Abstract

. We evaluate constructions for building pseudo-random functions (PRFs) from pseudo-random permutations (PRPs). We present two constructions: a slower construction which preserves the security of the PRP and a faster construction which has less security. One application of our construction is to build a wider block cipher given a block cipher as a building tool. We do not require any additional constructions---e.g. pseudo-random generators---to create the wider block cipher. The security of the resulting cipher will be as strong as the original block cipher. Keywords. pseudo-random permutations, pseudo-random functions, concrete security, block ciphers, cipher feedback mode. 1 Introduction and Background In this paper we examine building psuedo-random functions from pseudo-random permutations. There are several well known constructions for building pseudorandom permutations from pseudo-random functions, notably [LR88]. However, the only results we are aware of for going in t...

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