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chip::witness_point.rs: Constraints for non-identity point. 

The point_non_id() method returns an error if the given point is
the identity.

Co-authored-by: Daira Hopwood <daira@jacaranda.org>
This commit is contained in:
therealyingtong 2021-09-27 10:44:43 +02:00 committed by Sean Bowe
parent 88eb762cf2
commit df26a6c674
3 changed files with 146 additions and 42 deletions
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8
src/circuit/gadget/ecc.rs
View File

@ -615,6 +615,14 @@ mod tests {
)?
};
// Test witness non-identity point
{
super::chip::witness_point::tests::test_witness_non_id(
chip.clone(),
layouter.namespace(|| "witness non-identity point"),
)
}
// Test complete addition
{
super::chip::add::tests::test_add(

43
src/circuit/gadget/ecc/chip.rs
View File

@ -183,6 +183,8 @@ pub struct EccConfig {
/// Witness point
pub q_point: Selector,
/// Witness non-identity point
pub q_point_non_id: Selector,
/// Lookup range check using 10-bit lookup table
pub lookup_config: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
@ -279,11 +281,12 @@ impl EccChip {
q_mul_fixed_base_field: meta.selector(),
q_mul_fixed_running_sum,
q_point: meta.selector(),
q_point_non_id: meta.selector(),
lookup_config: range_check,
running_sum_config,
};
// Create witness point gate
// Create witness point gates
{
let config: witness_point::Config = (&config).into();
config.create_gate(meta);
@ -393,6 +396,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
type ScalarFixedShort = EccScalarFixedShort;
type ScalarVar = CellValue<pallas::Base>;
type Point = EccPoint;
type NonIdentityPoint = NonIdentityEccPoint;
type X = CellValue<pallas::Base>;
type FixedPoints = OrchardFixedBasesFull;
type FixedPointsBaseField = NullifierK;
@ -423,20 +427,33 @@ impl EccInstructions<pallas::Affine> for EccChip {
let config: witness_point::Config = self.config().into();
layouter.assign_region(
|| "witness point",
|mut region| config.assign_region(value, 0, &mut region),
|mut region| config.point(value, 0, &mut region),
)
}
fn extract_p(point: &Self::Point) -> &Self::X {
&point.x
fn witness_point_non_id(
&self,
layouter: &mut impl Layouter<pallas::Base>,
value: Option<pallas::Affine>,
) -> Result<Self::NonIdentityPoint, Error> {
let config: witness_point::Config = self.config().into();
layouter.assign_region(
|| "witness non-identity point",
|mut region| config.point_non_id(value, 0, &mut region),
)
}
fn extract_p<Point: Into<Self::Point> + Clone>(point: &Point) -> Self::X {
let point: EccPoint = (point.clone()).into();
point.x()
}
fn add_incomplete(
&self,
layouter: &mut impl Layouter<pallas::Base>,
a: &Self::Point,
b: &Self::Point,
) -> Result<Self::Point, Error> {
a: &Self::NonIdentityPoint,
b: &Self::NonIdentityPoint,
) -> Result<Self::NonIdentityPoint, Error> {
let config: add_incomplete::Config = self.config().into();
layouter.assign_region(
|| "incomplete point addition",
@ -444,16 +461,18 @@ impl EccInstructions<pallas::Affine> for EccChip {
)
}
fn add(
fn add<A: Into<Self::Point> + Clone, B: Into<Self::Point> + Clone>(
&self,
layouter: &mut impl Layouter<pallas::Base>,
a: &Self::Point,
b: &Self::Point,
a: &A,
b: &B,
) -> Result<Self::Point, Error> {
let config: add::Config = self.config().into();
layouter.assign_region(
|| "complete point addition",
|mut region| config.assign_region(a, b, 0, &mut region),
|mut region| {
config.assign_region(&(a.clone()).into(), &(b.clone()).into(), 0, &mut region)
},
)
}
@ -461,7 +480,7 @@ impl EccInstructions<pallas::Affine> for EccChip {
&self,
layouter: &mut impl Layouter<pallas::Base>,
scalar: &Self::Var,
base: &Self::Point,
base: &Self::NonIdentityPoint,
) -> Result<(Self::Point, Self::ScalarVar), Error> {
let config: mul::Config = self.config().into();
config.assign(

137
src/circuit/gadget/ecc/chip/witness_point.rs
View File

@ -1,10 +1,10 @@
use super::{CellValue, EccConfig, EccPoint, Var};
use super::{CellValue, EccConfig, EccPoint, NonIdentityEccPoint, Var};
use group::prime::PrimeCurveAffine;
use halo2::{
circuit::Region,
plonk::{Advice, Column, ConstraintSystem, Error, Expression, Selector},
plonk::{Advice, Column, ConstraintSystem, Error, Expression, Selector, VirtualCells},
poly::Rotation,
};
use pasta_curves::{arithmetic::CurveAffine, pallas};
@ -12,6 +12,7 @@ use pasta_curves::{arithmetic::CurveAffine, pallas};
#[derive(Clone, Debug)]
pub struct Config {
q_point: Selector,
q_point_non_id: Selector,
// x-coordinate
pub x: Column<Advice>,
// y-coordinate
@ -22,6 +23,7 @@ impl From<&EccConfig> for Config {
fn from(ecc_config: &EccConfig) -> Self {
Self {
q_point: ecc_config.q_point,
q_point_non_id: ecc_config.q_point_non_id,
x: ecc_config.advices[0],
y: ecc_config.advices[1],
}
@ -30,8 +32,18 @@ impl From<&EccConfig> for Config {
impl Config {
pub(super) fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
let curve_eqn = |meta: &mut VirtualCells<pallas::Base>| {
let x = meta.query_advice(self.x, Rotation::cur());
let y = meta.query_advice(self.y, Rotation::cur());
// y^2 = x^3 + b
y.clone().square()
- (x.clone().square() * x.clone())
- Expression::Constant(pallas::Affine::b())
};
meta.create_gate("witness point", |meta| {
// Check that either the point being witness is either:
// Check that the point being witnessed is either:
// - the identity, which is mapped to (0, 0) in affine coordinates; or
// - a valid curve point y^2 = x^3 + b, where b = 5 in the Pallas equation
@ -39,37 +51,28 @@ impl Config {
let x = meta.query_advice(self.x, Rotation::cur());
let y = meta.query_advice(self.y, Rotation::cur());
// y^2 = x^3 + b
let curve_eqn = y.clone().square()
- (x.clone().square() * x.clone())
- Expression::Constant(pallas::Affine::b());
vec![
("x == 0 ∨ on_curve", q_point.clone() * x * curve_eqn.clone()),
("y == 0 ∨ on_curve", q_point * y * curve_eqn),
("x == 0 v on_curve", q_point.clone() * x * curve_eqn(meta)),
("y == 0 v on_curve", q_point * y * curve_eqn(meta)),
]
});
meta.create_gate("witness non-identity point", |meta| {
// Check that the point being witnessed is a valid curve point y^2 = x^3 + b,
// where b = 5 in the Pallas equation
let q_point_non_id = meta.query_selector(self.q_point_non_id);
vec![("on_curve", q_point_non_id * curve_eqn(meta))]
});
}
pub(super) fn assign_region(
fn assign_xy(
&self,
value: Option<pallas::Affine>,
value: Option<(pallas::Base, pallas::Base)>,
offset: usize,
region: &mut Region<'_, pallas::Base>,
) -> Result<EccPoint, Error> {
// Enable `q_point` selector
self.q_point.enable(region, offset)?;
let value = value.map(|value| {
// Map the identity to (0, 0).
if value == pallas::Affine::identity() {
(pallas::Base::zero(), pallas::Base::zero())
} else {
let value = value.coordinates().unwrap();
(*value.x(), *value.y())
}
});
) -> Result<(CellValue<pallas::Base>, CellValue<pallas::Base>), Error> {
// Assign `x` value
let x_val = value.map(|value| value.0);
let x_var = region.assign_advice(
@ -88,9 +91,83 @@ impl Config {
|| y_val.ok_or(Error::SynthesisError),
)?;
Ok(EccPoint {
x: CellValue::<pallas::Base>::new(x_var, x_val),
y: CellValue::<pallas::Base>::new(y_var, y_val),
})
Ok((
CellValue::<pallas::Base>::new(x_var, x_val),
CellValue::<pallas::Base>::new(y_var, y_val),
))
}
/// Assigns a point that can be the identity.
pub(super) fn point(
&self,
value: Option<pallas::Affine>,
offset: usize,
region: &mut Region<'_, pallas::Base>,
) -> Result<EccPoint, Error> {
// Enable `q_point` selector
self.q_point.enable(region, offset)?;
let value = value.map(|value| {
// Map the identity to (0, 0).
if value == pallas::Affine::identity() {
(pallas::Base::zero(), pallas::Base::zero())
} else {
let value = value.coordinates().unwrap();
(*value.x(), *value.y())
}
});
self.assign_xy(value, offset, region)
.map(|(x, y)| EccPoint { x, y })
}
/// Assigns a non-identity point.
pub(super) fn point_non_id(
&self,
value: Option<pallas::Affine>,
offset: usize,
region: &mut Region<'_, pallas::Base>,
) -> Result<NonIdentityEccPoint, Error> {
// Enable `q_point_non_id` selector
self.q_point_non_id.enable(region, offset)?;
if let Some(value) = value {
// Return an error if the point is the identity.
if value == pallas::Affine::identity() {
return Err(Error::SynthesisError);
}
};
let value = value.map(|value| {
let value = value.coordinates().unwrap();
(*value.x(), *value.y())
});
self.assign_xy(value, offset, region)
.map(|(x, y)| NonIdentityEccPoint { x, y })
}
}
#[cfg(test)]
pub mod tests {
use halo2::circuit::Layouter;
use pasta_curves::pallas;
use super::*;
use crate::circuit::gadget::ecc::{EccInstructions, NonIdentityPoint};
pub fn test_witness_non_id<
EccChip: EccInstructions<pallas::Affine> + Clone + Eq + std::fmt::Debug,
>(
chip: EccChip,
mut layouter: impl Layouter<pallas::Base>,
) {
// Witnessing the identity should return an error.
NonIdentityPoint::new(
chip,
layouter.namespace(|| "witness identity"),
Some(pallas::Affine::identity()),
)
.expect_err("witnessing 𝒪 should return an error");
}
}