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?
12 * How do I check the authenticity of the OpenSSL distribution?
14 [LEGAL] Legal questions
16 * Do I need patent licenses to use OpenSSL?
17 * Can I use OpenSSL with GPL software?
19 [USER] Questions on using the OpenSSL applications
21 * Why do I get a "PRNG not seeded" error message?
22 * Why do I get an "unable to write 'random state'" error message?
23 * How do I create certificates or certificate requests?
24 * Why can't I create certificate requests?
25 * Why does <SSL program> fail with a certificate verify error?
26 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
27 * How can I create DSA certificates?
28 * Why can't I make an SSL connection using a DSA certificate?
29 * How can I remove the passphrase on a private key?
30 * Why can't I use OpenSSL certificates with SSL client authentication?
31 * Why does my browser give a warning about a mismatched hostname?
32 * How do I install a CA certificate into a browser?
33 * Why is OpenSSL x509 DN output not conformant to RFC2253?
35 [BUILD] Questions about building and testing OpenSSL
37 * Why does the linker complain about undefined symbols?
38 * Why does the OpenSSL test fail with "bc: command not found"?
39 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
40 * Why does the OpenSSL test fail with "bc: stack empty"?
41 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
42 * Why does the OpenSSL compilation fail with "ar: command not found"?
43 * Why does the OpenSSL compilation fail on Win32 with VC++?
44 * What is special about OpenSSL on Redhat?
45 * Why does the OpenSSL compilation fail on MacOS X?
46 * Why does the OpenSSL test suite fail on MacOS X?
47 * Why does the OpenSSL test suite fail in BN_sqr test?
49 [PROG] Questions about programming with OpenSSL
51 * Is OpenSSL thread-safe?
52 * I've compiled a program under Windows and it crashes: why?
53 * How do I read or write a DER encoded buffer using the ASN1 functions?
54 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
55 * I've called <some function> and it fails, why?
56 * I just get a load of numbers for the error output, what do they mean?
57 * Why do I get errors about unknown algorithms?
58 * Why can't the OpenSSH configure script detect OpenSSL?
59 * Can I use OpenSSL's SSL library with non-blocking I/O?
60 * Why doesn't my server application receive a client certificate?
61 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
63 ===============================================================================
65 [MISC] ========================================================================
67 * Which is the current version of OpenSSL?
69 The current version is available from <URL: http://www.openssl.org>.
70 OpenSSL 0.9.6h was released on December 5, 2002.
72 In addition to the current stable release, you can also access daily
73 snapshots of the OpenSSL development version at <URL:
74 ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
77 * Where is the documentation?
79 OpenSSL is a library that provides cryptographic functionality to
80 applications such as secure web servers. Be sure to read the
81 documentation of the application you want to use. The INSTALL file
82 explains how to install this library.
84 OpenSSL includes a command line utility that can be used to perform a
85 variety of cryptographic functions. It is described in the openssl(1)
86 manpage. Documentation for developers is currently being written. A
87 few manual pages already are available; overviews over libcrypto and
88 libssl are given in the crypto(3) and ssl(3) manpages.
90 The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
91 different directory if you specified one as described in INSTALL).
92 In addition, you can read the most current versions at
93 <URL: http://www.openssl.org/docs/>.
95 For information on parts of libcrypto that are not yet documented, you
96 might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
97 predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
98 of this still applies to OpenSSL.
100 There is some documentation about certificate extensions and PKCS#12
103 The original SSLeay documentation is included in OpenSSL as
104 doc/ssleay.txt. It may be useful when none of the other resources
105 help, but please note that it reflects the obsolete version SSLeay
109 * How can I contact the OpenSSL developers?
111 The README file describes how to submit bug reports and patches to
112 OpenSSL. Information on the OpenSSL mailing lists is available from
113 <URL: http://www.openssl.org>.
116 * Where can I get a compiled version of OpenSSL?
118 Some applications that use OpenSSL are distributed in binary form.
119 When using such an application, you don't need to install OpenSSL
120 yourself; the application will include the required parts (e.g. DLLs).
122 If you want to install OpenSSL on a Windows system and you don't have
123 a C compiler, read the "Mingw32" section of INSTALL.W32 for information
124 on how to obtain and install the free GNU C compiler.
126 A number of Linux and *BSD distributions include OpenSSL.
129 * Why aren't tools like 'autoconf' and 'libtool' used?
131 autoconf will probably be used in future OpenSSL versions. If it was
132 less Unix-centric, it might have been used much earlier.
134 * What is an 'engine' version?
136 With version 0.9.6 OpenSSL was extended to interface to external crypto
137 hardware. This was realized in a special release '0.9.6-engine'. With
138 version 0.9.7 (not yet released) the changes were merged into the main
139 development line, so that the special release is no longer necessary.
141 * How do I check the authenticity of the OpenSSL distribution?
143 We provide MD5 digests and ASC signatures of each tarball.
144 Use MD5 to check that a tarball from a mirror site is identical:
146 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
148 You can check authenticity using pgp or gpg. You need the OpenSSL team
149 member public key used to sign it (download it from a key server). Then
154 [LEGAL] =======================================================================
156 * Do I need patent licenses to use OpenSSL?
158 The patents section of the README file lists patents that may apply to
159 you if you want to use OpenSSL. For information on intellectual
160 property rights, please consult a lawyer. The OpenSSL team does not
163 You can configure OpenSSL so as not to use RC5 and IDEA by using
164 ./config no-rc5 no-idea
167 * Can I use OpenSSL with GPL software?
169 On many systems including the major Linux and BSD distributions, yes (the
170 GPL does not place restrictions on using libraries that are part of the
171 normal operating system distribution).
173 On other systems, the situation is less clear. Some GPL software copyright
174 holders claim that you infringe on their rights if you use OpenSSL with
175 their software on operating systems that don't normally include OpenSSL.
177 If you develop open source software that uses OpenSSL, you may find it
178 useful to choose an other license than the GPL, or state explicitly that
179 "This program is released under the GPL with the additional exemption that
180 compiling, linking, and/or using OpenSSL is allowed." If you are using
181 GPL software developed by others, you may want to ask the copyright holder
182 for permission to use their software with OpenSSL.
185 [USER] ========================================================================
187 * Why do I get a "PRNG not seeded" error message?
189 Cryptographic software needs a source of unpredictable data to work
190 correctly. Many open source operating systems provide a "randomness
191 device" that serves this purpose. On other systems, applications have
192 to call the RAND_add() or RAND_seed() function with appropriate data
193 before generating keys or performing public key encryption.
194 (These functions initialize the pseudo-random number generator, PRNG.)
196 Some broken applications do not do this. As of version 0.9.5, the
197 OpenSSL functions that need randomness report an error if the random
198 number generator has not been seeded with at least 128 bits of
199 randomness. If this error occurs, please contact the author of the
200 application you are using. It is likely that it never worked
201 correctly. OpenSSL 0.9.5 and later make the error visible by refusing
202 to perform potentially insecure encryption.
204 On systems without /dev/urandom and /dev/random, it is a good idea to
205 use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
206 details. Starting with version 0.9.7, OpenSSL will automatically look
207 for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
210 Most components of the openssl command line utility automatically try
211 to seed the random number generator from a file. The name of the
212 default seeding file is determined as follows: If environment variable
213 RANDFILE is set, then it names the seeding file. Otherwise if
214 environment variable HOME is set, then the seeding file is $HOME/.rnd.
215 If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
216 use file .rnd in the current directory while OpenSSL 0.9.6a uses no
217 default seeding file at all. OpenSSL 0.9.6b and later will behave
218 similarly to 0.9.6a, but will use a default of "C:\" for HOME on
219 Windows systems if the environment variable has not been set.
221 If the default seeding file does not exist or is too short, the "PRNG
222 not seeded" error message may occur.
224 The openssl command line utility will write back a new state to the
225 default seeding file (and create this file if necessary) unless
226 there was no sufficient seeding.
228 Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
229 Use the "-rand" option of the OpenSSL command line tools instead.
230 The $RANDFILE environment variable and $HOME/.rnd are only used by the
231 OpenSSL command line tools. Applications using the OpenSSL library
232 provide their own configuration options to specify the entropy source,
233 please check out the documentation coming the with application.
235 For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
236 installing the SUNski package from Sun patch 105710-01 (Sparc) which
237 adds a /dev/random device and make sure it gets used, usually through
238 $RANDFILE. There are probably similar patches for the other Solaris
239 versions. An official statement from Sun with respect to /dev/random
240 support can be found at
241 http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski
242 However, be warned that /dev/random is usually a blocking device, which
243 may have some effects on OpenSSL.
244 A third party /dev/random solution for Solaris is available at
245 http://www.cosy.sbg.ac.at/~andi/
248 * Why do I get an "unable to write 'random state'" error message?
251 Sometimes the openssl command line utility does not abort with
252 a "PRNG not seeded" error message, but complains that it is
253 "unable to write 'random state'". This message refers to the
254 default seeding file (see previous answer). A possible reason
255 is that no default filename is known because neither RANDFILE
256 nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
257 current directory in this case, but this has changed with 0.9.6a.)
260 * How do I create certificates or certificate requests?
262 Check out the CA.pl(1) manual page. This provides a simple wrapper round
263 the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
264 out the manual pages for the individual utilities and the certificate
265 extensions documentation (currently in doc/openssl.txt).
268 * Why can't I create certificate requests?
270 You typically get the error:
272 unable to find 'distinguished_name' in config
273 problems making Certificate Request
275 This is because it can't find the configuration file. Check out the
276 DIAGNOSTICS section of req(1) for more information.
279 * Why does <SSL program> fail with a certificate verify error?
281 This problem is usually indicated by log messages saying something like
282 "unable to get local issuer certificate" or "self signed certificate".
283 When a certificate is verified its root CA must be "trusted" by OpenSSL
284 this typically means that the CA certificate must be placed in a directory
285 or file and the relevant program configured to read it. The OpenSSL program
286 'verify' behaves in a similar way and issues similar error messages: check
287 the verify(1) program manual page for more information.
290 * Why can I only use weak ciphers when I connect to a server using OpenSSL?
292 This is almost certainly because you are using an old "export grade" browser
293 which only supports weak encryption. Upgrade your browser to support 128 bit
297 * How can I create DSA certificates?
299 Check the CA.pl(1) manual page for a DSA certificate example.
302 * Why can't I make an SSL connection to a server using a DSA certificate?
304 Typically you'll see a message saying there are no shared ciphers when
305 the same setup works fine with an RSA certificate. There are two possible
306 causes. The client may not support connections to DSA servers most web
307 browsers (including Netscape and MSIE) only support connections to servers
308 supporting RSA cipher suites. The other cause is that a set of DH parameters
309 has not been supplied to the server. DH parameters can be created with the
310 dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
311 check the source to s_server in apps/s_server.c for an example.
314 * How can I remove the passphrase on a private key?
316 Firstly you should be really *really* sure you want to do this. Leaving
317 a private key unencrypted is a major security risk. If you decide that
318 you do have to do this check the EXAMPLES sections of the rsa(1) and
322 * Why can't I use OpenSSL certificates with SSL client authentication?
324 What will typically happen is that when a server requests authentication
325 it will either not include your certificate or tell you that you have
326 no client certificates (Netscape) or present you with an empty list box
327 (MSIE). The reason for this is that when a server requests a client
328 certificate it includes a list of CAs names which it will accept. Browsers
329 will only let you select certificates from the list on the grounds that
330 there is little point presenting a certificate which the server will
333 The solution is to add the relevant CA certificate to your servers "trusted
334 CA list". How you do this depends on the server software in uses. You can
335 print out the servers list of acceptable CAs using the OpenSSL s_client tool:
337 openssl s_client -connect www.some.host:443 -prexit
339 If your server only requests certificates on certain URLs then you may need
340 to manually issue an HTTP GET command to get the list when s_client connects:
342 GET /some/page/needing/a/certificate.html
344 If your CA does not appear in the list then this confirms the problem.
347 * Why does my browser give a warning about a mismatched hostname?
349 Browsers expect the server's hostname to match the value in the commonName
350 (CN) field of the certificate. If it does not then you get a warning.
353 * How do I install a CA certificate into a browser?
355 The usual way is to send the DER encoded certificate to the browser as
356 MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
357 link. On MSIE certain extensions such as .der or .cacert may also work, or you
358 can import the certificate using the certificate import wizard.
360 You can convert a certificate to DER form using the command:
362 openssl x509 -in ca.pem -outform DER -out ca.der
364 Occasionally someone suggests using a command such as:
366 openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
368 DO NOT DO THIS! This command will give away your CAs private key and
369 reduces its security to zero: allowing anyone to forge certificates in
370 whatever name they choose.
372 * Why is OpenSSL x509 DN output not conformant to RFC2253?
374 The ways to print out the oneline format of the DN (Distinguished Name) have
375 been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex()
376 interface, the "-nameopt" option could be introduded. See the manual
377 page of the "openssl x509" commandline tool for details. The old behaviour
378 has however been left as default for the sake of compatibility.
380 [BUILD] =======================================================================
382 * Why does the linker complain about undefined symbols?
384 Maybe the compilation was interrupted, and make doesn't notice that
385 something is missing. Run "make clean; make".
387 If you used ./Configure instead of ./config, make sure that you
388 selected the right target. File formats may differ slightly between
389 OS versions (for example sparcv8/sparcv9, or a.out/elf).
391 In case you get errors about the following symbols, use the config
392 option "no-asm", as described in INSTALL:
394 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
395 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
396 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
397 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
398 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
399 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
400 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
402 If none of these helps, you may want to try using the current snapshot.
403 If the problem persists, please submit a bug report.
406 * Why does the OpenSSL test fail with "bc: command not found"?
408 You didn't install "bc", the Unix calculator. If you want to run the
409 tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
412 * Why does the OpenSSL test fail with "bc: 1 no implemented"?
414 On some SCO installations or versions, bc has a bug that gets triggered
415 when you run the test suite (using "make test"). The message returned is
416 "bc: 1 not implemented".
418 The best way to deal with this is to find another implementation of bc
419 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
420 for download instructions) can be safely used, for example.
423 * Why does the OpenSSL test fail with "bc: stack empty"?
425 On some DG/ux versions, bc seems to have a too small stack for calculations
426 that the OpenSSL bntest throws at it. This gets triggered when you run the
427 test suite (using "make test"). The message returned is "bc: stack empty".
429 The best way to deal with this is to find another implementation of bc
430 and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
431 for download instructions) can be safely used, for example.
434 * Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
436 On some Alpha installations running Tru64 Unix and Compaq C, the compilation
437 of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
438 memory to continue compilation.' As far as the tests have shown, this may be
439 a compiler bug. What happens is that it eats up a lot of resident memory
440 to build something, probably a table. The problem is clearly in the
441 optimization code, because if one eliminates optimization completely (-O0),
442 the compilation goes through (and the compiler consumes about 2MB of resident
443 memory instead of 240MB or whatever one's limit is currently).
445 There are three options to solve this problem:
447 1. set your current data segment size soft limit higher. Experience shows
448 that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
449 this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
450 kbytes to set the limit to.
452 2. If you have a hard limit that is lower than what you need and you can't
453 get it changed, you can compile all of OpenSSL with -O0 as optimization
454 level. This is however not a very nice thing to do for those who expect to
455 get the best result from OpenSSL. A bit more complicated solution is the
458 ----- snip:start -----
459 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
460 sed -e 's/ -O[0-9] / -O0 /'`"
461 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
465 This will only compile sha_dgst.c with -O0, the rest with the optimization
466 level chosen by the configuration process. When the above is done, do the
467 test and installation and you're set.
470 * Why does the OpenSSL compilation fail with "ar: command not found"?
472 Getting this message is quite usual on Solaris 2, because Sun has hidden
473 away 'ar' and other development commands in directories that aren't in
474 $PATH by default. One of those directories is '/usr/ccs/bin'. The
475 quickest way to fix this is to do the following (it assumes you use sh
476 or any sh-compatible shell):
478 ----- snip:start -----
479 PATH=${PATH}:/usr/ccs/bin; export PATH
482 and then redo the compilation. What you should really do is make sure
483 '/usr/ccs/bin' is permanently in your $PATH, for example through your
484 '.profile' (again, assuming you use a sh-compatible shell).
487 * Why does the OpenSSL compilation fail on Win32 with VC++?
489 Sometimes, you may get reports from VC++ command line (cl) that it
490 can't find standard include files like stdio.h and other weirdnesses.
491 One possible cause is that the environment isn't correctly set up.
492 To solve that problem, one should run VCVARS32.BAT which is found in
493 the 'bin' subdirectory of the VC++ installation directory (somewhere
494 under 'Program Files'). This needs to be done prior to running NMAKE,
495 and the changes are only valid for the current DOS session.
498 * What is special about OpenSSL on Redhat?
500 Red Hat Linux (release 7.0 and later) include a preinstalled limited
501 version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2
502 is disabled in this version. The same may apply to other Linux distributions.
503 Users may therefore wish to install more or all of the features left out.
505 To do this you MUST ensure that you do not overwrite the openssl that is in
506 /usr/bin on your Red Hat machine. Several packages depend on this file,
507 including sendmail and ssh. /usr/local/bin is a good alternative choice. The
508 libraries that come with Red Hat 7.0 onwards have different names and so are
509 not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and
510 /lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and
511 /lib/libcrypto.so.2 respectively).
513 Please note that we have been advised by Red Hat attempting to recompile the
514 openssl rpm with all the cryptography enabled will not work. All other
515 packages depend on the original Red Hat supplied openssl package. It is also
516 worth noting that due to the way Red Hat supplies its packages, updates to
517 openssl on each distribution never change the package version, only the
518 build number. For example, on Red Hat 7.1, the latest openssl package has
519 version number 0.9.6 and build number 9 even though it contains all the
520 relevant updates in packages up to and including 0.9.6b.
522 A possible way around this is to persuade Red Hat to produce a non-US
523 version of Red Hat Linux.
525 FYI: Patent numbers and expiry dates of US patents:
526 MDC-2: 4,908,861 13/03/2007
527 IDEA: 5,214,703 25/05/2010
528 RC5: 5,724,428 03/03/2015
531 * Why does the OpenSSL compilation fail on MacOS X?
533 If the failure happens when trying to build the "openssl" binary, with
534 a large number of undefined symbols, it's very probable that you have
535 OpenSSL 0.9.6b delivered with the operating system (you can find out by
536 running '/usr/bin/openssl version') and that you were trying to build
537 OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in
538 MacOS X has a misfeature that's quite difficult to go around.
539 Look in the file PROBLEMS for a more detailed explanation and for possible
543 * Why does the OpenSSL test suite fail on MacOS X?
545 If the failure happens when running 'make test' and the RC4 test fails,
546 it's very probable that you have OpenSSL 0.9.6b delivered with the
547 operating system (you can find out by running '/usr/bin/openssl version')
548 and that you were trying to build OpenSSL 0.9.6d. The problem is that
549 the loader ('ld') in MacOS X has a misfeature that's quite difficult to
550 go around and has linked the programs "openssl" and the test programs
551 with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the
552 libraries you just built.
553 Look in the file PROBLEMS for a more detailed explanation and for possible
556 * Why does the OpenSSL test suite fail in BN_sqr test?
558 Failure in BN_sqr test is most likely caused by a failure to configure the
559 toolkit for current platform. Run ./config -t and ./apps/openssl version -p.
560 Do these platform identifiers match? If they don't, then you most likely
561 failed to run ./config and you're hereby advised to do so before filing a
562 bug report. If it's ./config itself that fails to run, the it's most
563 likely problem with your local environment and you should turn to your
564 system administrator (or similar).
566 [PROG] ========================================================================
568 * Is OpenSSL thread-safe?
570 Yes (with limitations: an SSL connection may not concurrently be used
571 by multiple threads). On Windows and many Unix systems, OpenSSL
572 automatically uses the multi-threaded versions of the standard
573 libraries. If your platform is not one of these, consult the INSTALL
576 Multi-threaded applications must provide two callback functions to
577 OpenSSL. This is described in the threads(3) manpage.
580 * I've compiled a program under Windows and it crashes: why?
582 This is usually because you've missed the comment in INSTALL.W32.
583 Your application must link against the same version of the Win32
584 C-Runtime against which your openssl libraries were linked. The
585 default version for OpenSSL is /MD - "Multithreaded DLL".
587 If you are using Microsoft Visual C++'s IDE (Visual Studio), in
588 many cases, your new project most likely defaulted to "Debug
589 Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
590 program will crash, typically on the first BIO related read or write
593 For each of the six possible link stage configurations within Win32,
594 your application must link against the same by which OpenSSL was
595 built. If you are using MS Visual C++ (Studio) this can be changed
598 1. Select Settings... from the Project Menu.
599 2. Select the C/C++ Tab.
600 3. Select "Code Generation from the "Category" drop down list box
601 4. Select the Appropriate library (see table below) from the "Use
602 run-time library" drop down list box. Perform this step for both
603 your debug and release versions of your application (look at the
604 top left of the settings panel to change between the two)
606 Single Threaded /ML - MS VC++ often defaults to
608 version of a new project.
609 Debug Single Threaded /MLd - MS VC++ often defaults to
610 this for the debug version
613 Debug Multithreaded /MTd
614 Multithreaded DLL /MD - OpenSSL defaults to this.
615 Debug Multithreaded DLL /MDd
617 Note that debug and release libraries are NOT interchangeable. If you
618 built OpenSSL with /MD your application must use /MD and cannot use /MDd.
621 * How do I read or write a DER encoded buffer using the ASN1 functions?
623 You have two options. You can either use a memory BIO in conjunction
624 with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
625 i2d_XXX(), d2i_XXX() functions directly. Since these are often the
626 cause of grief here are some code fragments using PKCS7 as an example:
628 unsigned char *buf, *p;
631 len = i2d_PKCS7(p7, NULL);
632 buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
636 At this point buf contains the len bytes of the DER encoding of
639 The opposite assumes we already have len bytes in buf:
643 p7 = d2i_PKCS7(NULL, &p, len);
645 At this point p7 contains a valid PKCS7 structure of NULL if an error
646 occurred. If an error occurred ERR_print_errors(bio) should give more
649 The reason for the temporary variable 'p' is that the ASN1 functions
650 increment the passed pointer so it is ready to read or write the next
651 structure. This is often a cause of problems: without the temporary
652 variable the buffer pointer is changed to point just after the data
653 that has been read or written. This may well be uninitialized data
654 and attempts to free the buffer will have unpredictable results
655 because it no longer points to the same address.
658 * I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
660 This usually happens when you try compiling something using the PKCS#12
661 macros with a C++ compiler. There is hardly ever any need to use the
662 PKCS#12 macros in a program, it is much easier to parse and create
663 PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
664 documented in doc/openssl.txt and with examples in demos/pkcs12. The
665 'pkcs12' application has to use the macros because it prints out
666 debugging information.
669 * I've called <some function> and it fails, why?
671 Before submitting a report or asking in one of the mailing lists, you
672 should try to determine the cause. In particular, you should call
673 ERR_print_errors() or ERR_print_errors_fp() after the failed call
674 and see if the message helps. Note that the problem may occur earlier
675 than you think -- you should check for errors after every call where
676 it is possible, otherwise the actual problem may be hidden because
677 some OpenSSL functions clear the error state.
680 * I just get a load of numbers for the error output, what do they mean?
682 The actual format is described in the ERR_print_errors() manual page.
683 You should call the function ERR_load_crypto_strings() before hand and
684 the message will be output in text form. If you can't do this (for example
685 it is a pre-compiled binary) you can use the errstr utility on the error
686 code itself (the hex digits after the second colon).
689 * Why do I get errors about unknown algorithms?
691 This can happen under several circumstances such as reading in an
692 encrypted private key or attempting to decrypt a PKCS#12 file. The cause
693 is forgetting to load OpenSSL's table of algorithms with
694 OpenSSL_add_all_algorithms(). See the manual page for more information.
697 * Why can't the OpenSSH configure script detect OpenSSL?
699 Several reasons for problems with the automatic detection exist.
700 OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
701 Sometimes the distribution has installed an older version in the system
702 locations that is detected instead of a new one installed. The OpenSSL
703 library might have been compiled for another CPU or another mode (32/64 bits).
704 Permissions might be wrong.
706 The general answer is to check the config.log file generated when running
707 the OpenSSH configure script. It should contain the detailed information
708 on why the OpenSSL library was not detected or considered incompatible.
710 * Can I use OpenSSL's SSL library with non-blocking I/O?
712 Yes; make sure to read the SSL_get_error(3) manual page!
714 A pitfall to avoid: Don't assume that SSL_read() will just read from
715 the underlying transport or that SSL_write() will just write to it --
716 it is also possible that SSL_write() cannot do any useful work until
717 there is data to read, or that SSL_read() cannot do anything until it
718 is possible to send data. One reason for this is that the peer may
719 request a new TLS/SSL handshake at any time during the protocol,
720 requiring a bi-directional message exchange; both SSL_read() and
721 SSL_write() will try to continue any pending handshake.
724 * Why doesn't my server application receive a client certificate?
726 Due to the TLS protocol definition, a client will only send a certificate,
727 if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
728 SSL_CTX_set_verify() function to enable the use of client certificates.
731 * Why does compilation fail due to an undefined symbol NID_uniqueIdentifier?
733 For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier
734 versions, uniqueIdentifier was incorrectly used for X.509 certificates.
735 The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier.
736 Change your code to use the new name when compiling against OpenSSL 0.9.7.
739 ===============================================================================