Abstract: This cryptographic curve generation technique provides a faster way of constructing a genus 2 curve. The technique provides a procedure to compute isogenies between genus 2 curves over finite fields. Instead of looping over possible roots, as is typically done when solving Igusa class polynomials, the technique only finds one root and then applies the isogenies to find the others. The technique computes a set of polynomials that define all isogenies. To do this, for a given root of an Igusa class polynomial over a finite field, the technique computes a value of a small modular function ƒ. To the value of this function ƒ, the technique applies an isogeny to find an isogenous ƒ-value. The technique then transforms the ƒ-value back into an Igusa value. Once the Igusa class polynomials are solved they can be used to generate a genus 2 curve which can be used in cryptographic applications.

Abstract: Techniques are disclosed for representing and evaluating large prime degree isogenies for use in cryptographic signature and encryption schemes. An isogeny of prime degree 1 may be represented as an ideal in the form (1, A*alpha+B), where 1 comprises the degree of a prime number, the prime number is split into integers a and b, and alpha is a known endomorphism. For a given degree 1, integers a and b define a unique isogeny, allowing the isogeny to be stored with 3 log(1) bits of information. Techniques are also disclosed to evaluate the isogeny at a given point by decomposing the isogeny into an integer and a plurality of smaller degree isogenies, evaluating the smaller degree isogenies at the point with traditional means, and multiplying the results of the evaluations together and with the integer.

Abstract: This cryptographic curve generation technique provides a faster way of constructing a genus 2 curve. The technique provides a procedure to compute isogenies between genus 2 curves over finite fields. Instead of looping over possible roots, as is typically done when solving Igusa class polynomials, the technique only finds one root and then applies the isogenies to find the others. The technique computes a set of polynomials that define all isogenies. To do this, for a given root of an Igusa class polynomial over a finite field, the technique computes a value of a small modular function ƒ. To the value of this function ƒ, the technique applies an isogeny to find an isogenous ƒ-value. The technique then transforms the ƒ-value back into an Igusa value. Once the Igusa class polynomials are solved they can be used to generate a genus 2 curve which can be used in cryptographic applications.

Abstract: Techniques are disclosed for representing and evaluating large prime degree isogenies for use in cryptographic signature and encryption schemes. An isogeny of prime degree 1 may be represented as an ideal in the form (1, A*alpha+B), where 1 comprises the degree of a prime number, the prime number is split into integers a and b, and alpha is a known endomorphism. For a given degree 1, integers a and b define a unique isogeny, allowing the isogeny to be stored with 3 log(1) bits of information. Techniques are also disclosed to evaluate the isogeny at a given point by decomposing the isogeny into an integer and a plurality of smaller degree isogenies, evaluating the smaller degree isogenies at the point with traditional means, and multiplying the results of the evaluations together and with the integer.