stunnel4/doc/stunnel.8

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.\" ========================================================================
.\"
.IX Title "STUNNEL 8"
.TH STUNNEL 8 "2012.01.14" "4.53" "stunnel"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
stunnel \- universal SSL tunnel
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.IP "\fBUnix:\fR" 4
.IX Item "Unix:"
\&\fBstunnel\fR [<filename>] | \-fd n | \-help | \-version | \-sockets
.IP "\fB\s-1WIN32:\s0\fR" 4
.IX Item "WIN32:"
\&\fBstunnel\fR [ [\-install | \-uninstall | \-start | \-stop] | \-exit]
    [\-quiet] [<filename>] ] | \-help | \-version | \-sockets
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBstunnel\fR program is designed to work as \fI\s-1SSL\s0\fR encryption wrapper 
between remote clients and local (\fIinetd\fR\-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 \s-1SSL\s0 channels.
.PP
\&\fBstunnel\fR can be used to add \s-1SSL\s0 functionality to commonly used \fIInetd\fR
daemons like \s-1POP\-2\s0, \s-1POP\-3\s0, and \s-1IMAP\s0 servers, to standalone daemons like
\&\s-1NNTP\s0, \s-1SMTP\s0 and \s-1HTTP\s0, and in tunneling \s-1PPP\s0 over network sockets without
changes to the source code.
.PP
This product includes cryptographic software written by
Eric Young (eay@cryptsoft.com)
.SH "OPTIONS"
.IX Header "OPTIONS"
.IP "<\fBfilename\fR>" 4
.IX Item "<filename>"
Use specified configuration file
.IP "\fB\-fd n\fR (Unix only)" 4
.IX Item "-fd n (Unix only)"
Read the config file from specified file descriptor
.IP "\fB\-help\fR" 4
.IX Item "-help"
Print \fBstunnel\fR help menu
.IP "\fB\-version\fR" 4
.IX Item "-version"
Print \fBstunnel\fR version and compile time defaults
.IP "\fB\-sockets\fR" 4
.IX Item "-sockets"
Print default socket options
.IP "\fB\-install\fR (\s-1NT/2000/XP\s0 only)" 4
.IX Item "-install (NT/2000/XP only)"
Install \s-1NT\s0 Service
.IP "\fB\-uninstall\fR (\s-1NT/2000/XP\s0 only)" 4
.IX Item "-uninstall (NT/2000/XP only)"
Uninstall \s-1NT\s0 Service
.IP "\fB\-start\fR (\s-1NT/2000/XP\s0 only)" 4
.IX Item "-start (NT/2000/XP only)"
Start \s-1NT\s0 Service
.IP "\fB\-stop\fR (\s-1NT/2000/XP\s0 only)" 4
.IX Item "-stop (NT/2000/XP only)"
Stop \s-1NT\s0 Service
.IP "\fB\-exit\fR (Win32 only)" 4
.IX Item "-exit (Win32 only)"
Exit an already started stunnel
.IP "\fB\-quiet\fR (\s-1NT/2000/XP\s0 only)" 4
.IX Item "-quiet (NT/2000/XP only)"
Don't display any message boxes
.SH "CONFIGURATION FILE"
.IX Header "CONFIGURATION FILE"
Each line of the configuration file can be either:
.IP "\(bu" 4
an empty line (ignored)
.IP "\(bu" 4
a comment starting with ';' (ignored)
.IP "\(bu" 4
an 'option_name = option_value' pair
.IP "\(bu" 4
\&'[service_name]' indicating a start of a service definition
.PP
An address parameter of an option may be either:
.IP "\(bu" 4
a port number
.IP "\(bu" 4
a colon-separated pair of \s-1IP\s0 address (either IPv4, IPv6, or domain name) and port number
.IP "\(bu" 4
a Unix socket path (Unix only)
.SS "\s-1GLOBAL\s0 \s-1OPTIONS\s0"
.IX Subsection "GLOBAL OPTIONS"
.IP "\fBchroot\fR = directory (Unix only)" 4
.IX Item "chroot = directory (Unix only)"
directory to chroot \fBstunnel\fR process
.Sp
\&\fBchroot\fR keeps \fBstunnel\fR in chrooted jail.  \fICApath\fR, \fICRLpath\fR, \fIpid\fR
and \fIexec\fR are located inside the jail and the patches have to be relative
to the directory specified with \fBchroot\fR.
.IP "\fBcompression\fR = deflate | zlib | rle" 4
.IX Item "compression = deflate | zlib | rle"
select data compression algorithm
.Sp
default: no compression
.Sp
deflate is the standard compression method as described in \s-1RFC\s0 1951.
.Sp
zlib compression of OpenSSL 0.9.8 or above is not backward compatible with
OpenSSL 0.9.7.
.Sp
rle compression is currently not implemented by the OpenSSL library.
.IP "\fBdebug\fR = [facility.]level" 4
.IX Item "debug = [facility.]level"
debugging level
.Sp
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 \fIdebug = debug\fR or
\&\fIdebug = 7\fR for greatest debugging output.  The default is notice (5).
.Sp
The syslog facility 'daemon' will be used unless a facility name is supplied.
(Facilities are not supported on Win32.)
.Sp
Case is ignored for both facilities and levels.
.IP "\fB\s-1EGD\s0\fR = egd path (Unix only)" 4
.IX Item "EGD = egd path (Unix only)"
path to Entropy Gathering Daemon socket
.Sp
Entropy Gathering Daemon socket to use to feed OpenSSL random number
generator.  (Available only if compiled with OpenSSL 0.9.5a or higher)
.IP "\fBengine\fR = auto | <engine id>" 4
.IX Item "engine = auto | <engine id>"
select hardware engine
.Sp
default: software-only cryptography
.Sp
Here is an example of advanced engine configuration to read private key from an
OpenSC engine
.Sp
.Vb 7
\&    engine=dynamic
\&    engineCtrl=SO_PATH:/usr/lib/opensc/engine_pkcs11.so
\&    engineCtrl=ID:pkcs11
\&    engineCtrl=LIST_ADD:1
\&    engineCtrl=LOAD
\&    engineCtrl=MODULE_PATH:/usr/lib/pkcs11/opensc\-pkcs11.so
\&    engineCtrl=INIT
\&
\&    [service]
\&    engineNum=1
\&    key=id_45
.Ve
.IP "\fBengineCtrl\fR = command[:parameter]" 4
.IX Item "engineCtrl = command[:parameter]"
control hardware engine
.Sp
Special commands \*(L"\s-1LOAD\s0\*(R" and \*(L"\s-1INIT\s0\*(R" can be used to load and initialize the
engine cryptogaphic module.
.IP "\fBfips\fR = yes | no" 4
.IX Item "fips = yes | no"
Enable or disable \s-1FIPS\s0 140\-2 mode.
.Sp
This option allows to disable entering \s-1FIPS\s0 mode if stunnel was compiled with
\&\s-1FIPS\s0 140\-2 support.
.Sp
default: yes
.IP "\fBforeground\fR = yes | no (Unix only)" 4
.IX Item "foreground = yes | no (Unix only)"
foreground mode
.Sp
Stay in foreground (don't fork) and log to stderr
instead of via syslog (unless \fIoutput\fR is specified).
.Sp
default: background in daemon mode
.IP "\fBoutput\fR = file" 4
.IX Item "output = file"
append log messages to a file
.Sp
/dev/stdout device can be used to send log messages to the standard
output (for example to log them with daemontools splogger).
.IP "\fBpid\fR = file (Unix only)" 4
.IX Item "pid = file (Unix only)"
pid file location
.Sp
If the argument is empty, then no pid file will be created.
.Sp
\&\fIpid\fR path is relative to \fIchroot\fR directory if specified.
.IP "\fBRNDbytes\fR = bytes" 4
.IX Item "RNDbytes = bytes"
bytes to read from random seed files
.Sp
Number of bytes of data read from random seed files.  With \s-1SSL\s0 versions
less than 0.9.5a, also determines how many bytes of data are considered
sufficient to seed the \s-1PRNG\s0.  More recent OpenSSL versions have a builtin
function to determine when sufficient randomness is available.
.IP "\fBRNDfile\fR = file" 4
.IX Item "RNDfile = file"
path to file with random seed data
.Sp
The \s-1SSL\s0 library will use data from this file first to seed the random
number generator.
.IP "\fBRNDoverwrite\fR = yes | no" 4
.IX Item "RNDoverwrite = yes | no"
overwrite the random seed files with new random data
.Sp
default: yes
.IP "\fBservice\fR = servicename (Unix only)" 4
.IX Item "service = servicename (Unix only)"
use specified string as \fIinetd\fR mode service name for \s-1TCP\s0 Wrapper library
.Sp
default: stunnel
.IP "\fBsetgid\fR = groupname (Unix only)" 4
.IX Item "setgid = groupname (Unix only)"
\&\fIsetgid()\fR to groupname in daemon mode and clears all other groups
.IP "\fBsetuid\fR = username (Unix only)" 4
.IX Item "setuid = username (Unix only)"
\&\fIsetuid()\fR to username in daemon mode
.IP "\fBsocket\fR = a|l|r:option=value[:value]" 4
.IX Item "socket = a|l|r:option=value[:value]"
Set an option on accept/local/remote socket
.Sp
The values for linger option are l_onof:l_linger.
The values for time are tv_sec:tv_usec.
.Sp
Examples:
.Sp
.Vb 9
\&    socket = l:SO_LINGER=1:60
\&        set one minute timeout for closing local socket
\&    socket = r:SO_OOBINLINE=yes
\&        place out\-of\-band data directly into the
\&        receive data stream for remote sockets
\&    socket = a:SO_REUSEADDR=no
\&        disable address reuse (enabled by default)
\&    socket = a:SO_BINDTODEVICE=lo
\&        only accept connections on loopback interface
.Ve
.IP "\fBsyslog\fR = yes | no (Unix only)" 4
.IX Item "syslog = yes | no (Unix only)"
enable logging via syslog
.Sp
default: yes
.IP "\fBtaskbar\fR = yes | no (\s-1WIN32\s0 only)" 4
.IX Item "taskbar = yes | no (WIN32 only)"
enable the taskbar icon
.Sp
default: yes
.SS "SERVICE-LEVEL \s-1OPTIONS\s0"
.IX Subsection "SERVICE-LEVEL OPTIONS"
Each configuration section begins with service name in square brackets.
The service name is used for libwrap (\s-1TCP\s0 Wrappers) access control and lets
you distinguish \fBstunnel\fR services in your log files.
.PP
Note that if you wish to run \fBstunnel\fR in \fIinetd\fR mode (where it
is provided a network socket by a server such as \fIinetd\fR, \fIxinetd\fR,
or \fItcpserver\fR) then you should read the section entitled \fI\s-1INETD\s0 \s-1MODE\s0\fR
below.
.IP "\fBaccept\fR = address" 4
.IX Item "accept = address"
accept connections on specified address
.Sp
If no host specified, defaults to all IPv4 addresses for the local host.
.Sp
To listen on all IPv6 addresses use:
.Sp
.Vb 1
\&    connect = :::port
.Ve
.IP "\fBCApath\fR = directory" 4
.IX Item "CApath = directory"
Certificate Authority directory
.Sp
This is the directory in which \fBstunnel\fR will look for certificates when using
the \fIverify\fR.  Note that the certificates in this directory should be named
\&\s-1XXXXXXXX\s0.0 where \s-1XXXXXXXX\s0 is the hash value of the \s-1DER\s0 encoded subject of the
cert.
.Sp
The hash algorithm has been changed in OpenSSL 1.0.0.  It is required to
c_rehash the directory on upgrade from OpenSSL 0.x.x to OpenSSL 1.x.x.
.Sp
\&\fICApath\fR path is relative to \fIchroot\fR directory if specified.
.IP "\fBCAfile\fR = certfile" 4
.IX Item "CAfile = certfile"
Certificate Authority file
.Sp
This file contains multiple \s-1CA\s0 certificates, used with the \fIverify\fR.
.IP "\fBcert\fR = pemfile" 4
.IX Item "cert = pemfile"
certificate chain \s-1PEM\s0 file name
.Sp
A \s-1PEM\s0 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 \s-1PEM\s0 format and must be sorted starting with the
certificate to the highest level (root \s-1CA\s0).
.IP "\fBciphers\fR = cipherlist" 4
.IX Item "ciphers = cipherlist"
Select permitted \s-1SSL\s0 ciphers
.Sp
A colon delimited list of the ciphers to allow in the \s-1SSL\s0 connection.
For example \s-1DES\-CBC3\-SHA:IDEA\-CBC\-MD5\s0
.IP "\fBclient\fR = yes | no" 4
.IX Item "client = yes | no"
client mode (remote service uses \s-1SSL\s0)
.Sp
default: no (server mode)
.IP "\fBconnect\fR = address" 4
.IX Item "connect = address"
connect to a remote address
.Sp
If no host is specified, the host defaults to localhost.
.Sp
Multiple \fBconnect\fR options are allowed in a single service section.
.Sp
If host resolves to multiple addresses and/or if multiple \fIconnect\fR
options are specified, then the remote address is chosen using a
round-robin algorithm.
.IP "\fBCRLpath\fR = directory" 4
.IX Item "CRLpath = directory"
Certificate Revocation Lists directory
.Sp
This is the directory in which \fBstunnel\fR will look for CRLs when
using the \fIverify\fR. Note that the CRLs in this directory should
be named \s-1XXXXXXXX\s0.r0 where \s-1XXXXXXXX\s0 is the hash value of the \s-1CRL\s0.
.Sp
The hash algorithm has been changed in OpenSSL 1.0.0.  It is required to
c_rehash the directory on upgrade from OpenSSL 0.x.x to OpenSSL 1.x.x.
.Sp
\&\fICRLpath\fR path is relative to \fIchroot\fR directory if specified.
.IP "\fBCRLfile\fR = certfile" 4
.IX Item "CRLfile = certfile"
Certificate Revocation Lists file
.Sp
This file contains multiple CRLs, used with the \fIverify\fR.
.IP "\fBcurve\fR = nid" 4
.IX Item "curve = nid"
specify \s-1ECDH\s0 curve name
.Sp
To get a list of supported cuves use:
.Sp
.Vb 1
\&    openssl ecparam \-list_curves
.Ve
.Sp
default: prime256v1
.IP "\fBdelay\fR = yes | no" 4
.IX Item "delay = yes | no"
delay \s-1DNS\s0 lookup for 'connect' option
.Sp
This option is useful for dynamic \s-1DNS\s0, or when \s-1DNS\s0 is not available during
stunnel startup (road warrior \s-1VPN\s0, dial-up configurations).
.IP "\fBengineNum\fR = engine number" 4
.IX Item "engineNum = engine number"
select engine number to read private key
.Sp
The engines are numbered starting from 1.
.IP "\fBexec\fR = executable_path" 4
.IX Item "exec = executable_path"
execute local inetd-type program
.Sp
\&\fIexec\fR path is relative to \fIchroot\fR directory if specified.
.ie n .IP "\fBexecargs\fR = $0 $1 $2 ..." 4
.el .IP "\fBexecargs\fR = \f(CW$0\fR \f(CW$1\fR \f(CW$2\fR ..." 4
.IX Item "execargs = $0 $1 $2 ..."
arguments for \fIexec\fR including program name ($0)
.Sp
Quoting is currently not supported.
Arguments are separated with arbitrary number of whitespaces.
.IP "\fBfailover\fR = rr | prio" 4
.IX Item "failover = rr | prio"
Failover strategy for multiple \*(L"connect\*(R" targets.
.Sp
.Vb 2
\&    rr (round robin) \- fair load distribution
\&    prio (priority) \- use the order specified in config file
.Ve
.Sp
default: rr
.IP "\fBident\fR = username" 4
.IX Item "ident = username"
use \s-1IDENT\s0 (\s-1RFC\s0 1413) username checking
.IP "\fBkey\fR = keyfile" 4
.IX Item "key = keyfile"
private key for certificate specified with \fIcert\fR option
.Sp
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:
.Sp
.Vb 1
\&    chmod 600 keyfile
.Ve
.Sp
default: value of \fIcert\fR option
.IP "\fBlibwrap\fR = yes | no" 4
.IX Item "libwrap = yes | no"
Enable or disable the use of /etc/hosts.allow and /etc/hosts.deny.
.Sp
default: yes
.IP "\fBlocal\fR = host" 4
.IX Item "local = host"
\&\s-1IP\s0 of the outgoing interface is used as source for remote connections.
Use this option to bind a static local \s-1IP\s0 address, instead.
.IP "\fBsni\fR = service_name:server_name (server mode)" 4
.IX Item "sni = service_name:server_name (server mode)"
Use the service as a slave service (a name-based virtual server) for Server
Name Indication \s-1TLS\s0 extension (\s-1RFC\s0 3546).
.Sp
\&\fIservice_name\fR specifies the master service that accepts client connections
with \fIaccept\fR option.  \fIserver_name\fR specifies the host name to be redirected.
Multiple slave services are normally specified for a single master service.
\&\fIsni\fR option can also be specified more than once within a single slave service.
.Sp
This service, as well as the master service, may not be configured in client mode.
\&\fIconnect\fR option of the slave service is ignored when \fIprotocol\fR option is
specified, as \fIprotocol\fR connects remote host before \s-1TLS\s0 handshake.
Libwrap checks (Unix only) are performed twice: with master service name after
\&\s-1TCP\s0 connection is accepted, and with slave service name during \s-1TLS\s0 handshake.
.Sp
Option \fIsni\fR is only available when compiled with OpenSSL 1.0.0 and later.
.IP "\fBsni\fR = server_name (client mode)" 4
.IX Item "sni = server_name (client mode)"
Use the parameter as the value of \s-1TLS\s0 Server Name Indication (\s-1RFC\s0 3546)
extension.
.Sp
Option \fIsni\fR is only available when compiled with OpenSSL 1.0.0 and later.
.IP "\fB\s-1OCSP\s0\fR = url" 4
.IX Item "OCSP = url"
select \s-1OCSP\s0 server for certificate verification
.IP "\fBOCSPflag\fR = flag" 4
.IX Item "OCSPflag = flag"
specify \s-1OCSP\s0 server flag
.Sp
Several \fIOCSPflag\fR can be used to specify multiple flags.
.Sp
currently supported flags: \s-1NOCERTS\s0, \s-1NOINTERN\s0 \s-1NOSIGS\s0, \s-1NOCHAIN\s0, \s-1NOVERIFY\s0,
\&\s-1NOEXPLICIT\s0, \s-1NOCASIGN\s0, \s-1NODELEGATED\s0, \s-1NOCHECKS\s0, \s-1TRUSTOTHER\s0, \s-1RESPID_KEY\s0, \s-1NOTIME\s0
.IP "\fBoptions\fR = SSL_options" 4
.IX Item "options = SSL_options"
OpenSSL library options
.Sp
The parameter is the OpenSSL option name as described in the
\&\fI\fISSL_CTX_set_options\fI\|(3ssl)\fR manual, but without \fI\s-1SSL_OP_\s0\fR prefix.
Several \fIoptions\fR can be used to specify multiple options.
.Sp
For example for compatibility with erroneous Eudora \s-1SSL\s0 implementation
the following option can be used:
.Sp
.Vb 1
\&    options = DONT_INSERT_EMPTY_FRAGMENTS
.Ve
.IP "\fBprotocol\fR = proto" 4
.IX Item "protocol = proto"
application protocol to negotiate \s-1SSL\s0 (e.g. \fIstarttls\fR or \fIstls\fR)
.Sp
\&\fIprotocol\fR option should not be used with \s-1SSL\s0 encryption on a separate port.
.Sp
Currently supported protocols:
.RS 4
.IP "\fIcifs\fR" 4
.IX Item "cifs"
Proprietary (undocummented) extension of \s-1CIFS\s0 protocol implemented in Samba.
Support for this extension was dropped in Samba 3.0.0.
.IP "\fIconnect\fR" 4
.IX Item "connect"
Based on \s-1RFC\s0 2817 \- \fIUpgrading to \s-1TLS\s0 Within \s-1HTTP/1\s0.1\fR, section 5.2 \- \fIRequesting a Tunnel with \s-1CONNECT\s0\fR
.Sp
This protocol is only supported in client mode.
.IP "\fIimap\fR" 4
.IX Item "imap"
Based on \s-1RFC\s0 2595 \- \fIUsing \s-1TLS\s0 with \s-1IMAP\s0, \s-1POP3\s0 and \s-1ACAP\s0\fR
.IP "\fInntp\fR" 4
.IX Item "nntp"
Based on \s-1RFC\s0 4642 \- \fIUsing Transport Layer Security (\s-1TLS\s0) with Network News Transfer Protocol (\s-1NNTP\s0)\fR
.Sp
This protocol is only supported in client mode.
.IP "\fIpgsql\fR" 4
.IX Item "pgsql"
Based on http://www.postgresql.org/docs/8.3/static/protocol\-flow.html#AEN73982
.IP "\fIpop3\fR" 4
.IX Item "pop3"
Based on \s-1RFC\s0 2449 \- \fI\s-1POP3\s0 Extension Mechanism\fR
.IP "\fIproxy\fR" 4
.IX Item "proxy"
Haproxy client \s-1IP\s0 address http://haproxy.1wt.eu/download/1.5/doc/proxy\-protocol.txt
.IP "\fIsmtp\fR" 4
.IX Item "smtp"
Based on \s-1RFC\s0 2487 \- \fI\s-1SMTP\s0 Service Extension for Secure \s-1SMTP\s0 over \s-1TLS\s0\fR
.RE
.RS 4
.RE
.IP "\fBprotocolAuthentication\fR = auth_type" 4
.IX Item "protocolAuthentication = auth_type"
authentication type for protocol negotiations
.Sp
currently supported: basic, \s-1NTLM\s0
.Sp
Currently authentication type only applies to 'connect' protocol.
.Sp
default: basic
.IP "\fBprotocolHost\fR = host:port" 4
.IX Item "protocolHost = host:port"
destination address for protocol negotiations
.IP "\fBprotocolPassword\fR = password" 4
.IX Item "protocolPassword = password"
password for protocol negotiations
.IP "\fBprotocolUsername\fR = username" 4
.IX Item "protocolUsername = username"
username for protocol negotiations
.IP "\fBpty\fR = yes | no (Unix only)" 4
.IX Item "pty = yes | no (Unix only)"
allocate pseudo terminal for 'exec' option
.IP "\fBretry\fR = yes | no (Unix only)" 4
.IX Item "retry = yes | no (Unix only)"
reconnect a connect+exec section after it's disconnected
.Sp
default: no
.IP "\fBsession\fR = timeout" 4
.IX Item "session = timeout"
session cache timeout
.IP "\fBsessiond\fR = host:port" 4
.IX Item "sessiond = host:port"
address of sessiond \s-1SSL\s0 cache server
.IP "\fBsslVersion\fR = version" 4
.IX Item "sslVersion = version"
select version of \s-1SSL\s0 protocol
.Sp
Allowed options: all, SSLv2, SSLv3, TLSv1
.IP "\fBstack\fR = bytes (except for \s-1FORK\s0 model)" 4
.IX Item "stack = bytes (except for FORK model)"
thread stack size
.IP "\fBTIMEOUTbusy\fR = seconds" 4
.IX Item "TIMEOUTbusy = seconds"
time to wait for expected data
.IP "\fBTIMEOUTclose\fR = seconds" 4
.IX Item "TIMEOUTclose = seconds"
time to wait for close_notify (set to 0 for buggy \s-1MSIE\s0)
.IP "\fBTIMEOUTconnect\fR = seconds" 4
.IX Item "TIMEOUTconnect = seconds"
time to wait to connect a remote host
.IP "\fBTIMEOUTidle\fR = seconds" 4
.IX Item "TIMEOUTidle = seconds"
time to keep an idle connection
.IP "\fBtransparent\fR = none | source | destination | both (Unix only)" 4
.IX Item "transparent = none | source | destination | both (Unix only)"
enable transparent proxy support on selected platforms
.Sp
Supported values:
.RS 4
.IP "\fInone\fR" 4
.IX Item "none"
Disable transparent proxy support.  This is the default.
.IP "\fIsource\fR" 4
.IX Item "source"
Re-write address to appear as if wrapped daemon is connecting
from the \s-1SSL\s0 client machine instead of the machine running \fBstunnel\fR.
.Sp
This option is currently available in:
.RS 4
.IP "Remote mode (\fIconnect\fR option) on \fILinux >=2.6.28\fR" 4
.IX Item "Remote mode (connect option) on Linux >=2.6.28"
This configuration requires stunnel to be executed as root and without
\&\fIsetuid\fR option.
.Sp
This configuration requires the following setup for iptables and routing
(possibly in /etc/rc.local or equivalent file):
.Sp
.Vb 7
\&    iptables \-t mangle \-N DIVERT
\&    iptables \-t mangle \-A PREROUTING \-p tcp \-m socket \-j DIVERT
\&    iptables \-t mangle \-A DIVERT \-j MARK \-\-set\-mark 1
\&    iptables \-t mangle \-A DIVERT \-j ACCEPT
\&    ip rule add fwmark 1 lookup 100
\&    ip route add local 0.0.0.0/0 dev lo table 100
\&    echo 0 >/proc/sys/net/ipv4/conf/lo/rp_filter
.Ve
.Sp
\&\fBstunnel\fR must also to be executed as root and without \fIsetuid\fR option.
.IP "Remote mode (\fIconnect\fR option) on \fILinux 2.2.x\fR" 4
.IX Item "Remote mode (connect option) on Linux 2.2.x"
This configuration requires kernel to be compiled with \fItransparent proxy\fR option.
Connected service must be installed on a separate host.
Routing towards the clients has to go through the stunnel box.
.Sp
\&\fBstunnel\fR must also to be executed as root and without \fIsetuid\fR option.
.IP "Remote mode (\fIconnect\fR option) on \fIFreeBSD >=8.0\fR" 4
.IX Item "Remote mode (connect option) on FreeBSD >=8.0"
This configuration requires additional firewall and routing setup.
\&\fBstunnel\fR must also to be executed as root and without \fIsetuid\fR option.
.IP "Local mode (\fIexec\fR option)" 4
.IX Item "Local mode (exec option)"
This configuration works by pre-loading \fIlibstunnel.so\fR shared library.
_RLD_LIST environment variable is used on Tru64, and \s-1LD_PRELOAD\s0 variable on
other platforms.
.RE
.RS 4
.RE
.IP "\fIdestination\fR" 4
.IX Item "destination"
Original destination is used instead of \fIconnect\fR option.
.Sp
A service section for transparent destination may look like this:
.Sp
.Vb 4
\&    [transparent]
\&    client=yes
\&    accept=<stunnel_port>
\&    transparent=destination
.Ve
.Sp
This configuration requires the following setup for iptables
(possibly in /etc/rc.local or equivalent file):
.Sp
.Vb 2
\&    /sbin/iptables \-I INPUT \-i eth0 \-p tcp \-\-dport <stunnel_port> \-j ACCEPT
\&    /sbin/iptables \-t nat \-I PREROUTING \-i eth0 \-p tcp \-\-dport <redirected_port> \-j DNAT \-\-to\-destination <local_ip>:<stunnel_port>
.Ve
.Sp
Transparent destination option is currently only supported on Linux.
.IP "\fIboth\fR" 4
.IX Item "both"
Use both \fIsource\fR and \fIdestination\fR transparent proxy.
.RE
.RS 4
.Sp
Two legacy options are also supported for backward compatibility:
.IP "\fIyes\fR" 4
.IX Item "yes"
This options has been renamed to \fIsource\fR.
.IP "\fIno\fR" 4
.IX Item "no"
This options has been renamed to \fInone\fR.
.RE
.RS 4
.RE
.IP "\fBverify\fR = level" 4
.IX Item "verify = level"
verify peer certificate
.RS 4
.IP "\fIlevel 0\fR \- request and ignore peer certificate" 4
.IX Item "level 0 - request and ignore peer certificate"
.PD 0
.IP "\fIlevel 1\fR \- verify peer certificate if present" 4
.IX Item "level 1 - verify peer certificate if present"
.IP "\fIlevel 2\fR \- verify peer certificate" 4
.IX Item "level 2 - verify peer certificate"
.IP "\fIlevel 3\fR \- verify peer with locally installed certificate" 4
.IX Item "level 3 - verify peer with locally installed certificate"
.IP "\fIlevel 4\fR \- ignore \s-1CA\s0 chain and only verify peer certificate" 4
.IX Item "level 4 - ignore CA chain and only verify peer certificate"
.IP "\fIdefault\fR \- no verify" 4
.IX Item "default - no verify"
.RE
.RS 4
.PD
.Sp
It is important to understand, that this option was solely designed for access
control and not for authorization.  Specifically for level 2 every non-revoked
certificate is accepted regardless of its Common Name.  For this reason a
dedicated \s-1CA\s0 should be used with level 2, and not a generic \s-1CA\s0 commonly used
for webservers.  Level 3 is preferred for point-to-point connections.
.RE
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fBstunnel\fR returns zero on success, non-zero on error.
.SH "SIGNALS"
.IX Header "SIGNALS"
The following signals can be used to control stunnel in Unix environment:
.IP "\s-1SIGHUP\s0" 4
.IX Item "SIGHUP"
Force a reload of the configuration file.
.Sp
Some global options will not be reloaded:
.RS 4
.IP "\(bu" 4
chroot
.IP "\(bu" 4
foreground
.IP "\(bu" 4
pid
.IP "\(bu" 4
setgid
.IP "\(bu" 4
setuid
.RE
.RS 4
.Sp
The use of 'setuid' option will also prevent stunnel from binding privileged
(<1024) ports during configuration reloading.
.Sp
When 'chroot' option is used, stunnel will look for all its files (including
configuration file, certificates, log file and pid file) within the chroot
jail.
.RE
.IP "\s-1SIGUSR1\s0" 4
.IX Item "SIGUSR1"
Close and reopen stunnel log file.
This function can be used for log rotation.
.IP "\s-1SIGTERM\s0, \s-1SIGQUIT\s0, \s-1SIGINT\s0" 4
.IX Item "SIGTERM, SIGQUIT, SIGINT"
Shut stunnel down.
.PP
The result of sending any other signals to the server is undefined.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
In order to provide \s-1SSL\s0 encapsulation to your local \fIimapd\fR service, use
.PP
.Vb 4
\&    [imapd]
\&    accept = 993
\&    exec = /usr/sbin/imapd
\&    execargs = imapd
.Ve
.PP
If you want to provide tunneling to your \fIpppd\fR daemon on port 2020,
use something like
.PP
.Vb 5
\&    [vpn]
\&    accept = 2020
\&    exec = /usr/sbin/pppd
\&    execargs = pppd local
\&    pty = yes
.Ve
.PP
If you want to use \fBstunnel\fR in \fIinetd\fR mode to launch your imapd
process, you'd use this \fIstunnel.conf\fR.
Note there must be no \fI[service_name]\fR section.
.PP
.Vb 2
\&    exec = /usr/sbin/imapd
\&    execargs = imapd
.Ve
.SH "NOTES"
.IX Header "NOTES"
.SS "\s-1RESTRICTIONS\s0"
.IX Subsection "RESTRICTIONS"
\&\fBstunnel\fR cannot be used for the \s-1FTP\s0 daemon because of the nature
of the \s-1FTP\s0 protocol which utilizes multiple ports for data transfers.
There are available \s-1SSL\s0 enabled versions of \s-1FTP\s0 and telnet daemons, however.
.SS "\s-1INETD\s0 \s-1MODE\s0"
.IX Subsection "INETD MODE"
The most common use of \fBstunnel\fR 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 \fIexec\fR option.
However there is a special case when you wish to have
some other program accept incoming connections and
launch \fBstunnel\fR, for example with \fIinetd\fR, \fIxinetd\fR,
or \fItcpserver\fR.
.PP
For example, if you have the following line in \fIinetd.conf\fR:
.PP
.Vb 1
\&    imaps stream tcp nowait root /usr/bin/stunnel stunnel /etc/stunnel/imaps.conf
.Ve
.PP
In these cases, the \fIinetd\fR\-style program is responsible
for binding a network socket (\fIimaps\fR above) and handing
it to \fBstunnel\fR when a connection is received.
Thus you do not want \fBstunnel\fR to have any \fIaccept\fR option.
All the \fIService Level Options\fR should be placed in the
global options section, and no \fI[service_name]\fR section
will be present.  See the \fI\s-1EXAMPLES\s0\fR section for example
configurations.
.SS "\s-1CERTIFICATES\s0"
.IX Subsection "CERTIFICATES"
Each \s-1SSL\s0 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 \fIOpenSSL\fR package. You can find more
information on certificates generation on pages listed below.
.PP
The order of contents of the \fI.pem\fR file is 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:
.PP
.Vb 8
\&    \-\-\-\-\-BEGIN RSA PRIVATE KEY\-\-\-\-\-
\&    [encoded key]
\&    \-\-\-\-\-END RSA PRIVATE KEY\-\-\-\-\-
\&    [empty line]
\&    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
\&    [encoded certificate]
\&    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
\&    [empty line]
.Ve
.SS "\s-1RANDOMNESS\s0"
.IX Subsection "RANDOMNESS"
\&\fBstunnel\fR needs to seed the \s-1PRNG\s0 (pseudo random number generator) in
order for \s-1SSL\s0 to use good randomness.  The following sources are loaded
in order until sufficient random data has been gathered:
.IP "\(bu" 4
The file specified with the \fIRNDfile\fR flag.
.IP "\(bu" 4
The file specified by the \s-1RANDFILE\s0 environment variable, if set.
.IP "\(bu" 4
The file .rnd in your home directory, if \s-1RANDFILE\s0 not set.
.IP "\(bu" 4
The file specified with '\-\-with\-random' at compile time.
.IP "\(bu" 4
The contents of the screen if running on Windows.
.IP "\(bu" 4
The egd socket specified with the \fI\s-1EGD\s0\fR flag.
.IP "\(bu" 4
The egd socket specified with '\-\-with\-egd\-sock' at compile time.
.IP "\(bu" 4
The /dev/urandom device.
.PP
With recent (>=OpenSSL 0.9.5a) version of \s-1SSL\s0 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 \s-1SSL\s0 function exists to tell when enough data is available.
.PP
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 \fIRNDfile\fR flag.
.PP
Note that the file specified with the \fIRNDfile\fR flag should contain
random data \*(-- that means it should contain different information
each time \fBstunnel\fR is run.  This is handled automatically
unless the \fIRNDoverwrite\fR flag is used.  If you wish to update this file
manually, the \fIopenssl rand\fR command in recent versions of OpenSSL,
would be useful.
.PP
One important note \*(-- if /dev/urandom is available, OpenSSL has a habit of
seeding the \s-1PRNG\s0 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 \fBstunnel's\fR behaviour, it's
OpenSSLs.
.SS "\s-1DH\s0 \s-1PARAMETERS\s0"
.IX Subsection "DH PARAMETERS"
Stunnel 4.40 and later contains hardcoded 2048\-bit \s-1DH\s0 parameters.
.PP
It is also possible to specify \s-1DH\s0 parameters in the certificate file:
.PP
.Vb 1
\&    openssl dhparam 2048 >> stunnel.pem
.Ve
.PP
\&\s-1DH\s0 parameter generation may take several minutes.
.SH "FILES"
.IX Header "FILES"
.IP "\fIstunnel.conf\fR" 4
.IX Item "stunnel.conf"
\&\fBstunnel\fR configuration file
.SH "BUGS"
.IX Header "BUGS"
Option \fIexecargs\fR does not support quoting.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP "\fItcpd\fR\|(8)" 4
.IX Item "tcpd"
access control facility for internet services
.IP "\fIinetd\fR\|(8)" 4
.IX Item "inetd"
internet 'super\-server'
.IP "\fIhttp://www.stunnel.org/\fR" 4
.IX Item "http://www.stunnel.org/"
\&\fBstunnel\fR homepage
.IP "\fIhttp://www.openssl.org/\fR" 4
.IX Item "http://www.openssl.org/"
OpenSSL project website
.SH "AUTHOR"
.IX Header "AUTHOR"
.IP "Michał Trojnara" 4
.IX Item "Michał Trojnara"
<\fIMichal.Trojnara@mirt.net\fR>