Cryptology ePrint Archive: Report 2018/317

Sliding-Window Correlation Attacks Against Encryption Devices with an Unstable Clock

Dor Fledel and Avishai Wool

Abstract: Power analysis side channel attacks rely on aligned traces. As a counter-measure, devices can use a jittered clock to misalign the power traces. In this paper we suggest a way to overcome this counter-measure, using an old method of integrating samples over time followed by a correlation attack (Sliding Window CPA). We theoretically re-analyze this general method with characteristics of jittered clocks and show that it is stronger than previously believed. We show that integration of samples over a suitably chosen window size actually amplifies the correlation both with and without jitter - as long as multiple leakage points are present within the window. We then validate our analysis on a new data-set of traces measured on a board implementing a jittered clock. Our experiments show that the SW-CPA attack with a well-chosen window size is very successful against a jittered clock counter-measure and significantly outperforms previous suggestions, requiring a much smaller set of traces to correctly identify the correct key.

Category / Keywords: implementation / Power analysis, SW-CPA, Jittered clocks

Date: received 31 Mar 2018, last revised 3 Apr 2018

Contact author: dorfledel at gmail com

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Note: Asked by eprint

Version: 20180404:131910 (All versions of this report)

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