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In computing, Secure shell, or SSH, is both
a computer program and an associated network protocol designed for logging into and executing commands on a
remote computer. It is intended to replace the earlier rlogin, telnet and rsh protocols, and
provides secure encrypted communications between two untrusted hosts over an insecure network. X11
connections and arbitrary TCP ports can
also be forwarded over the secure channel.
The first version was written by Tatu Ylönen from Espoo, Finland in 1995. He soon formed a company called SSH Communications
Security Oy to exploit this innovation. The original version of SSH used various pieces of free software, such as GNU libgmp, but later versions released by SSH Secure Communications evolved
into increasingly proprietary software. SSH Communications
Security subsequently relicensed SSH to F-secure Oy (formerly known as Data Fellows Oy). SSH Secure
Communications has a USA subsidiary in Palo Alto,
California.
The program is a common Unix shell
program for client connections, accompanied by a daemon for accepting remote connections. Implementations exist for most modern platforms,
including Microsoft Windows (where one of the most popular is
PuTTY) and Mac OS. There are commercial
versions, freeware versions, and open source versions.
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. OpenSSH
derives from the original, free implementation of SSH.
The GNU Project has its own implementation of SSH, lsh.
An IETF working group, "secsh", is currently in the process of standardizing the
protocol.
External links
This article (or an earlier version of it) contains material from FOLDOC, used
with permission.
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