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stunnel(8)		       stunnel TLS Proxy		    stunnel(8)

NAME
       stunnel - TLS offloading	and load-balancing proxy

SYNOPSIS
       Unix:
	   stunnel [FILE] | -fdA N | -help | -version |	-sockets | -options

       WIN32:
	   stunnel [ [ -install	| -uninstall | -start |	-stop |
	       -reload | -reopen | -exit ] [-quiet] [FILE] ] |
	       -help | -version	| -sockets | -options

DESCRIPTION
       The stunnel program is designed to work as TLS encryption wrapper
       between remote clients and local	(inetd-startable) or remote servers.
       The concept is that having non-TLS aware	daemons	running	on your	system
       you can easily set them up to communicate with clients over secure TLS
       channels.

       stunnel can be used to add TLS 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
       FILE
	   Use specified configuration file

       -fd N (Unix only)
	   Read	the config file	from specified file descriptor

       -help
	   Print stunnel help menu

       -version
	   Print stunnel version and compile time defaults

       -sockets
	   Print default socket	options

       -options
	   Print supported TLS options

       -install	(Windows NT and	later only)
	   Install NT Service

       -uninstall (Windows NT and later	only)
	   Uninstall NT	Service

       -start (Windows NT and later only)
	   Start NT Service

       -stop (Windows NT and later only)
	   Stop	NT Service

       -reload (Windows	NT and later only)
	   Reload the configuration file of the	running	NT Service

       -reopen (Windows	NT and later only)
	   Reopen the log file of the running NT Service

       -exit (Win32 only)
	   Exit	an already started stunnel

       -quiet (Win32 only)
	   Don't display any message boxes

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.

       An address parameter of an option may be	either:

       o   A port number.

       o   A colon-separated pair of IP	address	(either	IPv4, IPv6, or domain
	   name) and port number.

       o   A Unix socket path (Unix only).

   GLOBAL OPTIONS
       chroot =	DIRECTORY (Unix	only)
	   directory to	chroot stunnel process

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

	   Several functions of	the operating system also need their files to
	   be located within the chroot	jail, e.g.:

	   o   Delayed resolver	typically needs	/etc/nsswitch.conf and
	       /etc/resolv.conf.

	   o   Local time in log files needs /etc/timezone.

	   o   Some other functions may	need devices, e.g. /dev/zero or
	       /dev/null.

       compression = deflate | zlib
	   select data compression algorithm

	   default: no compression

	   Deflate is the standard compression method as described in RFC
	   1951.

       debug = [FACILITY.]LEVEL
	   debugging level

	   Level is 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 'daemon'	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 the OpenSSL random
	   number generator.

       engine =	auto | ENGINE_ID
	   select hardware or software cryptographic engine

	   default: software-only cryptography

	   See Examples	section	for an engine configuration to use the
	   certificate and the corresponding private key from a	cryptographic
	   device.

       engineCtrl = COMMAND[:PARAMETER]
	   control hardware engine

       engineDefault = TASK_LIST
	   set OpenSSL tasks delegated to the current engine

	   The parameter specifies a comma-separated list of task to be
	   delegated to	the current engine.

	   The following tasks may be available, if supported by the engine:
	   ALL,	RSA, DSA, ECDH,	ECDSA, DH, RAND, CIPHERS, DIGESTS, PKEY,
	   PKEY_CRYPTO,	PKEY_ASN1.

       fips = yes | no
	   enable or disable FIPS 140-2	mode.

	   This	option allows you to disable entering FIPS mode	if stunnel was
	   compiled with FIPS 140-2 support.

	   default: no (since version 5.00)

       foreground = yes	| quiet	| no (Unix only)
	   foreground mode

	   Stay	in foreground (don't fork).

	   With	the yes	parameter it also logs to stderr in addition to	the
	   destinations	specified with syslog and output.

	   default: background in daemon mode

       iconActive = ICON_FILE (GUI only)
	   GUI icon to be displayed when there are established connections

	   On Windows platform the parameter should be an .ico file containing
	   a 16x16 pixel image.

       iconError = ICON_FILE (GUI only)
	   GUI icon to be displayed when no valid configuration	is loaded

	   On Windows platform the parameter should be an .ico file containing
	   a 16x16 pixel image.

       iconIdle	= ICON_FILE (GUI only)
	   GUI icon to be displayed when there are no established connections

	   On Windows platform the parameter should be an .ico file containing
	   a 16x16 pixel image.

       log = append | overwrite
	   log file handling

	   This	option allows you to choose whether the	log file (specified
	   with	the output option) is appended or overwritten when opened or
	   re-opened.

	   default: append

       output =	FILE
	   append log messages to a file

	   /dev/stdout device can be used to send log messages to the standard
	   output (for example to log them with	daemontools splogger).

       pid = FILE (Unix	only)
	   pid file location

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

	   pid path is relative	to the chroot directory	if specified.

       RNDbytes	= BYTES
	   bytes to read from random seed files

       RNDfile = FILE
	   path	to file	with random seed data

	   The OpenSSL library will use	data from this file first to seed the
	   random number generator.

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

	   default: yes

       service = SERVICE (Unix only)
	   stunnel service name

	   The specified service name is used for syslog and as	the inetd mode
	   service name	for TCP	Wrappers.  While this option can technically
	   be specified	in the service sections, it is only useful in global
	   options.

	   default: stunnel

       socket =	a|l|r:OPTION=VALUE[:VALUE]
	   Set an option on the	accept/local/remote socket

	   The values for the linger option are	l_onof:l_linger.  The values
	   for the time	are tv_sec:tv_usec.

	   Examples:

	       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

       syslog =	yes | no (Unix only)
	   enable logging via syslog

	   default: yes

       taskbar = yes | no (WIN32 only)
	   enable the taskbar icon

	   default: yes

   SERVICE-LEVEL OPTIONS
       Each configuration section begins with a	service	name in	square
       brackets.  The service name is used for libwrap (TCP Wrappers) access
       control and lets	you distinguish	stunnel	services 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 entitled INETD MODE below.

       accept =	[HOST:]PORT
	   accept connections on specified address

	   If no host specified, defaults to all IPv4 addresses	for the	local
	   host.

	   To listen on	all IPv6 addresses use:

	       accept =	:::PORT

       CApath =	DIRECTORY
	   Certificate Authority directory

	   This	is the directory in which stunnel will look for	certificates
	   when	using the verifyChain or verifyPeer options.  Note that	the
	   certificates	in this	directory should be named XXXXXXXX.0 where
	   XXXXXXXX is the hash	value of the DER encoded subject of the	cert.

	   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.

	   CApath path is relative to the chroot directory if specified.

       CAfile =	CA_FILE
	   Certificate Authority file

	   This	file contains multiple CA certificates,	to be used with	the
	   verifyChain and verifyPeer options.

       cert = CERT_FILE
	   certificate chain file name

	   The parameter specifies the file containing certificates used by
	   stunnel to authenticate itself against the remote client or server.
	   The file should contain the whole certificate chain starting	from
	   the actual server/client certificate, and ending with the self-
	   signed root CA certificate.	The file must be either	in PEM or P12
	   format.

	   A certificate chain is required in server mode, and optional	in
	   client mode.

	   This	parameter is also used as the certificate identifier when a
	   hardware engine is enabled.

       checkEmail = EMAIL
	   email address of the	peer certificate subject

	   Multiple checkEmail options are allowed in a	single service
	   section.  Certificates are accepted if no checkEmail	option was
	   specified, or the email address of the peer certificate matches any
	   of the email	addresses specified with checkEmail.

	   This	option requires	OpenSSL	1.0.2 or later.

       checkHost = HOST
	   host	of the peer certificate	subject

	   Multiple checkHost options are allowed in a single service section.
	   Certificates	are accepted if	no checkHost option was	specified, or
	   the host name of the	peer certificate matches any of	the hosts
	   specified with checkHost.

	   This	option requires	OpenSSL	1.0.2 or later.

       checkIP = IP
	   IP address of the peer certificate subject

	   Multiple checkIP options are	allowed	in a single service section.
	   Certificates	are accepted if	no checkIP option was specified, or
	   the IP address of the peer certificate matches any of the IP
	   addresses specified with checkIP.

	   This	option requires	OpenSSL	1.0.2 or later.

       ciphers = CIPHER_LIST
	   Select permitted TLS	ciphers

	   A colon-delimited list of the ciphers to allow in the TLS
	   connection, for example DES-CBC3-SHA:IDEA-CBC-MD5.

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

	   default: no (server mode)

       config =	COMMAND[:PARAMETER]
	   OpenSSL configuration command

	   The OpenSSL configuration command is	executed with the specified
	   parameter.  This allows any configuration commands to be invoked
	   from	the stunnel configuration file.	 Supported commands are
	   described on	the SSL_CONF_cmd(3ssl) manual page.

	   Several config lines	can be used to specify multiple	configuration
	   commands.

	   This	option requires	OpenSSL	1.0.2 or later.

       connect = [HOST:]PORT
	   connect to a	remote address

	   If no host is specified, the	host defaults to localhost.

	   Multiple connect options are	allowed	in a single service section.

	   If host resolves to multiple	addresses and/or if multiple connect
	   options are specified, then the remote address is chosen using a
	   round-robin algorithm.

       CRLpath = DIRECTORY
	   Certificate Revocation Lists	directory

	   This	is the directory in which stunnel will look for	CRLs when
	   using the verifyChain and verifyPeer	options. Note that the CRLs in
	   this	directory should be named XXXXXXXX.r0 where XXXXXXXX is	the
	   hash	value of the CRL.

	   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.

	   CRLpath path	is relative to the chroot directory if specified.

       CRLfile = CRL_FILE
	   Certificate Revocation Lists	file

	   This	file contains multiple CRLs, used with the verifyChain and
	   verifyPeer options.

       curve = NID
	   specify ECDH	curve name

	   To get a list of supported curves use:

	       openssl ecparam -list_curves

	   default: prime256v1

       logId = TYPE
	   connection identifier type

	   This	identifier allows you to distinguish log entries generated for
	   each	of the connections.

	   Currently supported types:

	   sequential
	       The numeric sequential identifier is only unique	within a
	       single instance of stunnel, but very compact.  It is most
	       useful for manual log analysis.

	   unique
	       This alphanumeric identifier is globally	unique,	but longer
	       than the	sequential number.  It is most useful for automated
	       log analysis.

	   thread
	       The operating system thread identifier is neither unique	(even
	       within a	single instance	of stunnel) nor	short.	It is most
	       useful for debugging software or	configuration issues.

	   process
	       The operating system process identifier (PID) may be useful in
	       the inetd mode.

	   default: sequential

       debug = 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).

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

	   This	option is useful for dynamic DNS, or when DNS is not available
	   during stunnel startup (road	warrior	VPN, dial-up configurations).

	   Delayed resolver mode is automatically engaged when stunnel fails
	   to resolve on startup any of	the connect targets for	a service.

	   Delayed resolver inflicts failover =	prio.

	   default: no

       engineId	= ENGINE_ID
	   select engine ID for	the service

       engineNum = ENGINE_NUMBER
	   select engine number	for the	service

	   The engines are numbered starting from 1.

       exec = EXECUTABLE_PATH
	   execute a local inetd-type program

	   exec	path is	relative to the	chroot directory if specified.

	   The following environmental variables are set on Unix platforms:
	   REMOTE_HOST,	REMOTE_PORT, SSL_CLIENT_DN, SSL_CLIENT_I_DN.

       execArgs	= $0 $1	$2 ...
	   arguments for exec including	the program name ($0)

	   Quoting is currently	not supported.	Arguments are separated	with
	   an arbitrary	amount of whitespace.

       failover	= rr | prio
	   Failover strategy for multiple "connect" targets.

	   rr  round robin - fair load distribution

	   prio
	       priority	- use the order	specified in config file

	   default: rr

       ident = USERNAME
	   use IDENT (RFC 1413)	username checking

       include = DIRECTORY
	   include all configuration file parts	located	in DIRECTORY

	   The files are included in the ascending alphabetical	order of their
	   names.

       key = KEY_FILE
	   private key for the certificate specified with cert option

	   A private key is needed to authenticate the certificate owner.
	   Since this file should be kept secret it should only	be readable by
	   its owner.  On Unix systems you can use the following command:

	       chmod 600 keyfile

	   This	parameter is also used as the private key identifier when a
	   hardware engine is enabled.

	   default: the	value of the cert option

       libwrap = yes | no
	   Enable or disable the use of	/etc/hosts.allow and /etc/hosts.deny.

	   default: no (since version 5.00)

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

       OCSP = URL
	   select OCSP responder for certificate verification

       OCSPaia = yes | no
	   validate certificates with their AIA	OCSP responders

	   This	option enables stunnel to validate certificates	with the list
	   of OCSP responder URLs retrieved from their AIA (Authority
	   Information Access) extension.

       OCSPflag	= OCSP_FLAG
	   specify OCSP	responder flag

	   Several OCSPflag can	be used	to specify multiple flags.

	   currently supported flags: NOCERTS, NOINTERN, NOSIGS, NOCHAIN,
	   NOVERIFY, NOEXPLICIT, NOCASIGN, NODELEGATED,	NOCHECKS, TRUSTOTHER,
	   RESPID_KEY, NOTIME

       OCSPnonce = yes | no
	   send	and verify the OCSP nonce extension

	   This	option protects	the OCSP protocol against replay attacks.  Due
	   to its computational	overhead, the nonce extension is usually only
	   supported on	internal (e.g. corporate) responders, and not on
	   public OCSP responders.

       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.
	   stunnel -options lists the options found to be allowed in the
	   current combination of stunnel and the OpenSSL library used to
	   build it.

	   Several option lines	can be used to specify multiple	options.  An
	   option name can be prepended	with a dash ("-") to disable the
	   option.

	   For example,	for compatibility with the erroneous Eudora TLS
	   implementation, the following option	can be used:

	       options = DONT_INSERT_EMPTY_FRAGMENTS

	   default:

	       options = NO_SSLv2
	       options = NO_SSLv3

       protocol	= PROTO
	   application protocol	to negotiate TLS

	   This	option enables initial,	protocol-specific negotiation of the
	   TLS encryption.  The	protocol option	should not be used with	TLS
	   encryption on a separate port.

	   Currently supported protocols:

	   cifs
	       Proprietary (undocummented) extension of	CIFS protocol
	       implemented in Samba.  Support for this extension was dropped
	       in Samba	3.0.0.

	   connect
	       Based on	RFC 2817 - Upgrading to	TLS Within HTTP/1.1, section
	       5.2 - Requesting	a Tunnel with CONNECT

	       This protocol is	only supported in client mode.

	   imap
	       Based on	RFC 2595 - Using TLS with IMAP,	POP3 and ACAP

	   nntp
	       Based on	RFC 4642 - Using Transport Layer Security (TLS)	with
	       Network News Transfer Protocol (NNTP)

	       This protocol is	only supported in client mode.

	   pgsql
	       Based on
	       http://www.postgresql.org/docs/8.3/static/protocol-flow.html#AEN73982

	   pop3
	       Based on	RFC 2449 - POP3	Extension Mechanism

	   proxy
	       Haproxy client IP address
	       http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt

	   smtp
	       Based on	RFC 2487 - SMTP	Service	Extension for Secure SMTP over
	       TLS

	   socks
	       SOCKS versions 4, 4a, and 5 are supported.  The SOCKS protocol
	       itself is encapsulated within TLS encryption layer to protect
	       the final destination address.

	       http://www.openssh.com/txt/socks4.protocol

	       http://www.openssh.com/txt/socks4a.protocol

	       The BIND	command	of the SOCKS protocol is not supported.	 The
	       USERID parameter	is ignored.

	       See Examples section for	sample configuration files for VPN
	       based on	SOCKS encryption.

       protocolAuthentication =	AUTHENTICATION
	   authentication type for the protocol	negotiations

	   Currently, this option is only supported in the client-side
	   'connect' and 'smtp'	protocols.

	   Supported authentication types for the 'connect' protocol are
	   'basic' or 'ntlm'.  The default 'connect' authentication type is
	   'basic'.

	   Supported authentication types for the 'smtp' protocol are 'plain'
	   or 'login'.	The default 'smtp' authentication type is 'plain'.

       protocolDomain =	DOMAIN
	   domain for the protocol negotiations

	   Currently, this option is only supported in the client-side
	   'connect' protocol.

       protocolHost = HOST:PORT
	   destination address for the protocol	negotiations

	   protocolHost	specifies the final TLS	server to be connected to by
	   the proxy, and not the proxy	server directly	connected by stunnel.
	   The proxy server should be specified	with the 'connect' option.

	   Currently the protocol destination address only applies to the
	   'connect' protocol.

       protocolPassword	= PASSWORD
	   password for	the protocol negotiations

	   Currently, this option is only supported in the client-side
	   'connect' and 'smtp'	protocols.

       protocolUsername	= USERNAME
	   username for	the protocol negotiations

	   Currently, this option is only supported in the client-side
	   'connect' and 'smtp'	protocols.

       PSKidentity = IDENTITY
	   PSK identity	for the	PSK client

	   PSKidentity can be used on stunnel clients to select	the PSK
	   identity used for authentication.  This option is ignored in	server
	   sections.

	   default: the	first identity specified in the	PSKsecrets file.

       PSKsecrets = FILE
	   file	with PSK identities and	corresponding keys

	   Each	line of	the file in the	following format:

	       IDENTITY:KEY

	   The key is required to be at	least 20 characters long.  The file
	   should not be world-readable	nor world-writable.

       pty = yes | no (Unix only)
	   allocate a pseudoterminal for 'exec'	option

       redirect	= [HOST:]PORT
	   redirect TLS	client connections on certificate-based	authentication
	   failures

	   This	option only works in server mode.  Some	protocol negotiations
	   are also incompatible with the redirect option.

       renegotiation = yes | no
	   support TLS renegotiation

	   Applications	of the TLS renegotiation include some authentication
	   scenarios, or re-keying long	lasting	connections.

	   On the other	hand this feature can facilitate a trivial CPU-
	   exhaustion DoS attack:

	   http://vincent.bernat.im/en/blog/2011-ssl-dos-mitigation.html

	   Please note that disabling TLS renegotiation	does not fully
	   mitigate this issue.

	   default: yes	(if supported by OpenSSL)

       reset = yes | no
	   attempt to use the TCP RST flag to indicate an error

	   This	option is not supported	on some	platforms.

	   default: yes

       retry = yes | no
	   reconnect a connect+exec section after it was disconnected

	   default: no

       requireCert = yes | no
	   require a client certificate	for verifyChain	or verifyPeer

	   With	requireCert set	to no, the stunnel server accepts client
	   connections that did	not present a certificate.

	   Both	verifyChain = yes and verifyPeer = yes imply requireCert =
	   yes.

	   default: no

       setgid =	GROUP (Unix only)
	   Unix	group id

	   As a	global option: setgid()	to the specified group in daemon mode
	   and clear all other groups.

	   As a	service-level option: set the group of the Unix	socket
	   specified with "accept".

       setuid =	USER (Unix only)
	   Unix	user id

	   As a	global option: setuid()	to the specified user in daemon	mode.

	   As a	service-level option: set the owner of the Unix	socket
	   specified with "accept".

       sessionCacheSize	= NUM_ENTRIES
	   session cache size

	   sessionCacheSize specifies the maximum number of the	internal
	   session cache entries.

	   The value of	0 can be used for unlimited size.  It is not
	   recommended for production use due to the risk of a memory
	   exhaustion DoS attack.

       sessionCacheTimeout = TIMEOUT
	   session cache timeout

	   This	is the number of seconds to keep cached	TLS sessions.

       sessiond	= HOST:PORT
	   address of sessiond TLS cache server

       sni = SERVICE_NAME:SERVER_NAME_PATTERN (server mode)
	   Use the service as a	slave service (a name-based virtual server)
	   for Server Name Indication TLS extension (RFC 3546).

	   SERVICE_NAME	specifies the master service that accepts client
	   connections with the	accept option.	SERVER_NAME_PATTERN specifies
	   the host name to be redirected.  The	pattern	may start with the '*'
	   character, e.g.  '*.example.com'.  Multiple slave services are
	   normally specified for a single master service.  The	sni option can
	   also	be specified more than once within a single slave service.

	   This	service, as well as the	master service,	may not	be configured
	   in client mode.

	   The connect option of the slave service is ignored when the
	   protocol option is specified, as protocol connects to the remote
	   host	before TLS handshake.

	   Libwrap checks (Unix	only) are performed twice: with	the master
	   service name	after TCP connection is	accepted, and with the slave
	   service name	during the TLS handshake.

	   The sni option is only available when compiled with OpenSSL 1.0.0
	   and later.

       sni = SERVER_NAME (client mode)
	   Use the parameter as	the value of TLS Server	Name Indication	(RFC
	   3546) extension.

	   Empty SERVER_NAME disables sending the SNI extension.

	   The sni option is only available when compiled with OpenSSL 1.0.0
	   and later.

       sslVersion = SSL_VERSION
	   select the TLS protocol version

	   Supported values: all, SSLv2, SSLv3,	TLSv1, TLSv1.1,	TLSv1.2

	   Availability	of specific protocols depends on the linked OpenSSL
	   library.  Older versions of OpenSSL do not support TLSv1.1 and
	   TLSv1.2.  Newer versions of OpenSSL do not support SSLv2.

	   Obsolete SSLv2 and SSLv3 are	currently disabled by default.	See
	   the options option documentation for	details.

       stack = BYTES (except for FORK model)
	   thread stack	size

       TIMEOUTbusy = SECONDS
	   time	to wait	for expected data

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

       TIMEOUTconnect =	SECONDS
	   time	to wait	to connect to a	remote host

       TIMEOUTidle = SECONDS
	   time	to keep	an idle	connection

       transparent = none | source | destination | both	(Unix only)
	   enable transparent proxy support on selected	platforms

	   Supported values:

	   none
	       Disable transparent proxy support.  This	is the default.

	   source
	       Re-write	the address to appear as if a wrapped daemon is
	       connecting from the TLS client machine instead of the machine
	       running stunnel.

	       This option is currently	available in:

	       Remote mode (connect option) on Linux _=2.6.28
		   This	configuration requires stunnel to be executed as root
		   and without the setuid option.

		   This	configuration requires the following setup for
		   iptables and	routing	(possibly in /etc/rc.local or
		   equivalent file):

		       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

		   stunnel must	also to	be executed as root and	without	the
		   setuid option.

	       Remote mode (connect option) on Linux 2.2.x
		   This	configuration requires the kernel to be	compiled with
		   the transparent proxy option.  Connected service must be
		   installed on	a separate host.  Routing towards the clients
		   has to go through the stunnel box.

		   stunnel must	also to	be executed as root and	without	the
		   setuid option.

	       Remote mode (connect option) on FreeBSD _=8.0
		   This	configuration requires additional firewall and routing
		   setup.  stunnel must	also to	be executed as root and
		   without the setuid option.

	       Local mode (exec	option)
		   This	configuration works by pre-loading the libstunnel.so
		   shared library.  _RLD_LIST environment variable is used on
		   Tru64, and LD_PRELOAD variable on other platforms.

	   destination
	       The original destination	is used	instead	of the connect option.

	       A service section for transparent destination may look like
	       this:

		   [transparent]
		   client = yes
		   accept = <stunnel_port>
		   transparent = destination

	       This configuration requires iptables setup to work, possibly in
	       /etc/rc.local or	equivalent file.

	       For a connect target installed on the same host:

		   /sbin/iptables -t nat -I OUTPUT -p tcp --dport <redirected_port> \
		       -m ! --uid-owner	<stunnel_user_id> \
		       -j DNAT --to-destination	<local_ip>:<stunnel_port>

	       For a connect target installed on a remote host:

		   /sbin/iptables -I INPUT -i eth0 -p tcp --dport <stunnel_port> -j ACCEPT
		   /sbin/iptables -t nat -I PREROUTING -p tcp --dport <redirected_port>	\
		       -i eth0 -j DNAT --to-destination	<local_ip>:<stunnel_port>

	       The transparent destination option is currently only supported
	       on Linux.

	   both
	       Use both	source and destination transparent proxy.

	   Two legacy options are also supported for backward compatibility:

	   yes This option has been renamed to source.

	   no  This option has been renamed to none.

       verify =	LEVEL
	   verify the peer certificate

	   This	option is obsolete and should be replaced with the verifyChain
	   and verifyPeer options.

	   level 0
	       Request and ignore the peer certificate.

	   level 1
	       Verify the peer certificate if present.

	   level 2
	       Verify the peer certificate.

	   level 3
	       Verify the peer against a locally installed certificate.

	   level 4
	       Ignore the chain	and only verify	the peer certificate.

	   default
	       No verify.

       verifyChain = yes | no
	   verify the peer certificate chain starting from the root CA

	   For server certificate verification it is essential to also require
	   a specific certificate with checkHost or checkIP.

	   The self-signed root	CA certificate needs to	be stored either in
	   the file specified with CAfile, or in the directory specified with
	   CApath.

	   default: no

       verifyPeer = yes	| no
	   verify the peer certificate

	   The peer certificate	needs to be stored either in the file
	   specified with CAfile, or in	the directory specified	with CApath.

	   default: no

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

SIGNALS
       The following signals can be used to control stunnel in Unix
       environment:

       SIGHUP
	   Force a reload of the configuration file.

	   Some	global options will not	be reloaded:

	   o   chroot

	   o   foreground

	   o   pid

	   o   setgid

	   o   setuid

	   The use of the 'setuid' option will also prevent stunnel from
	   binding to privileged (<1024) ports during configuration reloading.

	   When	the 'chroot' option is used, stunnel will look for all its
	   files (including the	configuration file, certificates, the log file
	   and the pid file) within the	chroot jail.

       SIGUSR1
	   Close and reopen the	stunnel	log file.  This	function can be	used
	   for log rotation.

       SIGTERM,	SIGQUIT, SIGINT
	   Shut	stunnel	down.

       The result of sending any other signals to the server is	undefined.

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

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

       or in remote mode:

	   [imapd]
	   accept = 993
	   connect = 143

       In order	to let your local e-mail client	connect	to a TLS-enabled imapd
       service on another server, configure the	e-mail client to connect to
       localhost on port 119 and use:

	   [imap]
	   client = yes
	   accept = 143
	   connect = servername:993

       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

       To setup	SOCKS VPN configure the	following client service:

	   [socks_client]
	   client = yes
	   accept = 127.0.0.1:1080
	   connect = vpn_server:9080
	   verifyPeer =	yes
	   CAfile = stunnel.pem

       The corresponding configuration on the vpn_server host:

	   [socks_server]
	   protocol = socks
	   accept = 9080
	   cert	= stunnel.pem
	   key = stunnel.key

       Now test	your configuration on the client machine with:

	   curl	--socks4a localhost http://www.example.com/

       An example server mode SNI configuration:

	   [virtual]
	   ; master service
	   accept = 443
	   cert	=  default.pem
	   connect = default.internal.mydomain.com:8080

	   [sni1]
	   ; slave service 1
	   sni = virtual:server1.mydomain.com
	   cert	= server1.pem
	   connect = server1.internal.mydomain.com:8081

	   [sni2]
	   ; slave service 2
	   sni = virtual:server2.mydomain.com
	   cert	= server2.pem
	   connect = server2.internal.mydomain.com:8082
	   verifyPeer =	yes
	   CAfile = server2-allowed-clients.pem

       An example of advanced engine configuration allows for authentication
       with private keys stored	in the Windows certificate store (Windows
       only).  With the	CAPI engine you	don't need to manually select the
       client key to use.  The client key is automatically selected based on
       the list	of CAs trusted by the server.

	   engine = capi

	   [service]
	   engineId = capi
	   client = yes
	   accept = 127.0.0.1:8080
	   connect = example.com:8443

       An example of advanced engine configuration to use the certificate and
       the corresponding private key from a pkcs11 engine:

	   engine = pkcs11
	   engineCtrl =	MODULE_PATH:opensc-pkcs11.so
	   engineCtrl =	PIN:123456

	   [service]
	   engineId = pkcs11
	   client = yes
	   accept = 127.0.0.1:8080
	   connect = example.com:843
	   cert	= pkcs11:token=MyToken;object=MyCert
	   key = pkcs11:token=MyToken;object=MyKey

       An example of advanced engine configuration to use the certificate and
       the corresponding private key from a SoftHSM token:

	   engine = pkcs11
	   engineCtrl =	MODULE_PATH:softhsm2.dll
	   engineCtrl =	PIN:12345

	   [service]
	   engineId = pkcs11
	   client = yes
	   accept = 127.0.0.1:8080
	   connect = example.com:843
	   cert	= pkcs11:token=MyToken;object=KeyCert

NOTES
   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 TLS-enabled versions of FTP and telnet daemons, however.

   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.  However there is a special case
       when you	wish to	have some other	program	accept incoming	connections
       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/local/bin/stunnel stunnel /usr/local/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 TLS-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.

       The order of contents of	the .pem file is important.  It	should contain
       the unencrypted private key first, then a signed	certificate (not
       certificate request).  There should also	be empty lines after the
       certificate and the private key.	 Any 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 TLS 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.

       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 manually,
       the openssl rand	command	in recent versions of OpenSSL, would be
       useful.

       Important note: If /dev/urandom is available, OpenSSL often seeds the
       PRNG with it while checking the random state.  On systems with
       /dev/urandom OpenSSL is likely to use it	even though it is listed at
       the very	bottom of the list above.  This	is the behaviour of OpenSSL
       and not stunnel.

   DH PARAMETERS
       stunnel 4.40 and	later contains hardcoded 2048-bit DH parameters.
       Starting	with stunnel 5.18, these hardcoded DH parameters are replaced
       every 24	hours with autogenerated temporary DH parameters.  DH
       parameter generation may	take several minutes.

       Alternatively, it is possible to	specify	static DH parameters in	the
       certificate file, which disables	generating temporary DH	parameters:

	   openssl dhparam 2048	>> stunnel.pem

FILES
       @sysconfdir@/stunnel/stunnel.conf
	   stunnel configuration file

BUGS
       The execArgs option and the Win32 command line do not support quoting.

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

       inetd(8)
	   internet 'super-server'

       http://www.stunnel.org/
	   stunnel homepage

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

AUTHOR
       MichaA Trojnara
	   <Michal.Trojnara@stunnel.org>

5.41				  2017.04.01			    stunnel(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONFIGURATION FILE | RETURN VALUE | SIGNALS | EXAMPLES | NOTES | FILES | BUGS | SEE ALSO | AUTHOR

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