NICV: Normalized inter-class variance for detection of side-channel leakage

Side-Channel Attacks (SCA) are considered a serious threat against embedded cryptography. Therefore security critical chips must be tested for SCA resistance before deployment or certification. SCA are powerful but can need a lot of computation power, especially in the presence of countermeasures. With the advancement of electromagnetic (EM) measurement techniques in side-channel, high quality traces with enhanced resolution (or more points) are used in order to carry out SCA evaluations. The computation complexity of these attacks can be reduced by selecting a small subset of points where leakage prevails. In this paper, we propose a method to detect relevant leakage points in side-channel traces. The method is based on Normalized Inter-Class Variance (NICV). A key advantage of NICV over state-of-the-art is that NICV does neither need a clone device nor the knowledge of secret parameters of the crypto-system. NICV has a low computation requirement and it detects leakage using public information like input plaintexts or output ciphertexts only. It can also be used to test the efficiency of leakage models, the quality of traces and robustness of countermeasures. It is shown that NICV can be related to Pearson correlation and signal to noise ratio (SNR) which are standard metric in side-channel and EMC community. A theoretical rationale of NICV with practical application on real crypto-systems are provided to support our claims.