An Improved Time-Bound Hierarchical Key Assignment Scheme

Recently, Chien proposed a time-bound hierarchical key assignment scheme based on tamper-resistant devices. Chien´s scheme greatly reduces computation load and implementation cost. However, it has a security weakness against X. Yi´s three-party collusion attack. In this paper, we improved Chien´s scheme without public key cryptography and our scheme is resistant to X. Yi´s three-party collusion attack. The most important is that our scheme is as efficient as Chien´s. Finally, we have made an experiment to verify our conclusion.