Paper 2015/350 Original: eprint.iacr.org/2015/350 ↗
Improving Local Collisions: New Attacks on Reduced SHA-256
Abstract
In this paper, we focus on the construction of semi-free-start collisions for SHA-256, and show how to turn them into collisions. We present a collision attack on 28 steps of the hash function with practical complexity. Using a two-block approach we are able to turn a semi-free-start collision into a collision for 31 steps with a complexity of at most $2^{65.5}$. The main improvement of our work is to extend the size of the local collisions used in these attacks. To construct differential characteristics and confirming message pairs for longer local collisions, we had to improve the search strategy of our automated search tool. To test the limits of our techniques we present a semi-free-start collision for 38 steps.
Metadata
- Available format(s)
PDF- Category
- Secret-key cryptography
- Publication info
- Preprint.
- History
- 2015-04-23: last updated
- 2015-04-23: published
- Short URL
- https://ia.cr/2015/350
- License
- https://creativecommons.org/licenses/by/4.0/
BibTeX
@misc{cryptoeprint:2015/350,
author = {Florian Mendel and Tomislav Nad and Martin Schläffer},
title = {Improving Local Collisions: New Attacks on Reduced SHA-256},
howpublished = {Cryptology {ePrint} Archive, Paper 2015/350},
year = {2015},
url = {https://eprint.iacr.org/2015/350}
}