CryptoDB
Could The 1-MSB Input Difference Be The Fastest Collision Attack For MD5 ?
| Authors: | |
|---|---|
| Download: | |
| Abstract: | So far, two different 2-block collision differentials, both with 3-bit input differences for MD5, have been found by Wang etc in 2005 and Xie etc in 2008 respectively, and those differentials have been improved later on to generate a collision respectively within around one minute and half an hour on a desktop PC. Are there more collision differentials for MD5? Can a more efficient algorithm be developed to find MD5 collisions? In this paper, we list the whole set of 1-bit to 3-bit input difference patterns that are possibly qualified to construct a feasible collision differential, and from which a new collision differential with only 1-MSB input difference is then analyzed in detail, finally the performances are compared with the prior two 3-bit collision attacks according to seven criteria proposed in this paper. In our approach, a two-block message is still needed to produce a collision, the first block being only one MSB different while the second block remains the same. Although the differential path appears to be computationally infeasible, most of the conditions that a collision differential path must satisfy can be fulfilled by multi-step modifications, and the collision searching efficiency can be much improved further by a specific divide-and-conquer technique, which transforms a multiplicative accumulation of the computational complexities into an addition by properly grouping of the conditional bits. In particular, a tunneling-like technique is applied to enhance the attack algorithm by introducing some additional conditions. As a result, the fastest attack algorithm is obtained with an averaged computational complexity of 2^20.96 MD5 compressions, which implies that it is able to search a collision within a second on a common PC for arbitrary random initial values. With a reasonable probability a collision can be found within milliseconds, allowing for instancing an attack during the execution of a practical protocol. The collision searching algorithm, however, is very complex, but the algorithm has been implemented which is available from the website http://www.is.iscas.ac.cn/gnomon, and we suggest you download the implementation program from the website for a personal experience if you are interested in it. |
BibTeX
@misc{eprint-2008-18095,
title={Could The 1-MSB Input Difference Be The Fastest Collision Attack For MD5 ?},
booktitle={IACR Eprint archive},
keywords={foundations / MD5, Collision Attack, Collision Differentials, Differential Path},
url={http://eprint.iacr.org/2008/391},
note={ hamishxie@vip.sina.com 14208 received 12 Sep 2008, last revised 25 Nov 2008},
author={Tao Xie FanBao Liu DengGuo Feng},
year=2008
}