Efficient multiplication in finite field extensions of degree 5

  • Authors:
  • Nadia El Mrabet;Aurore Guillevic;Sorina Ionica

  • Affiliations:
  • LIASD, Université Paris 8, France;Laboratoire Chiffre, Thales Communications S.A., Colombes Cedex, France and Équipe Crypto DI, École Normale Supérieure, France;TANC, Inria Saclay and LIX, École Polytechnique, France

  • Venue:
  • AFRICACRYPT'11 Proceedings of the 4th international conference on Progress in cryptology in Africa
  • Year:
  • 2011

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Abstract

Small degree extensions of finite fields are commonly used for cryptographic purposes. For extension fields of degree 2 and 3, the Karatsuba and Toom Cook formulæ perform a multiplication in the extension field using 3 and 5 multiplications in the base field, respectively. For degree 5 extensions, Montgomery has given a method to multiply two elements in the extension field with 13 base field multiplications. We propose a faster algorithm, which requires only 9 base field multiplications. Our method, based on Newton's interpolation, uses a larger number of additions than Montgomery's one but our implementation of the two methods shows that for cryptographic sizes, our algorithm is much faster.