Configuring key-based SSH authentication (ssh-keygen, ssh-copy-id, ~/.ssh permissions, sshd_config)

SSH (Secure Shell) key authentication replaces a typed password with a key pair. The private key stays on your client; the public key is copied to the server. When you connect, the server challenges the client to prove it holds the matching private key, and the private key itself never crosses the network. Keys resist password guessing, allow automation, and are expected on the RHCSA whenever a task says passwordless login.