Remote Secure Shell servers are authenticated by a public-key procedure. The client trusts the server if it has a private key that matches one of the public keys in the global hostkeys directory or in the user's hostkeys directory. When a server presents a key that is not in the hostkeys directories, the user checks the fingerprint of the remote server's public key. When the user has approved the public key, it is stored in the user's
$HOME/.ssh2/hostkeys directory and will be used automatically thereafter.
The verification step requires user interaction, so even for users that are set up to run client programs unattended, the first connection must be done by a person who logs in as the user, accesses the remote server, and goes through the fingerprint check dialog. The same steps must be repeated if the remote host's key is changed.
For more information on server authentication, see Server Authentication with Public Keys in File and Tectia Server for IBM z/OS User Manual.