TITLE:
Diffusion Analysis of Message Expansion in STITCH-256
AUTHORS:
Norziana Jamil, Ramlan Mahmod, Muhammad Reza Z’aba, Nur Izura Udzir, Zuriati Ahmad Zukarnain
KEYWORDS:
STITCH-256; Message Expansion; Diffusion; Hash Function
JOURNAL NAME:
Journal of Information Security,
Vol.4 No.3,
July
12,
2013
ABSTRACT: Cryptographic hash functions are built up from individual
components, namely pre-processing, step transformation, and final processing.
Some of the hash functions, such as SHA-256 and STITCH-256, employ non-linear
message expansion in their pre-processing stage. However, STITCH-256 was claimed
to produce high diffusion in its message expansion. In a
cryptographic algorithm, high diffusion is desirable as it helps prevent an
attacker finding collision-producing differences, which would allow one to find
collisions of the whole function without resorting to a brute force search. In
this paper, we analyzed the diffusion property of message expansion of STITCH-256 by
observing the effect of a single bit difference over the output bits, and
compare the result with that of SHA-256. We repeated the same procedure in 3
experiments of different round. The results from the experiments showed that
the minimal weight in the message expansion of STITCH-256 is very much lower than
that in the message expansion of SHA-256, i.e. message expansion of STITCH-256 produce high diffusion. Significantly, we
showed that the probability to construct differential characteristic in
the message expansion of STITCH-256 is reduced.