The Secure Shell Protocol ( SSH ) is a cryptographic network protocol
for operating network services securely over an unsecured network. Its most
notable applications are remote login and command-line execution.
SSH applications are based on a client–server architecture, connecting an SSH
client instance with an SSH server. SSH operates as a layered protocol suite
comprising three principal hierarchical components: the transport layer
provides server authentication, confidentiality, and integrity; the user
authentication protocol validates the user to the server; and the connection
protocol multiplexes the encrypted tunnel into multiple logical communication
channels.