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Paper 2019/1294

Finite field mapping to elliptic curves of $j$-invariant $1728$

Dmitrii Koshelev

Abstract

This article generalizes the simplified Shallue--van de Woestijne--Ulas (SWU) method of deterministic finite field mapping $\mathbb{F}_{\!q} \to E(\mathbb{F}_{\!q})$ to the case of any elliptic $\mathbb{F}_{\!q}$-curve $E$ of $j$-invariant $1728$. More precisely, we obtain a rational $\mathbb{F}_{\!q}$-curve $C$ (and its explicit quite simple proper $\mathbb{F}_{\!q}$-parametrization $par\!: \mathbb{P}^1 \to C$) on the Kummer surface $K$ associated with the direct product $E \!\times\! E^\prime$, where $E^\prime$ is the quadratic $\mathbb{F}_{\!q}$-twist of $E$. The SWU method consists in computing the direct image of $par$ and a subsequent inverse image $(P,Q)$ of the natural two-sheeted covering $\rho\!: E \!\times\! E^\prime \to K$. Denoting by $\sigma\!:E^\prime \to E$ the corresponding $\mathbb{F}_{\!q^2}$-isomorphism, it is easily seen that $P \in E(\mathbb{F}_{\!q})$ or $\sigma(Q) \in E(\mathbb{F}_{\!q})$. We produce the curve $C$ as one of two absolutely irreducible $\mathbb{F}_{\!q}$-components of $pr^{{-}1}(C_8)$ for some rational $\mathbb{F}_{\!q}$-curve $C_8$ of bidegree $(8,8)$ with $42$ singular points, where $pr\!: K \to \mathbb{P}^1 \!\times\! \mathbb{P}^1$ is the two-sheeted projection to $x$-coordinates of $E$ and $E^\prime$.

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Implementation
Publication info
Preprint. MINOR revision.
Keywords
finite fieldspairing-based cryptographyelliptic curves of $j$-invariant $1728$Kummer surfacesrational curvesWeil restrictionisogenies
Contact author(s)
dishport @ ya ru
History
2021-06-21: last of 12 revisions
2019-11-07: received
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Short URL
https://ia.cr/2019/1294
License
Creative Commons Attribution
CC BY
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