A Collision Attack on a Double-Block-Length Compression Function Instantiated with 8-/9-Round AES-256

Jiageng CHEN, Shoichi HIROSE, Hidenori KUWAKADO, Atsuko MIYAJI
2016 IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences  
This paper presents the first non-trivial collision attack on the double-block-length compression function presented at FSE 2006 instantiated with round-reduced AES-256: where ∥ represents concatenation, E is AES-256 and c is a 16-byte nonzero constant. The proposed attack is a free-start collision attack using the rebound attack proposed by Mendel et al. The success of the proposed attack largely depends on the configuration of the constant c: the number of its non-zero bytes and their
more » ... s and their positions. For the instantiation with AES-256 reduced from 14 rounds to 8 rounds, it is effective if the constant c has at most four non-zero bytes at some specific positions, and the time complexity is 2 64 or 2 96 . For the instantiation with AES-256 reduced to 9 rounds, it is effective if the constant c has four non-zero bytes at some specific positions, and the time complexity is 2 120 . The space complexity is negligible in both cases. key words: double-block-length compression function, free-start collision attack, rebound attack,
doi:10.1587/transfun.e99.a.14 fatcat:z2hucpb3dnhotai2ubqs5kcepe