Application of Simple Power Analysis to Stream Ciphers Constructed Using Feedback Shift Registers
Abdulah Abdulah Zadeh, Howard M. Heys · The Computer Journal · 2014
Although power analysis attacks have been extensively applied to block ciphers, only limited research has been done to analyze their effectiveness on stream cipher hardware implementations. In this paper, we investigate methods of simple power analysis applied to stream ciphers based on multiple feedback shift registers (FSRs) and demonstrate the effectiveness of the methods by examining the cipher Grain which involves both a linear and a nonlinear FSR. A divide-and-conquer attack is presented where the attacker guesses the bit values of the FSRs independently and then checks the correctness of the guess using information derived from measured power consumption of the cipher core. Experimental results of the attack applied to simulated power data obtained for a CMOS implementation of Grain show that it is possible to recover directly the cipher state using only about 3000 power samples. For ciphers constructed using a general architecture of multiple FSRs, the attack has the potential to be successful with a complexity substantially less than exhaustive key search.