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RedHat 9 (Linux i386) - man page for stunnel (redhat section 8)

STUNNEL(8)				     stunnel				       STUNNEL(8)

NAME
       stunnel - universal SSL tunnel

SYNOPSIS
       stunnel [filename] | -help | -version | -sockets

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
       [filename]
	   Use specified configuration file

       -help
	   Print stunnel help menu

       -version
	   Print stunnel version and compile time defaults

       -sockets
	   Print default socket options

       -install (NT/2000/XP only)
	   Install NT Service

       -uninstall (NT/2000/XP only)
	   Uninstall NT Service

CONFIGURATION FILE
       Each line of the configuration file can be either:

       o   an empty line (ignored)

       o   a comment starting with "#" (ignored)

       o   an "option_name = option_value" pair

       o   "[service_name]" indicating a start of a service definition

       GLOBAL OPTIONS

       CApath = directory
	   Certificate Authority directory

	   This is the directory in which stunnel will look for certificates when using the ver-
	   ify. Note that the certificates in this directory should be named XXXXXXXX.0 where
	   XXXXXXXX is the hash value of the cert.

       CAfile = certfile
	   Certificate Authority file

	   This file contains multiple CA certificates, used with the verify.

       cert = 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).

       chroot = directory (Unix only)
	   directory to chroot stunnel process

	   chroot keeps stunnel in chrooted jail.  CApath, pid and exec are located inside the
	   jail and the patches have to be relative to the directory specified with chroot.

	   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.

       ciphers = 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

       client = yes | no
	   client mode (remote service uses SSL)

	   default: no (server mode)

       debug = [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 debug = debug or
	   debug = 7 for greatest debugging output.  The default is notice(5).

	   The syslog facility 'authpriv' will be used unless a facility name is supplied.
	   (Facilities are not supported on Win32.)

	   Case is ignored for both facilities and levels.

       EGD = 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)

       foreground = yes | no (Unix only)
	   foreground mode

	   Stay in foreground (don't fork) and log to stderr instead of via syslog (unless output
	   is specified).

	   default: background in daemon mode

       key = keyfile
	   private key for certificate specified with cert 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 cert option

       options = SSL_options
	   OpenSSL library options

	   The parameter is the OpenSSL option name as described in the SSL_CTX_set_options(3ssl)
	   manual, but without SSL_OP_ prefix.	Several options 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

       output = file
	   append log messages to a file instead of using syslog

       pid = file (Unix only)
	   pid file location

	   If the argument is empty, then no pid file will be created.

       RNDbytes = 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 suffi-
	   cient randomness is available.

       RNDfile = file
	   path to file with random seed data

	   The SSL library will use data from this file first to seed the random number genera-
	   tor.

       RNDoverwrite = yes | no
	   overwrite the random seed files with new random data

	   default: yes

       service = servicename
	   use specified string as the service name

	   On Unix: inetd mode service name for TCP Wrapper library.

	   On NT/2000/XP: NT service name in the Control Panel.

	   default: stunnel

       session = timeout
	   session cache timeout

       setgid = groupname (Unix only)
	   setgid() to groupname in daemon mode and clears all other groups

       setuid = username (Unix only)
	   setuid() to username in daemon mode

       socket = 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

       verify = 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

       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 stunnel ser-
       vices in your log files.

       Note that if you wish to run stunnel in inetd mode (where it is provided a network socket
       by a server such as inetd, xinetd, or tcpserver) then you should read the section enti-
       tiled INETD MODE below.

       accept = [host:]port
	   accept connections on specified host:port

	   If no host specified, defaults to all IP addresses for the local host.

       connect = [host:]port
	   connect to remote host:port

	   If no host specified, defaults to localhost.

       delay = yes | no
	   delay DNS lookup for 'connect' option

       exec = executable_path (Unix only)
	   execute local inetd-type program

       execargs = $0 $1 $2 ... (Unix only)
	   arguments for exec including program name ($0)

	   Quoting is currently not supported.	Arguments are speparated with arbitrary number of
	   whitespaces.

       ident = username
	   use IDENT (RFC 1413) username checking

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

       protocol = proto
	   Negotiate SSL with specified protocol

	   currently supported: smtp, pop3, nntp

       pty = yes | no (Unix only)
	   allocate pseudo terminal for 'exec' option

       TIMEOUTbusy = seconds
	   time to wait for expected data

       TIMEOUTclose = seconds
	   time to wait for close_notify (set to 0 for buggy MSIE)

       TIMEOUTidle = seconds
	   time to keep an idle connection

       transparent = 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 stunnel.  This option is only available in
	   local mode (exec option) by LD_PRELOADing env.so shared library or in remote mode
	   (connect option) on Linux 2.2 kernel compiled with transparent proxy option and then
	   only in server mode. Note that this option will not combine with proxy mode (connect)
	   unless the client's default route to the target machine lies through the host running
	   stunnel, which cannot be localhost.

RETURN VALUE
       stunnel returns zero on success, non-zero on error.

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

	   [imapd]
	   accept = 993
	   exec = /usr/sbin/imapd
	   execargs = imapd

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

	   [vpn]
	   accept = 2020
	   exec = /usr/sbin/pppd
	   execargs = pppd local
	   pty = yes

       If you want to use stunnel in inetd mode to launch your imapd process, you'd use this
       stunnel.conf.  Note there must be no [service_name] section.

	   exec = /usr/sbin/imapd
	   execargs = imapd

FILES
       stunnel.conf
	   stunnel configuration file

       stunnel.pem
	   stunnel certificate and private key

BUGS
       Option execargs does not support quoting.

RESTRICTIONS
       stunnel 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.

NOTES
       INETD MODE

       The most common use of stunnel 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 exec option.  How-
       ever there is a special case when you wish to have some other program accept incoming con-
       nections and launch stunnel, for example with inetd, xinetd, or tcpserver.

       For example, if you have the following line in inetd.conf:

	   imaps stream tcp nowait root /usr/sbin/stunnel stunnel /etc/stunnel/imaps.conf

       In these cases, the inetd-style program is responsible for binding a network socket (imaps
       above) and handing it to stunnel when a connection is received.	Thus you do not want
       stunnel to have any accept option.  All the Service Level Options should be placed in the
       global options section, and no [service_name] section will be present.  See the EXAMPLES
       section for example configurations.

       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 OpenSSL package. You can find more information
       on certificates generation on pages listed below.

       Two things are important when generating certificate-key pairs for stunnel. 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 -nodes option when running the req command
       from the OpenSSL kit.

       The order of contents of the .pem file is also important.  It should contain the unen-
       crypted 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]

       RANDOMNESS

       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 RNDfile 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 EGD 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 automati-
       cally 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 RNDfile flag.

       Note that the file specified with the RNDfile flag should contain random data -- that
       means it should contain different information each time stunnel is run.	This is handled
       automatically unless the RNDoverwrite flag is used.  If you wish to update this file manu-
       ally, the openssl rand 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
       stunnel's behaviour, it's OpenSSLs.

SEE ALSO
       tcpd(8)
	   access control facility for internet services

       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>

3rd Berkeley Distribution		    2002.12.26				       STUNNEL(8)


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