Attack on the Koyama-Ohta Identity Based Key Distribution Scheme
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.