=head1 NAME stunnel - universal SSL tunnel =head1 SYNOPSIS B S<[filename]> | S<-fd [n]> | S<-help> | S<-version> | S<-sockets> =head1 DESCRIPTION The B program is designed to work as I encryption wrapper between remote clients and local (I-startable) or remote servers. The concept is that having non-SSL aware daemons running on your system you can easily set them up to communicate with clients over secure SSL channels. B can be used to add SSL functionality to commonly used I daemons like POP-2, POP-3, and IMAP servers, to standalone daemons like NNTP, SMTP and HTTP, and in tunneling PPP over network sockets without changes to the source code. This product includes cryptographic software written by Eric Young (eay@cryptsoft.com) =head1 OPTIONS =over 4 =item B<[filename]> Use specified configuration file =item B<-fd [n]> (Unix only) Read the config file from specified file descriptor =item B<-help> Print B help menu =item B<-version> Print B version and compile time defaults =item B<-sockets> Print default socket options =item B<-install> (NT/2000/XP only) Install NT Service =item B<-uninstall> (NT/2000/XP only) Uninstall NT Service =back =head1 CONFIGURATION FILE Each line of the configuration file can be either: =over 4 =item * an empty line (ignored) =item * a comment starting with "#" (ignored) =item * an "option_name = option_value" pair =item * "[service_name]" indicating a start of a service definition =back =head2 GLOBAL OPTIONS =over 4 =item B = directory Certificate Authority directory This is the directory in which B will look for certificates when using the I. Note that the certificates in this directory should be named XXXXXXXX.0 where XXXXXXXX is the hash value of the cert. =item B = certfile Certificate Authority file This file contains multiple CA certificates, used with the I. =item B = pemfile certificate chain PEM file name A PEM is always needed in server mode. Specifying this flag in client mode will use this certificate chain as a client side certificate chain. Using client side certs is optional. The certificates must be in PEM format and must be sorted starting with the certificate to the highest level (root CA). =item B = directory (Unix only) directory to chroot B process B keeps B in chrooted jail. I, I and I are located inside the jail and the patches have to be relative to the directory specified with B. To have libwrap (TCP Wrappers) control effective in a chrooted environment you also have to copy its configuration files (/etc/hosts.allow and /etc/hosts.deny) there. =item B = cipherlist Select permitted SSL ciphers A colon delimited list of the ciphers to allow in the SSL connection. For example DES-CBC3-SHA:IDEA-CBC-MD5 =item B = yes | no client mode (remote service uses SSL) default: no (server mode) =item B = directory Certificate Revocation Lists directory This is the directory in which B will look for CRLs when using the I. Note that the CRLs in this directory should be named XXXXXXXX.0 where XXXXXXXX is the hash value of the CRL. =item B = certfile Certificate Revocation Lists file This file contains multiple CRLs, used with the I. =item B = [facility.]level debugging level Level is a one of the syslog level names or numbers emerg (0), alert (1), crit (2), err (3), warning (4), notice (5), info (6), or debug (7). All logs for the specified level and all levels numerically less than it will be shown. Use B or B for greatest debugging output. The default is notice (5). The syslog facility 'daemon' will be used unless a facility name is supplied. (Facilities are not supported on Win32.) Case is ignored for both facilities and levels. =item B = egd path (Unix only) path to Entropy Gathering Daemon socket Entropy Gathering Daemon socket to use to feed OpenSSL random number generator. (Available only if compiled with OpenSSL 0.9.5a or higher) =item B = yes | no (Unix only) foreground mode Stay in foreground (don't fork) and log to stderr instead of via syslog (unless B is specified). default: background in daemon mode =item B = keyfile private key for certificate specified with I option Private key is needed to authenticate certificate owner. Since this file should be kept secret it should only be readable to its owner. On Unix systems you can use the following command: chmod 600 keyfile default: value of I option =item B = SSL_options OpenSSL library options The parameter is the OpenSSL option name as described in the I manual, but without I prefix. Several I can be used to specify multiple options. For example for compatibility with erroneous Eudora SSL implementation the following option can be used: options = DONT_INSERT_EMPTY_FRAGMENTS =item B = file append log messages to a file instead of using syslog /dev/stdout device can be used to redirect log messages to the standard output (for example to log them with daemontools splogger). =item B = file (Unix only) pid file location If the argument is empty, then no pid file will be created. =item B = bytes bytes to read from random seed files Number of bytes of data read from random seed files. With SSL versions less than 0.9.5a, also determines how many bytes of data are considered sufficient to seed the PRNG. More recent OpenSSL versions have a builtin function to determine when sufficient randomness is available. =item B = file path to file with random seed data The SSL library will use data from this file first to seed the random number generator. =item B = yes | no overwrite the random seed files with new random data default: yes =item B = servicename use specified string as the service name On Unix: I mode service name for TCP Wrapper library. On NT/2000/XP: NT service name in the Control Panel. default: stunnel =item B = timeout session cache timeout =item B = groupname (Unix only) setgid() to groupname in daemon mode and clears all other groups =item B = username (Unix only) setuid() to username in daemon mode =item B = a|l|r:option=value[:value] Set an option on accept/local/remote socket The values for linger option are l_onof:l_linger. The values for time are tv_sec:tv_usec. Examples: socket = l:SO_LINGER=1:60 set one minute timeout for closing local socket socket = r:TCP_NODELAY=1 turn off the Nagle algorithm for remote sockets socket = r:SO_OOBINLINE=1 place out-of-band data directly into the receive data stream for remote sockets socket = a:SO_REUSEADDR=0 disable address reuse (enabled by default) socket = a:SO_BINDTODEVICE=lo only accept connections on loopback interface =item B = yes | no (WIN32 only) enable the taskbar icon default: yes =item B = level verify peer certificate level 1 - verify peer certificate if present level 2 - verify peer certificate level 3 - verify peer with locally installed certificate default - no verify =back =head2 SERVICE-LEVEL OPTIONS Each configuration section begins with service name in square brackets. The service name is used for libwrap (TCP Wrappers) access control and lets you distinguish B services in your log files. Note that if you wish to run B in I mode (where it is provided a network socket by a server such as I, I, or I) then you should read the section entitiled I below. =over 4 =item B = [host:]port accept connections on specified host:port If no host specified, defaults to all IP addresses for the local host. =item B = [host:]port connect to remote host:port If no host specified, defaults to localhost. =item B = yes | no delay DNS lookup for 'connect' option =item B = executable_path (Unix only) execute local inetd-type program =item B = $0 $1 $2 ... (Unix only) arguments for I including program name ($0) Quoting is currently not supported. Arguments are speparated with arbitrary number of whitespaces. =item B = username use IDENT (RFC 1413) username checking =item B = host IP of the outgoing interface is used as source for remote connections. Use this option to bind a static local IP address, instead. =item B = proto Negotiate SSL with specified protocol currently supported: cifs, nntp, pop3, smtp =item B = yes | no (Unix only) allocate pseudo terminal for 'exec' option =item B = seconds time to wait for expected data =item B = seconds time to wait for close_notify (set to 0 for buggy MSIE) =item B = seconds time to keep an idle connection =item B = yes | no (Unix only) transparent proxy mode Re-write address to appear as if wrapped daemon is connecting from the SSL client machine instead of the machine running B. This option is only available in local mode (I option) by LD_PRELOADing env.so shared library or in remote mode (I option) on Linux 2.2 kernel compiled with I option and then only in server mode. Note that this option will not combine with proxy mode (I) unless the client's default route to the target machine lies through the host running B, which cannot be localhost. =back =head1 RETURN VALUE B returns zero on success, non-zero on error. =head1 EXAMPLES In order to provide SSL encapsulation to your local I service, use [imapd] accept = 993 exec = /usr/sbin/imapd execargs = imapd If you want to provide tunneling to your I daemon on port 2020, use something like [vpn] accept = 2020 exec = /usr/sbin/pppd execargs = pppd local pty = yes If you want to use B in I mode to launch your imapd process, you'd use this I. Note there must be no I<[service_name]> section. exec = /usr/sbin/imapd execargs = imapd =head1 FILES =over 4 =item F B configuration file =item F B certificate and private key =back =head1 BUGS Option I does not support quoting. =head1 RESTRICTIONS B cannot be used for the FTP daemon because of the nature of the FTP protocol which utilizes multiple ports for data transfers. There are available SSL enabled versions of FTP and telnet daemons, however. =head1 NOTES =head2 INETD MODE The most common use of B is to listen on a network port and establish communication with either a new port via the connect option, or a new program via the I option. However there is a special case when you wish to have some other program accept incoming connections and launch B, for example with I, I, or I. For example, if you have the following line in I: imaps stream tcp nowait root /usr/sbin/stunnel stunnel /etc/stunnel/imaps.conf In these cases, the I-style program is responsible for binding a network socket (I above) and handing it to B when a connection is received. Thus you do not want B to have any I option. All the I should be placed in the global options section, and no I<[service_name]> section will be present. See the I section for example configurations. =head2 CERTIFICATES Each SSL enabled daemon needs to present a valid X.509 certificate to the peer. It also needs a private key to decrypt the incoming data. The easiest way to obtain a certificate and a key is to generate them with the free I package. You can find more information on certificates generation on pages listed below. Two things are important when generating certificate-key pairs for B. The private key cannot be encrypted, because the server has no way to obtain the password from the user. To produce an unencrypted key add the I<-nodes> option when running the B command from the I kit. The order of contents of the I<.pem> file is also important. It should contain the unencrypted private key first, then a signed certificate (not certificate request). There should be also empty lines after certificate and private key. Plaintext certificate information appended on the top of generated certificate should be discarded. So the file should look like this: -----BEGIN RSA PRIVATE KEY----- [encoded key] -----END RSA PRIVATE KEY----- [empty line] -----BEGIN CERTIFICATE----- [encoded certificate] -----END CERTIFICATE----- [empty line] =head2 RANDOMNESS B needs to seed the PRNG (pseudo random number generator) in order for SSL to use good randomness. The following sources are loaded in order until sufficient random data has been gathered: =over 4 =item * The file specified with the I flag. =item * The file specified by the RANDFILE environment variable, if set. =item * The file .rnd in your home directory, if RANDFILE not set. =item * The file specified with '--with-random' at compile time. =item * The contents of the screen if running on Windows. =item * The egd socket specified with the I flag. =item * The egd socket specified with '--with-egd-sock' at compile time. =item * The /dev/urandom device. =back With recent (>=OpenSSL 0.9.5a) version of SSL it will stop loading random data automatically when sufficient entropy has been gathered. With previous versions it will continue to gather from all the above sources since no SSL function exists to tell when enough data is available. Note that on Windows machines that do not have console user interaction (mouse movements, creating windows, etc) the screen contents are not variable enough to be sufficient, and you should provide a random file for use with the I flag. Note that the file specified with the I flag should contain random data -- that means it should contain different information each time B is run. This is handled automatically unless the I flag is used. If you wish to update this file manually, the I command in recent versions of OpenSSL, would be useful. One important note -- if /dev/urandom is available, OpenSSL has a habit of seeding the PRNG with it even when checking the random state, so on systems with /dev/urandom you're likely to use it even though it's listed at the very bottom of the list above. This isn't B behaviour, it's OpenSSLs. =head1 SEE ALSO =over 4 =item L access control facility for internet services =item L internet ``super-server'' =item F B homepage =item F B Frequently Asked Questions =item F OpenSSL project website =back =head1 AUTHOR =over 4 =item Michal Trojnara > =back