主要介绍一种针对GSM系统中的加密算法A5/2算法的实时唯密文攻击算法。在系统中信道编码在信息加密之前,利用明文中的冗余进行破解。此算法不需要已知明文,仅需少量密文即可完成破解,增加了可实现性;且此算法具有实时性,可在5.5小时的预计算之后,于1秒内获取会话密钥。 This paper mainly introduces a real-time ciphertext attack algorithm aimed at the encryption algorithm A5 / 2 in GSM system. Channel coding in the system prior to the encryption of information, the use of clear text in the crack. This algorithm does not need known plaintext and only needs a few ciphertexts to complete the solution, which increases the implementability. Moreover, the algorithm is real-time and can obtain the session key within one second after 5.5 hours pre-computation.