Comparing balanced sequences obtained from ElGamal function to random balanced sequences

Abstract

In this paper, we investigate the randomness properties of sequences in $\mathbb {Z}_{v}$ derived from permutations in $\mathbb {Z}_{p}^{*}$ using the remainder function modulo v, where p is a prime integer. Motivated by earlier studies with a cryptographic focus we compare sequences constructed from the discrete exponential function, or “ElGamal function”, x → g^x for $x\in \mathbb {Z}_{>0}$ and g a primitive element of $\mathbb {Z}_{p}^{*}$, to sequences constructed from random permutations of $\mathbb {Z}_{p}^{*}$. We prove that sequences obtained from ElGamal have maximal period and behave similarly to random permutations with respect to the balance and run properties of Golomb’s postulates for pseudo-random sequences. Additionally we show that they behave similarly to random permutations for the tuple balance property. This requires some significant work determining properties of random balanced periodic sequences. In general, for these properties and excepting for very unlikely events, the ElGamal sequences behave the same as random balanced sequences.