editor This document specifies a mechanism for Mobile IP network access authentication and key distribution using the GSM Subscriber Identity Module (SIM). The mechanism uses new subtypes of the generalized key distribution extensions [1] for Mobile IP Registration Request and Registration Reply. After the registration keys have been generated, the default Mobile IP authentication with these keys can be used (MD5 in prefix + suffix mode). The keys can be used for several subsequent registrations. However, there are lifetimes for the keys and before the lifetimes expire, new keys can be generated with the same procedure.