mirror of https://github.com/openssl/openssl.git
621 lines
26 KiB
Plaintext
621 lines
26 KiB
Plaintext
OpenSSL - Frequently Asked Questions
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--------------------------------------
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[MISC] Miscellaneous questions
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* Which is the current version of OpenSSL?
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* Where is the documentation?
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* How can I contact the OpenSSL developers?
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* Where can I get a compiled version of OpenSSL?
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* Why aren't tools like 'autoconf' and 'libtool' used?
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* What is an 'engine' version?
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[LEGAL] Legal questions
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* Do I need patent licenses to use OpenSSL?
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* Can I use OpenSSL with GPL software?
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[USER] Questions on using the OpenSSL applications
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* Why do I get a "PRNG not seeded" error message?
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* Why do I get an "unable to write 'random state'" error message?
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* How do I create certificates or certificate requests?
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* Why can't I create certificate requests?
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* Why does <SSL program> fail with a certificate verify error?
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* Why can I only use weak ciphers when I connect to a server using OpenSSL?
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* How can I create DSA certificates?
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* Why can't I make an SSL connection using a DSA certificate?
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* How can I remove the passphrase on a private key?
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* Why can't I use OpenSSL certificates with SSL client authentication?
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* Why does my browser give a warning about a mismatched hostname?
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* How do I install a CA certificate into a browser?
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[BUILD] Questions about building and testing OpenSSL
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* Why does the linker complain about undefined symbols?
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* Why does the OpenSSL test fail with "bc: command not found"?
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* Why does the OpenSSL test fail with "bc: 1 no implemented"?
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* Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
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* Why does the OpenSSL compilation fail with "ar: command not found"?
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* Why does the OpenSSL compilation fail on Win32 with VC++?
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[PROG] Questions about programming with OpenSSL
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* Is OpenSSL thread-safe?
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* I've compiled a program under Windows and it crashes: why?
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* How do I read or write a DER encoded buffer using the ASN1 functions?
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* I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
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* I've called <some function> and it fails, why?
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* I just get a load of numbers for the error output, what do they mean?
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* Why do I get errors about unknown algorithms?
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* Why can't the OpenSSH configure script detect OpenSSL?
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* Can I use OpenSSL's SSL library with non-blocking I/O?
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* Why doesn't my server application receive a client certificate?
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===============================================================================
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[MISC] ========================================================================
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* Which is the current version of OpenSSL?
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The current version is available from <URL: http://www.openssl.org>.
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OpenSSL 0.9.6c was released on December 21st, 2001.
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In addition to the current stable release, you can also access daily
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snapshots of the OpenSSL development version at <URL:
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ftp://ftp.openssl.org/snapshot/>, or get it by anonymous CVS access.
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* Where is the documentation?
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OpenSSL is a library that provides cryptographic functionality to
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applications such as secure web servers. Be sure to read the
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documentation of the application you want to use. The INSTALL file
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explains how to install this library.
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OpenSSL includes a command line utility that can be used to perform a
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variety of cryptographic functions. It is described in the openssl(1)
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manpage. Documentation for developers is currently being written. A
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few manual pages already are available; overviews over libcrypto and
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libssl are given in the crypto(3) and ssl(3) manpages.
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The OpenSSL manpages are installed in /usr/local/ssl/man/ (or a
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different directory if you specified one as described in INSTALL).
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In addition, you can read the most current versions at
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<URL: http://www.openssl.org/docs/>.
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For information on parts of libcrypto that are not yet documented, you
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might want to read Ariel Glenn's documentation on SSLeay 0.9, OpenSSL's
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predecessor, at <URL: http://www.columbia.edu/~ariel/ssleay/>. Much
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of this still applies to OpenSSL.
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There is some documentation about certificate extensions and PKCS#12
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in doc/openssl.txt
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The original SSLeay documentation is included in OpenSSL as
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doc/ssleay.txt. It may be useful when none of the other resources
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help, but please note that it reflects the obsolete version SSLeay
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0.6.6.
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* How can I contact the OpenSSL developers?
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The README file describes how to submit bug reports and patches to
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OpenSSL. Information on the OpenSSL mailing lists is available from
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<URL: http://www.openssl.org>.
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* Where can I get a compiled version of OpenSSL?
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Some applications that use OpenSSL are distributed in binary form.
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When using such an application, you don't need to install OpenSSL
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yourself; the application will include the required parts (e.g. DLLs).
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If you want to install OpenSSL on a Windows system and you don't have
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a C compiler, read the "Mingw32" section of INSTALL.W32 for information
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on how to obtain and install the free GNU C compiler.
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A number of Linux and *BSD distributions include OpenSSL.
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* Why aren't tools like 'autoconf' and 'libtool' used?
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autoconf will probably be used in future OpenSSL versions. If it was
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less Unix-centric, it might have been used much earlier.
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* What is an 'engine' version?
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With version 0.9.6 OpenSSL was extended to interface to external crypto
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hardware. This was realized in a special release '0.9.6-engine'. With
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version 0.9.7 (not yet released) the changes were merged into the main
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development line, so that the special release is no longer necessary.
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[LEGAL] =======================================================================
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* Do I need patent licenses to use OpenSSL?
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The patents section of the README file lists patents that may apply to
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you if you want to use OpenSSL. For information on intellectual
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property rights, please consult a lawyer. The OpenSSL team does not
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offer legal advice.
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You can configure OpenSSL so as not to use RC5 and IDEA by using
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./config no-rc5 no-idea
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* Can I use OpenSSL with GPL software?
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On many systems including the major Linux and BSD distributions, yes (the
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GPL does not place restrictions on using libraries that are part of the
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normal operating system distribution).
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On other systems, the situation is less clear. Some GPL software copyright
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holders claim that you infringe on their rights if you use OpenSSL with
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their software on operating systems that don't normally include OpenSSL.
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If you develop open source software that uses OpenSSL, you may find it
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useful to choose an other license than the GPL, or state explicitly that
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"This program is released under the GPL with the additional exemption that
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compiling, linking, and/or using OpenSSL is allowed." If you are using
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GPL software developed by others, you may want to ask the copyright holder
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for permission to use their software with OpenSSL.
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[USER] ========================================================================
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* Why do I get a "PRNG not seeded" error message?
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Cryptographic software needs a source of unpredictable data to work
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correctly. Many open source operating systems provide a "randomness
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device" that serves this purpose. On other systems, applications have
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to call the RAND_add() or RAND_seed() function with appropriate data
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before generating keys or performing public key encryption.
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(These functions initialize the pseudo-random number generator, PRNG.)
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Some broken applications do not do this. As of version 0.9.5, the
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OpenSSL functions that need randomness report an error if the random
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number generator has not been seeded with at least 128 bits of
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randomness. If this error occurs, please contact the author of the
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application you are using. It is likely that it never worked
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correctly. OpenSSL 0.9.5 and later make the error visible by refusing
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to perform potentially insecure encryption.
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On systems without /dev/urandom and /dev/random, it is a good idea to
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use the Entropy Gathering Demon (EGD); see the RAND_egd() manpage for
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details. Starting with version 0.9.7, OpenSSL will automatically look
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for an EGD socket at /var/run/egd-pool, /dev/egd-pool, /etc/egd-pool and
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/etc/entropy.
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Most components of the openssl command line utility automatically try
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to seed the random number generator from a file. The name of the
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default seeding file is determined as follows: If environment variable
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RANDFILE is set, then it names the seeding file. Otherwise if
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environment variable HOME is set, then the seeding file is $HOME/.rnd.
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If neither RANDFILE nor HOME is set, versions up to OpenSSL 0.9.6 will
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use file .rnd in the current directory while OpenSSL 0.9.6a uses no
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default seeding file at all. OpenSSL 0.9.6b and later will behave
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similarly to 0.9.6a, but will use a default of "C:\" for HOME on
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Windows systems if the environment variable has not been set.
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If the default seeding file does not exist or is too short, the "PRNG
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not seeded" error message may occur.
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The openssl command line utility will write back a new state to the
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default seeding file (and create this file if necessary) unless
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there was no sufficient seeding.
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Pointing $RANDFILE to an Entropy Gathering Daemon socket does not work.
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Use the "-rand" option of the OpenSSL command line tools instead.
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The $RANDFILE environment variable and $HOME/.rnd are only used by the
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OpenSSL command line tools. Applications using the OpenSSL library
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provide their own configuration options to specify the entropy source,
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please check out the documentation coming the with application.
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For Solaris 2.6, Tim Nibbe <tnibbe@sprint.net> and others have suggested
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installing the SUNski package from Sun patch 105710-01 (Sparc) which
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adds a /dev/random device and make sure it gets used, usually through
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$RANDFILE. There are probably similar patches for the other Solaris
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versions. However, be warned that /dev/random is usually a blocking
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device, which may have some effects on OpenSSL.
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* Why do I get an "unable to write 'random state'" error message?
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Sometimes the openssl command line utility does not abort with
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a "PRNG not seeded" error message, but complains that it is
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"unable to write 'random state'". This message refers to the
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default seeding file (see previous answer). A possible reason
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is that no default filename is known because neither RANDFILE
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nor HOME is set. (Versions up to 0.9.6 used file ".rnd" in the
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current directory in this case, but this has changed with 0.9.6a.)
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* How do I create certificates or certificate requests?
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Check out the CA.pl(1) manual page. This provides a simple wrapper round
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the 'req', 'verify', 'ca' and 'pkcs12' utilities. For finer control check
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out the manual pages for the individual utilities and the certificate
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extensions documentation (currently in doc/openssl.txt).
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* Why can't I create certificate requests?
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You typically get the error:
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unable to find 'distinguished_name' in config
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problems making Certificate Request
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This is because it can't find the configuration file. Check out the
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DIAGNOSTICS section of req(1) for more information.
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* Why does <SSL program> fail with a certificate verify error?
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This problem is usually indicated by log messages saying something like
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"unable to get local issuer certificate" or "self signed certificate".
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When a certificate is verified its root CA must be "trusted" by OpenSSL
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this typically means that the CA certificate must be placed in a directory
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or file and the relevant program configured to read it. The OpenSSL program
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'verify' behaves in a similar way and issues similar error messages: check
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the verify(1) program manual page for more information.
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* Why can I only use weak ciphers when I connect to a server using OpenSSL?
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This is almost certainly because you are using an old "export grade" browser
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which only supports weak encryption. Upgrade your browser to support 128 bit
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ciphers.
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* How can I create DSA certificates?
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Check the CA.pl(1) manual page for a DSA certificate example.
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* Why can't I make an SSL connection to a server using a DSA certificate?
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Typically you'll see a message saying there are no shared ciphers when
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the same setup works fine with an RSA certificate. There are two possible
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causes. The client may not support connections to DSA servers most web
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browsers (including Netscape and MSIE) only support connections to servers
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supporting RSA cipher suites. The other cause is that a set of DH parameters
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has not been supplied to the server. DH parameters can be created with the
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dhparam(1) command and loaded using the SSL_CTX_set_tmp_dh() for example:
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check the source to s_server in apps/s_server.c for an example.
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* How can I remove the passphrase on a private key?
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Firstly you should be really *really* sure you want to do this. Leaving
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a private key unencrypted is a major security risk. If you decide that
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you do have to do this check the EXAMPLES sections of the rsa(1) and
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dsa(1) manual pages.
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* Why can't I use OpenSSL certificates with SSL client authentication?
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What will typically happen is that when a server requests authentication
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it will either not include your certificate or tell you that you have
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no client certificates (Netscape) or present you with an empty list box
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(MSIE). The reason for this is that when a server requests a client
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certificate it includes a list of CAs names which it will accept. Browsers
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will only let you select certificates from the list on the grounds that
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there is little point presenting a certificate which the server will
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reject.
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The solution is to add the relevant CA certificate to your servers "trusted
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CA list". How you do this depends on the server software in uses. You can
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print out the servers list of acceptable CAs using the OpenSSL s_client tool:
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openssl s_client -connect www.some.host:443 -prexit
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If your server only requests certificates on certain URLs then you may need
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to manually issue an HTTP GET command to get the list when s_client connects:
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GET /some/page/needing/a/certificate.html
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If your CA does not appear in the list then this confirms the problem.
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* Why does my browser give a warning about a mismatched hostname?
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Browsers expect the server's hostname to match the value in the commonName
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(CN) field of the certificate. If it does not then you get a warning.
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* How do I install a CA certificate into a browser?
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The usual way is to send the DER encoded certificate to the browser as
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MIME type application/x-x509-ca-cert, for example by clicking on an appropriate
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link. On MSIE certain extensions such as .der or .cacert may also work, or you
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can import the certificate using the certificate import wizard.
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You can convert a certificate to DER form using the command:
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openssl x509 -in ca.pem -outform DER -out ca.der
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Occasionally someone suggests using a command such as:
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openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cakey.pem
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DO NOT DO THIS! This command will give away your CAs private key and
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reduces its security to zero: allowing anyone to forge certificates in
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whatever name they choose.
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[BUILD] =======================================================================
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* Why does the linker complain about undefined symbols?
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Maybe the compilation was interrupted, and make doesn't notice that
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something is missing. Run "make clean; make".
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If you used ./Configure instead of ./config, make sure that you
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selected the right target. File formats may differ slightly between
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OS versions (for example sparcv8/sparcv9, or a.out/elf).
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In case you get errors about the following symbols, use the config
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option "no-asm", as described in INSTALL:
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BF_cbc_encrypt, BF_decrypt, BF_encrypt, CAST_cbc_encrypt,
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CAST_decrypt, CAST_encrypt, RC4, RC5_32_cbc_encrypt, RC5_32_decrypt,
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RC5_32_encrypt, bn_add_words, bn_div_words, bn_mul_add_words,
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bn_mul_comba4, bn_mul_comba8, bn_mul_words, bn_sqr_comba4,
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bn_sqr_comba8, bn_sqr_words, bn_sub_words, des_decrypt3,
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des_ede3_cbc_encrypt, des_encrypt, des_encrypt2, des_encrypt3,
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des_ncbc_encrypt, md5_block_asm_host_order, sha1_block_asm_data_order
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If none of these helps, you may want to try using the current snapshot.
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If the problem persists, please submit a bug report.
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* Why does the OpenSSL test fail with "bc: command not found"?
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You didn't install "bc", the Unix calculator. If you want to run the
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tests, get GNU bc from ftp://ftp.gnu.org or from your OS distributor.
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* Why does the OpenSSL test fail with "bc: 1 no implemented"?
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On some SCO installations or versions, bc has a bug that gets triggered
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when you run the test suite (using "make test"). The message returned is
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"bc: 1 not implemented".
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The best way to deal with this is to find another implementation of bc
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and compile/install it. GNU bc (see http://www.gnu.org/software/software.html
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for download instructions) can be safely used, for example.
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* Why does the OpenSSL compilation fail on Alpha Tru64 Unix?
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On some Alpha installations running Tru64 Unix and Compaq C, the compilation
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of crypto/sha/sha_dgst.c fails with the message 'Fatal: Insufficient virtual
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memory to continue compilation.' As far as the tests have shown, this may be
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a compiler bug. What happens is that it eats up a lot of resident memory
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to build something, probably a table. The problem is clearly in the
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optimization code, because if one eliminates optimization completely (-O0),
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the compilation goes through (and the compiler consumes about 2MB of resident
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memory instead of 240MB or whatever one's limit is currently).
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There are three options to solve this problem:
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1. set your current data segment size soft limit higher. Experience shows
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that about 241000 kbytes seems to be enough on an AlphaServer DS10. You do
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this with the command 'ulimit -Sd nnnnnn', where 'nnnnnn' is the number of
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kbytes to set the limit to.
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2. If you have a hard limit that is lower than what you need and you can't
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get it changed, you can compile all of OpenSSL with -O0 as optimization
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level. This is however not a very nice thing to do for those who expect to
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get the best result from OpenSSL. A bit more complicated solution is the
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following:
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----- snip:start -----
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make DIRS=crypto SDIRS=sha "`grep '^CFLAG=' Makefile.ssl | \
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sed -e 's/ -O[0-9] / -O0 /'`"
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rm `ls crypto/*.o crypto/sha/*.o | grep -v 'sha_dgst\.o'`
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make
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----- snip:end -----
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This will only compile sha_dgst.c with -O0, the rest with the optimization
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level chosen by the configuration process. When the above is done, do the
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test and installation and you're set.
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* Why does the OpenSSL compilation fail with "ar: command not found"?
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Getting this message is quite usual on Solaris 2, because Sun has hidden
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away 'ar' and other development commands in directories that aren't in
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$PATH by default. One of those directories is '/usr/ccs/bin'. The
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quickest way to fix this is to do the following (it assumes you use sh
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or any sh-compatible shell):
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----- snip:start -----
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PATH=${PATH}:/usr/ccs/bin; export PATH
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----- snip:end -----
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and then redo the compilation. What you should really do is make sure
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'/usr/ccs/bin' is permanently in your $PATH, for example through your
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'.profile' (again, assuming you use a sh-compatible shell).
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* Why does the OpenSSL compilation fail on Win32 with VC++?
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Sometimes, you may get reports from VC++ command line (cl) that it
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can't find standard include files like stdio.h and other weirdnesses.
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One possible cause is that the environment isn't correctly set up.
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To solve that problem, one should run VCVARS32.BAT which is found in
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the 'bin' subdirectory of the VC++ installation directory (somewhere
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under 'Program Files'). This needs to be done prior to running NMAKE,
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and the changes are only valid for the current DOS session.
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[PROG] ========================================================================
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* Is OpenSSL thread-safe?
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Yes (with limitations: an SSL connection may not concurrently be used
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by multiple threads). On Windows and many Unix systems, OpenSSL
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automatically uses the multi-threaded versions of the standard
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libraries. If your platform is not one of these, consult the INSTALL
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file.
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Multi-threaded applications must provide two callback functions to
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OpenSSL. This is described in the threads(3) manpage.
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* I've compiled a program under Windows and it crashes: why?
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This is usually because you've missed the comment in INSTALL.W32.
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Your application must link against the same version of the Win32
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C-Runtime against which your openssl libraries were linked. The
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default version for OpenSSL is /MD - "Multithreaded DLL".
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If you are using Microsoft Visual C++'s IDE (Visual Studio), in
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many cases, your new project most likely defaulted to "Debug
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Singlethreaded" - /ML. This is NOT interchangeable with /MD and your
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program will crash, typically on the first BIO related read or write
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operation.
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For each of the six possible link stage configurations within Win32,
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your application must link against the same by which OpenSSL was
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built. If you are using MS Visual C++ (Studio) this can be changed
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by:
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1. Select Settings... from the Project Menu.
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2. Select the C/C++ Tab.
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3. Select "Code Generation from the "Category" drop down list box
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4. Select the Appropriate library (see table below) from the "Use
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run-time library" drop down list box. Perform this step for both
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your debug and release versions of your application (look at the
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top left of the settings panel to change between the two)
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Single Threaded /ML - MS VC++ often defaults to
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this for the release
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version of a new project.
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Debug Single Threaded /MLd - MS VC++ often defaults to
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this for the debug version
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of a new project.
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Multithreaded /MT
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Debug Multithreaded /MTd
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Multithreaded DLL /MD - OpenSSL defaults to this.
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Debug Multithreaded DLL /MDd
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Note that debug and release libraries are NOT interchangeable. If you
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built OpenSSL with /MD your application must use /MD and cannot use /MDd.
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* How do I read or write a DER encoded buffer using the ASN1 functions?
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You have two options. You can either use a memory BIO in conjunction
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with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
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i2d_XXX(), d2i_XXX() functions directly. Since these are often the
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cause of grief here are some code fragments using PKCS7 as an example:
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unsigned char *buf, *p;
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int len;
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len = i2d_PKCS7(p7, NULL);
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buf = OPENSSL_malloc(len); /* or Malloc, error checking omitted */
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p = buf;
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i2d_PKCS7(p7, &p);
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At this point buf contains the len bytes of the DER encoding of
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p7.
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The opposite assumes we already have len bytes in buf:
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unsigned char *p;
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p = buf;
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p7 = d2i_PKCS7(NULL, &p, len);
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At this point p7 contains a valid PKCS7 structure of NULL if an error
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occurred. If an error occurred ERR_print_errors(bio) should give more
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information.
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The reason for the temporary variable 'p' is that the ASN1 functions
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increment the passed pointer so it is ready to read or write the next
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structure. This is often a cause of problems: without the temporary
|
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variable the buffer pointer is changed to point just after the data
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that has been read or written. This may well be uninitialized data
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and attempts to free the buffer will have unpredictable results
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because it no longer points to the same address.
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* I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
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This usually happens when you try compiling something using the PKCS#12
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macros with a C++ compiler. There is hardly ever any need to use the
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PKCS#12 macros in a program, it is much easier to parse and create
|
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PKCS#12 files using the PKCS12_parse() and PKCS12_create() functions
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documented in doc/openssl.txt and with examples in demos/pkcs12. The
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'pkcs12' application has to use the macros because it prints out
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debugging information.
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* I've called <some function> and it fails, why?
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Before submitting a report or asking in one of the mailing lists, you
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|
should try to determine the cause. In particular, you should call
|
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ERR_print_errors() or ERR_print_errors_fp() after the failed call
|
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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
|
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it is possible, otherwise the actual problem may be hidden because
|
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some OpenSSL functions clear the error state.
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* I just get a load of numbers for the error output, what do they mean?
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The actual format is described in the ERR_print_errors() manual page.
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You should call the function ERR_load_crypto_strings() before hand and
|
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the message will be output in text form. If you can't do this (for example
|
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it is a pre-compiled binary) you can use the errstr utility on the error
|
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code itself (the hex digits after the second colon).
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* Why do I get errors about unknown algorithms?
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|
|
|
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.
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* Why can't the OpenSSH configure script detect OpenSSL?
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|
|
Several reasons for problems with the automatic detection exist.
|
|
OpenSSH requires at least version 0.9.5a of the OpenSSL libraries.
|
|
Sometimes the distribution has installed an older version in the system
|
|
locations that is detected instead of a new one installed. The OpenSSL
|
|
library might have been compiled for another CPU or another mode (32/64 bits).
|
|
Permissions might be wrong.
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|
|
The general answer is to check the config.log file generated when running
|
|
the OpenSSH configure script. It should contain the detailed information
|
|
on why the OpenSSL library was not detected or considered incompatible.
|
|
|
|
* 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.
|
|
|
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|
|
* Why doesn't my server application receive a client certificate?
|
|
|
|
Due to the TLS protocol definition, a client will only send a certificate,
|
|
if explicitly asked by the server. Use the SSL_VERIFY_PEER flag of the
|
|
SSL_CTX_set_verify() function to enable the use of client certificates.
|
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|
===============================================================================
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