1 OpenSSL - Frequently Asked Questions
2 --------------------------------------
4 [MISC] Miscellaneous questions
6 * Which is the current version of OpenSSL?
7 * Where is the documentation?
8 * How can I contact the OpenSSL developers?
9 * Where can I get a compiled version of OpenSSL?
10 * Why aren't tools like 'autoconf' and 'libtool' used?
11 * What is an 'engine' version?
12 * How do I check the authenticity of the OpenSSL distribution?
14 [LEGAL] Legal questions
16 * Do I need patent licenses to use OpenSSL?
17 * Can I use OpenSSL with GPL software?
19 [USER] Questions on using the OpenSSL applications
21 * Why do I get a "PRNG not seeded" error message?
22 * Why do I get an "unable to write 'random state'" error message?
23 * How do I create certificates or certificate requests?
24 * Why can't I create certificate requests?
25 * Why does <SSL program> fail with a certificate verify error?
26 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
27 * How can I create DSA certificates?
28 * Why can't I make an SSL connection using a DSA certificate?
29 * How can I remove the passphrase on a private key?
30 * Why can't I use OpenSSL certificates with SSL client authentication?
31 * Why does my browser give a warning about a mismatched hostname?
32 * How do I install a CA certificate into a browser?
33 * Why is OpenSSL x509 DN output not conformant to RFC2253?
35 [BUILD] Questions about building and testing OpenSSL
37 * Why does the linker complain about undefined symbols?
38 * Why does the OpenSSL test fail with "bc: command not found"?
39 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
40 * Why does the OpenSSL test fail with "bc: stack empty"?
41 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
42 * Why does the OpenSSL compilation fail with "ar: command not found"?
43 * Why does the OpenSSL compilation fail on Win32 with VC++?
44 * What is special about OpenSSL on Redhat?
45 * Why does the OpenSSL compilation fail on MacOS X?
46 * Why does the OpenSSL test suite fail on MacOS X?
47 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
48 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented
51 [PROG] Questions about programming with OpenSSL
53 * Is OpenSSL thread-safe?
54 * I've compiled a program under Windows and it crashes: why?
55 * How do I read or write a DER encoded buffer using the ASN1 functions?
56 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
57 * I've called <some function> and it fails, why?
58 * I just get a load of numbers for the error output, what do they mean?
59 * Why do I get errors about unknown algorithms?
60 * Why can't the OpenSSH configure script detect OpenSSL?
61 * Can I use OpenSSL's SSL library with non-blocking I/O?
62 * Why doesn't my server application receive a client certificate?
63 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
65 ===============================================================================
67 [MISC] ========================================================================
69 * Which is the current version of OpenSSL?
71 The current version is available from <URL: http://www.openssl.org>.
72 OpenSSL 0.9.6h was released on December 5, 2002.
74 In addition to the current stable release, you can also access daily
75 snapshots of the OpenSSL development version at <URL:
76 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
79 * Where is the documentation?
81 OpenSSL is a library that provides cryptographic functionality to
82 applications such as secure web servers. Be sure to read the
83 documentation of the application you want to use. The INSTALL file
84 explains how to install this library.
86 OpenSSL includes a command line utility that can be used to perform a
87 variety of cryptographic functions. It is described in the openssl(1)
88 manpage. Documentation for developers is currently being written. A
89 few manual pages already are available; overviews over libcrypto and
90 libssl are given in the crypto(3) and ssl(3) manpages.
92 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
93 different directory if you specified one as described in INSTALL).
94 In addition, you can read the most current versions at
95 <URL: http://www.openssl.org/docs/>.
97 For information on parts of libcrypto that are not yet documented, you
98 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
99 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
100 of this still applies to OpenSSL.
102 There is some documentation about certificate extensions and PKCS#12
105 The original SSLeay documentation is included in OpenSSL as
106 doc/ssleay.txt. It may be useful when none of the other resources
107 help, but please note that it reflects the obsolete version SSLeay
111 * How can I contact the OpenSSL developers?
113 The README file describes how to submit bug reports and patches to
114 OpenSSL. Information on the OpenSSL mailing lists is available from
115 <URL: http://www.openssl.org>.
118 * Where can I get a compiled version of OpenSSL?
120 Some applications that use OpenSSL are distributed in binary form.
121 When using such an application, you don't need to install OpenSSL
122 yourself; the application will include the required parts (e.g. DLLs).
124 If you want to install OpenSSL on a Windows system and you don't have
125 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
126 on how to obtain and install the free GNU C compiler.
128 A number of Linux and *BSD distributions include OpenSSL.
131 * Why aren't tools like 'autoconf' and 'libtool' used?
133 autoconf will probably be used in future OpenSSL versions. If it was
134 less Unix-centric, it might have been used much earlier.
136 * What is an 'engine' version?
138 With version 0.9.6 OpenSSL was extended to interface to external crypto
139 hardware. This was realized in a special release '0.9.6-engine'. With
140 version 0.9.7 (not yet released) the changes were merged into the main
141 development line, so that the special release is no longer necessary.
143 * How do I check the authenticity of the OpenSSL distribution?
145 We provide MD5 digests and ASC signatures of each tarball.
146 Use MD5 to check that a tarball from a mirror site is identical:
148 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
150 You can check authenticity using pgp or gpg. You need the OpenSSL team
151 member public key used to sign it (download it from a key server). Then
156 [LEGAL] =======================================================================
158 * Do I need patent licenses to use OpenSSL?
160 The patents section of the README file lists patents that may apply to
161 you if you want to use OpenSSL. For information on intellectual
162 property rights, please consult a lawyer. The OpenSSL team does not
165 You can configure OpenSSL so as not to use RC5 and IDEA by using
166 ./config no-rc5 no-idea
169 * Can I use OpenSSL with GPL software?
171 On many systems including the major Linux and BSD distributions, yes (the
172 GPL does not place restrictions on using libraries that are part of the
173 normal operating system distribution).
175 On other systems, the situation is less clear. Some GPL software copyright
176 holders claim that you infringe on their rights if you use OpenSSL with
177 their software on operating systems that don't normally include OpenSSL.
179 If you develop open source software that uses OpenSSL, you may find it
180 useful to choose an other license than the GPL, or state explicitly that
181 "This program is released under the GPL with the additional exemption that
182 compiling, linking, and/or using OpenSSL is allowed." If you are using
183 GPL software developed by others, you may want to ask the copyright holder
184 for permission to use their software with OpenSSL.
187 [USER] ========================================================================
189 * Why do I get a "PRNG not seeded" error message?
191 Cryptographic software needs a source of unpredictable data to work
192 correctly. Many open source operating systems provide a "randomness
193 device" that serves this purpose. On other systems, applications have
194 to call the RAND_add() or RAND_seed() function with appropriate data
195 before generating keys or performing public key encryption.
196 (These functions initialize the pseudo-random number generator, PRNG.)
198 Some broken applications do not do this. As of version 0.9.5, the
199 OpenSSL functions that need randomness report an error if the random
200 number generator has not been seeded with at least 128 bits of
201 randomness. If this error occurs, please contact the author of the
202 application you are using. It is likely that it never worked
203 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
204 to perform potentially insecure encryption.
206 On systems without /dev/urandom and /dev/random, it is a good idea to
207 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
208 details. Starting with version 0.9.7, OpenSSL will automatically look
209 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
212 Most components of the openssl command line utility automatically try
213 to seed the random number generator from a file. The name of the
214 default seeding file is determined as follows: If environment variable
215 RANDFILE is set, then it names the seeding file. Otherwise if
216 environment variable HOME is set, then the seeding file is $HOME/.rnd.
217 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
218 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
219 default seeding file at all. OpenSSL 0.9.6b and later will behave
220 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
221 Windows systems if the environment variable has not been set.
223 If the default seeding file does not exist or is too short, the "PRNG
224 not seeded" error message may occur.
226 The openssl command line utility will write back a new state to the
227 default seeding file (and create this file if necessary) unless
228 there was no sufficient seeding.
230 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
231 Use the "-rand" option of the OpenSSL command line tools instead.
232 The $RANDFILE environment variable and $HOME/.rnd are only used by the
233 OpenSSL command line tools. Applications using the OpenSSL library
234 provide their own configuration options to specify the entropy source,
235 please check out the documentation coming the with application.
237 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
238 installing the SUNski package from Sun patch 105710-01 (Sparc) which
239 adds a /dev/random device and make sure it gets used, usually through
240 $RANDFILE. There are probably similar patches for the other Solaris
241 versions. An official statement from Sun with respect to /dev/random
242 support can be found at
243 http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski
244 However, be warned that /dev/random is usually a blocking device, which
245 may have some effects on OpenSSL.
246 A third party /dev/random solution for Solaris is available at
247 http://www.cosy.sbg.ac.at/~andi/
250 * Why do I get an "unable to write 'random state'" error message?
253 Sometimes the openssl command line utility does not abort with
254 a "PRNG not seeded" error message, but complains that it is
255 "unable to write 'random state'". This message refers to the
256 default seeding file (see previous answer). A possible reason
257 is that no default filename is known because neither RANDFILE
258 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
259 current directory in this case, but this has changed with 0.9.6a.)
262 * How do I create certificates or certificate requests?
264 Check out the CA.pl(1) manual page. This provides a simple wrapper round
265 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
266 out the manual pages for the individual utilities and the certificate
267 extensions documentation (currently in doc/openssl.txt).
270 * Why can't I create certificate requests?
272 You typically get the error:
274 unable to find 'distinguished_name' in config
275 problems making Certificate Request
277 This is because it can't find the configuration file. Check out the
278 DIAGNOSTICS section of req(1) for more information.
281 * Why does <SSL program> fail with a certificate verify error?
283 This problem is usually indicated by log messages saying something like
284 "unable to get local issuer certificate" or "self signed certificate".
285 When a certificate is verified its root CA must be "trusted" by OpenSSL
286 this typically means that the CA certificate must be placed in a directory
287 or file and the relevant program configured to read it. The OpenSSL program
288 'verify' behaves in a similar way and issues similar error messages: check
289 the verify(1) program manual page for more information.
292 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
294 This is almost certainly because you are using an old "export grade" browser
295 which only supports weak encryption. Upgrade your browser to support 128 bit
299 * How can I create DSA certificates?
301 Check the CA.pl(1) manual page for a DSA certificate example.
304 * Why can't I make an SSL connection to a server using a DSA certificate?
306 Typically you'll see a message saying there are no shared ciphers when
307 the same setup works fine with an RSA certificate. There are two possible
308 causes. The client may not support connections to DSA servers most web
309 browsers (including Netscape and MSIE) only support connections to servers
310 supporting RSA cipher suites. The other cause is that a set of DH parameters
311 has not been supplied to the server. DH parameters can be created with the
312 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
313 check the source to s_server in apps/s_server.c for an example.
316 * How can I remove the passphrase on a private key?
318 Firstly you should be really *really* sure you want to do this. Leaving
319 a private key unencrypted is a major security risk. If you decide that
320 you do have to do this check the EXAMPLES sections of the rsa(1) and
324 * Why can't I use OpenSSL certificates with SSL client authentication?
326 What will typically happen is that when a server requests authentication
327 it will either not include your certificate or tell you that you have
328 no client certificates (Netscape) or present you with an empty list box
329 (MSIE). The reason for this is that when a server requests a client
330 certificate it includes a list of CAs names which it will accept. Browsers
331 will only let you select certificates from the list on the grounds that
332 there is little point presenting a certificate which the server will
335 The solution is to add the relevant CA certificate to your servers "trusted
336 CA list". How you do this depends on the server software in uses. You can
337 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
339 openssl s_client -connect www.some.host:443 -prexit
341 If your server only requests certificates on certain URLs then you may need
342 to manually issue an HTTP GET command to get the list when s_client connects:
344 GET /some/page/needing/a/certificate.html
346 If your CA does not appear in the list then this confirms the problem.
349 * Why does my browser give a warning about a mismatched hostname?
351 Browsers expect the server's hostname to match the value in the commonName
352 (CN) field of the certificate. If it does not then you get a warning.
355 * How do I install a CA certificate into a browser?
357 The usual way is to send the DER encoded certificate to the browser as
358 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
359 link. On MSIE certain extensions such as .der or .cacert may also work, or you
360 can import the certificate using the certificate import wizard.
362 You can convert a certificate to DER form using the command:
364 openssl x509 -in ca.pem -outform DER -out ca.der
366 Occasionally someone suggests using a command such as:
368 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
370 DO NOT DO THIS! This command will give away your CAs private key and
371 reduces its security to zero: allowing anyone to forge certificates in
372 whatever name they choose.
374 * Why is OpenSSL x509 DN output not conformant to RFC2253?
376 The ways to print out the oneline format of the DN (Distinguished Name) have
377 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
378 interface, the "-nameopt" option could be introduded. See the manual
379 page of the "openssl x509" commandline tool for details. The old behaviour
380 has however been left as default for the sake of compatibility.
382 [BUILD] =======================================================================
384 * Why does the linker complain about undefined symbols?
386 Maybe the compilation was interrupted, and make doesn't notice that
387 something is missing. Run "make clean; make".
389 If you used ./Configure instead of ./config, make sure that you
390 selected the right target. File formats may differ slightly between
391 OS versions (for example sparcv8/sparcv9, or a.out/elf).
393 In case you get errors about the following symbols, use the config
394 option "no-asm", as described in INSTALL:
396 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
397 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
398 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
399 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
400 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
401 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
402 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
404 If none of these helps, you may want to try using the current snapshot.
405 If the problem persists, please submit a bug report.
408 * Why does the OpenSSL test fail with "bc: command not found"?
410 You didn't install "bc", the Unix calculator. If you want to run the
411 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
414 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
416 On some SCO installations or versions, bc has a bug that gets triggered
417 when you run the test suite (using "make test"). The message returned is
418 "bc: 1 not implemented".
420 The best way to deal with this is to find another implementation of bc
421 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
422 for download instructions) can be safely used, for example.
425 * Why does the OpenSSL test fail with "bc: stack empty"?
427 On some DG/ux versions, bc seems to have a too small stack for calculations
428 that the OpenSSL bntest throws at it. This gets triggered when you run the
429 test suite (using "make test"). The message returned is "bc: stack empty".
431 The best way to deal with this is to find another implementation of bc
432 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
433 for download instructions) can be safely used, for example.
436 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
438 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
439 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
440 memory to continue compilation.' As far as the tests have shown, this may be
441 a compiler bug. What happens is that it eats up a lot of resident memory
442 to build something, probably a table. The problem is clearly in the
443 optimization code, because if one eliminates optimization completely (-O0),
444 the compilation goes through (and the compiler consumes about 2MB of resident
445 memory instead of 240MB or whatever one's limit is currently).
447 There are three options to solve this problem:
449 1. set your current data segment size soft limit higher. Experience shows
450 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
451 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
452 kbytes to set the limit to.
454 2. If you have a hard limit that is lower than what you need and you can't
455 get it changed, you can compile all of OpenSSL with -O0 as optimization
456 level. This is however not a very nice thing to do for those who expect to
457 get the best result from OpenSSL. A bit more complicated solution is the
460 ----- snip:start -----
461 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
462 sed -e 's/ -O[0-9] / -O0 /'`"
463 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
467 This will only compile sha_dgst.c with -O0, the rest with the optimization
468 level chosen by the configuration process. When the above is done, do the
469 test and installation and you're set.
472 * Why does the OpenSSL compilation fail with "ar: command not found"?
474 Getting this message is quite usual on Solaris 2, because Sun has hidden
475 away 'ar' and other development commands in directories that aren't in
476 $PATH by default. One of those directories is '/usr/ccs/bin'. The
477 quickest way to fix this is to do the following (it assumes you use sh
478 or any sh-compatible shell):
480 ----- snip:start -----
481 PATH=${PATH}:/usr/ccs/bin; export PATH
484 and then redo the compilation. What you should really do is make sure
485 '/usr/ccs/bin' is permanently in your $PATH, for example through your
486 '.profile' (again, assuming you use a sh-compatible shell).
489 * Why does the OpenSSL compilation fail on Win32 with VC++?
491 Sometimes, you may get reports from VC++ command line (cl) that it
492 can't find standard include files like stdio.h and other weirdnesses.
493 One possible cause is that the environment isn't correctly set up.
494 To solve that problem, one should run VCVARS32.BAT which is found in
495 the 'bin' subdirectory of the VC++ installation directory (somewhere
496 under 'Program Files'). This needs to be done prior to running NMAKE,
497 and the changes are only valid for the current DOS session.
500 * What is special about OpenSSL on Redhat?
502 Red Hat Linux (release 7.0 and later) include a preinstalled limited
503 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
504 is disabled in this version. The same may apply to other Linux distributions.
505 Users may therefore wish to install more or all of the features left out.
507 To do this you MUST ensure that you do not overwrite the openssl that is in
508 /usr/bin on your Red Hat machine. Several packages depend on this file,
509 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
510 libraries that come with Red Hat 7.0 onwards have different names and so are
511 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
512 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
513 /lib/libcrypto.so.2 respectively).
515 Please note that we have been advised by Red Hat attempting to recompile the
516 openssl rpm with all the cryptography enabled will not work. All other
517 packages depend on the original Red Hat supplied openssl package. It is also
518 worth noting that due to the way Red Hat supplies its packages, updates to
519 openssl on each distribution never change the package version, only the
520 build number. For example, on Red Hat 7.1, the latest openssl package has
521 version number 0.9.6 and build number 9 even though it contains all the
522 relevant updates in packages up to and including 0.9.6b.
524 A possible way around this is to persuade Red Hat to produce a non-US
525 version of Red Hat Linux.
527 FYI: Patent numbers and expiry dates of US patents:
528 MDC-2: 4,908,861 13/03/2007
529 IDEA: 5,214,703 25/05/2010
530 RC5: 5,724,428 03/03/2015
533 * Why does the OpenSSL compilation fail on MacOS X?
535 If the failure happens when trying to build the "openssl" binary, with
536 a large number of undefined symbols, it's very probable that you have
537 OpenSSL 0.9.6b delivered with the operating system (you can find out by
538 running '/usr/bin/openssl version') and that you were trying to build
539 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
540 MacOS X has a misfeature that's quite difficult to go around.
541 Look in the file PROBLEMS for a more detailed explanation and for possible
545 * Why does the OpenSSL test suite fail on MacOS X?
547 If the failure happens when running 'make test' and the RC4 test fails,
548 it's very probable that you have OpenSSL 0.9.6b delivered with the
549 operating system (you can find out by running '/usr/bin/openssl version')
550 and that you were trying to build OpenSSL 0.9.6d. The problem is that
551 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
552 go around and has linked the programs "openssl" and the test programs
553 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
554 libraries you just built.
555 Look in the file PROBLEMS for a more detailed explanation and for possible
558 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
560 Failure in BN_sqr test is most likely caused by a failure to configure the
561 toolkit for current platform or lack of support for the platform in question.
562 Run './config -t' and './apps/openssl version -p'. Do these platform
563 identifiers match? If they don't, then you most likely failed to run
564 ./config and you're hereby advised to do so before filing a bug report.
565 If ./config itself fails to run, then it's most likely problem with your
566 local environment and you should turn to your system administrator (or
567 similar). If identifiers match (and/or no alternative identifier is
568 suggested by ./config script), then the platform is unsupported. There might
569 or might not be a workaround. Most notably on SPARC64 platforms with GNU
570 C compiler you should be able to produce a working build by running
571 './config -m32'. I understand that -m32 might not be what you want/need,
572 but the build should be operational. For further details turn to
573 <openssl-dev@openssl.org>.
575 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented
578 As of 0.9.7 assembler routines were overhauled for position independency
579 of the machine code, which is essential for shared library support. Now
580 for some reason OpenBSD is equipped with out-of-date GNU assembler which
581 finds the new code offending. To work the problem around configure with
582 no-asm (and sacrifice a great deal of performance) or upgrade /usr/bin/as.
583 For your convenience a pre-compiled replacement binary is provided as
584 http://www.openssl.org/~appro/i386-openbsd3-as, which is compiled from
585 binutils-2.8 released in 1997.
587 [PROG] ========================================================================
589 * Is OpenSSL thread-safe?
591 Yes (with limitations: an SSL connection may not concurrently be used
592 by multiple threads). On Windows and many Unix systems, OpenSSL
593 automatically uses the multi-threaded versions of the standard
594 libraries. If your platform is not one of these, consult the INSTALL
597 Multi-threaded applications must provide two callback functions to
598 OpenSSL. This is described in the threads(3) manpage.
601 * I've compiled a program under Windows and it crashes: why?
603 This is usually because you've missed the comment in INSTALL.W32.
604 Your application must link against the same version of the Win32
605 C-Runtime against which your openssl libraries were linked. The
606 default version for OpenSSL is /MD - "Multithreaded DLL".
608 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
609 many cases, your new project most likely defaulted to "Debug
610 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
611 program will crash, typically on the first BIO related read or write
614 For each of the six possible link stage configurations within Win32,
615 your application must link against the same by which OpenSSL was
616 built. If you are using MS Visual C++ (Studio) this can be changed
619 1. Select Settings... from the Project Menu.
620 2. Select the C/C++ Tab.
621 3. Select "Code Generation from the "Category" drop down list box
622 4. Select the Appropriate library (see table below) from the "Use
623 run-time library" drop down list box. Perform this step for both
624 your debug and release versions of your application (look at the
625 top left of the settings panel to change between the two)
627 Single Threaded /ML - MS VC++ often defaults to
629 version of a new project.
630 Debug Single Threaded /MLd - MS VC++ often defaults to
631 this for the debug version
634 Debug Multithreaded /MTd
635 Multithreaded DLL /MD - OpenSSL defaults to this.
636 Debug Multithreaded DLL /MDd
638 Note that debug and release libraries are NOT interchangeable. If you
639 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
642 * How do I read or write a DER encoded buffer using the ASN1 functions?
644 You have two options. You can either use a memory BIO in conjunction
645 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
646 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
647 cause of grief here are some code fragments using PKCS7 as an example:
649 unsigned char *buf, *p;
652 len = i2d_PKCS7(p7, NULL);
653 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
657 At this point buf contains the len bytes of the DER encoding of
660 The opposite assumes we already have len bytes in buf:
664 p7 = d2i_PKCS7(NULL, &p, len);
666 At this point p7 contains a valid PKCS7 structure of NULL if an error
667 occurred. If an error occurred ERR_print_errors(bio) should give more
670 The reason for the temporary variable 'p' is that the ASN1 functions
671 increment the passed pointer so it is ready to read or write the next
672 structure. This is often a cause of problems: without the temporary
673 variable the buffer pointer is changed to point just after the data
674 that has been read or written. This may well be uninitialized data
675 and attempts to free the buffer will have unpredictable results
676 because it no longer points to the same address.
679 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
681 This usually happens when you try compiling something using the PKCS#12
682 macros with a C++ compiler. There is hardly ever any need to use the
683 PKCS#12 macros in a program, it is much easier to parse and create
684 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
685 documented in doc/openssl.txt and with examples in demos/pkcs12. The
686 'pkcs12' application has to use the macros because it prints out
687 debugging information.
690 * I've called <some function> and it fails, why?
692 Before submitting a report or asking in one of the mailing lists, you
693 should try to determine the cause. In particular, you should call
694 ERR_print_errors() or ERR_print_errors_fp() after the failed call
695 and see if the message helps. Note that the problem may occur earlier
696 than you think -- you should check for errors after every call where
697 it is possible, otherwise the actual problem may be hidden because
698 some OpenSSL functions clear the error state.
701 * I just get a load of numbers for the error output, what do they mean?
703 The actual format is described in the ERR_print_errors() manual page.
704 You should call the function ERR_load_crypto_strings() before hand and
705 the message will be output in text form. If you can't do this (for example
706 it is a pre-compiled binary) you can use the errstr utility on the error
707 code itself (the hex digits after the second colon).
710 * Why do I get errors about unknown algorithms?
712 This can happen under several circumstances such as reading in an
713 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
714 is forgetting to load OpenSSL's table of algorithms with
715 OpenSSL_add_all_algorithms(). See the manual page for more information.
718 * Why can't the OpenSSH configure script detect OpenSSL?
720 Several reasons for problems with the automatic detection exist.
721 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
722 Sometimes the distribution has installed an older version in the system
723 locations that is detected instead of a new one installed. The OpenSSL
724 library might have been compiled for another CPU or another mode (32/64 bits).
725 Permissions might be wrong.
727 The general answer is to check the config.log file generated when running
728 the OpenSSH configure script. It should contain the detailed information
729 on why the OpenSSL library was not detected or considered incompatible.
731 * Can I use OpenSSL's SSL library with non-blocking I/O?
733 Yes; make sure to read the SSL_get_error(3) manual page!
735 A pitfall to avoid: Don't assume that SSL_read() will just read from
736 the underlying transport or that SSL_write() will just write to it --
737 it is also possible that SSL_write() cannot do any useful work until
738 there is data to read, or that SSL_read() cannot do anything until it
739 is possible to send data. One reason for this is that the peer may
740 request a new TLS/SSL handshake at any time during the protocol,
741 requiring a bi-directional message exchange; both SSL_read() and
742 SSL_write() will try to continue any pending handshake.
745 * Why doesn't my server application receive a client certificate?
747 Due to the TLS protocol definition, a client will only send a certificate,
748 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
749 SSL_CTX_set_verify() function to enable the use of client certificates.
752 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
754 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
755 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
756 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
757 Change your code to use the new name when compiling against OpenSSL 0.9.7.
760 ===============================================================================