Using SSH over Telnet

What is SSH?

SSH (Secured Shell) is a protocol which allows users to communicate with a remote system securely. All communication between the systems is encrypted to prevent a sniffer from getting any sensitive information.

How does it work (Host keys) ?

SSH uses a public and private key on each system. The first time a user uses SSH to connect to a remote system, their SSH client program exchanges the public keys, unless keys have been exchanged manually. If keys are exchanged over the network during the first connection, user is essentially trusting the security of network during the key exchange.

On subsequent connections to the same system, SSH program will check that the keys haven't changed, to ensure that it is still the same system.

Why use SSH?

Telnet on the other hand communicates without any encryption, allowing a sniffer to capture information, e.g. passwords.

As a system administrator you may consider shutting down telnet services from your servers, and forcing your users to use SSH instead. All major operating systems have ssh clients, so this won't be an invconvenience to your users.

SSH Client Programs:

Linux/UNIX and Mac OS X: ssh command
Windows: PuTTY, SecureCRT
Mac OS 8/9: NiftyTelnet SSH