SSH: Secure Shell is a low level secure protocol. Its meant to replace telnet, rlogin, rsh and rcp also ssh2 as a replacement for ftp:sftp. It encrypts passwords and other data.
SSH consists of:
1) Transport lyaer protocol (ssh-trans) provides secure authentication,cont, net integrity
2) User authentication protocol (ssh-userAuth) authenticate the client-side user to the server runs over transport layer protocol.
3) The connection protocol (SHH-conn) Multiplexes the encrypted tunnel into several logical channels. It runs over the user authentication protocol.
SSH uses public key encyption as the main metod for a user authentication but rhosts/shosts authentication can be used as well.
SSH provides protection from:
1) packet spoofing
2) IP/Host Spoofing
3) Password Sniffing
4) Eaves dropping