sslh/README

===== sslh -- A ssl/ssh multiplexer. =====

sslh lets one accept both HTTPS and SSH connections on the
same port. It makes it possible to connect to an SSH server
on port 443 (e.g. from inside a corporate firewall) while
still serving HTTPS on that port. 

==== Compile and install ====

If you're lucky, the Makefile will work for you:

make install

(see below for configuration hints)


Otherwise:

Compilation instructions (the binary produced won't contain
the version number, which is stored only in the Makefile)

Solaris:
  cc -o sslh sslh.c -lresolv -lsocket -lnsl

LynxOS:
  gcc -o tcproxy tcproxy.c -lnetinet

Linux:
  cc -o sslh sslh.c -lnet
or:
  cc -o sslh sslh.c

To compile with libwrap support:
  cc -o sslh -DLIBWRAP sslh.c -lwrap

To install:

make
cp sslh /usr/local/sbin
cp scripts/etc.default.sslh /etc/default/sslh

For Debian:
cp scripts/etc.init.d.sslh /etc/init.d/sslh
For CentOS:
cp scripts/etc.rc.d.init.d.sslh /etc/rc.d/init.d/sslh

and probably create links in /etc/rc<x>.d so that the server
start automatically at boot-up, e.g. under Debian:
update-rc.d sslh defaults



==== Configuration ====

You can edit settings in /etc/default/sslh:

LISTEN=ifname:443
SSH=localhost:22
SSL=localhost:443

A good scheme is to use the external name of the machine in
$LISTEN, and bind httpd to localhost:443 (instead of all
binding to all interfaces): that way, https connections
coming from inside your network don't need to go through
sslh, and sslh is only there as a frontal for connections
coming from the internet.

Note that 'external name' in this context refers to the
actual IP address of the machine as seen from your network,
i.e. that that is not 127.0.0.1 in the output of
ifconfig(8).

==== Libwrap support ====

Sslh can optionnaly perform libwrap checks for the sshd
service: because the connection to sshd will be coming
locally from sslh, sshd cannot determine the IP of the
client.

==== OpenVPN support ====

OpenVPN clients reportedly take more than one second between
the time the TCP connexion is established and the time they
send the first data packet. This results in sslh with
default settings timing out and assuming an SSH connexion.
To support OpenVPN connexions reliably, it is necessary to
increase sslh's timeout to 5 seconds.

==== IP_TPROXY support ====

There is a netfilter patch that adds an option to the Linux
TCP/IP stack to allow a program to set the source address
of an IP packet that it sends. This could let sslh set the
address of packets to that of the actual client, so that
sshd would see and log the IP address of the client, making
sslh transparent.

This is not, and won't be, implemented in sslh for the
following reasons (in increasing order of importance):

  * It's not vital: the real connecting IP address can be
    found in logs. Little gain.
  * It's Linux only: it means increased complexity for no
    gain to some users.
  * It's a patch: it means it'd only be useful to Linux
    users who compile their own kernel.
  * Only root can use the feature: that's a definite no-no.
    Sslh should not, must not, will never run as root.

This isn't to mean that it won't eventually get implemented,
when/if the feature finds its way into the main kernel and
it becomes usuable by non-root processes.


Comments? questions? sslh@rutschle.net