SSHrelated

SSH-related refers to topics and technologies surrounding the Secure Shell (SSH) protocol and its ecosystem. SSH provides encrypted remote access to systems and secure transfer of data over insecure networks. The term encompasses protocol specifications, software implementations, authentication methods, key management, and related utilities that enable secure administration, file transfer, and tunneling.

The current widely used version is SSH-2, defined by RFCs 4250–4254. SSH-1, an older version, is considered insecure and deprecated. SSH offers strong crypto, mutual authentication, and session encryption to protect confidentiality and integrity of communications.

Common implementations include the OpenSSH project (server: sshd; client: ssh), Dropbear, and libssh-based libraries. Client programs such as the OpenSSH client or PuTTY, and libraries used by scripting languages (Paramiko, Netmiko) enable automated access. Server configurations are typically controlled by sshd_config.

Core concepts include public-key authentication, with key pairs stored in ~/.ssh and authorized_keys on the server. Tools such as ssh-keygen create keys, ssh-agent and ssh-add manage keys, and known_hosts verifies remote hosts. Client-side and server-side configurations reside in ssh_config and sshd_config respectively.

SSH supports features such as port forwarding (local, remote, and dynamic), X11 forwarding, and secure file transfer via SCP or SFTP. It also enables tunneling to bypass certain network restrictions and to secure application-layer protocols.

Security best practices emphasize using key-based authentication with a passphrase, disabling password login, restricting root access, keeping software updated, and monitoring host keys and access logs. Strong, modern key types (ed25519, RSA with adequate length) are recommended.