2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/160202A 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.30 pages, Submitted to IEEE Transactions on Information TheoryCryptography and SecurityInformation Theorytext