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Improved Indifferentiability Security Analysis of chopMD Hash Function

  • Donghoon Chang
  • Mridul Nandi
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 5086)

Abstract

The classical design principle Merkle-Damgård [13,6] is scrutinized by many ways such as Joux’s multicollision attack, Kelsey-Schneier second preimage attack etc. In TCC’04, Maurer et al. introduced a strong security notion called as “indifferentiability” for a hash function based on a compression function. The classical design principle is also insecure against this strong security notion whereas chopMD hash is secure with the security bound roughly σ 2/2 s where s is the number of chopped bits and σ is the total number of message blocks queried by a distinguisher. In case of n = 2s where n is the output size of a compression function, the value σ to get a significant bound is 2 s/2 which is the birthday complexity, where the hash output size is s-bit. In this paper, we present an improved security bound for chopMD. The improved bound shown in this paper is (3(n − s) + 1)q/2 s  + q/2 n − s − 1 + σ 2/2 n + 1 where q is the total number of queries. In case of n = 2s, chopMD is indifferentiably-secure if q = O(2 s /(3s + 1)) and σ = O(2 n/2) which are beyond the birthday complexity. We also present a design principle for an n-bit hash function based on a compression function \(f : {0,1}^{2n+b} {\Rightarrow} {0,1}^n\) and show that the indifferentiability security bound for this hash function is roughly (3n + 1)σ/2 n . So, the new design of hash function is second-preimage and r-multicollision secure as long as the query complexity (the number of message blocks queried) of an attacker is less than 2 n /(3n + 1) or 2 n(r − 1)/r respectively.

Keywords

Hash Function Security Analysis Random Oracle Query Complexity Compression Function 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • Donghoon Chang
    • 1
  • Mridul Nandi
    • 2
  1. 1.Center for Information Security Technologies (CIST)Korea UniversitySeoulKorea
  2. 2.CINVESTAV-IPNMexico City 

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