Security Benefits (continued)

Host Authentication
A host key is used by a server to prove its identity to a client and by a client to verify a "known" host. Host keys are described as persistent (they are changed infrequently) and are asymmetric—much like the public/private key pairs discussed above in the Public key section. If a machine is running only one SSH server, a single host key serves to identify both the machine and the server. If a machine is running multiple SSH servers, it may either have multiple host keys or use a single key for multiple servers. Host authentication guards against the Man-in-the-Middle attack. Host keys are often confused with session keys, which are used in the data encryption process discussed below.