Sciweavers

SACRYPT
2015
Springer

Cryptanalysis of Feistel Networks with Secret Round Functions

7 years 11 months ago
Cryptanalysis of Feistel Networks with Secret Round Functions
Generic distinguishers against Feistel Network with up to 5 rounds exist in the regular setting and up to 6 rounds in a multi-key setting. We present new cryptanalyses against Feistel Networks with 5, 6 and 7 rounds which are not simply distinguishers but actually recover completely the unknown Feistel functions. When an exclusive-or is used to combine the output of the round function with the other branch, we use the so-called yoyo game which we improved using a heuristic based on particular cycle structures. The complexity of a complete recovery is equivalent to O(22n ) encryptions where n is the branch size. This attack can be used against 6- and 7-round Feistel Networks in time respectively O(2n2n−1 +2n ) and O(2n2n +2n ). However when modular addition is used, this attack does not work. In this case, we use an optimized guess-and-determine strategy to attack 5 rounds with complexity O(2n23n/4 ). Our results are, to the best of our knowledge, the first recovery attacks against g...
Alex Biryukov, Gaëtan Leurent, Léo Per
Added 17 Apr 2016
Updated 17 Apr 2016
Type Journal
Year 2015
Where SACRYPT
Authors Alex Biryukov, Gaëtan Leurent, Léo Perrin
Comments (0)