We present a generalization to genus 2 of the probabilistic algorithm of
Sutherland for computing Hilbert class polynomials. The improvement over the
Bröker-Gruenewald-Lauter algorithm for the genus 2 case is that we do not need to
find a curve in the isogeny class whose endomorphism ring is the maximal order;
rather, we present a probabilistic algorithm for “going up” to a maximal curve (a
curve with maximal endomorphism ring), once we find any curve in the right isogeny
class. Then we use the structure of the Shimura class group and the computation of
-isogenies
to compute all isogenous maximal curves from an initial one.
Keywords
class field polynomials, CRT, hyperelliptic curve
cryptography, isogenies