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feat: implement From on EC structs #4148

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feat: implement From on EC structs #4148

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517077b
feat: implement `From` to convert between affine and curvegroup EC st…
TomAFrench Jan 24, 2024
d749d99
chore: switch to usage of `Into`
TomAFrench Jan 24, 2024
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90 changes: 70 additions & 20 deletions noir_stdlib/src/ec/montcurve.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ mod affine {
use crate::ec::sqrt;
use crate::ec::ZETA;
use crate::cmp::Eq;
use crate::from::From;

// Curve specification
struct Curve { // Montgomery Curve configuration (ky^2 = x^3 + j*x^2 + x)
Expand Down Expand Up @@ -41,12 +42,7 @@ mod affine {

// Conversion to CurveGroup coordinates
fn into_group(self) -> curvegroup::Point {
if self.is_zero() {
curvegroup::Point::zero()
} else {
let (x,y) = (self.x, self.y);
curvegroup::Point::new(x,y,1)
}
self.into()
}

// Additive identity
Expand Down Expand Up @@ -79,6 +75,31 @@ mod affine {
}
}

impl From<curvegroup::Point> for Point {
fn from(input: curvegroup::Point) -> Point {
if input.is_zero() {
Point::zero()
} else {
let (x,y,z) = (input.x, input.y, input.z);
Point::new(x/z, y/z)
}
}
}

impl From<TEPoint> for Point {
fn from(input: TEPoint) -> Point {
if input.is_zero() {
Point::zero()
} else {
let TEPoint {x, y} = input;
let x0 = (1+y)/(1-y);
let y0 = (1+y)/(x*(1-y));

Point::new(x0,y0)
}
}
}

impl Curve {
// Curve constructor
pub fn new(j: Field, k: Field, gen: Point) -> Self {
Expand All @@ -96,7 +117,7 @@ mod affine {

// Conversion to CurveGroup coordinates
fn into_group(self) -> curvegroup::Curve {
curvegroup::Curve::new(self.j, self.k, self.gen.into_group())
self.into()
}

// Membership check
Expand Down Expand Up @@ -211,6 +232,22 @@ mod affine {
self.map_from_swcurve(self.into_swcurve().swu_map(z,u))
}
}

impl From<curvegroup::Curve> for Curve {
fn from(input: curvegroup::Curve) -> Curve {
Curve::new(input.j, input.k, input.gen.into())
}
}

impl From<TECurve> for Curve {
fn from(input: TECurve) -> Curve {
let j = 2*(input.a + input.d)/(input.a - input.d);
let k = 4/(input.a - input.d);
let gen_montcurve = input.gen.into();

Curve::new(j, k, gen_montcurve)
}
}
}
mod curvegroup {
// Affine representation of Montgomery curves
Expand All @@ -223,6 +260,7 @@ mod curvegroup {
use crate::ec::tecurve::curvegroup::Curve as TECurve;
use crate::ec::tecurve::curvegroup::Point as TEPoint;
use crate::cmp::Eq;
use crate::from::From;

struct Curve { // Montgomery Curve configuration (ky^2 z = x*(x^2 + j*x*z + z*z))
j: Field,
Expand Down Expand Up @@ -250,12 +288,7 @@ mod curvegroup {

// Conversion to affine coordinates
fn into_affine(self) -> affine::Point {
if self.is_zero() {
affine::Point::zero()
} else {
let (x,y,z) = (self.x, self.y, self.z);
affine::Point::new(x/z, y/z)
}
self.into()
}

// Additive identity
Expand All @@ -272,7 +305,7 @@ mod curvegroup {

// Map into equivalent Twisted Edwards curve
fn into_tecurve(self) -> TEPoint {
self.into_affine().into_tecurve().into_group()
self.into_affine().into_tecurve().into()
}
}

Expand All @@ -282,6 +315,17 @@ mod curvegroup {
}
}

impl From<affine::Point> for Point {
fn from(input: affine::Point) -> Point {
if input.is_zero() {
Point::zero()
} else {
let (x,y) = (input.x, input.y);
Point::new(x,y,1)
}
}
}

impl Curve {
// Curve constructor
pub fn new(j: Field, k: Field, gen: Point) -> Self {
Expand All @@ -299,7 +343,7 @@ mod curvegroup {

// Conversion to affine coordinates
fn into_affine(self) -> affine::Curve {
affine::Curve::new(self.j, self.k, self.gen.into_affine())
self.into()
}

// Membership check
Expand All @@ -312,7 +356,7 @@ mod curvegroup {

// Point addition
pub fn add(self, p1: Point, p2: Point) -> Point {
self.into_affine().add(p1.into_affine(), p2.into_affine()).into_group()
self.into_affine().add(p1.into(), p2.into()).into()
}

// Scalar multiplication with scalar represented by a bit array (little-endian convention).
Expand Down Expand Up @@ -361,22 +405,28 @@ mod curvegroup {

// Point mapping into equivalent Short Weierstraß curve
pub fn map_into_swcurve(self, p: Point) -> SWPoint {
self.into_affine().map_into_swcurve(p.into_affine()).into_group()
self.into_affine().map_into_swcurve(p.into()).into()
}

// Point mapping from equivalent Short Weierstraß curve
fn map_from_swcurve(self, p: SWPoint) -> Point {
self.into_affine().map_from_swcurve(p.into_affine()).into_group()
self.into_affine().map_from_swcurve(p.into()).into()
}

// Elligator 2 map-to-curve method
fn elligator2_map(self, u: Field) -> Point {
self.into_affine().elligator2_map(u).into_group()
self.into_affine().elligator2_map(u).into()
}

// SWU map-to-curve method (via rational map)
fn swu_map(self, z: Field, u: Field) -> Point {
self.into_affine().swu_map(z,u).into_group()
self.into_affine().swu_map(z,u).into()
}
}

impl From<affine::Curve> for Curve {
fn from(input: affine::Curve) -> Curve {
Curve::new(input.j, input.k, input.gen.into())
}
}
}
75 changes: 50 additions & 25 deletions noir_stdlib/src/ec/swcurve.nr
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ mod affine {
use crate::ec::is_square;
use crate::ec::sqrt;
use crate::cmp::Eq;
use crate::from::From;

// Curve specification
struct Curve { // Short Weierstraß curve
Expand Down Expand Up @@ -37,13 +38,7 @@ mod affine {

// Conversion to CurveGroup coordinates
fn into_group(self) -> curvegroup::Point {
let Self {x, y, infty} = self;

if infty {
curvegroup::Point::zero()
} else {
curvegroup::Point::new(x, y, 1)
}
self.into()
}

// Additive identity
Expand All @@ -68,6 +63,18 @@ mod affine {
}
}

impl From<curvegroup::Point> for Point {
fn from(input: curvegroup::Point) -> Point {
let curvegroup::Point {x, y, z} = input;

if z == 0 {
Point::zero()
} else {
Point::new(x/(z*z), y/(z*z*z))
}
}
}

impl Curve {
// Curve constructor
pub fn new(a: Field, b: Field, gen: Point) -> Curve {
Expand All @@ -84,9 +91,7 @@ mod affine {

// Conversion to CurveGroup coordinates
fn into_group(self) -> curvegroup::Curve {
let Curve{a, b, gen} = self;

curvegroup::Curve {a, b, gen: gen.into_group()}
self.into()
}

// Membership check
Expand All @@ -97,7 +102,7 @@ mod affine {

// Point addition, implemented in terms of mixed addition for reasons of efficiency
pub fn add(self, p1: Point, p2: Point) -> Point {
self.mixed_add(p1, p2.into_group()).into_affine()
self.mixed_add(p1, p2.into()).into()
}

// Mixed point addition, i.e. first argument in affine, second in CurveGroup coordinates.
Expand All @@ -118,7 +123,7 @@ mod affine {
if s1 != s2 {
curvegroup::Point::zero()
} else {
self.into_group().double(p2)
curvegroup::Curve::from(self).double(p2)
}
} else
{
Expand All @@ -136,12 +141,12 @@ mod affine {
// Scalar multiplication with scalar represented by a bit array (little-endian convention).
// If k is the natural number represented by `bits`, then this computes p + ... + p k times.
fn bit_mul<N>(self, bits: [u1; N], p: Point) -> Point {
self.into_group().bit_mul(bits, p.into_group()).into_affine()
self.into_group().bit_mul(bits, p.into()).into()
}

// Scalar multiplication (p + ... + p n times)
pub fn mul(self, n: Field, p: Point) -> Point {
self.into_group().mul(n, p.into_group()).into_affine()
self.into_group().mul(n, p.into()).into()
}

// Multi-scalar multiplication (n[0]*p[0] + ... + n[N]*p[N], where * denotes scalar multiplication)
Expand Down Expand Up @@ -178,6 +183,14 @@ mod affine {
Point::new(x, if u.sgn0() != y.sgn0() {0-y} else {y})
}
}

impl From<curvegroup::Curve> for Curve {
fn from(input: curvegroup::Curve) -> Curve {
let curvegroup::Curve {a, b, gen} = input;

Curve {a, b, gen: gen.into()}
}
}
}

mod curvegroup {
Expand All @@ -186,6 +199,7 @@ mod curvegroup {
// See <https://en.wikibooks.org/wiki/Cryptography/Prime_Curve/Jacobian_Coordinates> for details.
use crate::ec::swcurve::affine;
use crate::cmp::Eq;
use crate::from::From;

// Curve specification
struct Curve { // Short Weierstraß curve
Expand Down Expand Up @@ -215,21 +229,14 @@ mod curvegroup {

// Conversion to affine coordinates
pub fn into_affine(self) -> affine::Point {
let Self {x, y, z} = self;

if z == 0 {
affine::Point::zero()
} else {
affine::Point::new(x/(z*z), y/(z*z*z))
}
self.into()
}

// Additive identity
pub fn zero() -> Self {
Self {x: 0, y: 0, z: 0}
}


// Negation
fn negate(self) -> Self {
let Self {x, y, z} = self;
Expand All @@ -246,6 +253,18 @@ mod curvegroup {
}
}

impl From<affine::Point> for Point {
fn from(input: affine::Point) -> Point {
let affine::Point {x, y, infty} = input;

if infty {
Point::zero()
} else {
Point::new(x, y, 1)
}
}
}

impl Curve {
// Curve constructor
pub fn new(a: Field, b: Field, gen: Point) -> Curve {
Expand All @@ -262,9 +281,7 @@ mod curvegroup {

// Conversion to affine coordinates
pub fn into_affine(self) -> affine::Curve {
let Curve{a, b, gen} = self;

affine::Curve {a, b, gen: gen.into_affine()}
self.into()
}

// Membership check
Expand Down Expand Up @@ -378,4 +395,12 @@ mod curvegroup {
self.into_affine().swu_map(z,u).into_group()
}
}

impl From<affine::Curve> for Curve {
fn from(input: affine::Curve) -> Curve {
let affine::Curve {a, b, gen} = input;

Curve {a, b, gen: gen.into()}
}
}
}
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