Power trace alignment for cryptosystems featuring random frequency countermeasures

Using a random number generator for the control of the input clock in FPGA-based cryptographic systems causes misalignments in the power traces, which can be exploited as a countermeasure against Correlation Power Analysis (CPA). In this paper we propose a method to process such misaligned traces in order to identify power peaks dynamically and to align them partially. After removing the misalignment caused by such a countermeasure and a subsequent trace processing the cryptosystem may easily be attacked by the CPA method. By means of a comprehensive measurement and analysis process of an AES 128 bit block cipher we demonstrate that the proposed method can deal with misaligned traces very efficiently.