This paper describes the support provided for mobility and fault tolerance in Mykil, which is a key distribution protocol for large, secure group multicast. Mykil is based on a combination of group-based hierarchy and key-based hierarchy systems. Important advantages of Mykil include a fast and efficient rekeying operation for large group sizes, continuous availability of the key management service in a disconnected network environment, an ability to map group structure to the underlying network infrastructure, fault tolerance, and support for member mobility and smaller hand-held devices.