State Transition Analysis of GSM Encryption Algorithm A5/1

Abstract

A5/1 stream cipher is used in Global System for Mobile Communication(GSM) phones for secure communication. A5/1 encrypts the message transferred from a mobile user. In this paper, we present the implementation of cryptanalytic on A5/1 techniques such as minimized state recovery for recovering the session key. The number of state transitions/updations needed for a state S to reoccur is maintained in the lookup table. This table can be used to recover the initial state from which the keystream was produced. Experiments are carried out for reduced version, full A5/1 cipher on 3.20 GHz machine, and cluster computing facility.

Keywords

• a5/1 stream cipher
• cryptanalysis
• precomputed tables
• keystream
• initial state transition
• periodicity