On the Security of an Efficient Time-Bound Hierarchical Key Management Scheme

Recently, Bertino et al. proposed a new time-bound key management scheme for broadcasting. The security of their scheme is planted on the hardness breaking of elliptic curve discrete log problem, HMAC, and tamper-resistance devices. They claimed that as long as the three assumptions hold, their scheme is secure. By means of secure, users cannot access resources that they are not granted, even if users collude. In this paper, we demonstrate that this scheme is insecure against the collusion attack. We also provide some possible amendments to this scheme.