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Introducing a New Variant of Fast Algebraic Attacks and Minimizing Their Successive Data Complexity

Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3715)

Abstract

Algebraic attacks have established themselves as a powerful method for the cryptanalysis of LFSR-based keystream generators (e.g., E 0 used in Bluetooth). The attack is based on solving an overdetermined system of low-degree equations R t =0, where R t is an expression in the state of the LFSRs at clock t and one or several successive keystream bits z t ,...,z t + δ .

In fast algebraic attacks, new equations of a lower degree are constructed in a precomputation step. This is done by computing appropriate linear combinations of T successive initial equations R t =0. The successive data complexity of the attack is the number T of successive equations.

We propose a new variant of fast algebraic attacks where the same approach is employed to eliminate some unknowns, making a divide-and-conquer attack possible. In some cases, our variant is applicable whereas the first one is not.

Both variants can have a high successive data complexity (e.g., T≥ 8.822.188 for E 0). We describe how to keep it to a minimum and introduce suitable efficient algorithms for the precomputation step.

Keywords

fast algebraic attacks stream ciphers linear feedback shift registers Bluetooth 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  1. 1.Theoretische InformatikUniversität MannheimMannheimGermany
  2. 2.IRMARUniversity of RennesRennesFrance

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