Cryptology ePrint Archive: Report 2017/272

Dissecting Leakage Resilient PRFs with Multivariate Localized EM Attacks - A Practical Security Evaluation on FPGA

Florian Unterstein and Johann Heyszl and Fabrizio De Santis and Robert Specht

Abstract: In leakage-resilient symmetric cryptography, two important concepts have been proposed in order to decrease the success rate of differential side-channel attacks. The first one is to limit the attacker’s data complexity by restricting the number of observable inputs; the second one is to create correlated algorithmic noise by using parallel S-boxes with equal inputs. The latter hinders the typical divide and conquer approach of differential side-channel attacks and makes key recovery much more difficult in practice. The use of localized electromagnetic (EM) measurements has already been shown to limit the effectiveness of such measures in previous works based on PRESENT S-boxes and 90nm FPGAs. However, it has been left for future investigation in recent publications based on AES S-boxes. We aim at providing helpful results and insights from LDA-preprocessed, multivariate, localized EM attacks against a 45nm FPGA implementation using AES S-boxes. We show, that even in the case of densely placed S-boxes (with identical routing constraints), and even when limiting the data complexity to the minimum of only two inputs, the guessing entropy of the key is reduced to only 2^48 , which remains well within the key enumeration capabilities of today’s adversaries. Relaxing the S-box placement constraints further reduces the guessing entropy. Also, increasing the data complexity for efficiency, decreases it down to a direct key recovery. While our results are empirical and reflective of one device and implementation, they emphasize the threat of multivariate localized EM attacks to such AES-based leakage-resilient constructions, more than currently believed.

Category / Keywords: AES, side-channel attack, localized EM measurements, leakage resilience, PRF

Original Publication (in the same form): 8th International Workshop on Constructive Side-Channel Analysis and Secure Design (COSADE 2017)

Date: received 24 Mar 2017, last revised 12 Dec 2017

Contact author: florian unterstein at aisec fraunhofer de

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Version: 20171212:144236 (All versions of this report)

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