Fault Analysis of Stream Ciphers

A fault attack is a powerful cryptanalytic tool which can be applied to many types of cryptosystems which are not vulnerable to direct attacks. The research literature contains many examples of fault attacks on public key cryptosystems and block ciphers, but surprisingly we could not find any systematic study of the applicability of fault attacks to stream ciphers. Our goal in this paper is to develop general techniques which can be used to attack the standard constructions of stream ciphers based on LFSR’s, as well as more specialized techniques which can be used against specific stream ciphers such as RC4, LILI-128 and SOBERt32. While most of the schemes can be successfully attacked, we point out several interesting open problems such as an attack on FSM filtered constructions and the analysis of high Hamming weight faults in LFSR’s.