Modifying twist algorithms for determining the key length of a Vigenère cipher

Abstract

In this article, we analyze and improve upon the twist-based algorithms introduced by Barr--Simoson and Park--Kim--Cho--Yum for determining the key length of a Vigenère cipher. We provide an in-depth discussion on how the domain of the twist index affects the accuracy of these algorithms along with supporting experimental evidence. We also introduce a new twist-based algorithm, the twist${}^{++}$ algorithm, and show this algorithm is more accurate than the twist${}^{+}$ algorithm for a wide range of key lengths and text lengths.