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Dissecting leakage resilient PRFs with multivariate localized EM attacks

A practical security evaluation on FPGA
: Unterstein, F.; Heyszl, J.; Santis, F. de; Specht, R.


Guilley, S.:
Constructive side-channel analysis and secure design. 8th International Workshop, COSADE 2017 : Paris, France, April 13-14, 2017; Revised selected papers
Cham: Springer International Publishing, 2017 (Lecture Notes in Computer Science 10348)
ISBN: 978-3-319-64646-6 (Print)
ISBN: 978-3-319-64647-3 (Online)
International Workshop on Constructive Side-Channel Analysis and Secure Design (COSADE) <8, 2017, Paris>
Fraunhofer AISEC ()

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 90 nm 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 45 nm 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 248, 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.