Semi-quantum key agreement protocol based on four-particle entangled χ-state and experiment verification on IBM qiskit

By using a four-particle entangled χ-state, this paper proposes a three-party semi-quantum key agreement protocol. It allows one quantum participant and two classical participants to negotiate the final key equally. The three parties encrypt the key using two round hash functions, which make the proposed protocol more secure. In the process of joint measurement, this paper uses IBM Qiskit to calculate the error rate by comparing the measurement results with the four-particle entangled χ-state. Security analyses show that the presented protocol can resist participants’ attacks and some common external attacks. In the process of the intercept-resend attack, this paper uses simulation to detail the operation of eavesdroppers and the method for detecting eavesdropping. Efficiency analysis shows that the proposed three-party SQKA protocol has higher qubit efficiency than the existing SQKA protocol. Besides, this paper extends the proposed three-party SQKA protocol into the multi-party SQKA protocol and compares it with other multi-party SQKA protocols. The results show that when the number of participants exceeds 6, the qubit efficiency of the presented protocol is higher than other protocols.