Negation and addition formulae for nonsingular points in Jacobian coordinates #
Let W
be a Weierstrass curve over a field F
. The nonsingular Jacobian points on W
can be given
negation and addition operations defined by an analogue of the secant-and-tangent process in
Mathlib/AlgebraicGeometry/EllipticCurve/Affine.lean
, but the polynomials involved are
(2, 3, 1)
-homogeneous, so any instances of division become multiplication in the Z
-coordinate.
Most computational proofs are immediate from their analogous proofs for affine coordinates.
This file defines polynomials associated to negation, doubling, and addition of Jacobian point
representatives. The group operations and the group law on actual nonsingular Jacobian points will
be defined in Mathlib/AlgebraicGeometry/EllipticCurve/Jacobian/Point.lean
.
Main definitions #
WeierstrassCurve.Jacobian.negY
: theY
-coordinate of-P
.WeierstrassCurve.Jacobian.dblZ
: theZ
-coordinate of2 • P
.WeierstrassCurve.Jacobian.dblX
: theX
-coordinate of2 • P
.WeierstrassCurve.Jacobian.negDblY
: theY
-coordinate of-(2 • P)
.WeierstrassCurve.Jacobian.dblY
: theY
-coordinate of2 • P
.WeierstrassCurve.Jacobian.addZ
: theZ
-coordinate ofP + Q
.WeierstrassCurve.Jacobian.addX
: theX
-coordinate ofP + Q
.WeierstrassCurve.Jacobian.negAddY
: theY
-coordinate of-(P + Q)
.WeierstrassCurve.Jacobian.addY
: theY
-coordinate ofP + Q
.
Implementation notes #
The definitions of WeierstrassCurve.Jacobian.addX
and WeierstrassCurve.Jacobian.negAddY
are
given explicitly by large polynomials that are homogeneous of degrees 8
and 12
respectively.
Clearing the denominators of their corresponding affine rational functions in
Mathlib/AlgebraicGeometry/EllipticCurve/Affine.lean
would give polynomials that are
homogeneous of degrees 12
and 18
respectively, so their actual definitions are off by powers of
a certain polynomial factor that is homogeneous of degree 2
. This factor divides their
corresponding affine polynomials only modulo the (2, 3, 1)
-homogeneous Weierstrass equation, so
their large quotient polynomials are calculated explicitly in a computer algebra system. All of this
is done to ensure that the definitions of both WeierstrassCurve.Jacobian.dblXYZ
and
WeierstrassCurve.Jacobian.addXYZ
are (2, 3, 1)
-homogeneous of degree 4
.
Whenever possible, all changes to documentation and naming of definitions and theorems should be
mirrored in Mathlib/AlgebraicGeometry/EllipticCurve/Projective/Formula.lean
.
References #
J Silverman, The Arithmetic of Elliptic Curves
Tags #
elliptic curve, Jacobian, negation, doubling, addition, group law
Negation formulae in Jacobian coordinates #
Doubling formulae in Jacobian coordinates #
The unit associated to a representative of 2 • P
for a Jacobian point representative P
on a
Weierstrass curve W
that is 2
-torsion.
More specifically, the unit u
such that W.add P P = u • ![1, 1, 0]
where P = W.neg P
.
Equations
- W'.dblU P = (MvPolynomial.eval P) W'.polynomialX
Instances For
The X
-coordinate of a representative of 2 • P
for a Jacobian point representative P
on a
Weierstrass curve.
Equations
Instances For
The Y
-coordinate of a representative of -(2 • P)
for a Jacobian point representative P
on
a Weierstrass curve.
Equations
Instances For
The Y
-coordinate of a representative of 2 • P
for a Jacobian point representative P
on a
Weierstrass curve.
Instances For
Addition formulae in Jacobian coordinates #
The unit associated to a representative of P + Q
for two Jacobian point representatives P
and Q
on a Weierstrass curve W
that are not 2
-torsion.
More specifically, the unit u
such that W.add P Q = u • ![1, 1, 0]
where
P x / P z ^ 2 = Q x / Q z ^ 2
but P ≠ W.neg P
.
Instances For
The Z
-coordinate of a representative of P + Q
for two distinct Jacobian point
representatives P
and Q
on a Weierstrass curve.
If the representatives of P
and Q
are equal, then this returns the value 0
.
Instances For
The X
-coordinate of a representative of P + Q
for two distinct Jacobian point
representatives P
and Q
on a Weierstrass curve.
If the representatives of P
and Q
are equal, then this returns the value 0
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The Y
-coordinate of a representative of -(P + Q)
for two distinct Jacobian point
representatives P
and Q
on a Weierstrass curve.
If the representatives of P
and Q
are equal, then this returns the value 0
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The Y
-coordinate of a representative of P + Q
for two distinct Jacobian point
representatives P
and Q
on a Weierstrass curve.
If the representatives of P
and Q
are equal, then this returns the value 0
.
Instances For
The coordinates of a representative of P + Q
for two distinct Jacobian point
representatives P
and Q
on a Weierstrass curve.
If the representatives of P
and Q
are equal, then this returns the value ![0, 0, 0]
.