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?
13 * How does the versioning scheme work?
15 [LEGAL] Legal questions
17 * Do I need patent licenses to use OpenSSL?
18 * Can I use OpenSSL with GPL software?
20 [USER] Questions on using the OpenSSL applications
22 * Why do I get a "PRNG not seeded" error message?
23 * Why do I get an "unable to write 'random state'" error message?
24 * How do I create certificates or certificate requests?
25 * Why can't I create certificate requests?
26 * Why does <SSL program> fail with a certificate verify error?
27 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
28 * How can I create DSA certificates?
29 * Why can't I make an SSL connection using a DSA certificate?
30 * How can I remove the passphrase on a private key?
31 * Why can't I use OpenSSL certificates with SSL client authentication?
32 * Why does my browser give a warning about a mismatched hostname?
33 * How do I install a CA certificate into a browser?
34 * Why is OpenSSL x509 DN output not conformant to RFC2253?
35 * What is a "128 bit certificate"? Can I create one with OpenSSL?
36 * Why does OpenSSL set the authority key identifier extension incorrectly?
37 * How can I set up a bundle of commercial root CA certificates?
38 * Some secure servers 'hang' with OpenSSL 1.0.1, is this a bug?
40 [BUILD] Questions about building and testing OpenSSL
42 * Why does the linker complain about undefined symbols?
43 * Why does the OpenSSL test fail with "bc: command not found"?
44 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
45 * Why does the OpenSSL test fail with "bc: stack empty"?
46 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
47 * Why does the OpenSSL compilation fail with "ar: command not found"?
48 * Why does the OpenSSL compilation fail on Win32 with VC++?
49 * What is special about OpenSSL on Redhat?
50 * Why does the OpenSSL compilation fail on MacOS X?
51 * Why does the OpenSSL test suite fail on MacOS X?
52 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
53 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"?
54 * Why does the OpenSSL test suite fail in sha512t on x86 CPU?
55 * Why does compiler fail to compile sha512.c?
56 * Test suite still fails, what to do?
57 * I think I've found a bug, what should I do?
58 * I'm SURE I've found a bug, how do I report it?
59 * I've found a security issue, how do I report it?
61 [PROG] Questions about programming with OpenSSL
63 * Is OpenSSL thread-safe?
64 * I've compiled a program under Windows and it crashes: why?
65 * How do I read or write a DER encoded buffer using the ASN1 functions?
66 * OpenSSL uses DER but I need BER format: does OpenSSL support BER?
67 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
68 * I've called <some function> and it fails, why?
69 * I just get a load of numbers for the error output, what do they mean?
70 * Why do I get errors about unknown algorithms?
71 * Why can't the OpenSSH configure script detect OpenSSL?
72 * Can I use OpenSSL's SSL library with non-blocking I/O?
73 * Why doesn't my server application receive a client certificate?
74 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
75 * I think I've detected a memory leak, is this a bug?
76 * Why does Valgrind complain about the use of uninitialized data?
77 * Why doesn't a memory BIO work when a file does?
78 * Where are the declarations and implementations of d2i_X509() etc?
80 ===============================================================================
82 [MISC] ========================================================================
84 * Which is the current version of OpenSSL?
86 The current version is available from <URL: http://www.openssl.org>.
87 OpenSSL 1.0.1e was released on Feb 11, 2013.
89 In addition to the current stable release, you can also access daily
90 snapshots of the OpenSSL development version at <URL:
91 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous Git access.
94 * Where is the documentation?
96 OpenSSL is a library that provides cryptographic functionality to
97 applications such as secure web servers. Be sure to read the
98 documentation of the application you want to use. The INSTALL file
99 explains how to install this library.
101 OpenSSL includes a command line utility that can be used to perform a
102 variety of cryptographic functions. It is described in the openssl(1)
103 manpage. Documentation for developers is currently being written. Many
104 manual pages are available; overviews over libcrypto and
105 libssl are given in the crypto(3) and ssl(3) manpages.
107 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
108 different directory if you specified one as described in INSTALL).
109 In addition, you can read the most current versions at
110 <URL: http://www.openssl.org/docs/>. Note that the online documents refer
111 to the very latest development versions of OpenSSL and may include features
112 not present in released versions. If in doubt refer to the documentation
113 that came with the version of OpenSSL you are using. The pod format
114 documentation is included in each OpenSSL distribution under the docs
117 For information on parts of libcrypto that are not yet documented, you
118 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
119 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
120 of this still applies to OpenSSL.
122 There is some documentation about certificate extensions and PKCS#12
125 The original SSLeay documentation is included in OpenSSL as
126 doc/ssleay.txt. It may be useful when none of the other resources
127 help, but please note that it reflects the obsolete version SSLeay
131 * How can I contact the OpenSSL developers?
133 The README file describes how to submit bug reports and patches to
134 OpenSSL. Information on the OpenSSL mailing lists is available from
135 <URL: http://www.openssl.org>.
138 * Where can I get a compiled version of OpenSSL?
140 You can finder pointers to binary distributions in
141 <URL: http://www.openssl.org/related/binaries.html> .
143 Some applications that use OpenSSL are distributed in binary form.
144 When using such an application, you don't need to install OpenSSL
145 yourself; the application will include the required parts (e.g. DLLs).
147 If you want to build OpenSSL on a Windows system and you don't have
148 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
149 on how to obtain and install the free GNU C compiler.
151 A number of Linux and *BSD distributions include OpenSSL.
154 * Why aren't tools like 'autoconf' and 'libtool' used?
156 autoconf will probably be used in future OpenSSL versions. If it was
157 less Unix-centric, it might have been used much earlier.
159 * What is an 'engine' version?
161 With version 0.9.6 OpenSSL was extended to interface to external crypto
162 hardware. This was realized in a special release '0.9.6-engine'. With
163 version 0.9.7 the changes were merged into the main development line,
164 so that the special release is no longer necessary.
166 * How do I check the authenticity of the OpenSSL distribution?
168 We provide MD5 digests and ASC signatures of each tarball.
169 Use MD5 to check that a tarball from a mirror site is identical:
171 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
173 You can check authenticity using pgp or gpg. You need the OpenSSL team
174 member public key used to sign it (download it from a key server, see a
175 list of keys at <URL: http://www.openssl.org/about/>). Then
180 * How does the versioning scheme work?
182 After the release of OpenSSL 1.0.0 the versioning scheme changed. Letter
183 releases (e.g. 1.0.1a) can only contain bug and security fixes and no
184 new features. Minor releases change the last number (e.g. 1.0.2) and
185 can contain new features that retain binary compatibility. Changes to
186 the middle number are considered major releases and neither source nor
187 binary compatibility is guaranteed.
189 Therefore the answer to the common question "when will feature X be
190 backported to OpenSSL 1.0.0/0.9.8?" is "never" but it could appear
191 in the next minor release.
193 * What happens when the letter release reaches z?
195 It was decided after the release of OpenSSL 0.9.8y the next version should
196 be 0.9.8za then 0.9.8zb and so on.
199 [LEGAL] =======================================================================
201 * Do I need patent licenses to use OpenSSL?
203 The patents section of the README file lists patents that may apply to
204 you if you want to use OpenSSL. For information on intellectual
205 property rights, please consult a lawyer. The OpenSSL team does not
208 You can configure OpenSSL so as not to use IDEA, MDC2 and RC5 by using
209 ./config no-idea no-mdc2 no-rc5
212 * Can I use OpenSSL with GPL software?
214 On many systems including the major Linux and BSD distributions, yes (the
215 GPL does not place restrictions on using libraries that are part of the
216 normal operating system distribution).
218 On other systems, the situation is less clear. Some GPL software copyright
219 holders claim that you infringe on their rights if you use OpenSSL with
220 their software on operating systems that don't normally include OpenSSL.
222 If you develop open source software that uses OpenSSL, you may find it
223 useful to choose an other license than the GPL, or state explicitly that
224 "This program is released under the GPL with the additional exemption that
225 compiling, linking, and/or using OpenSSL is allowed." If you are using
226 GPL software developed by others, you may want to ask the copyright holder
227 for permission to use their software with OpenSSL.
230 [USER] ========================================================================
232 * Why do I get a "PRNG not seeded" error message?
234 Cryptographic software needs a source of unpredictable data to work
235 correctly. Many open source operating systems provide a "randomness
236 device" (/dev/urandom or /dev/random) that serves this purpose.
237 All OpenSSL versions try to use /dev/urandom by default; starting with
238 version 0.9.7, OpenSSL also tries /dev/random if /dev/urandom is not
241 On other systems, applications have to call the RAND_add() or
242 RAND_seed() function with appropriate data before generating keys or
243 performing public key encryption. (These functions initialize the
244 pseudo-random number generator, PRNG.) Some broken applications do
245 not do this. As of version 0.9.5, the OpenSSL functions that need
246 randomness report an error if the random number generator has not been
247 seeded with at least 128 bits of randomness. If this error occurs and
248 is not discussed in the documentation of the application you are
249 using, please contact the author of that application; it is likely
250 that it never worked correctly. OpenSSL 0.9.5 and later make the
251 error visible by refusing to perform potentially insecure encryption.
253 If you are using Solaris 8, you can add /dev/urandom and /dev/random
254 devices by installing patch 112438 (Sparc) or 112439 (x86), which are
255 available via the Patchfinder at <URL: http://sunsolve.sun.com>
256 (Solaris 9 includes these devices by default). For /dev/random support
257 for earlier Solaris versions, see Sun's statement at
258 <URL: http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski>
259 (the SUNWski package is available in patch 105710).
261 On systems without /dev/urandom and /dev/random, it is a good idea to
262 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
263 details. Starting with version 0.9.7, OpenSSL will automatically look
264 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
267 Most components of the openssl command line utility automatically try
268 to seed the random number generator from a file. The name of the
269 default seeding file is determined as follows: If environment variable
270 RANDFILE is set, then it names the seeding file. Otherwise if
271 environment variable HOME is set, then the seeding file is $HOME/.rnd.
272 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
273 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
274 default seeding file at all. OpenSSL 0.9.6b and later will behave
275 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
276 Windows systems if the environment variable has not been set.
278 If the default seeding file does not exist or is too short, the "PRNG
279 not seeded" error message may occur.
281 The openssl command line utility will write back a new state to the
282 default seeding file (and create this file if necessary) unless
283 there was no sufficient seeding.
285 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
286 Use the "-rand" option of the OpenSSL command line tools instead.
287 The $RANDFILE environment variable and $HOME/.rnd are only used by the
288 OpenSSL command line tools. Applications using the OpenSSL library
289 provide their own configuration options to specify the entropy source,
290 please check out the documentation coming the with application.
293 * Why do I get an "unable to write 'random state'" error message?
296 Sometimes the openssl command line utility does not abort with
297 a "PRNG not seeded" error message, but complains that it is
298 "unable to write 'random state'". This message refers to the
299 default seeding file (see previous answer). A possible reason
300 is that no default filename is known because neither RANDFILE
301 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
302 current directory in this case, but this has changed with 0.9.6a.)
305 * How do I create certificates or certificate requests?
307 Check out the CA.pl(1) manual page. This provides a simple wrapper round
308 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
309 out the manual pages for the individual utilities and the certificate
310 extensions documentation (in ca(1), req(1), x509v3_config(5) )
313 * Why can't I create certificate requests?
315 You typically get the error:
317 unable to find 'distinguished_name' in config
318 problems making Certificate Request
320 This is because it can't find the configuration file. Check out the
321 DIAGNOSTICS section of req(1) for more information.
324 * Why does <SSL program> fail with a certificate verify error?
326 This problem is usually indicated by log messages saying something like
327 "unable to get local issuer certificate" or "self signed certificate".
328 When a certificate is verified its root CA must be "trusted" by OpenSSL
329 this typically means that the CA certificate must be placed in a directory
330 or file and the relevant program configured to read it. The OpenSSL program
331 'verify' behaves in a similar way and issues similar error messages: check
332 the verify(1) program manual page for more information.
335 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
337 This is almost certainly because you are using an old "export grade" browser
338 which only supports weak encryption. Upgrade your browser to support 128 bit
342 * How can I create DSA certificates?
344 Check the CA.pl(1) manual page for a DSA certificate example.
347 * Why can't I make an SSL connection to a server using a DSA certificate?
349 Typically you'll see a message saying there are no shared ciphers when
350 the same setup works fine with an RSA certificate. There are two possible
351 causes. The client may not support connections to DSA servers most web
352 browsers (including Netscape and MSIE) only support connections to servers
353 supporting RSA cipher suites. The other cause is that a set of DH parameters
354 has not been supplied to the server. DH parameters can be created with the
355 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
356 check the source to s_server in apps/s_server.c for an example.
359 * How can I remove the passphrase on a private key?
361 Firstly you should be really *really* sure you want to do this. Leaving
362 a private key unencrypted is a major security risk. If you decide that
363 you do have to do this check the EXAMPLES sections of the rsa(1) and
367 * Why can't I use OpenSSL certificates with SSL client authentication?
369 What will typically happen is that when a server requests authentication
370 it will either not include your certificate or tell you that you have
371 no client certificates (Netscape) or present you with an empty list box
372 (MSIE). The reason for this is that when a server requests a client
373 certificate it includes a list of CAs names which it will accept. Browsers
374 will only let you select certificates from the list on the grounds that
375 there is little point presenting a certificate which the server will
378 The solution is to add the relevant CA certificate to your servers "trusted
379 CA list". How you do this depends on the server software in uses. You can
380 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
382 openssl s_client -connect www.some.host:443 -prexit
384 If your server only requests certificates on certain URLs then you may need
385 to manually issue an HTTP GET command to get the list when s_client connects:
387 GET /some/page/needing/a/certificate.html
389 If your CA does not appear in the list then this confirms the problem.
392 * Why does my browser give a warning about a mismatched hostname?
394 Browsers expect the server's hostname to match the value in the commonName
395 (CN) field of the certificate. If it does not then you get a warning.
398 * How do I install a CA certificate into a browser?
400 The usual way is to send the DER encoded certificate to the browser as
401 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
402 link. On MSIE certain extensions such as .der or .cacert may also work, or you
403 can import the certificate using the certificate import wizard.
405 You can convert a certificate to DER form using the command:
407 openssl x509 -in ca.pem -outform DER -out ca.der
409 Occasionally someone suggests using a command such as:
411 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
413 DO NOT DO THIS! This command will give away your CAs private key and
414 reduces its security to zero: allowing anyone to forge certificates in
415 whatever name they choose.
417 * Why is OpenSSL x509 DN output not conformant to RFC2253?
419 The ways to print out the oneline format of the DN (Distinguished Name) have
420 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
421 interface, the "-nameopt" option could be introduded. See the manual
422 page of the "openssl x509" commandline tool for details. The old behaviour
423 has however been left as default for the sake of compatibility.
425 * What is a "128 bit certificate"? Can I create one with OpenSSL?
427 The term "128 bit certificate" is a highly misleading marketing term. It does
428 *not* refer to the size of the public key in the certificate! A certificate
429 containing a 128 bit RSA key would have negligible security.
431 There were various other names such as "magic certificates", "SGC
432 certificates", "step up certificates" etc.
434 You can't generally create such a certificate using OpenSSL but there is no
435 need to any more. Nowadays web browsers using unrestricted strong encryption
436 are generally available.
438 When there were tight restrictions on the export of strong encryption
439 software from the US only weak encryption algorithms could be freely exported
440 (initially 40 bit and then 56 bit). It was widely recognised that this was
441 inadequate. A relaxation of the rules allowed the use of strong encryption but
442 only to an authorised server.
444 Two slighly different techniques were developed to support this, one used by
445 Netscape was called "step up", the other used by MSIE was called "Server Gated
446 Cryptography" (SGC). When a browser initially connected to a server it would
447 check to see if the certificate contained certain extensions and was issued by
448 an authorised authority. If these test succeeded it would reconnect using
451 Only certain (initially one) certificate authorities could issue the
452 certificates and they generally cost more than ordinary certificates.
454 Although OpenSSL can create certificates containing the appropriate extensions
455 the certificate would not come from a permitted authority and so would not
458 The export laws were later changed to allow almost unrestricted use of strong
459 encryption so these certificates are now obsolete.
462 * Why does OpenSSL set the authority key identifier (AKID) extension incorrectly?
464 It doesn't: this extension is often the cause of confusion.
466 Consider a certificate chain A->B->C so that A signs B and B signs C. Suppose
467 certificate C contains AKID.
469 The purpose of this extension is to identify the authority certificate B. This
470 can be done either by including the subject key identifier of B or its issuer
471 name and serial number.
473 In this latter case because it is identifying certifcate B it must contain the
474 issuer name and serial number of B.
476 It is often wrongly assumed that it should contain the subject name of B. If it
477 did this would be redundant information because it would duplicate the issuer
481 * How can I set up a bundle of commercial root CA certificates?
483 The OpenSSL software is shipped without any root CA certificate as the
484 OpenSSL project does not have any policy on including or excluding
485 any specific CA and does not intend to set up such a policy. Deciding
486 about which CAs to support is up to application developers or
489 Other projects do have other policies so you can for example extract the CA
490 bundle used by Mozilla and/or modssl as described in this article:
492 <URL: http://www.mail-archive.com/modssl-users@modssl.org/msg16980.html>
495 * Some secure servers 'hang' with OpenSSL 1.0.1, is this a bug?
497 OpenSSL 1.0.1 is the first release to support TLS 1.2, among other things,
498 this increases the size of the default ClientHello message to more than
499 255 bytes in length. Some software cannot handle this and hangs. For more
500 details and workarounds see:
502 <URL: http://rt.openssl.org/Ticket/Display.html?user=guest&pass=guest&id=2771>
505 [BUILD] =======================================================================
507 * Why does the linker complain about undefined symbols?
509 Maybe the compilation was interrupted, and make doesn't notice that
510 something is missing. Run "make clean; make".
512 If you used ./Configure instead of ./config, make sure that you
513 selected the right target. File formats may differ slightly between
514 OS versions (for example sparcv8/sparcv9, or a.out/elf).
516 In case you get errors about the following symbols, use the config
517 option "no-asm", as described in INSTALL:
519 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
520 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
521 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
522 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
523 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
524 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
525 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
527 If none of these helps, you may want to try using the current snapshot.
528 If the problem persists, please submit a bug report.
531 * Why does the OpenSSL test fail with "bc: command not found"?
533 You didn't install "bc", the Unix calculator. If you want to run the
534 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
537 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
539 On some SCO installations or versions, bc has a bug that gets triggered
540 when you run the test suite (using "make test"). The message returned is
541 "bc: 1 not implemented".
543 The best way to deal with this is to find another implementation of bc
544 and compile/install it. GNU bc (see <URL: http://www.gnu.org/software/software.html>
545 for download instructions) can be safely used, for example.
548 * Why does the OpenSSL test fail with "bc: stack empty"?
550 On some DG/ux versions, bc seems to have a too small stack for calculations
551 that the OpenSSL bntest throws at it. This gets triggered when you run the
552 test suite (using "make test"). The message returned is "bc: stack empty".
554 The best way to deal with this is to find another implementation of bc
555 and compile/install it. GNU bc (see <URL: http://www.gnu.org/software/software.html>
556 for download instructions) can be safely used, for example.
559 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
561 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
562 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
563 memory to continue compilation.' As far as the tests have shown, this may be
564 a compiler bug. What happens is that it eats up a lot of resident memory
565 to build something, probably a table. The problem is clearly in the
566 optimization code, because if one eliminates optimization completely (-O0),
567 the compilation goes through (and the compiler consumes about 2MB of resident
568 memory instead of 240MB or whatever one's limit is currently).
570 There are three options to solve this problem:
572 1. set your current data segment size soft limit higher. Experience shows
573 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
574 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
575 kbytes to set the limit to.
577 2. If you have a hard limit that is lower than what you need and you can't
578 get it changed, you can compile all of OpenSSL with -O0 as optimization
579 level. This is however not a very nice thing to do for those who expect to
580 get the best result from OpenSSL. A bit more complicated solution is the
583 ----- snip:start -----
584 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
585 sed -e 's/ -O[0-9] / -O0 /'`"
586 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
590 This will only compile sha_dgst.c with -O0, the rest with the optimization
591 level chosen by the configuration process. When the above is done, do the
592 test and installation and you're set.
594 3. Reconfigure the toolkit with no-sha0 option to leave out SHA0. It
595 should not be used and is not used in SSL/TLS nor any other recognized
596 protocol in either case.
599 * Why does the OpenSSL compilation fail with "ar: command not found"?
601 Getting this message is quite usual on Solaris 2, because Sun has hidden
602 away 'ar' and other development commands in directories that aren't in
603 $PATH by default. One of those directories is '/usr/ccs/bin'. The
604 quickest way to fix this is to do the following (it assumes you use sh
605 or any sh-compatible shell):
607 ----- snip:start -----
608 PATH=${PATH}:/usr/ccs/bin; export PATH
611 and then redo the compilation. What you should really do is make sure
612 '/usr/ccs/bin' is permanently in your $PATH, for example through your
613 '.profile' (again, assuming you use a sh-compatible shell).
616 * Why does the OpenSSL compilation fail on Win32 with VC++?
618 Sometimes, you may get reports from VC++ command line (cl) that it
619 can't find standard include files like stdio.h and other weirdnesses.
620 One possible cause is that the environment isn't correctly set up.
621 To solve that problem for VC++ versions up to 6, one should run
622 VCVARS32.BAT which is found in the 'bin' subdirectory of the VC++
623 installation directory (somewhere under 'Program Files'). For VC++
624 version 7 (and up?), which is also called VS.NET, the file is called
625 VSVARS32.BAT instead.
626 This needs to be done prior to running NMAKE, and the changes are only
627 valid for the current DOS session.
630 * What is special about OpenSSL on Redhat?
632 Red Hat Linux (release 7.0 and later) include a preinstalled limited
633 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
634 is disabled in this version. The same may apply to other Linux distributions.
635 Users may therefore wish to install more or all of the features left out.
637 To do this you MUST ensure that you do not overwrite the openssl that is in
638 /usr/bin on your Red Hat machine. Several packages depend on this file,
639 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
640 libraries that come with Red Hat 7.0 onwards have different names and so are
641 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
642 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
643 /lib/libcrypto.so.2 respectively).
645 Please note that we have been advised by Red Hat attempting to recompile the
646 openssl rpm with all the cryptography enabled will not work. All other
647 packages depend on the original Red Hat supplied openssl package. It is also
648 worth noting that due to the way Red Hat supplies its packages, updates to
649 openssl on each distribution never change the package version, only the
650 build number. For example, on Red Hat 7.1, the latest openssl package has
651 version number 0.9.6 and build number 9 even though it contains all the
652 relevant updates in packages up to and including 0.9.6b.
654 A possible way around this is to persuade Red Hat to produce a non-US
655 version of Red Hat Linux.
657 FYI: Patent numbers and expiry dates of US patents:
658 MDC-2: 4,908,861 13/03/2007
659 IDEA: 5,214,703 25/05/2010
660 RC5: 5,724,428 03/03/2015
663 * Why does the OpenSSL compilation fail on MacOS X?
665 If the failure happens when trying to build the "openssl" binary, with
666 a large number of undefined symbols, it's very probable that you have
667 OpenSSL 0.9.6b delivered with the operating system (you can find out by
668 running '/usr/bin/openssl version') and that you were trying to build
669 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
670 MacOS X has a misfeature that's quite difficult to go around.
671 Look in the file PROBLEMS for a more detailed explanation and for possible
675 * Why does the OpenSSL test suite fail on MacOS X?
677 If the failure happens when running 'make test' and the RC4 test fails,
678 it's very probable that you have OpenSSL 0.9.6b delivered with the
679 operating system (you can find out by running '/usr/bin/openssl version')
680 and that you were trying to build OpenSSL 0.9.6d. The problem is that
681 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
682 go around and has linked the programs "openssl" and the test programs
683 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
684 libraries you just built.
685 Look in the file PROBLEMS for a more detailed explanation and for possible
688 * Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]?
690 Failure in BN_sqr test is most likely caused by a failure to configure the
691 toolkit for current platform or lack of support for the platform in question.
692 Run './config -t' and './apps/openssl version -p'. Do these platform
693 identifiers match? If they don't, then you most likely failed to run
694 ./config and you're hereby advised to do so before filing a bug report.
695 If ./config itself fails to run, then it's most likely problem with your
696 local environment and you should turn to your system administrator (or
697 similar). If identifiers match (and/or no alternative identifier is
698 suggested by ./config script), then the platform is unsupported. There might
699 or might not be a workaround. Most notably on SPARC64 platforms with GNU
700 C compiler you should be able to produce a working build by running
701 './config -m32'. I understand that -m32 might not be what you want/need,
702 but the build should be operational. For further details turn to
703 <openssl-dev@openssl.org>.
705 * Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"?
707 As of 0.9.7 assembler routines were overhauled for position independence
708 of the machine code, which is essential for shared library support. For
709 some reason OpenBSD is equipped with an out-of-date GNU assembler which
710 finds the new code offensive. To work around the problem, configure with
711 no-asm (and sacrifice a great deal of performance) or patch your assembler
712 according to <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.patch>.
713 For your convenience a pre-compiled replacement binary is provided at
714 <URL: http://www.openssl.org/~appro/gas-1.92.3.static.aout.bin>.
715 Reportedly elder *BSD a.out platforms also suffer from this problem and
716 remedy should be same. Provided binary is statically linked and should be
717 working across wider range of *BSD branches, not just OpenBSD.
719 * Why does the OpenSSL test suite fail in sha512t on x86 CPU?
721 If the test program in question fails withs SIGILL, Illegal Instruction
722 exception, then you more than likely to run SSE2-capable CPU, such as
723 Intel P4, under control of kernel which does not support SSE2
724 instruction extensions. See accompanying INSTALL file and
725 OPENSSL_ia32cap(3) documentation page for further information.
727 * Why does compiler fail to compile sha512.c?
729 OpenSSL SHA-512 implementation depends on compiler support for 64-bit
730 integer type. Few elder compilers [ULTRIX cc, SCO compiler to mention a
731 couple] lack support for this and therefore are incapable of compiling
732 the module in question. The recommendation is to disable SHA-512 by
733 adding no-sha512 to ./config [or ./Configure] command line. Another
734 possible alternative might be to switch to GCC.
736 * Test suite still fails, what to do?
738 Another common reason for failure to complete some particular test is
739 simply bad code generated by a buggy component in toolchain or deficiency
740 in run-time environment. There are few cases documented in PROBLEMS file,
741 consult it for possible workaround before you beat the drum. Even if you
742 don't find solution or even mention there, do reserve for possibility of
743 a compiler bug. Compiler bugs might appear in rather bizarre ways, they
744 never make sense, and tend to emerge when you least expect them. In order
745 to identify one, drop optimization level, e.g. by editing CFLAG line in
746 top-level Makefile, recompile and re-run the test.
748 * I think I've found a bug, what should I do?
750 If you are a new user then it is quite likely you haven't found a bug and
751 something is happening you aren't familiar with. Check this FAQ, the associated
752 documentation and the mailing lists for similar queries. If you are still
753 unsure whether it is a bug or not submit a query to the openssl-users mailing
757 * I'm SURE I've found a bug, how do I report it?
759 Bug reports with no security implications should be sent to the request
760 tracker. This can be done by mailing the report to <rt@openssl.org> (or its
761 alias <openssl-bugs@openssl.org>), please note that messages sent to the
762 request tracker also appear in the public openssl-dev mailing list.
764 The report should be in plain text. Any patches should be sent as
765 plain text attachments because some mailers corrupt patches sent inline.
766 If your issue affects multiple versions of OpenSSL check any patches apply
767 cleanly and, if possible include patches to each affected version.
769 The report should be given a meaningful subject line briefly summarising the
770 issue. Just "bug in OpenSSL" or "bug in OpenSSL 0.9.8n" is not very helpful.
772 By sending reports to the request tracker the bug can then be given a priority
773 and assigned to the appropriate maintainer. The history of discussions can be
774 accessed and if the issue has been addressed or a reason why not. If patches
775 are only sent to openssl-dev they can be mislaid if a team member has to
776 wade through months of old messages to review the discussion.
778 See also <URL: http://www.openssl.org/support/rt.html>
781 * I've found a security issue, how do I report it?
783 If you think your bug has security implications then please send it to
784 openssl-security@openssl.org if you don't get a prompt reply at least
785 acknowledging receipt then resend or mail it directly to one of the
786 more active team members (e.g. Steve).
788 [PROG] ========================================================================
790 * Is OpenSSL thread-safe?
792 Yes (with limitations: an SSL connection may not concurrently be used
793 by multiple threads). On Windows and many Unix systems, OpenSSL
794 automatically uses the multi-threaded versions of the standard
795 libraries. If your platform is not one of these, consult the INSTALL
798 Multi-threaded applications must provide two callback functions to
799 OpenSSL by calling CRYPTO_set_locking_callback() and
800 CRYPTO_set_id_callback(), for all versions of OpenSSL up to and
801 including 0.9.8[abc...]. As of version 1.0.0, CRYPTO_set_id_callback()
802 and associated APIs are deprecated by CRYPTO_THREADID_set_callback()
803 and friends. This is described in the threads(3) manpage.
805 * I've compiled a program under Windows and it crashes: why?
807 This is usually because you've missed the comment in INSTALL.W32.
808 Your application must link against the same version of the Win32
809 C-Runtime against which your openssl libraries were linked. The
810 default version for OpenSSL is /MD - "Multithreaded DLL".
812 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
813 many cases, your new project most likely defaulted to "Debug
814 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
815 program will crash, typically on the first BIO related read or write
818 For each of the six possible link stage configurations within Win32,
819 your application must link against the same by which OpenSSL was
820 built. If you are using MS Visual C++ (Studio) this can be changed
823 1. Select Settings... from the Project Menu.
824 2. Select the C/C++ Tab.
825 3. Select "Code Generation from the "Category" drop down list box
826 4. Select the Appropriate library (see table below) from the "Use
827 run-time library" drop down list box. Perform this step for both
828 your debug and release versions of your application (look at the
829 top left of the settings panel to change between the two)
831 Single Threaded /ML - MS VC++ often defaults to
833 version of a new project.
834 Debug Single Threaded /MLd - MS VC++ often defaults to
835 this for the debug version
838 Debug Multithreaded /MTd
839 Multithreaded DLL /MD - OpenSSL defaults to this.
840 Debug Multithreaded DLL /MDd
842 Note that debug and release libraries are NOT interchangeable. If you
843 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
845 As per 0.9.8 the above limitation is eliminated for .DLLs. OpenSSL
846 .DLLs compiled with some specific run-time option [we insist on the
847 default /MD] can be deployed with application compiled with different
848 option or even different compiler. But there is a catch! Instead of
849 re-compiling OpenSSL toolkit, as you would have to with prior versions,
850 you have to compile small C snippet with compiler and/or options of
851 your choice. The snippet gets installed as
852 <install-root>/include/openssl/applink.c and should be either added to
853 your application project or simply #include-d in one [and only one]
854 of your application source files. Failure to link this shim module
855 into your application manifests itself as fatal "no OPENSSL_Applink"
856 run-time error. An explicit reminder is due that in this situation
857 [mixing compiler options] it is as important to add CRYPTO_malloc_init
858 prior first call to OpenSSL.
860 * How do I read or write a DER encoded buffer using the ASN1 functions?
862 You have two options. You can either use a memory BIO in conjunction
863 with the i2d_*_bio() or d2i_*_bio() functions or you can use the
864 i2d_*(), d2i_*() functions directly. Since these are often the
865 cause of grief here are some code fragments using PKCS7 as an example:
867 unsigned char *buf, *p;
870 len = i2d_PKCS7(p7, NULL);
871 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
875 At this point buf contains the len bytes of the DER encoding of
878 The opposite assumes we already have len bytes in buf:
882 p7 = d2i_PKCS7(NULL, &p, len);
884 At this point p7 contains a valid PKCS7 structure or NULL if an error
885 occurred. If an error occurred ERR_print_errors(bio) should give more
888 The reason for the temporary variable 'p' is that the ASN1 functions
889 increment the passed pointer so it is ready to read or write the next
890 structure. This is often a cause of problems: without the temporary
891 variable the buffer pointer is changed to point just after the data
892 that has been read or written. This may well be uninitialized data
893 and attempts to free the buffer will have unpredictable results
894 because it no longer points to the same address.
896 Memory allocation and encoding can also be combined in a single
897 operation by the ASN1 routines:
899 unsigned char *buf = NULL; /* mandatory */
901 len = i2d_PKCS7(p7, &buf);
904 /* Do some things with 'buf' */
905 /* Finished with buf: free it */
908 In this special case the "buf" parameter is *not* incremented, it points
909 to the start of the encoding.
912 * OpenSSL uses DER but I need BER format: does OpenSSL support BER?
914 The short answer is yes, because DER is a special case of BER and OpenSSL
915 ASN1 decoders can process BER.
917 The longer answer is that ASN1 structures can be encoded in a number of
918 different ways. One set of ways is the Basic Encoding Rules (BER) with various
919 permissible encodings. A restriction of BER is the Distinguished Encoding
920 Rules (DER): these uniquely specify how a given structure is encoded.
922 Therefore, because DER is a special case of BER, DER is an acceptable encoding
926 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
928 This usually happens when you try compiling something using the PKCS#12
929 macros with a C++ compiler. There is hardly ever any need to use the
930 PKCS#12 macros in a program, it is much easier to parse and create
931 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
932 documented in doc/openssl.txt and with examples in demos/pkcs12. The
933 'pkcs12' application has to use the macros because it prints out
934 debugging information.
937 * I've called <some function> and it fails, why?
939 Before submitting a report or asking in one of the mailing lists, you
940 should try to determine the cause. In particular, you should call
941 ERR_print_errors() or ERR_print_errors_fp() after the failed call
942 and see if the message helps. Note that the problem may occur earlier
943 than you think -- you should check for errors after every call where
944 it is possible, otherwise the actual problem may be hidden because
945 some OpenSSL functions clear the error state.
948 * I just get a load of numbers for the error output, what do they mean?
950 The actual format is described in the ERR_print_errors() manual page.
951 You should call the function ERR_load_crypto_strings() before hand and
952 the message will be output in text form. If you can't do this (for example
953 it is a pre-compiled binary) you can use the errstr utility on the error
954 code itself (the hex digits after the second colon).
957 * Why do I get errors about unknown algorithms?
959 The cause is forgetting to load OpenSSL's table of algorithms with
960 OpenSSL_add_all_algorithms(). See the manual page for more information. This
961 can cause several problems such as being unable to read in an encrypted
962 PEM file, unable to decrypt a PKCS#12 file or signature failure when
963 verifying certificates.
965 * Why can't the OpenSSH configure script detect OpenSSL?
967 Several reasons for problems with the automatic detection exist.
968 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
969 Sometimes the distribution has installed an older version in the system
970 locations that is detected instead of a new one installed. The OpenSSL
971 library might have been compiled for another CPU or another mode (32/64 bits).
972 Permissions might be wrong.
974 The general answer is to check the config.log file generated when running
975 the OpenSSH configure script. It should contain the detailed information
976 on why the OpenSSL library was not detected or considered incompatible.
979 * Can I use OpenSSL's SSL library with non-blocking I/O?
981 Yes; make sure to read the SSL_get_error(3) manual page!
983 A pitfall to avoid: Don't assume that SSL_read() will just read from
984 the underlying transport or that SSL_write() will just write to it --
985 it is also possible that SSL_write() cannot do any useful work until
986 there is data to read, or that SSL_read() cannot do anything until it
987 is possible to send data. One reason for this is that the peer may
988 request a new TLS/SSL handshake at any time during the protocol,
989 requiring a bi-directional message exchange; both SSL_read() and
990 SSL_write() will try to continue any pending handshake.
993 * Why doesn't my server application receive a client certificate?
995 Due to the TLS protocol definition, a client will only send a certificate,
996 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
997 SSL_CTX_set_verify() function to enable the use of client certificates.
1000 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
1002 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
1003 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
1004 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
1005 Change your code to use the new name when compiling against OpenSSL 0.9.7.
1008 * I think I've detected a memory leak, is this a bug?
1010 In most cases the cause of an apparent memory leak is an OpenSSL internal table
1011 that is allocated when an application starts up. Since such tables do not grow
1012 in size over time they are harmless.
1014 These internal tables can be freed up when an application closes using various
1015 functions. Currently these include following:
1017 Thread-local cleanup functions:
1021 Application-global cleanup functions that are aware of usage (and therefore
1024 ENGINE_cleanup() and CONF_modules_unload()
1026 "Brutal" (thread-unsafe) Application-global cleanup functions:
1028 ERR_free_strings(), EVP_cleanup() and CRYPTO_cleanup_all_ex_data().
1031 * Why does Valgrind complain about the use of uninitialized data?
1033 When OpenSSL's PRNG routines are called to generate random numbers the supplied
1034 buffer contents are mixed into the entropy pool: so it technically does not
1035 matter whether the buffer is initialized at this point or not. Valgrind (and
1036 other test tools) will complain about this. When using Valgrind, make sure the
1037 OpenSSL library has been compiled with the PURIFY macro defined (-DPURIFY)
1038 to get rid of these warnings.
1041 * Why doesn't a memory BIO work when a file does?
1043 This can occur in several cases for example reading an S/MIME email message.
1044 The reason is that a memory BIO can do one of two things when all the data
1045 has been read from it.
1047 The default behaviour is to indicate that no more data is available and that
1048 the call should be retried, this is to allow the application to fill up the BIO
1051 Alternatively it can indicate that no more data is available and that EOF has
1054 If a memory BIO is to behave in the same way as a file this second behaviour
1055 is needed. This must be done by calling:
1057 BIO_set_mem_eof_return(bio, 0);
1059 See the manual pages for more details.
1062 * Where are the declarations and implementations of d2i_X509() etc?
1064 These are defined and implemented by macros of the form:
1067 DECLARE_ASN1_FUNCTIONS(X509) and IMPLEMENT_ASN1_FUNCTIONS(X509)
1069 The implementation passes an ASN1 "template" defining the structure into an
1070 ASN1 interpreter using generalised functions such as ASN1_item_d2i().
1073 ===============================================================================