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?
28 * Why does my browser give a warning about a mismatched hostname?
30 [BUILD] Questions about building and testing OpenSSL
32 * Why does the linker complain about undefined symbols?
33 * Why does the OpenSSL test fail with "bc: command not found"?
34 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
35 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
36 * Why does the OpenSSL compilation fail with "ar: command not found"?
37 * Why does the OpenSSL compilation fail on Win32 with VC++?
39 [PROG] Questions about programming with OpenSSL
41 * Is OpenSSL thread-safe?
42 * I've compiled a program under Windows and it crashes: why?
43 * How do I read or write a DER encoded buffer using the ASN1 functions?
44 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
45 * I've called <some function> and it fails, why?
46 * I just get a load of numbers for the error output, what do they mean?
47 * Why do I get errors about unknown algorithms?
48 * Why can't the OpenSSH configure script detect OpenSSL?
49 * Can I use OpenSSL's SSL library with non-blocking I/O?
50 * Why doesn't my server application receive a client certificate?
52 ===============================================================================
54 [MISC] ========================================================================
56 * Which is the current version of OpenSSL?
58 The current version is available from <URL: http://www.openssl.org>.
59 OpenSSL 0.9.6a was released on April 5th, 2001.
61 In addition to the current stable release, you can also access daily
62 snapshots of the OpenSSL development version at <URL:
63 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
66 * Where is the documentation?
68 OpenSSL is a library that provides cryptographic functionality to
69 applications such as secure web servers. Be sure to read the
70 documentation of the application you want to use. The INSTALL file
71 explains how to install this library.
73 OpenSSL includes a command line utility that can be used to perform a
74 variety of cryptographic functions. It is described in the openssl(1)
75 manpage. Documentation for developers is currently being written. A
76 few manual pages already are available; overviews over libcrypto and
77 libssl are given in the crypto(3) and ssl(3) manpages.
79 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
80 different directory if you specified one as described in INSTALL).
81 In addition, you can read the most current versions at
82 <URL: http://www.openssl.org/docs/>.
84 For information on parts of libcrypto that are not yet documented, you
85 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
86 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
87 of this still applies to OpenSSL.
89 There is some documentation about certificate extensions and PKCS#12
92 The original SSLeay documentation is included in OpenSSL as
93 doc/ssleay.txt. It may be useful when none of the other resources
94 help, but please note that it reflects the obsolete version SSLeay
98 * How can I contact the OpenSSL developers?
100 The README file describes how to submit bug reports and patches to
101 OpenSSL. Information on the OpenSSL mailing lists is available from
102 <URL: http://www.openssl.org>.
105 * Where can I get a compiled version of OpenSSL?
107 Some applications that use OpenSSL are distributed in binary form.
108 When using such an application, you don't need to install OpenSSL
109 yourself; the application will include the required parts (e.g. DLLs).
111 If you want to install OpenSSL on a Windows system and you don't have
112 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
113 on how to obtain and install the free GNU C compiler.
115 A number of Linux and *BSD distributions include OpenSSL.
118 * Why aren't tools like 'autoconf' and 'libtool' used?
120 autoconf will probably be used in future OpenSSL versions. If it was
121 less Unix-centric, it might have been used much earlier.
124 [LEGAL] =======================================================================
126 * Do I need patent licenses to use OpenSSL?
128 The patents section of the README file lists patents that may apply to
129 you if you want to use OpenSSL. For information on intellectual
130 property rights, please consult a lawyer. The OpenSSL team does not
133 You can configure OpenSSL so as not to use RC5 and IDEA by using
134 ./config no-rc5 no-idea
137 * Can I use OpenSSL with GPL software?
139 On many systems including the major Linux and BSD distributions, yes (the
140 GPL does not place restrictions on using libraries that are part of the
141 normal operating system distribution).
143 On other systems, the situation is less clear. Some GPL software copyright
144 holders claim that you infringe on their rights if you use OpenSSL with
145 their software on operating systems that don't normally include OpenSSL.
147 If you develop open source software that uses OpenSSL, you may find it
148 useful to choose an other license than the GPL, or state explicitely that
149 "This program is released under the GPL with the additional exemption that
150 compiling, linking, and/or using OpenSSL is allowed." If you are using
151 GPL software developed by others, you may want to ask the copyright holder
152 for permission to use their software with OpenSSL.
155 [USER] ========================================================================
157 * Why do I get a "PRNG not seeded" error message?
159 Cryptographic software needs a source of unpredictable data to work
160 correctly. Many open source operating systems provide a "randomness
161 device" that serves this purpose. On other systems, applications have
162 to call the RAND_add() or RAND_seed() function with appropriate data
163 before generating keys or performing public key encryption.
165 Some broken applications do not do this. As of version 0.9.5, the
166 OpenSSL functions that need randomness report an error if the random
167 number generator has not been seeded with at least 128 bits of
168 randomness. If this error occurs, please contact the author of the
169 application you are using. It is likely that it never worked
170 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
171 to perform potentially insecure encryption.
173 On systems without /dev/urandom, it is a good idea to use the Entropy
174 Gathering Demon; see the RAND_egd() manpage for details.
176 Most components of the openssl command line tool try to use the
177 file $HOME/.rnd (or $RANDFILE, if this environment variable is set)
178 for seeding the PRNG. If this file does not exist or is too short,
179 the "PRNG not seeded" error message may occur.
181 [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version
182 0.9.5 does not do this and will fail on systems without /dev/urandom
183 when trying to password-encrypt an RSA key! This is a bug in the
184 library; try a later version instead.]
186 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
187 installing the SUNski package from Sun patch 105710-01 (Sparc) which
188 adds a /dev/random device and make sure it gets used, usually through
189 $RANDFILE. There are probably similar patches for the other Solaris
190 versions. However, be warned that /dev/random is usually a blocking
191 device, which may have some effects on OpenSSL.
194 * How do I create certificates or certificate requests?
196 Check out the CA.pl(1) manual page. This provides a simple wrapper round
197 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
198 out the manual pages for the individual utilities and the certificate
199 extensions documentation (currently in doc/openssl.txt).
202 * Why can't I create certificate requests?
204 You typically get the error:
206 unable to find 'distinguished_name' in config
207 problems making Certificate Request
209 This is because it can't find the configuration file. Check out the
210 DIAGNOSTICS section of req(1) for more information.
213 * Why does <SSL program> fail with a certificate verify error?
215 This problem is usually indicated by log messages saying something like
216 "unable to get local issuer certificate" or "self signed certificate".
217 When a certificate is verified its root CA must be "trusted" by OpenSSL
218 this typically means that the CA certificate must be placed in a directory
219 or file and the relevant program configured to read it. The OpenSSL program
220 'verify' behaves in a similar way and issues similar error messages: check
221 the verify(1) program manual page for more information.
224 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
226 This is almost certainly because you are using an old "export grade" browser
227 which only supports weak encryption. Upgrade your browser to support 128 bit
231 * How can I create DSA certificates?
233 Check the CA.pl(1) manual page for a DSA certificate example.
236 * Why can't I make an SSL connection to a server using a DSA certificate?
238 Typically you'll see a message saying there are no shared ciphers when
239 the same setup works fine with an RSA certificate. There are two possible
240 causes. The client may not support connections to DSA servers most web
241 browsers (including Netscape and MSIE) only support connections to servers
242 supporting RSA cipher suites. The other cause is that a set of DH parameters
243 has not been supplied to the server. DH parameters can be created with the
244 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
245 check the source to s_server in apps/s_server.c for an example.
248 * How can I remove the passphrase on a private key?
250 Firstly you should be really *really* sure you want to do this. Leaving
251 a private key unencrypted is a major security risk. If you decide that
252 you do have to do this check the EXAMPLES sections of the rsa(1) and
256 * Why can't I use OpenSSL certificates with SSL client authentication?
258 What will typically happen is that when a server requests authentication
259 it will either not include your certificate or tell you that you have
260 no client certificates (Netscape) or present you with an empty list box
261 (MSIE). The reason for this is that when a server requests a client
262 certificate it includes a list of CAs names which it will accept. Browsers
263 will only let you select certificates from the list on the grounds that
264 there is little point presenting a certificate which the server will
267 The solution is to add the relevant CA certificate to your servers "trusted
268 CA list". How you do this depends on the server sofware in uses. You can
269 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
271 openssl s_client -connect www.some.host:443 -prexit
273 If your server only requests certificates on certain URLs then you may need
274 to manually issue an HTTP GET command to get the list when s_client connects:
276 GET /some/page/needing/a/certificate.html
278 If your CA does not appear in the list then this confirms the problem.
281 * Why does my browser give a warning about a mismatched hostname?
283 Browsers expect the server's hostname to match the value in the commonName
284 (CN) field of the certificate. If it does not then you get a warning.
287 [BUILD] =======================================================================
289 * Why does the linker complain about undefined symbols?
291 Maybe the compilation was interrupted, and make doesn't notice that
292 something is missing. Run "make clean; make".
294 If you used ./Configure instead of ./config, make sure that you
295 selected the right target. File formats may differ slightly between
296 OS versions (for example sparcv8/sparcv9, or a.out/elf).
298 In case you get errors about the following symbols, use the config
299 option "no-asm", as described in INSTALL:
301 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
302 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
303 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
304 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
305 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
306 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
307 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
309 If none of these helps, you may want to try using the current snapshot.
310 If the problem persists, please submit a bug report.
313 * Why does the OpenSSL test fail with "bc: command not found"?
315 You didn't install "bc", the Unix calculator. If you want to run the
316 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
319 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
321 On some SCO installations or versions, bc has a bug that gets triggered
322 when you run the test suite (using "make test"). The message returned is
323 "bc: 1 not implemented".
325 The best way to deal with this is to find another implementation of bc
326 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
327 for download instructions) can be safely used, for example.
330 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
332 On some Alpha installations running True64 Unix and Compaq C, the compilation
333 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
334 memory to continue compilation.' As far as the tests have shown, this may be
335 a compiler bug. What happens is that it eats up a lot of resident memory
336 to build something, probably a table. The problem is clearly in the
337 optimization code, because if one eliminates optimization completely (-O0),
338 the compilation goes through (and the compiler consumes about 2MB of resident
339 memory instead of 240MB or whatever one's limit is currently).
341 There are three options to solve this problem:
343 1. set your current data segment size soft limit higher. Experience shows
344 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
345 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
346 kbytes to set the limit to.
348 2. If you have a hard limit that is lower than what you need and you can't
349 get it changed, you can compile all of OpenSSL with -O0 as optimization
350 level. This is however not a very nice thing to do for those who expect to
351 get the best result from OpenSSL. A bit more complicated solution is the
354 ----- snip:start -----
355 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
356 sed -e 's/ -O[0-9] / -O0 /'`"
357 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
361 This will only compile sha_dgst.c with -O0, the rest with the optimization
362 level chosen by the configuration process. When the above is done, do the
363 test and installation and you're set.
366 * Why does the OpenSSL compilation fail with "ar: command not found"?
368 Getting this message is quite usual on Solaris 2, because Sun has hidden
369 away 'ar' and other development commands in directories that aren't in
370 $PATH by default. One of those directories is '/usr/ccs/bin'. The
371 quickest way to fix this is to do the following (it assumes you use sh
372 or any sh-compatible shell):
374 ----- snip:start -----
375 PATH=${PATH}:/usr/ccs/bin; export PATH
378 and then redo the compilation. What you should really do is make sure
379 '/usr/ccs/bin' is permanently in your $PATH, for example through your
380 '.profile' (again, assuming you use a sh-compatible shell).
383 * Why does the OpenSSL compilation fail on Win32 with VC++?
385 Sometimes, you may get reports from VC++ command line (cl) that it
386 can't find standard include files like stdio.h and other weirdnesses.
387 One possible cause is that the environment isn't correctly set up.
388 To solve that problem, one should run VCVARS32.BAT which is found in
389 the 'bin' subdirectory of the VC++ installation directory (somewhere
390 under 'Program Files'). This needs to be done prior to running NMAKE,
391 and the changes are only valid for the current DOS session.
394 [PROG] ========================================================================
396 * Is OpenSSL thread-safe?
398 Yes (with limitations: an SSL connection may not concurrently be used
399 by multiple threads). On Windows and many Unix systems, OpenSSL
400 automatically uses the multi-threaded versions of the standard
401 libraries. If your platform is not one of these, consult the INSTALL
404 Multi-threaded applications must provide two callback functions to
405 OpenSSL. This is described in the threads(3) manpage.
408 * I've compiled a program under Windows and it crashes: why?
410 This is usually because you've missed the comment in INSTALL.W32. You
411 must link with the multithreaded DLL version of the VC++ runtime library
412 otherwise the conflict will cause a program to crash: typically on the
413 first BIO related read or write operation.
416 * How do I read or write a DER encoded buffer using the ASN1 functions?
418 You have two options. You can either use a memory BIO in conjunction
419 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
420 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
421 cause of grief here are some code fragments using PKCS7 as an example:
423 unsigned char *buf, *p;
426 len = i2d_PKCS7(p7, NULL);
427 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
431 At this point buf contains the len bytes of the DER encoding of
434 The opposite assumes we already have len bytes in buf:
438 p7 = d2i_PKCS7(NULL, &p, len);
440 At this point p7 contains a valid PKCS7 structure of NULL if an error
441 occurred. If an error occurred ERR_print_errors(bio) should give more
444 The reason for the temporary variable 'p' is that the ASN1 functions
445 increment the passed pointer so it is ready to read or write the next
446 structure. This is often a cause of problems: without the temporary
447 variable the buffer pointer is changed to point just after the data
448 that has been read or written. This may well be uninitialized data
449 and attempts to free the buffer will have unpredictable results
450 because it no longer points to the same address.
453 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
455 This usually happens when you try compiling something using the PKCS#12
456 macros with a C++ compiler. There is hardly ever any need to use the
457 PKCS#12 macros in a program, it is much easier to parse and create
458 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
459 documented in doc/openssl.txt and with examples in demos/pkcs12. The
460 'pkcs12' application has to use the macros because it prints out
461 debugging information.
464 * I've called <some function> and it fails, why?
466 Before submitting a report or asking in one of the mailing lists, you
467 should try to determine the cause. In particular, you should call
468 ERR_print_errors() or ERR_print_errors_fp() after the failed call
469 and see if the message helps. Note that the problem may occur earlier
470 than you think -- you should check for errors after every call where
471 it is possible, otherwise the actual problem may be hidden because
472 some OpenSSL functions clear the error state.
475 * I just get a load of numbers for the error output, what do they mean?
477 The actual format is described in the ERR_print_errors() manual page.
478 You should call the function ERR_load_crypto_strings() before hand and
479 the message will be output in text form. If you can't do this (for example
480 it is a pre-compiled binary) you can use the errstr utility on the error
481 code itself (the hex digits after the second colon).
484 * Why do I get errors about unknown algorithms?
486 This can happen under several circumstances such as reading in an
487 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
488 is forgetting to load OpenSSL's table of algorithms with
489 OpenSSL_add_all_algorithms(). See the manual page for more information.
492 * Why can't the OpenSSH configure script detect OpenSSL?
494 There is a problem with OpenSSH 1.2.2p1, in that the configure script
495 can't find the installed OpenSSL libraries. The problem is actually
496 a small glitch that is easily solved with the following patch to be
497 applied to the OpenSSH distribution:
499 ----- snip:start -----
500 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
501 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
502 @@ -152,10 +152,10 @@
503 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
504 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
505 if test ! -z "$ssldir" ; then
506 - LIBS="$saved_LIBS -L$ssldir"
507 + LIBS="$saved_LIBS -L$ssldir/lib"
508 CFLAGS="$CFLAGS -I$ssldir/include"
509 if test "x$need_dash_r" = "x1" ; then
510 - LIBS="$LIBS -R$ssldir"
511 + LIBS="$LIBS -R$ssldir/lib"
514 LIBS="$LIBS -lcrypto"
515 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
516 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
517 @@ -1890,10 +1890,10 @@
518 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
519 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
520 if test ! -z "$ssldir" ; then
521 - LIBS="$saved_LIBS -L$ssldir"
522 + LIBS="$saved_LIBS -L$ssldir/lib"
523 CFLAGS="$CFLAGS -I$ssldir/include"
524 if test "x$need_dash_r" = "x1" ; then
525 - LIBS="$LIBS -R$ssldir"
526 + LIBS="$LIBS -R$ssldir/lib"
529 LIBS="$LIBS -lcrypto"
533 * Can I use OpenSSL's SSL library with non-blocking I/O?
535 Yes; make sure to read the SSL_get_error(3) manual page!
537 A pitfall to avoid: Don't assume that SSL_read() will just read from
538 the underlying transport or that SSL_write() will just write to it --
539 it is also possible that SSL_write() cannot do any useful work until
540 there is data to read, or that SSL_read() cannot do anything until it
541 is possible to send data. One reason for this is that the peer may
542 request a new TLS/SSL handshake at any time during the protocol,
543 requiring a bi-directional message exchange; both SSL_read() and
544 SSL_write() will try to continue any pending handshake.
547 * Why doesn't my server application receive a client certificate?
549 Due to the TLS protocol definition, a client will only send a certificate,
550 if explicitely asked by the server. Use the SSL_VERIFY_PEER flag of the
551 SSL_CTX_set_verify() function to enable the use of client certificates.
554 ===============================================================================