On the minimal embedding field

  • Authors:
  • Laura Hitt

  • Affiliations:
  • Department of Mathematics, The University of Texas at Austin, Austin, TX

  • Venue:
  • Pairing'07 Proceedings of the First international conference on Pairing-Based Cryptography
  • Year:
  • 2007

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Abstract

Let C be a curve of genus g, defined over a finite field Fq, where q = pm for a prime p. Let N be a large integer coprime to p, dividing the order of the Jacobian variety associated to C. Pairings can transport the discrete logarithm problem (DLP) from the curve to a finite field where there are more efficient methods for solving the discrete logarithm. The embedding degree is defined to be the smallest positive integer k such that N divides qk -1. We show that the minimal embedding field is not necessarily Fqk, as is traditionally understood, but rather is FpordNp = FqordNp/m, which can be a field of significantly smaller size. This fact reveals that attacks on the DLP can be dramatically faster than otherwise expected, so a parameter separate from the embedding degree k needs to be used to indicate security.