Cryptanalysis of a Polynomial-Based Key Management Scheme for Secure Group Communication

Piao et al. proposed a polynomial-based key management scheme for secure intra-group and inter-group communication. In this paper, the authors present a simple attack on this scheme and show that it does not satisfy group forward and backward secrecy. In other words, they show that when a node leaves a group, it can easily compute the new intra-group key based on its old key and the publicly broad-casted data. Similarly, they also show that when a node joins a group, it can discover the old keys.