Preuves de sécurité en cryptographie symétrique à l'aide de la technique du coupling. (Security proofs in symmetric cryptography using the coupling technique)
نویسنده
چکیده
In this thesis, we study blockciphers, meaning that the encryption (and decryption)sends a block of n bits on a block of n bits. There is essentially two main structures usedfor a blockcipher: the Feistel structure (used for DES) and the SPN structure (used forAES). The study of the security of these structures and schemes has led to many practicaland theoretical advances. We present in this thesis proofs of security for the iterated Even-Mansour scheme, the tweakable blockcipher CLRW and the key-alternating Feistel cipher.These proofs use a probabilistic technique, called coupling, introduced in cryptography in2002 by Mironov [Mir02]. We present this technique in the context of probabilities, thenwe present how to use the coupling to prove the security for the schemes mentioned above.We also present an analysis of the security of the Even-Mansour cipher with two roundsand some properties (same round keys or same internal permutations for example) and,finally, we compare the different techniques to prove indistinguishability.
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