Beyond-birthday-bound security based on tweakable block cipher

Abstract

This paper studies how to build a 2n-bit block cipher which is hard to distinguish from a truly random permutation against attacks with q≈2 n/2 queries, i.e., birthday attacks. Unlike previous approaches using pseudorandom functions, we present a simple and efficient proposal using a tweakable block cipher as an internal module. Our proposal is provably secure against birthday attacks, if underlying tweakable block cipher is also secure against birthday attacks. We also study how to build such tweakable block ciphers from ordinary block ciphers, which may be of independent interest. © 2009 Springer Berlin Heidelberg.