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Séminaire de Théorie Algorithmique des Nombres

Canonical Lift of Genus 2 Curves

Abdoulaye Maiga

( IMB )

Salle 385

le 14 janvier 2020 à 10:00

Let A/Fq\mathcal{A}/\mathbb{F}_q (with q=pnq=p^n) be an ordinary abelian variety, a classical result due to Lubin, Serre and Tate says that there exists a unique abelian variety A~\tilde{\mathcal{A}} over Zq\mathbb{Z}_q such that the modulo pp reduction of A~\tilde{\mathcal{A}} is A\mathcal{A} and End(A~)End(A)End(\tilde{\mathcal{A}})\cong End(\mathcal{A}) as a ring. In 2000 T.Satoh introduced a point-counting algorithm on elliptic curves over Fq\mathbb{F}_q based on canonical lift. In fact the action of the lifted Verschiebung on the tangent space gives Frobenius eigenvalues and hence the characteristic polynomial of the ordinary elliptic curves over Fq\mathbb{F}_q. We propose to extend the canonical lift algorithm introduced by T.Satoh to genus 2 curves over finite fields, using the modular polynomials in dimension 2. We first prove the Kronecker condition in dimension 2 case and then succeed to lift the endomorphism ring of A\mathcal{A} in dimension 2 case using a general lift algorithm of a pp-torsion group of an ordinary abelian variety. These results provide an algorithm to compute the characteristic polynomial of a genus 2 curves in quasi-quadratic time complexity.