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 * Why do I get an "unable to write 'random state'" error message?
21 * How do I create certificates or certificate requests?
22 * Why can't I create certificate requests?
23 * Why does <SSL program> fail with a certificate verify error?
24 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
25 * How can I create DSA certificates?
26 * Why can't I make an SSL connection using a DSA certificate?
27 * How can I remove the passphrase on a private key?
28 * Why can't I use OpenSSL certificates with SSL client authentication?
29 * Why does my browser give a warning about a mismatched hostname?
31 [BUILD] Questions about building and testing OpenSSL
33 * Why does the linker complain about undefined symbols?
34 * Why does the OpenSSL test fail with "bc: command not found"?
35 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
36 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
37 * Why does the OpenSSL compilation fail with "ar: command not found"?
38 * Why does the OpenSSL compilation fail on Win32 with VC++?
40 [PROG] Questions about programming with OpenSSL
42 * Is OpenSSL thread-safe?
43 * I've compiled a program under Windows and it crashes: why?
44 * How do I read or write a DER encoded buffer using the ASN1 functions?
45 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
46 * I've called <some function> and it fails, why?
47 * I just get a load of numbers for the error output, what do they mean?
48 * Why do I get errors about unknown algorithms?
49 * Why can't the OpenSSH configure script detect OpenSSL?
50 * Can I use OpenSSL's SSL library with non-blocking I/O?
51 * Why doesn't my server application receive a client certificate?
53 ===============================================================================
55 [MISC] ========================================================================
57 * Which is the current version of OpenSSL?
59 The current version is available from <URL: http://www.openssl.org>.
60 OpenSSL 0.9.6a was released on April 5th, 2001.
62 In addition to the current stable release, you can also access daily
63 snapshots of the OpenSSL development version at <URL:
64 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
67 * Where is the documentation?
69 OpenSSL is a library that provides cryptographic functionality to
70 applications such as secure web servers. Be sure to read the
71 documentation of the application you want to use. The INSTALL file
72 explains how to install this library.
74 OpenSSL includes a command line utility that can be used to perform a
75 variety of cryptographic functions. It is described in the openssl(1)
76 manpage. Documentation for developers is currently being written. A
77 few manual pages already are available; overviews over libcrypto and
78 libssl are given in the crypto(3) and ssl(3) manpages.
80 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
81 different directory if you specified one as described in INSTALL).
82 In addition, you can read the most current versions at
83 <URL: http://www.openssl.org/docs/>.
85 For information on parts of libcrypto that are not yet documented, you
86 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
87 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
88 of this still applies to OpenSSL.
90 There is some documentation about certificate extensions and PKCS#12
93 The original SSLeay documentation is included in OpenSSL as
94 doc/ssleay.txt. It may be useful when none of the other resources
95 help, but please note that it reflects the obsolete version SSLeay
99 * How can I contact the OpenSSL developers?
101 The README file describes how to submit bug reports and patches to
102 OpenSSL. Information on the OpenSSL mailing lists is available from
103 <URL: http://www.openssl.org>.
106 * Where can I get a compiled version of OpenSSL?
108 Some applications that use OpenSSL are distributed in binary form.
109 When using such an application, you don't need to install OpenSSL
110 yourself; the application will include the required parts (e.g. DLLs).
112 If you want to install OpenSSL on a Windows system and you don't have
113 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
114 on how to obtain and install the free GNU C compiler.
116 A number of Linux and *BSD distributions include OpenSSL.
119 * Why aren't tools like 'autoconf' and 'libtool' used?
121 autoconf will probably be used in future OpenSSL versions. If it was
122 less Unix-centric, it might have been used much earlier.
125 [LEGAL] =======================================================================
127 * Do I need patent licenses to use OpenSSL?
129 The patents section of the README file lists patents that may apply to
130 you if you want to use OpenSSL. For information on intellectual
131 property rights, please consult a lawyer. The OpenSSL team does not
134 You can configure OpenSSL so as not to use RC5 and IDEA by using
135 ./config no-rc5 no-idea
138 * Can I use OpenSSL with GPL software?
140 On many systems including the major Linux and BSD distributions, yes (the
141 GPL does not place restrictions on using libraries that are part of the
142 normal operating system distribution).
144 On other systems, the situation is less clear. Some GPL software copyright
145 holders claim that you infringe on their rights if you use OpenSSL with
146 their software on operating systems that don't normally include OpenSSL.
148 If you develop open source software that uses OpenSSL, you may find it
149 useful to choose an other license than the GPL, or state explicitely that
150 "This program is released under the GPL with the additional exemption that
151 compiling, linking, and/or using OpenSSL is allowed." If you are using
152 GPL software developed by others, you may want to ask the copyright holder
153 for permission to use their software with OpenSSL.
156 [USER] ========================================================================
158 * Why do I get a "PRNG not seeded" error message?
160 Cryptographic software needs a source of unpredictable data to work
161 correctly. Many open source operating systems provide a "randomness
162 device" that serves this purpose. On other systems, applications have
163 to call the RAND_add() or RAND_seed() function with appropriate data
164 before generating keys or performing public key encryption.
165 (These functions initialize the pseudo-random number generator, PRNG.)
167 Some broken applications do not do this. As of version 0.9.5, the
168 OpenSSL functions that need randomness report an error if the random
169 number generator has not been seeded with at least 128 bits of
170 randomness. If this error occurs, please contact the author of the
171 application you are using. It is likely that it never worked
172 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
173 to perform potentially insecure encryption.
175 On systems without /dev/urandom and /dev/random, it is a good idea to
176 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
177 details. Starting with version 0.9.7, OpenSSL will automatically look
178 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
181 Most components of the openssl command line utility automatically try
182 to seed the random number generator from a file. The name of the
183 default seeding file is determined as follows: If environment variable
184 RANDFILE is set, then it names the seeding file. Otherwise if
185 environment variable HOME is set, then the seeding file is $HOME/.rnd.
186 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
187 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
188 default seeding file at all. OpenSSL 0.9.6b and later will behave
189 similarly to 0.9.6a, but will use a default of "C:" for HOME on
190 Windows systems if the environment variable has not been set.
192 If the default seeding file does not exist or is too short, the "PRNG
193 not seeded" error message may occur.
195 The openssl command line utility will write back a new state to the
196 default seeding file (and create this file if necessary) unless
197 there was no sufficient seeding.
199 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
200 Use the "-rand" option of the OpenSSL command line tools instead.
201 The $RANDFILE environment variable and $HOME/.rnd are only used by the
202 OpenSSL command line tools. Applications using the OpenSSL library
203 provide their own configuration options to specify the entropy source,
204 please check out the documentation coming the with application.
206 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
207 installing the SUNski package from Sun patch 105710-01 (Sparc) which
208 adds a /dev/random device and make sure it gets used, usually through
209 $RANDFILE. There are probably similar patches for the other Solaris
210 versions. However, be warned that /dev/random is usually a blocking
211 device, which may have some effects on OpenSSL.
214 * Why do I get an "unable to write 'random state'" error message?
217 Sometimes the openssl command line utility does not abort with
218 a "PRNG not seeded" error message, but complains that it is
219 "unable to write 'random state'". This message refers to the
220 default seeding file (see previous answer). A possible reason
221 is that no default filename is known because neither RANDFILE
222 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
223 current directory in this case, but this has changed with 0.9.6a.)
226 * How do I create certificates or certificate requests?
228 Check out the CA.pl(1) manual page. This provides a simple wrapper round
229 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
230 out the manual pages for the individual utilities and the certificate
231 extensions documentation (currently in doc/openssl.txt).
234 * Why can't I create certificate requests?
236 You typically get the error:
238 unable to find 'distinguished_name' in config
239 problems making Certificate Request
241 This is because it can't find the configuration file. Check out the
242 DIAGNOSTICS section of req(1) for more information.
245 * Why does <SSL program> fail with a certificate verify error?
247 This problem is usually indicated by log messages saying something like
248 "unable to get local issuer certificate" or "self signed certificate".
249 When a certificate is verified its root CA must be "trusted" by OpenSSL
250 this typically means that the CA certificate must be placed in a directory
251 or file and the relevant program configured to read it. The OpenSSL program
252 'verify' behaves in a similar way and issues similar error messages: check
253 the verify(1) program manual page for more information.
256 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
258 This is almost certainly because you are using an old "export grade" browser
259 which only supports weak encryption. Upgrade your browser to support 128 bit
263 * How can I create DSA certificates?
265 Check the CA.pl(1) manual page for a DSA certificate example.
268 * Why can't I make an SSL connection to a server using a DSA certificate?
270 Typically you'll see a message saying there are no shared ciphers when
271 the same setup works fine with an RSA certificate. There are two possible
272 causes. The client may not support connections to DSA servers most web
273 browsers (including Netscape and MSIE) only support connections to servers
274 supporting RSA cipher suites. The other cause is that a set of DH parameters
275 has not been supplied to the server. DH parameters can be created with the
276 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
277 check the source to s_server in apps/s_server.c for an example.
280 * How can I remove the passphrase on a private key?
282 Firstly you should be really *really* sure you want to do this. Leaving
283 a private key unencrypted is a major security risk. If you decide that
284 you do have to do this check the EXAMPLES sections of the rsa(1) and
288 * Why can't I use OpenSSL certificates with SSL client authentication?
290 What will typically happen is that when a server requests authentication
291 it will either not include your certificate or tell you that you have
292 no client certificates (Netscape) or present you with an empty list box
293 (MSIE). The reason for this is that when a server requests a client
294 certificate it includes a list of CAs names which it will accept. Browsers
295 will only let you select certificates from the list on the grounds that
296 there is little point presenting a certificate which the server will
299 The solution is to add the relevant CA certificate to your servers "trusted
300 CA list". How you do this depends on the server sofware in uses. You can
301 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
303 openssl s_client -connect www.some.host:443 -prexit
305 If your server only requests certificates on certain URLs then you may need
306 to manually issue an HTTP GET command to get the list when s_client connects:
308 GET /some/page/needing/a/certificate.html
310 If your CA does not appear in the list then this confirms the problem.
313 * Why does my browser give a warning about a mismatched hostname?
315 Browsers expect the server's hostname to match the value in the commonName
316 (CN) field of the certificate. If it does not then you get a warning.
319 [BUILD] =======================================================================
321 * Why does the linker complain about undefined symbols?
323 Maybe the compilation was interrupted, and make doesn't notice that
324 something is missing. Run "make clean; make".
326 If you used ./Configure instead of ./config, make sure that you
327 selected the right target. File formats may differ slightly between
328 OS versions (for example sparcv8/sparcv9, or a.out/elf).
330 In case you get errors about the following symbols, use the config
331 option "no-asm", as described in INSTALL:
333 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
334 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
335 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
336 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
337 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
338 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
339 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
341 If none of these helps, you may want to try using the current snapshot.
342 If the problem persists, please submit a bug report.
345 * Why does the OpenSSL test fail with "bc: command not found"?
347 You didn't install "bc", the Unix calculator. If you want to run the
348 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
351 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
353 On some SCO installations or versions, bc has a bug that gets triggered
354 when you run the test suite (using "make test"). The message returned is
355 "bc: 1 not implemented".
357 The best way to deal with this is to find another implementation of bc
358 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
359 for download instructions) can be safely used, for example.
362 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
364 On some Alpha installations running True64 Unix and Compaq C, the compilation
365 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
366 memory to continue compilation.' As far as the tests have shown, this may be
367 a compiler bug. What happens is that it eats up a lot of resident memory
368 to build something, probably a table. The problem is clearly in the
369 optimization code, because if one eliminates optimization completely (-O0),
370 the compilation goes through (and the compiler consumes about 2MB of resident
371 memory instead of 240MB or whatever one's limit is currently).
373 There are three options to solve this problem:
375 1. set your current data segment size soft limit higher. Experience shows
376 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
377 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
378 kbytes to set the limit to.
380 2. If you have a hard limit that is lower than what you need and you can't
381 get it changed, you can compile all of OpenSSL with -O0 as optimization
382 level. This is however not a very nice thing to do for those who expect to
383 get the best result from OpenSSL. A bit more complicated solution is the
386 ----- snip:start -----
387 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
388 sed -e 's/ -O[0-9] / -O0 /'`"
389 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
393 This will only compile sha_dgst.c with -O0, the rest with the optimization
394 level chosen by the configuration process. When the above is done, do the
395 test and installation and you're set.
398 * Why does the OpenSSL compilation fail with "ar: command not found"?
400 Getting this message is quite usual on Solaris 2, because Sun has hidden
401 away 'ar' and other development commands in directories that aren't in
402 $PATH by default. One of those directories is '/usr/ccs/bin'. The
403 quickest way to fix this is to do the following (it assumes you use sh
404 or any sh-compatible shell):
406 ----- snip:start -----
407 PATH=${PATH}:/usr/ccs/bin; export PATH
410 and then redo the compilation. What you should really do is make sure
411 '/usr/ccs/bin' is permanently in your $PATH, for example through your
412 '.profile' (again, assuming you use a sh-compatible shell).
415 * Why does the OpenSSL compilation fail on Win32 with VC++?
417 Sometimes, you may get reports from VC++ command line (cl) that it
418 can't find standard include files like stdio.h and other weirdnesses.
419 One possible cause is that the environment isn't correctly set up.
420 To solve that problem, one should run VCVARS32.BAT which is found in
421 the 'bin' subdirectory of the VC++ installation directory (somewhere
422 under 'Program Files'). This needs to be done prior to running NMAKE,
423 and the changes are only valid for the current DOS session.
426 [PROG] ========================================================================
428 * Is OpenSSL thread-safe?
430 Yes (with limitations: an SSL connection may not concurrently be used
431 by multiple threads). On Windows and many Unix systems, OpenSSL
432 automatically uses the multi-threaded versions of the standard
433 libraries. If your platform is not one of these, consult the INSTALL
436 Multi-threaded applications must provide two callback functions to
437 OpenSSL. This is described in the threads(3) manpage.
440 * I've compiled a program under Windows and it crashes: why?
442 This is usually because you've missed the comment in INSTALL.W32. You
443 must link with the multithreaded DLL version of the VC++ runtime library
444 otherwise the conflict will cause a program to crash: typically on the
445 first BIO related read or write operation.
448 * How do I read or write a DER encoded buffer using the ASN1 functions?
450 You have two options. You can either use a memory BIO in conjunction
451 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
452 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
453 cause of grief here are some code fragments using PKCS7 as an example:
455 unsigned char *buf, *p;
458 len = i2d_PKCS7(p7, NULL);
459 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
463 At this point buf contains the len bytes of the DER encoding of
466 The opposite assumes we already have len bytes in buf:
470 p7 = d2i_PKCS7(NULL, &p, len);
472 At this point p7 contains a valid PKCS7 structure of NULL if an error
473 occurred. If an error occurred ERR_print_errors(bio) should give more
476 The reason for the temporary variable 'p' is that the ASN1 functions
477 increment the passed pointer so it is ready to read or write the next
478 structure. This is often a cause of problems: without the temporary
479 variable the buffer pointer is changed to point just after the data
480 that has been read or written. This may well be uninitialized data
481 and attempts to free the buffer will have unpredictable results
482 because it no longer points to the same address.
485 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
487 This usually happens when you try compiling something using the PKCS#12
488 macros with a C++ compiler. There is hardly ever any need to use the
489 PKCS#12 macros in a program, it is much easier to parse and create
490 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
491 documented in doc/openssl.txt and with examples in demos/pkcs12. The
492 'pkcs12' application has to use the macros because it prints out
493 debugging information.
496 * I've called <some function> and it fails, why?
498 Before submitting a report or asking in one of the mailing lists, you
499 should try to determine the cause. In particular, you should call
500 ERR_print_errors() or ERR_print_errors_fp() after the failed call
501 and see if the message helps. Note that the problem may occur earlier
502 than you think -- you should check for errors after every call where
503 it is possible, otherwise the actual problem may be hidden because
504 some OpenSSL functions clear the error state.
507 * I just get a load of numbers for the error output, what do they mean?
509 The actual format is described in the ERR_print_errors() manual page.
510 You should call the function ERR_load_crypto_strings() before hand and
511 the message will be output in text form. If you can't do this (for example
512 it is a pre-compiled binary) you can use the errstr utility on the error
513 code itself (the hex digits after the second colon).
516 * Why do I get errors about unknown algorithms?
518 This can happen under several circumstances such as reading in an
519 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
520 is forgetting to load OpenSSL's table of algorithms with
521 OpenSSL_add_all_algorithms(). See the manual page for more information.
524 * Why can't the OpenSSH configure script detect OpenSSL?
526 There is a problem with OpenSSH 1.2.2p1, in that the configure script
527 can't find the installed OpenSSL libraries. The problem is actually
528 a small glitch that is easily solved with the following patch to be
529 applied to the OpenSSH distribution:
531 ----- snip:start -----
532 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
533 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
534 @@ -152,10 +152,10 @@
535 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
536 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
537 if test ! -z "$ssldir" ; then
538 - LIBS="$saved_LIBS -L$ssldir"
539 + LIBS="$saved_LIBS -L$ssldir/lib"
540 CFLAGS="$CFLAGS -I$ssldir/include"
541 if test "x$need_dash_r" = "x1" ; then
542 - LIBS="$LIBS -R$ssldir"
543 + LIBS="$LIBS -R$ssldir/lib"
546 LIBS="$LIBS -lcrypto"
547 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
548 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
549 @@ -1890,10 +1890,10 @@
550 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
551 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
552 if test ! -z "$ssldir" ; then
553 - LIBS="$saved_LIBS -L$ssldir"
554 + LIBS="$saved_LIBS -L$ssldir/lib"
555 CFLAGS="$CFLAGS -I$ssldir/include"
556 if test "x$need_dash_r" = "x1" ; then
557 - LIBS="$LIBS -R$ssldir"
558 + LIBS="$LIBS -R$ssldir/lib"
561 LIBS="$LIBS -lcrypto"
565 * Can I use OpenSSL's SSL library with non-blocking I/O?
567 Yes; make sure to read the SSL_get_error(3) manual page!
569 A pitfall to avoid: Don't assume that SSL_read() will just read from
570 the underlying transport or that SSL_write() will just write to it --
571 it is also possible that SSL_write() cannot do any useful work until
572 there is data to read, or that SSL_read() cannot do anything until it
573 is possible to send data. One reason for this is that the peer may
574 request a new TLS/SSL handshake at any time during the protocol,
575 requiring a bi-directional message exchange; both SSL_read() and
576 SSL_write() will try to continue any pending handshake.
579 * Why doesn't my server application receive a client certificate?
581 Due to the TLS protocol definition, a client will only send a certificate,
582 if explicitely asked by the server. Use the SSL_VERIFY_PEER flag of the
583 SSL_CTX_set_verify() function to enable the use of client certificates.
586 ===============================================================================