1 OpenSSL - Frequently Asked Questions
2 --------------------------------------
4 * Which is the current version of OpenSSL?
5 * Where is the documentation?
6 * How can I contact the OpenSSL developers?
7 * Do I need patent licenses to use OpenSSL?
8 * Is OpenSSL thread-safe?
9 * Why do I get a "PRNG not seeded" error message?
10 * Why does the linker complain about undefined symbols?
11 * Where can I get a compiled version of OpenSSL?
12 * I've compiled a program under Windows and it crashes: why?
13 * How do I read or write a DER encoded buffer using the ASN1 functions?
14 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
15 * I've called <some function> and it fails, why?
16 * I just get a load of numbers for the error output, what do they mean?
17 * Why do I get errors about unknown algorithms?
18 * How do I create certificates or certificate requests?
19 * Why can't I create certificate requests?
20 * Why does <SSL program> fail with a certificate verify error?
21 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
22 * How can I create DSA certificates?
23 * Why can't I make an SSL connection using a DSA certificate?
24 * How can I remove the passphrase on a private key?
25 * Why can't the OpenSSH configure script detect OpenSSL?
26 * Why does the OpenSSL test fail with "bc: command not found"?
27 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
28 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
29 * Why does the OpenSSL compilation fail with "ar: command not found"?
32 * Which is the current version of OpenSSL?
34 The current version is available from <URL: http://www.openssl.org>.
35 OpenSSL 0.9.5a was released on April 1st, 2000.
37 In addition to the current stable release, you can also access daily
38 snapshots of the OpenSSL development version at <URL:
39 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
42 * Where is the documentation?
44 OpenSSL is a library that provides cryptographic functionality to
45 applications such as secure web servers. Be sure to read the
46 documentation of the application you want to use. The INSTALL file
47 explains how to install this library.
49 OpenSSL includes a command line utility that can be used to perform a
50 variety of cryptographic functions. It is described in the openssl(1)
51 manpage. Documentation for developers is currently being written. A
52 few manual pages already are available; overviews over libcrypto and
53 libssl are given in the crypto(3) and ssl(3) manpages.
55 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
56 different directory if you specified one as described in INSTALL).
57 In addition, you can read the most current versions at
58 <URL: http://www.openssl.org/docs/>.
60 For information on parts of libcrypto that are not yet documented, you
61 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
62 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
63 of this still applies to OpenSSL.
65 There is some documentation about certificate extensions and PKCS#12
68 The original SSLeay documentation is included in OpenSSL as
69 doc/ssleay.txt. It may be useful when none of the other resources
70 help, but please note that it reflects the obsolete version SSLeay
74 * How can I contact the OpenSSL developers?
76 The README file describes how to submit bug reports and patches to
77 OpenSSL. Information on the OpenSSL mailing lists is available from
78 <URL: http://www.openssl.org>.
81 * Do I need patent licenses to use OpenSSL?
83 The patents section of the README file lists patents that may apply to
84 you if you want to use OpenSSL. For information on intellectual
85 property rights, please consult a lawyer. The OpenSSL team does not
88 You can configure OpenSSL so as not to use RC5 and IDEA by using
89 ./config no-rc5 no-idea
92 * Is OpenSSL thread-safe?
94 Yes (with limitations: an SSL connection may not concurrently be used
95 by multiple threads). On Windows and many Unix systems, OpenSSL
96 automatically uses the multi-threaded versions of the standard
97 libraries. If your platform is not one of these, consult the INSTALL
100 Multi-threaded applications must provide two callback functions to
101 OpenSSL. This is described in the threads(3) manpage.
104 * Why do I get a "PRNG not seeded" error message?
106 Cryptographic software needs a source of unpredictable data to work
107 correctly. Many open source operating systems provide a "randomness
108 device" that serves this purpose. On other systems, applications have
109 to call the RAND_add() or RAND_seed() function with appropriate data
110 before generating keys or performing public key encryption.
112 Some broken applications do not do this. As of version 0.9.5, the
113 OpenSSL functions that need randomness report an error if the random
114 number generator has not been seeded with at least 128 bits of
115 randomness. If this error occurs, please contact the author of the
116 application you are using. It is likely that it never worked
117 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
118 to perform potentially insecure encryption.
120 On systems without /dev/urandom, it is a good idea to use the Entropy
121 Gathering Demon; see the RAND_egd() manpage for details.
123 Most components of the openssl command line tool try to use the
124 file $HOME/.rnd (or $RANDFILE, if this environment variable is set)
125 for seeding the PRNG. If this file does not exist or is too short,
126 the "PRNG not seeded" error message may occur.
128 [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version
129 0.9.5 does not do this and will fail on systems without /dev/urandom
130 when trying to password-encrypt an RSA key! This is a bug in the
131 library; try a later version instead.]
133 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
134 installing the SUNski package from Sun patch 105710-01 (Sparc) which
135 adds a /dev/random device and make sure it gets used, usually through
136 $RANDFILE. There are probably similar patches for the other Solaris
137 versions. However, be warned that /dev/random is usually a blocking
138 device, which may have som effects on OpenSSL.
141 * Why does the linker complain about undefined symbols?
143 Maybe the compilation was interrupted, and make doesn't notice that
144 something is missing. Run "make clean; make".
146 If you used ./Configure instead of ./config, make sure that you
147 selected the right target. File formats may differ slightly between
148 OS versions (for example sparcv8/sparcv9, or a.out/elf).
150 In case you get errors about the following symbols, use the config
151 option "no-asm", as described in INSTALL:
153 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
154 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
155 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
156 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
157 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
158 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
159 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
161 If none of these helps, you may want to try using the current snapshot.
162 If the problem persists, please submit a bug report.
165 * Where can I get a compiled version of OpenSSL?
167 Some applications that use OpenSSL are distributed in binary form.
168 When using such an application, you don't need to install OpenSSL
169 yourself; the application will include the required parts (e.g. DLLs).
171 If you want to install OpenSSL on a Windows system and you don't have
172 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
173 on how to obtain and install the free GNU C compiler.
175 A number of Linux and *BSD distributions include OpenSSL.
178 * I've compiled a program under Windows and it crashes: why?
180 This is usually because you've missed the comment in INSTALL.W32. You
181 must link with the multithreaded DLL version of the VC++ runtime library
182 otherwise the conflict will cause a program to crash: typically on the
183 first BIO related read or write operation.
186 * How do I read or write a DER encoded buffer using the ASN1 functions?
188 You have two options. You can either use a memory BIO in conjunction
189 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
190 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
191 cause of grief here are some code fragments using PKCS7 as an example:
193 unsigned char *buf, *p;
196 len = i2d_PKCS7(p7, NULL);
197 buf = OPENSSL_Malloc(len); /* or Malloc, error checking omitted */
201 At this point buf contains the len bytes of the DER encoding of
204 The opposite assumes we already have len bytes in buf:
208 p7 = d2i_PKCS7(NULL, &p, len);
210 At this point p7 contains a valid PKCS7 structure of NULL if an error
211 occurred. If an error occurred ERR_print_errors(bio) should give more
214 The reason for the temporary variable 'p' is that the ASN1 functions
215 increment the passed pointer so it is ready to read or write the next
216 structure. This is often a cause of problems: without the temporary
217 variable the buffer pointer is changed to point just after the data
218 that has been read or written. This may well be uninitialized data
219 and attempts to free the buffer will have unpredictable results
220 because it no longer points to the same address.
223 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
225 This usually happens when you try compiling something using the PKCS#12
226 macros with a C++ compiler. There is hardly ever any need to use the
227 PKCS#12 macros in a program, it is much easier to parse and create
228 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
229 documented in doc/openssl.txt and with examples in demos/pkcs12. The
230 'pkcs12' application has to use the macros because it prints out
231 debugging information.
234 * I've called <some function> and it fails, why?
236 Before submitting a report or asking in one of the mailing lists, you
237 should try to determine the cause. In particular, you should call
238 ERR_print_errors() or ERR_print_errors_fp() after the failed call
239 and see if the message helps. Note that the problem may occur earlier
240 than you think -- you should check for errors after every call where
241 it is possible, otherwise the actual problem may be hidden because
242 some OpenSSL functions clear the error state.
245 * I just get a load of numbers for the error output, what do they mean?
247 The actual format is described in the ERR_print_errors() manual page.
248 You should call the function ERR_load_crypto_strings() before hand and
249 the message will be output in text form. If you can't do this (for example
250 it is a pre-compiled binary) you can use the errstr utility on the error
251 code itself (the hex digits after the second colon).
254 * Why do I get errors about unknown algorithms?
256 This can happen under several circumstances such as reading in an
257 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
258 is forgetting to load OpenSSL's table of algorithms with
259 OpenSSL_add_all_algorithms(). See the manual page for more information.
262 * How do I create certificates or certificate requests?
264 Check out the CA.pl(1) manual page. This provides a simple wrapper round
265 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
266 out the manual pages for the individual utilities and the certificate
267 extensions documentation (currently in doc/openssl.txt).
270 * Why can't I create certificate requests?
272 You typically get the error:
274 unable to find 'distinguished_name' in config
275 problems making Certificate Request
277 This is because it can't find the configuration file. Check out the
278 DIAGNOSTICS section of req(1) for more information.
281 * Why does <SSL program> fail with a certificate verify error?
283 This problem is usually indicated by log messages saying something like
284 "unable to get local issuer certificate" or "self signed certificate".
285 When a certificate is verified its root CA must be "trusted" by OpenSSL
286 this typically means that the CA certificate must be placed in a directory
287 or file and the relevant program configured to read it. The OpenSSL program
288 'verify' behaves in a similar way and issues similar error messages: check
289 the verify(1) program manual page for more information.
292 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
294 This is almost certainly because you are using an old "export grade" browser
295 which only supports weak encryption. Upgrade your browser to support 128 bit
299 * How can I create DSA certificates?
301 Check the CA.pl(1) manual page for a DSA certificate example.
304 * Why can't I make an SSL connection to a server using a DSA certificate?
306 Typically you'll see a message saying there are no shared ciphers when
307 the same setup works fine with an RSA certificate. There are two possible
308 causes. The client may not support connections to DSA servers most web
309 browsers (including Netscape and MSIE) only support connections to servers
310 supporting RSA cipher suites. The other cause is that a set of DH parameters
311 has not been supplied to the server. DH parameters can be created with the
312 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
313 check the source to s_server in apps/s_server.c for an example.
316 * How can I remove the passphrase on a private key?
318 Firstly you should be really *really* sure you want to do this. Leaving
319 a private key unencrypted is a major security risk. If you decide that
320 you do have to do this check the EXAMPLES sections of the rsa(1) and
324 * Why can't the OpenSSH configure script detect OpenSSL?
326 There is a problem with OpenSSH 1.2.2p1, in that the configure script
327 can't find the installed OpenSSL libraries. The problem is actually
328 a small glitch that is easily solved with the following patch to be
329 applied to the OpenSSH distribution:
331 ----- snip:start -----
332 --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000
333 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000
334 @@ -152,10 +152,10 @@
335 AC_MSG_CHECKING([for OpenSSL/SSLeay directory])
336 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
337 if test ! -z "$ssldir" ; then
338 - LIBS="$saved_LIBS -L$ssldir"
339 + LIBS="$saved_LIBS -L$ssldir/lib"
340 CFLAGS="$CFLAGS -I$ssldir/include"
341 if test "x$need_dash_r" = "x1" ; then
342 - LIBS="$LIBS -R$ssldir"
343 + LIBS="$LIBS -R$ssldir/lib"
346 LIBS="$LIBS -lcrypto"
347 --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000
348 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000
349 @@ -1890,10 +1890,10 @@
350 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5
351 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do
352 if test ! -z "$ssldir" ; then
353 - LIBS="$saved_LIBS -L$ssldir"
354 + LIBS="$saved_LIBS -L$ssldir/lib"
355 CFLAGS="$CFLAGS -I$ssldir/include"
356 if test "x$need_dash_r" = "x1" ; then
357 - LIBS="$LIBS -R$ssldir"
358 + LIBS="$LIBS -R$ssldir/lib"
361 LIBS="$LIBS -lcrypto"
365 * Why does the OpenSSL test fail with "bc: command not found"?
367 You didn't install "bc", the Unix calculator. If you want to run the
368 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
371 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
373 On some SCO installations or versions, bc has a bug that gets triggered when
374 you run the test suite (using "make test"). The message returned is "bc:
375 1 not implemented". The best way to deal with this is to find another
376 implementation of bc and compile/install it. For example, GNU bc (see
377 http://www.gnu.org/software/software.html for download instructions) can
381 * Why does the OpenSSL compilation fail on Alpha True64 Unix?
383 On some Alpha installations running True64 Unix and Compaq C, the compilation
384 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
385 memory to continue compilation.' As far as the tests have shown, this may be
386 a compiler bug. What happens is that it eats up a lot of resident memory
387 to build something, probably a table. The problem is clearly in the
388 optimization code, because if one eliminates optimization completely (-O0),
389 the compilation goes through (and the compiler consumes about 2MB of resident
390 memory instead of 240MB or whatever one's limit is currently).
392 There are three options to solve this problem:
394 1. set your current data segment size soft limit higher. Experience shows
395 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
396 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
397 kbytes to set the limit to.
399 2. If you have a hard limit that is lower than what you need and you can't
400 get it changed, you can compile all of OpenSSL with -O0 as optimization
401 level. This is however not a very nice thing to do for those who expect to
402 get the best result from OpenSSL. A bit more complicated solution is the
405 ----- snip:start -----
406 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
407 sed -e 's/ -O[0-9] / -O0 /'`"
408 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
412 This will only compile sha_dgst.c with -O0, the rest with the optimization
413 level chosen by the configuration process. When the above is done, do the
414 test and installation and you're set.
417 * Why does the OpenSSL compilation fail with "ar: command not found"?
419 Getting this message is quite usual on Solaris 2, because Sun has hidden
420 away 'ar' and other development commands in directories that aren't in
421 $PATH by default. One of those directories is '/usr/ccs/bin'. The
422 quickest way to fix this is to do the following (it assumes you use sh
423 or any sh-compatible shell):
425 ----- snip:start -----
426 PATH=${PATH}:/usr/ccs/bin; export PATH
429 and then redo the compilation. What you should really do is make sure
430 '/usr/ccs/bin' is permanently in your $PATH, for example through your
431 '.profile' (again, assuming you use a sh-compatible shell).