FAQ revision 79998
1OpenSSL - Frequently Asked Questions 2-------------------------------------- 3 4[MISC] Miscellaneous questions 5 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 12[LEGAL] Legal questions 13 14* Do I need patent licenses to use OpenSSL? 15* Can I use OpenSSL with GPL software? 16 17[USER] Questions on using the OpenSSL applications 18 19* Why do I get a "PRNG not seeded" error message? 20* Why do I get an "unable to write 'random state'" error message? 21* How do I create certificates or certificate requests? 22* Why can't I create certificate requests? 23* Why does <SSL program> fail with a certificate verify error? 24* Why can I only use weak ciphers when I connect to a server using OpenSSL? 25* How can I create DSA certificates? 26* Why can't I make an SSL connection using a DSA certificate? 27* How can I remove the passphrase on a private key? 28* Why can't I use OpenSSL certificates with SSL client authentication? 29* Why does my browser give a warning about a mismatched hostname? 30 31[BUILD] Questions about building and testing OpenSSL 32 33* Why does the linker complain about undefined symbols? 34* Why does the OpenSSL test fail with "bc: command not found"? 35* Why does the OpenSSL test fail with "bc: 1 no implemented"? 36* Why does the OpenSSL compilation fail on Alpha True64 Unix? 37* Why does the OpenSSL compilation fail with "ar: command not found"? 38* Why does the OpenSSL compilation fail on Win32 with VC++? 39 40[PROG] Questions about programming with OpenSSL 41 42* Is OpenSSL thread-safe? 43* I've compiled a program under Windows and it crashes: why? 44* How do I read or write a DER encoded buffer using the ASN1 functions? 45* I've tried using <M_some_evil_pkcs12_macro> and I get errors why? 46* I've called <some function> and it fails, why? 47* I just get a load of numbers for the error output, what do they mean? 48* Why do I get errors about unknown algorithms? 49* Why can't the OpenSSH configure script detect OpenSSL? 50* Can I use OpenSSL's SSL library with non-blocking I/O? 51* Why doesn't my server application receive a client certificate? 52 53=============================================================================== 54 55[MISC] ======================================================================== 56 57* Which is the current version of OpenSSL? 58 59The current version is available from <URL: http://www.openssl.org>. 60OpenSSL 0.9.6b was released on July 9th, 2001. 61 62In addition to the current stable release, you can also access daily 63snapshots of the OpenSSL development version at <URL: 64ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access. 65 66 67* Where is the documentation? 68 69OpenSSL is a library that provides cryptographic functionality to 70applications such as secure web servers. Be sure to read the 71documentation of the application you want to use. The INSTALL file 72explains how to install this library. 73 74OpenSSL includes a command line utility that can be used to perform a 75variety of cryptographic functions. It is described in the openssl(1) 76manpage. Documentation for developers is currently being written. A 77few manual pages already are available; overviews over libcrypto and 78libssl are given in the crypto(3) and ssl(3) manpages. 79 80The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a 81different directory if you specified one as described in INSTALL). 82In addition, you can read the most current versions at 83<URL: http://www.openssl.org/docs/>. 84 85For information on parts of libcrypto that are not yet documented, you 86might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's 87predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much 88of this still applies to OpenSSL. 89 90There is some documentation about certificate extensions and PKCS#12 91in doc/openssl.txt 92 93The original SSLeay documentation is included in OpenSSL as 94doc/ssleay.txt. It may be useful when none of the other resources 95help, but please note that it reflects the obsolete version SSLeay 960.6.6. 97 98 99* How can I contact the OpenSSL developers? 100 101The README file describes how to submit bug reports and patches to 102OpenSSL. Information on the OpenSSL mailing lists is available from 103<URL: http://www.openssl.org>. 104 105 106* Where can I get a compiled version of OpenSSL? 107 108Some applications that use OpenSSL are distributed in binary form. 109When using such an application, you don't need to install OpenSSL 110yourself; the application will include the required parts (e.g. DLLs). 111 112If you want to install OpenSSL on a Windows system and you don't have 113a C compiler, read the "Mingw32" section of INSTALL.W32 for information 114on how to obtain and install the free GNU C compiler. 115 116A number of Linux and *BSD distributions include OpenSSL. 117 118 119* Why aren't tools like 'autoconf' and 'libtool' used? 120 121autoconf will probably be used in future OpenSSL versions. If it was 122less Unix-centric, it might have been used much earlier. 123 124 125[LEGAL] ======================================================================= 126 127* Do I need patent licenses to use OpenSSL? 128 129The patents section of the README file lists patents that may apply to 130you if you want to use OpenSSL. For information on intellectual 131property rights, please consult a lawyer. The OpenSSL team does not 132offer legal advice. 133 134You can configure OpenSSL so as not to use RC5 and IDEA by using 135 ./config no-rc5 no-idea 136 137 138* Can I use OpenSSL with GPL software? 139 140On many systems including the major Linux and BSD distributions, yes (the 141GPL does not place restrictions on using libraries that are part of the 142normal operating system distribution). 143 144On other systems, the situation is less clear. Some GPL software copyright 145holders claim that you infringe on their rights if you use OpenSSL with 146their software on operating systems that don't normally include OpenSSL. 147 148If you develop open source software that uses OpenSSL, you may find it 149useful to choose an other license than the GPL, or state explicitely that 150"This program is released under the GPL with the additional exemption that 151compiling, linking, and/or using OpenSSL is allowed." If you are using 152GPL software developed by others, you may want to ask the copyright holder 153for permission to use their software with OpenSSL. 154 155 156[USER] ======================================================================== 157 158* Why do I get a "PRNG not seeded" error message? 159 160Cryptographic software needs a source of unpredictable data to work 161correctly. Many open source operating systems provide a "randomness 162device" that serves this purpose. On other systems, applications have 163to call the RAND_add() or RAND_seed() function with appropriate data 164before generating keys or performing public key encryption. 165(These functions initialize the pseudo-random number generator, PRNG.) 166 167Some broken applications do not do this. As of version 0.9.5, the 168OpenSSL functions that need randomness report an error if the random 169number generator has not been seeded with at least 128 bits of 170randomness. If this error occurs, please contact the author of the 171application you are using. It is likely that it never worked 172correctly. OpenSSL 0.9.5 and later make the error visible by refusing 173to perform potentially insecure encryption. 174 175On systems without /dev/urandom and /dev/random, it is a good idea to 176use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for 177details. Starting with version 0.9.7, OpenSSL will automatically look 178for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and 179/etc/entropy. 180 181Most components of the openssl command line utility automatically try 182to seed the random number generator from a file. The name of the 183default seeding file is determined as follows: If environment variable 184RANDFILE is set, then it names the seeding file. Otherwise if 185environment variable HOME is set, then the seeding file is $HOME/.rnd. 186If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will 187use file .rnd in the current directory while OpenSSL 0.9.6a uses no 188default seeding file at all. OpenSSL 0.9.6b and later will behave 189similarly to 0.9.6a, but will use a default of "C:" for HOME on 190Windows systems if the environment variable has not been set. 191 192If the default seeding file does not exist or is too short, the "PRNG 193not seeded" error message may occur. 194 195The openssl command line utility will write back a new state to the 196default seeding file (and create this file if necessary) unless 197there was no sufficient seeding. 198 199Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work. 200Use the "-rand" option of the OpenSSL command line tools instead. 201The $RANDFILE environment variable and $HOME/.rnd are only used by the 202OpenSSL command line tools. Applications using the OpenSSL library 203provide their own configuration options to specify the entropy source, 204please check out the documentation coming the with application. 205 206For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested 207installing the SUNski package from Sun patch 105710-01 (Sparc) which 208adds a /dev/random device and make sure it gets used, usually through 209$RANDFILE. There are probably similar patches for the other Solaris 210versions. However, be warned that /dev/random is usually a blocking 211device, which may have some effects on OpenSSL. 212 213 214* Why do I get an "unable to write 'random state'" error message? 215 216 217Sometimes the openssl command line utility does not abort with 218a "PRNG not seeded" error message, but complains that it is 219"unable to write 'random state'". This message refers to the 220default seeding file (see previous answer). A possible reason 221is that no default filename is known because neither RANDFILE 222nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the 223current directory in this case, but this has changed with 0.9.6a.) 224 225 226* How do I create certificates or certificate requests? 227 228Check out the CA.pl(1) manual page. This provides a simple wrapper round 229the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check 230out the manual pages for the individual utilities and the certificate 231extensions documentation (currently in doc/openssl.txt). 232 233 234* Why can't I create certificate requests? 235 236You typically get the error: 237 238 unable to find 'distinguished_name' in config 239 problems making Certificate Request 240 241This is because it can't find the configuration file. Check out the 242DIAGNOSTICS section of req(1) for more information. 243 244 245* Why does <SSL program> fail with a certificate verify error? 246 247This problem is usually indicated by log messages saying something like 248"unable to get local issuer certificate" or "self signed certificate". 249When a certificate is verified its root CA must be "trusted" by OpenSSL 250this typically means that the CA certificate must be placed in a directory 251or file and the relevant program configured to read it. The OpenSSL program 252'verify' behaves in a similar way and issues similar error messages: check 253the verify(1) program manual page for more information. 254 255 256* Why can I only use weak ciphers when I connect to a server using OpenSSL? 257 258This is almost certainly because you are using an old "export grade" browser 259which only supports weak encryption. Upgrade your browser to support 128 bit 260ciphers. 261 262 263* How can I create DSA certificates? 264 265Check the CA.pl(1) manual page for a DSA certificate example. 266 267 268* Why can't I make an SSL connection to a server using a DSA certificate? 269 270Typically you'll see a message saying there are no shared ciphers when 271the same setup works fine with an RSA certificate. There are two possible 272causes. The client may not support connections to DSA servers most web 273browsers (including Netscape and MSIE) only support connections to servers 274supporting RSA cipher suites. The other cause is that a set of DH parameters 275has not been supplied to the server. DH parameters can be created with the 276dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example: 277check the source to s_server in apps/s_server.c for an example. 278 279 280* How can I remove the passphrase on a private key? 281 282Firstly you should be really *really* sure you want to do this. Leaving 283a private key unencrypted is a major security risk. If you decide that 284you do have to do this check the EXAMPLES sections of the rsa(1) and 285dsa(1) manual pages. 286 287 288* Why can't I use OpenSSL certificates with SSL client authentication? 289 290What will typically happen is that when a server requests authentication 291it will either not include your certificate or tell you that you have 292no client certificates (Netscape) or present you with an empty list box 293(MSIE). The reason for this is that when a server requests a client 294certificate it includes a list of CAs names which it will accept. Browsers 295will only let you select certificates from the list on the grounds that 296there is little point presenting a certificate which the server will 297reject. 298 299The solution is to add the relevant CA certificate to your servers "trusted 300CA list". How you do this depends on the server sofware in uses. You can 301print out the servers list of acceptable CAs using the OpenSSL s_client tool: 302 303openssl s_client -connect www.some.host:443 -prexit 304 305If your server only requests certificates on certain URLs then you may need 306to manually issue an HTTP GET command to get the list when s_client connects: 307 308GET /some/page/needing/a/certificate.html 309 310If your CA does not appear in the list then this confirms the problem. 311 312 313* Why does my browser give a warning about a mismatched hostname? 314 315Browsers expect the server's hostname to match the value in the commonName 316(CN) field of the certificate. If it does not then you get a warning. 317 318 319[BUILD] ======================================================================= 320 321* Why does the linker complain about undefined symbols? 322 323Maybe the compilation was interrupted, and make doesn't notice that 324something is missing. Run "make clean; make". 325 326If you used ./Configure instead of ./config, make sure that you 327selected the right target. File formats may differ slightly between 328OS versions (for example sparcv8/sparcv9, or a.out/elf). 329 330In case you get errors about the following symbols, use the config 331option "no-asm", as described in INSTALL: 332 333 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt, 334 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt, 335 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words, 336 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4, 337 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3, 338 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3, 339 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order 340 341If none of these helps, you may want to try using the current snapshot. 342If the problem persists, please submit a bug report. 343 344 345* Why does the OpenSSL test fail with "bc: command not found"? 346 347You didn't install "bc", the Unix calculator. If you want to run the 348tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor. 349 350 351* Why does the OpenSSL test fail with "bc: 1 no implemented"? 352 353On some SCO installations or versions, bc has a bug that gets triggered 354when you run the test suite (using "make test"). The message returned is 355"bc: 1 not implemented". 356 357The best way to deal with this is to find another implementation of bc 358and compile/install it. GNU bc (see http://www.gnu.org/software/software.html 359for download instructions) can be safely used, for example. 360 361 362* Why does the OpenSSL compilation fail on Alpha True64 Unix? 363 364On some Alpha installations running True64 Unix and Compaq C, the compilation 365of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual 366memory to continue compilation.' As far as the tests have shown, this may be 367a compiler bug. What happens is that it eats up a lot of resident memory 368to build something, probably a table. The problem is clearly in the 369optimization code, because if one eliminates optimization completely (-O0), 370the compilation goes through (and the compiler consumes about 2MB of resident 371memory instead of 240MB or whatever one's limit is currently). 372 373There are three options to solve this problem: 374 3751. set your current data segment size soft limit higher. Experience shows 376that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do 377this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of 378kbytes to set the limit to. 379 3802. If you have a hard limit that is lower than what you need and you can't 381get it changed, you can compile all of OpenSSL with -O0 as optimization 382level. This is however not a very nice thing to do for those who expect to 383get the best result from OpenSSL. A bit more complicated solution is the 384following: 385 386----- snip:start ----- 387 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \ 388 sed -e 's/ -O[0-9] / -O0 /'`" 389 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'` 390 make 391----- snip:end ----- 392 393This will only compile sha_dgst.c with -O0, the rest with the optimization 394level chosen by the configuration process. When the above is done, do the 395test and installation and you're set. 396 397 398* Why does the OpenSSL compilation fail with "ar: command not found"? 399 400Getting this message is quite usual on Solaris 2, because Sun has hidden 401away 'ar' and other development commands in directories that aren't in 402$PATH by default. One of those directories is '/usr/ccs/bin'. The 403quickest way to fix this is to do the following (it assumes you use sh 404or any sh-compatible shell): 405 406----- snip:start ----- 407 PATH=${PATH}:/usr/ccs/bin; export PATH 408----- snip:end ----- 409 410and then redo the compilation. What you should really do is make sure 411'/usr/ccs/bin' is permanently in your $PATH, for example through your 412'.profile' (again, assuming you use a sh-compatible shell). 413 414 415* Why does the OpenSSL compilation fail on Win32 with VC++? 416 417Sometimes, you may get reports from VC++ command line (cl) that it 418can't find standard include files like stdio.h and other weirdnesses. 419One possible cause is that the environment isn't correctly set up. 420To solve that problem, one should run VCVARS32.BAT which is found in 421the 'bin' subdirectory of the VC++ installation directory (somewhere 422under 'Program Files'). This needs to be done prior to running NMAKE, 423and the changes are only valid for the current DOS session. 424 425 426[PROG] ======================================================================== 427 428* Is OpenSSL thread-safe? 429 430Yes (with limitations: an SSL connection may not concurrently be used 431by multiple threads). On Windows and many Unix systems, OpenSSL 432automatically uses the multi-threaded versions of the standard 433libraries. If your platform is not one of these, consult the INSTALL 434file. 435 436Multi-threaded applications must provide two callback functions to 437OpenSSL. This is described in the threads(3) manpage. 438 439 440* I've compiled a program under Windows and it crashes: why? 441 442This is usually because you've missed the comment in INSTALL.W32. You 443must link with the multithreaded DLL version of the VC++ runtime library 444otherwise the conflict will cause a program to crash: typically on the 445first BIO related read or write operation. 446 447 448* How do I read or write a DER encoded buffer using the ASN1 functions? 449 450You have two options. You can either use a memory BIO in conjunction 451with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the 452i2d_XXX(), d2i_XXX() functions directly. Since these are often the 453cause of grief here are some code fragments using PKCS7 as an example: 454 455unsigned char *buf, *p; 456int len; 457 458len = i2d_PKCS7(p7, NULL); 459buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */ 460p = buf; 461i2d_PKCS7(p7, &p); 462 463At this point buf contains the len bytes of the DER encoding of 464p7. 465 466The opposite assumes we already have len bytes in buf: 467 468unsigned char *p; 469p = buf; 470p7 = d2i_PKCS7(NULL, &p, len); 471 472At this point p7 contains a valid PKCS7 structure of NULL if an error 473occurred. If an error occurred ERR_print_errors(bio) should give more 474information. 475 476The reason for the temporary variable 'p' is that the ASN1 functions 477increment the passed pointer so it is ready to read or write the next 478structure. This is often a cause of problems: without the temporary 479variable the buffer pointer is changed to point just after the data 480that has been read or written. This may well be uninitialized data 481and attempts to free the buffer will have unpredictable results 482because it no longer points to the same address. 483 484 485* I've tried using <M_some_evil_pkcs12_macro> and I get errors why? 486 487This usually happens when you try compiling something using the PKCS#12 488macros with a C++ compiler. There is hardly ever any need to use the 489PKCS#12 macros in a program, it is much easier to parse and create 490PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions 491documented in doc/openssl.txt and with examples in demos/pkcs12. The 492'pkcs12' application has to use the macros because it prints out 493debugging information. 494 495 496* I've called <some function> and it fails, why? 497 498Before submitting a report or asking in one of the mailing lists, you 499should try to determine the cause. In particular, you should call 500ERR_print_errors() or ERR_print_errors_fp() after the failed call 501and see if the message helps. Note that the problem may occur earlier 502than you think -- you should check for errors after every call where 503it is possible, otherwise the actual problem may be hidden because 504some OpenSSL functions clear the error state. 505 506 507* I just get a load of numbers for the error output, what do they mean? 508 509The actual format is described in the ERR_print_errors() manual page. 510You should call the function ERR_load_crypto_strings() before hand and 511the message will be output in text form. If you can't do this (for example 512it is a pre-compiled binary) you can use the errstr utility on the error 513code itself (the hex digits after the second colon). 514 515 516* Why do I get errors about unknown algorithms? 517 518This can happen under several circumstances such as reading in an 519encrypted private key or attempting to decrypt a PKCS#12 file. The cause 520is forgetting to load OpenSSL's table of algorithms with 521OpenSSL_add_all_algorithms(). See the manual page for more information. 522 523 524* Why can't the OpenSSH configure script detect OpenSSL? 525 526There is a problem with OpenSSH 1.2.2p1, in that the configure script 527can't find the installed OpenSSL libraries. The problem is actually 528a small glitch that is easily solved with the following patch to be 529applied to the OpenSSH distribution: 530 531----- snip:start ----- 532--- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000 533+++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000 534@@ -152,10 +152,10 @@ 535 AC_MSG_CHECKING([for OpenSSL/SSLeay directory]) 536 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do 537 if test ! -z "$ssldir" ; then 538- LIBS="$saved_LIBS -L$ssldir" 539+ LIBS="$saved_LIBS -L$ssldir/lib" 540 CFLAGS="$CFLAGS -I$ssldir/include" 541 if test "x$need_dash_r" = "x1" ; then 542- LIBS="$LIBS -R$ssldir" 543+ LIBS="$LIBS -R$ssldir/lib" 544 fi 545 fi 546 LIBS="$LIBS -lcrypto" 547--- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000 548+++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000 549@@ -1890,10 +1890,10 @@ 550 echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5 551 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do 552 if test ! -z "$ssldir" ; then 553- LIBS="$saved_LIBS -L$ssldir" 554+ LIBS="$saved_LIBS -L$ssldir/lib" 555 CFLAGS="$CFLAGS -I$ssldir/include" 556 if test "x$need_dash_r" = "x1" ; then 557- LIBS="$LIBS -R$ssldir" 558+ LIBS="$LIBS -R$ssldir/lib" 559 fi 560 fi 561 LIBS="$LIBS -lcrypto" 562----- snip:end ----- 563 564 565* Can I use OpenSSL's SSL library with non-blocking I/O? 566 567Yes; make sure to read the SSL_get_error(3) manual page! 568 569A pitfall to avoid: Don't assume that SSL_read() will just read from 570the underlying transport or that SSL_write() will just write to it -- 571it is also possible that SSL_write() cannot do any useful work until 572there is data to read, or that SSL_read() cannot do anything until it 573is possible to send data. One reason for this is that the peer may 574request a new TLS/SSL handshake at any time during the protocol, 575requiring a bi-directional message exchange; both SSL_read() and 576SSL_write() will try to continue any pending handshake. 577 578 579* Why doesn't my server application receive a client certificate? 580 581Due to the TLS protocol definition, a client will only send a certificate, 582if explicitely asked by the server. Use the SSL_VERIFY_PEER flag of the 583SSL_CTX_set_verify() function to enable the use of client certificates. 584 585 586=============================================================================== 587 588