Combining algebraic and side channel attacks on stream ciphers

Abstract

A cryptanalysis technique can be termed successful if its complexity is better than brute force attack, even though it may not be practically feasible due to high complexity. However, it is a proven fact that combining different type of attack techniques in past has paid dividends with regards to overall complexity. We, in this paper propose novel idea of combining algebraic and side channel attacks on stream ciphers. Algebraic cryptanalysis has a high cost when pitched against stream ciphers with nonlinear update and for side channel attacks, adversary needs to have a continued access to cipher's implementation. On the other hand combining both these attacks can overcome their individual shortcomings to a great extent, thereby making it practically feasible. Algebraic and side channel attacks have been earlier combined on block ciphers, but no work on applying such attacks against stream ciphers has been published so far.