IETF RFC 4256 PDF

The Secure Shell Protocol (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes a general purpose authentication method for the SSH protocol, suitable for interactive authentications where the authentication data should be entered via a keyboard (or equivalent alphanumeric input device). The major goal of this method is to allow the SSH client to support a whole class of authentication mechanism(s) without knowing the specifics of the actual authentication mechanism(s).