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Erschienen in:
2009 | OriginalPaper | Buchkapitel
Preimages for Step-Reduced SHA-2
verfasst von : Kazumaro Aoki, Jian Guo, Krystian Matusiewicz, Yu Sasaki, Lei Wang
Erschienen in: Advances in Cryptology – ASIACRYPT 2009
Verlag: Springer Berlin Heidelberg
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In this paper, we present preimage attacks on up to 43-step SHA-256 (around 67% of the total 64 steps) and 46-step SHA-512 (around 57.5% of the total 80 steps), which significantly increases the number of attacked steps compared to the best previously published preimage attack working for 24 steps. The time complexities are 2
251.9
, 2
509
for finding pseudo-preimages and 2
254.9
, 2
511.5
compression function operations for full preimages. The memory requirements are modest, around 2
6
words for 43-step SHA-256 and 46-step SHA-512. The pseudo-preimage attack also applies to 43-step SHA-224 and SHA-384. Our attack is a meet-in-the-middle attack that uses a range of novel techniques to split the function into two independent parts that can be computed separately and then matched in a birthday-style phase.