A Passive Attack against an Asymmetric Key Exchange Protocol

Constructing key exchange protocols which can resist the quantum-attack is a hot topic. In China Crypt2014, S. Mao et al claimed a new quantum-resistant key exchange protocol and also recommended a set of practical parameter. In this paper, we present a passive attack against this key exchange protocol. Specifically, an eavesdropper can recover the exchange key in polynomial time provided with an oracle solving the discrete logarithm problem. Particularly, this key exchange protocol with the recommended parameter can be attacked by a polynomial time algorithm.