Towards Exploring Fundamental Limits of System-Specific Cryptanalysis Within Limited Attack Classes: Application to ABSG

TL;DR

This paper introduces a method to determine the fundamental limits of specific cryptanalytic attack classes, applied to the ABSG stream cipher, providing lower bounds on attack complexity using information theory concepts.

Contribution

It presents a novel approach to analyze the limits of system-specific cryptanalysis within limited attack classes, applied to LFSR-based ciphers like ABSG.

Findings

Derived tight lower bounds on attack complexity.

Applied information theory to cryptanalysis.

Provided insights into attack feasibility under practical assumptions.

Abstract

A new approach on cryptanalysis is proposed where the goal is to explore the fundamental limits of a specific class of attacks against a particular cryptosystem. As a first step, the approach is applied on ABSG, which is an LFSR-based stream cipher where irregular decimation techniques are utilized. Consequently, under some mild assumptions, which are common in cryptanalysis, the tight lower bounds on the algorithmic complexity of successful Query-Based Key-Recovery attacks are derived for two different setups of practical interest. The proofs rely on the concept of ``typicality'' of information theory.