An SSH private key is the secret half of an SSH key pair used to prove identity to remote systems. Unlike a password, it is a file that must remain confidential; anyone who gets a copy can often authenticate as that user to servers, Git hosts, or automation systems. Common examples include files such as id_ed25519 or id_rsa.
In cyber security, private keys are high-value targets because they can enable direct login and lateral movement without triggering password resets. Attackers try to steal them from compromised endpoints, backup folders, build servers, or overly broad application sandboxes. Defenders reduce risk by limiting file access, using strong passphrases, storing keys in hardware-backed tools when possible, rotating exposed keys quickly, and preferring short-lived SSH certificates or other temporary credentials over long-lived private keys.