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?
31 * How do I install a CA certificate into a browser?
32 * Why is OpenSSL x509 DN output not conformant to RFC2253?
34 [BUILD] Questions about building and testing OpenSSL
36 * Why does the linker complain about undefined symbols?
37 * Why does the OpenSSL test fail with "bc: command not found"?
38 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
39 * Why does the OpenSSL test fail with "bc: stack empty"?
40 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
41 * Why does the OpenSSL compilation fail with "ar: command not found"?
42 * Why does the OpenSSL compilation fail on Win32 with VC++?
43 * What is special about OpenSSL on Redhat?
44 * Why does the OpenSSL compilation fail on MacOS X?
45 * Why does the OpenSSL test suite fail on MacOS X?
47 [PROG] Questions about programming with OpenSSL
49 * Is OpenSSL thread-safe?
50 * I've compiled a program under Windows and it crashes: why?
51 * How do I read or write a DER encoded buffer using the ASN1 functions?
52 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
53 * I've called <some function> and it fails, why?
54 * I just get a load of numbers for the error output, what do they mean?
55 * Why do I get errors about unknown algorithms?
56 * Why can't the OpenSSH configure script detect OpenSSL?
57 * Can I use OpenSSL's SSL library with non-blocking I/O?
58 * Why doesn't my server application receive a client certificate?
59 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
61 ===============================================================================
63 [MISC] ========================================================================
65 * Which is the current version of OpenSSL?
67 The current version is available from <URL: http://www.openssl.org>.
68 OpenSSL 0.9.6g was released on August 9, 2002.
70 In addition to the current stable release, you can also access daily
71 snapshots of the OpenSSL development version at <URL:
72 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
75 * Where is the documentation?
77 OpenSSL is a library that provides cryptographic functionality to
78 applications such as secure web servers. Be sure to read the
79 documentation of the application you want to use. The INSTALL file
80 explains how to install this library.
82 OpenSSL includes a command line utility that can be used to perform a
83 variety of cryptographic functions. It is described in the openssl(1)
84 manpage. Documentation for developers is currently being written. A
85 few manual pages already are available; overviews over libcrypto and
86 libssl are given in the crypto(3) and ssl(3) manpages.
88 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
89 different directory if you specified one as described in INSTALL).
90 In addition, you can read the most current versions at
91 <URL: http://www.openssl.org/docs/>.
93 For information on parts of libcrypto that are not yet documented, you
94 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
95 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
96 of this still applies to OpenSSL.
98 There is some documentation about certificate extensions and PKCS#12
101 The original SSLeay documentation is included in OpenSSL as
102 doc/ssleay.txt. It may be useful when none of the other resources
103 help, but please note that it reflects the obsolete version SSLeay
107 * How can I contact the OpenSSL developers?
109 The README file describes how to submit bug reports and patches to
110 OpenSSL. Information on the OpenSSL mailing lists is available from
111 <URL: http://www.openssl.org>.
114 * Where can I get a compiled version of OpenSSL?
116 Some applications that use OpenSSL are distributed in binary form.
117 When using such an application, you don't need to install OpenSSL
118 yourself; the application will include the required parts (e.g. DLLs).
120 If you want to install OpenSSL on a Windows system and you don't have
121 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
122 on how to obtain and install the free GNU C compiler.
124 A number of Linux and *BSD distributions include OpenSSL.
127 * Why aren't tools like 'autoconf' and 'libtool' used?
129 autoconf will probably be used in future OpenSSL versions. If it was
130 less Unix-centric, it might have been used much earlier.
132 * What is an 'engine' version?
134 With version 0.9.6 OpenSSL was extended to interface to external crypto
135 hardware. This was realized in a special release '0.9.6-engine'. With
136 version 0.9.7 (not yet released) the changes were merged into the main
137 development line, so that the special release is no longer necessary.
139 [LEGAL] =======================================================================
141 * Do I need patent licenses to use OpenSSL?
143 The patents section of the README file lists patents that may apply to
144 you if you want to use OpenSSL. For information on intellectual
145 property rights, please consult a lawyer. The OpenSSL team does not
148 You can configure OpenSSL so as not to use RC5 and IDEA by using
149 ./config no-rc5 no-idea
152 * Can I use OpenSSL with GPL software?
154 On many systems including the major Linux and BSD distributions, yes (the
155 GPL does not place restrictions on using libraries that are part of the
156 normal operating system distribution).
158 On other systems, the situation is less clear. Some GPL software copyright
159 holders claim that you infringe on their rights if you use OpenSSL with
160 their software on operating systems that don't normally include OpenSSL.
162 If you develop open source software that uses OpenSSL, you may find it
163 useful to choose an other license than the GPL, or state explicitly that
164 "This program is released under the GPL with the additional exemption that
165 compiling, linking, and/or using OpenSSL is allowed." If you are using
166 GPL software developed by others, you may want to ask the copyright holder
167 for permission to use their software with OpenSSL.
170 [USER] ========================================================================
172 * Why do I get a "PRNG not seeded" error message?
174 Cryptographic software needs a source of unpredictable data to work
175 correctly. Many open source operating systems provide a "randomness
176 device" that serves this purpose. On other systems, applications have
177 to call the RAND_add() or RAND_seed() function with appropriate data
178 before generating keys or performing public key encryption.
179 (These functions initialize the pseudo-random number generator, PRNG.)
181 Some broken applications do not do this. As of version 0.9.5, the
182 OpenSSL functions that need randomness report an error if the random
183 number generator has not been seeded with at least 128 bits of
184 randomness. If this error occurs, please contact the author of the
185 application you are using. It is likely that it never worked
186 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
187 to perform potentially insecure encryption.
189 On systems without /dev/urandom and /dev/random, it is a good idea to
190 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
191 details. Starting with version 0.9.7, OpenSSL will automatically look
192 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
195 Most components of the openssl command line utility automatically try
196 to seed the random number generator from a file. The name of the
197 default seeding file is determined as follows: If environment variable
198 RANDFILE is set, then it names the seeding file. Otherwise if
199 environment variable HOME is set, then the seeding file is $HOME/.rnd.
200 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
201 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
202 default seeding file at all. OpenSSL 0.9.6b and later will behave
203 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
204 Windows systems if the environment variable has not been set.
206 If the default seeding file does not exist or is too short, the "PRNG
207 not seeded" error message may occur.
209 The openssl command line utility will write back a new state to the
210 default seeding file (and create this file if necessary) unless
211 there was no sufficient seeding.
213 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
214 Use the "-rand" option of the OpenSSL command line tools instead.
215 The $RANDFILE environment variable and $HOME/.rnd are only used by the
216 OpenSSL command line tools. Applications using the OpenSSL library
217 provide their own configuration options to specify the entropy source,
218 please check out the documentation coming the with application.
220 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
221 installing the SUNski package from Sun patch 105710-01 (Sparc) which
222 adds a /dev/random device and make sure it gets used, usually through
223 $RANDFILE. There are probably similar patches for the other Solaris
224 versions. An official statement from Sun with respect to /dev/random
225 support can be found at
226 http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski
227 However, be warned that /dev/random is usually a blocking device, which
228 may have some effects on OpenSSL.
231 * Why do I get an "unable to write 'random state'" error message?
234 Sometimes the openssl command line utility does not abort with
235 a "PRNG not seeded" error message, but complains that it is
236 "unable to write 'random state'". This message refers to the
237 default seeding file (see previous answer). A possible reason
238 is that no default filename is known because neither RANDFILE
239 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
240 current directory in this case, but this has changed with 0.9.6a.)
243 * How do I create certificates or certificate requests?
245 Check out the CA.pl(1) manual page. This provides a simple wrapper round
246 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
247 out the manual pages for the individual utilities and the certificate
248 extensions documentation (currently in doc/openssl.txt).
251 * Why can't I create certificate requests?
253 You typically get the error:
255 unable to find 'distinguished_name' in config
256 problems making Certificate Request
258 This is because it can't find the configuration file. Check out the
259 DIAGNOSTICS section of req(1) for more information.
262 * Why does <SSL program> fail with a certificate verify error?
264 This problem is usually indicated by log messages saying something like
265 "unable to get local issuer certificate" or "self signed certificate".
266 When a certificate is verified its root CA must be "trusted" by OpenSSL
267 this typically means that the CA certificate must be placed in a directory
268 or file and the relevant program configured to read it. The OpenSSL program
269 'verify' behaves in a similar way and issues similar error messages: check
270 the verify(1) program manual page for more information.
273 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
275 This is almost certainly because you are using an old "export grade" browser
276 which only supports weak encryption. Upgrade your browser to support 128 bit
280 * How can I create DSA certificates?
282 Check the CA.pl(1) manual page for a DSA certificate example.
285 * Why can't I make an SSL connection to a server using a DSA certificate?
287 Typically you'll see a message saying there are no shared ciphers when
288 the same setup works fine with an RSA certificate. There are two possible
289 causes. The client may not support connections to DSA servers most web
290 browsers (including Netscape and MSIE) only support connections to servers
291 supporting RSA cipher suites. The other cause is that a set of DH parameters
292 has not been supplied to the server. DH parameters can be created with the
293 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
294 check the source to s_server in apps/s_server.c for an example.
297 * How can I remove the passphrase on a private key?
299 Firstly you should be really *really* sure you want to do this. Leaving
300 a private key unencrypted is a major security risk. If you decide that
301 you do have to do this check the EXAMPLES sections of the rsa(1) and
305 * Why can't I use OpenSSL certificates with SSL client authentication?
307 What will typically happen is that when a server requests authentication
308 it will either not include your certificate or tell you that you have
309 no client certificates (Netscape) or present you with an empty list box
310 (MSIE). The reason for this is that when a server requests a client
311 certificate it includes a list of CAs names which it will accept. Browsers
312 will only let you select certificates from the list on the grounds that
313 there is little point presenting a certificate which the server will
316 The solution is to add the relevant CA certificate to your servers "trusted
317 CA list". How you do this depends on the server software in uses. You can
318 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
320 openssl s_client -connect www.some.host:443 -prexit
322 If your server only requests certificates on certain URLs then you may need
323 to manually issue an HTTP GET command to get the list when s_client connects:
325 GET /some/page/needing/a/certificate.html
327 If your CA does not appear in the list then this confirms the problem.
330 * Why does my browser give a warning about a mismatched hostname?
332 Browsers expect the server's hostname to match the value in the commonName
333 (CN) field of the certificate. If it does not then you get a warning.
336 * How do I install a CA certificate into a browser?
338 The usual way is to send the DER encoded certificate to the browser as
339 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
340 link. On MSIE certain extensions such as .der or .cacert may also work, or you
341 can import the certificate using the certificate import wizard.
343 You can convert a certificate to DER form using the command:
345 openssl x509 -in ca.pem -outform DER -out ca.der
347 Occasionally someone suggests using a command such as:
349 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
351 DO NOT DO THIS! This command will give away your CAs private key and
352 reduces its security to zero: allowing anyone to forge certificates in
353 whatever name they choose.
355 * Why is OpenSSL x509 DN output not conformant to RFC2253?
357 The ways to print out the oneline format of the DN (Distinguished Name) have
358 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
359 interface, the "-nameopt" option could be introduded. See the manual
360 page of the "openssl x509" commandline tool for details. The old behaviour
361 has however been left as default for the sake of compatibility.
363 [BUILD] =======================================================================
365 * Why does the linker complain about undefined symbols?
367 Maybe the compilation was interrupted, and make doesn't notice that
368 something is missing. Run "make clean; make".
370 If you used ./Configure instead of ./config, make sure that you
371 selected the right target. File formats may differ slightly between
372 OS versions (for example sparcv8/sparcv9, or a.out/elf).
374 In case you get errors about the following symbols, use the config
375 option "no-asm", as described in INSTALL:
377 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
378 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
379 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
380 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
381 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
382 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
383 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
385 If none of these helps, you may want to try using the current snapshot.
386 If the problem persists, please submit a bug report.
389 * Why does the OpenSSL test fail with "bc: command not found"?
391 You didn't install "bc", the Unix calculator. If you want to run the
392 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
395 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
397 On some SCO installations or versions, bc has a bug that gets triggered
398 when you run the test suite (using "make test"). The message returned is
399 "bc: 1 not implemented".
401 The best way to deal with this is to find another implementation of bc
402 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
403 for download instructions) can be safely used, for example.
406 * Why does the OpenSSL test fail with "bc: stack empty"?
408 On some DG/ux versions, bc seems to have a too small stack for calculations
409 that the OpenSSL bntest throws at it. This gets triggered when you run the
410 test suite (using "make test"). The message returned is "bc: stack empty".
412 The best way to deal with this is to find another implementation of bc
413 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
414 for download instructions) can be safely used, for example.
417 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
419 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
420 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
421 memory to continue compilation.' As far as the tests have shown, this may be
422 a compiler bug. What happens is that it eats up a lot of resident memory
423 to build something, probably a table. The problem is clearly in the
424 optimization code, because if one eliminates optimization completely (-O0),
425 the compilation goes through (and the compiler consumes about 2MB of resident
426 memory instead of 240MB or whatever one's limit is currently).
428 There are three options to solve this problem:
430 1. set your current data segment size soft limit higher. Experience shows
431 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
432 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
433 kbytes to set the limit to.
435 2. If you have a hard limit that is lower than what you need and you can't
436 get it changed, you can compile all of OpenSSL with -O0 as optimization
437 level. This is however not a very nice thing to do for those who expect to
438 get the best result from OpenSSL. A bit more complicated solution is the
441 ----- snip:start -----
442 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
443 sed -e 's/ -O[0-9] / -O0 /'`"
444 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
448 This will only compile sha_dgst.c with -O0, the rest with the optimization
449 level chosen by the configuration process. When the above is done, do the
450 test and installation and you're set.
453 * Why does the OpenSSL compilation fail with "ar: command not found"?
455 Getting this message is quite usual on Solaris 2, because Sun has hidden
456 away 'ar' and other development commands in directories that aren't in
457 $PATH by default. One of those directories is '/usr/ccs/bin'. The
458 quickest way to fix this is to do the following (it assumes you use sh
459 or any sh-compatible shell):
461 ----- snip:start -----
462 PATH=${PATH}:/usr/ccs/bin; export PATH
465 and then redo the compilation. What you should really do is make sure
466 '/usr/ccs/bin' is permanently in your $PATH, for example through your
467 '.profile' (again, assuming you use a sh-compatible shell).
470 * Why does the OpenSSL compilation fail on Win32 with VC++?
472 Sometimes, you may get reports from VC++ command line (cl) that it
473 can't find standard include files like stdio.h and other weirdnesses.
474 One possible cause is that the environment isn't correctly set up.
475 To solve that problem, one should run VCVARS32.BAT which is found in
476 the 'bin' subdirectory of the VC++ installation directory (somewhere
477 under 'Program Files'). This needs to be done prior to running NMAKE,
478 and the changes are only valid for the current DOS session.
481 * What is special about OpenSSL on Redhat?
483 Red Hat Linux (release 7.0 and later) include a preinstalled limited
484 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
485 is disabled in this version. The same may apply to other Linux distributions.
486 Users may therefore wish to install more or all of the features left out.
488 To do this you MUST ensure that you do not overwrite the openssl that is in
489 /usr/bin on your Red Hat machine. Several packages depend on this file,
490 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
491 libraries that come with Red Hat 7.0 onwards have different names and so are
492 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
493 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
494 /lib/libcrypto.so.2 respectively).
496 Please note that we have been advised by Red Hat attempting to recompile the
497 openssl rpm with all the cryptography enabled will not work. All other
498 packages depend on the original Red Hat supplied openssl package. It is also
499 worth noting that due to the way Red Hat supplies its packages, updates to
500 openssl on each distribution never change the package version, only the
501 build number. For example, on Red Hat 7.1, the latest openssl package has
502 version number 0.9.6 and build number 9 even though it contains all the
503 relevant updates in packages up to and including 0.9.6b.
505 A possible way around this is to persuade Red Hat to produce a non-US
506 version of Red Hat Linux.
508 FYI: Patent numbers and expiry dates of US patents:
509 MDC-2: 4,908,861 13/03/2007
510 IDEA: 5,214,703 25/05/2010
511 RC5: 5,724,428 03/03/2015
514 * Why does the OpenSSL compilation fail on MacOS X?
516 If the failure happens when trying to build the "openssl" binary, with
517 a large number of undefined symbols, it's very probable that you have
518 OpenSSL 0.9.6b delivered with the operating system (you can find out by
519 running '/usr/bin/openssl version') and that you were trying to build
520 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
521 MacOS X has a misfeature that's quite difficult to go around.
522 Look in the file PROBLEMS for a more detailed explanation and for possible
526 * Why does the OpenSSL test suite fail on MacOS X?
528 If the failure happens when running 'make test' and the RC4 test fails,
529 it's very probable that you have OpenSSL 0.9.6b delivered with the
530 operating system (you can find out by running '/usr/bin/openssl version')
531 and that you were trying to build OpenSSL 0.9.6d. The problem is that
532 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
533 go around and has linked the programs "openssl" and the test programs
534 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
535 libraries you just built.
536 Look in the file PROBLEMS for a more detailed explanation and for possible
539 [PROG] ========================================================================
541 * Is OpenSSL thread-safe?
543 Yes (with limitations: an SSL connection may not concurrently be used
544 by multiple threads). On Windows and many Unix systems, OpenSSL
545 automatically uses the multi-threaded versions of the standard
546 libraries. If your platform is not one of these, consult the INSTALL
549 Multi-threaded applications must provide two callback functions to
550 OpenSSL. This is described in the threads(3) manpage.
553 * I've compiled a program under Windows and it crashes: why?
555 This is usually because you've missed the comment in INSTALL.W32.
556 Your application must link against the same version of the Win32
557 C-Runtime against which your openssl libraries were linked. The
558 default version for OpenSSL is /MD - "Multithreaded DLL".
560 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
561 many cases, your new project most likely defaulted to "Debug
562 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
563 program will crash, typically on the first BIO related read or write
566 For each of the six possible link stage configurations within Win32,
567 your application must link against the same by which OpenSSL was
568 built. If you are using MS Visual C++ (Studio) this can be changed
571 1. Select Settings... from the Project Menu.
572 2. Select the C/C++ Tab.
573 3. Select "Code Generation from the "Category" drop down list box
574 4. Select the Appropriate library (see table below) from the "Use
575 run-time library" drop down list box. Perform this step for both
576 your debug and release versions of your application (look at the
577 top left of the settings panel to change between the two)
579 Single Threaded /ML - MS VC++ often defaults to
581 version of a new project.
582 Debug Single Threaded /MLd - MS VC++ often defaults to
583 this for the debug version
586 Debug Multithreaded /MTd
587 Multithreaded DLL /MD - OpenSSL defaults to this.
588 Debug Multithreaded DLL /MDd
590 Note that debug and release libraries are NOT interchangeable. If you
591 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
594 * How do I read or write a DER encoded buffer using the ASN1 functions?
596 You have two options. You can either use a memory BIO in conjunction
597 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
598 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
599 cause of grief here are some code fragments using PKCS7 as an example:
601 unsigned char *buf, *p;
604 len = i2d_PKCS7(p7, NULL);
605 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
609 At this point buf contains the len bytes of the DER encoding of
612 The opposite assumes we already have len bytes in buf:
616 p7 = d2i_PKCS7(NULL, &p, len);
618 At this point p7 contains a valid PKCS7 structure of NULL if an error
619 occurred. If an error occurred ERR_print_errors(bio) should give more
622 The reason for the temporary variable 'p' is that the ASN1 functions
623 increment the passed pointer so it is ready to read or write the next
624 structure. This is often a cause of problems: without the temporary
625 variable the buffer pointer is changed to point just after the data
626 that has been read or written. This may well be uninitialized data
627 and attempts to free the buffer will have unpredictable results
628 because it no longer points to the same address.
631 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
633 This usually happens when you try compiling something using the PKCS#12
634 macros with a C++ compiler. There is hardly ever any need to use the
635 PKCS#12 macros in a program, it is much easier to parse and create
636 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
637 documented in doc/openssl.txt and with examples in demos/pkcs12. The
638 'pkcs12' application has to use the macros because it prints out
639 debugging information.
642 * I've called <some function> and it fails, why?
644 Before submitting a report or asking in one of the mailing lists, you
645 should try to determine the cause. In particular, you should call
646 ERR_print_errors() or ERR_print_errors_fp() after the failed call
647 and see if the message helps. Note that the problem may occur earlier
648 than you think -- you should check for errors after every call where
649 it is possible, otherwise the actual problem may be hidden because
650 some OpenSSL functions clear the error state.
653 * I just get a load of numbers for the error output, what do they mean?
655 The actual format is described in the ERR_print_errors() manual page.
656 You should call the function ERR_load_crypto_strings() before hand and
657 the message will be output in text form. If you can't do this (for example
658 it is a pre-compiled binary) you can use the errstr utility on the error
659 code itself (the hex digits after the second colon).
662 * Why do I get errors about unknown algorithms?
664 This can happen under several circumstances such as reading in an
665 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
666 is forgetting to load OpenSSL's table of algorithms with
667 OpenSSL_add_all_algorithms(). See the manual page for more information.
670 * Why can't the OpenSSH configure script detect OpenSSL?
672 Several reasons for problems with the automatic detection exist.
673 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
674 Sometimes the distribution has installed an older version in the system
675 locations that is detected instead of a new one installed. The OpenSSL
676 library might have been compiled for another CPU or another mode (32/64 bits).
677 Permissions might be wrong.
679 The general answer is to check the config.log file generated when running
680 the OpenSSH configure script. It should contain the detailed information
681 on why the OpenSSL library was not detected or considered incompatible.
683 * Can I use OpenSSL's SSL library with non-blocking I/O?
685 Yes; make sure to read the SSL_get_error(3) manual page!
687 A pitfall to avoid: Don't assume that SSL_read() will just read from
688 the underlying transport or that SSL_write() will just write to it --
689 it is also possible that SSL_write() cannot do any useful work until
690 there is data to read, or that SSL_read() cannot do anything until it
691 is possible to send data. One reason for this is that the peer may
692 request a new TLS/SSL handshake at any time during the protocol,
693 requiring a bi-directional message exchange; both SSL_read() and
694 SSL_write() will try to continue any pending handshake.
697 * Why doesn't my server application receive a client certificate?
699 Due to the TLS protocol definition, a client will only send a certificate,
700 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
701 SSL_CTX_set_verify() function to enable the use of client certificates.
704 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
706 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
707 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
708 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
709 Change your code to use the new name when compiling against OpenSSL 0.9.7.
712 ===============================================================================