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?
12 [LEGAL] Legal questions
14 * Do I need patent licenses to use OpenSSL?
15 * Can I use OpenSSL with GPL software?
17 [USER] Questions on using the OpenSSL applications
19 * Why do I get a "PRNG not seeded" error message?
20 * How do I create certificates or certificate requests?
21 * Why can't I create certificate requests?
22 * Why does <SSL program> fail with a certificate verify error?
23 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
24 * How can I create DSA certificates?
25 * Why can't I make an SSL connection using a DSA certificate?
26 * How can I remove the passphrase on a private key?
27 * Why can't I use OpenSSL certificates with SSL client authentication?
29 [BUILD] Questions about building and testing OpenSSL
31 * Why does the linker complain about undefined symbols?
32 * Why does the OpenSSL test fail with "bc: command not found"?
33 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
34 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
35 * Why does the OpenSSL compilation fail with "ar: command not found"?
36 * Why does the OpenSSL compilation fail on Win32 with VC++?
38 [PROG] Questions about programming with OpenSSL
40 * Is OpenSSL thread-safe?
41 * I've compiled a program under Windows and it crashes: why?
42 * How do I read or write a DER encoded buffer using the ASN1 functions?
43 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
44 * I've called <some function> and it fails, why?
45 * I just get a load of numbers for the error output, what do they mean?
46 * Why do I get errors about unknown algorithms?
47 * Why can't the OpenSSH configure script detect OpenSSL?
48 * Can I use OpenSSL's SSL library with non-blocking I/O?
50 ===============================================================================
52 [MISC] ========================================================================
54 * Which is the current version of OpenSSL?
56 The current version is available from <URL: http://www.openssl.org>.
57 OpenSSL 0.9.6 was released on September 24th, 2000.
59 In addition to the current stable release, you can also access daily
60 snapshots of the OpenSSL development version at <URL:
61 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
64 * Where is the documentation?
66 OpenSSL is a library that provides cryptographic functionality to
67 applications such as secure web servers. Be sure to read the
68 documentation of the application you want to use. The INSTALL file
69 explains how to install this library.
71 OpenSSL includes a command line utility that can be used to perform a
72 variety of cryptographic functions. It is described in the openssl(1)
73 manpage. Documentation for developers is currently being written. A
74 few manual pages already are available; overviews over libcrypto and
75 libssl are given in the crypto(3) and ssl(3) manpages.
77 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
78 different directory if you specified one as described in INSTALL).
79 In addition, you can read the most current versions at
80 <URL: http://www.openssl.org/docs/>.
82 For information on parts of libcrypto that are not yet documented, you
83 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
84 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
85 of this still applies to OpenSSL.
87 There is some documentation about certificate extensions and PKCS#12
90 The original SSLeay documentation is included in OpenSSL as
91 doc/ssleay.txt. It may be useful when none of the other resources
92 help, but please note that it reflects the obsolete version SSLeay
96 * How can I contact the OpenSSL developers?
98 The README file describes how to submit bug reports and patches to
99 OpenSSL. Information on the OpenSSL mailing lists is available from
100 <URL: http://www.openssl.org>.
103 * Where can I get a compiled version of OpenSSL?
105 Some applications that use OpenSSL are distributed in binary form.
106 When using such an application, you don't need to install OpenSSL
107 yourself; the application will include the required parts (e.g. DLLs).
109 If you want to install OpenSSL on a Windows system and you don't have
110 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
111 on how to obtain and install the free GNU C compiler.
113 A number of Linux and *BSD distributions include OpenSSL.
116 * Why aren't tools like 'autoconf' and 'libtool' used?
118 autoconf is a nice tool, but is unfortunately very Unix-centric.
119 Although one can come up with solution to have ports keep in track,
120 there's also some work needed for that, and can be quite painful at
121 times. If there was a 'autoconf'-like tool that generated perl
122 scripts or something similarly general, it would probably be used
123 in OpenSSL much earlier.
125 libtool has repeatadly been reported by some members of the OpenSSL
126 development and others to be a pain to use. So far, those in the
127 development team who have said anything about this have expressed
128 a wish to avoid libtool for that reason.
131 [LEGAL] =======================================================================
133 * Do I need patent licenses to use OpenSSL?
135 The patents section of the README file lists patents that may apply to
136 you if you want to use OpenSSL. For information on intellectual
137 property rights, please consult a lawyer. The OpenSSL team does not
140 You can configure OpenSSL so as not to use RC5 and IDEA by using
141 ./config no-rc5 no-idea
144 * Can I use OpenSSL with GPL software?
146 On many systems including the major Linux and BSD distributions, yes (the
147 GPL does not place restrictions on using libraries that are part of the
148 normal operating system distribution).
150 On other systems, the situation is less clear. Some GPL software copyright
151 holders claim that you infringe on their rights if you use OpenSSL with
152 their software on operating systems that don't normally include OpenSSL.
154 If you develop open source software that uses OpenSSL, you may find it
155 useful to choose an other license than the GPL, or state explicitely that
156 "This program is released under the GPL with the additional exemption that
157 compiling, linking, and/or using OpenSSL is allowed." If you are using
158 GPL software developed by others, you may want to ask the copyright holder
159 for permission to use their software with OpenSSL.
162 [USER] ========================================================================
164 * Why do I get a "PRNG not seeded" error message?
166 Cryptographic software needs a source of unpredictable data to work
167 correctly. Many open source operating systems provide a "randomness
168 device" that serves this purpose. On other systems, applications have
169 to call the RAND_add() or RAND_seed() function with appropriate data
170 before generating keys or performing public key encryption.
172 Some broken applications do not do this. As of version 0.9.5, the
173 OpenSSL functions that need randomness report an error if the random
174 number generator has not been seeded with at least 128 bits of
175 randomness. If this error occurs, please contact the author of the
176 application you are using. It is likely that it never worked
177 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
178 to perform potentially insecure encryption.
180 On systems without /dev/urandom, it is a good idea to use the Entropy
181 Gathering Demon; see the RAND_egd() manpage for details.
183 Most components of the openssl command line tool try to use the
184 file $HOME/.rnd (or $RANDFILE, if this environment variable is set)
185 for seeding the PRNG. If this file does not exist or is too short,
186 the "PRNG not seeded" error message may occur.
188 [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version
189 0.9.5 does not do this and will fail on systems without /dev/urandom
190 when trying to password-encrypt an RSA key! This is a bug in the
191 library; try a later version instead.]
193 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
194 installing the SUNski package from Sun patch 105710-01 (Sparc) which
195 adds a /dev/random device and make sure it gets used, usually through
196 $RANDFILE. There are probably similar patches for the other Solaris
197 versions. However, be warned that /dev/random is usually a blocking
198 device, which may have some effects on OpenSSL.
201 * How do I create certificates or certificate requests?
203 Check out the CA.pl(1) manual page. This provides a simple wrapper round
204 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
205 out the manual pages for the individual utilities and the certificate
206 extensions documentation (currently in doc/openssl.txt).
209 * Why can't I create certificate requests?
211 You typically get the error:
213 unable to find 'distinguished_name' in config
214 problems making Certificate Request
216 This is because it can't find the configuration file. Check out the
217 DIAGNOSTICS section of req(1) for more information.
220 * Why does <SSL program> fail with a certificate verify error?
222 This problem is usually indicated by log messages saying something like
223 "unable to get local issuer certificate" or "self signed certificate".
224 When a certificate is verified its root CA must be "trusted" by OpenSSL
225 this typically means that the CA certificate must be placed in a directory
226 or file and the relevant program configured to read it. The OpenSSL program
227 'verify' behaves in a similar way and issues similar error messages: check
228 the verify(1) program manual page for more information.
231 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
233 This is almost certainly because you are using an old "export grade" browser
234 which only supports weak encryption. Upgrade your browser to support 128 bit
238 * How can I create DSA certificates?
240 Check the CA.pl(1) manual page for a DSA certificate example.
243 * Why can't I make an SSL connection to a server using a DSA certificate?
245 Typically you'll see a message saying there are no shared ciphers when
246 the same setup works fine with an RSA certificate. There are two possible
247 causes. The client may not support connections to DSA servers most web
248 browsers (including Netscape and MSIE) only support connections to servers
249 supporting RSA cipher suites. The other cause is that a set of DH parameters
250 has not been supplied to the server. DH parameters can be created with the
251 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
252 check the source to s_server in apps/s_server.c for an example.
255 * How can I remove the passphrase on a private key?
257 Firstly you should be really *really* sure you want to do this. Leaving
258 a private key unencrypted is a major security risk. If you decide that
259 you do have to do this check the EXAMPLES sections of the rsa(1) and
263 * Why can't I use OpenSSL certificates with SSL client authentication?
265 What will typically happen is that when a server requests authentication
266 it will either not include your certificate or tell you that you have
267 no client certificates (Netscape) or present you with an empty list box
268 (MSIE). The reason for this is that when a server requests a client
269 certificate it includes a list of CAs names which it will accept. Browsers
270 will only let you select certificates from the list on the grounds that
271 there is little point presenting a certificate which the server will
274 The solution is to add the relevant CA certificate to your servers "trusted
275 CA list". How you do this depends on the server sofware in uses. You can
276 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
278 openssl s_client -connect www.some.host:443 -prexit
280 if your server only requests certificates on certain URLs then you may need
281 to manually issue an HTTP GET command to get the list when s_client connects:
283 GET /some/page/needing/a/certificate.html
285 If your CA does not appear in the list then this confirms the problem.
288 * Why does my browser give a warning about a mismatched hostname?
290 Browsers expect the server's hostname to match the value in the commonName
291 (CN) field of the certificate. If it does not then you get a warning.
294 [BUILD] =======================================================================
296 * Why does the linker complain about undefined symbols?
298 Maybe the compilation was interrupted, and make doesn't notice that
299 something is missing. Run "make clean; make".
301 If you used ./Configure instead of ./config, make sure that you
302 selected the right target. File formats may differ slightly between
303 OS versions (for example sparcv8/sparcv9, or a.out/elf).
305 In case you get errors about the following symbols, use the config
306 option "no-asm", as described in INSTALL:
308 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
309 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
310 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
311 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
312 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
313 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
314 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
316 If none of these helps, you may want to try using the current snapshot.
317 If the problem persists, please submit a bug report.
320 * Why does the OpenSSL test fail with "bc: command not found"?
322 You didn't install "bc", the Unix calculator. If you want to run the
323 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
326 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
328 On some SCO installations or versions, bc has a bug that gets triggered when
329 you run the test suite (using "make test"). The message returned is "bc:
330 1 not implemented". The best way to deal with this is to find another
331 implementation of bc and compile/install it. For example, GNU bc (see
332 http://www.gnu.org/software/software.html for download instructions) can
336 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
338 On some Alpha installations running True64 Unix and Compaq C, the compilation
339 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
340 memory to continue compilation.' As far as the tests have shown, this may be
341 a compiler bug. What happens is that it eats up a lot of resident memory
342 to build something, probably a table. The problem is clearly in the
343 optimization code, because if one eliminates optimization completely (-O0),
344 the compilation goes through (and the compiler consumes about 2MB of resident
345 memory instead of 240MB or whatever one's limit is currently).
347 There are three options to solve this problem:
349 1. set your current data segment size soft limit higher. Experience shows
350 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
351 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
352 kbytes to set the limit to.
354 2. If you have a hard limit that is lower than what you need and you can't
355 get it changed, you can compile all of OpenSSL with -O0 as optimization
356 level. This is however not a very nice thing to do for those who expect to
357 get the best result from OpenSSL. A bit more complicated solution is the
360 ----- snip:start -----
361 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
362 sed -e 's/ -O[0-9] / -O0 /'`"
363 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
367 This will only compile sha_dgst.c with -O0, the rest with the optimization
368 level chosen by the configuration process. When the above is done, do the
369 test and installation and you're set.
372 * Why does the OpenSSL compilation fail with "ar: command not found"?
374 Getting this message is quite usual on Solaris 2, because Sun has hidden
375 away 'ar' and other development commands in directories that aren't in
376 $PATH by default. One of those directories is '/usr/ccs/bin'. The
377 quickest way to fix this is to do the following (it assumes you use sh
378 or any sh-compatible shell):
380 ----- snip:start -----
381 PATH=${PATH}:/usr/ccs/bin; export PATH
384 and then redo the compilation. What you should really do is make sure
385 '/usr/ccs/bin' is permanently in your $PATH, for example through your
386 '.profile' (again, assuming you use a sh-compatible shell).
389 * Why does the OpenSSL compilation fail on Win32 with VC++?
391 Sometimes, you may get reports from VC++ command line (cl) that it
392 can't find standard include files like stdio.h and other weirdnesses.
393 One possible cause is that the environment isn't correctly set up.
394 To solve that problem, one should run VCVARS32.BAT which is found in
395 the 'bin' subdirectory of the VC++ installation directory (somewhere
396 under 'Program Files'). This needs to be done prior to running NMAKE,
397 and the changes are only valid for the current DOS session.
400 [PROG] ========================================================================
402 * Is OpenSSL thread-safe?
404 Yes (with limitations: an SSL connection may not concurrently be used
405 by multiple threads). On Windows and many Unix systems, OpenSSL
406 automatically uses the multi-threaded versions of the standard
407 libraries. If your platform is not one of these, consult the INSTALL
410 Multi-threaded applications must provide two callback functions to
411 OpenSSL. This is described in the threads(3) manpage.
414 * I've compiled a program under Windows and it crashes: why?
416 This is usually because you've missed the comment in INSTALL.W32. You
417 must link with the multithreaded DLL version of the VC++ runtime library
418 otherwise the conflict will cause a program to crash: typically on the
419 first BIO related read or write operation.
422 * How do I read or write a DER encoded buffer using the ASN1 functions?
424 You have two options. You can either use a memory BIO in conjunction
425 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
426 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
427 cause of grief here are some code fragments using PKCS7 as an example:
429 unsigned char *buf, *p;
432 len = i2d_PKCS7(p7, NULL);
433 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
437 At this point buf contains the len bytes of the DER encoding of
440 The opposite assumes we already have len bytes in buf:
444 p7 = d2i_PKCS7(NULL, &p, len);
446 At this point p7 contains a valid PKCS7 structure of NULL if an error
447 occurred. If an error occurred ERR_print_errors(bio) should give more
450 The reason for the temporary variable 'p' is that the ASN1 functions
451 increment the passed pointer so it is ready to read or write the next
452 structure. This is often a cause of problems: without the temporary
453 variable the buffer pointer is changed to point just after the data
454 that has been read or written. This may well be uninitialized data
455 and attempts to free the buffer will have unpredictable results
456 because it no longer points to the same address.
459 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
461 This usually happens when you try compiling something using the PKCS#12
462 macros with a C++ compiler. There is hardly ever any need to use the
463 PKCS#12 macros in a program, it is much easier to parse and create
464 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
465 documented in doc/openssl.txt and with examples in demos/pkcs12. The
466 'pkcs12' application has to use the macros because it prints out
467 debugging information.
470 * I've called <some function> and it fails, why?
472 Before submitting a report or asking in one of the mailing lists, you
473 should try to determine the cause. In particular, you should call
474 ERR_print_errors() or ERR_print_errors_fp() after the failed call
475 and see if the message helps. Note that the problem may occur earlier
476 than you think -- you should check for errors after every call where
477 it is possible, otherwise the actual problem may be hidden because
478 some OpenSSL functions clear the error state.
481 * I just get a load of numbers for the error output, what do they mean?
483 The actual format is described in the ERR_print_errors() manual page.
484 You should call the function ERR_load_crypto_strings() before hand and
485 the message will be output in text form. If you can't do this (for example
486 it is a pre-compiled binary) you can use the errstr utility on the error
487 code itself (the hex digits after the second colon).
490 * Why do I get errors about unknown algorithms?
492 This can happen under several circumstances such as reading in an
493 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
494 is forgetting to load OpenSSL's table of algorithms with
495 OpenSSL_add_all_algorithms(). See the manual page for more information.
498 * Why can't the OpenSSH configure script detect OpenSSL?
500 There is a problem with OpenSSH 1.2.2p1, in that the configure script
501 can't find the installed OpenSSL libraries. The problem is actually
502 a small glitch that is easily solved with the following patch to be
503 applied to the OpenSSH distribution:
505 ----- snip:start -----
506 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
507 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
508 @@ -152,10 +152,10 @@
509 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
510 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
511 if test ! -z "$ssldir" ; then
512 - LIBS="$saved_LIBS -L$ssldir"
513 + LIBS="$saved_LIBS -L$ssldir/lib"
514 CFLAGS="$CFLAGS -I$ssldir/include"
515 if test "x$need_dash_r" = "x1" ; then
516 - LIBS="$LIBS -R$ssldir"
517 + LIBS="$LIBS -R$ssldir/lib"
520 LIBS="$LIBS -lcrypto"
521 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
522 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
523 @@ -1890,10 +1890,10 @@
524 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
525 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
526 if test ! -z "$ssldir" ; then
527 - LIBS="$saved_LIBS -L$ssldir"
528 + LIBS="$saved_LIBS -L$ssldir/lib"
529 CFLAGS="$CFLAGS -I$ssldir/include"
530 if test "x$need_dash_r" = "x1" ; then
531 - LIBS="$LIBS -R$ssldir"
532 + LIBS="$LIBS -R$ssldir/lib"
535 LIBS="$LIBS -lcrypto"
539 * Can I use OpenSSL's SSL library with non-blocking I/O?
541 Yes; make sure to read the SSL_get_error(3) manual page!
543 A pitfall to avoid: Don't assume that SSL_read() will just read from
544 the underlying transport or that SSL_write() will just write to it --
545 it is also possible that SSL_write() cannot do any useful work until
546 there is data to read, or that SSL_read() cannot do anything until it
547 is possible to send data. One reason for this is that the peer may
548 request a new TLS/SSL handshake at any time during the protocol,
549 requiring a bi-directional message exchange; both SSL_read() and
550 SSL_write() will try to continue any pending handshake.
553 ===============================================================================