Portability of templates

• Published in: Journal of cryptographic engineering Vol. 2; no. 1; pp. 63 - 74
• Main Authors: Elaabid, M. Abdelaziz, Guilley, Sylvain
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.05.2012; Springer
• Subjects: Circuits and Systems; Communications Engineering; Computer Communication Networks; Computer Science; Cryptography and Security; Cryptology; Data Structures and Information Theory; Networks; Operating Systems; Regular Paper; Resynchronization; Template attack; Side-channel attacks
• ISSN: 2190-8508; 2190-8516
• DOI: 10.1007/s13389-012-0030-6

Template attacks consist of two stages: a profiling and a matching step. This way of attacking a circuit can be shown to be optimal when the profiling exactly describes the side-channel leakage of the circuit to be attacked. On the contrary, this article focuses on identifying the problems that arise when there is a discrepancy between the templates and the traces to match. Based on a real-world case study, we show that two phenomena can hinder the success of template attacks when the precharacterized templates are outdated: the traces can be desynchronized and the amplitudes can be scaled differently. We observe that the consequence of these distortions can be as dramatic as ranking the correct key last, which is the worst degradation possible for a side-channel distinguisher, since an attacker is usually interested in the first keys in the rankings. Then we suggest two ways to correct the templates mismatches: waveform realignment and acquisition campaigns normalization. After this processing, it appears that the template attacks almost do not lose any efficiency in terms of success rate and guessing entropy with respect to an attack with ideal templates.