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arXiv · 0705.1423

Counting hyperelliptic curves that admit a Koblitz model

Cevahir Demirkiran·Enric Nart
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Abstract

Let k be a finite field of odd characteristic. We find a closed formula for the number of k-isomorphism classes of pointed, and non-pointed, hyperelliptic curves of genus g over k, admitting a Koblitz model. These numbers are expressed as a polynomial in the cardinality q of k, with integer coefficients (for pointed curves) and rational coefficients (for non-pointed curves). The coefficients depend on g and the set of divisors of q-1 and q+1. These formulas show that the number of hyperelliptic curves of genus g suitable (in principle) of cryptographic applications is asymptotically (1-e^{-1})2q^{2g-1}, and not 2q^{2g-1} as it was believed. The curves of genus g=2 and g=3 are more resistant to the attacks to the DLP; for these values of g the number of curves is respectively (91/72)q^3+O(q^2) and (3641/2880)q^5+O(q^4).

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BibTeXRIS

Cevahir Demirkiran, Enric Nart. 2007-05-10. Counting hyperelliptic curves that admit a Koblitz model. https://arxiv.org/abs/0705.1423

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