Side-Channel Leakage in Masked Circuits Caused by Higher-Order Circuit Effects

Abstract. Hardware masking is a well-known countermeasure against Side-Channel Attacks (SCA). Like many other countermeasures, the side-channel resistance of masked circuits is susceptible to low-level cir-cuit effects. However, no detailed analysis is available that explains how, and to what extent, these low-level circuit effects are causing side-channel leakage. Our first contribution is a unified and consistent analysis to ex-plain how glitches and inter-wire capacitance cause side-channel leakage on masked hardware. Our second contribution is to show that inter-wire capacitance and glitches are causing side-channel leakage of comparable magnitude according to HSPICE simulations. Our third contribution is to confirm our analysis with a successful DPA-attack on a 90nm COMS FPGA implementation of a glitch-free masked AES S-Box. According to existing literature, this circuit would be side-channel resistant, while ac-cording to our analysis and measurement, it shows side-channel leakage. Our conclusion is that circuit-level effects, not only glitches, present a practical concern for masking schemes.