It provides strong authentication and secured communication channels between the local and the remote machines, protecting any data sent between these machines by means of encryption.
Secure shell provides several security improvements over the telnet and rlogin protocols.
In particular, passwords are never sent over the network in a cleartext format as they are when using either telnet or rlogin. This prevents anyone who is surreptitously monitoring network traffic from stealing passwords, which could then be used to obtain access to accounts other than their own. All connections between the local and the remote hosts are encrypted, protectecting the data sent between these machines from the same type of snooping mentioned above. Although the most common use of SSH is for logging into remote computers, it can be used to tunnel unsecure protocols over encrypted connections. Many departments on campus also allow SSH connections to their computers.