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New Collision attacks Against Up To 24-step SHA-2.
TLDR
New and improved attacks against 22, 23 and 24-step SHA-2 family using a local collision given by Sanadhya and Sarkar (SS) at ACISP '08 are provided.Abstract:
In this work, we provide new and improved attacks against 22, 23 and 24-step SHA-2 family using a local collision given by Sanadhya and Sarkar (SS) at ACISP ’08. The success probability of our 22-step attack is 1 for both SHA-256 and SHA-512. The computational efforts for the 23-step and 24step SHA-256 attacks are respectively 2 and 2 calls to the corresponding step reduced SHA-256. The corresponding values for the 23 and 24-step SHA-512 attack are respectively 2 and 2 calls. Using a look-up table having 2 (resp. 2) entries the computational effort for finding 24-step SHA-256 (resp. SHA-512) collisions can be reduced to 2 (resp. 2) calls. We exhibit colliding message pairs for 22, 23 and 24-step SHA-256 and SHA-512. This is the first time that a colliding message pair for 24-step SHA-512 is provided. The previous work on 23 and 24-step SHA-2 attacks is due to Indesteege et al. and utilizes the local collision presented by Nikolic and Biryukov (NB) at FSE ’08. The reported computational efforts are 2 and 2 for 23 and 24-step SHA-256 respectively and 2 and 2 for 23 and 24-step SHA-512. The previous 23 and 24-step attacks first constructed a pseudo-collision and later converted it into a collision for the reduced round SHA-2 family. We show that this two step procedure is unnecessary. Although these attacks improve upon the existing reduced round SHA-2 attacks, they do not threaten the security of the full SHA-2 family.read more
Citations
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References
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Journal Article
Security analysis of SHA-256 and sisters
Henri Gilbert,Helena Handschuh +1 more
TL;DR: In this article, the security of SHA-256, SHA-384 and SHA-512 against collision attacks was studied. But the authors concluded that neither Chabaud and Joux's attack, nor Dobbertin-style attacks also don't apply on the underlying structure.
Book ChapterDOI
Security Analysis of SHA-256 and Sisters
Henri Gilbert,Helena Handschuh +1 more
TL;DR: It is shown that slightly simplified versions of the hash functions are surprisingly weak : whenever symmetric constants and initialization values are used throughout the computations, and modular additions are replaced by exclusive or operations, symmetric messages hash to symmetric digests.
Journal Article
Analysis of step-reduced SHA-256
TL;DR: In this paper, the authors analyzed the security of SHA-256 against fast collision search and showed that the low probability of a single local collision may give rise to a false sense of security.
Book ChapterDOI
Collisions for Step-Reduced SHA-256
Ivica Nikolic,Alex Biryukov +1 more
TL;DR: A differential that holds with high probability if the message satisfies certain conditions is developed, which helps to find collisions for step-reduced SHA-256.
Book ChapterDOI
New local collisions for the SHA-2 hash family
TL;DR: In this paper, the authors make a systematic study of local collisions for the SHA-2 family and identify certain impossible conditions for linear approximations of the constituent Boolean functions and compute the probabilities of the various differential paths.