Security of Bertino-Shang-Wagstaff time-bound hierarchical key management scheme for secure broadcasting

Recently, Bertino, Shang and Wagstaff proposed a time-bound hierarchical key management scheme for secure broadcasting. Their scheme is built on elliptic curve cryptography and implemented with tamper-resistant devices. In this paper, we present two collusion attacks on Bertino-Shang-Wagstaff scheme. The first attack does not need to compromise any decryption device, while the second attack requires to compromise single decryption device only. Both attacks are feasible and effective.