OpenSSL - Frequently Asked Questions -------------------------------------- [MISC] Miscellaneous questions * Which is the current version of OpenSSL? * Where is the documentation? * How can I contact the OpenSSL developers? * Where can I get a compiled version of OpenSSL? * Why aren't tools like 'autoconf' and 'libtool' used? [LEGAL] Legal questions * Do I need patent licenses to use OpenSSL? * Can I use OpenSSL with GPL software? [USER] Questions on using the OpenSSL applications * Why do I get a "PRNG not seeded" error message? * How do I create certificates or certificate requests? * Why can't I create certificate requests? * Why does fail with a certificate verify error? * Why can I only use weak ciphers when I connect to a server using OpenSSL? * How can I create DSA certificates? * Why can't I make an SSL connection using a DSA certificate? * How can I remove the passphrase on a private key? * Why can't I use OpenSSL certificates with SSL client authentication? * Why does my browser give a warning about a mismatched hostname? [BUILD] Questions about building and testing OpenSSL * Why does the linker complain about undefined symbols? * Why does the OpenSSL test fail with "bc: command not found"? * Why does the OpenSSL test fail with "bc: 1 no implemented"? * Why does the OpenSSL compilation fail on Alpha True64 Unix? * Why does the OpenSSL compilation fail with "ar: command not found"? * Why does the OpenSSL compilation fail on Win32 with VC++? [PROG] Questions about programming with OpenSSL * Is OpenSSL thread-safe? * I've compiled a program under Windows and it crashes: why? * How do I read or write a DER encoded buffer using the ASN1 functions? * I've tried using and I get errors why? * I've called and it fails, why? * I just get a load of numbers for the error output, what do they mean? * Why do I get errors about unknown algorithms? * Why can't the OpenSSH configure script detect OpenSSL? * Can I use OpenSSL's SSL library with non-blocking I/O? =============================================================================== [MISC] ======================================================================== * Which is the current version of OpenSSL? The current version is available from . OpenSSL 0.9.6 was released on September 24th, 2000. In addition to the current stable release, you can also access daily snapshots of the OpenSSL development version at , or get it by anonymous CVS access. * Where is the documentation? OpenSSL is a library that provides cryptographic functionality to applications such as secure web servers. Be sure to read the documentation of the application you want to use. The INSTALL file explains how to install this library. OpenSSL includes a command line utility that can be used to perform a variety of cryptographic functions. It is described in the openssl(1) manpage. Documentation for developers is currently being written. A few manual pages already are available; overviews over libcrypto and libssl are given in the crypto(3) and ssl(3) manpages. The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a different directory if you specified one as described in INSTALL). In addition, you can read the most current versions at . For information on parts of libcrypto that are not yet documented, you might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's predecessor, at . Much of this still applies to OpenSSL. There is some documentation about certificate extensions and PKCS#12 in doc/openssl.txt The original SSLeay documentation is included in OpenSSL as doc/ssleay.txt. It may be useful when none of the other resources help, but please note that it reflects the obsolete version SSLeay 0.6.6. * How can I contact the OpenSSL developers? The README file describes how to submit bug reports and patches to OpenSSL. Information on the OpenSSL mailing lists is available from . * Where can I get a compiled version of OpenSSL? Some applications that use OpenSSL are distributed in binary form. When using such an application, you don't need to install OpenSSL yourself; the application will include the required parts (e.g. DLLs). If you want to install OpenSSL on a Windows system and you don't have a C compiler, read the "Mingw32" section of INSTALL.W32 for information on how to obtain and install the free GNU C compiler. A number of Linux and *BSD distributions include OpenSSL. * Why aren't tools like 'autoconf' and 'libtool' used? autoconf is a nice tool, but is unfortunately very Unix-centric. Although one can come up with solution to have ports keep in track, there's also some work needed for that, and can be quite painful at times. If there was a 'autoconf'-like tool that generated perl scripts or something similarly general, it would probably be used in OpenSSL much earlier. libtool has repeatadly been reported by some members of the OpenSSL development and others to be a pain to use. So far, those in the development team who have said anything about this have expressed a wish to avoid libtool for that reason. [LEGAL] ======================================================================= * Do I need patent licenses to use OpenSSL? The patents section of the README file lists patents that may apply to you if you want to use OpenSSL. For information on intellectual property rights, please consult a lawyer. The OpenSSL team does not offer legal advice. You can configure OpenSSL so as not to use RC5 and IDEA by using ./config no-rc5 no-idea * Can I use OpenSSL with GPL software? On many systems including the major Linux and BSD distributions, yes (the GPL does not place restrictions on using libraries that are part of the normal operating system distribution). On other systems, the situation is less clear. Some GPL software copyright holders claim that you infringe on their rights if you use OpenSSL with their software on operating systems that don't normally include OpenSSL. If you develop open source software that uses OpenSSL, you may find it useful to choose an other license than the GPL, or state explicitely that "This program is released under the GPL with the additional exemption that compiling, linking, and/or using OpenSSL is allowed." If you are using GPL software developed by others, you may want to ask the copyright holder for permission to use their software with OpenSSL. [USER] ======================================================================== * Why do I get a "PRNG not seeded" error message? Cryptographic software needs a source of unpredictable data to work correctly. Many open source operating systems provide a "randomness device" that serves this purpose. On other systems, applications have to call the RAND_add() or RAND_seed() function with appropriate data before generating keys or performing public key encryption. Some broken applications do not do this. As of version 0.9.5, the OpenSSL functions that need randomness report an error if the random number generator has not been seeded with at least 128 bits of randomness. If this error occurs, please contact the author of the application you are using. It is likely that it never worked correctly. OpenSSL 0.9.5 and later make the error visible by refusing to perform potentially insecure encryption. On systems without /dev/urandom, it is a good idea to use the Entropy Gathering Demon; see the RAND_egd() manpage for details. Most components of the openssl command line tool try to use the file $HOME/.rnd (or $RANDFILE, if this environment variable is set) for seeding the PRNG. If this file does not exist or is too short, the "PRNG not seeded" error message may occur. [Note to OpenSSL 0.9.5 users: The command "openssl rsa" in version 0.9.5 does not do this and will fail on systems without /dev/urandom when trying to password-encrypt an RSA key! This is a bug in the library; try a later version instead.] For Solaris 2.6, Tim Nibbe and others have suggested installing the SUNski package from Sun patch 105710-01 (Sparc) which adds a /dev/random device and make sure it gets used, usually through $RANDFILE. There are probably similar patches for the other Solaris versions. However, be warned that /dev/random is usually a blocking device, which may have some effects on OpenSSL. * How do I create certificates or certificate requests? Check out the CA.pl(1) manual page. This provides a simple wrapper round the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check out the manual pages for the individual utilities and the certificate extensions documentation (currently in doc/openssl.txt). * Why can't I create certificate requests? You typically get the error: unable to find 'distinguished_name' in config problems making Certificate Request This is because it can't find the configuration file. Check out the DIAGNOSTICS section of req(1) for more information. * Why does fail with a certificate verify error? This problem is usually indicated by log messages saying something like "unable to get local issuer certificate" or "self signed certificate". When a certificate is verified its root CA must be "trusted" by OpenSSL this typically means that the CA certificate must be placed in a directory or file and the relevant program configured to read it. The OpenSSL program 'verify' behaves in a similar way and issues similar error messages: check the verify(1) program manual page for more information. * Why can I only use weak ciphers when I connect to a server using OpenSSL? This is almost certainly because you are using an old "export grade" browser which only supports weak encryption. Upgrade your browser to support 128 bit ciphers. * How can I create DSA certificates? Check the CA.pl(1) manual page for a DSA certificate example. * Why can't I make an SSL connection to a server using a DSA certificate? Typically you'll see a message saying there are no shared ciphers when the same setup works fine with an RSA certificate. There are two possible causes. The client may not support connections to DSA servers most web browsers (including Netscape and MSIE) only support connections to servers supporting RSA cipher suites. The other cause is that a set of DH parameters has not been supplied to the server. DH parameters can be created with the dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example: check the source to s_server in apps/s_server.c for an example. * How can I remove the passphrase on a private key? Firstly you should be really *really* sure you want to do this. Leaving a private key unencrypted is a major security risk. If you decide that you do have to do this check the EXAMPLES sections of the rsa(1) and dsa(1) manual pages. * Why can't I use OpenSSL certificates with SSL client authentication? What will typically happen is that when a server requests authentication it will either not include your certificate or tell you that you have no client certificates (Netscape) or present you with an empty list box (MSIE). The reason for this is that when a server requests a client certificate it includes a list of CAs names which it will accept. Browsers will only let you select certificates from the list on the grounds that there is little point presenting a certificate which the server will reject. The solution is to add the relevant CA certificate to your servers "trusted CA list". How you do this depends on the server sofware in uses. You can print out the servers list of acceptable CAs using the OpenSSL s_client tool: openssl s_client -connect www.some.host:443 -prexit If your server only requests certificates on certain URLs then you may need to manually issue an HTTP GET command to get the list when s_client connects: GET /some/page/needing/a/certificate.html If your CA does not appear in the list then this confirms the problem. * Why does my browser give a warning about a mismatched hostname? Browsers expect the server's hostname to match the value in the commonName (CN) field of the certificate. If it does not then you get a warning. [BUILD] ======================================================================= * Why does the linker complain about undefined symbols? Maybe the compilation was interrupted, and make doesn't notice that something is missing. Run "make clean; make". If you used ./Configure instead of ./config, make sure that you selected the right target. File formats may differ slightly between OS versions (for example sparcv8/sparcv9, or a.out/elf). In case you get errors about the following symbols, use the config option "no-asm", as described in INSTALL: BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt, CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt, RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words, bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4, bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3, des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3, des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order If none of these helps, you may want to try using the current snapshot. If the problem persists, please submit a bug report. * Why does the OpenSSL test fail with "bc: command not found"? You didn't install "bc", the Unix calculator. If you want to run the tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor. * Why does the OpenSSL test fail with "bc: 1 no implemented"? On some SCO installations or versions, bc has a bug that gets triggered when you run the test suite (using "make test"). The message returned is "bc: 1 not implemented". The best way to deal with this is to find another implementation of bc and compile/install it. For example, GNU bc (see http://www.gnu.org/software/software.html for download instructions) can be safely used. * Why does the OpenSSL compilation fail on Alpha True64 Unix? On some Alpha installations running True64 Unix and Compaq C, the compilation of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual memory to continue compilation.' As far as the tests have shown, this may be a compiler bug. What happens is that it eats up a lot of resident memory to build something, probably a table. The problem is clearly in the optimization code, because if one eliminates optimization completely (-O0), the compilation goes through (and the compiler consumes about 2MB of resident memory instead of 240MB or whatever one's limit is currently). There are three options to solve this problem: 1. set your current data segment size soft limit higher. Experience shows that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of kbytes to set the limit to. 2. If you have a hard limit that is lower than what you need and you can't get it changed, you can compile all of OpenSSL with -O0 as optimization level. This is however not a very nice thing to do for those who expect to get the best result from OpenSSL. A bit more complicated solution is the following: ----- snip:start ----- make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \ sed -e 's/ -O[0-9] / -O0 /'`" rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'` make ----- snip:end ----- This will only compile sha_dgst.c with -O0, the rest with the optimization level chosen by the configuration process. When the above is done, do the test and installation and you're set. * Why does the OpenSSL compilation fail with "ar: command not found"? Getting this message is quite usual on Solaris 2, because Sun has hidden away 'ar' and other development commands in directories that aren't in $PATH by default. One of those directories is '/usr/ccs/bin'. The quickest way to fix this is to do the following (it assumes you use sh or any sh-compatible shell): ----- snip:start ----- PATH=${PATH}:/usr/ccs/bin; export PATH ----- snip:end ----- and then redo the compilation. What you should really do is make sure '/usr/ccs/bin' is permanently in your $PATH, for example through your '.profile' (again, assuming you use a sh-compatible shell). * Why does the OpenSSL compilation fail on Win32 with VC++? Sometimes, you may get reports from VC++ command line (cl) that it can't find standard include files like stdio.h and other weirdnesses. One possible cause is that the environment isn't correctly set up. To solve that problem, one should run VCVARS32.BAT which is found in the 'bin' subdirectory of the VC++ installation directory (somewhere under 'Program Files'). This needs to be done prior to running NMAKE, and the changes are only valid for the current DOS session. [PROG] ======================================================================== * Is OpenSSL thread-safe? Yes (with limitations: an SSL connection may not concurrently be used by multiple threads). On Windows and many Unix systems, OpenSSL automatically uses the multi-threaded versions of the standard libraries. If your platform is not one of these, consult the INSTALL file. Multi-threaded applications must provide two callback functions to OpenSSL. This is described in the threads(3) manpage. * I've compiled a program under Windows and it crashes: why? This is usually because you've missed the comment in INSTALL.W32. You must link with the multithreaded DLL version of the VC++ runtime library otherwise the conflict will cause a program to crash: typically on the first BIO related read or write operation. * How do I read or write a DER encoded buffer using the ASN1 functions? You have two options. You can either use a memory BIO in conjunction with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the i2d_XXX(), d2i_XXX() functions directly. Since these are often the cause of grief here are some code fragments using PKCS7 as an example: unsigned char *buf, *p; int len; len = i2d_PKCS7(p7, NULL); buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */ p = buf; i2d_PKCS7(p7, &p); At this point buf contains the len bytes of the DER encoding of p7. The opposite assumes we already have len bytes in buf: unsigned char *p; p = buf; p7 = d2i_PKCS7(NULL, &p, len); At this point p7 contains a valid PKCS7 structure of NULL if an error occurred. If an error occurred ERR_print_errors(bio) should give more information. The reason for the temporary variable 'p' is that the ASN1 functions increment the passed pointer so it is ready to read or write the next structure. This is often a cause of problems: without the temporary variable the buffer pointer is changed to point just after the data that has been read or written. This may well be uninitialized data and attempts to free the buffer will have unpredictable results because it no longer points to the same address. * I've tried using and I get errors why? This usually happens when you try compiling something using the PKCS#12 macros with a C++ compiler. There is hardly ever any need to use the PKCS#12 macros in a program, it is much easier to parse and create PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions documented in doc/openssl.txt and with examples in demos/pkcs12. The 'pkcs12' application has to use the macros because it prints out debugging information. * I've called and it fails, why? Before submitting a report or asking in one of the mailing lists, you should try to determine the cause. In particular, you should call ERR_print_errors() or ERR_print_errors_fp() after the failed call and see if the message helps. Note that the problem may occur earlier than you think -- you should check for errors after every call where it is possible, otherwise the actual problem may be hidden because some OpenSSL functions clear the error state. * I just get a load of numbers for the error output, what do they mean? The actual format is described in the ERR_print_errors() manual page. You should call the function ERR_load_crypto_strings() before hand and the message will be output in text form. If you can't do this (for example it is a pre-compiled binary) you can use the errstr utility on the error code itself (the hex digits after the second colon). * Why do I get errors about unknown algorithms? This can happen under several circumstances such as reading in an encrypted private key or attempting to decrypt a PKCS#12 file. The cause is forgetting to load OpenSSL's table of algorithms with OpenSSL_add_all_algorithms(). See the manual page for more information. * Why can't the OpenSSH configure script detect OpenSSL? There is a problem with OpenSSH 1.2.2p1, in that the configure script can't find the installed OpenSSL libraries. The problem is actually a small glitch that is easily solved with the following patch to be applied to the OpenSSH distribution: ----- snip:start ----- --- openssh-1.2.2p1/configure.in.orig Thu Mar 23 18:56:58 2000 +++ openssh-1.2.2p1/configure.in Thu Mar 23 18:55:05 2000 @@ -152,10 +152,10 @@ AC_MSG_CHECKING([for OpenSSL/SSLeay directory]) for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do if test ! -z "$ssldir" ; then - LIBS="$saved_LIBS -L$ssldir" + LIBS="$saved_LIBS -L$ssldir/lib" CFLAGS="$CFLAGS -I$ssldir/include" if test "x$need_dash_r" = "x1" ; then - LIBS="$LIBS -R$ssldir" + LIBS="$LIBS -R$ssldir/lib" fi fi LIBS="$LIBS -lcrypto" --- openssh-1.2.2p1/configure.orig Thu Mar 23 18:55:02 2000 +++ openssh-1.2.2p1/configure Thu Mar 23 18:57:08 2000 @@ -1890,10 +1890,10 @@ echo "configure:1891: checking for OpenSSL/SSLeay directory" >&5 for ssldir in "" $tryssldir /usr /usr/local/openssl /usr/lib/openssl /usr/local/ssl /usr/lib/ssl /usr/local /usr/pkg /opt /opt/openssl ; do if test ! -z "$ssldir" ; then - LIBS="$saved_LIBS -L$ssldir" + LIBS="$saved_LIBS -L$ssldir/lib" CFLAGS="$CFLAGS -I$ssldir/include" if test "x$need_dash_r" = "x1" ; then - LIBS="$LIBS -R$ssldir" + LIBS="$LIBS -R$ssldir/lib" fi fi LIBS="$LIBS -lcrypto" ----- snip:end ----- * Can I use OpenSSL's SSL library with non-blocking I/O? Yes; make sure to read the SSL_get_error(3) manual page! A pitfall to avoid: Don't assume that SSL_read() will just read from the underlying transport or that SSL_write() will just write to it -- it is also possible that SSL_write() cannot do any useful work until there is data to read, or that SSL_read() cannot do anything until it is possible to send data. One reason for this is that the peer may request a new TLS/SSL handshake at any time during the protocol, requiring a bi-directional message exchange; both SSL_read() and SSL_write() will try to continue any pending handshake. ===============================================================================