In this paper we present 411, a password distribution system for high performance environments that provides security and scalability. We show that existing solutions such as NIS and Kerberos do not provide sufficient performance in large, tightly coupled systems such as computational clusters. Unlike existing single-signon services, the 411 design removes the need for communication during password lookup by using aggressive replication techniques. We demonstrate the use of shared keys to efficiently protect user information, and the careful management of system wide consistency and fault tolerance. A theoretical analysis of the behavior of 411 is matched with quantitative evidence of its performance and suitability to a clustered environment. We further show the system effectively responds to stress by simulating 50% message loss on a 60-node cluster. This protocol is currently used worldwide in hundreds of Rocks-based production systems to provide password and login information service.