Secure shell

Secure shell or SSH is both a program and a network protocol for logging
into and executing commands on a remote computer. It is intended to replace
rlogin, telnet and rsh, and provides secure encrypted communications between
two untrusted hosts over an insecure network. X11 connections and arbitrary
TCP/IP ports can also be forwarded over the secure channel.

The program is a common Unix shell program, but there exists implementations
for most modern platforms, including Microsoft Windows (where one of the
most popular is PuTTY) and Mac OS.

A later version of the protocol was released under the name SSH2.

OpenSSH is an open source implementation of SSH. Corkscrew is a tool
enabling the user to run SSH over HTTPS proxy servers.

An IETF working group, secsh, is currently in the process of standardizing
the protocol.