Secure Shell (SSH), known as Secure Socket Shell, is a UNIX-based command interface and protocol for securely getting access to a remote computer. It is widely used by network administrators to control Web and other kinds of servers remotely.
SSH is actually a suite of three utilities-slogin, ssh, and scp- that are secure versions of the earlier UNIX utilities, rlogin, rsh, and rcp. SSH commands are encrypted and secure in several ways. Both ends of the client/server connection are authenticated using a digital certificate and passwords are protected by being encrypted. SSH used RSA public key cryptography for both connection and authentication. Encryption algorithms include Blowfish, DES, and IDEA. IDEA is the default. The SSH feature is primarily for advanced users with a working knowledge of UNIX.