in the Administrators group.  To work around that,
 start the command prompt by right-clicking on it and choosing "Run as
 Administrator" before running 'nmake install'.  The other solution
 is, of course, to choose a different set of directories by using
 --prefix and --openssldir when configuring.

 mingw and mingw64

 * MSYS2 shell and development environment installation:

   Download MSYS2 from and follow installation
   instructions. Once up and running install even make, perl, (git if
   needed,) mingw-w64-i686-gcc and/or mingw-w64-x86_64-gcc. You should
   have corresponding MinGW items on your start menu, use *them*, not
   generic MSYS2. As implied in opening note, difference between them
   is which compiler is found 1st on $PATH. At this point ./config
   should recognize correct target, roll as if it was Unix...

 * It is also possible to build mingw[64] on Linux or Cygwin by
   configuring with corresponding --cross-compile-prefix= option. For

     ./Configure mingw --cross-compile-prefix=i686-w64-mingw32- ...


     ./Configure mingw64 --cross-compile-prefix=x86_64-w64-mingw32- ...

   This naturally implies that you've installed corresponding add-on

 Independently of the method chosen to build for mingw, the installation
 paths are similar to those used when building with VC-* targets, except
 that in case the fallbacks mentioned there aren't possible (typically
 when cross compiling on Linux), the paths will be the following:

 For mingw:

     PREFIX:      C:/Program Files (x86)/OpenSSL
     OPENSSLDIR   C:/Program Files (x86)/Common Files/SSL

 For mingw64:

     PREFIX:      C:/Program Files/OpenSSL
     OPENSSLDIR   C:/Program Files/Common Files/SSL

 Linking your application

 This section applies to all "native" builds.

 If you link with static OpenSSL libraries then you're expected to
 additionally link your application with WS2_32.LIB, GDI32.LIB,
 ADVAPI32.LIB, CRYPT32.LIB and USER32.LIB. Those developing
 non-interactive service applications might feel concerned about
 linking with GDI32.LIB and USER32.LIB, as they are justly associated
 with interactive desktop, which is not available to service
 processes. The toolkit is designed to detect in which context it's
 currently executed, GUI, console app or service, and act accordingly,
 namely whether or not to actually make GUI calls. Additionally those
 who wish to /DELAYLOAD:GDI32.DLL and /DELAYLOAD:USER32.DLL and
 actually keep them off service process should consider implementing
 and exporting from .exe image in question own _OPENSSL_isservice not
 relying on USER32.DLL. E.g., on Windows Vista and later you could:

	__declspec(dllexport) __cdecl BOOL _OPENSSL_isservice(void)
	{   DWORD sess;
	    if (ProcessIdToSessionId(GetCurrentProcessId(),&sess))
	        return sess==0;
	    return FALSE;

 If you link with OpenSSL .DLLs, then you're expected to include into
 your application code small "shim" snippet, which provides glue between
 OpenSSL BIO layer and your compiler run-time. See the OPENSSL_Applink
 manual page for further details.

 Cygwin, "hosted" environment

 Cygwin implements a Posix/Unix runtime system (cygwin1.dll) on top of the
 Windows subsystem and provides a bash shell and GNU tools environment.
 Consequently, a make of OpenSSL with Cygwin is virtually identical to the
 Unix procedure.

 To build OpenSSL using Cygwin, you need to:

 * Install Cygwin (see

 * Install Cygwin Perl and ensure it is in the path. Recall that
   as least 5.10.0 is required.

 * Run the Cygwin bash shell

 Apart from that, follow the Unix instructions in INSTALL.

 NOTE: "make test" and normal file operations may fail in directories
 mounted as text (i.e. mount -t c:\somewhere /home) due to Cygwin
 stripping of carriage returns. To avoid this ensure that a binary
 mount is used, e.g. mount -b c:\somewhere /home.