This work presents a set of fundamental protocols for building secure information distribution systems. Applications include wireless broadcast, IP multicast, sensor networks and webs, ad hoc networks and satellite broadcast. The book presents and compares techniques for basic operations including: key distribution for access control; source authentication of transmissions; and non-repudiation of streams. It discusses how to realize these operations both with high performance processors and resource constrained processors, and shows how to protect against adversaries who inject packets or eavesdrop. The focus is on functional descriptions rather than theoretical discussions. Protocols are presented as basic building blocks that can be combined with each other and traditional security protocols. The book illustrates these protocols in practice by presenting a real implementation that provides security for an ad hoc sensor network. The book can serve as a textbook or supplementary reading in graduate level courses on security or networking, or can be used for self study.