New Local Collisions for the SHA-2 Hash Family
نویسندگان
چکیده
The starting point for collision attacks on practical hash functions is a local collision. In this paper, we make a systematic study of local collisions for the SHA-2 family. The possible linear approximations of the constituent Boolean functions are considered and certain impossible conditions for such approximations are identified. Based on appropriate approximations, we describe a general method for finding local collisions. Applying this method, we obtain several local collisions and compute the probabilities of the various differential paths. Previously, only one local collision due to GilbertHandschuh was known. We point out two impossible conditions in the GH local collision and provide an example of an impossible differential path for linearized SHA-2 using this local collision. Sixteen new local collisions are obtained none of which have any impossible conditions. The probabilities of these local collisions are a little less than the GH local collision. On the other hand, the absence of impossible conditions may make them more suitable for (reduced round) collision search attacks on the SHA-2 family.
منابع مشابه
Non-linear Reduced Round Attacks against SHA-2 Hash Family
Most of the attacks against (reduced) SHA-2 family in literature have used local collisions which are valid for linearized version of SHA-2 hash functions. Recently, at FSE ’08, an attack against reduced round SHA-256 was presented by Nikolić and Biryukov which used a local collision which is valid for the actual SHA-256 function. It is a 9-step local collision which starts by introducing a mod...
متن کاملNew Collision Attacks on SHA-1 Based on Optimal Joint Local-Collision Analysis
The main contributions of this paper are two-fold. Firstly, we present a novel direction in the cryptanalysis of the cryptographic hash function SHA-1. Our work builds on previous cryptanalytic efforts on SHA-1 based on combinations of local collisions. Due to dependencies, previous approaches used heuristic corrections when combining the success probabilities and message conditions of the indi...
متن کاملFinding Collisions in the Full SHA-1
In this paper, we present new collision search attacks on the hash function SHA-1. We show that collisions of SHA-1 can be found with complexity less than 2 hash operations. This is the first attack on the full 80-step SHA-1 with complexity less than the 2 theoretical bound.
متن کاملImproving Local Collisions: New Attacks on Reduced SHA-256
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-freestart collision into a collision for 31 steps with a complexity of at most 2. The main improvement of our work is to ex...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2007