SSH: As already noted, SSH is an encrypted secure remote login protocol, which uses port 22 by default. Telnet: Like rlogin, Telnet (telecommunication network) is an unencrypted remote login protocol. It typically uses port 23 and is available on many systems other than UNIX.What is SSH public key authentication?
The key-based authentication mechanism in SSH is called public key authentication. Essentially, some session-specific data is signed using the private identity key. The signature is then sent to the server that checks if the key used for signing is configured as an authorized key.