stunnel3


SYNOPSIS
       stunnel [-c | -T] [-D [facility.]level] [-O a|l|r:option=value[:value]]
       [-o file] [-C cipherlist] [-p pemfile] [-v level] [-A certfile]
       [-S sources] [-a directory] [-t timeout] [-u ident_username]
       [-s setuid_user] [-g setgid_group] [-n protocol] [-P { file-
       name | '' } ] [-B bytes] [-R randfile] [-W] [-E socket] [-I host]
       [-d [host:]port [-f] ] [ -r [host:]port | { -l | -L } program [-- prog-
       name args] ]

DESCRIPTION
       The stunnel program is designed to work as SSL encryption wrapper
       between remote clients and local (inetd-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.

       stunnel can be used to add SSL functionality to commonly used inetd
       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)

OPTIONS
       -h  Print stunnel help menu

       -D 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 numeri-
           cally less than it will be shown.  Use -D debug or -D 7 for great-
           est 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 windows.)

           Case is ignored for both facilities and levels.

       -O 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:

           -O l:SO_LINGER=1:60 - set one minute timeout for closing local
           socket

           -O r:TCP_NODELAY=1 - turn off the Nagle algorithm for remote sock-
               SO_DEBUG            --        --        --             0
               SO_DONTROUTE        --        --        --             0
               SO_KEEPALIVE        --        --        --             0
               SO_LINGER           --        --        --    0:0
               SO_OOBINLINE        --        --        --             0
               SO_RCVBUF           --        --        --         87380
               SO_SNDBUF           --        --        --         16384
               SO_RCVLOWAT         --        --        --             1
               SO_SNDLOWAT         --        --        --             1
               SO_RCVTIMEO         --        --        --         0:0
               SO_SNDTIMEO         --        --        --         0:0
               SO_REUSEADDR             1    --        --             0
               SO_BINDTODEVICE     --        --        --        --
               IP_TOS              --        --        --             0
               IP_TTL              --        --        --            64
               TCP_NODELAY         --        --        --             0

       -o file
           Append log messages to a file.

       -C cipherlist
           Select permitted SSL ciphers

           A colon delimited list of the ciphers to allow in the SSL connec-
           tion.  For example DES-CBC3-SHA:IDEA-CBC-MD5

       -c  client mode (remote service uses SSL)

           default: server mode

       -T  transparent proxy mode

           Re-write address to appear as if wrapped daemon is connecting from
           the SSL client machine instead of the machine running stunnel.
           Available only on some operating systems (Linux only, we believe)
           and then only in server mode. Note that this option will not com-
           bine with proxy mode (-r) unless the client's default route to the
           target machine lies through the host running stunnel, which cannot
           be localhost.

       -p pemfile
           private key and certificate chain PEM file name

           A PEM is always needed in server mode (by default located in
           /etc/stunnel/stunnel.pem). Specifying this flag in client mode will
           use this key and 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).

       -v level
           verify peer certificate

           o       level 1 - verify peer certificate if present
           directory should be named XXXXXXXX.0 where XXXXXXXX is the hash
           value of the cert.

       -A certfile
           Certificate Authority file

           This file contains multiple CA certificates, used with the -v
           options.

       -t timeout
           session cache timeout

           default: 300 seconds.

       -N servicename
           Service name to use for tcpwrappers. If not specified then a tcp-
           wrapper service name will be generated automatically for you. This
           will also be used when auto-generating pid filenames.

       -u ident_username
           Use IDENT (RFC 1413) username checking

       -n proto
           Negotiate SSL with specified protocol

           currently supported: smtp, pop3, nntp

       -E socket
           Entropy Gathering Daemon socket to use to feed OpenSSL random num-
           ber generator.  (Available only if compiled with OpenSSL 0.9.5a or
           higher)

       -R filename
           File containing random input.  The SSL library will use data from
           this file first to seed the random number generator.

       -W  Do not overwrite the random seed files with new random data.

       -B bytes
           Number of bytes of data read from random seed files.  With SSL ver-
           sions less than 0.9.5a, also determines how many bytes of data are
           considered sufficient to seed the PRNG.  More recent OpenSSL ver-
           sions have a builtin function to determine when sufficient random-
           ness is available.

       -I host
           IP of the outgoing interface is used as source for remote connec-
           tions.  Use this option to bind a static local IP address, instead.

       -d [host:]port
           daemon mode

           Listen for connections on [host:]port. If no host specified,
           defaults to all IP addresses for the local host.

       -L program [-- programname [arg1 arg2 arg3...]  ]
           open local pty and execute program.

       -s username
           setuid() to username in daemon mode

       -g groupname
           setgid() to groupname in daemon mode. Clears all other groups.

       -P { file | '' }
           Pid file location

           If the argument is a filename, then that filename will be used for
           the pid. If the argument is empty ('', not missing), then no pid
           file will be created.

       -r [host:]port
           connect to remote service

           If no host specified, defaults to localhost.

EXAMPLES
       In order to provide SSL encapsulation to your local imapd service, use

         stunnel -d 993 -l /usr/sbin/imapd -- imapd

       If you want to provide tunneling to your pppd daemon on port 2020, use
       something like

         stunnel -d 2020 -L /usr/sbin/pppd -- pppd local

ENVIRONMENT
       If Stunnel is used to create local processes using the -l or -L
       options, it will set the following environment variables

       REMOTE_HOST
           The IP address of the remote end of the connection.

       SSL_CLIENT_DN
           The DN (Distinguished Name, aka subject name) of the peer certifi-
           cate, if a certificate was present and verified.

       SSL_CLIENT_I_DN
           The Issuer's DN of the peer's certificate, if a certificate was
           present and verified.

CERTIFICATES
       o   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 gen-
           erate them with the free openssl package. You can find more infor-
           mation on certificates generation on pages listed below.


             -----BEGIN RSA PRIVATE KEY-----
             [encoded key]
             -----END RSA PRIVATE KEY-----
             [empty line]
             -----BEGIN CERTIFICATE-----
             [encoded certificate]
             -----END CERTIFICATE-----
             [empty line]

RANDOMNESS
       o   stunnel 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:

           o       The file specified with the -R flag.

           o       The file specified by the RANDFILE environment variable, if
                   set.

           o       The file .rnd in your home directory, if RANDFILE not set.

           o       The file specified with '--with-random' at compile time.

           o       The contents of the screen if running on Windows.

           o       The egd socket specified with the -E flag.

           o       The egd socket specified with '--with-egd-sock' at compile
                   time.

           o       The /dev/urandom device.

           With recent (>=OpenSSL 0.9.5a) version of SSL it will stop loading
           random data automatically when sufficient entropy has been gath-
           ered.  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 inter-
           action (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 -R flag.

           Note that the file specified with the -R flag should contain random
           data -- that means it should contain different information each
           time stunnel is run.  This is handled automatically unless the -W
           flag is used.  If you wish to update this file manually, the
           openssl rand command in recent versions of OpenSSL, would be use-
           ful.

           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
           inetd(8)
                   internet ``super-server''

           http://stunnel.mirt.net/
                   Stunnel homepage

           http://www.stunnel.org/
                   Stunnel Frequently Asked Questions

           http://www.openssl.org/
                   OpenSSL project website

AUTHOR
           Michal Trojnara
                   <Michal.Trojnara@mirt.net>



                                  2003-08-01                        STUNNEL(8)
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