Cryptology ePrint Archive: Report 2006/264

A Simple and Unified Method of Proving Unpredictability

Mridul Nandi

Abstract: Recently Bernstein has provided a simpler proof of unpredictability of CBC construction which is giving insight of the construction. Unpredictability of any function intuitively means that the function behaves very closely to a uniform random function. In this paper we make a unifying and simple approach to prove unpredictability of many existing constructions. We first revisit Bernstein's proof. Using this idea we can show a simpler proof of unpredictability of a class of DAG based construction, XCBC, TMAC, OMAC and PMAC. We also provide a simpler proof for stronger bound of CBC and a simpler proof of security of on-line Hash-CBC. We note that there is a flaw in the original security proof of Hash-CBC. This paper will help to understand security analysis of unpredictability of many constructions in a simpler way.

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Date: received 3 Aug 2006

Contact author: mridul nandi at gmail com

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Version: 20060808:002244 (All versions of this report)

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