Constructing pairing-friendly algebraic curves of genus 2 curves with small rho-value

Abstract

For pairing-based cryptographic protocols to be both efficient and secure, the underlying genus 2 curves defined over finite fields used must satisfy pairing-friendly conditions, and have small rho-value, which are not likely to be satisfied with random curves. In this thesis, we study two specific families of genus 2 curves defined over finite fields whose Jacobians do not split over the ground fields into a product of elliptic curves, but geometrically split over an extension of the ground field of prescribed degree n=3, 4, or 6. These curves were also studied extensively recently by Kawazoe and Takahashi in 2008, and by Freeman and Satoh in 2009 in their searches of pairing-friendly curves. We present a new method for constructing and identifying suitable curves in these two families which satisfy the pairing-friendly conditions and have rho-values around 4. The computational results of the rho-values obtained in this thesis are consistent with those found by Freeman and Satoh in 2009. An extension of our new method has led to a cryptographic example of a pairing-friendly curve in one of the two families which has rho-value 2.969, and it is the lowest rho-value ever recorded for curves of this type. Our method is different from the method proposed by Freeman and Satoh, since we can prescribe the minimal degree n =3,4 or 6 extension of the ground fields which the Jacobians of the curves split over.