Side-Channel Attack on the A5/1 Stream Cipher
Martin Jureček, Jiří Buček, Róbert Lórencz · 2019
In this paper we present cryptanalysis of the A5/1 stream cipher used in GSM mobile phones. Our attack is based on power analysis where we assume that the power consumption while clocking 3 LFSRs is different than when clocking 2 LFSRs. We demonstrate a simple power analysis (SPA) attack and discuss existing differential power analysis (DPA). We present the attack for recovering secret key based on the information on clocking bits of LFSRs that was deduced from power analysis. The attack has a 100% success rate, requires minimal storage and it does not requires any single bit of a keystream. An average time complexity of our attack based on SPA is around 233where the computation unit is a resolution of system of linear equations over the Z2. Recovering the secret key using information from the DPA has a constant complexity.