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?
16 [USER] Questions on using the OpenSSL applications
18 * Why do I get a "PRNG not seeded" error message?
19 * How do I create certificates or certificate requests?
20 * Why can't I create certificate requests?
21 * Why does <SSL program> fail with a certificate verify error?
22 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
23 * How can I create DSA certificates?
24 * Why can't I make an SSL connection using a DSA certificate?
25 * How can I remove the passphrase on a private key?
27 [BUILD] Questions about building and testing OpenSSL
29 * Why does the linker complain about undefined symbols?
30 * Why does the OpenSSL test fail with "bc: command not found"?
31 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
32 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
33 * Why does the OpenSSL compilation fail with "ar: command not found"?
34 * Why does the OpenSSL compilation fail on Win32 with VC++?
36 [PROG] Questions about programming with OpenSSL
38 * Is OpenSSL thread-safe?
39 * I've compiled a program under Windows and it crashes: why?
40 * How do I read or write a DER encoded buffer using the ASN1 functions?
41 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
42 * I've called <some function> and it fails, why?
43 * I just get a load of numbers for the error output, what do they mean?
44 * Why do I get errors about unknown algorithms?
45 * Why can't the OpenSSH configure script detect OpenSSL?
46 * Can I use OpenSSL's SSL library with non-blocking I/O?
48 ===============================================================================
50 [MISC] ========================================================================
52 * Which is the current version of OpenSSL?
54 The current version is available from <URL: http://www.openssl.org>.
55 OpenSSL 0.9.6 was released on September 24th, 2000.
57 In addition to the current stable release, you can also access daily
58 snapshots of the OpenSSL development version at <URL:
59 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
62 * Where is the documentation?
64 OpenSSL is a library that provides cryptographic functionality to
65 applications such as secure web servers. Be sure to read the
66 documentation of the application you want to use. The INSTALL file
67 explains how to install this library.
69 OpenSSL includes a command line utility that can be used to perform a
70 variety of cryptographic functions. It is described in the openssl(1)
71 manpage. Documentation for developers is currently being written. A
72 few manual pages already are available; overviews over libcrypto and
73 libssl are given in the crypto(3) and ssl(3) manpages.
75 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
76 different directory if you specified one as described in INSTALL).
77 In addition, you can read the most current versions at
78 <URL: http://www.openssl.org/docs/>.
80 For information on parts of libcrypto that are not yet documented, you
81 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
82 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
83 of this still applies to OpenSSL.
85 There is some documentation about certificate extensions and PKCS#12
88 The original SSLeay documentation is included in OpenSSL as
89 doc/ssleay.txt. It may be useful when none of the other resources
90 help, but please note that it reflects the obsolete version SSLeay
94 * How can I contact the OpenSSL developers?
96 The README file describes how to submit bug reports and patches to
97 OpenSSL. Information on the OpenSSL mailing lists is available from
98 <URL: http://www.openssl.org>.
101 * Where can I get a compiled version of OpenSSL?
103 Some applications that use OpenSSL are distributed in binary form.
104 When using such an application, you don't need to install OpenSSL
105 yourself; the application will include the required parts (e.g. DLLs).
107 If you want to install OpenSSL on a Windows system and you don't have
108 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
109 on how to obtain and install the free GNU C compiler.
111 A number of Linux and *BSD distributions include OpenSSL.
114 * Why aren't tools like 'autoconf' and 'libtool' used?
116 autoconf is a nice tool, but is unfortunately very Unix-centric.
117 Although one can come up with solution to have ports keep in track,
118 there's also some work needed for that, and can be quite painful at
119 times. If there was a 'autoconf'-like tool that generated perl
120 scripts or something similarly general, it would probably be used
121 in OpenSSL much earlier.
123 libtool has repeatadly been reported by some members of the OpenSSL
124 development and others to be a pain to use. So far, those in the
125 development team who have said anything about this have expressed
126 a wish to avoid libtool for that reason.
129 [LEGAL] =======================================================================
131 * Do I need patent licenses to use OpenSSL?
133 The patents section of the README file lists patents that may apply to
134 you if you want to use OpenSSL. For information on intellectual
135 property rights, please consult a lawyer. The OpenSSL team does not
138 You can configure OpenSSL so as not to use RC5 and IDEA by using
139 ./config no-rc5 no-idea
142 [USER] ========================================================================
144 * Why do I get a "PRNG not seeded" error message?
146 Cryptographic software needs a source of unpredictable data to work
147 correctly. Many open source operating systems provide a "randomness
148 device" that serves this purpose. On other systems, applications have
149 to call the RAND_add() or RAND_seed() function with appropriate data
150 before generating keys or performing public key encryption.
152 Some broken applications do not do this. As of version 0.9.5, the
153 OpenSSL functions that need randomness report an error if the random
154 number generator has not been seeded with at least 128 bits of
155 randomness. If this error occurs, please contact the author of the
156 application you are using. It is likely that it never worked
157 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
158 to perform potentially insecure encryption.
160 On systems without /dev/urandom, it is a good idea to use the Entropy
161 Gathering Demon; see the RAND_egd() manpage for details.
163 Most components of the openssl command line tool try to use the
164 file $HOME/.rnd (or $RANDFILE, if this environment variable is set)
165 for seeding the PRNG. If this file does not exist or is too short,
166 the "PRNG not seeded" error message may occur.
168 [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version
169 0.9.5 does not do this and will fail on systems without /dev/urandom
170 when trying to password-encrypt an RSA key! This is a bug in the
171 library; try a later version instead.]
173 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
174 installing the SUNski package from Sun patch 105710-01 (Sparc) which
175 adds a /dev/random device and make sure it gets used, usually through
176 $RANDFILE. There are probably similar patches for the other Solaris
177 versions. However, be warned that /dev/random is usually a blocking
178 device, which may have some effects on OpenSSL.
181 * How do I create certificates or certificate requests?
183 Check out the CA.pl(1) manual page. This provides a simple wrapper round
184 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
185 out the manual pages for the individual utilities and the certificate
186 extensions documentation (currently in doc/openssl.txt).
189 * Why can't I create certificate requests?
191 You typically get the error:
193 unable to find 'distinguished_name' in config
194 problems making Certificate Request
196 This is because it can't find the configuration file. Check out the
197 DIAGNOSTICS section of req(1) for more information.
200 * Why does <SSL program> fail with a certificate verify error?
202 This problem is usually indicated by log messages saying something like
203 "unable to get local issuer certificate" or "self signed certificate".
204 When a certificate is verified its root CA must be "trusted" by OpenSSL
205 this typically means that the CA certificate must be placed in a directory
206 or file and the relevant program configured to read it. The OpenSSL program
207 'verify' behaves in a similar way and issues similar error messages: check
208 the verify(1) program manual page for more information.
211 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
213 This is almost certainly because you are using an old "export grade" browser
214 which only supports weak encryption. Upgrade your browser to support 128 bit
218 * How can I create DSA certificates?
220 Check the CA.pl(1) manual page for a DSA certificate example.
223 * Why can't I make an SSL connection to a server using a DSA certificate?
225 Typically you'll see a message saying there are no shared ciphers when
226 the same setup works fine with an RSA certificate. There are two possible
227 causes. The client may not support connections to DSA servers most web
228 browsers (including Netscape and MSIE) only support connections to servers
229 supporting RSA cipher suites. The other cause is that a set of DH parameters
230 has not been supplied to the server. DH parameters can be created with the
231 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
232 check the source to s_server in apps/s_server.c for an example.
235 * How can I remove the passphrase on a private key?
237 Firstly you should be really *really* sure you want to do this. Leaving
238 a private key unencrypted is a major security risk. If you decide that
239 you do have to do this check the EXAMPLES sections of the rsa(1) and
243 [BUILD] =======================================================================
245 * Why does the linker complain about undefined symbols?
247 Maybe the compilation was interrupted, and make doesn't notice that
248 something is missing. Run "make clean; make".
250 If you used ./Configure instead of ./config, make sure that you
251 selected the right target. File formats may differ slightly between
252 OS versions (for example sparcv8/sparcv9, or a.out/elf).
254 In case you get errors about the following symbols, use the config
255 option "no-asm", as described in INSTALL:
257 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
258 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
259 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
260 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
261 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
262 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
263 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
265 If none of these helps, you may want to try using the current snapshot.
266 If the problem persists, please submit a bug report.
269 * Why does the OpenSSL test fail with "bc: command not found"?
271 You didn't install "bc", the Unix calculator. If you want to run the
272 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
275 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
277 On some SCO installations or versions, bc has a bug that gets triggered when
278 you run the test suite (using "make test"). The message returned is "bc:
279 1 not implemented". The best way to deal with this is to find another
280 implementation of bc and compile/install it. For example, GNU bc (see
281 http://www.gnu.org/software/software.html for download instructions) can
285 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
287 On some Alpha installations running True64 Unix and Compaq C, the compilation
288 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
289 memory to continue compilation.' As far as the tests have shown, this may be
290 a compiler bug. What happens is that it eats up a lot of resident memory
291 to build something, probably a table. The problem is clearly in the
292 optimization code, because if one eliminates optimization completely (-O0),
293 the compilation goes through (and the compiler consumes about 2MB of resident
294 memory instead of 240MB or whatever one's limit is currently).
296 There are three options to solve this problem:
298 1. set your current data segment size soft limit higher. Experience shows
299 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
300 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
301 kbytes to set the limit to.
303 2. If you have a hard limit that is lower than what you need and you can't
304 get it changed, you can compile all of OpenSSL with -O0 as optimization
305 level. This is however not a very nice thing to do for those who expect to
306 get the best result from OpenSSL. A bit more complicated solution is the
309 ----- snip:start -----
310 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
311 sed -e 's/ -O[0-9] / -O0 /'`"
312 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
316 This will only compile sha_dgst.c with -O0, the rest with the optimization
317 level chosen by the configuration process. When the above is done, do the
318 test and installation and you're set.
321 * Why does the OpenSSL compilation fail with "ar: command not found"?
323 Getting this message is quite usual on Solaris 2, because Sun has hidden
324 away 'ar' and other development commands in directories that aren't in
325 $PATH by default. One of those directories is '/usr/ccs/bin'. The
326 quickest way to fix this is to do the following (it assumes you use sh
327 or any sh-compatible shell):
329 ----- snip:start -----
330 PATH=${PATH}:/usr/ccs/bin; export PATH
333 and then redo the compilation. What you should really do is make sure
334 '/usr/ccs/bin' is permanently in your $PATH, for example through your
335 '.profile' (again, assuming you use a sh-compatible shell).
338 * Why does the OpenSSL compilation fail on Win32 with VC++?
340 Sometimes, you may get reports from VC++ command line (cl) that it
341 can't find standard include files like stdio.h and other weirdnesses.
342 One possible cause is that the environment isn't correctly set up.
343 To solve that problem, one should run VCVARS32.BAT which is found in
344 the 'bin' subdirectory of the VC++ installation directory (somewhere
345 under 'Program Files'). This needs to be done prior to running NMAKE,
346 and the changes are only valid for the current DOS session.
349 [PROG] ========================================================================
351 * Is OpenSSL thread-safe?
353 Yes (with limitations: an SSL connection may not concurrently be used
354 by multiple threads). On Windows and many Unix systems, OpenSSL
355 automatically uses the multi-threaded versions of the standard
356 libraries. If your platform is not one of these, consult the INSTALL
359 Multi-threaded applications must provide two callback functions to
360 OpenSSL. This is described in the threads(3) manpage.
363 * I've compiled a program under Windows and it crashes: why?
365 This is usually because you've missed the comment in INSTALL.W32. You
366 must link with the multithreaded DLL version of the VC++ runtime library
367 otherwise the conflict will cause a program to crash: typically on the
368 first BIO related read or write operation.
371 * How do I read or write a DER encoded buffer using the ASN1 functions?
373 You have two options. You can either use a memory BIO in conjunction
374 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
375 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
376 cause of grief here are some code fragments using PKCS7 as an example:
378 unsigned char *buf, *p;
381 len = i2d_PKCS7(p7, NULL);
382 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
386 At this point buf contains the len bytes of the DER encoding of
389 The opposite assumes we already have len bytes in buf:
393 p7 = d2i_PKCS7(NULL, &p, len);
395 At this point p7 contains a valid PKCS7 structure of NULL if an error
396 occurred. If an error occurred ERR_print_errors(bio) should give more
399 The reason for the temporary variable 'p' is that the ASN1 functions
400 increment the passed pointer so it is ready to read or write the next
401 structure. This is often a cause of problems: without the temporary
402 variable the buffer pointer is changed to point just after the data
403 that has been read or written. This may well be uninitialized data
404 and attempts to free the buffer will have unpredictable results
405 because it no longer points to the same address.
408 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
410 This usually happens when you try compiling something using the PKCS#12
411 macros with a C++ compiler. There is hardly ever any need to use the
412 PKCS#12 macros in a program, it is much easier to parse and create
413 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
414 documented in doc/openssl.txt and with examples in demos/pkcs12. The
415 'pkcs12' application has to use the macros because it prints out
416 debugging information.
419 * I've called <some function> and it fails, why?
421 Before submitting a report or asking in one of the mailing lists, you
422 should try to determine the cause. In particular, you should call
423 ERR_print_errors() or ERR_print_errors_fp() after the failed call
424 and see if the message helps. Note that the problem may occur earlier
425 than you think -- you should check for errors after every call where
426 it is possible, otherwise the actual problem may be hidden because
427 some OpenSSL functions clear the error state.
430 * I just get a load of numbers for the error output, what do they mean?
432 The actual format is described in the ERR_print_errors() manual page.
433 You should call the function ERR_load_crypto_strings() before hand and
434 the message will be output in text form. If you can't do this (for example
435 it is a pre-compiled binary) you can use the errstr utility on the error
436 code itself (the hex digits after the second colon).
439 * Why do I get errors about unknown algorithms?
441 This can happen under several circumstances such as reading in an
442 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
443 is forgetting to load OpenSSL's table of algorithms with
444 OpenSSL_add_all_algorithms(). See the manual page for more information.
447 * Why can't the OpenSSH configure script detect OpenSSL?
449 There is a problem with OpenSSH 1.2.2p1, in that the configure script
450 can't find the installed OpenSSL libraries. The problem is actually
451 a small glitch that is easily solved with the following patch to be
452 applied to the OpenSSH distribution:
454 ----- snip:start -----
455 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
456 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
457 @@ -152,10 +152,10 @@
458 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
459 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
460 if test ! -z "$ssldir" ; then
461 - LIBS="$saved_LIBS -L$ssldir"
462 + LIBS="$saved_LIBS -L$ssldir/lib"
463 CFLAGS="$CFLAGS -I$ssldir/include"
464 if test "x$need_dash_r" = "x1" ; then
465 - LIBS="$LIBS -R$ssldir"
466 + LIBS="$LIBS -R$ssldir/lib"
469 LIBS="$LIBS -lcrypto"
470 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
471 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
472 @@ -1890,10 +1890,10 @@
473 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
474 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
475 if test ! -z "$ssldir" ; then
476 - LIBS="$saved_LIBS -L$ssldir"
477 + LIBS="$saved_LIBS -L$ssldir/lib"
478 CFLAGS="$CFLAGS -I$ssldir/include"
479 if test "x$need_dash_r" = "x1" ; then
480 - LIBS="$LIBS -R$ssldir"
481 + LIBS="$LIBS -R$ssldir/lib"
484 LIBS="$LIBS -lcrypto"
488 * Can I use OpenSSL's SSL library with non-blocking I/O?
490 Yes; make sure to read the SSL_get_error(3) manual page!
492 A pitfall to avoid: Don't assume that SSL_read() will just read from
493 the underlying transport or that SSL_write() will just write to it --
494 it is also possible that SSL_write() cannot do any useful work until
495 there is data to read, or that SSL_read() cannot do anything until it
496 is possible to send data. One reason for this is that the peer may
497 request a new TLS/SSL handshake at any time during the protocol,
498 requiring a bi-directional message exchange; both SSL_read() and
499 SSL_write() will try to continue any pending handshake.
502 ===============================================================================