Collision attack

About: Collision attack is a research topic. Over the lifetime, 1093 publications have been published within this topic receiving 28389 citations.

Second preimage attacks on dithered hash functions

Abstract: We develop a new generic long-message second preimage attack, based on combining the techniques in the second preimage attacks of Dean [8] and Kelsey and Schneier [16] with the herding attack of Kelsey and Kohno [15]. We show that these generic attacks apply to hash functions using the Merkle-Damgard construction with only slightly more work than the previously known attack, but allow enormously more control of the contents of the second preimage found. Additionally, we show that our new attack applies to several hash function constructions which are not vulnerable to the previously known attack, including the dithered hash proposal of Rivest [25], Shoup's UOWHF[26] and the ROX hash construction [2].We analyze the properties of the dithering sequence used in [25], and develop a time-memory tradeoff which allows us to apply our second preimage attack to a wide range of dithering sequences, including sequences which are much stronger than those in Rivest's proposals. Finally, we show that both the existing second preimage attacks [8,16] and our new attack can be applied even more efficiently to multiple target messages; in general, given a set of many target messages with a total of 2R message blocks, these second preimage attacks can find a second preimage for one of those target messages with no more work than would be necessary to find a second preimage for a single target message of 2R message blocks.

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 265.5. 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.

Cryptographic hash function Blue Midnight Wish

Abstract: The cryptographic hash function Blue Midnight Wish was submitted as a candidate for SHA-3 hash competition organized by National Institute of Standards and Technology (NIST).

Freestart Collision for Full SHA-1

Abstract: This article presents an explicit freestart colliding pair for SHA-1, i.e. a collision for its internal compression function. This is the first practical break of the full SHA-1, reaching all 80 out of 80 steps. Only 10i¾?days of computation on a 64-GPU cluster were necessary to perform this attack, for a runtime cost equivalent to approximately $$2^{57.5}$$257.5 calls to the compression function of SHA-1 on GPU. This work builds on a continuous series of cryptanalytic advancements on SHA-1 since the theoretical collision attack breakthrough of 2005. In particular, we reuse the recent work on 76-step SHA-1 of Karpman et al. from CRYPTO 2015 that introduced an efficient framework to implement freestart collisions on GPUs; we extend it by incorporating more sophisticated accelerating techniques such as boomerangs. We also rely on the results of Stevens from EUROCRYPT 2013 to obtain optimal attack conditions; using these techniques required further refinements for this work. Freestart collisions do not directly imply a collision for the full hash function. However, this work is an important milestone towards an actual SHA-1 collision and it further shows how GPUs can be used very efficiently for this kind of attack. Based on the state-of-the-art collision attack on SHA-1 by Stevens from EUROCRYPT 2013, we are able to present new projections on the computational and financial cost required for a SHA-1 collision computation. These projections are significantly lower than what was previously anticipated by the industry, due to the use of the more cost efficient GPUs compared to regular CPUs. We therefore recommend the industry, in particular Internet browser vendors and Certification Authorities, to retract SHA-1 quickly. We hope the industry has learned from the events surrounding the cryptanalytic breaks of MD5 and will retract SHA-1 before concrete attacks such as signature forgeries appear in the near future.

Cryptanalysis of GRINDAHL

Abstract: Due to recent breakthroughs in hash functions cryptanalysis, some new hash schemes have been proposed. GRINDAHL is a novel hash function, designed by Knudsen, Rechberger and Thomsen and published at FSE 2007. It has the particularity that it follows the RIJNDAEL design strategy, with an efficiency comparable to SHA-256. This paper provides the first cryptanalytic work on this new scheme. We show that the 256-bit version of GRINDAHL is not collision resistant. With a work effort of approximatively 2112 hash computations, one can generate a collision.