SSH

SSH (Secure Shell) is a cryptographic network protocol, used for operating network services securely over an unsecured network. Its primary applications include remote command-line login and execution, but it also supports tunneling (port forwarding), file transfers (via SFTP and SCP), and other secure network services. SSH operates on a client-server model. The SSH client initiates a connection to an SSH server, typically running on the standard port 22. During the connection setup, the client and server negotiate cryptographic algorithms (for key exchange, encryption, message authentication, and host authentication) and establish a secure, encrypted channel. Host authentication is typically achieved using [public-key cryptography](/ru/terms/public-key-cryptography), where the server presents its public host key, which the client verifies against a known list or a trusted Certificate Authority. User authentication can be performed using passwords, public-key cryptography (SSH keys), or other methods like keyboard-interactive authentication. Once authenticated, all subsequent traffic between the client and server is encrypted, protecting data confidentiality and integrity.