Low-cost design of stealthy hardware trojan for bit-level fault attacks on block ciphers

Abstract

Fault analysis is a very powerful technique to break cryptographic implementations. In particular, bit-level fault analysis (BLFA), where faults are injected by flipping one or a few isolated bits, are among the most efficient of the lot. BLFA requires both precise fault injection capabilities and sophisticated key extraction skills. Algebraic fault analysis (AFA) is a good analysis technique for BLFA. Compared with differential fault analysis (DFA), AFA relies on the automation from machine solvers. Since it fully utilizes the leakages along propagation paths, it can extract the whole key when there is only one or a few bits infected, and when the injection is into the much deeper rounds. In practice, it is very difficult to inject precise bit-level faults and expensive equipments are indeed required. However, if the underlying cryptographic hardware is maliciously modified, BLFA can be easily achieved. This recent security threat is popularly known as Hardware trojan horse (HTH). HTH is a by-product of much popular and economically necessary outsourcing trend in semiconductors. A well designed HTH can precisely inject any type of faults to enable AFA and bypass detections, by having low cost and with low activation rate.