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