]>
Commit | Line | Data |
---|---|---|
f9a7c34f UM |
1 | OpenSSL - Frequently Asked Questions |
2 | -------------------------------------- | |
3 | ||
0ae485dc RL |
4 | [MISC] Miscellaneous questions |
5 | ||
49976df5 | 6 | * Which is the current version of OpenSSL? |
f9a7c34f UM |
7 | * Where is the documentation? |
8 | * How can I contact the OpenSSL developers? | |
0ae485dc RL |
9 | * Where can I get a compiled version of OpenSSL? |
10 | * Why aren't tools like 'autoconf' and 'libtool' used? | |
9c11a0e5 | 11 | * What is an 'engine' version? |
0ae485dc RL |
12 | |
13 | [LEGAL] Legal questions | |
14 | ||
c1ce32f1 | 15 | * Do I need patent licenses to use OpenSSL? |
17e75747 | 16 | * Can I use OpenSSL with GPL software? |
0ae485dc RL |
17 | |
18 | [USER] Questions on using the OpenSSL applications | |
19 | ||
f9a7c34f | 20 | * Why do I get a "PRNG not seeded" error message? |
24cc290b | 21 | * Why do I get an "unable to write 'random state'" error message? |
46e80a30 DSH |
22 | * How do I create certificates or certificate requests? |
23 | * Why can't I create certificate requests? | |
afee764c | 24 | * Why does <SSL program> fail with a certificate verify error? |
a331a305 | 25 | * Why can I only use weak ciphers when I connect to a server using OpenSSL? |
afee764c DSH |
26 | * How can I create DSA certificates? |
27 | * Why can't I make an SSL connection using a DSA certificate? | |
a331a305 | 28 | * How can I remove the passphrase on a private key? |
1a7b2d33 | 29 | * Why can't I use OpenSSL certificates with SSL client authentication? |
7522254b | 30 | * Why does my browser give a warning about a mismatched hostname? |
0b33bc6b | 31 | * How do I install a CA certificate into a browser? |
0ae485dc RL |
32 | |
33 | [BUILD] Questions about building and testing OpenSSL | |
34 | ||
35 | * Why does the linker complain about undefined symbols? | |
c32364f5 | 36 | * Why does the OpenSSL test fail with "bc: command not found"? |
a6ed5dd6 | 37 | * Why does the OpenSSL test fail with "bc: 1 no implemented"? |
6bc847e4 | 38 | * Why does the OpenSSL compilation fail on Alpha Tru64 Unix? |
b364e5d2 | 39 | * Why does the OpenSSL compilation fail with "ar: command not found"? |
bf55ece1 | 40 | * Why does the OpenSSL compilation fail on Win32 with VC++? |
f9a7c34f | 41 | |
0ae485dc RL |
42 | [PROG] Questions about programming with OpenSSL |
43 | ||
44 | * Is OpenSSL thread-safe? | |
45 | * I've compiled a program under Windows and it crashes: why? | |
46 | * How do I read or write a DER encoded buffer using the ASN1 functions? | |
47 | * I've tried using <M_some_evil_pkcs12_macro> and I get errors why? | |
48 | * I've called <some function> and it fails, why? | |
49 | * I just get a load of numbers for the error output, what do they mean? | |
50 | * Why do I get errors about unknown algorithms? | |
51 | * Why can't the OpenSSH configure script detect OpenSSL? | |
52 | * Can I use OpenSSL's SSL library with non-blocking I/O? | |
19732245 | 53 | * Why doesn't my server application receive a client certificate? |
0ae485dc RL |
54 | |
55 | =============================================================================== | |
56 | ||
57 | [MISC] ======================================================================== | |
f9a7c34f | 58 | |
49976df5 UM |
59 | * Which is the current version of OpenSSL? |
60 | ||
61 | The current version is available from <URL: http://www.openssl.org>. | |
3c89d78d | 62 | OpenSSL 0.9.6c was released on December 21st, 2001. |
49976df5 UM |
63 | |
64 | In addition to the current stable release, you can also access daily | |
65 | snapshots of the OpenSSL development version at <URL: | |
66 | ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access. | |
67 | ||
68 | ||
f9a7c34f UM |
69 | * Where is the documentation? |
70 | ||
71 | OpenSSL is a library that provides cryptographic functionality to | |
72 | applications such as secure web servers. Be sure to read the | |
73 | documentation of the application you want to use. The INSTALL file | |
74 | explains how to install this library. | |
75 | ||
76 | OpenSSL includes a command line utility that can be used to perform a | |
77 | variety of cryptographic functions. It is described in the openssl(1) | |
78 | manpage. Documentation for developers is currently being written. A | |
79 | few manual pages already are available; overviews over libcrypto and | |
80 | libssl are given in the crypto(3) and ssl(3) manpages. | |
81 | ||
82 | The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a | |
83 | different directory if you specified one as described in INSTALL). | |
84 | In addition, you can read the most current versions at | |
85 | <URL: http://www.openssl.org/docs/>. | |
86 | ||
87 | For information on parts of libcrypto that are not yet documented, you | |
88 | might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's | |
89 | predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much | |
90 | of this still applies to OpenSSL. | |
91 | ||
fbb41ae0 DSH |
92 | There is some documentation about certificate extensions and PKCS#12 |
93 | in doc/openssl.txt | |
94 | ||
f9a7c34f | 95 | The original SSLeay documentation is included in OpenSSL as |
cacbb51e | 96 | doc/ssleay.txt. It may be useful when none of the other resources |
f9a7c34f UM |
97 | help, but please note that it reflects the obsolete version SSLeay |
98 | 0.6.6. | |
99 | ||
100 | ||
101 | * How can I contact the OpenSSL developers? | |
102 | ||
103 | The README file describes how to submit bug reports and patches to | |
104 | OpenSSL. Information on the OpenSSL mailing lists is available from | |
105 | <URL: http://www.openssl.org>. | |
106 | ||
107 | ||
0ae485dc | 108 | * Where can I get a compiled version of OpenSSL? |
f9a7c34f | 109 | |
0ae485dc RL |
110 | Some applications that use OpenSSL are distributed in binary form. |
111 | When using such an application, you don't need to install OpenSSL | |
112 | yourself; the application will include the required parts (e.g. DLLs). | |
f9a7c34f | 113 | |
0ae485dc RL |
114 | If you want to install OpenSSL on a Windows system and you don't have |
115 | a C compiler, read the "Mingw32" section of INSTALL.W32 for information | |
116 | on how to obtain and install the free GNU C compiler. | |
f9a7c34f | 117 | |
0ae485dc | 118 | A number of Linux and *BSD distributions include OpenSSL. |
f9a7c34f | 119 | |
f9a7c34f | 120 | |
0ae485dc | 121 | * Why aren't tools like 'autoconf' and 'libtool' used? |
f9a7c34f | 122 | |
ba93fd6a UM |
123 | autoconf will probably be used in future OpenSSL versions. If it was |
124 | less Unix-centric, it might have been used much earlier. | |
f9a7c34f | 125 | |
a0256f46 | 126 | * What is an 'engine' version? |
679df234 LJ |
127 | |
128 | With version 0.9.6 OpenSSL was extended to interface to external crypto | |
129 | hardware. This was realized in a special release '0.9.6-engine'. With | |
a0256f46 LJ |
130 | version 0.9.7 (not yet released) the changes were merged into the main |
131 | development line, so that the special release is no longer necessary. | |
b1d6e3f5 | 132 | |
0ae485dc | 133 | [LEGAL] ======================================================================= |
b1d6e3f5 | 134 | |
0ae485dc | 135 | * Do I need patent licenses to use OpenSSL? |
b1d6e3f5 | 136 | |
0ae485dc RL |
137 | The patents section of the README file lists patents that may apply to |
138 | you if you want to use OpenSSL. For information on intellectual | |
139 | property rights, please consult a lawyer. The OpenSSL team does not | |
140 | offer legal advice. | |
141 | ||
142 | You can configure OpenSSL so as not to use RC5 and IDEA by using | |
143 | ./config no-rc5 no-idea | |
144 | ||
145 | ||
17e75747 UM |
146 | * Can I use OpenSSL with GPL software? |
147 | ||
148 | On many systems including the major Linux and BSD distributions, yes (the | |
149 | GPL does not place restrictions on using libraries that are part of the | |
150 | normal operating system distribution). | |
151 | ||
152 | On other systems, the situation is less clear. Some GPL software copyright | |
153 | holders claim that you infringe on their rights if you use OpenSSL with | |
154 | their software on operating systems that don't normally include OpenSSL. | |
155 | ||
156 | If you develop open source software that uses OpenSSL, you may find it | |
e3fefbfd | 157 | useful to choose an other license than the GPL, or state explicitly that |
17e75747 UM |
158 | "This program is released under the GPL with the additional exemption that |
159 | compiling, linking, and/or using OpenSSL is allowed." If you are using | |
160 | GPL software developed by others, you may want to ask the copyright holder | |
161 | for permission to use their software with OpenSSL. | |
162 | ||
163 | ||
0ae485dc | 164 | [USER] ======================================================================== |
b1d6e3f5 | 165 | |
f9a7c34f UM |
166 | * Why do I get a "PRNG not seeded" error message? |
167 | ||
168 | Cryptographic software needs a source of unpredictable data to work | |
169 | correctly. Many open source operating systems provide a "randomness | |
170 | device" that serves this purpose. On other systems, applications have | |
171 | to call the RAND_add() or RAND_seed() function with appropriate data | |
172 | before generating keys or performing public key encryption. | |
24cc290b | 173 | (These functions initialize the pseudo-random number generator, PRNG.) |
f9a7c34f UM |
174 | |
175 | Some broken applications do not do this. As of version 0.9.5, the | |
176 | OpenSSL functions that need randomness report an error if the random | |
177 | number generator has not been seeded with at least 128 bits of | |
178 | randomness. If this error occurs, please contact the author of the | |
179 | application you are using. It is likely that it never worked | |
8311d323 UM |
180 | correctly. OpenSSL 0.9.5 and later make the error visible by refusing |
181 | to perform potentially insecure encryption. | |
182 | ||
d9a770e6 BM |
183 | On systems without /dev/urandom and /dev/random, it is a good idea to |
184 | use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for | |
185 | details. Starting with version 0.9.7, OpenSSL will automatically look | |
186 | for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and | |
187 | /etc/entropy. | |
2b670ea2 | 188 | |
24cc290b BM |
189 | Most components of the openssl command line utility automatically try |
190 | to seed the random number generator from a file. The name of the | |
191 | default seeding file is determined as follows: If environment variable | |
192 | RANDFILE is set, then it names the seeding file. Otherwise if | |
193 | environment variable HOME is set, then the seeding file is $HOME/.rnd. | |
194 | If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will | |
195 | use file .rnd in the current directory while OpenSSL 0.9.6a uses no | |
196 | default seeding file at all. OpenSSL 0.9.6b and later will behave | |
6af59bc0 | 197 | similarly to 0.9.6a, but will use a default of "C:\" for HOME on |
24cc290b BM |
198 | Windows systems if the environment variable has not been set. |
199 | ||
200 | If the default seeding file does not exist or is too short, the "PRNG | |
201 | not seeded" error message may occur. | |
202 | ||
203 | The openssl command line utility will write back a new state to the | |
204 | default seeding file (and create this file if necessary) unless | |
205 | there was no sufficient seeding. | |
206 | ||
35feed50 LJ |
207 | Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work. |
208 | Use the "-rand" option of the OpenSSL command line tools instead. | |
209 | The $RANDFILE environment variable and $HOME/.rnd are only used by the | |
210 | OpenSSL command line tools. Applications using the OpenSSL library | |
211 | provide their own configuration options to specify the entropy source, | |
212 | please check out the documentation coming the with application. | |
8311d323 | 213 | |
9b296157 RL |
214 | For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested |
215 | installing the SUNski package from Sun patch 105710-01 (Sparc) which | |
216 | adds a /dev/random device and make sure it gets used, usually through | |
217 | $RANDFILE. There are probably similar patches for the other Solaris | |
218 | versions. However, be warned that /dev/random is usually a blocking | |
7cae5f9f | 219 | device, which may have some effects on OpenSSL. |
9b296157 | 220 | |
2b670ea2 | 221 | |
24cc290b BM |
222 | * Why do I get an "unable to write 'random state'" error message? |
223 | ||
224 | ||
225 | Sometimes the openssl command line utility does not abort with | |
226 | a "PRNG not seeded" error message, but complains that it is | |
227 | "unable to write 'random state'". This message refers to the | |
228 | default seeding file (see previous answer). A possible reason | |
229 | is that no default filename is known because neither RANDFILE | |
230 | nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the | |
231 | current directory in this case, but this has changed with 0.9.6a.) | |
232 | ||
233 | ||
0ae485dc RL |
234 | * How do I create certificates or certificate requests? |
235 | ||
236 | Check out the CA.pl(1) manual page. This provides a simple wrapper round | |
237 | the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check | |
238 | out the manual pages for the individual utilities and the certificate | |
239 | extensions documentation (currently in doc/openssl.txt). | |
240 | ||
241 | ||
242 | * Why can't I create certificate requests? | |
243 | ||
244 | You typically get the error: | |
245 | ||
246 | unable to find 'distinguished_name' in config | |
247 | problems making Certificate Request | |
248 | ||
249 | This is because it can't find the configuration file. Check out the | |
250 | DIAGNOSTICS section of req(1) for more information. | |
251 | ||
252 | ||
253 | * Why does <SSL program> fail with a certificate verify error? | |
254 | ||
255 | This problem is usually indicated by log messages saying something like | |
256 | "unable to get local issuer certificate" or "self signed certificate". | |
257 | When a certificate is verified its root CA must be "trusted" by OpenSSL | |
258 | this typically means that the CA certificate must be placed in a directory | |
259 | or file and the relevant program configured to read it. The OpenSSL program | |
260 | 'verify' behaves in a similar way and issues similar error messages: check | |
261 | the verify(1) program manual page for more information. | |
262 | ||
263 | ||
264 | * Why can I only use weak ciphers when I connect to a server using OpenSSL? | |
265 | ||
266 | This is almost certainly because you are using an old "export grade" browser | |
267 | which only supports weak encryption. Upgrade your browser to support 128 bit | |
268 | ciphers. | |
269 | ||
270 | ||
271 | * How can I create DSA certificates? | |
272 | ||
273 | Check the CA.pl(1) manual page for a DSA certificate example. | |
274 | ||
275 | ||
276 | * Why can't I make an SSL connection to a server using a DSA certificate? | |
277 | ||
278 | Typically you'll see a message saying there are no shared ciphers when | |
279 | the same setup works fine with an RSA certificate. There are two possible | |
280 | causes. The client may not support connections to DSA servers most web | |
281 | browsers (including Netscape and MSIE) only support connections to servers | |
282 | supporting RSA cipher suites. The other cause is that a set of DH parameters | |
283 | has not been supplied to the server. DH parameters can be created with the | |
284 | dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example: | |
285 | check the source to s_server in apps/s_server.c for an example. | |
286 | ||
287 | ||
288 | * How can I remove the passphrase on a private key? | |
289 | ||
290 | Firstly you should be really *really* sure you want to do this. Leaving | |
291 | a private key unencrypted is a major security risk. If you decide that | |
292 | you do have to do this check the EXAMPLES sections of the rsa(1) and | |
293 | dsa(1) manual pages. | |
294 | ||
295 | ||
1a7b2d33 DSH |
296 | * Why can't I use OpenSSL certificates with SSL client authentication? |
297 | ||
298 | What will typically happen is that when a server requests authentication | |
299 | it will either not include your certificate or tell you that you have | |
300 | no client certificates (Netscape) or present you with an empty list box | |
301 | (MSIE). The reason for this is that when a server requests a client | |
302 | certificate it includes a list of CAs names which it will accept. Browsers | |
303 | will only let you select certificates from the list on the grounds that | |
304 | there is little point presenting a certificate which the server will | |
305 | reject. | |
306 | ||
307 | The solution is to add the relevant CA certificate to your servers "trusted | |
e3fefbfd | 308 | CA list". How you do this depends on the server software in uses. You can |
1a7b2d33 DSH |
309 | print out the servers list of acceptable CAs using the OpenSSL s_client tool: |
310 | ||
311 | openssl s_client -connect www.some.host:443 -prexit | |
312 | ||
959f67d6 | 313 | If your server only requests certificates on certain URLs then you may need |
1a7b2d33 DSH |
314 | to manually issue an HTTP GET command to get the list when s_client connects: |
315 | ||
316 | GET /some/page/needing/a/certificate.html | |
317 | ||
318 | If your CA does not appear in the list then this confirms the problem. | |
319 | ||
320 | ||
321 | * Why does my browser give a warning about a mismatched hostname? | |
322 | ||
323 | Browsers expect the server's hostname to match the value in the commonName | |
324 | (CN) field of the certificate. If it does not then you get a warning. | |
325 | ||
326 | ||
0b33bc6b DSH |
327 | * How do I install a CA certificate into a browser? |
328 | ||
329 | The usual way is to send the DER encoded certificate to the browser as | |
330 | MIME type application/x-x509-ca-cert, for example by clicking on an appropriate | |
331 | link. On MSIE certain extensions such as .der or .cacert may also work, or you | |
332 | can import the certificate using the certificate import wizard. | |
333 | ||
334 | You can convert a certificate to DER form using the command: | |
335 | ||
336 | openssl x509 -in ca.pem -outform DER -out ca.der | |
337 | ||
338 | Occasionally someone suggests using a command such as: | |
339 | ||
340 | openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem | |
341 | ||
342 | DO NOT DO THIS! This command will give away your CAs private key and | |
343 | reduces its security to zero: allowing anyone to forge certificates in | |
344 | whatever name they choose. | |
345 | ||
346 | ||
0ae485dc RL |
347 | [BUILD] ======================================================================= |
348 | ||
49976df5 UM |
349 | * Why does the linker complain about undefined symbols? |
350 | ||
cacbb51e | 351 | Maybe the compilation was interrupted, and make doesn't notice that |
49976df5 UM |
352 | something is missing. Run "make clean; make". |
353 | ||
354 | If you used ./Configure instead of ./config, make sure that you | |
355 | selected the right target. File formats may differ slightly between | |
356 | OS versions (for example sparcv8/sparcv9, or a.out/elf). | |
357 | ||
0816bc22 UM |
358 | In case you get errors about the following symbols, use the config |
359 | option "no-asm", as described in INSTALL: | |
360 | ||
361 | BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt, | |
362 | CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt, | |
363 | RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words, | |
364 | bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4, | |
365 | bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3, | |
366 | des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3, | |
367 | des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order | |
368 | ||
569be071 | 369 | If none of these helps, you may want to try using the current snapshot. |
49976df5 UM |
370 | If the problem persists, please submit a bug report. |
371 | ||
372 | ||
0ae485dc | 373 | * Why does the OpenSSL test fail with "bc: command not found"? |
2b670ea2 | 374 | |
0ae485dc RL |
375 | You didn't install "bc", the Unix calculator. If you want to run the |
376 | tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor. | |
2b670ea2 | 377 | |
2b670ea2 | 378 | |
a6ed5dd6 | 379 | * Why does the OpenSSL test fail with "bc: 1 no implemented"? |
0ae485dc | 380 | |
1417f2dc RL |
381 | On some SCO installations or versions, bc has a bug that gets triggered |
382 | when you run the test suite (using "make test"). The message returned is | |
a6ed5dd6 | 383 | "bc: 1 not implemented". |
1417f2dc RL |
384 | |
385 | The best way to deal with this is to find another implementation of bc | |
386 | and compile/install it. GNU bc (see http://www.gnu.org/software/software.html | |
387 | for download instructions) can be safely used, for example. | |
0ae485dc RL |
388 | |
389 | ||
6bc847e4 | 390 | * Why does the OpenSSL compilation fail on Alpha Tru64 Unix? |
0ae485dc | 391 | |
6bc847e4 | 392 | On some Alpha installations running Tru64 Unix and Compaq C, the compilation |
0ae485dc RL |
393 | of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual |
394 | memory to continue compilation.' As far as the tests have shown, this may be | |
395 | a compiler bug. What happens is that it eats up a lot of resident memory | |
396 | to build something, probably a table. The problem is clearly in the | |
397 | optimization code, because if one eliminates optimization completely (-O0), | |
398 | the compilation goes through (and the compiler consumes about 2MB of resident | |
399 | memory instead of 240MB or whatever one's limit is currently). | |
400 | ||
401 | There are three options to solve this problem: | |
402 | ||
403 | 1. set your current data segment size soft limit higher. Experience shows | |
404 | that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do | |
405 | this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of | |
406 | kbytes to set the limit to. | |
407 | ||
408 | 2. If you have a hard limit that is lower than what you need and you can't | |
409 | get it changed, you can compile all of OpenSSL with -O0 as optimization | |
410 | level. This is however not a very nice thing to do for those who expect to | |
411 | get the best result from OpenSSL. A bit more complicated solution is the | |
412 | following: | |
413 | ||
414 | ----- snip:start ----- | |
415 | make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \ | |
416 | sed -e 's/ -O[0-9] / -O0 /'`" | |
417 | rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'` | |
418 | make | |
419 | ----- snip:end ----- | |
420 | ||
421 | This will only compile sha_dgst.c with -O0, the rest with the optimization | |
422 | level chosen by the configuration process. When the above is done, do the | |
423 | test and installation and you're set. | |
424 | ||
425 | ||
426 | * Why does the OpenSSL compilation fail with "ar: command not found"? | |
427 | ||
428 | Getting this message is quite usual on Solaris 2, because Sun has hidden | |
429 | away 'ar' and other development commands in directories that aren't in | |
430 | $PATH by default. One of those directories is '/usr/ccs/bin'. The | |
431 | quickest way to fix this is to do the following (it assumes you use sh | |
432 | or any sh-compatible shell): | |
433 | ||
434 | ----- snip:start ----- | |
435 | PATH=${PATH}:/usr/ccs/bin; export PATH | |
436 | ----- snip:end ----- | |
437 | ||
438 | and then redo the compilation. What you should really do is make sure | |
439 | '/usr/ccs/bin' is permanently in your $PATH, for example through your | |
440 | '.profile' (again, assuming you use a sh-compatible shell). | |
441 | ||
442 | ||
443 | * Why does the OpenSSL compilation fail on Win32 with VC++? | |
444 | ||
445 | Sometimes, you may get reports from VC++ command line (cl) that it | |
446 | can't find standard include files like stdio.h and other weirdnesses. | |
447 | One possible cause is that the environment isn't correctly set up. | |
448 | To solve that problem, one should run VCVARS32.BAT which is found in | |
449 | the 'bin' subdirectory of the VC++ installation directory (somewhere | |
450 | under 'Program Files'). This needs to be done prior to running NMAKE, | |
451 | and the changes are only valid for the current DOS session. | |
452 | ||
453 | ||
454 | [PROG] ======================================================================== | |
455 | ||
456 | * Is OpenSSL thread-safe? | |
457 | ||
458 | Yes (with limitations: an SSL connection may not concurrently be used | |
459 | by multiple threads). On Windows and many Unix systems, OpenSSL | |
460 | automatically uses the multi-threaded versions of the standard | |
461 | libraries. If your platform is not one of these, consult the INSTALL | |
462 | file. | |
463 | ||
464 | Multi-threaded applications must provide two callback functions to | |
465 | OpenSSL. This is described in the threads(3) manpage. | |
e8dbc159 | 466 | |
afee764c | 467 | |
46e80a30 DSH |
468 | * I've compiled a program under Windows and it crashes: why? |
469 | ||
a542db90 RL |
470 | This is usually because you've missed the comment in INSTALL.W32. |
471 | Your application must link against the same version of the Win32 | |
472 | C-Runtime against which your openssl libraries were linked. The | |
473 | default version for OpenSSL is /MD - "Multithreaded DLL". | |
474 | ||
475 | If you are using Microsoft Visual C++'s IDE (Visual Studio), in | |
476 | many cases, your new project most likely defaulted to "Debug | |
477 | Singlethreaded" - /ML. This is NOT interchangeable with /MD and your | |
478 | program will crash, typically on the first BIO related read or write | |
479 | operation. | |
480 | ||
481 | For each of the six possible link stage configurations within Win32, | |
482 | your application must link against the same by which OpenSSL was | |
483 | built. If you are using MS Visual C++ (Studio) this can be changed | |
484 | by: | |
485 | ||
486 | 1. Select Settings... from the Project Menu. | |
487 | 2. Select the C/C++ Tab. | |
488 | 3. Select "Code Generation from the "Category" drop down list box | |
489 | 4. Select the Appropriate library (see table below) from the "Use | |
490 | run-time library" drop down list box. Perform this step for both | |
491 | your debug and release versions of your application (look at the | |
492 | top left of the settings panel to change between the two) | |
493 | ||
494 | Single Threaded /ML - MS VC++ often defaults to | |
495 | this for the release | |
496 | version of a new project. | |
497 | Debug Single Threaded /MLd - MS VC++ often defaults to | |
498 | this for the debug version | |
499 | of a new project. | |
500 | Multithreaded /MT | |
501 | Debug Multithreaded /MTd | |
502 | Multithreaded DLL /MD - OpenSSL defaults to this. | |
503 | Debug Multithreaded DLL /MDd | |
504 | ||
505 | Note that debug and release libraries are NOT interchangeable. If you | |
506 | built OpenSSL with /MD your application must use /MD and cannot use /MDd. | |
46e80a30 DSH |
507 | |
508 | ||
c5a3b7e7 DSH |
509 | * How do I read or write a DER encoded buffer using the ASN1 functions? |
510 | ||
511 | You have two options. You can either use a memory BIO in conjunction | |
512 | with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the | |
513 | i2d_XXX(), d2i_XXX() functions directly. Since these are often the | |
514 | cause of grief here are some code fragments using PKCS7 as an example: | |
515 | ||
516 | unsigned char *buf, *p; | |
517 | int len; | |
518 | ||
519 | len = i2d_PKCS7(p7, NULL); | |
7cae5f9f | 520 | buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */ |
c5a3b7e7 DSH |
521 | p = buf; |
522 | i2d_PKCS7(p7, &p); | |
523 | ||
524 | At this point buf contains the len bytes of the DER encoding of | |
525 | p7. | |
526 | ||
527 | The opposite assumes we already have len bytes in buf: | |
528 | ||
529 | unsigned char *p; | |
530 | p = buf; | |
531 | p7 = d2i_PKCS7(NULL, &p, len); | |
532 | ||
533 | At this point p7 contains a valid PKCS7 structure of NULL if an error | |
534 | occurred. If an error occurred ERR_print_errors(bio) should give more | |
535 | information. | |
536 | ||
537 | The reason for the temporary variable 'p' is that the ASN1 functions | |
538 | increment the passed pointer so it is ready to read or write the next | |
539 | structure. This is often a cause of problems: without the temporary | |
540 | variable the buffer pointer is changed to point just after the data | |
541 | that has been read or written. This may well be uninitialized data | |
542 | and attempts to free the buffer will have unpredictable results | |
543 | because it no longer points to the same address. | |
544 | ||
545 | ||
84b65340 DSH |
546 | * I've tried using <M_some_evil_pkcs12_macro> and I get errors why? |
547 | ||
548 | This usually happens when you try compiling something using the PKCS#12 | |
549 | macros with a C++ compiler. There is hardly ever any need to use the | |
550 | PKCS#12 macros in a program, it is much easier to parse and create | |
551 | PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions | |
552 | documented in doc/openssl.txt and with examples in demos/pkcs12. The | |
553 | 'pkcs12' application has to use the macros because it prints out | |
554 | debugging information. | |
555 | ||
556 | ||
35af460f DSH |
557 | * I've called <some function> and it fails, why? |
558 | ||
02859fb7 BM |
559 | Before submitting a report or asking in one of the mailing lists, you |
560 | should try to determine the cause. In particular, you should call | |
35af460f | 561 | ERR_print_errors() or ERR_print_errors_fp() after the failed call |
02859fb7 BM |
562 | and see if the message helps. Note that the problem may occur earlier |
563 | than you think -- you should check for errors after every call where | |
564 | it is possible, otherwise the actual problem may be hidden because | |
565 | some OpenSSL functions clear the error state. | |
35af460f DSH |
566 | |
567 | ||
568 | * I just get a load of numbers for the error output, what do they mean? | |
569 | ||
570 | The actual format is described in the ERR_print_errors() manual page. | |
571 | You should call the function ERR_load_crypto_strings() before hand and | |
572 | the message will be output in text form. If you can't do this (for example | |
573 | it is a pre-compiled binary) you can use the errstr utility on the error | |
574 | code itself (the hex digits after the second colon). | |
575 | ||
576 | ||
46e80a30 DSH |
577 | * Why do I get errors about unknown algorithms? |
578 | ||
579 | This can happen under several circumstances such as reading in an | |
580 | encrypted private key or attempting to decrypt a PKCS#12 file. The cause | |
581 | is forgetting to load OpenSSL's table of algorithms with | |
582 | OpenSSL_add_all_algorithms(). See the manual page for more information. | |
583 | ||
584 | ||
e8dbc159 RL |
585 | * Why can't the OpenSSH configure script detect OpenSSL? |
586 | ||
a116afa4 LJ |
587 | Several reasons for problems with the automatic detection exist. |
588 | OpenSSH requires at least version 0.9.5a of the OpenSSL libraries. | |
589 | Sometimes the distribution has installed an older version in the system | |
590 | locations that is detected instead of a new one installed. The OpenSSL | |
591 | library might have been compiled for another CPU or another mode (32/64 bits). | |
592 | Permissions might be wrong. | |
593 | ||
594 | The general answer is to check the config.log file generated when running | |
595 | the OpenSSH configure script. It should contain the detailed information | |
596 | on why the OpenSSL library was not detected or considered incompatible. | |
31efc3a7 | 597 | |
0ae485dc | 598 | * Can I use OpenSSL's SSL library with non-blocking I/O? |
bf55ece1 | 599 | |
0ae485dc | 600 | Yes; make sure to read the SSL_get_error(3) manual page! |
bf55ece1 | 601 | |
0ae485dc RL |
602 | A pitfall to avoid: Don't assume that SSL_read() will just read from |
603 | the underlying transport or that SSL_write() will just write to it -- | |
604 | it is also possible that SSL_write() cannot do any useful work until | |
605 | there is data to read, or that SSL_read() cannot do anything until it | |
606 | is possible to send data. One reason for this is that the peer may | |
607 | request a new TLS/SSL handshake at any time during the protocol, | |
608 | requiring a bi-directional message exchange; both SSL_read() and | |
609 | SSL_write() will try to continue any pending handshake. | |
bf55ece1 | 610 | |
bf55ece1 | 611 | |
19732245 LJ |
612 | * Why doesn't my server application receive a client certificate? |
613 | ||
614 | Due to the TLS protocol definition, a client will only send a certificate, | |
e3fefbfd | 615 | if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the |
19732245 LJ |
616 | SSL_CTX_set_verify() function to enable the use of client certificates. |
617 | ||
618 | ||
0ae485dc | 619 | =============================================================================== |
bf55ece1 | 620 |