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Another look at weak feedback polynomials in the nonlinear combiner

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Author

Summary, in English

Feedback polynomials with low degree multiples of low weight should be avoided in linear feedback shift registers when used in nonlinear combiners. We consider another class of weak feedback polynomials, namely the class when taps are located in small groups. This class was introduced in 2004 demonstrating that the resulting distinguishing attack can sometimes be better than the one using low weight multiples. In this paper we take another look at these polynomials and give further insight to the theory behind the attack complexity. Using the Walsh transform we show an easy way to determine the attack complexity given a polynomial. Further, we show that the size of the vectors should sometimes be larger than previously known. We also give a simple relation showing when the new attack will outperform the simple attack based on low weight multiples.

Publishing year

2009

Language

English

Pages

1115-1119

Document type

Conference paper

Topic

  • Electrical Engineering, Electronic Engineering, Information Engineering

Keywords

  • weak feedback polynomials
  • stream ciphers
  • cryptography
  • LFSR

Conference name

IEEE International Symposium on Information Theory (ISIT), 2009

Conference date

2009-06-28 - 2009-07-03

Conference place

Seoul, Korea, Democratic People's Republic of

Status

Published

Research group

  • Crypto and Security