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?
51 ===============================================================================
53 [MISC] ========================================================================
55 * Which is the current version of OpenSSL?
57 The current version is available from <URL: http://www.openssl.org>.
58 OpenSSL 0.9.6 was released on September 24th, 2000.
60 In addition to the current stable release, you can also access daily
61 snapshots of the OpenSSL development version at <URL:
62 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
65 * Where is the documentation?
67 OpenSSL is a library that provides cryptographic functionality to
68 applications such as secure web servers. Be sure to read the
69 documentation of the application you want to use. The INSTALL file
70 explains how to install this library.
72 OpenSSL includes a command line utility that can be used to perform a
73 variety of cryptographic functions. It is described in the openssl(1)
74 manpage. Documentation for developers is currently being written. A
75 few manual pages already are available; overviews over libcrypto and
76 libssl are given in the crypto(3) and ssl(3) manpages.
78 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
79 different directory if you specified one as described in INSTALL).
80 In addition, you can read the most current versions at
81 <URL: http://www.openssl.org/docs/>.
83 For information on parts of libcrypto that are not yet documented, you
84 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
85 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
86 of this still applies to OpenSSL.
88 There is some documentation about certificate extensions and PKCS#12
91 The original SSLeay documentation is included in OpenSSL as
92 doc/ssleay.txt. It may be useful when none of the other resources
93 help, but please note that it reflects the obsolete version SSLeay
97 * How can I contact the OpenSSL developers?
99 The README file describes how to submit bug reports and patches to
100 OpenSSL. Information on the OpenSSL mailing lists is available from
101 <URL: http://www.openssl.org>.
104 * Where can I get a compiled version of OpenSSL?
106 Some applications that use OpenSSL are distributed in binary form.
107 When using such an application, you don't need to install OpenSSL
108 yourself; the application will include the required parts (e.g. DLLs).
110 If you want to install OpenSSL on a Windows system and you don't have
111 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
112 on how to obtain and install the free GNU C compiler.
114 A number of Linux and *BSD distributions include OpenSSL.
117 * Why aren't tools like 'autoconf' and 'libtool' used?
119 autoconf will probably be used in future OpenSSL versions. If it was
120 less Unix-centric, it might have been used much earlier.
122 libtool has repeatadly been reported by some members of the OpenSSL
123 development and others to be a pain to use. So far, those in the
124 development team who have said anything about this have expressed
125 a wish to avoid libtool for that reason.
128 [LEGAL] =======================================================================
130 * Do I need patent licenses to use OpenSSL?
132 The patents section of the README file lists patents that may apply to
133 you if you want to use OpenSSL. For information on intellectual
134 property rights, please consult a lawyer. The OpenSSL team does not
137 You can configure OpenSSL so as not to use RC5 and IDEA by using
138 ./config no-rc5 no-idea
141 * Can I use OpenSSL with GPL software?
143 On many systems including the major Linux and BSD distributions, yes (the
144 GPL does not place restrictions on using libraries that are part of the
145 normal operating system distribution).
147 On other systems, the situation is less clear. Some GPL software copyright
148 holders claim that you infringe on their rights if you use OpenSSL with
149 their software on operating systems that don't normally include OpenSSL.
151 If you develop open source software that uses OpenSSL, you may find it
152 useful to choose an other license than the GPL, or state explicitely that
153 "This program is released under the GPL with the additional exemption that
154 compiling, linking, and/or using OpenSSL is allowed." If you are using
155 GPL software developed by others, you may want to ask the copyright holder
156 for permission to use their software with OpenSSL.
159 [USER] ========================================================================
161 * Why do I get a "PRNG not seeded" error message?
163 Cryptographic software needs a source of unpredictable data to work
164 correctly. Many open source operating systems provide a "randomness
165 device" that serves this purpose. On other systems, applications have
166 to call the RAND_add() or RAND_seed() function with appropriate data
167 before generating keys or performing public key encryption.
169 Some broken applications do not do this. As of version 0.9.5, the
170 OpenSSL functions that need randomness report an error if the random
171 number generator has not been seeded with at least 128 bits of
172 randomness. If this error occurs, please contact the author of the
173 application you are using. It is likely that it never worked
174 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
175 to perform potentially insecure encryption.
177 On systems without /dev/urandom, it is a good idea to use the Entropy
178 Gathering Demon; see the RAND_egd() manpage for details.
180 Most components of the openssl command line tool try to use the
181 file $HOME/.rnd (or $RANDFILE, if this environment variable is set)
182 for seeding the PRNG. If this file does not exist or is too short,
183 the "PRNG not seeded" error message may occur.
185 [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version
186 0.9.5 does not do this and will fail on systems without /dev/urandom
187 when trying to password-encrypt an RSA key! This is a bug in the
188 library; try a later version instead.]
190 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
191 installing the SUNski package from Sun patch 105710-01 (Sparc) which
192 adds a /dev/random device and make sure it gets used, usually through
193 $RANDFILE. There are probably similar patches for the other Solaris
194 versions. However, be warned that /dev/random is usually a blocking
195 device, which may have some effects on OpenSSL.
198 * How do I create certificates or certificate requests?
200 Check out the CA.pl(1) manual page. This provides a simple wrapper round
201 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
202 out the manual pages for the individual utilities and the certificate
203 extensions documentation (currently in doc/openssl.txt).
206 * Why can't I create certificate requests?
208 You typically get the error:
210 unable to find 'distinguished_name' in config
211 problems making Certificate Request
213 This is because it can't find the configuration file. Check out the
214 DIAGNOSTICS section of req(1) for more information.
217 * Why does <SSL program> fail with a certificate verify error?
219 This problem is usually indicated by log messages saying something like
220 "unable to get local issuer certificate" or "self signed certificate".
221 When a certificate is verified its root CA must be "trusted" by OpenSSL
222 this typically means that the CA certificate must be placed in a directory
223 or file and the relevant program configured to read it. The OpenSSL program
224 'verify' behaves in a similar way and issues similar error messages: check
225 the verify(1) program manual page for more information.
228 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
230 This is almost certainly because you are using an old "export grade" browser
231 which only supports weak encryption. Upgrade your browser to support 128 bit
235 * How can I create DSA certificates?
237 Check the CA.pl(1) manual page for a DSA certificate example.
240 * Why can't I make an SSL connection to a server using a DSA certificate?
242 Typically you'll see a message saying there are no shared ciphers when
243 the same setup works fine with an RSA certificate. There are two possible
244 causes. The client may not support connections to DSA servers most web
245 browsers (including Netscape and MSIE) only support connections to servers
246 supporting RSA cipher suites. The other cause is that a set of DH parameters
247 has not been supplied to the server. DH parameters can be created with the
248 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
249 check the source to s_server in apps/s_server.c for an example.
252 * How can I remove the passphrase on a private key?
254 Firstly you should be really *really* sure you want to do this. Leaving
255 a private key unencrypted is a major security risk. If you decide that
256 you do have to do this check the EXAMPLES sections of the rsa(1) and
260 * Why can't I use OpenSSL certificates with SSL client authentication?
262 What will typically happen is that when a server requests authentication
263 it will either not include your certificate or tell you that you have
264 no client certificates (Netscape) or present you with an empty list box
265 (MSIE). The reason for this is that when a server requests a client
266 certificate it includes a list of CAs names which it will accept. Browsers
267 will only let you select certificates from the list on the grounds that
268 there is little point presenting a certificate which the server will
271 The solution is to add the relevant CA certificate to your servers "trusted
272 CA list". How you do this depends on the server sofware in uses. You can
273 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
275 openssl s_client -connect www.some.host:443 -prexit
277 If your server only requests certificates on certain URLs then you may need
278 to manually issue an HTTP GET command to get the list when s_client connects:
280 GET /some/page/needing/a/certificate.html
282 If your CA does not appear in the list then this confirms the problem.
285 * Why does my browser give a warning about a mismatched hostname?
287 Browsers expect the server's hostname to match the value in the commonName
288 (CN) field of the certificate. If it does not then you get a warning.
291 [BUILD] =======================================================================
293 * Why does the linker complain about undefined symbols?
295 Maybe the compilation was interrupted, and make doesn't notice that
296 something is missing. Run "make clean; make".
298 If you used ./Configure instead of ./config, make sure that you
299 selected the right target. File formats may differ slightly between
300 OS versions (for example sparcv8/sparcv9, or a.out/elf).
302 In case you get errors about the following symbols, use the config
303 option "no-asm", as described in INSTALL:
305 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
306 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
307 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
308 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
309 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
310 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
311 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
313 If none of these helps, you may want to try using the current snapshot.
314 If the problem persists, please submit a bug report.
317 * Why does the OpenSSL test fail with "bc: command not found"?
319 You didn't install "bc", the Unix calculator. If you want to run the
320 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
323 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
325 On some SCO installations or versions, bc has a bug that gets triggered
326 when you run the test suite (using "make test"). The message returned is
327 "bc: 1 not implemented".
329 The best way to deal with this is to find another implementation of bc
330 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
331 for download instructions) can be safely used, for example.
334 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
336 On some Alpha installations running True64 Unix and Compaq C, the compilation
337 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
338 memory to continue compilation.' As far as the tests have shown, this may be
339 a compiler bug. What happens is that it eats up a lot of resident memory
340 to build something, probably a table. The problem is clearly in the
341 optimization code, because if one eliminates optimization completely (-O0),
342 the compilation goes through (and the compiler consumes about 2MB of resident
343 memory instead of 240MB or whatever one's limit is currently).
345 There are three options to solve this problem:
347 1. set your current data segment size soft limit higher. Experience shows
348 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
349 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
350 kbytes to set the limit to.
352 2. If you have a hard limit that is lower than what you need and you can't
353 get it changed, you can compile all of OpenSSL with -O0 as optimization
354 level. This is however not a very nice thing to do for those who expect to
355 get the best result from OpenSSL. A bit more complicated solution is the
358 ----- snip:start -----
359 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
360 sed -e 's/ -O[0-9] / -O0 /'`"
361 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
365 This will only compile sha_dgst.c with -O0, the rest with the optimization
366 level chosen by the configuration process. When the above is done, do the
367 test and installation and you're set.
370 * Why does the OpenSSL compilation fail with "ar: command not found"?
372 Getting this message is quite usual on Solaris 2, because Sun has hidden
373 away 'ar' and other development commands in directories that aren't in
374 $PATH by default. One of those directories is '/usr/ccs/bin'. The
375 quickest way to fix this is to do the following (it assumes you use sh
376 or any sh-compatible shell):
378 ----- snip:start -----
379 PATH=${PATH}:/usr/ccs/bin; export PATH
382 and then redo the compilation. What you should really do is make sure
383 '/usr/ccs/bin' is permanently in your $PATH, for example through your
384 '.profile' (again, assuming you use a sh-compatible shell).
387 * Why does the OpenSSL compilation fail on Win32 with VC++?
389 Sometimes, you may get reports from VC++ command line (cl) that it
390 can't find standard include files like stdio.h and other weirdnesses.
391 One possible cause is that the environment isn't correctly set up.
392 To solve that problem, one should run VCVARS32.BAT which is found in
393 the 'bin' subdirectory of the VC++ installation directory (somewhere
394 under 'Program Files'). This needs to be done prior to running NMAKE,
395 and the changes are only valid for the current DOS session.
398 [PROG] ========================================================================
400 * Is OpenSSL thread-safe?
402 Yes (with limitations: an SSL connection may not concurrently be used
403 by multiple threads). On Windows and many Unix systems, OpenSSL
404 automatically uses the multi-threaded versions of the standard
405 libraries. If your platform is not one of these, consult the INSTALL
408 Multi-threaded applications must provide two callback functions to
409 OpenSSL. This is described in the threads(3) manpage.
412 * I've compiled a program under Windows and it crashes: why?
414 This is usually because you've missed the comment in INSTALL.W32. You
415 must link with the multithreaded DLL version of the VC++ runtime library
416 otherwise the conflict will cause a program to crash: typically on the
417 first BIO related read or write operation.
420 * How do I read or write a DER encoded buffer using the ASN1 functions?
422 You have two options. You can either use a memory BIO in conjunction
423 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
424 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
425 cause of grief here are some code fragments using PKCS7 as an example:
427 unsigned char *buf, *p;
430 len = i2d_PKCS7(p7, NULL);
431 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
435 At this point buf contains the len bytes of the DER encoding of
438 The opposite assumes we already have len bytes in buf:
442 p7 = d2i_PKCS7(NULL, &p, len);
444 At this point p7 contains a valid PKCS7 structure of NULL if an error
445 occurred. If an error occurred ERR_print_errors(bio) should give more
448 The reason for the temporary variable 'p' is that the ASN1 functions
449 increment the passed pointer so it is ready to read or write the next
450 structure. This is often a cause of problems: without the temporary
451 variable the buffer pointer is changed to point just after the data
452 that has been read or written. This may well be uninitialized data
453 and attempts to free the buffer will have unpredictable results
454 because it no longer points to the same address.
457 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
459 This usually happens when you try compiling something using the PKCS#12
460 macros with a C++ compiler. There is hardly ever any need to use the
461 PKCS#12 macros in a program, it is much easier to parse and create
462 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
463 documented in doc/openssl.txt and with examples in demos/pkcs12. The
464 'pkcs12' application has to use the macros because it prints out
465 debugging information.
468 * I've called <some function> and it fails, why?
470 Before submitting a report or asking in one of the mailing lists, you
471 should try to determine the cause. In particular, you should call
472 ERR_print_errors() or ERR_print_errors_fp() after the failed call
473 and see if the message helps. Note that the problem may occur earlier
474 than you think -- you should check for errors after every call where
475 it is possible, otherwise the actual problem may be hidden because
476 some OpenSSL functions clear the error state.
479 * I just get a load of numbers for the error output, what do they mean?
481 The actual format is described in the ERR_print_errors() manual page.
482 You should call the function ERR_load_crypto_strings() before hand and
483 the message will be output in text form. If you can't do this (for example
484 it is a pre-compiled binary) you can use the errstr utility on the error
485 code itself (the hex digits after the second colon).
488 * Why do I get errors about unknown algorithms?
490 This can happen under several circumstances such as reading in an
491 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
492 is forgetting to load OpenSSL's table of algorithms with
493 OpenSSL_add_all_algorithms(). See the manual page for more information.
496 * Why can't the OpenSSH configure script detect OpenSSL?
498 There is a problem with OpenSSH 1.2.2p1, in that the configure script
499 can't find the installed OpenSSL libraries. The problem is actually
500 a small glitch that is easily solved with the following patch to be
501 applied to the OpenSSH distribution:
503 ----- snip:start -----
504 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
505 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
506 @@ -152,10 +152,10 @@
507 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
508 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
509 if test ! -z "$ssldir" ; then
510 - LIBS="$saved_LIBS -L$ssldir"
511 + LIBS="$saved_LIBS -L$ssldir/lib"
512 CFLAGS="$CFLAGS -I$ssldir/include"
513 if test "x$need_dash_r" = "x1" ; then
514 - LIBS="$LIBS -R$ssldir"
515 + LIBS="$LIBS -R$ssldir/lib"
518 LIBS="$LIBS -lcrypto"
519 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
520 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
521 @@ -1890,10 +1890,10 @@
522 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
523 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
524 if test ! -z "$ssldir" ; then
525 - LIBS="$saved_LIBS -L$ssldir"
526 + LIBS="$saved_LIBS -L$ssldir/lib"
527 CFLAGS="$CFLAGS -I$ssldir/include"
528 if test "x$need_dash_r" = "x1" ; then
529 - LIBS="$LIBS -R$ssldir"
530 + LIBS="$LIBS -R$ssldir/lib"
533 LIBS="$LIBS -lcrypto"
537 * Can I use OpenSSL's SSL library with non-blocking I/O?
539 Yes; make sure to read the SSL_get_error(3) manual page!
541 A pitfall to avoid: Don't assume that SSL_read() will just read from
542 the underlying transport or that SSL_write() will just write to it --
543 it is also possible that SSL_write() cannot do any useful work until
544 there is data to read, or that SSL_read() cannot do anything until it
545 is possible to send data. One reason for this is that the peer may
546 request a new TLS/SSL handshake at any time during the protocol,
547 requiring a bi-directional message exchange; both SSL_read() and
548 SSL_write() will try to continue any pending handshake.
551 ===============================================================================