Lattice problems in NP ∩ coNP

  • Authors:
  • Dorit Aharonov;Oded Regev

  • Affiliations:
  • The Hebrew University, Jerusalem, Israel;Tel-Aviv University, Tel-Aviv, Israel

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 2005

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Abstract

We show that the problems of approximating the shortest and closest vector in a lattice to within a factor of &nradic; lie in NP intersect coNP. The result (almost) subsumes the three mutually-incomparable previous results regarding these lattice problems: Banaszczyk [1993], Goldreich and Goldwasser [2000], and Aharonov and Regev [2003]. Our technique is based on a simple fact regarding succinct approximation of functions using their Fourier series over the lattice. This technique might be useful elsewhere---we demonstrate this by giving a simple and efficient algorithm for one other lattice problem (CVPP) improving on a previous result of Regev[2003]. An interesting fact is that our result emerged from a “dequantization” of our previous quantum result in Aharonov and Regev [2003]. This route to proving purely classical results might be beneficial elsewhere.