Key exchange method, key exchange system, communication device and storage medium therefore

Abstract

Plurality of users share a common key while permitting dynamic member change and computational complexity required for key exchange is reduced. The first key generation unitof the communication devices Ucomputes Rand c, or cbased on a twisted pseudo-random function. A session ID generation unitof a key distribution device S generates sid based on a target-collision resistant hash function and transmits sid to the communication devices U. A second key generation unitof the communication devices Ucomputes Tbased on a pseudo-random function. A third key generation unitof the key distribution device S computes k' and T′based on the twisted pseudo-random function. A session key generation unitof the communication devices Ugenerates the common key Kbased on a pseudo-random function.