## Cryptology ePrint Archive: Report 2004/151

Suitable Curves for Genus-4 HCC over Prime Fields: Point Counting Formulae for Hyperelliptic Curves of type $y^2=x^{2k+1}+ax$

Mitsuhiro Haneda and Mitsuru Kawazoe and Tetsuya Takahashi

Abstract: Computing the order of the Jacobian group of a hyperelliptic curve over a finite field is very important to construct a hyperelliptic curve cryptosystem (HCC), because to construct secure HCC, we need Jacobian groups of order in the form $l(J\(Bcdot c$ where $l$ is a prime greater than about $2^{160}$ and $c$ is a very small integer. But even in the case of genus two, known algorithms to compute the order of a Jacobian group for a general curve need a very long running time over a large prime field. In the case of genus three, only a few examples of suitable curves for HCC are known. In the case of genus four, no example has been known over a large prime field. In this article, we give explicit formulae of the order of Jacobian groups for hyperelliptic curves over a finite prime field of type $y^2=x^{2k+1}+a x$, which allows us to search suitable curves for HCC. By using these formulae, we can find many suitable curves for genus-4 HCC and show some examples.

Category / Keywords: public-key cryptography / hyperelliptic curve cryptosystem, number theory

Date: received 1 Jul 2004, last revised 15 Jul 2004

Contact author: kawazoe at mi cias osakafu-u ac jp

Available format(s): PDF | BibTeX Citation

Note: a minor error corrected.

Short URL: ia.cr/2004/151

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