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Published in:
2009 | OriginalPaper | Chapter
Characterizing Padding Rules of MD Hash Functions Preserving Collision Security
Author : Mridul Nandi
Published in: Information Security and Privacy
Publisher: Springer Berlin Heidelberg
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This paper characterizes collision preserving padding rules and provides variants of Merkle-Damgård (MD) which are having less or no overhead costs due to length. We first show that suffix-free property of padding rule is necessary as well as sufficient to preserve the collision security of MD hash function for an arbitrary domain {0,1}
*
. Knowing this, we propose a simple suffix-free padding rule padding only log|
M
| bits for a message
M
, which is less than that of Damgard’s and Sarkar’s padding rules. We also prove that the length-padding is not absolutely necessary. We show that a simple variant of MD with 10
d
-padding (or any injective padding) is collision resistant provided that the underlying compression function is collision resistant after chopping the last-bit. Finally, we design another variant of MD hash function preserving all three basic security notions of hash functions, namely collision and (2nd) preimage, which is an improvement over a recently designed (SAC-08) three-property preserving hash function.