EM Frequency Domain Correlation Analysis on Cipher Chips

Inserting random time delay into cipher device´s running process is a general countermeasure against time domain correlation side channel attacks. In which way the interesting intermediate operations will occur at different time in different runs of the cipher. To break this countermeasure, based on the property that the data dependence of the electromagnetic (EM) signals emitted from the cipher chips can remain when they are transformed from time domain to frequency domain, and power spectrum density will not be affected by inserting random delays into time domain signals, this paper presents a new EM frequency domain correlation analysis. Experiments of EM frequency domain correlation analysis on a micro-controller implemented AES show that the genuine key of AES can still be revealed after inserting random delays in source code, while correlation analysis in time domain is invalid.