OpenSSL - Frequently Asked Questions -------------------------------------- [MISC] Miscellaneous questions * Which is the current version of OpenSSL? * Where is the documentation? * How can I contact the OpenSSL developers? * Where can I get a compiled version of OpenSSL? * Why aren't tools like 'autoconf' and 'libtool' used? * What is an 'engine' version? * How do I check the authenticity of the OpenSSL distribution? [LEGAL] Legal questions * Do I need patent licenses to use OpenSSL? * Can I use OpenSSL with GPL software? [USER] Questions on using the OpenSSL applications * Why do I get a "PRNG not seeded" error message? * Why do I get an "unable to write 'random state'" error message? * How do I create certificates or certificate requests? * Why can't I create certificate requests? * Why does fail with a certificate verify error? * Why can I only use weak ciphers when I connect to a server using OpenSSL? * How can I create DSA certificates? * Why can't I make an SSL connection using a DSA certificate? * How can I remove the passphrase on a private key? * Why can't I use OpenSSL certificates with SSL client authentication? * Why does my browser give a warning about a mismatched hostname? * How do I install a CA certificate into a browser? * Why is OpenSSL x509 DN output not conformant to RFC2253? * What is a "128 bit certificate"? Can I create one with OpenSSL? [BUILD] Questions about building and testing OpenSSL * Why does the linker complain about undefined symbols? * Why does the OpenSSL test fail with "bc: command not found"? * Why does the OpenSSL test fail with "bc: 1 no implemented"? * Why does the OpenSSL test fail with "bc: stack empty"? * Why does the OpenSSL compilation fail on Alpha Tru64 Unix? * Why does the OpenSSL compilation fail with "ar: command not found"? * Why does the OpenSSL compilation fail on Win32 with VC++? * What is special about OpenSSL on Redhat? * Why does the OpenSSL compilation fail on MacOS X? * Why does the OpenSSL test suite fail on MacOS X? * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]? * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"? * Why does the OpenSSL test suite fail in sha512t on x86 CPU? * Why does compiler fail to compile sha512.c? * Test suite still fails, what to do? [PROG] Questions about programming with OpenSSL * Is OpenSSL thread-safe? * I've compiled a program under Windows and it crashes: why? * How do I read or write a DER encoded buffer using the ASN1 functions? * OpenSSL uses DER but I need BER format: does OpenSSL support BER? * I've tried using and I get errors why? * I've called and it fails, why? * I just get a load of numbers for the error output, what do they mean? * Why do I get errors about unknown algorithms? * Why can't the OpenSSH configure script detect OpenSSL? * Can I use OpenSSL's SSL library with non-blocking I/O? * Why doesn't my server application receive a client certificate? * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier? * I think I've detected a memory leak, is this a bug? =============================================================================== [MISC] ======================================================================== * Which is the current version of OpenSSL? The current version is available from . OpenSSL 0.9.8b was released on May 4th, 2006. In addition to the current stable release, you can also access daily snapshots of the OpenSSL development version at , or get it by anonymous CVS access. * Where is the documentation? OpenSSL is a library that provides cryptographic functionality to applications such as secure web servers. Be sure to read the documentation of the application you want to use. The INSTALL file explains how to install this library. OpenSSL includes a command line utility that can be used to perform a variety of cryptographic functions. It is described in the openssl(1) manpage. Documentation for developers is currently being written. A few manual pages already are available; overviews over libcrypto and libssl are given in the crypto(3) and ssl(3) manpages. The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a different directory if you specified one as described in INSTALL). In addition, you can read the most current versions at . For information on parts of libcrypto that are not yet documented, you might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's predecessor, at . Much of this still applies to OpenSSL. There is some documentation about certificate extensions and PKCS#12 in doc/openssl.txt The original SSLeay documentation is included in OpenSSL as doc/ssleay.txt. It may be useful when none of the other resources help, but please note that it reflects the obsolete version SSLeay 0.6.6. * How can I contact the OpenSSL developers? The README file describes how to submit bug reports and patches to OpenSSL. Information on the OpenSSL mailing lists is available from . * Where can I get a compiled version of OpenSSL? You can finder pointers to binary distributions in http://www.openssl.org/related/binaries.html . Some applications that use OpenSSL are distributed in binary form. When using such an application, you don't need to install OpenSSL yourself; the application will include the required parts (e.g. DLLs). If you want to build OpenSSL on a Windows system and you don't have a C compiler, read the "Mingw32" section of INSTALL.W32 for information on how to obtain and install the free GNU C compiler. A number of Linux and *BSD distributions include OpenSSL. * Why aren't tools like 'autoconf' and 'libtool' used? autoconf will probably be used in future OpenSSL versions. If it was less Unix-centric, it might have be
/* crypto/tmdiff.h */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

/* Header for dynamic hash table routines
 * Author - Eric Young
 */
/* ... erm yeah, "dynamic hash tables" you say?
 * 
 * And what would dynamic hash tables have to do with any of this code *now*?
 * AFAICS, this code is only referenced by crypto/bn/exp.c which is an unused
 * file that I doubt compiles any more. speed.c is the only thing that could
 * use this (and it has nothing to do with hash tables), yet it instead has its
 * own duplication of all this stuff and looks, if anything, more complete. See
 * the corresponding note in apps/speed.c.
 * The Bemused - Geoff
 */

#ifndef HEADER_TMDIFF_H
#define HEADER_TMDIFF_H

#ifdef  __cplusplus
extern "C" {
#endif

typedef struct ms_tm MS_TM;

MS_TM *ms_time_new(void );
void ms_time_free(MS_TM *a);
void ms_time_get(MS_TM *a);
double ms_time_diff(MS_TM *start, MS_TM *end);
int ms_time_cmp(const MS_TM *ap, const MS_TM *bp);

#ifdef  __cplusplus
}
#endif

#endif
t errors about the following symbols, use the config option "no-asm", as described in INSTALL: BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt, CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt, RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words, bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4, bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3, des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3, des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order If none of these helps, you may want to try using the current snapshot. If the problem persists, please submit a bug report. * Why does the OpenSSL test fail with "bc: command not found"? You didn't install "bc", the Unix calculator. If you want to run the tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor. * Why does the OpenSSL test fail with "bc: 1 no implemented"? On some SCO installations or versions, bc has a bug that gets triggered when you run the test suite (using "make test"). The message returned is "bc: 1 not implemented". The best way to deal with this is to find another implementation of bc and compile/install it. GNU bc (see http://www.gnu.org/software/software.html for download instructions) can be safely used, for example. * Why does the OpenSSL test fail with "bc: stack empty"? On some DG/ux versions, bc seems to have a too small stack for calculations that the OpenSSL bntest throws at it. This gets triggered when you run the test suite (using "make test"). The message returned is "bc: stack empty". The best way to deal with this is to find another implementation of bc and compile/install it. GNU bc (see http://www.gnu.org/software/software.html for download instructions) can be safely used, for example. * Why does the OpenSSL compilation fail on Alpha Tru64 Unix? On some Alpha installations running Tru64 Unix and Compaq C, the compilation of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual memory to continue compilation.' As far as the tests have shown, this may be a compiler bug. What happens is that it eats up a lot of resident memory to build something, probably a table. The problem is clearly in the optimization code, because if one eliminates optimization completely (-O0), the compilation goes through (and the compiler consumes about 2MB of resident memory instead of 240MB or whatever one's limit is currently). There are three options to solve this problem: 1. set your current data segment size soft limit higher. Experience shows that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of kbytes to set the limit to. 2. If you have a hard limit that is lower than what you need and you can't get it changed, you can compile all of OpenSSL with -O0 as optimization level. This is however not a very nice thing to do for those who expect to get the best result from OpenSSL. A bit more complicated solution is the following: ----- snip:start ----- make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \ sed -e 's/ -O[0-9] / -O0 /'`" rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'` make ----- snip:end ----- This will only compile sha_dgst.c with -O0, the rest with the optimization level chosen by the configuration process. When the above is done, do the test and installation and you're set. 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 . * 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 . For your convenience a pre-compiled replacement binary is provided at . 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 /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 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 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(). ===============================================================================