Efficient time-bound hierarchical key assignment scheme

The access privileges in distributed systems can be effectively organized as a hierarchical tree that consists of distinct classes. A hierarchical time-bound key assignment scheme is to assign distinct cryptographic keys to distinct classes according to their privileges so that users from a higher class can use their class key to derive the keys of lower classes, and the keys are different for each time period; therefore, key derivation is constrained by both the class relation and the time period. We propose, based on a tamper-resistant device, a new time-bound key assignment scheme that greatly improves the computational performance and reduces the implementation cost.