What does 'SSH' stand for?

SSH stands for Secure Shell. It is a cryptographic network protocol that lets users securely log in to remote computers, execute commands, and transfer data across an untrusted network.

Finnish computer scientist Tatu Ylönen created SSH in 1995 after a password-sniffing attack at Helsinki University of Technology. It was designed as a safer replacement for older tools such as Telnet, rlogin, and rsh, which could transmit credentials or other information in plaintext. SSH encrypts the connection and uses authentication mechanisms such as passwords or public-key cryptography.

SSH is more than a remote-login command. Its protocol has separate layers for transport security, user authentication, and multiplexed connections. It can also support port forwarding, tunneling, SFTP, SCP, and automated server administration. TCP port 22 is the conventional port for SSH; Ylönen chose it because it sits between Telnet’s port 23 and FTP’s port 21.

SSH is the protocol, while OpenSSH is a widely used open-source implementation.