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?
13 [LEGAL] Legal questions
15 * Do I need patent licenses to use OpenSSL?
16 * Can I use OpenSSL with GPL software?
18 [USER] Questions on using the OpenSSL applications
20 * Why do I get a "PRNG not seeded" error message?
21 * Why do I get an "unable to write 'random state'" error message?
22 * How do I create certificates or certificate requests?
23 * Why can't I create certificate requests?
24 * Why does <SSL program> fail with a certificate verify error?
25 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
26 * How can I create DSA certificates?
27 * Why can't I make an SSL connection using a DSA certificate?
28 * How can I remove the passphrase on a private key?
29 * Why can't I use OpenSSL certificates with SSL client authentication?
30 * Why does my browser give a warning about a mismatched hostname?
32 [BUILD] Questions about building and testing OpenSSL
34 * Why does the linker complain about undefined symbols?
35 * Why does the OpenSSL test fail with "bc: command not found"?
36 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
37 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
38 * Why does the OpenSSL compilation fail with "ar: command not found"?
39 * Why does the OpenSSL compilation fail on Win32 with VC++?
41 [PROG] Questions about programming with OpenSSL
43 * Is OpenSSL thread-safe?
44 * I've compiled a program under Windows and it crashes: why?
45 * How do I read or write a DER encoded buffer using the ASN1 functions?
46 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
47 * I've called <some function> and it fails, why?
48 * I just get a load of numbers for the error output, what do they mean?
49 * Why do I get errors about unknown algorithms?
50 * Why can't the OpenSSH configure script detect OpenSSL?
51 * Can I use OpenSSL's SSL library with non-blocking I/O?
52 * Why doesn't my server application receive a client certificate?
54 ===============================================================================
56 [MISC] ========================================================================
58 * Which is the current version of OpenSSL?
60 The current version is available from <URL: http://www.openssl.org>.
61 OpenSSL 0.9.6b was released on July 9th, 2001.
63 In addition to the current stable release, you can also access daily
64 snapshots of the OpenSSL development version at <URL:
65 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
68 * Where is the documentation?
70 OpenSSL is a library that provides cryptographic functionality to
71 applications such as secure web servers. Be sure to read the
72 documentation of the application you want to use. The INSTALL file
73 explains how to install this library.
75 OpenSSL includes a command line utility that can be used to perform a
76 variety of cryptographic functions. It is described in the openssl(1)
77 manpage. Documentation for developers is currently being written. A
78 few manual pages already are available; overviews over libcrypto and
79 libssl are given in the crypto(3) and ssl(3) manpages.
81 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
82 different directory if you specified one as described in INSTALL).
83 In addition, you can read the most current versions at
84 <URL: http://www.openssl.org/docs/>.
86 For information on parts of libcrypto that are not yet documented, you
87 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
88 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
89 of this still applies to OpenSSL.
91 There is some documentation about certificate extensions and PKCS#12
94 The original SSLeay documentation is included in OpenSSL as
95 doc/ssleay.txt. It may be useful when none of the other resources
96 help, but please note that it reflects the obsolete version SSLeay
100 * How can I contact the OpenSSL developers?
102 The README file describes how to submit bug reports and patches to
103 OpenSSL. Information on the OpenSSL mailing lists is available from
104 <URL: http://www.openssl.org>.
107 * Where can I get a compiled version of OpenSSL?
109 Some applications that use OpenSSL are distributed in binary form.
110 When using such an application, you don't need to install OpenSSL
111 yourself; the application will include the required parts (e.g. DLLs).
113 If you want to install OpenSSL on a Windows system and you don't have
114 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
115 on how to obtain and install the free GNU C compiler.
117 A number of Linux and *BSD distributions include OpenSSL.
120 * Why aren't tools like 'autoconf' and 'libtool' used?
122 autoconf will probably be used in future OpenSSL versions. If it was
123 less Unix-centric, it might have been used much earlier.
126 * What is an 'engine' version?
128 With version 0.9.6 OpenSSL was extended to interface to external crypto
129 hardware. This was realized in a special release '0.9.6-engine'. With
130 version 0.9.7 (not yet released) the changes were merged into the main
131 development line, so that the special release is no longer necessary.
134 [LEGAL] =======================================================================
136 * Do I need patent licenses to use OpenSSL?
138 The patents section of the README file lists patents that may apply to
139 you if you want to use OpenSSL. For information on intellectual
140 property rights, please consult a lawyer. The OpenSSL team does not
143 You can configure OpenSSL so as not to use RC5 and IDEA by using
144 ./config no-rc5 no-idea
147 * Can I use OpenSSL with GPL software?
149 On many systems including the major Linux and BSD distributions, yes (the
150 GPL does not place restrictions on using libraries that are part of the
151 normal operating system distribution).
153 On other systems, the situation is less clear. Some GPL software copyright
154 holders claim that you infringe on their rights if you use OpenSSL with
155 their software on operating systems that don't normally include OpenSSL.
157 If you develop open source software that uses OpenSSL, you may find it
158 useful to choose an other license than the GPL, or state explicitely that
159 "This program is released under the GPL with the additional exemption that
160 compiling, linking, and/or using OpenSSL is allowed." If you are using
161 GPL software developed by others, you may want to ask the copyright holder
162 for permission to use their software with OpenSSL.
165 [USER] ========================================================================
167 * Why do I get a "PRNG not seeded" error message?
169 Cryptographic software needs a source of unpredictable data to work
170 correctly. Many open source operating systems provide a "randomness
171 device" that serves this purpose. On other systems, applications have
172 to call the RAND_add() or RAND_seed() function with appropriate data
173 before generating keys or performing public key encryption.
174 (These functions initialize the pseudo-random number generator, PRNG.)
176 Some broken applications do not do this. As of version 0.9.5, the
177 OpenSSL functions that need randomness report an error if the random
178 number generator has not been seeded with at least 128 bits of
179 randomness. If this error occurs, please contact the author of the
180 application you are using. It is likely that it never worked
181 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
182 to perform potentially insecure encryption.
184 On systems without /dev/urandom and /dev/random, it is a good idea to
185 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
186 details. Starting with version 0.9.7, OpenSSL will automatically look
187 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
190 Most components of the openssl command line utility automatically try
191 to seed the random number generator from a file. The name of the
192 default seeding file is determined as follows: If environment variable
193 RANDFILE is set, then it names the seeding file. Otherwise if
194 environment variable HOME is set, then the seeding file is $HOME/.rnd.
195 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
196 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
197 default seeding file at all. OpenSSL 0.9.6b and later will behave
198 similarly to 0.9.6a, but will use a default of "C:" for HOME on
199 Windows systems if the environment variable has not been set.
201 If the default seeding file does not exist or is too short, the "PRNG
202 not seeded" error message may occur.
204 The openssl command line utility will write back a new state to the
205 default seeding file (and create this file if necessary) unless
206 there was no sufficient seeding.
208 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
209 Use the "-rand" option of the OpenSSL command line tools instead.
210 The $RANDFILE environment variable and $HOME/.rnd are only used by the
211 OpenSSL command line tools. Applications using the OpenSSL library
212 provide their own configuration options to specify the entropy source,
213 please check out the documentation coming the with application.
215 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
216 installing the SUNski package from Sun patch 105710-01 (Sparc) which
217 adds a /dev/random device and make sure it gets used, usually through
218 $RANDFILE. There are probably similar patches for the other Solaris
219 versions. However, be warned that /dev/random is usually a blocking
220 device, which may have some effects on OpenSSL.
223 * Why do I get an "unable to write 'random state'" error message?
226 Sometimes the openssl command line utility does not abort with
227 a "PRNG not seeded" error message, but complains that it is
228 "unable to write 'random state'". This message refers to the
229 default seeding file (see previous answer). A possible reason
230 is that no default filename is known because neither RANDFILE
231 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
232 current directory in this case, but this has changed with 0.9.6a.)
235 * How do I create certificates or certificate requests?
237 Check out the CA.pl(1) manual page. This provides a simple wrapper round
238 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
239 out the manual pages for the individual utilities and the certificate
240 extensions documentation (currently in doc/openssl.txt).
243 * Why can't I create certificate requests?
245 You typically get the error:
247 unable to find 'distinguished_name' in config
248 problems making Certificate Request
250 This is because it can't find the configuration file. Check out the
251 DIAGNOSTICS section of req(1) for more information.
254 * Why does <SSL program> fail with a certificate verify error?
256 This problem is usually indicated by log messages saying something like
257 "unable to get local issuer certificate" or "self signed certificate".
258 When a certificate is verified its root CA must be "trusted" by OpenSSL
259 this typically means that the CA certificate must be placed in a directory
260 or file and the relevant program configured to read it. The OpenSSL program
261 'verify' behaves in a similar way and issues similar error messages: check
262 the verify(1) program manual page for more information.
265 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
267 This is almost certainly because you are using an old "export grade" browser
268 which only supports weak encryption. Upgrade your browser to support 128 bit
272 * How can I create DSA certificates?
274 Check the CA.pl(1) manual page for a DSA certificate example.
277 * Why can't I make an SSL connection to a server using a DSA certificate?
279 Typically you'll see a message saying there are no shared ciphers when
280 the same setup works fine with an RSA certificate. There are two possible
281 causes. The client may not support connections to DSA servers most web
282 browsers (including Netscape and MSIE) only support connections to servers
283 supporting RSA cipher suites. The other cause is that a set of DH parameters
284 has not been supplied to the server. DH parameters can be created with the
285 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
286 check the source to s_server in apps/s_server.c for an example.
289 * How can I remove the passphrase on a private key?
291 Firstly you should be really *really* sure you want to do this. Leaving
292 a private key unencrypted is a major security risk. If you decide that
293 you do have to do this check the EXAMPLES sections of the rsa(1) and
297 * Why can't I use OpenSSL certificates with SSL client authentication?
299 What will typically happen is that when a server requests authentication
300 it will either not include your certificate or tell you that you have
301 no client certificates (Netscape) or present you with an empty list box
302 (MSIE). The reason for this is that when a server requests a client
303 certificate it includes a list of CAs names which it will accept. Browsers
304 will only let you select certificates from the list on the grounds that
305 there is little point presenting a certificate which the server will
308 The solution is to add the relevant CA certificate to your servers "trusted
309 CA list". How you do this depends on the server sofware in uses. You can
310 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
312 openssl s_client -connect www.some.host:443 -prexit
314 If your server only requests certificates on certain URLs then you may need
315 to manually issue an HTTP GET command to get the list when s_client connects:
317 GET /some/page/needing/a/certificate.html
319 If your CA does not appear in the list then this confirms the problem.
322 * Why does my browser give a warning about a mismatched hostname?
324 Browsers expect the server's hostname to match the value in the commonName
325 (CN) field of the certificate. If it does not then you get a warning.
328 [BUILD] =======================================================================
330 * Why does the linker complain about undefined symbols?
332 Maybe the compilation was interrupted, and make doesn't notice that
333 something is missing. Run "make clean; make".
335 If you used ./Configure instead of ./config, make sure that you
336 selected the right target. File formats may differ slightly between
337 OS versions (for example sparcv8/sparcv9, or a.out/elf).
339 In case you get errors about the following symbols, use the config
340 option "no-asm", as described in INSTALL:
342 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
343 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
344 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
345 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
346 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
347 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
348 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
350 If none of these helps, you may want to try using the current snapshot.
351 If the problem persists, please submit a bug report.
354 * Why does the OpenSSL test fail with "bc: command not found"?
356 You didn't install "bc", the Unix calculator. If you want to run the
357 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
360 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
362 On some SCO installations or versions, bc has a bug that gets triggered
363 when you run the test suite (using "make test"). The message returned is
364 "bc: 1 not implemented".
366 The best way to deal with this is to find another implementation of bc
367 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
368 for download instructions) can be safely used, for example.
371 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
373 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
374 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
375 memory to continue compilation.' As far as the tests have shown, this may be
376 a compiler bug. What happens is that it eats up a lot of resident memory
377 to build something, probably a table. The problem is clearly in the
378 optimization code, because if one eliminates optimization completely (-O0),
379 the compilation goes through (and the compiler consumes about 2MB of resident
380 memory instead of 240MB or whatever one's limit is currently).
382 There are three options to solve this problem:
384 1. set your current data segment size soft limit higher. Experience shows
385 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
386 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
387 kbytes to set the limit to.
389 2. If you have a hard limit that is lower than what you need and you can't
390 get it changed, you can compile all of OpenSSL with -O0 as optimization
391 level. This is however not a very nice thing to do for those who expect to
392 get the best result from OpenSSL. A bit more complicated solution is the
395 ----- snip:start -----
396 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
397 sed -e 's/ -O[0-9] / -O0 /'`"
398 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
402 This will only compile sha_dgst.c with -O0, the rest with the optimization
403 level chosen by the configuration process. When the above is done, do the
404 test and installation and you're set.
407 * Why does the OpenSSL compilation fail with "ar: command not found"?
409 Getting this message is quite usual on Solaris 2, because Sun has hidden
410 away 'ar' and other development commands in directories that aren't in
411 $PATH by default. One of those directories is '/usr/ccs/bin'. The
412 quickest way to fix this is to do the following (it assumes you use sh
413 or any sh-compatible shell):
415 ----- snip:start -----
416 PATH=${PATH}:/usr/ccs/bin; export PATH
419 and then redo the compilation. What you should really do is make sure
420 '/usr/ccs/bin' is permanently in your $PATH, for example through your
421 '.profile' (again, assuming you use a sh-compatible shell).
424 * Why does the OpenSSL compilation fail on Win32 with VC++?
426 Sometimes, you may get reports from VC++ command line (cl) that it
427 can't find standard include files like stdio.h and other weirdnesses.
428 One possible cause is that the environment isn't correctly set up.
429 To solve that problem, one should run VCVARS32.BAT which is found in
430 the 'bin' subdirectory of the VC++ installation directory (somewhere
431 under 'Program Files'). This needs to be done prior to running NMAKE,
432 and the changes are only valid for the current DOS session.
435 [PROG] ========================================================================
437 * Is OpenSSL thread-safe?
439 Yes (with limitations: an SSL connection may not concurrently be used
440 by multiple threads). On Windows and many Unix systems, OpenSSL
441 automatically uses the multi-threaded versions of the standard
442 libraries. If your platform is not one of these, consult the INSTALL
445 Multi-threaded applications must provide two callback functions to
446 OpenSSL. This is described in the threads(3) manpage.
449 * I've compiled a program under Windows and it crashes: why?
451 This is usually because you've missed the comment in INSTALL.W32. You
452 must link with the multithreaded DLL version of the VC++ runtime library
453 otherwise the conflict will cause a program to crash: typically on the
454 first BIO related read or write operation.
457 * How do I read or write a DER encoded buffer using the ASN1 functions?
459 You have two options. You can either use a memory BIO in conjunction
460 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
461 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
462 cause of grief here are some code fragments using PKCS7 as an example:
464 unsigned char *buf, *p;
467 len = i2d_PKCS7(p7, NULL);
468 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
472 At this point buf contains the len bytes of the DER encoding of
475 The opposite assumes we already have len bytes in buf:
479 p7 = d2i_PKCS7(NULL, &p, len);
481 At this point p7 contains a valid PKCS7 structure of NULL if an error
482 occurred. If an error occurred ERR_print_errors(bio) should give more
485 The reason for the temporary variable 'p' is that the ASN1 functions
486 increment the passed pointer so it is ready to read or write the next
487 structure. This is often a cause of problems: without the temporary
488 variable the buffer pointer is changed to point just after the data
489 that has been read or written. This may well be uninitialized data
490 and attempts to free the buffer will have unpredictable results
491 because it no longer points to the same address.
494 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
496 This usually happens when you try compiling something using the PKCS#12
497 macros with a C++ compiler. There is hardly ever any need to use the
498 PKCS#12 macros in a program, it is much easier to parse and create
499 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
500 documented in doc/openssl.txt and with examples in demos/pkcs12. The
501 'pkcs12' application has to use the macros because it prints out
502 debugging information.
505 * I've called <some function> and it fails, why?
507 Before submitting a report or asking in one of the mailing lists, you
508 should try to determine the cause. In particular, you should call
509 ERR_print_errors() or ERR_print_errors_fp() after the failed call
510 and see if the message helps. Note that the problem may occur earlier
511 than you think -- you should check for errors after every call where
512 it is possible, otherwise the actual problem may be hidden because
513 some OpenSSL functions clear the error state.
516 * I just get a load of numbers for the error output, what do they mean?
518 The actual format is described in the ERR_print_errors() manual page.
519 You should call the function ERR_load_crypto_strings() before hand and
520 the message will be output in text form. If you can't do this (for example
521 it is a pre-compiled binary) you can use the errstr utility on the error
522 code itself (the hex digits after the second colon).
525 * Why do I get errors about unknown algorithms?
527 This can happen under several circumstances such as reading in an
528 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
529 is forgetting to load OpenSSL's table of algorithms with
530 OpenSSL_add_all_algorithms(). See the manual page for more information.
533 * Why can't the OpenSSH configure script detect OpenSSL?
535 There is a problem with OpenSSH 1.2.2p1, in that the configure script
536 can't find the installed OpenSSL libraries. The problem is actually
537 a small glitch that is easily solved with the following patch to be
538 applied to the OpenSSH distribution:
540 ----- snip:start -----
541 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
542 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
543 @@ -152,10 +152,10 @@
544 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
545 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
546 if test ! -z "$ssldir" ; then
547 - LIBS="$saved_LIBS -L$ssldir"
548 + LIBS="$saved_LIBS -L$ssldir/lib"
549 CFLAGS="$CFLAGS -I$ssldir/include"
550 if test "x$need_dash_r" = "x1" ; then
551 - LIBS="$LIBS -R$ssldir"
552 + LIBS="$LIBS -R$ssldir/lib"
555 LIBS="$LIBS -lcrypto"
556 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
557 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
558 @@ -1890,10 +1890,10 @@
559 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
560 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
561 if test ! -z "$ssldir" ; then
562 - LIBS="$saved_LIBS -L$ssldir"
563 + LIBS="$saved_LIBS -L$ssldir/lib"
564 CFLAGS="$CFLAGS -I$ssldir/include"
565 if test "x$need_dash_r" = "x1" ; then
566 - LIBS="$LIBS -R$ssldir"
567 + LIBS="$LIBS -R$ssldir/lib"
570 LIBS="$LIBS -lcrypto"
574 * Can I use OpenSSL's SSL library with non-blocking I/O?
576 Yes; make sure to read the SSL_get_error(3) manual page!
578 A pitfall to avoid: Don't assume that SSL_read() will just read from
579 the underlying transport or that SSL_write() will just write to it --
580 it is also possible that SSL_write() cannot do any useful work until
581 there is data to read, or that SSL_read() cannot do anything until it
582 is possible to send data. One reason for this is that the peer may
583 request a new TLS/SSL handshake at any time during the protocol,
584 requiring a bi-directional message exchange; both SSL_read() and
585 SSL_write() will try to continue any pending handshake.
588 * Why doesn't my server application receive a client certificate?
590 Due to the TLS protocol definition, a client will only send a certificate,
591 if explicitely asked by the server. Use the SSL_VERIFY_PEER flag of the
592 SSL_CTX_set_verify() function to enable the use of client certificates.
595 ===============================================================================