IACR News item: 18 December 2012
Gaëtan Leurent
ePrint Report2009 as an extension of IDEA to larger block sizes (256 and 512 bits for
the main instances WIDEA-4 and WIDEA-8) and key sizes (512 and 1024
bits), with a focus on using them to design a hash function. WIDEA is
based on the trusted IDEA design, and was expected to inherit its good
security properties. WIDEA-w is composed of w parallel copies of the
IDEA block cipher, with an MDS matrix to provide diffusion between them.
In this paper we present low complexity attacks on WIDEA based on
truncated differentials. We show a distinguisher for the full WIDEA
with complexity only 2^65, and we use the distinguisher in a
key-recovery attack with complexity w·2^68. We also show a collision
attack on WIDEA-8 if it is used to build a hash function using the
Merkle-Damgård mode of operation.
The attacks exploit the parallel structure of WIDEA and the limited
diffusion between the IDEA instances, using differential trails where
the MDS diffusion layer is never active. In addition, we use structures
of plaintext to reduce the data complexity.
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