Abstract: Quantum key agreement (QKA) is an important branch of quantum cryptography. Fairness and security are two key requirements of QKA. However, the fairness has not been attracted enough attention in the design of QKA protocol. Some scholars recently proposed a quantum search algorithm(QSA) QKA protocol. Through the internal attack analysis of the protocol by using the entangling nature of state, it is found that the first participant can manipulate the final shared key without being detected by the receiving party. This means the protocol does not meet the requirement of fairness of QKA protocol. It sheds some light on designing more secure and fairer QKA protocol.

Key words: quantum key agreement protocol, quantum search algorithm, internal attacks