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stunnel4/doc/stunnel.pod
Mario Fetka ce7eba2efe Imported Upstream version 4.53
2017-03-28 09:58:13 +02:00

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=head1 NAME
=encoding utf8
stunnel - universal SSL tunnel
=head1 SYNOPSIS
=over 4
=item B<Unix:>
B<stunnel> [<S<filename>>] | S<-fd n> | S<-help> | S<-version> | S<-sockets>
=item B<WIN32:>
B<stunnel> [ [S<-install> | S<-uninstall> | S<-start> | S<-stop>] | S<-exit>]
[S<-quiet>] [<S<filename>>] ] | S<-help> | S<-version> | S<-sockets>
=back
=head1 DESCRIPTION
The B<stunnel> program is designed to work as I<SSL> encryption wrapper
between remote clients and local (I<inetd>-startable) or remote
servers. The concept is that having non-SSL aware daemons running on
your system you can easily set them up to communicate with clients over
secure SSL channels.
B<stunnel> can be used to add SSL functionality to commonly used I<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)
=head1 OPTIONS
=over 4
=item <B<filename>>
Use specified configuration file
=item B<-fd n> (Unix only)
Read the config file from specified file descriptor
=item B<-help>
Print B<stunnel> help menu
=item B<-version>
Print B<stunnel> version and compile time defaults
=item B<-sockets>
Print default socket options
=item B<-install> (NT/2000/XP only)
Install NT Service
=item B<-uninstall> (NT/2000/XP only)
Uninstall NT Service
=item B<-start> (NT/2000/XP only)
Start NT Service
=item B<-stop> (NT/2000/XP only)
Stop NT Service
=item B<-exit> (Win32 only)
Exit an already started stunnel
=item B<-quiet> (NT/2000/XP only)
Don't display any message boxes
=back
=head1 CONFIGURATION FILE
Each line of the configuration file can be either:
=over 4
=item * an empty line (ignored)
=item * a comment starting with ';' (ignored)
=item * an 'option_name = option_value' pair
=item * '[service_name]' indicating a start of a service definition
=back
An address parameter of an option may be either:
=over 4
=item * a port number
=item * a colon-separated pair of IP address (either IPv4, IPv6, or domain name) and port number
=item * a Unix socket path (Unix only)
=back
=head2 GLOBAL OPTIONS
=over 4
=item B<chroot> = directory (Unix only)
directory to chroot B<stunnel> process
B<chroot> keeps B<stunnel> in chrooted jail. I<CApath>, I<CRLpath>, I<pid>
and I<exec> are located inside the jail and the patches have to be relative
to the directory specified with B<chroot>.
=item B<compression> = deflate | zlib | rle
select data compression algorithm
default: no compression
deflate is the standard compression method as described in RFC 1951.
zlib compression of OpenSSL 0.9.8 or above is not backward compatible with
OpenSSL 0.9.7.
rle compression is currently not implemented by the OpenSSL library.
=item B<debug> = [facility.]level
debugging level
Level is a one of the syslog level names or numbers
emerg (0), alert (1), crit (2), err (3), warning (4), notice (5),
info (6), or debug (7). All logs for the specified level and
all levels numerically less than it will be shown. Use I<debug = debug> or
I<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.
=item B<EGD> = egd path (Unix only)
path to Entropy Gathering Daemon socket
Entropy Gathering Daemon socket to use to feed OpenSSL random number
generator. (Available only if compiled with OpenSSL 0.9.5a or higher)
=item B<engine> = auto | <engine id>
select hardware engine
default: software-only cryptography
Here is an example of advanced engine configuration to read private key from an
OpenSC engine
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
=item B<engineCtrl> = command[:parameter]
control hardware engine
Special commands "LOAD" and "INIT" can be used to load and initialize the
engine cryptogaphic module.
=item B<fips> = yes | no
Enable or disable FIPS 140-2 mode.
This option allows to disable entering FIPS mode if stunnel was compiled with
FIPS 140-2 support.
default: yes
=item B<foreground> = yes | no (Unix only)
foreground mode
Stay in foreground (don't fork) and log to stderr
instead of via syslog (unless I<output> is specified).
default: background in daemon mode
=item B<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).
=item B<pid> = file (Unix only)
pid file location
If the argument is empty, then no pid file will be created.
I<pid> path is relative to I<chroot> directory if specified.
=item B<RNDbytes> = bytes
bytes to read from random seed files
Number of bytes of data read from random seed files. With SSL versions
less than 0.9.5a, also determines how many bytes of data are considered
sufficient to seed the PRNG. More recent OpenSSL versions have a builtin
function to determine when sufficient randomness is available.
=item B<RNDfile> = file
path to file with random seed data
The SSL library will use data from this file first to seed the random
number generator.
=item B<RNDoverwrite> = yes | no
overwrite the random seed files with new random data
default: yes
=item B<service> = servicename (Unix only)
use specified string as I<inetd> mode service name for TCP Wrapper library
default: stunnel
=item B<setgid> = groupname (Unix only)
setgid() to groupname in daemon mode and clears all other groups
=item B<setuid> = username (Unix only)
setuid() to username in daemon mode
=item B<socket> = a|l|r:option=value[:value]
Set an option on accept/local/remote socket
The values for linger option are l_onof:l_linger.
The values for time are tv_sec:tv_usec.
Examples:
socket = l:SO_LINGER=1:60
set one minute timeout for closing local socket
socket = r: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
=item B<syslog> = yes | no (Unix only)
enable logging via syslog
default: yes
=item B<taskbar> = yes | no (WIN32 only)
enable the taskbar icon
default: yes
=back
=head2 SERVICE-LEVEL OPTIONS
Each configuration section begins with service name in square brackets.
The service name is used for libwrap (TCP Wrappers) access control and lets
you distinguish B<stunnel> services in your log files.
Note that if you wish to run B<stunnel> in I<inetd> mode (where it
is provided a network socket by a server such as I<inetd>, I<xinetd>,
or I<tcpserver>) then you should read the section entitled I<INETD MODE>
below.
=over 4
=item B<accept> = address
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:
connect = :::port
=item B<CApath> = directory
Certificate Authority directory
This is the directory in which B<stunnel> will look for certificates when using
the I<verify>. 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.
I<CApath> path is relative to I<chroot> directory if specified.
=item B<CAfile> = certfile
Certificate Authority file
This file contains multiple CA certificates, used with the I<verify>.
=item B<cert> = pemfile
certificate chain PEM file name
A PEM is always needed in server mode.
Specifying this flag in client mode will use this certificate chain
as a client side certificate chain. Using client side certs is optional.
The certificates must be in PEM format and must be sorted starting with the
certificate to the highest level (root CA).
=item B<ciphers> = cipherlist
Select permitted SSL ciphers
A colon delimited list of the ciphers to allow in the SSL connection.
For example DES-CBC3-SHA:IDEA-CBC-MD5
=item B<client> = yes | no
client mode (remote service uses SSL)
default: no (server mode)
=item B<connect> = address
connect to a remote address
If no host is specified, the host defaults to localhost.
Multiple B<connect> options are allowed in a single service section.
If host resolves to multiple addresses and/or if multiple I<connect>
options are specified, then the remote address is chosen using a
round-robin algorithm.
=item B<CRLpath> = directory
Certificate Revocation Lists directory
This is the directory in which B<stunnel> will look for CRLs when
using the I<verify>. 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.
I<CRLpath> path is relative to I<chroot> directory if specified.
=item B<CRLfile> = certfile
Certificate Revocation Lists file
This file contains multiple CRLs, used with the I<verify>.
=item B<curve> = nid
specify ECDH curve name
To get a list of supported cuves use:
openssl ecparam -list_curves
default: prime256v1
=item B<delay> = yes | no
delay DNS lookup for 'connect' option
This option is useful for dynamic DNS, or when DNS is not available during
stunnel startup (road warrior VPN, dial-up configurations).
=item B<engineNum> = engine number
select engine number to read private key
The engines are numbered starting from 1.
=item B<exec> = executable_path
execute local inetd-type program
I<exec> path is relative to I<chroot> directory if specified.
=item B<execargs> = $0 $1 $2 ...
arguments for I<exec> including program name ($0)
Quoting is currently not supported.
Arguments are separated with arbitrary number of whitespaces.
=item B<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
=item B<ident> = username
use IDENT (RFC 1413) username checking
=item B<key> = keyfile
private key for certificate specified with I<cert> option
Private key is needed to authenticate certificate owner.
Since this file should be kept secret it should only be readable
to its owner. On Unix systems you can use the following command:
chmod 600 keyfile
default: value of I<cert> option
=item B<libwrap> = yes | no
Enable or disable the use of /etc/hosts.allow and /etc/hosts.deny.
default: yes
=item B<local> = host
IP of the outgoing interface is used as source for remote connections.
Use this option to bind a static local IP address, instead.
=item B<sni> = service_name:server_name (server mode)
Use the service as a slave service (a name-based virtual server) for Server
Name Indication TLS extension (RFC 3546).
I<service_name> specifies the master service that accepts client connections
with I<accept> option. I<server_name> specifies the host name to be redirected.
Multiple slave services are normally specified for a single master service.
I<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.
I<connect> option of the slave service is ignored when I<protocol> option is
specified, as I<protocol> connects remote host before TLS handshake.
Libwrap checks (Unix only) are performed twice: with master service name after
TCP connection is accepted, and with slave service name during TLS handshake.
Option I<sni> is only available when compiled with OpenSSL 1.0.0 and later.
=item B<sni> = server_name (client mode)
Use the parameter as the value of TLS Server Name Indication (RFC 3546)
extension.
Option I<sni> is only available when compiled with OpenSSL 1.0.0 and later.
=item B<OCSP> = url
select OCSP server for certificate verification
=item B<OCSPflag> = flag
specify OCSP server flag
Several I<OCSPflag> can be used to specify multiple flags.
currently supported flags: NOCERTS, NOINTERN NOSIGS, NOCHAIN, NOVERIFY,
NOEXPLICIT, NOCASIGN, NODELEGATED, NOCHECKS, TRUSTOTHER, RESPID_KEY, NOTIME
=item B<options> = SSL_options
OpenSSL library options
The parameter is the OpenSSL option name as described in the
I<SSL_CTX_set_options(3ssl)> manual, but without I<SSL_OP_> prefix.
Several I<options> can be used to specify multiple options.
For example for compatibility with erroneous Eudora SSL implementation
the following option can be used:
options = DONT_INSERT_EMPTY_FRAGMENTS
=item B<protocol> = proto
application protocol to negotiate SSL (e.g. I<starttls> or I<stls>)
I<protocol> option should not be used with SSL encryption on a separate port.
Currently supported protocols:
=over 4
=item I<cifs>
Proprietary (undocummented) extension of CIFS protocol implemented in Samba.
Support for this extension was dropped in Samba 3.0.0.
=item I<connect>
Based on RFC 2817 - I<Upgrading to TLS Within HTTP/1.1>, section 5.2 - I<Requesting a Tunnel with CONNECT>
This protocol is only supported in client mode.
=item I<imap>
Based on RFC 2595 - I<Using TLS with IMAP, POP3 and ACAP>
=item I<nntp>
Based on RFC 4642 - I<Using Transport Layer Security (TLS) with Network News Transfer Protocol (NNTP)>
This protocol is only supported in client mode.
=item I<pgsql>
Based on http://www.postgresql.org/docs/8.3/static/protocol-flow.html#AEN73982
=item I<pop3>
Based on RFC 2449 - I<POP3 Extension Mechanism>
=item I<proxy>
Haproxy client IP address http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt
=item I<smtp>
Based on RFC 2487 - I<SMTP Service Extension for Secure SMTP over TLS>
=back
=item B<protocolAuthentication> = auth_type
authentication type for protocol negotiations
currently supported: basic, NTLM
Currently authentication type only applies to 'connect' protocol.
default: basic
=item B<protocolHost> = host:port
destination address for protocol negotiations
=item B<protocolPassword> = password
password for protocol negotiations
=item B<protocolUsername> = username
username for protocol negotiations
=item B<pty> = yes | no (Unix only)
allocate pseudo terminal for 'exec' option
=item B<retry> = yes | no (Unix only)
reconnect a connect+exec section after it's disconnected
default: no
=item B<session> = timeout
session cache timeout
=item B<sessiond> = host:port
address of sessiond SSL cache server
=item B<sslVersion> = version
select version of SSL protocol
Allowed options: all, SSLv2, SSLv3, TLSv1
=item B<stack> = bytes (except for FORK model)
thread stack size
=item B<TIMEOUTbusy> = seconds
time to wait for expected data
=item B<TIMEOUTclose> = seconds
time to wait for close_notify (set to 0 for buggy MSIE)
=item B<TIMEOUTconnect> = seconds
time to wait to connect a remote host
=item B<TIMEOUTidle> = seconds
time to keep an idle connection
=item B<transparent> = none | source | destination | both (Unix only)
enable transparent proxy support on selected platforms
Supported values:
=over 4
=item I<none>
Disable transparent proxy support. This is the default.
=item I<source>
Re-write address to appear as if wrapped daemon is connecting
from the SSL client machine instead of the machine running B<stunnel>.
This option is currently available in:
=over 4
=item Remote mode (I<connect> option) on I<Linux E<gt>=2.6.28>
This configuration requires stunnel to be executed as root and without
I<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
B<stunnel> must also to be executed as root and without I<setuid> option.
=item Remote mode (I<connect> option) on I<Linux 2.2.x>
This configuration requires kernel to be compiled with I<transparent proxy> option.
Connected service must be installed on a separate host.
Routing towards the clients has to go through the stunnel box.
B<stunnel> must also to be executed as root and without I<setuid> option.
=item Remote mode (I<connect> option) on I<FreeBSD E<gt>=8.0>
This configuration requires additional firewall and routing setup.
B<stunnel> must also to be executed as root and without I<setuid> option.
=item Local mode (I<exec> option)
This configuration works by pre-loading I<libstunnel.so> shared library.
_RLD_LIST environment variable is used on Tru64, and LD_PRELOAD variable on
other platforms.
=back
=item I<destination>
Original destination is used instead of I<connect> option.
A service section for transparent destination may look like this:
[transparent]
client=yes
accept=<stunnel_port>
transparent=destination
This configuration requires the following setup for iptables
(possibly in /etc/rc.local or equivalent file):
/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>
Transparent destination option is currently only supported on Linux.
=item I<both>
Use both I<source> and I<destination> transparent proxy.
=back
Two legacy options are also supported for backward compatibility:
=over 4
=item I<yes>
This options has been renamed to I<source>.
=item I<no>
This options has been renamed to I<none>.
=back
=item B<verify> = level
verify peer certificate
=over 4
=item I<level 0> - request and ignore peer certificate
=item I<level 1> - verify peer certificate if present
=item I<level 2> - verify peer certificate
=item I<level 3> - verify peer with locally installed certificate
=item I<level 4> - ignore CA chain and only verify peer certificate
=item I<default> - no verify
=back
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 CA should be used with level 2, and not a generic CA commonly used
for webservers. Level 3 is preferred for point-to-point connections.
=back
=head1 RETURN VALUE
B<stunnel> returns zero on success, non-zero on error.
=head1 SIGNALS
The following signals can be used to control stunnel in Unix environment:
=over 4
=item SIGHUP
Force a reload of the configuration file.
Some global options will not be reloaded:
=over 4
=item * chroot
=item * foreground
=item * pid
=item * setgid
=item * setuid
=back
The use of 'setuid' option will also prevent stunnel from binding privileged
(<1024) ports during configuration reloading.
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.
=item SIGUSR1
Close and reopen stunnel log file.
This function can be used for log rotation.
=item SIGTERM, SIGQUIT, SIGINT
Shut stunnel down.
=back
The result of sending any other signals to the server is undefined.
=head1 EXAMPLES
In order to provide SSL encapsulation to your local I<imapd> service, use
[imapd]
accept = 993
exec = /usr/sbin/imapd
execargs = imapd
If you want to provide tunneling to your I<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 B<stunnel> in I<inetd> mode to launch your imapd
process, you'd use this I<stunnel.conf>.
Note there must be no I<[service_name]> section.
exec = /usr/sbin/imapd
execargs = imapd
=head1 NOTES
=head2 RESTRICTIONS
B<stunnel> cannot be used for the FTP daemon because of the nature
of the FTP protocol which utilizes multiple ports for data transfers.
There are available SSL enabled versions of FTP and telnet daemons, however.
=head2 INETD MODE
The most common use of B<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 I<exec> option.
However there is a special case when you wish to have
some other program accept incoming connections and
launch B<stunnel>, for example with I<inetd>, I<xinetd>,
or I<tcpserver>.
For example, if you have the following line in I<inetd.conf>:
imaps stream tcp nowait root /usr/bin/stunnel stunnel /etc/stunnel/imaps.conf
In these cases, the I<inetd>-style program is responsible
for binding a network socket (I<imaps> above) and handing
it to B<stunnel> when a connection is received.
Thus you do not want B<stunnel> to have any I<accept> option.
All the I<Service Level Options> should be placed in the
global options section, and no I<[service_name]> section
will be present. See the I<EXAMPLES> section for example
configurations.
=head2 CERTIFICATES
Each SSL enabled daemon needs to present a valid X.509 certificate
to the peer. It also needs a private key to decrypt the incoming
data. The easiest way to obtain a certificate and a key is to
generate them with the free I<OpenSSL> package. You can find more
information on certificates generation on pages listed below.
The order of contents of the I<.pem> 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:
-----BEGIN RSA PRIVATE KEY-----
[encoded key]
-----END RSA PRIVATE KEY-----
[empty line]
-----BEGIN CERTIFICATE-----
[encoded certificate]
-----END CERTIFICATE-----
[empty line]
=head2 RANDOMNESS
B<stunnel> needs to seed the PRNG (pseudo random number generator) in
order for SSL to use good randomness. The following sources are loaded
in order until sufficient random data has been gathered:
=over 4
=item * The file specified with the I<RNDfile> flag.
=item * The file specified by the RANDFILE environment variable, if set.
=item * The file .rnd in your home directory, if RANDFILE not set.
=item * The file specified with '--with-random' at compile time.
=item * The contents of the screen if running on Windows.
=item * The egd socket specified with the I<EGD> flag.
=item * The egd socket specified with '--with-egd-sock' at compile time.
=item * The /dev/urandom device.
=back
With recent (>=OpenSSL 0.9.5a) version of SSL 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 SSL function exists to tell when enough data is available.
Note that on Windows machines that do not have console user interaction
(mouse movements, creating windows, etc.) the screen contents are not
variable enough to be sufficient, and you should provide a random file
for use with the I<RNDfile> flag.
Note that the file specified with the I<RNDfile> flag should contain
random data -- that means it should contain different information
each time B<stunnel> is run. This is handled automatically
unless the I<RNDoverwrite> flag is used. If you wish to update this file
manually, the I<openssl rand> command in recent versions of OpenSSL,
would be useful.
One important note -- if /dev/urandom is available, OpenSSL has a habit of
seeding the PRNG with it even when checking the random state, so on
systems with /dev/urandom you're likely to use it even though it's listed
at the very bottom of the list above. This isn't B<stunnel's> behaviour, it's
OpenSSLs.
=head2 DH PARAMETERS
Stunnel 4.40 and later contains hardcoded 2048-bit DH parameters.
It is also possible to specify DH parameters in the certificate file:
openssl dhparam 2048 >> stunnel.pem
DH parameter generation may take several minutes.
=head1 FILES
=over 4
=item F<stunnel.conf>
B<stunnel> configuration file
=back
=head1 BUGS
Option I<execargs> does not support quoting.
=head1 SEE ALSO
=over 4
=item L<tcpd(8)>
access control facility for internet services
=item L<inetd(8)>
internet 'super-server'
=item F<http://www.stunnel.org/>
B<stunnel> homepage
=item F<http://www.openssl.org/>
OpenSSL project website
=back
=head1 AUTHOR
=over 4
=item Michał Trojnara
<F<Michal.Trojnara@mirt.net>>
=back
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