A collusion attack on asymmetric group key exchange

Abstract

In Eurocrypt 2009, Wu et al. introduced the notion of asymmetric group key agreement ASGKA and presented a generic construction of ASGKA protocols with one communication round. Most of ASGKA protocols are designed under that generic construction. In asymmetric group key agreement protocols, users obtain different decryption keys. Any subset of group members may collude to construct pirate decryption keys, which are different from those of colluders but can correctly decrypt ciphertexts. If a pirate decryption box is found, it is possible to find traitors since their decryption keys are related to their identities. In this paper, a collusion attack on the generic construction of ASGKA by Wu et al. is proposed. It is formally proved that each of colluders participating in the proposed collusion attack is unable to be traced. The attack is additionally applied to a concrete protocol to exemplify the collusion attack. Copyright © 2014 John Wiley & Sons, Ltd.