path: root/doc/stunnel.8.in

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.\" ========================================================================
.\"
.IX Title "stunnel 8"
.TH stunnel 8 "2019.06.10" "5.55" "stunnel TLS Proxy"
.\" 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 \- TLS offloading and load\-balancing proxy
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.IP "\fBUnix:\fR" 4
.IX Item "Unix:"
\&\fBstunnel\fR [\s-1FILE\s0] | \-fd N | \-help | \-version | \-sockets | \-options
.IP "\fB\s-1WIN32:\s0\fR" 4
.IX Item "WIN32:"
\&\fBstunnel\fR [ [ \-install | \-uninstall | \-start | \-stop |
    \-reload | \-reopen | \-exit ] [\-quiet] [\s-1FILE\s0] ] |
    \-help | \-version | \-sockets | \-options
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBstunnel\fR program is designed to work as \fI\s-1TLS\s0\fR encryption wrapper
between remote clients and local (\fIinetd\fR\-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 \fI\s-1TLS\s0\fR channels.
.PP
\&\fBstunnel\fR can be used to add \fI\s-1TLS\s0\fR functionality to commonly used \fIInetd\fR
daemons like \s-1POP\-2, POP\-3,\s0 and \s-1IMAP\s0 servers, to standalone daemons like
\&\s-1NNTP, SMTP\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 "\fB\s-1FILE\s0\fR" 4
.IX Item "FILE"
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\-options\fR" 4
.IX Item "-options"
Print supported \s-1TLS\s0 options
.IP "\fB\-install\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-install (Windows NT and later only)"
Install \s-1NT\s0 Service
.IP "\fB\-uninstall\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-uninstall (Windows NT and later only)"
Uninstall \s-1NT\s0 Service
.IP "\fB\-start\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-start (Windows NT and later only)"
Start \s-1NT\s0 Service
.IP "\fB\-stop\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-stop (Windows NT and later only)"
Stop \s-1NT\s0 Service
.IP "\fB\-reload\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-reload (Windows NT and later only)"
Reload the configuration file of the running \s-1NT\s0 Service
.IP "\fB\-reopen\fR (Windows \s-1NT\s0 and later only)" 4
.IX Item "-reopen (Windows NT and later only)"
Reopen the log file of the running \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 (Win32 only)" 4
.IX Item "-quiet (Win32 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 OPTIONS\s0"
.IX Subsection "GLOBAL OPTIONS"
.IP "\fBchroot\fR = \s-1DIRECTORY\s0 (Unix only)" 4
.IX Item "chroot = DIRECTORY (Unix only)"
directory to chroot \fBstunnel\fR process
.Sp
\&\fBchroot\fR keeps \fBstunnel\fR in a 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.
.Sp
Several functions of the operating system also need their files to be located within the chroot jail, e.g.:
.RS 4
.IP "\(bu" 4
Delayed resolver typically needs /etc/nsswitch.conf and /etc/resolv.conf.
.IP "\(bu" 4
Local time in log files needs /etc/timezone.
.IP "\(bu" 4
Some other functions may need devices, e.g. /dev/zero or /dev/null.
.RE
.RS 4
.RE
.IP "\fBcompression\fR = deflate | zlib" 4
.IX Item "compression = deflate | zlib"
select data compression algorithm
.Sp
default: no compression
.Sp
Deflate is the standard compression method as described in \s-1RFC 1951.\s0
.IP "\fBdebug\fR = [\s-1FACILITY.\s0]LEVEL" 4
.IX Item "debug = [FACILITY.]LEVEL"
debugging level
.Sp
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 \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 = \s-1EGD_PATH\s0 (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 the \fBOpenSSL\fR random number
generator.
.IP "\fBengine\fR = auto | \s-1ENGINE_ID\s0" 4
.IX Item "engine = auto | ENGINE_ID"
select hardware or software cryptographic engine
.Sp
default: software-only cryptography
.Sp
See Examples section for an engine configuration to use the certificate and the corresponding private key from a cryptographic device.
.IP "\fBengineCtrl\fR = COMMAND[:PARAMETER]" 4
.IX Item "engineCtrl = COMMAND[:PARAMETER]"
control hardware engine
.IP "\fBengineDefault\fR = \s-1TASK_LIST\s0" 4
.IX Item "engineDefault = TASK_LIST"
set OpenSSL tasks delegated to the current engine
.Sp
The parameter specifies a comma-separated list of task to be delegated to the
current engine.
.Sp
The following tasks may be available, if supported by the engine: \s-1ALL, RSA,
DSA, ECDH, ECDSA, DH, RAND, CIPHERS, DIGESTS, PKEY, PKEY_CRYPTO, PKEY_ASN1.\s0
.IP "\fBfips\fR = yes | no" 4
.IX Item "fips = yes | no"
enable or disable \s-1FIPS 140\-2\s0 mode.
.Sp
This option allows you to disable entering \s-1FIPS\s0 mode if \fBstunnel\fR was compiled
with \s-1FIPS 140\-2\s0 support.
.Sp
default: no (since version 5.00)
.IP "\fBforeground\fR = yes | quiet | no (Unix only)" 4
.IX Item "foreground = yes | quiet | no (Unix only)"
foreground mode
.Sp
Stay in foreground (don't fork).
.Sp
With the \fIyes\fR parameter it also logs to stderr in addition to
the destinations specified with \fIsyslog\fR and \fIoutput\fR.
.Sp
default: background in daemon mode
.IP "\fBiconActive\fR = \s-1ICON_FILE\s0 (\s-1GUI\s0 only)" 4
.IX Item "iconActive = ICON_FILE (GUI only)"
\&\s-1GUI\s0 icon to be displayed when there are established connections
.Sp
On Windows platform the parameter should be an .ico file containing a 16x16
pixel image.
.IP "\fBiconError\fR = \s-1ICON_FILE\s0 (\s-1GUI\s0 only)" 4
.IX Item "iconError = ICON_FILE (GUI only)"
\&\s-1GUI\s0 icon to be displayed when no valid configuration is loaded
.Sp
On Windows platform the parameter should be an .ico file containing a 16x16
pixel image.
.IP "\fBiconIdle\fR = \s-1ICON_FILE\s0 (\s-1GUI\s0 only)" 4
.IX Item "iconIdle = ICON_FILE (GUI only)"
\&\s-1GUI\s0 icon to be displayed when there are no established connections
.Sp
On Windows platform the parameter should be an .ico file containing a 16x16
pixel image.
.IP "\fBlog\fR = append | overwrite" 4
.IX Item "log = append | overwrite"
log file handling
.Sp
This option allows you to choose whether the log file (specified with the \fIoutput\fR
option) is appended or overwritten when opened or re-opened.
.Sp
default: append
.IP "\fBoutput\fR = \s-1FILE\s0" 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 = \s-1FILE\s0 (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 the \fIchroot\fR directory if specified.
.IP "\fBRNDbytes\fR = \s-1BYTES\s0" 4
.IX Item "RNDbytes = BYTES"
bytes to read from random seed files
.IP "\fBRNDfile\fR = \s-1FILE\s0" 4
.IX Item "RNDfile = FILE"
path to file with random seed data
.Sp
The OpenSSL 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 = \s-1SERVICE\s0 (Unix only)" 4
.IX Item "service = SERVICE (Unix only)"
stunnel service name
.Sp
The specified service name is used for syslog and as the \fIinetd\fR mode service
name for \s-1TCP\s0 Wrappers.  While this option can technically be specified in the
service sections, it is only useful in global options.
.Sp
default: stunnel
.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 a 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 MODE\s0\fR
below.
.IP "\fBaccept\fR = [\s-1HOST:\s0]PORT" 4
.IX Item "accept = [HOST:]PORT"
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
\&    accept = :::PORT
.Ve
.IP "\fBCApath\fR = \s-1DIRECTORY\s0" 4
.IX Item "CApath = DIRECTORY"
Certificate Authority directory
.Sp
This is the directory in which \fBstunnel\fR will look for certificates when using
the \fIverifyChain\fR or \fIverifyPeer\fR options.  Note that the certificates in
this directory should be named \s-1XXXXXXXX.0\s0 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 \fBOpenSSL 1.0.0\fR.  It is required to
c_rehash the directory on upgrade from \fBOpenSSL 0.x.x\fR to \fBOpenSSL 1.x.x\fR.
.Sp
\&\fICApath\fR path is relative to the \fIchroot\fR directory if specified.
.IP "\fBCAfile\fR = \s-1CA_FILE\s0" 4
.IX Item "CAfile = CA_FILE"
Certificate Authority file
.Sp
This file contains multiple \s-1CA\s0 certificates, to be used with the \fIverifyChain\fR
and \fIverifyPeer\fR options.
.IP "\fBcert\fR = \s-1CERT_FILE\s0" 4
.IX Item "cert = CERT_FILE"
certificate chain file name
.Sp
The parameter specifies the file containing certificates used by \fBstunnel\fR
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 \s-1CA\s0 certificate.
The file must be either in \s-1PEM\s0 or P12 format.
.Sp
A certificate chain is required in server mode, and optional in client mode.
.Sp
This parameter is also used as the certificate identifier when a hardware
engine is enabled.
.IP "\fBcheckEmail\fR = \s-1EMAIL\s0" 4
.IX Item "checkEmail = EMAIL"
email address of the peer certificate subject
.Sp
Multiple \fIcheckEmail\fR options are allowed in a single service section.
Certificates are accepted if no subject checks were specified, or the email
address of the peer certificate matches any of the email addresses specified
with \fIcheckEmail\fR.
.Sp
This option requires OpenSSL 1.0.2 or later.
.IP "\fBcheckHost\fR = \s-1HOST\s0" 4
.IX Item "checkHost = HOST"
host of the peer certificate subject
.Sp
Multiple \fIcheckHost\fR options are allowed in a single service section.
Certificates are accepted if no subject checks were specified, or the host name
of the peer certificate matches any of the hosts specified with \fIcheckHost\fR.
.Sp
This option requires OpenSSL 1.0.2 or later.
.IP "\fBcheckIP\fR = \s-1IP\s0" 4
.IX Item "checkIP = IP"
\&\s-1IP\s0 address of the peer certificate subject
.Sp
Multiple \fIcheckIP\fR options are allowed in a single service section.
Certificates are accepted if no subject checks were specified, or the \s-1IP\s0
address of the peer certificate matches any of the \s-1IP\s0 addresses specified with
\&\fIcheckIP\fR.
.Sp
This option requires OpenSSL 1.0.2 or later.
.IP "\fBciphers\fR = \s-1CIPHER_LIST\s0" 4
.IX Item "ciphers = CIPHER_LIST"
select permitted \s-1TLS\s0 ciphers (TLSv1.2 and below)
.Sp
This option does not impact TLSv1.3 ciphersuites.
.Sp
A colon-delimited list of the ciphers to allow in the \s-1TLS\s0 connection,
for example \s-1DES\-CBC3\-SHA:IDEA\-CBC\-MD5.\s0
.IP "\fBciphersuites\fR = \s-1CIPHERSUITES_LIST\s0" 4
.IX Item "ciphersuites = CIPHERSUITES_LIST"
select permitted TLSv1.3 ciphersuites
.Sp
A colon-delimited list of TLSv1.3 ciphersuites names in order of preference.
.Sp
This option requires OpenSSL 1.1.1 or later.
.Sp
default: \s-1TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256\s0
.IP "\fBclient\fR = yes | no" 4
.IX Item "client = yes | no"
client mode (remote service uses \s-1TLS\s0)
.Sp
default: no (server mode)
.IP "\fBconfig\fR = COMMAND[:PARAMETER]" 4
.IX Item "config = COMMAND[:PARAMETER]"
\&\fBOpenSSL\fR configuration command
.Sp
The \fBOpenSSL\fR 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
\&\fI\f(BISSL_CONF_cmd\fI\|(3ssl)\fR manual page.
.Sp
Several \fIconfig\fR lines can be used to specify multiple configuration commands.
.Sp
This option requires OpenSSL 1.0.2 or later.
.IP "\fBconnect\fR = [\s-1HOST:\s0]PORT" 4
.IX Item "connect = [HOST:]PORT"
connect to a remote address
.Sp
If no host is specified, the host defaults to localhost.
.Sp
Multiple \fIconnect\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 = \s-1DIRECTORY\s0" 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
\&\fIverifyChain\fR and \fIverifyPeer\fR options. 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 \fBOpenSSL 1.0.0\fR.  It is required to
c_rehash the directory on upgrade from \fBOpenSSL 0.x.x\fR to \fBOpenSSL 1.x.x\fR.
.Sp
\&\fICRLpath\fR path is relative to the \fIchroot\fR directory if specified.
.IP "\fBCRLfile\fR = \s-1CRL_FILE\s0" 4
.IX Item "CRLfile = CRL_FILE"
Certificate Revocation Lists file
.Sp
This file contains multiple CRLs, used with the \fIverifyChain\fR and
\&\fIverifyPeer\fR options.
.IP "\fBcurves\fR = list" 4
.IX Item "curves = list"
\&\s-1ECDH\s0 curves separated with ':'
.Sp
Only a single curve name is allowed for OpenSSL older than 1.1.0.
.Sp
To get a list of supported curves use:
.Sp
.Vb 1
\&    openssl ecparam \-list_curves
.Ve
.Sp
default:
.Sp
.Vb 1
\&    X25519:P\-256:X448:P\-521:P\-384 (OpenSSL 1.1.1 or later)
\&
\&    prime256v1 (OpenSSL older than 1.1.1)
.Ve
.IP "\fBlogId\fR = \s-1TYPE\s0" 4
.IX Item "logId = TYPE"
connection identifier type
.Sp
This identifier allows you to distinguish log entries generated for each of the
connections.
.Sp
Currently supported types:
.RS 4
.IP "\fIsequential\fR" 4
.IX Item "sequential"
The numeric sequential identifier is only unique within a single instance of
\&\fBstunnel\fR, but very compact.  It is most useful for manual log analysis.
.IP "\fIunique\fR" 4
.IX Item "unique"
This alphanumeric identifier is globally unique, but longer than the sequential
number.  It is most useful for automated log analysis.
.IP "\fIthread\fR" 4
.IX Item "thread"
The operating system thread identifier is neither unique (even within a single
instance of \fBstunnel\fR) nor short.  It is most useful for debugging software
or configuration issues.
.IP "\fIprocess\fR" 4
.IX Item "process"
The operating system process identifier (\s-1PID\s0) may be useful in the inetd mode.
.RE
.RS 4
.Sp
default: sequential
.RE
.IP "\fBdebug\fR = \s-1LEVEL\s0" 4
.IX Item "debug = 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).
.IP "\fBdelay\fR = yes | no" 4
.IX Item "delay = yes | no"
delay \s-1DNS\s0 lookup for the \fIconnect\fR option
.Sp
This option is useful for dynamic \s-1DNS,\s0 or when \s-1DNS\s0 is not available during
\&\fBstunnel\fR startup (road warrior \s-1VPN,\s0 dial-up configurations).
.Sp
Delayed resolver mode is automatically engaged when stunnel fails to resolve on
startup any of the \fIconnect\fR targets for a service.
.Sp
Delayed resolver inflicts \fIfailover = prio\fR.
.Sp
default: no
.IP "\fBengineId\fR = \s-1ENGINE_ID\s0" 4
.IX Item "engineId = ENGINE_ID"
select engine \s-1ID\s0 for the service
.IP "\fBengineNum\fR = \s-1ENGINE_NUMBER\s0" 4
.IX Item "engineNum = ENGINE_NUMBER"
select engine number for the service
.Sp
The engines are numbered starting from 1.
.IP "\fBexec\fR = \s-1EXECUTABLE_PATH\s0" 4
.IX Item "exec = EXECUTABLE_PATH"
execute a local inetd-type program
.Sp
\&\fIexec\fR path is relative to the \fIchroot\fR directory if specified.
.Sp
The following environmental variables are set on Unix platforms:
\&\s-1REMOTE_HOST, REMOTE_PORT, SSL_CLIENT_DN, SSL_CLIENT_I_DN.\s0
.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 the program name ($0)
.Sp
Quoting is currently not supported.
Arguments are separated with an arbitrary amount of whitespace.
.IP "\fBfailover\fR = rr | prio" 4
.IX Item "failover = rr | prio"
Failover strategy for multiple \*(L"connect\*(R" targets.
.RS 4
.IP "\fIrr\fR" 4
.IX Item "rr"
round robin \- fair load distribution
.IP "\fIprio\fR" 4
.IX Item "prio"
priority \- use the order specified in config file
.RE
.RS 4
.Sp
default: prio
.RE
.IP "\fBident\fR = \s-1USERNAME\s0" 4
.IX Item "ident = USERNAME"
use \s-1IDENT\s0 (\s-1RFC 1413\s0) username checking
.IP "\fBinclude\fR = \s-1DIRECTORY\s0" 4
.IX Item "include = DIRECTORY"
include all configuration file parts located in \s-1DIRECTORY\s0
.Sp
The files are included in the ascending alphabetical order of their names. The recommended filename convention is
.Sp
for global options:
.Sp
.Vb 1
\&        00\-global.conf
.Ve
.Sp
for local service-level options:
.Sp
.Vb 1
\&        01\-service.conf
\&
\&        02\-service.conf
.Ve
.IP "\fBkey\fR = \s-1KEY_FILE\s0" 4
.IX Item "key = KEY_FILE"
private key for the certificate specified with \fIcert\fR option
.Sp
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:
.Sp
.Vb 1
\&    chmod 600 keyfile
.Ve
.Sp
This parameter is also used as the private key identifier when a hardware
engine is enabled.
.Sp
default: the value of the \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: no (since version 5.00)
.IP "\fBlocal\fR = \s-1HOST\s0" 4
.IX Item "local = HOST"
By default, the \s-1IP\s0 address of the outgoing interface is used as the source for
remote connections.  Use this option to bind a static local \s-1IP\s0 address instead.
.IP "\fB\s-1OCSP\s0\fR = \s-1URL\s0" 4
.IX Item "OCSP = URL"
select \s-1OCSP\s0 responder for certificate verification
.IP "\fBOCSPaia\fR = yes | no" 4
.IX Item "OCSPaia = yes | no"
validate certificates with their \s-1AIA OCSP\s0 responders
.Sp
This option enables \fIstunnel\fR to validate certificates with the list of
\&\s-1OCSP\s0 responder URLs retrieved from their \s-1AIA\s0 (Authority Information Access)
extension.
.IP "\fBOCSPflag\fR = \s-1OCSP_FLAG\s0" 4
.IX Item "OCSPflag = OCSP_FLAG"
specify \s-1OCSP\s0 responder flag
.Sp
Several \fIOCSPflag\fR can be used to specify multiple flags.
.Sp
currently supported flags: \s-1NOCERTS, NOINTERN, NOSIGS, NOCHAIN, NOVERIFY,
NOEXPLICIT, NOCASIGN, NODELEGATED, NOCHECKS, TRUSTOTHER, RESPID_KEY, NOTIME\s0
.IP "\fBOCSPnonce\fR = yes | no" 4
.IX Item "OCSPnonce = yes | no"
send and verify the \s-1OCSP\s0 nonce extension
.Sp
This option protects the \s-1OCSP\s0 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 \s-1OCSP\s0 responders.
.IP "\fBoptions\fR = \s-1SSL_OPTIONS\s0" 4
.IX Item "options = SSL_OPTIONS"
\&\fBOpenSSL\fR library options
.Sp
The parameter is the \fBOpenSSL\fR option name as described in the
\&\fI\f(BISSL_CTX_set_options\fI\|(3ssl)\fR manual, but without \fI\s-1SSL_OP_\s0\fR prefix.
\&\fIstunnel \-options\fR lists the options found to be allowed in the
current combination of \fIstunnel\fR and the \fIOpenSSL\fR library used
to build it.
.Sp
Several \fIoption\fR lines can be used to specify multiple options.
An option name can be prepended with a dash (\*(L"\-\*(R") to disable the option.
.Sp
For example, for compatibility with the erroneous Eudora \s-1TLS\s0
implementation, the following option can be used:
.Sp
.Vb 1
\&    options = DONT_INSERT_EMPTY_FRAGMENTS
.Ve
.Sp
default:
.Sp
.Vb 2
\&    options = NO_SSLv2
\&    options = NO_SSLv3
.Ve
.Sp
Use \fIsslVersionMax\fR or \fIsslVersionMin\fR option instead of disabling specific \s-1TLS\s0 protocol
versions when compiled with \fBOpenSSL 1.1.0\fR or later.
.IP "\fBprotocol\fR = \s-1PROTO\s0" 4
.IX Item "protocol = PROTO"
application protocol to negotiate \s-1TLS\s0
.Sp
This option enables initial, protocol-specific negotiation of the \s-1TLS\s0
encryption.
The \fIprotocol\fR option should not be used with \s-1TLS\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 2817\s0 \- \fIUpgrading to \s-1TLS\s0 Within \s-1HTTP/1.1\s0\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 2595\s0 \- \fIUsing \s-1TLS\s0 with \s-1IMAP, POP3\s0 and \s-1ACAP\s0\fR
.IP "\fInntp\fR" 4
.IX Item "nntp"
Based on \s-1RFC 4642\s0 \- \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
\&\fIhttp://www.postgresql.org/docs/8.3/static/protocol\-flow.html#AEN73982\fR
.IP "\fIpop3\fR" 4
.IX Item "pop3"
Based on \s-1RFC 2449\s0 \- \fI\s-1POP3\s0 Extension Mechanism\fR
.IP "\fIproxy\fR" 4
.IX Item "proxy"
Passing of the original client \s-1IP\s0 with HAProxy \s-1PROXY\s0 protocol version 1
\&\fIhttps://www.haproxy.org/download/1.8/doc/proxy\-protocol.txt\fR
.IP "\fIsmtp\fR" 4
.IX Item "smtp"
Based on \s-1RFC 2487\s0 \- \fI\s-1SMTP\s0 Service Extension for Secure \s-1SMTP\s0 over \s-1TLS\s0\fR
.IP "\fIsocks\fR" 4
.IX Item "socks"
\&\s-1SOCKS\s0 versions 4, 4a, and 5 are supported.  The \s-1SOCKS\s0 protocol itself
is encapsulated within \s-1TLS\s0 encryption layer to protect the final
destination address.
.Sp
\&\fIhttp://www.openssh.com/txt/socks4.protocol\fR
.Sp
\&\fIhttp://www.openssh.com/txt/socks4a.protocol\fR
.Sp
The \s-1BIND\s0 command of the \s-1SOCKS\s0 protocol is not supported.
The \s-1USERID\s0 parameter is ignored.
.Sp
See Examples section for sample configuration files for \s-1VPN\s0 based on \s-1SOCKS\s0
encryption.
.RE
.RS 4
.RE
.IP "\fBprotocolAuthentication\fR = \s-1AUTHENTICATION\s0" 4
.IX Item "protocolAuthentication = AUTHENTICATION"
authentication type for the protocol negotiations
.Sp
Currently, this option is only supported in the client-side 'connect' and
\&'smtp' protocols.
.Sp
Supported authentication types for the 'connect' protocol are 'basic' or
\&'ntlm'.  The default 'connect' authentication type is 'basic'.
.Sp
Supported authentication types for the 'smtp' protocol are 'plain' or 'login'.
The default 'smtp' authentication type is 'plain'.
.IP "\fBprotocolDomain\fR = \s-1DOMAIN\s0" 4
.IX Item "protocolDomain = DOMAIN"
domain for the protocol negotiations
.Sp
Currently, this option is only supported in the client-side 'connect' protocol.
.IP "\fBprotocolHost\fR = \s-1HOST:PORT\s0" 4
.IX Item "protocolHost = HOST:PORT"
destination address for the protocol negotiations
.Sp
\&\fIprotocolHost\fR specifies the final \s-1TLS\s0 server to be connected to by the proxy,
and not the proxy server directly connected by \fBstunnel\fR.
The proxy server should be specified with the 'connect' option.
.Sp
Currently the protocol destination address only applies to the 'connect'
protocol.
.IP "\fBprotocolPassword\fR = \s-1PASSWORD\s0" 4
.IX Item "protocolPassword = PASSWORD"
password for the protocol negotiations
.Sp
Currently, this option is only supported in the client-side 'connect' and
\&'smtp' protocols.
.IP "\fBprotocolUsername\fR = \s-1USERNAME\s0" 4
.IX Item "protocolUsername = USERNAME"
username for the protocol negotiations
.Sp
Currently, this option is only supported in the client-side 'connect' and
\&'smtp' protocols.
.IP "\fBPSKidentity\fR = \s-1IDENTITY\s0" 4
.IX Item "PSKidentity = IDENTITY"
\&\s-1PSK\s0 identity for the \s-1PSK\s0 client
.Sp
\&\fIPSKidentity\fR can be used on \fBstunnel\fR clients to select the \s-1PSK\s0 identity
used for authentication.  This option is ignored in server sections.
.Sp
default: the first identity specified in the \fIPSKsecrets\fR file.
.IP "\fBPSKsecrets\fR = \s-1FILE\s0" 4
.IX Item "PSKsecrets = FILE"
file with \s-1PSK\s0 identities and corresponding keys
.Sp
Each line of the file in the following format:
.Sp
.Vb 1
\&    IDENTITY:KEY
.Ve
.Sp
Hexadecimal keys are automatically converted to binary form.
Keys are required to be at least 16 bytes long, which implies
at least 32 characters for hexadecimal keys.
The file should neither be world-readable nor world-writable.
.IP "\fBpty\fR = yes | no (Unix only)" 4
.IX Item "pty = yes | no (Unix only)"
allocate a pseudoterminal for 'exec' option
.IP "\fBredirect\fR = [\s-1HOST:\s0]PORT" 4
.IX Item "redirect = [HOST:]PORT"
redirect \s-1TLS\s0 client connections on certificate-based authentication failures
.Sp
This option only works in server mode.
Some protocol negotiations are also incompatible with the \fIredirect\fR option.
.IP "\fBrenegotiation\fR = yes | no" 4
.IX Item "renegotiation = yes | no"
support \s-1TLS\s0 renegotiation
.Sp
Applications of the \s-1TLS\s0 renegotiation include some authentication scenarios,
or re-keying long lasting connections.
.Sp
On the other hand this feature can facilitate a trivial CPU-exhaustion
DoS attack:
.Sp
\&\fIhttp://vincent.bernat.im/en/blog/2011\-ssl\-dos\-mitigation.html\fR
.Sp
Please note that disabling \s-1TLS\s0 renegotiation does not fully mitigate
this issue.
.Sp
default: yes (if supported by \fBOpenSSL\fR)
.IP "\fBreset\fR = yes | no" 4
.IX Item "reset = yes | no"
attempt to use the \s-1TCP RST\s0 flag to indicate an error
.Sp
This option is not supported on some platforms.
.Sp
default: yes
.IP "\fBretry\fR = yes | no" 4
.IX Item "retry = yes | no"
reconnect a connect+exec section after it was disconnected
.Sp
default: no
.IP "\fBrequireCert\fR = yes | no" 4
.IX Item "requireCert = yes | no"
require a client certificate for \fIverifyChain\fR or \fIverifyPeer\fR
.Sp
With \fIrequireCert\fR set to \fIno\fR, the \fBstunnel\fR server accepts client
connections that did not present a certificate.
.Sp
Both \fIverifyChain = yes\fR and \fIverifyPeer = yes\fR imply \fIrequireCert = yes\fR.
.Sp
default: no
.IP "\fBsetgid\fR = \s-1GROUP\s0 (Unix only)" 4
.IX Item "setgid = GROUP (Unix only)"
Unix group id
.Sp
As a global option: \fBsetgid()\fR to the specified group in daemon mode and clear all other groups.
.Sp
As a service-level option: set the group of the Unix socket specified with \*(L"accept\*(R".
.IP "\fBsetuid\fR = \s-1USER\s0 (Unix only)" 4
.IX Item "setuid = USER (Unix only)"
Unix user id
.Sp
As a global option: \fBsetuid()\fR to the specified user in daemon mode.
.Sp
As a service-level option: set the owner of the Unix socket specified with \*(L"accept\*(R".
.IP "\fBsessionCacheSize\fR = \s-1NUM_ENTRIES\s0" 4
.IX Item "sessionCacheSize = NUM_ENTRIES"
session cache size
.Sp
\&\fIsessionCacheSize\fR specifies the maximum number of the internal session cache
entries.
.Sp
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.
.IP "\fBsessionCacheTimeout\fR = \s-1TIMEOUT\s0" 4
.IX Item "sessionCacheTimeout = TIMEOUT"
session cache timeout
.Sp
This is the number of seconds to keep cached \s-1TLS\s0 sessions.
.IP "\fBsessiond\fR = \s-1HOST:PORT\s0" 4
.IX Item "sessiond = HOST:PORT"
address of sessiond \s-1TLS\s0 cache server
.IP "\fBsni\fR = \s-1SERVICE_NAME:SERVER_NAME_PATTERN\s0 (server mode)" 4
.IX Item "sni = SERVICE_NAME:SERVER_NAME_PATTERN (server mode)"
Use the service as a slave service (a name-based virtual server) for Server
Name Indication \s-1TLS\s0 extension (\s-1RFC 3546\s0).
.Sp
\&\fI\s-1SERVICE_NAME\s0\fR specifies the master service that accepts client connections
with the \fIaccept\fR option.  \fI\s-1SERVER_NAME_PATTERN\s0\fR 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 \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.
.Sp
The \fIconnect\fR option of the slave service is ignored when the \fIprotocol\fR
option is specified, as \fIprotocol\fR connects to the remote host before \s-1TLS\s0
handshake.
.Sp
Libwrap checks (Unix only) are performed twice: with the master service name
after \s-1TCP\s0 connection is accepted, and with the slave service name during the
\&\s-1TLS\s0 handshake.
.Sp
The \fIsni\fR option is only available when compiled with \fBOpenSSL 1.0.0\fR and
later.
.IP "\fBsni\fR = \s-1SERVER_NAME\s0 (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 3546\s0)
extension.
.Sp
Empty \s-1SERVER_NAME\s0 disables sending the \s-1SNI\s0 extension.
.Sp
The \fIsni\fR option is only available when compiled with \fBOpenSSL 1.0.0\fR and
later.
.IP "\fBsocket\fR = a|l|r:OPTION=VALUE[:VALUE]" 4
.IX Item "socket = a|l|r:OPTION=VALUE[:VALUE]"
Set an option on the accept/local/remote socket
.Sp
The values for the linger option are l_onof:l_linger.
The values for the 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 "\fBsslVersion\fR = \s-1SSL_VERSION\s0" 4
.IX Item "sslVersion = SSL_VERSION"
select the \s-1TLS\s0 protocol version
.Sp
Supported versions: all, SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3
.Sp
Availability of specific protocols depends on the linked OpenSSL library.
Older versions of OpenSSL do not support TLSv1.1, TLSv1.2 and TLSv1.3.
Newer versions of OpenSSL do not support SSLv2.
.Sp
Obsolete SSLv2 and SSLv3 are currently disabled by default.
.Sp
Setting the option
.Sp
.Vb 1
\&    sslVersion = SSL_VERSION
.Ve
.Sp
is equivalent to options
.Sp
.Vb 2
\&    sslVersionMax = SSL_VERSION
\&    sslVersionMin = SSL_VERSION
.Ve
.Sp
when compiled with \fBOpenSSL 1.1.0\fR and later.
.IP "\fBsslVersionMax\fR = \s-1SSL_VERSION\s0" 4
.IX Item "sslVersionMax = SSL_VERSION"
maximum supported protocol versions
.Sp
Supported versions: all, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3
.Sp
\&\fIall\fR enable protocol versions up to the highest version supported by the
linked OpenSSL library.
.Sp
Availability of specific protocols depends on the linked OpenSSL library.
.Sp
The \fIsslVersionMax\fR option is only available when compiled with \fBOpenSSL 1.1.0\fR and later.
.Sp
default: all
.IP "\fBsslVersionMin\fR = \s-1SSL_VERSION\s0" 4
.IX Item "sslVersionMin = SSL_VERSION"
minimum supported protocol versions
.Sp
Supported versions: all, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3
.Sp
\&\fIall\fR enable protocol versions down to the lowest version supported by the
linked OpenSSL library.
.Sp
Availability of specific protocols depends on the linked OpenSSL library.
.Sp
The \fIsslVersionMin\fR option is only available when compiled with \fBOpenSSL 1.1.0\fR and later.
.Sp
default: TLSv1
.IP "\fBstack\fR = \s-1BYTES\s0 (except for \s-1FORK\s0 model)" 4
.IX Item "stack = BYTES (except for FORK model)"
\&\s-1CPU\s0 stack size of created threads
.Sp
Excessive thread stack size increases virtual memory usage.
Insufficient thread stack size may cause application crashes.
.Sp
default: 65536 bytes (sufficient for all platforms we tested)
.IP "\fBticketKeySecret\fR = \s-1SECRET\s0" 4
.IX Item "ticketKeySecret = SECRET"
hexadecimal symmetric key used for session ticket confidentiality protection
.Sp
Session tickets defined in \s-1RFC 5077\s0 provide an enhanced session resumption
capability, where the server-side caching is not required to maintain per
session state.
.Sp
Combining \fIticketKeySecret\fR and \fIticketMacSecret\fR options allow to resume a
negotiated session on other cluster nodes, or to resume resume a negotiated
session after server restart.
.Sp
The key is required to be either 16 or 32 bytes long, which implies exactly 32
or 64 hexadecimal digits.  Colons may optionally be used between two-character
hexadecimal bytes.
.Sp
This option only works in server mode.
.Sp
The \fIticketKeySecret\fR option is only available when compiled with
\&\fBOpenSSL 1.0.0\fR and later.
.Sp
Disabling \fI\s-1NO_TICKET\s0\fR option is required for the ticket support in OpenSSL
older than 1.1.1, but note that this option is incompatible with the
\&\fIredirect\fR option.
.IP "\fBticketMacSecret\fR = \s-1SECRET\s0" 4
.IX Item "ticketMacSecret = SECRET"
hexadecimal symmetric key used for session ticket integrity protection
.Sp
The key is required to be either 16 or 32 bytes long, which implies exactly 32
or 64 hexadecimal digits.  Colons may optionally be used between two-character
hexadecimal bytes.
.Sp
This option only works in server mode.
.Sp
The \fIticketMacSecret\fR option is only available when compiled with
\&\fBOpenSSL 1.0.0\fR and later.
.IP "\fBTIMEOUTbusy\fR = \s-1SECONDS\s0" 4
.IX Item "TIMEOUTbusy = SECONDS"
time to wait for expected data
.IP "\fBTIMEOUTclose\fR = \s-1SECONDS\s0" 4
.IX Item "TIMEOUTclose = SECONDS"
time to wait for close_notify (set to 0 for buggy \s-1MSIE\s0)
.IP "\fBTIMEOUTconnect\fR = \s-1SECONDS\s0" 4
.IX Item "TIMEOUTconnect = SECONDS"
time to wait to connect to a remote host
.IP "\fBTIMEOUTidle\fR = \s-1SECONDS\s0" 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 the address to appear as if a wrapped daemon is connecting
from the \s-1TLS\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 \fBstunnel\fR to be executed as root and without
the \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 the \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 the kernel to be compiled with the \fItransparent proxy\fR
option.
Connected service must be installed on a separate host.
Routing towards the clients has to go through the \fBstunnel\fR box.
.Sp
\&\fBstunnel\fR must also to be executed as root and without the \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 the \fIsetuid\fR option.
.IP "Local mode (\fIexec\fR option)" 4
.IX Item "Local mode (exec option)"
This configuration works by pre-loading the \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"
The original destination is used instead of the \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 iptables setup to work,
possibly in /etc/rc.local or equivalent file.
.Sp
For a connect target installed on the same host:
.Sp
.Vb 3
\&    /sbin/iptables \-t nat \-I OUTPUT \-p tcp \-\-dport <redirected_port> \e
\&        \-m ! \-\-uid\-owner <stunnel_user_id> \e
\&        \-j DNAT \-\-to\-destination <local_ip>:<stunnel_port>
.Ve
.Sp
For a connect target installed on a remote host:
.Sp
.Vb 3
\&    /sbin/iptables \-I INPUT \-i eth0 \-p tcp \-\-dport <stunnel_port> \-j ACCEPT
\&    /sbin/iptables \-t nat \-I PREROUTING \-p tcp \-\-dport <redirected_port> \e
\&        \-i eth0 \-j DNAT \-\-to\-destination <local_ip>:<stunnel_port>
.Ve
.Sp
The 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 option has been renamed to \fIsource\fR.
.IP "\fIno\fR" 4
.IX Item "no"
This option has been renamed to \fInone\fR.
.RE
.RS 4
.RE
.IP "\fBverify\fR = \s-1LEVEL\s0" 4
.IX Item "verify = LEVEL"
verify the peer certificate
.Sp
This option is obsolete and should be replaced with the \fIverifyChain\fR
and \fIverifyPeer\fR options.
.RS 4
.IP "level 0" 4
.IX Item "level 0"
Request and ignore the peer certificate.
.IP "level 1" 4
.IX Item "level 1"
Verify the peer certificate if present.
.IP "level 2" 4
.IX Item "level 2"
Verify the peer certificate.
.IP "level 3" 4
.IX Item "level 3"
Verify the peer against a locally installed certificate.
.IP "level 4" 4
.IX Item "level 4"
Ignore the chain and only verify the peer certificate.
.IP "default" 4
.IX Item "default"
No verify.
.RE
.RS 4
.RE
.IP "\fBverifyChain\fR = yes | no" 4
.IX Item "verifyChain = yes | no"
verify the peer certificate chain starting from the root \s-1CA\s0
.Sp
For server certificate verification it is essential to also require a specific
certificate with \fIcheckHost\fR or \fIcheckIP\fR.
.Sp
The self-signed root \s-1CA\s0 certificate needs to be stored either in the file
specified with \fICAfile\fR, or in the directory specified with \fICApath\fR.
.Sp
default: no
.IP "\fBverifyPeer\fR = yes | no" 4
.IX Item "verifyPeer = yes | no"
verify the peer certificate
.Sp
The peer certificate needs to be stored either in the file
specified with \fICAfile\fR, or in the directory specified with \fICApath\fR.
.Sp
default: no
.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 \fBstunnel\fR 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 the 'setuid' option will also prevent \fBstunnel\fR from binding to privileged
(<1024) ports during configuration reloading.
.Sp
When the 'chroot' option is used, \fBstunnel\fR will look for all its files (including
the configuration file, certificates, the log file and the pid file) within the chroot
jail.
.RE
.IP "\s-1SIGUSR1\s0" 4
.IX Item "SIGUSR1"
Close and reopen the \fBstunnel\fR log file.
This function can be used for log rotation.
.IP "\s-1SIGUSR2\s0" 4
.IX Item "SIGUSR2"
Log the list of active connections.
.IP "\s-1SIGTERM, SIGQUIT, SIGINT\s0" 4
.IX Item "SIGTERM, SIGQUIT, SIGINT"
Shut \fBstunnel\fR down.
.PP
The result of sending any other signals to the server is undefined.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
In order to provide \s-1TLS\s0 encapsulation to your local \fIimapd\fR service, use:
.PP
.Vb 4
\&    [imapd]
\&    accept = 993
\&    exec = /usr/sbin/imapd
\&    execArgs = imapd
.Ve
.PP
or in remote mode:
.PP
.Vb 3
\&    [imapd]
\&    accept = 993
\&    connect = 143
.Ve
.PP
In order to let your local e\-mail client connect to a TLS-enabled \fIimapd\fR
service on another server, configure the e\-mail client to connect to localhost
on port 119 and use:
.PP
.Vb 4
\&    [imap]
\&    client = yes
\&    accept = 143
\&    connect = servername:993
.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
.PP
To setup \s-1SOCKS VPN\s0 configure the following client service:
.PP
.Vb 6
\&    [socks_client]
\&    client = yes
\&    accept = 127.0.0.1:1080
\&    connect = vpn_server:9080
\&    verifyPeer = yes
\&    CAfile = stunnel.pem
.Ve
.PP
The corresponding configuration on the vpn_server host:
.PP
.Vb 5
\&    [socks_server]
\&    protocol = socks
\&    accept = 9080
\&    cert = stunnel.pem
\&    key = stunnel.key
.Ve
.PP
Now test your configuration on the client machine with:
.PP
.Vb 1
\&    curl \-\-socks4a localhost http://www.example.com/
.Ve
.PP
An example server mode \s-1SNI\s0 configuration:
.PP
.Vb 5
\&    [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
.Ve
.PP
An example of advanced engine configuration allows for authentication with private keys
stored in the Windows certificate store (Windows only).
With the \s-1CAPI\s0 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.
.PP
.Vb 1
\&    engine = capi
\&
\&    [service]
\&    engineId = capi
\&    client = yes
\&    accept = 127.0.0.1:8080
\&    connect = example.com:8443
.Ve
.PP
An example of advanced engine configuration to use the certificate and the corresponding private key from a pkcs11 engine:
.PP
.Vb 3
\&    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
.Ve
.PP
An example of advanced engine configuration to use the certificate and the corresponding private key from a SoftHSM token:
.PP
.Vb 3
\&    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
.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 TLS-enabled versions of \s-1FTP\s0 and telnet daemons, however.
.SS "\s-1INETD MODE\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 @bindir@/stunnel stunnel @sysconfdir@/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 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 \fBOpenSSL\fR package. You can find more
information on certificates generation on pages listed below.
.PP
The \fI.pem\fR file should contain the unencrypted private key and
a signed certificate (not certificate request).
So the file should look like this:
.PP
.Vb 6
\&    \-\-\-\-\-BEGIN RSA PRIVATE KEY\-\-\-\-\-
\&    [encoded key]
\&    \-\-\-\-\-END RSA PRIVATE KEY\-\-\-\-\-
\&    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
\&    [encoded certificate]
\&    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
.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-1TLS\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
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 \fBOpenSSL\fR,
would be useful.
.PP
Important note: If /dev/urandom is available, \fBOpenSSL\fR often seeds the \s-1PRNG\s0
with it while checking the random state.  On systems with /dev/urandom
\&\fBOpenSSL\fR is likely to use it even though it is listed at the very bottom of
the list above.  This is the behaviour of \fBOpenSSL\fR and not \fBstunnel\fR.
.SS "\s-1DH PARAMETERS\s0"
.IX Subsection "DH PARAMETERS"
\&\fBstunnel\fR 4.40 and later contains hardcoded 2048\-bit \s-1DH\s0 parameters.  Starting
with \fBstunnel\fR 5.18, these hardcoded \s-1DH\s0 parameters are replaced every 24 hours
with autogenerated temporary \s-1DH\s0 parameters.  \s-1DH\s0 parameter generation may take
several minutes.
.PP
Alternatively, it is possible to specify static \s-1DH\s0 parameters in the
certificate file, which disables generating temporary \s-1DH\s0 parameters:
.PP
.Vb 1
\&    openssl dhparam 2048 >> stunnel.pem
.Ve
.SH "FILES"
.IX Header "FILES"
.IP "\fI\f(CI@sysconfdir\fI@/stunnel/stunnel.conf\fR" 4
.IX Item "@sysconfdir@/stunnel/stunnel.conf"
\&\fBstunnel\fR configuration file
.SH "BUGS"
.IX Header "BUGS"
The \fIexecArgs\fR option and the Win32 command line do not support quoting.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP "\fBtcpd\fR\|(8)" 4
.IX Item "tcpd"
access control facility for internet services
.IP "\fBinetd\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/"
\&\fBOpenSSL\fR project website
.SH "AUTHOR"
.IX Header "AUTHOR"
.IP "Michał Trojnara" 4
.IX Item "Michał Trojnara"
<\fIMichal.Trojnara@stunnel.org\fR>