Predicting the shrinking generator with fixed connections

  • Authors:
  • Patrik Ekdahl;Willi Meier;Thomas Johansson

  • Affiliations:
  • Dept. of Information Technology, Lund University, Lund, Sweden;FH Aargau, Windisch, Switzerland;Dept. of Information Technology, Lund University, Lund, Sweden

  • Venue:
  • EUROCRYPT'03 Proceedings of the 22nd international conference on Theory and applications of cryptographic techniques
  • Year:
  • 2003

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Abstract

We propose a novel distinguishing attack on the shrinking generator with known feedback polynomial for the generating LFSR. The attack can e.g. reliably distinguish a shrinking generator with a weight 4 polynomial of degree as large as 10000, using 232 output bits. As the feedback polynomial of an arbitrary LFSR is known to have a polynomial multiple of low weight, our distinguisher applies to arbitrary shrunken LFSR's of moderate length. The analysis can also be used to predict the distribution of blocks in the generated keystream.