Abstract:
In this paper, we describe a new real-time attack on A5/1 stream ciphers thatachieves superior performance in terms of lower computation time and calculation complexity compared to most of the previous attacks of similar type. We introduce theconcept of "peculiar events" that can be applied to any array of mutually clock-controlledstop/go shift registers but works exceptionally well in A5/1 due to a set of subtle flaws inits design, particularly the position of its clocking tabs. The proposed attack is an advancement of the "peculiar events" concept by embedding it into an improved version ofM. Hellman̕s cryptanalytic time-memory tradeoff attack.We show that the proposed technique is suitable for real-time attacks oncommercially available computers with a pre-computational complexity of 241.33 clockings, a memory requirement of 240.21 bits (<160 GB), real-time complexity of 225 unitcomputation durations and ~3 seconds of known conversation.Finally, we compare our attack̕s performance with other widely accepted techniquesand conclude that ours achieves acceptable success rates at comparably lower memory, data and calculation complexity requirements.
