Secure Shell (SSH) is a cryptographic network protocol for operating network services securely over an ( 71 ) network, Typical applications include remotecommand-line, login, and remote command execution, but any network service can be secured with SSH. The protocol works in the ( 72 ) model，which means that the connection in established by the SSH client connecting to the SSH server.The SSH client drives the connection setup process and uses public key cryptography to verify the ( 73 ) of the SSH server. After the setup phase the SSH protocol uses strong ( 74 ) encryption and hashing algorithms to ensure the privacy and integnity of the data that is exchanged between the client and server. There are serveral options that can be used for user authentication.The most common ones are passwords and (75 ) key authentication.