Cryptology ePrint Archive: Report 2018/937

Improved Brute-Force Search Strategies for Single-Trace and Few-Traces Template Attacks on the DES Round Keys

Mathias Wagner and Stefan Heyse

Abstract: We present an improved search strategy for a template attack on the secret DES key of a widely-used smart card, which is based on a Common-Criteria certified chip. We use the logarithm of the probability function as returned by the template attack itself, averaged over all 28 template positions along the rings representing the C and D Registers of the DES key schedule, as the sorting criteria for the key candidates. For weak keys - which in this attack model have a minimal rest entropy of only two bits - we find that on average only 37.75 bits need to be recovered by brute force when using only a single trace in the Exploitation Phase. This effort goes down to just a few bits for a single DES key when using only a few traces in Exploitation Phase.

Category / Keywords: implementation / DES, TDES, Template Attack, Side-channel Attack, Smart Card, SCA, block cipher, key enumeration, brute-force attack

Date: received 2 Oct 2018

Contact author: mathias wagner at nxp com

Available format(s): PDF | BibTeX Citation

Version: 20181005:131028 (All versions of this report)

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