Improving the Efficiency of a Highly-Used Access Control Scheme

A flexible access control scheme, which was proposed by Chick et al. in CRYPTO89, has been applied to several essential cryptographic techniques (broadcast encryptions etc.) because of its high expandability. However, their scheme and all of its applications requires a lot of primes whose generation is costly. In this paper, we show how to replace the primes with a particular kind of hash values that makes the protocol dramatically efficient without loss of security or robustness. Moreover, this efficiency and flexibility creates a new possibility for privacy applications especially in dynamic environments.