FSE '99 Proceedings of the 6th International Workshop on Fast Software Encryption
Linear Slide Attacks on the KeeLoq Block Cipher
Information Security and Cryptology
Algebraic and Slide Attacks on KeeLoq
Fast Software Encryption
On the Power of Power Analysis in the Real World: A Complete Break of the KeeLoq Code Hopping Scheme
CRYPTO 2008 Proceedings of the 28th Annual conference on Cryptology: Advances in Cryptology
Analytic Combinatorics
EUROCRYPT'00 Proceedings of the 19th international conference on Theory and application of cryptographic techniques
EUROCRYPT'08 Proceedings of the theory and applications of cryptographic techniques 27th annual international conference on Advances in cryptology
Self-similarity attacks on block ciphers and application to keeloq
Cryptography and Security
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KeeLoq is a lightweight block cipher which is extensively used in the automotive industry [7,8,14,15]. Its periodic structure, and overall simplicity makes it vulnerable to many different attacks. Only certain attacks are considered as really "practical" attacks on KeeLoq: the brute force, and several other attacks which require up to 216 known plaintexts and are then much faster than brute force, developed by Courtois et al., [10] and (faster attack) by Dunkelman et al. [1]. On the other hand, due to the unusually small block size, there are yet many other attacks on KeeLoq, which require the knowledge of as much as about 232 known plaintexts but are much faster still. There are many scenarios in which such attacks are of practical interest, for example if a master key can be recovered, see Section 2 in [11] for a detailed discussion. The fastest of these attacks is an attack by Courtois, Bard and Wagner from [10] that has a very low complexity of about 228 KeeLoq encryptions on average. In this paper we will propose an improved and refined attack which is faster both on average and in the best case. We also present an exact mathematical analysis of probabilities that arise in these attacks using the methods of modern analytic combinatorics.