Quantum Key Agreement Via Non-maximally Entangled Cluster States

Abstract

In this paper, we present a quantum key agreement (QKA) protocol with non-maximally entangled four-qubit cluster states. In our scheme, each participant carries out two unitary operations on the same photons of each cluster state according to its own encryption key. Then, all participants generate identical four-bit shared keys by positive operator-valued measurement (POVM). Since POVM is probabilistic, it is necessary to prepare a longer raw key, and we only select sub-keys in public locations of qubit sequences where all participants succeed in POVMs as the final negotiation key. The advantage of our protocol is that non-maximally entangled cluster states are firstly utilized as the carrier of quantum information in quantum key agreement protocol. It also ensures that the shared key is decided by all participants, not by someone alone. In addition, it is proved that our protocol can resist external attacks and participant attacks, which demonstrates a high security.