18.2. SSH Protocol Versions

The SSH protocol allows any client and server programs built to the protocol's specifications to communicate securely and to be used interchangeably.

Two varieties of SSH currently exist. SSH version 1 makes use of several patented encryption algorithms (however, some of these patents have expired) and is vulnerable to a security hole that potentially allows an attacker to insert data into the communication stream. The OpenSSH suite under Red Hat Linux uses SSH version 2 by default, although it also supports version 1.


It is recommended that only SSH version 2-compatible servers and clients are used whenever possible.