+3. Reconfigure the toolkit with no-sha0 option to leave out SHA0. It
+should not be used and is not used in SSL/TLS nor any other recognized
+protocol in either case.
+
+
+* Why does the OpenSSL compilation fail with "ar: command not found"?
+
+Getting this message is quite usual on Solaris 2, because Sun has hidden
+away 'ar' and other development commands in directories that aren't in
+$PATH by default. One of those directories is '/usr/ccs/bin'. The
+quickest way to fix this is to do the following (it assumes you use sh
+or any sh-compatible shell):
+
+----- snip:start -----
+ PATH=${PATH}:/usr/ccs/bin; export PATH
+----- snip:end -----
+
+and then redo the compilation. What you should really do is make sure
+'/usr/ccs/bin' is permanently in your $PATH, for example through your
+'.profile' (again, assuming you use a sh-compatible shell).
+
+
+* Why does the OpenSSL compilation fail on Win32 with VC++?
+
+Sometimes, you may get reports from VC++ command line (cl) that it
+can't find standard include files like stdio.h and other weirdnesses.
+One possible cause is that the environment isn't correctly set up.
+To solve that problem for VC++ versions up to 6, one should run
+VCVARS32.BAT which is found in the 'bin' subdirectory of the VC++
+installation directory (somewhere under 'Program Files'). For VC++
+version 7 (and up?), which is also called VS.NET, the file is called
+VSVARS32.BAT instead.
+This needs to be done prior to running NMAKE, and the changes are only
+valid for the current DOS session.
+
+
+* What is special about OpenSSL on Redhat?
+
+Red Hat Linux (release 7.0 and later) include a preinstalled limited
+version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
+is disabled in this version. The same may apply to other Linux distributions.
+Users may therefore wish to install more or all of the features left out.
+
+To do this you MUST ensure that you do not overwrite the openssl that is in
+/usr/bin on your Red Hat machine. Several packages depend on this file,
+including sendmail and ssh. /usr/local/bin is a good alternative choice. The
+libraries that come with Red Hat 7.0 onwards have different names and so are
+not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
+/lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
+/lib/libcrypto.so.2 respectively).
+
+Please note that we have been advised by Red Hat attempting to recompile the
+openssl rpm with all the cryptography enabled will not work. All other
+packages depend on the original Red Hat supplied openssl package. It is also
+worth noting that due to the way Red Hat supplies its packages, updates to
+openssl on each distribution never change the package version, only the
+build number. For example, on Red Hat 7.1, the latest openssl package has
+version number 0.9.6 and build number 9 even though it contains all the
+relevant updates in packages up to and including 0.9.6b.
+
+A possible way around this is to persuade Red Hat to produce a non-US
+version of Red Hat Linux.
+
+FYI: Patent numbers and expiry dates of US patents:
+MDC-2: 4,908,861 13/03/2007
+IDEA: 5,214,703 25/05/2010
+RC5: 5,724,428 03/03/2015
+
+
+* Why does the OpenSSL compilation fail on MacOS X?
+
+If the failure happens when trying to build the "openssl" binary, with
+a large number of undefined symbols, it's very probable that you have
+OpenSSL 0.9.6b delivered with the operating system (you can find out by
+running '/usr/bin/openssl version') and that you were trying to build
+OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
+MacOS X has a misfeature that's quite difficult to go around.
+Look in the file PROBLEMS for a more detailed explanation and for possible
+solutions.
+
+
+* Why does the OpenSSL test suite fail on MacOS X?
+
+If the failure happens when running 'make test' and the RC4 test fails,
+it's very probable that you have OpenSSL 0.9.6b delivered with the
+operating system (you can find out by running '/usr/bin/openssl version')
+and that you were trying to build OpenSSL 0.9.6d. The problem is that
+the loader ('ld') in MacOS X has a misfeature that's quite difficult to
+go around and has linked the programs "openssl" and the test programs
+with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
+libraries you just built.
+Look in the file PROBLEMS for a more detailed explanation and for possible
+solutions.
+
+* Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
+
+Failure in BN_sqr test is most likely caused by a failure to configure the
+toolkit for current platform or lack of support for the platform in question.
+Run './config -t' and './apps/openssl version -p'. Do these platform
+identifiers match? If they don't, then you most likely failed to run
+./config and you're hereby advised to do so before filing a bug report.
+If ./config itself fails to run, then it's most likely problem with your
+local environment and you should turn to your system administrator (or
+similar). If identifiers match (and/or no alternative identifier is
+suggested by ./config script), then the platform is unsupported. There might
+or might not be a workaround. Most notably on SPARC64 platforms with GNU
+C compiler you should be able to produce a working build by running
+'./config -m32'. I understand that -m32 might not be what you want/need,
+but the build should be operational. For further details turn to
+<openssl-dev@openssl.org>.
+
+* Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"?
+
+As of 0.9.7 assembler routines were overhauled for position independence
+of the machine code, which is essential for shared library support. For
+some reason OpenBSD is equipped with an out-of-date GNU assembler which
+finds the new code offensive. To work around the problem, configure with
+no-asm (and sacrifice a great deal of performance) or patch your assembler
+according to <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.patch>.
+For your convenience a pre-compiled replacement binary is provided at
+<URL: http://www.openssl.org/~appro/gas-1.92.3.static.aout.bin>.
+Reportedly elder *BSD a.out platforms also suffer from this problem and
+remedy should be same. Provided binary is statically linked and should be
+working across wider range of *BSD branches, not just OpenBSD.
+
+* Why does the OpenSSL test suite fail in sha512t on x86 CPU?
+
+If the test program in question fails withs SIGILL, Illegal Instruction
+exception, then you more than likely to run SSE2-capable CPU, such as
+Intel P4, under control of kernel which does not support SSE2
+instruction extentions. See accompanying INSTALL file and
+OPENSSL_ia32cap(3) documentation page for further information.
+
+* Why does compiler fail to compile sha512.c?
+
+OpenSSL SHA-512 implementation depends on compiler support for 64-bit
+integer type. Few elder compilers [ULTRIX cc, SCO compiler to mention a
+couple] lack support for this and therefore are incapable of compiling
+the module in question. The recommendation is to disable SHA-512 by
+adding no-sha512 to ./config [or ./Configure] command line. Another
+possible alternative might be to switch to GCC.
+
+* Test suite still fails, what to do?
+
+Another common reason for failure to complete some particular test is
+simply bad code generated by a buggy component in toolchain or deficiency
+in run-time environment. There are few cases documented in PROBLEMS file,
+consult it for possible workaround before you beat the drum. Even if you
+don't find solution or even mention there, do reserve for possibility of
+a compiler bug. Compiler bugs might appear in rather bizarre ways, they
+never make sense, and tend to emerge when you least expect them. In order
+to identify one, drop optimization level, e.g. by editing CFLAG line in
+top-level Makefile, recompile and re-run the test.
+
+[PROG] ========================================================================
+
+* Is OpenSSL thread-safe?
+
+Yes (with limitations: an SSL connection may not concurrently be used
+by multiple threads). On Windows and many Unix systems, OpenSSL
+automatically uses the multi-threaded versions of the standard
+libraries. If your platform is not one of these, consult the INSTALL
+file.
+
+Multi-threaded applications must provide two callback functions to
+OpenSSL. This is described in the threads(3) manpage.
+
+
+* I've compiled a program under Windows and it crashes: why?
+
+This is usually because you've missed the comment in INSTALL.W32.
+Your application must link against the same version of the Win32
+C-Runtime against which your openssl libraries were linked. The
+default version for OpenSSL is /MD - "Multithreaded DLL".
+
+If you are using Microsoft Visual C++'s IDE (Visual Studio), in
+many cases, your new project most likely defaulted to "Debug
+Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
+program will crash, typically on the first BIO related read or write
+operation.
+
+For each of the six possible link stage configurations within Win32,
+your application must link against the same by which OpenSSL was
+built. If you are using MS Visual C++ (Studio) this can be changed
+by:
+
+ 1. Select Settings... from the Project Menu.
+ 2. Select the C/C++ Tab.
+ 3. Select "Code Generation from the "Category" drop down list box
+ 4. Select the Appropriate library (see table below) from the "Use
+ run-time library" drop down list box. Perform this step for both
+ your debug and release versions of your application (look at the
+ top left of the settings panel to change between the two)
+
+ Single Threaded /ML - MS VC++ often defaults to
+ this for the release
+ version of a new project.
+ Debug Single Threaded /MLd - MS VC++ often defaults to
+ this for the debug version
+ of a new project.
+ Multithreaded /MT
+ Debug Multithreaded /MTd
+ Multithreaded DLL /MD - OpenSSL defaults to this.
+ Debug Multithreaded DLL /MDd
+
+Note that debug and release libraries are NOT interchangeable. If you
+built OpenSSL with /MD your application must use /MD and cannot use /MDd.
+
+As per 0.9.8 the above limitation is eliminated for .DLLs. OpenSSL
+.DLLs compiled with some specific run-time option [we insist on the
+default /MD] can be deployed with application compiled with different
+option or even different compiler. But there is a catch! Instead of
+re-compiling OpenSSL toolkit, as you would have to with prior versions,
+you have to compile small C snippet with compiler and/or options of
+your choice. The snippet gets installed as
+<install-root>/include/openssl/applink.c and should be either added to
+your application project or simply #include-d in one [and only one]
+of your application source files. Failure to link this shim module
+into your application manifests itself as fatal "no OPENSSL_Applink"
+run-time error. An explicit reminder is due that in this situation
+[mixing compiler options] it is as important to add CRYPTO_malloc_init
+prior first call to OpenSSL.
+
+* How do I read or write a DER encoded buffer using the ASN1 functions?
+
+You have two options. You can either use a memory BIO in conjunction
+with the i2d_*_bio() or d2i_*_bio() functions or you can use the
+i2d_*(), d2i_*() functions directly. Since these are often the
+cause of grief here are some code fragments using PKCS7 as an example:
+
+ unsigned char *buf, *p;
+ int len;
+
+ len = i2d_PKCS7(p7, NULL);
+ buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
+ p = buf;
+ i2d_PKCS7(p7, &p);
+
+At this point buf contains the len bytes of the DER encoding of
+p7.
+
+The opposite assumes we already have len bytes in buf:
+
+ unsigned char *p;
+ p = buf;
+ p7 = d2i_PKCS7(NULL, &p, len);
+
+At this point p7 contains a valid PKCS7 structure of NULL if an error
+occurred. If an error occurred ERR_print_errors(bio) should give more
+information.
+
+The reason for the temporary variable 'p' is that the ASN1 functions
+increment the passed pointer so it is ready to read or write the next
+structure. This is often a cause of problems: without the temporary
+variable the buffer pointer is changed to point just after the data
+that has been read or written. This may well be uninitialized data
+and attempts to free the buffer will have unpredictable results
+because it no longer points to the same address.
+
+
+* OpenSSL uses DER but I need BER format: does OpenSSL support BER?
+
+The short answer is yes, because DER is a special case of BER and OpenSSL
+ASN1 decoders can process BER.
+
+The longer answer is that ASN1 structures can be encoded in a number of
+different ways. One set of ways is the Basic Encoding Rules (BER) with various
+permissible encodings. A restriction of BER is the Distinguished Encoding
+Rules (DER): these uniquely specify how a given structure is encoded.
+
+Therefore, because DER is a special case of BER, DER is an acceptable encoding
+for BER.
+
+
+* I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
+
+This usually happens when you try compiling something using the PKCS#12
+macros with a C++ compiler. There is hardly ever any need to use the
+PKCS#12 macros in a program, it is much easier to parse and create
+PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
+documented in doc/openssl.txt and with examples in demos/pkcs12. The
+'pkcs12' application has to use the macros because it prints out
+debugging information.
+
+
+* I've called <some function> and it fails, why?
+
+Before submitting a report or asking in one of the mailing lists, you
+should try to determine the cause. In particular, you should call
+ERR_print_errors() or ERR_print_errors_fp() after the failed call
+and see if the message helps. Note that the problem may occur earlier
+than you think -- you should check for errors after every call where
+it is possible, otherwise the actual problem may be hidden because
+some OpenSSL functions clear the error state.
+
+
+* I just get a load of numbers for the error output, what do they mean?
+
+The actual format is described in the ERR_print_errors() manual page.
+You should call the function ERR_load_crypto_strings() before hand and
+the message will be output in text form. If you can't do this (for example
+it is a pre-compiled binary) you can use the errstr utility on the error
+code itself (the hex digits after the second colon).
+
+
+* Why do I get errors about unknown algorithms?
+
+This can happen under several circumstances such as reading in an
+encrypted private key or attempting to decrypt a PKCS#12 file. The cause
+is forgetting to load OpenSSL's table of algorithms with
+OpenSSL_add_all_algorithms(). See the manual page for more information.
+
+
+* Why can't the OpenSSH configure script detect OpenSSL?
+
+Several reasons for problems with the automatic detection exist.
+OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
+Sometimes the distribution has installed an older version in the system
+locations that is detected instead of a new one installed. The OpenSSL
+library might have been compiled for another CPU or another mode (32/64 bits).
+Permissions might be wrong.
+
+The general answer is to check the config.log file generated when running
+the OpenSSH configure script. It should contain the detailed information
+on why the OpenSSL library was not detected or considered incompatible.
+
+
+* Can I use OpenSSL's SSL library with non-blocking I/O?
+
+Yes; make sure to read the SSL_get_error(3) manual page!
+
+A pitfall to avoid: Don't assume that SSL_read() will just read from
+the underlying transport or that SSL_write() will just write to it --
+it is also possible that SSL_write() cannot do any useful work until
+there is data to read, or that SSL_read() cannot do anything until it
+is possible to send data. One reason for this is that the peer may
+request a new TLS/SSL handshake at any time during the protocol,
+requiring a bi-directional message exchange; both SSL_read() and
+SSL_write() will try to continue any pending handshake.
+
+
+* Why doesn't my server application receive a client certificate?
+
+Due to the TLS protocol definition, a client will only send a certificate,
+if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
+SSL_CTX_set_verify() function to enable the use of client certificates.
+
+
+* Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
+
+For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
+versions, uniqueIdentifier was incorrectly used for X.509 certificates.
+The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
+Change your code to use the new name when compiling against OpenSSL 0.9.7.
+
+
+* I think I've detected a memory leak, is this a bug?
+
+In most cases the cause of an apparent memory leak is an OpenSSL internal table
+that is allocated when an application starts up. Since such tables do not grow
+in size over time they are harmless.
+
+These internal tables can be freed up when an application closes using various
+functions. Currently these include following:
+
+Thread-local cleanup functions:
+
+ ERR_remove_state()
+
+Application-global cleanup functions that are aware of usage (and therefore
+thread-safe):
+
+ ENGINE_cleanup() and CONF_modules_unload()
+
+"Brutal" (thread-unsafe) Application-global cleanup functions:
+
+ ERR_free_strings(), EVP_cleanup() and CRYPTO_cleanup_all_ex_data().
+
+
+===============================================================================
+