peridot/vendor/github.com/cloudflare/circl/ecc/goldilocks/isogeny.go
2024-10-16 12:56:53 +02:00

53 lines
1.7 KiB
Go

package goldilocks
import fp "github.com/cloudflare/circl/math/fp448"
func (Curve) pull(P *twistPoint) *Point { return twistCurve{}.push(P) }
func (twistCurve) pull(P *Point) *twistPoint { return Curve{}.push(P) }
// push sends a point on the Goldilocks curve to a point on the twist curve.
func (Curve) push(P *Point) *twistPoint {
Q := &twistPoint{}
Px, Py, Pz := &P.x, &P.y, &P.z
a, b, c, d, e, f, g, h := &Q.x, &Q.y, &Q.z, &fp.Elt{}, &Q.ta, &Q.x, &Q.y, &Q.tb
fp.Add(e, Px, Py) // x+y
fp.Sqr(a, Px) // A = x^2
fp.Sqr(b, Py) // B = y^2
fp.Sqr(c, Pz) // z^2
fp.Add(c, c, c) // C = 2*z^2
*d = *a // D = A
fp.Sqr(e, e) // (x+y)^2
fp.Sub(e, e, a) // (x+y)^2-A
fp.Sub(e, e, b) // E = (x+y)^2-A-B
fp.Add(h, b, d) // H = B+D
fp.Sub(g, b, d) // G = B-D
fp.Sub(f, c, h) // F = C-H
fp.Mul(&Q.z, f, g) // Z = F * G
fp.Mul(&Q.x, e, f) // X = E * F
fp.Mul(&Q.y, g, h) // Y = G * H, // T = E * H
return Q
}
// push sends a point on the twist curve to a point on the Goldilocks curve.
func (twistCurve) push(P *twistPoint) *Point {
Q := &Point{}
Px, Py, Pz := &P.x, &P.y, &P.z
a, b, c, d, e, f, g, h := &Q.x, &Q.y, &Q.z, &fp.Elt{}, &Q.ta, &Q.x, &Q.y, &Q.tb
fp.Add(e, Px, Py) // x+y
fp.Sqr(a, Px) // A = x^2
fp.Sqr(b, Py) // B = y^2
fp.Sqr(c, Pz) // z^2
fp.Add(c, c, c) // C = 2*z^2
fp.Neg(d, a) // D = -A
fp.Sqr(e, e) // (x+y)^2
fp.Sub(e, e, a) // (x+y)^2-A
fp.Sub(e, e, b) // E = (x+y)^2-A-B
fp.Add(h, b, d) // H = B+D
fp.Sub(g, b, d) // G = B-D
fp.Sub(f, c, h) // F = C-H
fp.Mul(&Q.z, f, g) // Z = F * G
fp.Mul(&Q.x, e, f) // X = E * F
fp.Mul(&Q.y, g, h) // Y = G * H, // T = E * H
return Q
}