Identity-based Conference Key Distribution Systems
CRYPTO '87 A Conference on the Theory and Applications of Cryptographic Techniques on Advances in Cryptology
Security of improved identity-based conference key distribution systems
Lecture Notes in Computer Science on Advances in Cryptology-EUROCRYPT'88
CRYPTO '89 Proceedings on Advances in cryptology
A Secure Fault-Tolerant Conference-Key Agreement Protocol
IEEE Transactions on Computers
Round-Efficient Conference Key Agreement Protocols with Provable Security
ASIACRYPT '00 Proceedings of the 6th International Conference on the Theory and Application of Cryptology and Information Security: Advances in Cryptology
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Koyama and Ohta proposed an identity based key distribution scheme. They considered three configurations: ring, complete graph, and star. The most practical configuration is the star which is used in teleconferencing. We show the Koyama-Ohta star scheme to be insecure. Specifically, we show that an active eavesdropper may cut one of the lines, and perform a bidirectional impersonation, thus establishing two separate keys. One with each side.