KeeLoq密码Courtois攻击方法的分析和修正

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。

Analysis and Correction of Courtois Attack to KeeLoq Cipher

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 at...