Hardness of Approximating the Minimum Distance of a Linear Code

  • Authors:
  • Ilya Dumer;Daniele Micciancio;Madhu Sudan

  • Affiliations:
  • -;-;-

  • Venue:
  • FOCS '99 Proceedings of the 40th Annual Symposium on Foundations of Computer Science
  • Year:
  • 1999

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Abstract

We show that the minimum distance of a linear code (or equivalently, the weight of the lightest code-word) is not approximable to within any constant factor in random polynomial time (RP), unless NP equals RP. Under the stronger assumption that NP is not contained in RQP (random quasi-polynomial time), we show that the minimum distance is not approximable to within the factor \math, for any \math, where n denotes the block length of the code.Our results hold for codes over every finite field, including the special case of binary codes. In the process we show that the nearest code-word problem is hard to solve even under the promise that the number of errors is (a constant factor) smaller than the distance of the code. This is a particularly meaningful version of the nearest code-word problem.Our results strengthen (though using stronger assumptions) a previous result of Vardy who showed that the minimum distance is NP-hard to compute exactly. Our results are obtained by adapting proofs of analogous results for integer lattices due to Ajtai and Micciancio. A critical component in the adaptation is our use of linear codes that perform better than random (linear) codes.