Computing multiplicative inverses in finite fields by long division

Otokar Grošek 1  and Tomáš Fabšič 1
  • 1 Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava, 812 19, Bratislava, Slovakia

Abstract

We study a method of computing multiplicative inverses in finite fields using long division. In the case of fields of a prime order p, we construct one fixed integer d(p) with the property that for any nonzero field element a, we can compute its inverse by dividing d(p) by a and by reducing the result modulo p. We show how to construct the smallest d(p) with this property. We demonstrate that a similar approach works in finite fields of a non-prime order, as well. However, we demonstrate that the studied method (in both cases) has worse asymptotic complexity than the extended Euclidean algorithm.

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