This two-year award supports U.S.-U.K. cooperative research in communications and network security between Yvo Desmedt of the University of Wisconsin, Milwaukee and Michael Burmmester and Frederick Piper of the University of London. The project is concerned with the possibility of communicating unintended secret messages in multi-sender and multi-receiver networks. The objective is to design secure communications and network systems to protect against abuses in cryptographic protocols. Dr. Desmedt brings to this collaboration his background in theoretical computer science and his understanding of practical issues in communication network systems. His recent research, in cooperation with the British investigators, has shown that a geometric approach to these problems could be useful for developing abuse-free cryptosystems and subliminal free authentication communication channels. British expertise in finite geometry and applications to multi-user network security complements Dr. Desmedt's background. Multi-user network security is likely to grow in importance with the development of large voice and data networks and their worldwide availability. Information security and protection of privacy are important issues in this area. This project offers an innovative geometric approach and possible solutions to these problems.