—PhoneFactor is a two-factor authentication service that combines the knowledge-based authenticator with an objectbased authenticator in which the object-based authenticator has advantages of hardware token-based systems without requiring the administration overhead of distribution of special hardware to every user in advance. For transaction scalability of this service, we propose a Distributed Real-Time Transaction Memory Cache (DReaM-Cache) approach. In this paper, we present the basic architecture and present reliability models for different data centers and node reliability factors, and show how reliability can be accomplished.