This document specifies a negotiation mechanism for the Generic Security Service Application Program Interface (GSS-API)@ which is described in RFC 2743. GSS-API peers can use this negotiation mechanism to choose from a common set of security mechanisms. If per-message integrity services are available on the established mechanism context@ then the negotiation is protected against an attacker that forces the selection of a mechanism not desired by the peers. This mechanism replaces RFC 2478 in order to fix defects in that specification and to describe how to inter-operate with implementations of that specification that are commonly deployed on the Internet.