The aT/protocol is the random cipher protocol and hides information by the quantum phase noise. In this paper, the security criterion of the protocol is deduced by developing a quantum channel model and calculating the amount of information obtained by the eavesdropper. The results show the security of the protocol depends mainly on the average photon number of the signal quantum states and the number of cipher-text symbols. Considering the above factors, the secure value region of the average photon number and cipher-text symbol number is calculated, which is against the beam splitter attack. Furthermore, the effective communication distance is simulated.%αη协议是一种利用量子噪声隐藏信息的随机加密协议．通过求解高斯噪声信道中窃听者获取信息量的计算公式，推导了该协议实际安全判据．结果表明，协议是否安全主要取决于信源量子态的平均光子数和密文符号数．基于此，计算了在光束分离攻击下两者的安全取值区间以及协议的有效通信距离．
展开▼
