This document defines protocols@ procedures@ and conventions to be employed by peers implementing the Generic Security Service Application Program Interface (GSS-API) when using the Kerberos Version 5 mechanism. RFC 1964 is updated and incremental changes are proposed in response to recent developments such as the introduction of Kerberos cryptosystem framework. These changes support the inclusion of new cryptosystems@ by defining new per-message tokens along with their encryption and checksum algorithms based on the cryptosystem profiles.