Multiparty Quantum Key Agreement with GHZ State

Quantum Key Agreement (QKA) signifies that two or more participants together generate a key and QKA has to satisfy the following conditions: (1) Every participant can change the key and the key is not decided by any participant individually. (2) Only participants can know the key, nonparticipants cannot get the key through illegal means. Because of the conditions of participating together, it makes transport inefficient in the current mainstream protocols. They use unicast to exchange messages one by one, so it will considerably limit transmission efficiency and increase cost time spent. This study proposes a protocol based on Multiparty Quantum Secret Direct Communication (MQSDC) with multicast. In addition to satisfying the above conditions, it uses multicast to not only achieve the effect and purpose of QKA, but also to defend against internal and external attacks at the same time. In regard to resource consumption, this study involves linear growth and is more efficient than other mainstream protocols which employ exponential growth.