hostkey

HostKey is a term commonly used in computer security, particularly within the context of secure network protocols like SSH (Secure Shell). A HostKey is essentially a digital certificate or public key that uniquely identifies a server or host. When a client connects to a server for the first time, the server presents its HostKey to the client. The client then verifies this HostKey against a known list of trusted keys or prompts the user to confirm its authenticity.

The primary purpose of a HostKey is to prevent man-in-the-middle attacks. In such an attack, an unauthorized third party intercepts communication between a client and a server. By verifying the HostKey, the client ensures that it is connecting to the legitimate server and not an imposter. If the HostKey presented by the server does not match the one stored by the client, it indicates a potential security breach, and the client will typically issue a warning or refuse the connection.

HostKeys are usually stored on the client machine in a file, often named known_hosts. This file maintains a record of the HostKeys for servers that the client has previously connected to and authenticated. When a subsequent connection is made, the client checks the presented HostKey against the entry in the known_hosts file. If a mismatch occurs, it signifies that the server's identity may have changed, potentially due to a security incident. This mechanism is crucial for establishing and maintaining trust in remote server connections.