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 segment type"?
50 [PROG] Questions about programming with OpenSSL
52 * Is OpenSSL thread-safe?
53 * I've compiled a program under Windows and it crashes: why?
54 * How do I read or write a DER encoded buffer using the ASN1 functions?
55 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
56 * I've called <some function> and it fails, why?
57 * I just get a load of numbers for the error output, what do they mean?
58 * Why do I get errors about unknown algorithms?
59 * Why can't the OpenSSH configure script detect OpenSSL?
60 * Can I use OpenSSL's SSL library with non-blocking I/O?
61 * Why doesn't my server application receive a client certificate?
62 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
64 ===============================================================================
66 [MISC] ========================================================================
68 * Which is the current version of OpenSSL?
70 The current version is available from <URL: http://www.openssl.org>.
71 OpenSSL 0.9.7 was released on December 31, 2002.
73 In addition to the current stable release, you can also access daily
74 snapshots of the OpenSSL development version at <URL:
75 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
78 * Where is the documentation?
80 OpenSSL is a library that provides cryptographic functionality to
81 applications such as secure web servers. Be sure to read the
82 documentation of the application you want to use. The INSTALL file
83 explains how to install this library.
85 OpenSSL includes a command line utility that can be used to perform a
86 variety of cryptographic functions. It is described in the openssl(1)
87 manpage. Documentation for developers is currently being written. A
88 few manual pages already are available; overviews over libcrypto and
89 libssl are given in the crypto(3) and ssl(3) manpages.
91 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
92 different directory if you specified one as described in INSTALL).
93 In addition, you can read the most current versions at
94 <URL: http://www.openssl.org/docs/>.
96 For information on parts of libcrypto that are not yet documented, you
97 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
98 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
99 of this still applies to OpenSSL.
101 There is some documentation about certificate extensions and PKCS#12
104 The original SSLeay documentation is included in OpenSSL as
105 doc/ssleay.txt. It may be useful when none of the other resources
106 help, but please note that it reflects the obsolete version SSLeay
110 * How can I contact the OpenSSL developers?
112 The README file describes how to submit bug reports and patches to
113 OpenSSL. Information on the OpenSSL mailing lists is available from
114 <URL: http://www.openssl.org>.
117 * Where can I get a compiled version of OpenSSL?
119 Some applications that use OpenSSL are distributed in binary form.
120 When using such an application, you don't need to install OpenSSL
121 yourself; the application will include the required parts (e.g. DLLs).
123 If you want to install OpenSSL on a Windows system and you don't have
124 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
125 on how to obtain and install the free GNU C compiler.
127 A number of Linux and *BSD distributions include OpenSSL.
130 * Why aren't tools like 'autoconf' and 'libtool' used?
132 autoconf will probably be used in future OpenSSL versions. If it was
133 less Unix-centric, it might have been used much earlier.
135 * What is an 'engine' version?
137 With version 0.9.6 OpenSSL was extended to interface to external crypto
138 hardware. This was realized in a special release '0.9.6-engine'. With
139 version 0.9.7 (not yet released) the changes were merged into the main
140 development line, so that the special release is no longer necessary.
142 * How do I check the authenticity of the OpenSSL distribution?
144 We provide MD5 digests and ASC signatures of each tarball.
145 Use MD5 to check that a tarball from a mirror site is identical:
147 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
149 You can check authenticity using pgp or gpg. You need the OpenSSL team
150 member public key used to sign it (download it from a key server). Then
155 [LEGAL] =======================================================================
157 * Do I need patent licenses to use OpenSSL?
159 The patents section of the README file lists patents that may apply to
160 you if you want to use OpenSSL. For information on intellectual
161 property rights, please consult a lawyer. The OpenSSL team does not
164 You can configure OpenSSL so as not to use RC5 and IDEA by using
165 ./config no-rc5 no-idea
168 * Can I use OpenSSL with GPL software?
170 On many systems including the major Linux and BSD distributions, yes (the
171 GPL does not place restrictions on using libraries that are part of the
172 normal operating system distribution).
174 On other systems, the situation is less clear. Some GPL software copyright
175 holders claim that you infringe on their rights if you use OpenSSL with
176 their software on operating systems that don't normally include OpenSSL.
178 If you develop open source software that uses OpenSSL, you may find it
179 useful to choose an other license than the GPL, or state explicitly that
180 "This program is released under the GPL with the additional exemption that
181 compiling, linking, and/or using OpenSSL is allowed." If you are using
182 GPL software developed by others, you may want to ask the copyright holder
183 for permission to use their software with OpenSSL.
186 [USER] ========================================================================
188 * Why do I get a "PRNG not seeded" error message?
190 Cryptographic software needs a source of unpredictable data to work
191 correctly. Many open source operating systems provide a "randomness
192 device" that serves this purpose. On other systems, applications have
193 to call the RAND_add() or RAND_seed() function with appropriate data
194 before generating keys or performing public key encryption.
195 (These functions initialize the pseudo-random number generator, PRNG.)
197 Some broken applications do not do this. As of version 0.9.5, the
198 OpenSSL functions that need randomness report an error if the random
199 number generator has not been seeded with at least 128 bits of
200 randomness. If this error occurs, please contact the author of the
201 application you are using. It is likely that it never worked
202 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
203 to perform potentially insecure encryption.
205 On systems without /dev/urandom and /dev/random, it is a good idea to
206 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
207 details. Starting with version 0.9.7, OpenSSL will automatically look
208 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
211 Most components of the openssl command line utility automatically try
212 to seed the random number generator from a file. The name of the
213 default seeding file is determined as follows: If environment variable
214 RANDFILE is set, then it names the seeding file. Otherwise if
215 environment variable HOME is set, then the seeding file is $HOME/.rnd.
216 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
217 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
218 default seeding file at all. OpenSSL 0.9.6b and later will behave
219 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
220 Windows systems if the environment variable has not been set.
222 If the default seeding file does not exist or is too short, the "PRNG
223 not seeded" error message may occur.
225 The openssl command line utility will write back a new state to the
226 default seeding file (and create this file if necessary) unless
227 there was no sufficient seeding.
229 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
230 Use the "-rand" option of the OpenSSL command line tools instead.
231 The $RANDFILE environment variable and $HOME/.rnd are only used by the
232 OpenSSL command line tools. Applications using the OpenSSL library
233 provide their own configuration options to specify the entropy source,
234 please check out the documentation coming the with application.
236 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
237 installing the SUNski package from Sun patch 105710-01 (Sparc) which
238 adds a /dev/random device and make sure it gets used, usually through
239 $RANDFILE. There are probably similar patches for the other Solaris
240 versions. An official statement from Sun with respect to /dev/random
241 support can be found at
242 http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski
243 However, be warned that /dev/random is usually a blocking device, which
244 may have some effects on OpenSSL.
245 A third party /dev/random solution for Solaris is available at
246 http://www.cosy.sbg.ac.at/~andi/
249 * Why do I get an "unable to write 'random state'" error message?
252 Sometimes the openssl command line utility does not abort with
253 a "PRNG not seeded" error message, but complains that it is
254 "unable to write 'random state'". This message refers to the
255 default seeding file (see previous answer). A possible reason
256 is that no default filename is known because neither RANDFILE
257 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
258 current directory in this case, but this has changed with 0.9.6a.)
261 * How do I create certificates or certificate requests?
263 Check out the CA.pl(1) manual page. This provides a simple wrapper round
264 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
265 out the manual pages for the individual utilities and the certificate
266 extensions documentation (currently in doc/openssl.txt).
269 * Why can't I create certificate requests?
271 You typically get the error:
273 unable to find 'distinguished_name' in config
274 problems making Certificate Request
276 This is because it can't find the configuration file. Check out the
277 DIAGNOSTICS section of req(1) for more information.
280 * Why does <SSL program> fail with a certificate verify error?
282 This problem is usually indicated by log messages saying something like
283 "unable to get local issuer certificate" or "self signed certificate".
284 When a certificate is verified its root CA must be "trusted" by OpenSSL
285 this typically means that the CA certificate must be placed in a directory
286 or file and the relevant program configured to read it. The OpenSSL program
287 'verify' behaves in a similar way and issues similar error messages: check
288 the verify(1) program manual page for more information.
291 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
293 This is almost certainly because you are using an old "export grade" browser
294 which only supports weak encryption. Upgrade your browser to support 128 bit
298 * How can I create DSA certificates?
300 Check the CA.pl(1) manual page for a DSA certificate example.
303 * Why can't I make an SSL connection to a server using a DSA certificate?
305 Typically you'll see a message saying there are no shared ciphers when
306 the same setup works fine with an RSA certificate. There are two possible
307 causes. The client may not support connections to DSA servers most web
308 browsers (including Netscape and MSIE) only support connections to servers
309 supporting RSA cipher suites. The other cause is that a set of DH parameters
310 has not been supplied to the server. DH parameters can be created with the
311 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
312 check the source to s_server in apps/s_server.c for an example.
315 * How can I remove the passphrase on a private key?
317 Firstly you should be really *really* sure you want to do this. Leaving
318 a private key unencrypted is a major security risk. If you decide that
319 you do have to do this check the EXAMPLES sections of the rsa(1) and
323 * Why can't I use OpenSSL certificates with SSL client authentication?
325 What will typically happen is that when a server requests authentication
326 it will either not include your certificate or tell you that you have
327 no client certificates (Netscape) or present you with an empty list box
328 (MSIE). The reason for this is that when a server requests a client
329 certificate it includes a list of CAs names which it will accept. Browsers
330 will only let you select certificates from the list on the grounds that
331 there is little point presenting a certificate which the server will
334 The solution is to add the relevant CA certificate to your servers "trusted
335 CA list". How you do this depends on the server software in uses. You can
336 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
338 openssl s_client -connect www.some.host:443 -prexit
340 If your server only requests certificates on certain URLs then you may need
341 to manually issue an HTTP GET command to get the list when s_client connects:
343 GET /some/page/needing/a/certificate.html
345 If your CA does not appear in the list then this confirms the problem.
348 * Why does my browser give a warning about a mismatched hostname?
350 Browsers expect the server's hostname to match the value in the commonName
351 (CN) field of the certificate. If it does not then you get a warning.
354 * How do I install a CA certificate into a browser?
356 The usual way is to send the DER encoded certificate to the browser as
357 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
358 link. On MSIE certain extensions such as .der or .cacert may also work, or you
359 can import the certificate using the certificate import wizard.
361 You can convert a certificate to DER form using the command:
363 openssl x509 -in ca.pem -outform DER -out ca.der
365 Occasionally someone suggests using a command such as:
367 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
369 DO NOT DO THIS! This command will give away your CAs private key and
370 reduces its security to zero: allowing anyone to forge certificates in
371 whatever name they choose.
373 * Why is OpenSSL x509 DN output not conformant to RFC2253?
375 The ways to print out the oneline format of the DN (Distinguished Name) have
376 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
377 interface, the "-nameopt" option could be introduded. See the manual
378 page of the "openssl x509" commandline tool for details. The old behaviour
379 has however been left as default for the sake of compatibility.
381 [BUILD] =======================================================================
383 * Why does the linker complain about undefined symbols?
385 Maybe the compilation was interrupted, and make doesn't notice that
386 something is missing. Run "make clean; make".
388 If you used ./Configure instead of ./config, make sure that you
389 selected the right target. File formats may differ slightly between
390 OS versions (for example sparcv8/sparcv9, or a.out/elf).
392 In case you get errors about the following symbols, use the config
393 option "no-asm", as described in INSTALL:
395 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
396 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
397 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
398 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
399 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
400 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
401 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
403 If none of these helps, you may want to try using the current snapshot.
404 If the problem persists, please submit a bug report.
407 * Why does the OpenSSL test fail with "bc: command not found"?
409 You didn't install "bc", the Unix calculator. If you want to run the
410 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
413 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
415 On some SCO installations or versions, bc has a bug that gets triggered
416 when you run the test suite (using "make test"). The message returned is
417 "bc: 1 not implemented".
419 The best way to deal with this is to find another implementation of bc
420 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
421 for download instructions) can be safely used, for example.
424 * Why does the OpenSSL test fail with "bc: stack empty"?
426 On some DG/ux versions, bc seems to have a too small stack for calculations
427 that the OpenSSL bntest throws at it. This gets triggered when you run the
428 test suite (using "make test"). The message returned is "bc: stack empty".
430 The best way to deal with this is to find another implementation of bc
431 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
432 for download instructions) can be safely used, for example.
435 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
437 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
438 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
439 memory to continue compilation.' As far as the tests have shown, this may be
440 a compiler bug. What happens is that it eats up a lot of resident memory
441 to build something, probably a table. The problem is clearly in the
442 optimization code, because if one eliminates optimization completely (-O0),
443 the compilation goes through (and the compiler consumes about 2MB of resident
444 memory instead of 240MB or whatever one's limit is currently).
446 There are three options to solve this problem:
448 1. set your current data segment size soft limit higher. Experience shows
449 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
450 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
451 kbytes to set the limit to.
453 2. If you have a hard limit that is lower than what you need and you can't
454 get it changed, you can compile all of OpenSSL with -O0 as optimization
455 level. This is however not a very nice thing to do for those who expect to
456 get the best result from OpenSSL. A bit more complicated solution is the
459 ----- snip:start -----
460 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
461 sed -e 's/ -O[0-9] / -O0 /'`"
462 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
466 This will only compile sha_dgst.c with -O0, the rest with the optimization
467 level chosen by the configuration process. When the above is done, do the
468 test and installation and you're set.
471 * Why does the OpenSSL compilation fail with "ar: command not found"?
473 Getting this message is quite usual on Solaris 2, because Sun has hidden
474 away 'ar' and other development commands in directories that aren't in
475 $PATH by default. One of those directories is '/usr/ccs/bin'. The
476 quickest way to fix this is to do the following (it assumes you use sh
477 or any sh-compatible shell):
479 ----- snip:start -----
480 PATH=${PATH}:/usr/ccs/bin; export PATH
483 and then redo the compilation. What you should really do is make sure
484 '/usr/ccs/bin' is permanently in your $PATH, for example through your
485 '.profile' (again, assuming you use a sh-compatible shell).
488 * Why does the OpenSSL compilation fail on Win32 with VC++?
490 Sometimes, you may get reports from VC++ command line (cl) that it
491 can't find standard include files like stdio.h and other weirdnesses.
492 One possible cause is that the environment isn't correctly set up.
493 To solve that problem, one should run VCVARS32.BAT which is found in
494 the 'bin' subdirectory of the VC++ installation directory (somewhere
495 under 'Program Files'). This needs to be done prior to running NMAKE,
496 and the changes are only valid for the current DOS session.
499 * What is special about OpenSSL on Redhat?
501 Red Hat Linux (release 7.0 and later) include a preinstalled limited
502 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
503 is disabled in this version. The same may apply to other Linux distributions.
504 Users may therefore wish to install more or all of the features left out.
506 To do this you MUST ensure that you do not overwrite the openssl that is in
507 /usr/bin on your Red Hat machine. Several packages depend on this file,
508 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
509 libraries that come with Red Hat 7.0 onwards have different names and so are
510 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
511 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
512 /lib/libcrypto.so.2 respectively).
514 Please note that we have been advised by Red Hat attempting to recompile the
515 openssl rpm with all the cryptography enabled will not work. All other
516 packages depend on the original Red Hat supplied openssl package. It is also
517 worth noting that due to the way Red Hat supplies its packages, updates to
518 openssl on each distribution never change the package version, only the
519 build number. For example, on Red Hat 7.1, the latest openssl package has
520 version number 0.9.6 and build number 9 even though it contains all the
521 relevant updates in packages up to and including 0.9.6b.
523 A possible way around this is to persuade Red Hat to produce a non-US
524 version of Red Hat Linux.
526 FYI: Patent numbers and expiry dates of US patents:
527 MDC-2: 4,908,861 13/03/2007
528 IDEA: 5,214,703 25/05/2010
529 RC5: 5,724,428 03/03/2015
532 * Why does the OpenSSL compilation fail on MacOS X?
534 If the failure happens when trying to build the "openssl" binary, with
535 a large number of undefined symbols, it's very probable that you have
536 OpenSSL 0.9.6b delivered with the operating system (you can find out by
537 running '/usr/bin/openssl version') and that you were trying to build
538 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
539 MacOS X has a misfeature that's quite difficult to go around.
540 Look in the file PROBLEMS for a more detailed explanation and for possible
544 * Why does the OpenSSL test suite fail on MacOS X?
546 If the failure happens when running 'make test' and the RC4 test fails,
547 it's very probable that you have OpenSSL 0.9.6b delivered with the
548 operating system (you can find out by running '/usr/bin/openssl version')
549 and that you were trying to build OpenSSL 0.9.6d. The problem is that
550 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
551 go around and has linked the programs "openssl" and the test programs
552 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
553 libraries you just built.
554 Look in the file PROBLEMS for a more detailed explanation and for possible
557 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
559 Failure in BN_sqr test is most likely caused by a failure to configure the
560 toolkit for current platform or lack of support for the platform in question.
561 Run './config -t' and './apps/openssl version -p'. Do these platform
562 identifiers match? If they don't, then you most likely failed to run
563 ./config and you're hereby advised to do so before filing a bug report.
564 If ./config itself fails to run, then it's most likely problem with your
565 local environment and you should turn to your system administrator (or
566 similar). If identifiers match (and/or no alternative identifier is
567 suggested by ./config script), then the platform is unsupported. There might
568 or might not be a workaround. Most notably on SPARC64 platforms with GNU
569 C compiler you should be able to produce a working build by running
570 './config -m32'. I understand that -m32 might not be what you want/need,
571 but the build should be operational. For further details turn to
572 <openssl-dev@openssl.org>.
574 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"?
576 As of 0.9.7 assembler routines were overhauled for position independence
577 of the machine code, which is essential for shared library support. For
578 some reason OpenBSD is equipped with an out-of-date GNU assembler which
579 finds the new code offensive. To work around the problem, configure with
580 no-asm (and sacrifice a great deal of performance) or patch your assembler
581 according to <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.patch>.
582 For your convenience a pre-compiled replacement binary is provided at
583 <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.bin>.
585 [PROG] ========================================================================
587 * Is OpenSSL thread-safe?
589 Yes (with limitations: an SSL connection may not concurrently be used
590 by multiple threads). On Windows and many Unix systems, OpenSSL
591 automatically uses the multi-threaded versions of the standard
592 libraries. If your platform is not one of these, consult the INSTALL
595 Multi-threaded applications must provide two callback functions to
596 OpenSSL. This is described in the threads(3) manpage.
599 * I've compiled a program under Windows and it crashes: why?
601 This is usually because you've missed the comment in INSTALL.W32.
602 Your application must link against the same version of the Win32
603 C-Runtime against which your openssl libraries were linked. The
604 default version for OpenSSL is /MD - "Multithreaded DLL".
606 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
607 many cases, your new project most likely defaulted to "Debug
608 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
609 program will crash, typically on the first BIO related read or write
612 For each of the six possible link stage configurations within Win32,
613 your application must link against the same by which OpenSSL was
614 built. If you are using MS Visual C++ (Studio) this can be changed
617 1. Select Settings... from the Project Menu.
618 2. Select the C/C++ Tab.
619 3. Select "Code Generation from the "Category" drop down list box
620 4. Select the Appropriate library (see table below) from the "Use
621 run-time library" drop down list box. Perform this step for both
622 your debug and release versions of your application (look at the
623 top left of the settings panel to change between the two)
625 Single Threaded /ML - MS VC++ often defaults to
627 version of a new project.
628 Debug Single Threaded /MLd - MS VC++ often defaults to
629 this for the debug version
632 Debug Multithreaded /MTd
633 Multithreaded DLL /MD - OpenSSL defaults to this.
634 Debug Multithreaded DLL /MDd
636 Note that debug and release libraries are NOT interchangeable. If you
637 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
640 * How do I read or write a DER encoded buffer using the ASN1 functions?
642 You have two options. You can either use a memory BIO in conjunction
643 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
644 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
645 cause of grief here are some code fragments using PKCS7 as an example:
647 unsigned char *buf, *p;
650 len = i2d_PKCS7(p7, NULL);
651 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
655 At this point buf contains the len bytes of the DER encoding of
658 The opposite assumes we already have len bytes in buf:
662 p7 = d2i_PKCS7(NULL, &p, len);
664 At this point p7 contains a valid PKCS7 structure of NULL if an error
665 occurred. If an error occurred ERR_print_errors(bio) should give more
668 The reason for the temporary variable 'p' is that the ASN1 functions
669 increment the passed pointer so it is ready to read or write the next
670 structure. This is often a cause of problems: without the temporary
671 variable the buffer pointer is changed to point just after the data
672 that has been read or written. This may well be uninitialized data
673 and attempts to free the buffer will have unpredictable results
674 because it no longer points to the same address.
677 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
679 This usually happens when you try compiling something using the PKCS#12
680 macros with a C++ compiler. There is hardly ever any need to use the
681 PKCS#12 macros in a program, it is much easier to parse and create
682 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
683 documented in doc/openssl.txt and with examples in demos/pkcs12. The
684 'pkcs12' application has to use the macros because it prints out
685 debugging information.
688 * I've called <some function> and it fails, why?
690 Before submitting a report or asking in one of the mailing lists, you
691 should try to determine the cause. In particular, you should call
692 ERR_print_errors() or ERR_print_errors_fp() after the failed call
693 and see if the message helps. Note that the problem may occur earlier
694 than you think -- you should check for errors after every call where
695 it is possible, otherwise the actual problem may be hidden because
696 some OpenSSL functions clear the error state.
699 * I just get a load of numbers for the error output, what do they mean?
701 The actual format is described in the ERR_print_errors() manual page.
702 You should call the function ERR_load_crypto_strings() before hand and
703 the message will be output in text form. If you can't do this (for example
704 it is a pre-compiled binary) you can use the errstr utility on the error
705 code itself (the hex digits after the second colon).
708 * Why do I get errors about unknown algorithms?
710 This can happen under several circumstances such as reading in an
711 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
712 is forgetting to load OpenSSL's table of algorithms with
713 OpenSSL_add_all_algorithms(). See the manual page for more information.
716 * Why can't the OpenSSH configure script detect OpenSSL?
718 Several reasons for problems with the automatic detection exist.
719 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
720 Sometimes the distribution has installed an older version in the system
721 locations that is detected instead of a new one installed. The OpenSSL
722 library might have been compiled for another CPU or another mode (32/64 bits).
723 Permissions might be wrong.
725 The general answer is to check the config.log file generated when running
726 the OpenSSH configure script. It should contain the detailed information
727 on why the OpenSSL library was not detected or considered incompatible.
729 * Can I use OpenSSL's SSL library with non-blocking I/O?
731 Yes; make sure to read the SSL_get_error(3) manual page!
733 A pitfall to avoid: Don't assume that SSL_read() will just read from
734 the underlying transport or that SSL_write() will just write to it --
735 it is also possible that SSL_write() cannot do any useful work until
736 there is data to read, or that SSL_read() cannot do anything until it
737 is possible to send data. One reason for this is that the peer may
738 request a new TLS/SSL handshake at any time during the protocol,
739 requiring a bi-directional message exchange; both SSL_read() and
740 SSL_write() will try to continue any pending handshake.
743 * Why doesn't my server application receive a client certificate?
745 Due to the TLS protocol definition, a client will only send a certificate,
746 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
747 SSL_CTX_set_verify() function to enable the use of client certificates.
750 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
752 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
753 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
754 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
755 Change your code to use the new name when compiling against OpenSSL 0.9.7.
758 ===============================================================================