FAQ revision 127128
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* What is an 'engine' version? 12* How do I check the authenticity of the OpenSSL distribution? 13 14[LEGAL] Legal questions 15 16* Do I need patent licenses to use OpenSSL? 17* Can I use OpenSSL with GPL software? 18 19[USER] Questions on using the OpenSSL applications 20 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? 34 35[BUILD] Questions about building and testing OpenSSL 36 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 [on a 64-bit platform]? 48* Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"? 49 50[PROG] Questions about programming with OpenSSL 51 52* Is OpenSSL thread-safe? 53* I've compiled a program under Windows and it crashes: why? 54* How do I read or write a DER encoded buffer using the ASN1 functions? 55* I've tried using <M_some_evil_pkcs12_macro> and I get errors why? 56* I've called <some function> and it fails, why? 57* I just get a load of numbers for the error output, what do they mean? 58* Why do I get errors about unknown algorithms? 59* Why can't the OpenSSH configure script detect OpenSSL? 60* Can I use OpenSSL's SSL library with non-blocking I/O? 61* Why doesn't my server application receive a client certificate? 62* Why does compilation fail due to an undefined symbol NID_uniqueIdentifier? 63 64=============================================================================== 65 66[MISC] ======================================================================== 67 68* Which is the current version of OpenSSL? 69 70The current version is available from <URL: http://www.openssl.org>. 71OpenSSL 0.9.7d was released on March 17, 2004. 72 73In addition to the current stable release, you can also access daily 74snapshots of the OpenSSL development version at <URL: 75ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access. 76 77 78* Where is the documentation? 79 80OpenSSL is a library that provides cryptographic functionality to 81applications such as secure web servers. Be sure to read the 82documentation of the application you want to use. The INSTALL file 83explains how to install this library. 84 85OpenSSL includes a command line utility that can be used to perform a 86variety of cryptographic functions. It is described in the openssl(1) 87manpage. Documentation for developers is currently being written. A 88few manual pages already are available; overviews over libcrypto and 89libssl are given in the crypto(3) and ssl(3) manpages. 90 91The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a 92different directory if you specified one as described in INSTALL). 93In addition, you can read the most current versions at 94<URL: http://www.openssl.org/docs/>. 95 96For information on parts of libcrypto that are not yet documented, you 97might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's 98predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much 99of this still applies to OpenSSL. 100 101There is some documentation about certificate extensions and PKCS#12 102in doc/openssl.txt 103 104The original SSLeay documentation is included in OpenSSL as 105doc/ssleay.txt. It may be useful when none of the other resources 106help, but please note that it reflects the obsolete version SSLeay 1070.6.6. 108 109 110* How can I contact the OpenSSL developers? 111 112The README file describes how to submit bug reports and patches to 113OpenSSL. Information on the OpenSSL mailing lists is available from 114<URL: http://www.openssl.org>. 115 116 117* Where can I get a compiled version of OpenSSL? 118 119You can finder pointers to binary distributions in 120http://www.openssl.org/related/binaries.html . 121 122Some applications that use OpenSSL are distributed in binary form. 123When using such an application, you don't need to install OpenSSL 124yourself; the application will include the required parts (e.g. DLLs). 125 126If you want to build OpenSSL on a Windows system and you don't have 127a C compiler, read the "Mingw32" section of INSTALL.W32 for information 128on how to obtain and install the free GNU C compiler. 129 130A number of Linux and *BSD distributions include OpenSSL. 131 132 133* Why aren't tools like 'autoconf' and 'libtool' used? 134 135autoconf will probably be used in future OpenSSL versions. If it was 136less Unix-centric, it might have been used much earlier. 137 138* What is an 'engine' version? 139 140With version 0.9.6 OpenSSL was extended to interface to external crypto 141hardware. This was realized in a special release '0.9.6-engine'. With 142version 0.9.7 (not yet released) the changes were merged into the main 143development line, so that the special release is no longer necessary. 144 145* How do I check the authenticity of the OpenSSL distribution? 146 147We provide MD5 digests and ASC signatures of each tarball. 148Use MD5 to check that a tarball from a mirror site is identical: 149 150 md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5 151 152You can check authenticity using pgp or gpg. You need the OpenSSL team 153member public key used to sign it (download it from a key server). Then 154just do: 155 156 pgp TARBALL.asc 157 158[LEGAL] ======================================================================= 159 160* Do I need patent licenses to use OpenSSL? 161 162The patents section of the README file lists patents that may apply to 163you if you want to use OpenSSL. For information on intellectual 164property rights, please consult a lawyer. The OpenSSL team does not 165offer legal advice. 166 167You can configure OpenSSL so as not to use RC5 and IDEA by using 168 ./config no-rc5 no-idea 169 170 171* Can I use OpenSSL with GPL software? 172 173On many systems including the major Linux and BSD distributions, yes (the 174GPL does not place restrictions on using libraries that are part of the 175normal operating system distribution). 176 177On other systems, the situation is less clear. Some GPL software copyright 178holders claim that you infringe on their rights if you use OpenSSL with 179their software on operating systems that don't normally include OpenSSL. 180 181If you develop open source software that uses OpenSSL, you may find it 182useful to choose an other license than the GPL, or state explicitly that 183"This program is released under the GPL with the additional exemption that 184compiling, linking, and/or using OpenSSL is allowed." If you are using 185GPL software developed by others, you may want to ask the copyright holder 186for permission to use their software with OpenSSL. 187 188 189[USER] ======================================================================== 190 191* Why do I get a "PRNG not seeded" error message? 192 193Cryptographic software needs a source of unpredictable data to work 194correctly. Many open source operating systems provide a "randomness 195device" (/dev/urandom or /dev/random) that serves this purpose. 196All OpenSSL versions try to use /dev/urandom by default; starting with 197version 0.9.7, OpenSSL also tries /dev/random if /dev/urandom is not 198available. 199 200On other systems, applications have to call the RAND_add() or 201RAND_seed() function with appropriate data before generating keys or 202performing public key encryption. (These functions initialize the 203pseudo-random number generator, PRNG.) Some broken applications do 204not do this. As of version 0.9.5, the OpenSSL functions that need 205randomness report an error if the random number generator has not been 206seeded with at least 128 bits of randomness. If this error occurs and 207is not discussed in the documentation of the application you are 208using, please contact the author of that application; it is likely 209that it never worked correctly. OpenSSL 0.9.5 and later make the 210error visible by refusing to perform potentially insecure encryption. 211 212If you are using Solaris 8, you can add /dev/urandom and /dev/random 213devices by installing patch 112438 (Sparc) or 112439 (x86), which are 214available via the Patchfinder at <URL: http://sunsolve.sun.com> 215(Solaris 9 includes these devices by default). For /dev/random support 216for earlier Solaris versions, see Sun's statement at 217<URL: http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsrdb/27606&zone_32=SUNWski> 218(the SUNWski package is available in patch 105710). 219 220On systems without /dev/urandom and /dev/random, it is a good idea to 221use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for 222details. Starting with version 0.9.7, OpenSSL will automatically look 223for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and 224/etc/entropy. 225 226Most components of the openssl command line utility automatically try 227to seed the random number generator from a file. The name of the 228default seeding file is determined as follows: If environment variable 229RANDFILE is set, then it names the seeding file. Otherwise if 230environment variable HOME is set, then the seeding file is $HOME/.rnd. 231If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will 232use file .rnd in the current directory while OpenSSL 0.9.6a uses no 233default seeding file at all. OpenSSL 0.9.6b and later will behave 234similarly to 0.9.6a, but will use a default of "C:\" for HOME on 235Windows systems if the environment variable has not been set. 236 237If the default seeding file does not exist or is too short, the "PRNG 238not seeded" error message may occur. 239 240The openssl command line utility will write back a new state to the 241default seeding file (and create this file if necessary) unless 242there was no sufficient seeding. 243 244Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work. 245Use the "-rand" option of the OpenSSL command line tools instead. 246The $RANDFILE environment variable and $HOME/.rnd are only used by the 247OpenSSL command line tools. Applications using the OpenSSL library 248provide their own configuration options to specify the entropy source, 249please check out the documentation coming the with application. 250 251 252* Why do I get an "unable to write 'random state'" error message? 253 254 255Sometimes the openssl command line utility does not abort with 256a "PRNG not seeded" error message, but complains that it is 257"unable to write 'random state'". This message refers to the 258default seeding file (see previous answer). A possible reason 259is that no default filename is known because neither RANDFILE 260nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the 261current directory in this case, but this has changed with 0.9.6a.) 262 263 264* How do I create certificates or certificate requests? 265 266Check out the CA.pl(1) manual page. This provides a simple wrapper round 267the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check 268out the manual pages for the individual utilities and the certificate 269extensions documentation (currently in doc/openssl.txt). 270 271 272* Why can't I create certificate requests? 273 274You typically get the error: 275 276 unable to find 'distinguished_name' in config 277 problems making Certificate Request 278 279This is because it can't find the configuration file. Check out the 280DIAGNOSTICS section of req(1) for more information. 281 282 283* Why does <SSL program> fail with a certificate verify error? 284 285This problem is usually indicated by log messages saying something like 286"unable to get local issuer certificate" or "self signed certificate". 287When a certificate is verified its root CA must be "trusted" by OpenSSL 288this typically means that the CA certificate must be placed in a directory 289or file and the relevant program configured to read it. The OpenSSL program 290'verify' behaves in a similar way and issues similar error messages: check 291the verify(1) program manual page for more information. 292 293 294* Why can I only use weak ciphers when I connect to a server using OpenSSL? 295 296This is almost certainly because you are using an old "export grade" browser 297which only supports weak encryption. Upgrade your browser to support 128 bit 298ciphers. 299 300 301* How can I create DSA certificates? 302 303Check the CA.pl(1) manual page for a DSA certificate example. 304 305 306* Why can't I make an SSL connection to a server using a DSA certificate? 307 308Typically you'll see a message saying there are no shared ciphers when 309the same setup works fine with an RSA certificate. There are two possible 310causes. The client may not support connections to DSA servers most web 311browsers (including Netscape and MSIE) only support connections to servers 312supporting RSA cipher suites. The other cause is that a set of DH parameters 313has not been supplied to the server. DH parameters can be created with the 314dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example: 315check the source to s_server in apps/s_server.c for an example. 316 317 318* How can I remove the passphrase on a private key? 319 320Firstly you should be really *really* sure you want to do this. Leaving 321a private key unencrypted is a major security risk. If you decide that 322you do have to do this check the EXAMPLES sections of the rsa(1) and 323dsa(1) manual pages. 324 325 326* Why can't I use OpenSSL certificates with SSL client authentication? 327 328What will typically happen is that when a server requests authentication 329it will either not include your certificate or tell you that you have 330no client certificates (Netscape) or present you with an empty list box 331(MSIE). The reason for this is that when a server requests a client 332certificate it includes a list of CAs names which it will accept. Browsers 333will only let you select certificates from the list on the grounds that 334there is little point presenting a certificate which the server will 335reject. 336 337The solution is to add the relevant CA certificate to your servers "trusted 338CA list". How you do this depends on the server software in uses. You can 339print out the servers list of acceptable CAs using the OpenSSL s_client tool: 340 341openssl s_client -connect www.some.host:443 -prexit 342 343If your server only requests certificates on certain URLs then you may need 344to manually issue an HTTP GET command to get the list when s_client connects: 345 346GET /some/page/needing/a/certificate.html 347 348If your CA does not appear in the list then this confirms the problem. 349 350 351* Why does my browser give a warning about a mismatched hostname? 352 353Browsers expect the server's hostname to match the value in the commonName 354(CN) field of the certificate. If it does not then you get a warning. 355 356 357* How do I install a CA certificate into a browser? 358 359The usual way is to send the DER encoded certificate to the browser as 360MIME type application/x-x509-ca-cert, for example by clicking on an appropriate 361link. On MSIE certain extensions such as .der or .cacert may also work, or you 362can import the certificate using the certificate import wizard. 363 364You can convert a certificate to DER form using the command: 365 366openssl x509 -in ca.pem -outform DER -out ca.der 367 368Occasionally someone suggests using a command such as: 369 370openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem 371 372DO NOT DO THIS! This command will give away your CAs private key and 373reduces its security to zero: allowing anyone to forge certificates in 374whatever name they choose. 375 376* Why is OpenSSL x509 DN output not conformant to RFC2253? 377 378The ways to print out the oneline format of the DN (Distinguished Name) have 379been extended in version 0.9.7 of OpenSSL. Using the new X509_NAME_print_ex() 380interface, the "-nameopt" option could be introduded. See the manual 381page of the "openssl x509" commandline tool for details. The old behaviour 382has however been left as default for the sake of compatibility. 383 384[BUILD] ======================================================================= 385 386* Why does the linker complain about undefined symbols? 387 388Maybe the compilation was interrupted, and make doesn't notice that 389something is missing. Run "make clean; make". 390 391If you used ./Configure instead of ./config, make sure that you 392selected the right target. File formats may differ slightly between 393OS versions (for example sparcv8/sparcv9, or a.out/elf). 394 395In case you get errors about the following symbols, use the config 396option "no-asm", as described in INSTALL: 397 398 BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt, 399 CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt, 400 RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words, 401 bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4, 402 bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3, 403 des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3, 404 des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order 405 406If none of these helps, you may want to try using the current snapshot. 407If the problem persists, please submit a bug report. 408 409 410* Why does the OpenSSL test fail with "bc: command not found"? 411 412You didn't install "bc", the Unix calculator. If you want to run the 413tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor. 414 415 416* Why does the OpenSSL test fail with "bc: 1 no implemented"? 417 418On some SCO installations or versions, bc has a bug that gets triggered 419when you run the test suite (using "make test"). The message returned is 420"bc: 1 not implemented". 421 422The best way to deal with this is to find another implementation of bc 423and compile/install it. GNU bc (see http://www.gnu.org/software/software.html 424for download instructions) can be safely used, for example. 425 426 427* Why does the OpenSSL test fail with "bc: stack empty"? 428 429On some DG/ux versions, bc seems to have a too small stack for calculations 430that the OpenSSL bntest throws at it. This gets triggered when you run the 431test suite (using "make test"). The message returned is "bc: stack empty". 432 433The best way to deal with this is to find another implementation of bc 434and compile/install it. GNU bc (see http://www.gnu.org/software/software.html 435for download instructions) can be safely used, for example. 436 437 438* Why does the OpenSSL compilation fail on Alpha Tru64 Unix? 439 440On some Alpha installations running Tru64 Unix and Compaq C, the compilation 441of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual 442memory to continue compilation.' As far as the tests have shown, this may be 443a compiler bug. What happens is that it eats up a lot of resident memory 444to build something, probably a table. The problem is clearly in the 445optimization code, because if one eliminates optimization completely (-O0), 446the compilation goes through (and the compiler consumes about 2MB of resident 447memory instead of 240MB or whatever one's limit is currently). 448 449There are three options to solve this problem: 450 4511. set your current data segment size soft limit higher. Experience shows 452that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do 453this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of 454kbytes to set the limit to. 455 4562. If you have a hard limit that is lower than what you need and you can't 457get it changed, you can compile all of OpenSSL with -O0 as optimization 458level. This is however not a very nice thing to do for those who expect to 459get the best result from OpenSSL. A bit more complicated solution is the 460following: 461 462----- snip:start ----- 463 make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \ 464 sed -e 's/ -O[0-9] / -O0 /'`" 465 rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'` 466 make 467----- snip:end ----- 468 469This will only compile sha_dgst.c with -O0, the rest with the optimization 470level chosen by the configuration process. When the above is done, do the 471test and installation and you're set. 472 473 474* Why does the OpenSSL compilation fail with "ar: command not found"? 475 476Getting this message is quite usual on Solaris 2, because Sun has hidden 477away 'ar' and other development commands in directories that aren't in 478$PATH by default. One of those directories is '/usr/ccs/bin'. The 479quickest way to fix this is to do the following (it assumes you use sh 480or any sh-compatible shell): 481 482----- snip:start ----- 483 PATH=${PATH}:/usr/ccs/bin; export PATH 484----- snip:end ----- 485 486and then redo the compilation. What you should really do is make sure 487'/usr/ccs/bin' is permanently in your $PATH, for example through your 488'.profile' (again, assuming you use a sh-compatible shell). 489 490 491* Why does the OpenSSL compilation fail on Win32 with VC++? 492 493Sometimes, you may get reports from VC++ command line (cl) that it 494can't find standard include files like stdio.h and other weirdnesses. 495One possible cause is that the environment isn't correctly set up. 496To solve that problem for VC++ versions up to 6, one should run 497VCVARS32.BAT which is found in the 'bin' subdirectory of the VC++ 498installation directory (somewhere under 'Program Files'). For VC++ 499version 7 (and up?), which is also called VS.NET, the file is called 500VSVARS32.BAT instead. 501This needs to be done prior to running NMAKE, and the changes are only 502valid for the current DOS session. 503 504 505* What is special about OpenSSL on Redhat? 506 507Red Hat Linux (release 7.0 and later) include a preinstalled limited 508version of OpenSSL. For patent reasons, support for IDEA, RC5 and MDC2 509is disabled in this version. The same may apply to other Linux distributions. 510Users may therefore wish to install more or all of the features left out. 511 512To do this you MUST ensure that you do not overwrite the openssl that is in 513/usr/bin on your Red Hat machine. Several packages depend on this file, 514including sendmail and ssh. /usr/local/bin is a good alternative choice. The 515libraries that come with Red Hat 7.0 onwards have different names and so are 516not affected. (eg For Red Hat 7.2 they are /lib/libssl.so.0.9.6b and 517/lib/libcrypto.so.0.9.6b with symlinks /lib/libssl.so.2 and 518/lib/libcrypto.so.2 respectively). 519 520Please note that we have been advised by Red Hat attempting to recompile the 521openssl rpm with all the cryptography enabled will not work. All other 522packages depend on the original Red Hat supplied openssl package. It is also 523worth noting that due to the way Red Hat supplies its packages, updates to 524openssl on each distribution never change the package version, only the 525build number. For example, on Red Hat 7.1, the latest openssl package has 526version number 0.9.6 and build number 9 even though it contains all the 527relevant updates in packages up to and including 0.9.6b. 528 529A possible way around this is to persuade Red Hat to produce a non-US 530version of Red Hat Linux. 531 532FYI: Patent numbers and expiry dates of US patents: 533MDC-2: 4,908,861 13/03/2007 534IDEA: 5,214,703 25/05/2010 535RC5: 5,724,428 03/03/2015 536 537 538* Why does the OpenSSL compilation fail on MacOS X? 539 540If the failure happens when trying to build the "openssl" binary, with 541a large number of undefined symbols, it's very probable that you have 542OpenSSL 0.9.6b delivered with the operating system (you can find out by 543running '/usr/bin/openssl version') and that you were trying to build 544OpenSSL 0.9.7 or newer. The problem is that the loader ('ld') in 545MacOS X has a misfeature that's quite difficult to go around. 546Look in the file PROBLEMS for a more detailed explanation and for possible 547solutions. 548 549 550* Why does the OpenSSL test suite fail on MacOS X? 551 552If the failure happens when running 'make test' and the RC4 test fails, 553it's very probable that you have OpenSSL 0.9.6b delivered with the 554operating system (you can find out by running '/usr/bin/openssl version') 555and that you were trying to build OpenSSL 0.9.6d. The problem is that 556the loader ('ld') in MacOS X has a misfeature that's quite difficult to 557go around and has linked the programs "openssl" and the test programs 558with /usr/lib/libcrypto.dylib and /usr/lib/libssl.dylib instead of the 559libraries you just built. 560Look in the file PROBLEMS for a more detailed explanation and for possible 561solutions. 562 563* Why does the OpenSSL test suite fail in BN_sqr test [on a 64-bit platform]? 564 565Failure in BN_sqr test is most likely caused by a failure to configure the 566toolkit for current platform or lack of support for the platform in question. 567Run './config -t' and './apps/openssl version -p'. Do these platform 568identifiers match? If they don't, then you most likely failed to run 569./config and you're hereby advised to do so before filing a bug report. 570If ./config itself fails to run, then it's most likely problem with your 571local environment and you should turn to your system administrator (or 572similar). If identifiers match (and/or no alternative identifier is 573suggested by ./config script), then the platform is unsupported. There might 574or might not be a workaround. Most notably on SPARC64 platforms with GNU 575C compiler you should be able to produce a working build by running 576'./config -m32'. I understand that -m32 might not be what you want/need, 577but the build should be operational. For further details turn to 578<openssl-dev@openssl.org>. 579 580* Why does OpenBSD-i386 build fail on des-586.s with "Unimplemented segment type"? 581 582As of 0.9.7 assembler routines were overhauled for position independence 583of the machine code, which is essential for shared library support. For 584some reason OpenBSD is equipped with an out-of-date GNU assembler which 585finds the new code offensive. To work around the problem, configure with 586no-asm (and sacrifice a great deal of performance) or patch your assembler 587according to <URL: http://www.openssl.org/~appro/gas-1.92.3.OpenBSD.patch>. 588For your convenience a pre-compiled replacement binary is provided at 589<URL: http://www.openssl.org/~appro/gas-1.92.3.static.aout.bin>. 590Reportedly elder *BSD a.out platforms also suffer from this problem and 591remedy should be same. Provided binary is statically linked and should be 592working across wider range of *BSD branches, not just OpenBSD. 593 594[PROG] ======================================================================== 595 596* Is OpenSSL thread-safe? 597 598Yes (with limitations: an SSL connection may not concurrently be used 599by multiple threads). On Windows and many Unix systems, OpenSSL 600automatically uses the multi-threaded versions of the standard 601libraries. If your platform is not one of these, consult the INSTALL 602file. 603 604Multi-threaded applications must provide two callback functions to 605OpenSSL. This is described in the threads(3) manpage. 606 607 608* I've compiled a program under Windows and it crashes: why? 609 610This is usually because you've missed the comment in INSTALL.W32. 611Your application must link against the same version of the Win32 612C-Runtime against which your openssl libraries were linked. The 613default version for OpenSSL is /MD - "Multithreaded DLL". 614 615If you are using Microsoft Visual C++'s IDE (Visual Studio), in 616many cases, your new project most likely defaulted to "Debug 617Singlethreaded" - /ML. This is NOT interchangeable with /MD and your 618program will crash, typically on the first BIO related read or write 619operation. 620 621For each of the six possible link stage configurations within Win32, 622your application must link against the same by which OpenSSL was 623built. If you are using MS Visual C++ (Studio) this can be changed 624by: 625 6261. Select Settings... from the Project Menu. 6272. Select the C/C++ Tab. 6283. Select "Code Generation from the "Category" drop down list box 6294. Select the Appropriate library (see table below) from the "Use 630 run-time library" drop down list box. Perform this step for both 631 your debug and release versions of your application (look at the 632 top left of the settings panel to change between the two) 633 634 Single Threaded /ML - MS VC++ often defaults to 635 this for the release 636 version of a new project. 637 Debug Single Threaded /MLd - MS VC++ often defaults to 638 this for the debug version 639 of a new project. 640 Multithreaded /MT 641 Debug Multithreaded /MTd 642 Multithreaded DLL /MD - OpenSSL defaults to this. 643 Debug Multithreaded DLL /MDd 644 645Note that debug and release libraries are NOT interchangeable. If you 646built OpenSSL with /MD your application must use /MD and cannot use /MDd. 647 648 649* How do I read or write a DER encoded buffer using the ASN1 functions? 650 651You have two options. You can either use a memory BIO in conjunction 652with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the 653i2d_XXX(), d2i_XXX() functions directly. Since these are often the 654cause of grief here are some code fragments using PKCS7 as an example: 655 656unsigned char *buf, *p; 657int len; 658 659len = i2d_PKCS7(p7, NULL); 660buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */ 661p = buf; 662i2d_PKCS7(p7, &p); 663 664At this point buf contains the len bytes of the DER encoding of 665p7. 666 667The opposite assumes we already have len bytes in buf: 668 669unsigned char *p; 670p = buf; 671p7 = d2i_PKCS7(NULL, &p, len); 672 673At this point p7 contains a valid PKCS7 structure of NULL if an error 674occurred. If an error occurred ERR_print_errors(bio) should give more 675information. 676 677The reason for the temporary variable 'p' is that the ASN1 functions 678increment the passed pointer so it is ready to read or write the next 679structure. This is often a cause of problems: without the temporary 680variable the buffer pointer is changed to point just after the data 681that has been read or written. This may well be uninitialized data 682and attempts to free the buffer will have unpredictable results 683because it no longer points to the same address. 684 685 686* I've tried using <M_some_evil_pkcs12_macro> and I get errors why? 687 688This usually happens when you try compiling something using the PKCS#12 689macros with a C++ compiler. There is hardly ever any need to use the 690PKCS#12 macros in a program, it is much easier to parse and create 691PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions 692documented in doc/openssl.txt and with examples in demos/pkcs12. The 693'pkcs12' application has to use the macros because it prints out 694debugging information. 695 696 697* I've called <some function> and it fails, why? 698 699Before submitting a report or asking in one of the mailing lists, you 700should try to determine the cause. In particular, you should call 701ERR_print_errors() or ERR_print_errors_fp() after the failed call 702and see if the message helps. Note that the problem may occur earlier 703than you think -- you should check for errors after every call where 704it is possible, otherwise the actual problem may be hidden because 705some OpenSSL functions clear the error state. 706 707 708* I just get a load of numbers for the error output, what do they mean? 709 710The actual format is described in the ERR_print_errors() manual page. 711You should call the function ERR_load_crypto_strings() before hand and 712the message will be output in text form. If you can't do this (for example 713it is a pre-compiled binary) you can use the errstr utility on the error 714code itself (the hex digits after the second colon). 715 716 717* Why do I get errors about unknown algorithms? 718 719This can happen under several circumstances such as reading in an 720encrypted private key or attempting to decrypt a PKCS#12 file. The cause 721is forgetting to load OpenSSL's table of algorithms with 722OpenSSL_add_all_algorithms(). See the manual page for more information. 723 724 725* Why can't the OpenSSH configure script detect OpenSSL? 726 727Several reasons for problems with the automatic detection exist. 728OpenSSH requires at least version 0.9.5a of the OpenSSL libraries. 729Sometimes the distribution has installed an older version in the system 730locations that is detected instead of a new one installed. The OpenSSL 731library might have been compiled for another CPU or another mode (32/64 bits). 732Permissions might be wrong. 733 734The general answer is to check the config.log file generated when running 735the OpenSSH configure script. It should contain the detailed information 736on why the OpenSSL library was not detected or considered incompatible. 737 738 739* Can I use OpenSSL's SSL library with non-blocking I/O? 740 741Yes; make sure to read the SSL_get_error(3) manual page! 742 743A pitfall to avoid: Don't assume that SSL_read() will just read from 744the underlying transport or that SSL_write() will just write to it -- 745it is also possible that SSL_write() cannot do any useful work until 746there is data to read, or that SSL_read() cannot do anything until it 747is possible to send data. One reason for this is that the peer may 748request a new TLS/SSL handshake at any time during the protocol, 749requiring a bi-directional message exchange; both SSL_read() and 750SSL_write() will try to continue any pending handshake. 751 752 753* Why doesn't my server application receive a client certificate? 754 755Due to the TLS protocol definition, a client will only send a certificate, 756if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the 757SSL_CTX_set_verify() function to enable the use of client certificates. 758 759 760* Why does compilation fail due to an undefined symbol NID_uniqueIdentifier? 761 762For OpenSSL 0.9.7 the OID table was extended and corrected. In earlier 763versions, uniqueIdentifier was incorrectly used for X.509 certificates. 764The correct name according to RFC2256 (LDAP) is x500UniqueIdentifier. 765Change your code to use the new name when compiling against OpenSSL 0.9.7. 766 767 768=============================================================================== 769 770