KeeLoq密码Courtois攻击方法的分析和修正
doi: 10.3724/SP.J.1146.2007.01962
Analysis and Correction of Courtois Attack to KeeLoq Cipher
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摘要: KeeLoq密码是由Willem Smit设计的分组密码算法，广泛应用于汽车的无线门锁装置。Courtois等人在2007年提出了破译KeeLoq的4种滑动-代数攻击方法，其中第4种滑动-代数攻击方法的计算复杂性最小。本文证明了Courtois的第4种滑动-代数攻击方法的攻击原理是错误的，因而无法实现对KeeLoq的破译。此外，本文还对该方法进行了修正，提出了改进的攻击方法，利用232个已知明文能够以O(248) 次加密的计算复杂性求出KeeLoq密码的密钥，成功率为1。对于KeeLoq密码26％的密钥，其连续64圈圈函数形成的复合函数至少具有两个不动点，此时改进的攻击方法的计算复杂性还可降至O(248) 次加密。Abstract: KeeLoq is a block cipher designed by Willem Smit which is used in wireless devices that unlock doors in cars. Four slide-algebraic attacks that can break KeeLoq in practice are presented by Courtois et al. in 2007. The computing complexity of the fourth slide-algebraic attack is the smallest. However, the principle of Courtois fourth slide-algebraic attack is proved to be wrong in this thesis, so it can not break KeeLoq. The correction is made on Courtois fourth slide-algebraic attack and the improving attack is proposed. With 232 known plaintexts, the computing complexity of the improving attack is about O(248) KeeLoq encryptions for obtaining key and the success rate is 1. For 26％ of keys in KeeLoq, the first 64 rounds of KeeLoq have 2 or more fixed points, then the computing complexity of the improving attack which uses algebraic attack could decrease to O(248) KeeLoq encryptions.
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