Semi-quantum Key Agreement Protocol Using W States

In response to the emerging security challenges brought about by advances in quantum technology, traditional key agreement methods are encountering vulnerabilities. To address this issue, We propose a semi-quantum key agreement (SQKA) protocol that utilizes four different forms of the W state, a particle state with strong interparticle entanglement. Classical parties are pre-specified to perform distinct operations on various forms of W states, but these operations are completely random to other parties or potential attackers. Based on the sequence of measurement results transmitted by the quantum square and the pre-defined coding rules, the classical party can infer the operation performed by the other party to achieve identity authentication, and then publish the private key to generate the final key. The analysis of the protocol shows that it can effectively resist common inside and outside attacks, and has the advantage of being more efficient. In summary, by adopting SQKA protocol, we achieve a secure, fair and efficient key negotiation process, providing a feasible solution for cooperation between quantum and classical parties.