[Resource Topic] 2022/150: The Generalized Montgomery Coordinate: A New Computational Tool for Isogeny-based Cryptography

Welcome to the resource topic for 2022/150

Title:
The Generalized Montgomery Coordinate: A New Computational Tool for Isogeny-based Cryptography

Authors: Tomoki Moriya, Hiroshi Onuki, Yusuke Aikawa, Tsuyoshi Takagi

Abstract:

Isogeny-based cryptography is one of the main candidates of post-quantum cryptography. To realize efficient computations, one usually uses formulas of scalar multiplications and isogeny computations on elliptic curves using only one coordinate in isogeny-based cryptography. The x-coordinate of Montgomery curves is the most standard, and we sometimes use the x-coordinate of Montgomery$^-$ curves, the w-coordinate of Edwards curves, and the w-coordinate of Huff’s curves. In this paper, we define a novel function on elliptic curves called the generalized Montgomery coordinate that has the four coordinates described above as special cases. For a generalized Montgomery coordinate, we construct an explicit formula of scalar multiplication which includes the division polynomial, and both a formula of an image point under an isogeny and that of a coefficient of the codomain curve. Finally, we expect numerous applications for the generalized Montgomery coefficient. As an experimental study, we present two applications of the theory of a generalized Montgomery coordinate. The first one is to construct a new efficient formula to compute isogenies on Montgomery curves. This formula is more efficient than the previous one for high degree isogenies as the \sqrt{\vphantom{2}}'{e}lu’s formula in our implementation. The second one is to construct a new generalized Montgomery coordinate for Montgomery$^-$ curves used for CSURF.

ePrint: https://eprint.iacr.org/2022/150

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