Secure shell

From Academic Kids

Internet protocol suite   edit  (
Application layer HTTP, HTTPS, SMTP, FTP, UUCP, NNTP,
SSH, IRC, SNMP, SIP, RTP, Telnet ,...
Transport layer TCP, UDP, SCTP, DCCP, ...
Network layer IPv4, IPv6, ICMP, ARP, IGMP, ...
Data link layer Ethernet, Wi-Fi, Token ring, FDDI, PPP, ...
Physical layer RS-232, EIA-422, RS-449, EIA-485...

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 networked computer. The designers of SSH aimed to replace the earlier rlogin, telnet and rsh protocols, and the resultant protocol provides secure encrypted communications between two untrusted hosts over an insecure network. Users of SSH can also use it for tunnelling, forwarding X11 connections and arbitrary TCP ports over the resultant secure channel; and can transfer files using the associated scp or sftp programs. An ssh server, by default, listens on the standard TCP port 22.

Tatu Ylönen from Espoo, Finland, designed the first version of the protocol (now called SSH-1) in 1995 and also wrote the first software to utilise it. He soon formed a company called SSH Communications Security to market this innovation. The original version of the SSH software 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 (formerly known as Data Fellows). SSH Secure Communications has a USA subsidiary in Palo Alto, California.

A later version of the protocol appeared under the name SSH-2. The IETF "secsh" working group has started to standardise SSH-2, which features both security and feature improvements over SSH-1. Better security, for example, comes through Diffie-Hellman key exchange and strong integrity checking via MACs. New features of SSH-2 include the ability to run any number of shell sessions over a single SSH connection. [1] (

The ssh program commonly appears for use in Unix shells for client connections. It generally links to by a daemon such as sshd for accepting remote connections. Implementations of SSH exist for most modern platforms, including Microsoft Windows (PuTTY has become a very popular Windows implementation) and Mac OS. Commercial versions, freeware versions, and open source versions all exist.


List of implementations

See also


  • Daniel J. Barrett, Richard E. Silverman, and Robert G. Byrnes — SSH: The Secure Shell (The Definitive Guide), O'Reilly 2005 (2nd</sub> edition). ISBN 0-596-00895-3 [8] (

External links

  • SSH Communications Security (
  • Info about SSH (
  • IETF working group ( (for SSH-2)
  • Connect.c ( consists of a small C program which enables users to run SSH over HTTPS proxy servers.
  • Proxytunnel (, another program, offers more generic capabilities.
  • autossh (, Automatically restarts SSH sessions and tunnels

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
de:Secure Shell

es:SSH fr:Secure shell it:Secure shell he:SSH nl:SSH ja:Secure Shell no:SSH pl:SSH pt:SSH ru:SSH fi:SSH sk:Secure Shell sl:SSH


Academic Kids Menu

  • Art and Cultures
    • Art (
    • Architecture (
    • Cultures (
    • Music (
    • Musical Instruments (
  • Biographies (
  • Clipart (
  • Geography (
    • Countries of the World (
    • Maps (
    • Flags (
    • Continents (
  • History (
    • Ancient Civilizations (
    • Industrial Revolution (
    • Middle Ages (
    • Prehistory (
    • Renaissance (
    • Timelines (
    • United States (
    • Wars (
    • World History (
  • Human Body (
  • Mathematics (
  • Reference (
  • Science (
    • Animals (
    • Aviation (
    • Dinosaurs (
    • Earth (
    • Inventions (
    • Physical Science (
    • Plants (
    • Scientists (
  • Social Studies (
    • Anthropology (
    • Economics (
    • Government (
    • Religion (
    • Holidays (
  • Space and Astronomy
    • Solar System (
    • Planets (
  • Sports (
  • Timelines (
  • Weather (
  • US States (


  • Home Page (
  • Contact Us (

  • Clip Art (
Personal tools