分析了约束集投影和4f相关器的光学加密系统的安全性,并提出一种基于双强度相位恢复的已知明文攻击方法。约束集投影和4f相关器的加密系统是典型的光学密码系统,由于其解密系统可以等价于一个标准的4f系统,并且加密密钥与解密密钥相同,因此本质上仍是一个线性系统,这就为系统的安全性留下了很大隐患。该攻击方法仅利用一对输入的相位信息和相应输出的强度信息即可成功得到加密系统的密钥,提高了攻击实施的可行性。

The security of the cryptosystem based on projection-onto-constraint-sets (POCS) and a 4f correlator is examined. A method of known-plaintext attack based on phase retrieval algorithm from two-intensity information is presented. In the field of information security the cryptosystem based on POCS and the 4f correlator is a typical approach. But its decryption system can be equivalent to the standard 4f system and the encryption and decryption keys are identical. So this linearity characteristic opens avenues of attacks. With the known-plaintext attack method, an attacker is able to break down the cryptosystem by only a pair of input phase data and output intensity data.