Paper 2015/876

10-Round Feistel is Indifferentiable from an Ideal Cipher

Dana Dachman-Soled and Jonathan Katz and Aishwarya Thiruvengadam

Abstract

We revisit the question of constructing an ideal cipher from a random oracle. Coron et al.~(Journal of Cryptology, 2014) proved that a 14-round Feistel network using random, independent, keyed round functions is indifferentiable from an ideal cipher, thus demonstrating the feasibility of such a construction. Left unresolved is the best possible efficiency of the transformation. We improve upon the result of Coron et al.\ and show that 10 rounds suffice.