Analysis of the Bit-Search Generator and Sequence Compression Techniques

Abstract

Abstract. Algebraic attacks on stream ciphers apply (at least theoretically) to all LFSR-based stream ciphers that are clocked in a simple and/or easily predictable way. One interesting approach to help resist such attacks is to add a component that de-synchronizes the output bits of the cipher from the clock of the LFSR. The Bit-search generator, recently proposed by Gouget and Sibert, is inspired by the so-called SelfShrinking Generator which is known for its simplicity (conception and implementation-wise) linked with some interesting properties. In this paper, we introduce two modified versions of the BSG, called MBSG and ABSG, and some of their properties are studied. We apply a range of cryptanalytic techniques in order to compare the security of the BSGs.

How to Strengthen Pseudo-random Generators by Using Compression

“…Such components include decimation components such as the Shrinking Generator [3] and the Self-Shrinking Generator [15]. Decimation has come back in focus recently with the Bit-Search Generator [9] and subsequent variations on it [10].…”

Side Channel Attacks on Irregularly Decimated Generators

“…In comparison, the attacker requires both time and data complexity of 2 64 in the attack on ABSG in [9]. Thus our timing attack can be viewed as a trade-off of a 2 23 increase in computational complexity in exchange for a savings of 2 64 in memory.…”

“…Examples of IDGs are Shrinking Generator (SG) [4], SelfShrinking Generator (SSG) [13] and Bit Search Generators (BSG) [8]. In this paper we focus on ABSG [9], a variant of BSG. We choose to study ABSG as it faciltates our analysis of DECIM later in the paper.…”

“…2 Outline of ABSG [9] [10] showed the insecurity of BSG (earlier variant of ABSG) after it was introduced a year before. To improve the security of BSG, the authors of [9] tweaked BSG into 2 different variants, ABSG and MBSG.…”

“…To improve the security of BSG, the authors of [9] tweaked BSG into 2 different variants, ABSG and MBSG. The security of ABSG and MBSG is similar and both require 2 L/2 time and data complexity to recover the full key, where L is the linear complexity of the input stream, which can be the length of the secret key.…”