Collisions for the WIDEA-8 compression function

Authors:
Florian Mendel;Vincent Rijmen;Deniz Toz;Kerem Varıcı
Affiliations:
IAIK, Graz University of Technology, Austria;ESAT/COSIC and iMinds, KU Leuven, Belgium;ESAT/COSIC and iMinds, KU Leuven, Belgium;ESAT/COSIC and iMinds, KU Leuven, Belgium
Venue:
CT-RSA'13 Proceedings of the 13th international conference on Topics in Cryptology
Year:
2013

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Abstract

WIDEA is a family of block ciphers inspired by the IDEA block cipher. The design uses n-parallel instances of IDEA with an improved key schedule to obtain block ciphers with larger block sizes. Moreover, the given design is suggested as the compression function for Davies-Meyer mode. In this paper, we discuss the security of the block cipher when used as a compression function. Inspired by the weak key attacks on IDEA, we take the advantage of slow diffusion mechanism of the key schedule and present free-start collisions for WIDEA-8 which is the specified version by designers. Our results are practical and we are able to obtain free-start collisions with a complexity of 213.53.