Strong Stationary Times and its use in Cryptography

Abstract

This paper presents applicability of Strong Stationary Times (SST) techniques in the area of cryptography. The applicability is in three areas: *) Propositions of a new class of cryptographic algorithms (pseudo-random permutation generators) which do not run for the predefined number of steps. Instead, these algorithms stop according to a stopping rule defined as SST, for which one can obtain provable properties: *** results are perfect samples from uniform distribution, *** immunity to timing attacks (no information about the resulting permutation leaks through the information about the number of steps SST algorithm *) We show how one can leverage properties of SST-based algorithms to construct an implementation (of a symmetric encryption scheme) which is immune to the timing-attack by reusing implementations which are not secure against timing-attacks. In symmetric key cryptography researchers mainly focus on constant time (re)implementations. Our approach goes in a different direction and explores ideas of input masking. *) Analysis of idealized (mathematical) models of existing cryptographic schemes -- i.e., we improve a result by Mironov ((Not So) Random Shuffles of RC4; Advances in Cryptology -- CRYPTO 2002)