sslhp - Online in the Cloud

PROGRAM:

NAME

sslh - Switch incoming connection between SSH and SSL/HTTPS servers

SYNOPSIS

sslh [ -v ] [ -p [host:]port ] [ -t timeout ]
[ --ssh [host:]port ] [ --ssl [host:]port ]

DESCRIPTION

sslh is a simple script that lets you switch an incoming connection on a single port
between distinct SSH and SSL/HTTPS servers.

sslh listens for connections on a port and is able to redirect them either to an HTTPS web
server or a SSH server.

This lets one setup both a HTTPS web server and a SSH server and access them through the
same host+port.

OPTIONS

The program follows the usual GNU command line syntax, with long options starting with two
dashes.

-p, --port [host:]port
The port the proxy will listen to. If no port is given, 443 is used by default. If
no host is given, "localhost" is used by default.

-s, --ssh [host:]port
The SSH server which the SSH connections must be forwarded to. If omitted, the
default is localhost:22.

-l, --ssl, --https [host:]port
The HTTPS server which the HTTPS connections must be forwarded to. If omitted, the
default is localhost:443.

-t, --timeout delay
Timeout in seconds before a silent incoming connection is considered as a SSH
connection. The number can be fractional.

The default is 2seconds.

-v, --verbose
Verbose output. This option can be used several times for more verbose output.

EXAMPLE OF USE

Is this tool actually useful? Yes.

For example one can use it to access both a SSH server and a secure web server via a
corporate proxy that only accepts to relay connections to port 443. Creating a tunnel that
passes SSH connection through a CONNECT-enabled web proxy is easy with connect-tunnel
(also included in the "Net::Proxy" distribution).

The proxy will let both SSH and HTTPS connections out (since they all point to port 443),
and the home server will connect those incoming connections to the appropriate server.
This only requires to run the HTTPS server on a non standard port (not 443).

TECHNICAL NOTE

How can this proxy find out what kind of protocol is using a TCP connection to port 443,
without being connected (yet) to the server? We actually rely on a slight difference
between the SSL and SSH protocols (found thanks to ethereal):

SSH Once the TCP connection is established, the server speaks first, presenting itself by
saying something like:

SSH-2.0-OpenSSH_3.6.1p2 Debian 1:3.6.1p2-1

SSL With SSL, it's always the client that speaks first.

This means that sslh can be used with any pair of protocols/services that share this
property (the client speaks first for one and the server speaks first for the other).

AUTHORS

Original idea and C version
Frederic Ple "<[email protected]>".

Perl versions
Philippe 'BooK' Bruhat "<[email protected]>".

SCRIPT HISTORY

Version 0.01 of the script was a quick hack designed in 2003 as a proof of concept.

Version 0.02 (and higher) are based on "Net::Proxy", and included with the "Net::Proxy"
distribution. Version 0.02 didn't work, though.

Version 0.03 correctly initialised the "in" connector.

Version 0.04 lets the proxy listen on any address (instead of "localhost", which is still
the default). Thanks to Dieter Voegtli for spotting this.

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