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SSH (Secure Shell)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

SSH is a "secure shell," which means it provides encrypted "virtual" terminal (Telnet) and file transfer sessions. It also supports authenticated remote logon. It is designed to replace UNIX commands such as rlogin, rsh, and rcp, which have been found to be vulnerable to attacks. SSH provides the mechanisms that allow clients and servers to negotiate secure connections. SSH can create secure remote X sessions for X Window System users.

The protocol was originally developed by Tatu Ylönen, who went on to start SSH Communications Security, now the primary supporter of SSH products. Other vendors, such as F-Secure and Van Dyke Corporation, implement SSH in their security products. SSH is available for Microsoft Windows, UNIX platforms, and other platforms.

SSH provides confidentiality through the support of encryption techniques such as DES, Triple-DES, IDEA, BlowFish, TwoFish, and CAST. Authentication and integrity is provided by passwords or public keys (DSA and RSA), or via Kerberos. Smart cards and token-based authentication are also supported.

Multiple SSH connections can be cascaded so an authenticated user can make secure connections to multiple hosts on a network through the same tunnel. Thus, a remote user can connect to a corporate network and access e-mail, file servers, and other services.

Two versions exist: SSH1 and SSH2. According to SSH Communication Security, SSH1 should be replaced with SSH2 to achieve improved flexibility, better scalability to organizations with thousands of users, and better security. Information about SSH2 is available at the company's Web site listed on the related entries page.

The IETF's secsh (Secure Shell) Working Group was working on SSH and SSH2, but the drafts that were developed are no longer up on the Web site and no RFCs have come out of this group.

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.