The Secure Socket Shell (SSH) protocol is an authentication protocol (described in RFC 4252) for securely getting access to a remote computer.
It is widely used to control servers remotely. SSH is actually a suite of three utilities — slogin, ssh, and scp — which are are secure versions of 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 uses RSA public key cryptography for both connection and authentication. Encryption algorithms include Blowfish, DES, and IDEA. IDEA is the default.