Cryptology ePrint Archive: Report 2009/473

A Simple Power Analysis Attack on the Serpent Key Schedule

Kevin J. Compton and Brian Timm and Joel VanLaven

Abstract: We describe an SPA attack on an 8-bit smart card implementation of the Serpent block cipher. Our attack uses measurements taken during an on-the-fly key expansion together with linearity in the cipher's key schedule algorithm to drastically reduce the search time for an initial key. An implementation finds 256-bit keys in 3.736 ms on average. Our work shows that linearity in key schedule design and other cryptographic applications should be carefully evaluated for susceptibility to side-channel attacks and that search algorithm design can greatly speed up side-channel attacks.

Category / Keywords: secret-key cryptography / Serpent, SPA, Power Attack, Linearity, Block Cipher

Date: received 24 Sep 2009

Contact author: kjc at umich edu

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Version: 20090926:044219 (All versions of this report)

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