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.
229 A third party /dev/random solution for Solaris is available at
230 http://www.cosy.sbg.ac.at/~andi/
233 * Why do I get an "unable to write 'random state'" error message?
236 Sometimes the openssl command line utility does not abort with
237 a "PRNG not seeded" error message, but complains that it is
238 "unable to write 'random state'". This message refers to the
239 default seeding file (see previous answer). A possible reason
240 is that no default filename is known because neither RANDFILE
241 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
242 current directory in this case, but this has changed with 0.9.6a.)
245 * How do I create certificates or certificate requests?
247 Check out the CA.pl(1) manual page. This provides a simple wrapper round
248 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
249 out the manual pages for the individual utilities and the certificate
250 extensions documentation (currently in doc/openssl.txt).
253 * Why can't I create certificate requests?
255 You typically get the error:
257 unable to find 'distinguished_name' in config
258 problems making Certificate Request
260 This is because it can't find the configuration file. Check out the
261 DIAGNOSTICS section of req(1) for more information.
264 * Why does <SSL program> fail with a certificate verify error?
266 This problem is usually indicated by log messages saying something like
267 "unable to get local issuer certificate" or "self signed certificate".
268 When a certificate is verified its root CA must be "trusted" by OpenSSL
269 this typically means that the CA certificate must be placed in a directory
270 or file and the relevant program configured to read it. The OpenSSL program
271 'verify' behaves in a similar way and issues similar error messages: check
272 the verify(1) program manual page for more information.
275 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
277 This is almost certainly because you are using an old "export grade" browser
278 which only supports weak encryption. Upgrade your browser to support 128 bit
282 * How can I create DSA certificates?
284 Check the CA.pl(1) manual page for a DSA certificate example.
287 * Why can't I make an SSL connection to a server using a DSA certificate?
289 Typically you'll see a message saying there are no shared ciphers when
290 the same setup works fine with an RSA certificate. There are two possible
291 causes. The client may not support connections to DSA servers most web
292 browsers (including Netscape and MSIE) only support connections to servers
293 supporting RSA cipher suites. The other cause is that a set of DH parameters
294 has not been supplied to the server. DH parameters can be created with the
295 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
296 check the source to s_server in apps/s_server.c for an example.
299 * How can I remove the passphrase on a private key?
301 Firstly you should be really *really* sure you want to do this. Leaving
302 a private key unencrypted is a major security risk. If you decide that
303 you do have to do this check the EXAMPLES sections of the rsa(1) and
307 * Why can't I use OpenSSL certificates with SSL client authentication?
309 What will typically happen is that when a server requests authentication
310 it will either not include your certificate or tell you that you have
311 no client certificates (Netscape) or present you with an empty list box
312 (MSIE). The reason for this is that when a server requests a client
313 certificate it includes a list of CAs names which it will accept. Browsers
314 will only let you select certificates from the list on the grounds that
315 there is little point presenting a certificate which the server will
318 The solution is to add the relevant CA certificate to your servers "trusted
319 CA list". How you do this depends on the server software in uses. You can
320 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
322 openssl s_client -connect www.some.host:443 -prexit
324 If your server only requests certificates on certain URLs then you may need
325 to manually issue an HTTP GET command to get the list when s_client connects:
327 GET /some/page/needing/a/certificate.html
329 If your CA does not appear in the list then this confirms the problem.
332 * Why does my browser give a warning about a mismatched hostname?
334 Browsers expect the server's hostname to match the value in the commonName
335 (CN) field of the certificate. If it does not then you get a warning.
338 * How do I install a CA certificate into a browser?
340 The usual way is to send the DER encoded certificate to the browser as
341 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
342 link. On MSIE certain extensions such as .der or .cacert may also work, or you
343 can import the certificate using the certificate import wizard.
345 You can convert a certificate to DER form using the command:
347 openssl x509 -in ca.pem -outform DER -out ca.der
349 Occasionally someone suggests using a command such as:
351 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
353 DO NOT DO THIS! This command will give away your CAs private key and
354 reduces its security to zero: allowing anyone to forge certificates in
355 whatever name they choose.
357 * Why is OpenSSL x509 DN output not conformant to RFC2253?
359 The ways to print out the oneline format of the DN (Distinguished Name) have
360 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
361 interface, the "-nameopt" option could be introduded. See the manual
362 page of the "openssl x509" commandline tool for details. The old behaviour
363 has however been left as default for the sake of compatibility.
365 [BUILD] =======================================================================
367 * Why does the linker complain about undefined symbols?
369 Maybe the compilation was interrupted, and make doesn't notice that
370 something is missing. Run "make clean; make".
372 If you used ./Configure instead of ./config, make sure that you
373 selected the right target. File formats may differ slightly between
374 OS versions (for example sparcv8/sparcv9, or a.out/elf).
376 In case you get errors about the following symbols, use the config
377 option "no-asm", as described in INSTALL:
379 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
380 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
381 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
382 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
383 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
384 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
385 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
387 If none of these helps, you may want to try using the current snapshot.
388 If the problem persists, please submit a bug report.
391 * Why does the OpenSSL test fail with "bc: command not found"?
393 You didn't install "bc", the Unix calculator. If you want to run the
394 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
397 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
399 On some SCO installations or versions, bc has a bug that gets triggered
400 when you run the test suite (using "make test"). The message returned is
401 "bc: 1 not implemented".
403 The best way to deal with this is to find another implementation of bc
404 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
405 for download instructions) can be safely used, for example.
408 * Why does the OpenSSL test fail with "bc: stack empty"?
410 On some DG/ux versions, bc seems to have a too small stack for calculations
411 that the OpenSSL bntest throws at it. This gets triggered when you run the
412 test suite (using "make test"). The message returned is "bc: stack empty".
414 The best way to deal with this is to find another implementation of bc
415 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
416 for download instructions) can be safely used, for example.
419 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
421 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
422 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
423 memory to continue compilation.' As far as the tests have shown, this may be
424 a compiler bug. What happens is that it eats up a lot of resident memory
425 to build something, probably a table. The problem is clearly in the
426 optimization code, because if one eliminates optimization completely (-O0),
427 the compilation goes through (and the compiler consumes about 2MB of resident
428 memory instead of 240MB or whatever one's limit is currently).
430 There are three options to solve this problem:
432 1. set your current data segment size soft limit higher. Experience shows
433 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
434 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
435 kbytes to set the limit to.
437 2. If you have a hard limit that is lower than what you need and you can't
438 get it changed, you can compile all of OpenSSL with -O0 as optimization
439 level. This is however not a very nice thing to do for those who expect to
440 get the best result from OpenSSL. A bit more complicated solution is the
443 ----- snip:start -----
444 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
445 sed -e 's/ -O[0-9] / -O0 /'`"
446 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
450 This will only compile sha_dgst.c with -O0, the rest with the optimization
451 level chosen by the configuration process. When the above is done, do the
452 test and installation and you're set.
455 * Why does the OpenSSL compilation fail with "ar: command not found"?
457 Getting this message is quite usual on Solaris 2, because Sun has hidden
458 away 'ar' and other development commands in directories that aren't in
459 $PATH by default. One of those directories is '/usr/ccs/bin'. The
460 quickest way to fix this is to do the following (it assumes you use sh
461 or any sh-compatible shell):
463 ----- snip:start -----
464 PATH=${PATH}:/usr/ccs/bin; export PATH
467 and then redo the compilation. What you should really do is make sure
468 '/usr/ccs/bin' is permanently in your $PATH, for example through your
469 '.profile' (again, assuming you use a sh-compatible shell).
472 * Why does the OpenSSL compilation fail on Win32 with VC++?
474 Sometimes, you may get reports from VC++ command line (cl) that it
475 can't find standard include files like stdio.h and other weirdnesses.
476 One possible cause is that the environment isn't correctly set up.
477 To solve that problem, one should run VCVARS32.BAT which is found in
478 the 'bin' subdirectory of the VC++ installation directory (somewhere
479 under 'Program Files'). This needs to be done prior to running NMAKE,
480 and the changes are only valid for the current DOS session.
483 * What is special about OpenSSL on Redhat?
485 Red Hat Linux (release 7.0 and later) include a preinstalled limited
486 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
487 is disabled in this version. The same may apply to other Linux distributions.
488 Users may therefore wish to install more or all of the features left out.
490 To do this you MUST ensure that you do not overwrite the openssl that is in
491 /usr/bin on your Red Hat machine. Several packages depend on this file,
492 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
493 libraries that come with Red Hat 7.0 onwards have different names and so are
494 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
495 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
496 /lib/libcrypto.so.2 respectively).
498 Please note that we have been advised by Red Hat attempting to recompile the
499 openssl rpm with all the cryptography enabled will not work. All other
500 packages depend on the original Red Hat supplied openssl package. It is also
501 worth noting that due to the way Red Hat supplies its packages, updates to
502 openssl on each distribution never change the package version, only the
503 build number. For example, on Red Hat 7.1, the latest openssl package has
504 version number 0.9.6 and build number 9 even though it contains all the
505 relevant updates in packages up to and including 0.9.6b.
507 A possible way around this is to persuade Red Hat to produce a non-US
508 version of Red Hat Linux.
510 FYI: Patent numbers and expiry dates of US patents:
511 MDC-2: 4,908,861 13/03/2007
512 IDEA: 5,214,703 25/05/2010
513 RC5: 5,724,428 03/03/2015
516 * Why does the OpenSSL compilation fail on MacOS X?
518 If the failure happens when trying to build the "openssl" binary, with
519 a large number of undefined symbols, it's very probable that you have
520 OpenSSL 0.9.6b delivered with the operating system (you can find out by
521 running '/usr/bin/openssl version') and that you were trying to build
522 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
523 MacOS X has a misfeature that's quite difficult to go around.
524 Look in the file PROBLEMS for a more detailed explanation and for possible
528 * Why does the OpenSSL test suite fail on MacOS X?
530 If the failure happens when running 'make test' and the RC4 test fails,
531 it's very probable that you have OpenSSL 0.9.6b delivered with the
532 operating system (you can find out by running '/usr/bin/openssl version')
533 and that you were trying to build OpenSSL 0.9.6d. The problem is that
534 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
535 go around and has linked the programs "openssl" and the test programs
536 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
537 libraries you just built.
538 Look in the file PROBLEMS for a more detailed explanation and for possible
541 [PROG] ========================================================================
543 * Is OpenSSL thread-safe?
545 Yes (with limitations: an SSL connection may not concurrently be used
546 by multiple threads). On Windows and many Unix systems, OpenSSL
547 automatically uses the multi-threaded versions of the standard
548 libraries. If your platform is not one of these, consult the INSTALL
551 Multi-threaded applications must provide two callback functions to
552 OpenSSL. This is described in the threads(3) manpage.
555 * I've compiled a program under Windows and it crashes: why?
557 This is usually because you've missed the comment in INSTALL.W32.
558 Your application must link against the same version of the Win32
559 C-Runtime against which your openssl libraries were linked. The
560 default version for OpenSSL is /MD - "Multithreaded DLL".
562 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
563 many cases, your new project most likely defaulted to "Debug
564 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
565 program will crash, typically on the first BIO related read or write
568 For each of the six possible link stage configurations within Win32,
569 your application must link against the same by which OpenSSL was
570 built. If you are using MS Visual C++ (Studio) this can be changed
573 1. Select Settings... from the Project Menu.
574 2. Select the C/C++ Tab.
575 3. Select "Code Generation from the "Category" drop down list box
576 4. Select the Appropriate library (see table below) from the "Use
577 run-time library" drop down list box. Perform this step for both
578 your debug and release versions of your application (look at the
579 top left of the settings panel to change between the two)
581 Single Threaded /ML - MS VC++ often defaults to
583 version of a new project.
584 Debug Single Threaded /MLd - MS VC++ often defaults to
585 this for the debug version
588 Debug Multithreaded /MTd
589 Multithreaded DLL /MD - OpenSSL defaults to this.
590 Debug Multithreaded DLL /MDd
592 Note that debug and release libraries are NOT interchangeable. If you
593 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
596 * How do I read or write a DER encoded buffer using the ASN1 functions?
598 You have two options. You can either use a memory BIO in conjunction
599 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
600 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
601 cause of grief here are some code fragments using PKCS7 as an example:
603 unsigned char *buf, *p;
606 len = i2d_PKCS7(p7, NULL);
607 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
611 At this point buf contains the len bytes of the DER encoding of
614 The opposite assumes we already have len bytes in buf:
618 p7 = d2i_PKCS7(NULL, &p, len);
620 At this point p7 contains a valid PKCS7 structure of NULL if an error
621 occurred. If an error occurred ERR_print_errors(bio) should give more
624 The reason for the temporary variable 'p' is that the ASN1 functions
625 increment the passed pointer so it is ready to read or write the next
626 structure. This is often a cause of problems: without the temporary
627 variable the buffer pointer is changed to point just after the data
628 that has been read or written. This may well be uninitialized data
629 and attempts to free the buffer will have unpredictable results
630 because it no longer points to the same address.
633 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
635 This usually happens when you try compiling something using the PKCS#12
636 macros with a C++ compiler. There is hardly ever any need to use the
637 PKCS#12 macros in a program, it is much easier to parse and create
638 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
639 documented in doc/openssl.txt and with examples in demos/pkcs12. The
640 'pkcs12' application has to use the macros because it prints out
641 debugging information.
644 * I've called <some function> and it fails, why?
646 Before submitting a report or asking in one of the mailing lists, you
647 should try to determine the cause. In particular, you should call
648 ERR_print_errors() or ERR_print_errors_fp() after the failed call
649 and see if the message helps. Note that the problem may occur earlier
650 than you think -- you should check for errors after every call where
651 it is possible, otherwise the actual problem may be hidden because
652 some OpenSSL functions clear the error state.
655 * I just get a load of numbers for the error output, what do they mean?
657 The actual format is described in the ERR_print_errors() manual page.
658 You should call the function ERR_load_crypto_strings() before hand and
659 the message will be output in text form. If you can't do this (for example
660 it is a pre-compiled binary) you can use the errstr utility on the error
661 code itself (the hex digits after the second colon).
664 * Why do I get errors about unknown algorithms?
666 This can happen under several circumstances such as reading in an
667 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
668 is forgetting to load OpenSSL's table of algorithms with
669 OpenSSL_add_all_algorithms(). See the manual page for more information.
672 * Why can't the OpenSSH configure script detect OpenSSL?
674 Several reasons for problems with the automatic detection exist.
675 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
676 Sometimes the distribution has installed an older version in the system
677 locations that is detected instead of a new one installed. The OpenSSL
678 library might have been compiled for another CPU or another mode (32/64 bits).
679 Permissions might be wrong.
681 The general answer is to check the config.log file generated when running
682 the OpenSSH configure script. It should contain the detailed information
683 on why the OpenSSL library was not detected or considered incompatible.
685 * Can I use OpenSSL's SSL library with non-blocking I/O?
687 Yes; make sure to read the SSL_get_error(3) manual page!
689 A pitfall to avoid: Don't assume that SSL_read() will just read from
690 the underlying transport or that SSL_write() will just write to it --
691 it is also possible that SSL_write() cannot do any useful work until
692 there is data to read, or that SSL_read() cannot do anything until it
693 is possible to send data. One reason for this is that the peer may
694 request a new TLS/SSL handshake at any time during the protocol,
695 requiring a bi-directional message exchange; both SSL_read() and
696 SSL_write() will try to continue any pending handshake.
699 * Why doesn't my server application receive a client certificate?
701 Due to the TLS protocol definition, a client will only send a certificate,
702 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
703 SSL_CTX_set_verify() function to enable the use of client certificates.
706 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
708 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
709 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
710 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
711 Change your code to use the new name when compiling against OpenSSL 0.9.7.
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