A Simple and Unified Method of Proving Unpredictability

Recently Bernstein [4] has provided a simpler proof of unpredictability of CBC construction [3] 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 [7], XCBC [5], TMAC [8], OMAC [9] and PMAC [6]. We also provide a simpler proof for stronger bound of CBC [1] and a simpler proof of security of on-line Hash-CBC [2]. We note that there is a flaw in the security proof of Hash-CBC in [2]. This paper will help to understand security analysis of unpredictability of many constructions in a simpler way.