OpenSSH

OpenSSH is a free implementation of the Secure Shell protocol, enabling secure encrypted communications between untrusted hosts. The client tools like ssh, scp, and sftp allow logging into remote machines, executing commands, and transferring files securely. X11 connections and TCP/IP ports can be forwarded over the secure channel, replacing obsolete insecure programs like rsh, rcp, and rlogin.

Key utilities such as ssh-agent, ssh-add, ssh-keygen, ssh-keyscan, ssh-copy-id, and ssh-argv0 facilitate public key authentication and key management. The server package provides sshd for hosting secure access from remote machines, with additional modules like openssh-sftp-server for SFTP support. GSS-API variants are available for Kerberos integration.

Note that in some countries, encryption use may require special permits. The metapackage 'ssh' installs both client and server for convenience.

OpenSSH implements the IETF secsh Secure Shell protocol, providing encrypted communications via ciphers, MACs, and key exchange. SSH clients connect to sshd servers, authenticating via passwords or public keys managed by ssh-agent. Port forwarding tunnels traffic securely, while SFTP implements SSH filexfer protocol revision 3. Keys are generated and scanned using specified algorithms like RSA, ECDSA, Ed25519.