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Characterizing Padding Rules of MD Hash Functions Preserving Collision Security



Mridul Nandi


This paper characterizes collision preserving padding rules and provides variants of Merkle-Damgaard (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.
Proceedings Title
Information Security and Privacy (Lecture Notes in Computer Science)
Conference Dates
July 1-3, 2009
Conference Location
Conference Title
14th Australasian Conference on Information Security and Privacy (ACISP 2009)


collision resistant, MD hash function, padding rule, suffix-free


Nandi, M. (2009), Characterizing Padding Rules of MD Hash Functions Preserving Collision Security, Information Security and Privacy (Lecture Notes in Computer Science), Brisbane, -1, [online], (Accessed March 1, 2024)
Created June 29, 2009, Updated November 10, 2018