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 * OpenSSL uses DER but I need BER format: does OpenSSL support BER?
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?
64 * I think I've detected a memory leak, is this a bug?
66 ===============================================================================
68 [MISC] ========================================================================
70 * Which is the current version of OpenSSL?
72 The current version is available from <URL: http://www.openssl.org>.
73 OpenSSL 0.9.7f was released on March 22, 2005.
75 In addition to the current stable release, you can also access daily
76 snapshots of the OpenSSL development version at <URL:
77 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
80 * Where is the documentation?
82 OpenSSL is a library that provides cryptographic functionality to
83 applications such as secure web servers. Be sure to read the
84 documentation of the application you want to use. The INSTALL file
85 explains how to install this library.
87 OpenSSL includes a command line utility that can be used to perform a
88 variety of cryptographic functions. It is described in the openssl(1)
89 manpage. Documentation for developers is currently being written. A
90 few manual pages already are available; overviews over libcrypto and
91 libssl are given in the crypto(3) and ssl(3) manpages.
93 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
94 different directory if you specified one as described in INSTALL).
95 In addition, you can read the most current versions at
96 <URL: http://www.openssl.org/docs/>.
98 For information on parts of libcrypto that are not yet documented, you
99 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
100 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
101 of this still applies to OpenSSL.
103 There is some documentation about certificate extensions and PKCS#12
106 The original SSLeay documentation is included in OpenSSL as
107 doc/ssleay.txt. It may be useful when none of the other resources
108 help, but please note that it reflects the obsolete version SSLeay
112 * How can I contact the OpenSSL developers?
114 The README file describes how to submit bug reports and patches to
115 OpenSSL. Information on the OpenSSL mailing lists is available from
116 <URL: http://www.openssl.org>.
119 * Where can I get a compiled version of OpenSSL?
121 You can finder pointers to binary distributions in
122 http://www.openssl.org/related/binaries.html .
124 Some applications that use OpenSSL are distributed in binary form.
125 When using such an application, you don't need to install OpenSSL
126 yourself; the application will include the required parts (e.g. DLLs).
128 If you want to build OpenSSL on a Windows system and you don't have
129 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
130 on how to obtain and install the free GNU C compiler.
132 A number of Linux and *BSD distributions include OpenSSL.
135 * Why aren't tools like 'autoconf' and 'libtool' used?
137 autoconf will probably be used in future OpenSSL versions. If it was
138 less Unix-centric, it might have been used much earlier.
140 * What is an 'engine' version?
142 With version 0.9.6 OpenSSL was extended to interface to external crypto
143 hardware. This was realized in a special release '0.9.6-engine'. With
144 version 0.9.7 (not yet released) the changes were merged into the main
145 development line, so that the special release is no longer necessary.
147 * How do I check the authenticity of the OpenSSL distribution?
149 We provide MD5 digests and ASC signatures of each tarball.
150 Use MD5 to check that a tarball from a mirror site is identical:
152 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
154 You can check authenticity using pgp or gpg. You need the OpenSSL team
155 member public key used to sign it (download it from a key server, see a
156 list of keys at <URL: http://www.openssl.org/about/>). Then
161 [LEGAL] =======================================================================
163 * Do I need patent licenses to use OpenSSL?
165 The patents section of the README file lists patents that may apply to
166 you if you want to use OpenSSL. For information on intellectual
167 property rights, please consult a lawyer. The OpenSSL team does not
170 You can configure OpenSSL so as not to use IDEA, MDC2 and RC5 by using
171 ./config no-idea no-mdc2 no-rc5
174 * Can I use OpenSSL with GPL software?
176 On many systems including the major Linux and BSD distributions, yes (the
177 GPL does not place restrictions on using libraries that are part of the
178 normal operating system distribution).
180 On other systems, the situation is less clear. Some GPL software copyright
181 holders claim that you infringe on their rights if you use OpenSSL with
182 their software on operating systems that don't normally include OpenSSL.
184 If you develop open source software that uses OpenSSL, you may find it
185 useful to choose an other license than the GPL, or state explicitly that
186 "This program is released under the GPL with the additional exemption that
187 compiling, linking, and/or using OpenSSL is allowed." If you are using
188 GPL software developed by others, you may want to ask the copyright holder
189 for permission to use their software with OpenSSL.
192 [USER] ========================================================================
194 * Why do I get a "PRNG not seeded" error message?
196 Cryptographic software needs a source of unpredictable data to work
197 correctly. Many open source operating systems provide a "randomness
198 device" (/dev/urandom or /dev/random) that serves this purpose.
199 All OpenSSL versions try to use /dev/urandom by default; starting with
200 version 0.9.7, OpenSSL also tries /dev/random if /dev/urandom is not
203 On other systems, applications have to call the RAND_add() or
204 RAND_seed() function with appropriate data before generating keys or
205 performing public key encryption. (These functions initialize the
206 pseudo-random number generator, PRNG.) Some broken applications do
207 not do this. As of version 0.9.5, the OpenSSL functions that need
208 randomness report an error if the random number generator has not been
209 seeded with at least 128 bits of randomness. If this error occurs and
210 is not discussed in the documentation of the application you are
211 using, please contact the author of that application; it is likely
212 that it never worked correctly. OpenSSL 0.9.5 and later make the
213 error visible by refusing to perform potentially insecure encryption.
215 If you are using Solaris 8, you can add /dev/urandom and /dev/random
216 devices by installing patch 112438 (Sparc) or 112439 (x86), which are
217 available via the Patchfinder at <URL: http://sunsolve.sun.com>
218 (Solaris 9 includes these devices by default). For /dev/random support
219 for earlier Solaris versions, see Sun's statement at
220 <URL: http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski>
221 (the SUNWski package is available in patch 105710).
223 On systems without /dev/urandom and /dev/random, it is a good idea to
224 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
225 details. Starting with version 0.9.7, OpenSSL will automatically look
226 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
229 Most components of the openssl command line utility automatically try
230 to seed the random number generator from a file. The name of the
231 default seeding file is determined as follows: If environment variable
232 RANDFILE is set, then it names the seeding file. Otherwise if
233 environment variable HOME is set, then the seeding file is $HOME/.rnd.
234 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
235 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
236 default seeding file at all. OpenSSL 0.9.6b and later will behave
237 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
238 Windows systems if the environment variable has not been set.
240 If the default seeding file does not exist or is too short, the "PRNG
241 not seeded" error message may occur.
243 The openssl command line utility will write back a new state to the
244 default seeding file (and create this file if necessary) unless
245 there was no sufficient seeding.
247 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
248 Use the "-rand" option of the OpenSSL command line tools instead.
249 The $RANDFILE environment variable and $HOME/.rnd are only used by the
250 OpenSSL command line tools. Applications using the OpenSSL library
251 provide their own configuration options to specify the entropy source,
252 please check out the documentation coming the with application.
255 * Why do I get an "unable to write 'random state'" error message?
258 Sometimes the openssl command line utility does not abort with
259 a "PRNG not seeded" error message, but complains that it is
260 "unable to write 'random state'". This message refers to the
261 default seeding file (see previous answer). A possible reason
262 is that no default filename is known because neither RANDFILE
263 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
264 current directory in this case, but this has changed with 0.9.6a.)
267 * How do I create certificates or certificate requests?
269 Check out the CA.pl(1) manual page. This provides a simple wrapper round
270 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
271 out the manual pages for the individual utilities and the certificate
272 extensions documentation (currently in doc/openssl.txt).
275 * Why can't I create certificate requests?
277 You typically get the error:
279 unable to find 'distinguished_name' in config
280 problems making Certificate Request
282 This is because it can't find the configuration file. Check out the
283 DIAGNOSTICS section of req(1) for more information.
286 * Why does <SSL program> fail with a certificate verify error?
288 This problem is usually indicated by log messages saying something like
289 "unable to get local issuer certificate" or "self signed certificate".
290 When a certificate is verified its root CA must be "trusted" by OpenSSL
291 this typically means that the CA certificate must be placed in a directory
292 or file and the relevant program configured to read it. The OpenSSL program
293 'verify' behaves in a similar way and issues similar error messages: check
294 the verify(1) program manual page for more information.
297 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
299 This is almost certainly because you are using an old "export grade" browser
300 which only supports weak encryption. Upgrade your browser to support 128 bit
304 * How can I create DSA certificates?
306 Check the CA.pl(1) manual page for a DSA certificate example.
309 * Why can't I make an SSL connection to a server using a DSA certificate?
311 Typically you'll see a message saying there are no shared ciphers when
312 the same setup works fine with an RSA certificate. There are two possible
313 causes. The client may not support connections to DSA servers most web
314 browsers (including Netscape and MSIE) only support connections to servers
315 supporting RSA cipher suites. The other cause is that a set of DH parameters
316 has not been supplied to the server. DH parameters can be created with the
317 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
318 check the source to s_server in apps/s_server.c for an example.
321 * How can I remove the passphrase on a private key?
323 Firstly you should be really *really* sure you want to do this. Leaving
324 a private key unencrypted is a major security risk. If you decide that
325 you do have to do this check the EXAMPLES sections of the rsa(1) and
329 * Why can't I use OpenSSL certificates with SSL client authentication?
331 What will typically happen is that when a server requests authentication
332 it will either not include your certificate or tell you that you have
333 no client certificates (Netscape) or present you with an empty list box
334 (MSIE). The reason for this is that when a server requests a client
335 certificate it includes a list of CAs names which it will accept. Browsers
336 will only let you select certificates from the list on the grounds that
337 there is little point presenting a certificate which the server will
340 The solution is to add the relevant CA certificate to your servers "trusted
341 CA list". How you do this depends on the server software in uses. You can
342 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
344 openssl s_client -connect www.some.host:443 -prexit
346 If your server only requests certificates on certain URLs then you may need
347 to manually issue an HTTP GET command to get the list when s_client connects:
349 GET /some/page/needing/a/certificate.html
351 If your CA does not appear in the list then this confirms the problem.
354 * Why does my browser give a warning about a mismatched hostname?
356 Browsers expect the server's hostname to match the value in the commonName
357 (CN) field of the certificate. If it does not then you get a warning.
360 * How do I install a CA certificate into a browser?
362 The usual way is to send the DER encoded certificate to the browser as
363 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
364 link. On MSIE certain extensions such as .der or .cacert may also work, or you
365 can import the certificate using the certificate import wizard.
367 You can convert a certificate to DER form using the command:
369 openssl x509 -in ca.pem -outform DER -out ca.der
371 Occasionally someone suggests using a command such as:
373 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
375 DO NOT DO THIS! This command will give away your CAs private key and
376 reduces its security to zero: allowing anyone to forge certificates in
377 whatever name they choose.
379 * Why is OpenSSL x509 DN output not conformant to RFC2253?
381 The ways to print out the oneline format of the DN (Distinguished Name) have
382 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
383 interface, the "-nameopt" option could be introduded. See the manual
384 page of the "openssl x509" commandline tool for details. The old behaviour
385 has however been left as default for the sake of compatibility.
387 [BUILD] =======================================================================
389 * Why does the linker complain about undefined symbols?
391 Maybe the compilation was interrupted, and make doesn't notice that
392 something is missing. Run "make clean; make".
394 If you used ./Configure instead of ./config, make sure that you
395 selected the right target. File formats may differ slightly between
396 OS versions (for example sparcv8/sparcv9, or a.out/elf).
398 In case you get errors about the following symbols, use the config
399 option "no-asm", as described in INSTALL:
401 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
402 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
403 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
404 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
405 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
406 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
407 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
409 If none of these helps, you may want to try using the current snapshot.
410 If the problem persists, please submit a bug report.
413 * Why does the OpenSSL test fail with "bc: command not found"?
415 You didn't install "bc", the Unix calculator. If you want to run the
416 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
419 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
421 On some SCO installations or versions, bc has a bug that gets triggered
422 when you run the test suite (using "make test"). The message returned is
423 "bc: 1 not implemented".
425 The best way to deal with this is to find another implementation of bc
426 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
427 for download instructions) can be safely used, for example.
430 * Why does the OpenSSL test fail with "bc: stack empty"?
432 On some DG/ux versions, bc seems to have a too small stack for calculations
433 that the OpenSSL bntest throws at it. This gets triggered when you run the
434 test suite (using "make test"). The message returned is "bc: stack empty".
436 The best way to deal with this is to find another implementation of bc
437 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
438 for download instructions) can be safely used, for example.
441 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
443 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
444 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
445 memory to continue compilation.' As far as the tests have shown, this may be
446 a compiler bug. What happens is that it eats up a lot of resident memory
447 to build something, probably a table. The problem is clearly in the
448 optimization code, because if one eliminates optimization completely (-O0),
449 the compilation goes through (and the compiler consumes about 2MB of resident
450 memory instead of 240MB or whatever one's limit is currently).
452 There are three options to solve this problem:
454 1. set your current data segment size soft limit higher. Experience shows
455 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
456 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
457 kbytes to set the limit to.
459 2. If you have a hard limit that is lower than what you need and you can't
460 get it changed, you can compile all of OpenSSL with -O0 as optimization
461 level. This is however not a very nice thing to do for those who expect to
462 get the best result from OpenSSL. A bit more complicated solution is the
465 ----- snip:start -----
466 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
467 sed -e 's/ -O[0-9] / -O0 /'`"
468 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
472 This will only compile sha_dgst.c with -O0, the rest with the optimization
473 level chosen by the configuration process. When the above is done, do the
474 test and installation and you're set.
476 3. Reconfigure the toolkit with no-sha0 option to leave out SHA0. It
477 should not be used and is not used in SSL/TLS nor any other recognized
478 protocol in either case.
481 * Why does the OpenSSL compilation fail with "ar: command not found"?
483 Getting this message is quite usual on Solaris 2, because Sun has hidden
484 away 'ar' and other development commands in directories that aren't in
485 $PATH by default. One of those directories is '/usr/ccs/bin'. The
486 quickest way to fix this is to do the following (it assumes you use sh
487 or any sh-compatible shell):
489 ----- snip:start -----
490 PATH=${PATH}:/usr/ccs/bin; export PATH
493 and then redo the compilation. What you should really do is make sure
494 '/usr/ccs/bin' is permanently in your $PATH, for example through your
495 '.profile' (again, assuming you use a sh-compatible shell).
498 * Why does the OpenSSL compilation fail on Win32 with VC++?
500 Sometimes, you may get reports from VC++ command line (cl) that it
501 can't find standard include files like stdio.h and other weirdnesses.
502 One possible cause is that the environment isn't correctly set up.
503 To solve that problem for VC++ versions up to 6, one should run
504 VCVARS32.BAT which is found in the 'bin' subdirectory of the VC++
505 installation directory (somewhere under 'Program Files'). For VC++
506 version 7 (and up?), which is also called VS.NET, the file is called
507 VSVARS32.BAT instead.
508 This needs to be done prior to running NMAKE, and the changes are only
509 valid for the current DOS session.
512 * What is special about OpenSSL on Redhat?
514 Red Hat Linux (release 7.0 and later) include a preinstalled limited
515 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
516 is disabled in this version. The same may apply to other Linux distributions.
517 Users may therefore wish to install more or all of the features left out.
519 To do this you MUST ensure that you do not overwrite the openssl that is in
520 /usr/bin on your Red Hat machine. Several packages depend on this file,
521 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
522 libraries that come with Red Hat 7.0 onwards have different names and so are
523 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
524 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
525 /lib/libcrypto.so.2 respectively).
527 Please note that we have been advised by Red Hat attempting to recompile the
528 openssl rpm with all the cryptography enabled will not work. All other
529 packages depend on the original Red Hat supplied openssl package. It is also
530 worth noting that due to the way Red Hat supplies its packages, updates to
531 openssl on each distribution never change the package version, only the
532 build number. For example, on Red Hat 7.1, the latest openssl package has
533 version number 0.9.6 and build number 9 even though it contains all the
534 relevant updates in packages up to and including 0.9.6b.
536 A possible way around this is to persuade Red Hat to produce a non-US
537 version of Red Hat Linux.
539 FYI: Patent numbers and expiry dates of US patents:
540 MDC-2: 4,908,861 13/03/2007
541 IDEA: 5,214,703 25/05/2010
542 RC5: 5,724,428 03/03/2015
545 * Why does the OpenSSL compilation fail on MacOS X?
547 If the failure happens when trying to build the "openssl" binary, with
548 a large number of undefined symbols, it's very probable that you have
549 OpenSSL 0.9.6b delivered with the operating system (you can find out by
550 running '/usr/bin/openssl version') and that you were trying to build
551 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
552 MacOS X has a misfeature that's quite difficult to go around.
553 Look in the file PROBLEMS for a more detailed explanation and for possible
557 * Why does the OpenSSL test suite fail on MacOS X?
559 If the failure happens when running 'make test' and the RC4 test fails,
560 it's very probable that you have OpenSSL 0.9.6b delivered with the
561 operating system (you can find out by running '/usr/bin/openssl version')
562 and that you were trying to build OpenSSL 0.9.6d. The problem is that
563 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
564 go around and has linked the programs "openssl" and the test programs
565 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
566 libraries you just built.
567 Look in the file PROBLEMS for a more detailed explanation and for possible
570 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
572 Failure in BN_sqr test is most likely caused by a failure to configure the
573 toolkit for current platform or lack of support for the platform in question.
574 Run './config -t' and './apps/openssl version -p'. Do these platform
575 identifiers match? If they don't, then you most likely failed to run
576 ./config and you're hereby advised to do so before filing a bug report.
577 If ./config itself fails to run, then it's most likely problem with your
578 local environment and you should turn to your system administrator (or
579 similar). If identifiers match (and/or no alternative identifier is
580 suggested by ./config script), then the platform is unsupported. There might
581 or might not be a workaround. Most notably on SPARC64 platforms with GNU
582 C compiler you should be able to produce a working build by running
583 './config -m32'. I understand that -m32 might not be what you want/need,
584 but the build should be operational. For further details turn to
585 <openssl-dev@openssl.org>.
587 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"?
589 As of 0.9.7 assembler routines were overhauled for position independence
590 of the machine code, which is essential for shared library support. For
591 some reason OpenBSD is equipped with an out-of-date GNU assembler which
592 finds the new code offensive. To work around the problem, configure with
593 no-asm (and sacrifice a great deal of performance) or patch your assembler
594 according to <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.patch>.
595 For your convenience a pre-compiled replacement binary is provided at
596 <URL: http://www.openssl.org/~appro/gas-1.92.3.static.aout.bin>.
597 Reportedly elder *BSD a.out platforms also suffer from this problem and
598 remedy should be same. Provided binary is statically linked and should be
599 working across wider range of *BSD branches, not just OpenBSD.
601 [PROG] ========================================================================
603 * Is OpenSSL thread-safe?
605 Yes (with limitations: an SSL connection may not concurrently be used
606 by multiple threads). On Windows and many Unix systems, OpenSSL
607 automatically uses the multi-threaded versions of the standard
608 libraries. If your platform is not one of these, consult the INSTALL
611 Multi-threaded applications must provide two callback functions to
612 OpenSSL. This is described in the threads(3) manpage.
615 * I've compiled a program under Windows and it crashes: why?
617 This is usually because you've missed the comment in INSTALL.W32.
618 Your application must link against the same version of the Win32
619 C-Runtime against which your openssl libraries were linked. The
620 default version for OpenSSL is /MD - "Multithreaded DLL".
622 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
623 many cases, your new project most likely defaulted to "Debug
624 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
625 program will crash, typically on the first BIO related read or write
628 For each of the six possible link stage configurations within Win32,
629 your application must link against the same by which OpenSSL was
630 built. If you are using MS Visual C++ (Studio) this can be changed
633 1. Select Settings... from the Project Menu.
634 2. Select the C/C++ Tab.
635 3. Select "Code Generation from the "Category" drop down list box
636 4. Select the Appropriate library (see table below) from the "Use
637 run-time library" drop down list box. Perform this step for both
638 your debug and release versions of your application (look at the
639 top left of the settings panel to change between the two)
641 Single Threaded /ML - MS VC++ often defaults to
643 version of a new project.
644 Debug Single Threaded /MLd - MS VC++ often defaults to
645 this for the debug version
648 Debug Multithreaded /MTd
649 Multithreaded DLL /MD - OpenSSL defaults to this.
650 Debug Multithreaded DLL /MDd
652 Note that debug and release libraries are NOT interchangeable. If you
653 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
656 * How do I read or write a DER encoded buffer using the ASN1 functions?
658 You have two options. You can either use a memory BIO in conjunction
659 with the i2d_*_bio() or d2i_*_bio() functions or you can use the
660 i2d_*(), d2i_*() functions directly. Since these are often the
661 cause of grief here are some code fragments using PKCS7 as an example:
663 unsigned char *buf, *p;
666 len = i2d_PKCS7(p7, NULL);
667 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
671 At this point buf contains the len bytes of the DER encoding of
674 The opposite assumes we already have len bytes in buf:
678 p7 = d2i_PKCS7(NULL, &p, len);
680 At this point p7 contains a valid PKCS7 structure of NULL if an error
681 occurred. If an error occurred ERR_print_errors(bio) should give more
684 The reason for the temporary variable 'p' is that the ASN1 functions
685 increment the passed pointer so it is ready to read or write the next
686 structure. This is often a cause of problems: without the temporary
687 variable the buffer pointer is changed to point just after the data
688 that has been read or written. This may well be uninitialized data
689 and attempts to free the buffer will have unpredictable results
690 because it no longer points to the same address.
693 * OpenSSL uses DER but I need BER format: does OpenSSL support BER?
695 The short answer is yes, because DER is a special case of BER and OpenSSL
696 ASN1 decoders can process BER.
698 The longer answer is that ASN1 structures can be encoded in a number of
699 different ways. One set of ways is the Basic Encoding Rules (BER) with various
700 permissible encodings. A restriction of BER is the Distinguished Encoding
701 Rules (DER): these uniquely specify how a given structure is encoded.
703 Therefore, because DER is a special case of BER, DER is an acceptable encoding
707 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
709 This usually happens when you try compiling something using the PKCS#12
710 macros with a C++ compiler. There is hardly ever any need to use the
711 PKCS#12 macros in a program, it is much easier to parse and create
712 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
713 documented in doc/openssl.txt and with examples in demos/pkcs12. The
714 'pkcs12' application has to use the macros because it prints out
715 debugging information.
718 * I've called <some function> and it fails, why?
720 Before submitting a report or asking in one of the mailing lists, you
721 should try to determine the cause. In particular, you should call
722 ERR_print_errors() or ERR_print_errors_fp() after the failed call
723 and see if the message helps. Note that the problem may occur earlier
724 than you think -- you should check for errors after every call where
725 it is possible, otherwise the actual problem may be hidden because
726 some OpenSSL functions clear the error state.
729 * I just get a load of numbers for the error output, what do they mean?
731 The actual format is described in the ERR_print_errors() manual page.
732 You should call the function ERR_load_crypto_strings() before hand and
733 the message will be output in text form. If you can't do this (for example
734 it is a pre-compiled binary) you can use the errstr utility on the error
735 code itself (the hex digits after the second colon).
738 * Why do I get errors about unknown algorithms?
740 This can happen under several circumstances such as reading in an
741 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
742 is forgetting to load OpenSSL's table of algorithms with
743 OpenSSL_add_all_algorithms(). See the manual page for more information.
746 * Why can't the OpenSSH configure script detect OpenSSL?
748 Several reasons for problems with the automatic detection exist.
749 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
750 Sometimes the distribution has installed an older version in the system
751 locations that is detected instead of a new one installed. The OpenSSL
752 library might have been compiled for another CPU or another mode (32/64 bits).
753 Permissions might be wrong.
755 The general answer is to check the config.log file generated when running
756 the OpenSSH configure script. It should contain the detailed information
757 on why the OpenSSL library was not detected or considered incompatible.
760 * Can I use OpenSSL's SSL library with non-blocking I/O?
762 Yes; make sure to read the SSL_get_error(3) manual page!
764 A pitfall to avoid: Don't assume that SSL_read() will just read from
765 the underlying transport or that SSL_write() will just write to it --
766 it is also possible that SSL_write() cannot do any useful work until
767 there is data to read, or that SSL_read() cannot do anything until it
768 is possible to send data. One reason for this is that the peer may
769 request a new TLS/SSL handshake at any time during the protocol,
770 requiring a bi-directional message exchange; both SSL_read() and
771 SSL_write() will try to continue any pending handshake.
774 * Why doesn't my server application receive a client certificate?
776 Due to the TLS protocol definition, a client will only send a certificate,
777 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
778 SSL_CTX_set_verify() function to enable the use of client certificates.
781 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
783 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
784 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
785 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
786 Change your code to use the new name when compiling against OpenSSL 0.9.7.
789 * I think I've detected a memory leak, is this a bug?
791 In most cases the cause of an apparent memory leak is an OpenSSL internal table
792 that is allocated when an application starts up. Since such tables do not grow
793 in size over time they are harmless.
795 These internal tables can be freed up when an application closes using various
796 functions. Currently these include: EVP_cleanup(), ERR_remove_state(),
797 ERR_free_strings(), ENGINE_cleanup(), CONF_modules_unload() and
798 CRYPTO_cleanup_all_ex_data().
801 ===============================================================================