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The Shell Game
An introduction to Secure SHell technology.

| Introduction |

If you've been using the Internet for any length of time, you'll be aware of the immense power this network of connected computers gives you. It allows you, for example, to access your email from anywhere in the world, to share data between users in different countries, and - in one memorable example - to participate in a live birth from a million miles away!

By allowing you to connect to, or "telnet" into, remote computers, the Internet also puts tremendous computing power at your disposal. Telnet allows you to remotely administer computers, to gain access to their information and computing power they possess, and to use that information and horsepower to solve your own problems in a faster, more efficient manner.

However, telnet is a relatively insecure way of working over the Internet. A telnet connection is typically unencrypted, and offers experienced hackers - or bored twelve-year-olds - a number of opportunities to tap into your connection and siphon off information from the data stream flowing back and forth. What is needed is a more secure communication protocol, one which is immune to IP-based attacks, and which uses hard-to-crack cryptographic techniques to protect the data it carries.


Like telnet, SSH is a program designed to let you log in to other computers on a network. However, unlike telnet, all the data flowing back and forth in an SSH session is encrypted, and thus secured from hackers attempting to eavesdrop on the connection. Passwords, for example, are sent over a telnet connection in clear-text, and are vulnerable to interception - however, SSH always encrypts data transmissions and thus secures sensitive information from falling into the hands of others.

SSH also offers numerous improvements to the other remote login programs - rlogin, rsh and rcp. Where rlogin and rsh depend on a flat file to establish whether or not to allow remote hosts and users access, SSH relies on public/private key authentication to avoid the use of IP-spoofing or DNS-based attacks.

Finally, SSH allows X11 forwarding, allowing the encryption of all X11 data, and TCP port forwarding, which makes it possible to communicate with other ports on the remote system [and systems that may be further connected to it] via the secure SSH channel, as well.

Sounds like a system administrator's dream come true? You're not far wrong...

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