On the (In)security of Stream Ciphers Based on Arrays and Modular Addition

Abstract. Stream ciphers play an important role in symmetric cryptology because of their suitability in high speed applications where block ciphers fall short. A large number of fast stream ciphers or pseudorandom bit generators (PRBGs) can be found in the literature that are based on arrays and simple operations such as modular additions, rotations and memory accesses (e.g. RC4, RC4A, Py, Py6, ISAAC etc.). This paper investigates the security of array-based stream ciphers (or PRBGs) against certain types of distinguishing attacks in a unified way. We argue, counter-intuitively, that the most useful characteristic of an array, namely, the association of array-elements with unique indices, may turn out to be the origins of distinguishing attacks if adequate caution is not maintained. In short, an adversary may attack a cipher simply exploiting the dependence of array-elements on the corresponding indices. Most importantly, the weaknesses are not eliminated even if the indices and the ar...

• Type: Conference
• Year: 2006
• Where: ASIACRYPT
• Authors: Souradyuti Paul, Bart Preneel
• Keywords: Array-based Stream Ciphers, ASIACRYPT 2006, Cryptology, Fast Stream Ciphers, Stream Ciphers