1. An RSA-Based Time-Bound Hierarchical Key Assignment Scheme for Electronic Article Subscription

2. Electronic Article Subscription ACM publishes lots of journals periodically Different packages of journals for subscription options Users subscribe packages for different time periods Only subscribed users can access the journals published in the time periods the users subscribed to

3. Electronic Article Subscription The journals can be just posted online, but encrypted Each journal is encrypted by a different key Each user has one user key The user key can be used to decrypt only the journals the user are entitled to access

4. Key Assignment All packages can be structured as a hierarchy If a user subscribes a package p_i for time periods from t_1 to t_2, then a user key K_i,(t_1,t_2) will be assigned to the user Each journal belong to package p_j, published in time t, will be encrypted by a key K_j,t

5. Key Derivation K_i,(t_1,t_2) can derive K_j,t if and only if P_i is a higher package than P_j and t_1 ≤ t ≤ t_2

6. An Example