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Introduce ScalarVar::new and ScalarVar::from_base gadget APIs.

This commit is contained in:
therealyingtong 2022-05-05 20:31:42 +02:00
parent 1c877f3caf
commit 5fd0834503
2 changed files with 54 additions and 9 deletions
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37
halo2_gadgets/src/ecc.rs
View File

@ -17,6 +17,10 @@ pub trait EccInstructions<C: CurveAffine>:
Chip<C::Base> + UtilitiesInstructions<C::Base> + Clone + Debug + Eq
{
/// Variable representing a scalar used in variable-base scalar mul.
///
/// This type is treated as a full-width scalar. However, if `Self` implements
/// [`BaseFitsInScalarInstructions`] then this may also be constructed from an element
/// of the base field.
type ScalarVar: Clone + Debug;
/// Variable representing a full-width element of the elliptic curve's
/// scalar field, to be used for fixed-base scalar mul.
@ -167,6 +171,35 @@ pub struct ScalarVar<C: CurveAffine, EccChip: EccInstructions<C>> {
inner: EccChip::ScalarVar,
}
impl<C: CurveAffine, EccChip: EccInstructions<C>> ScalarVar<C, EccChip> {
/// Witnesses the given full-width scalar.
///
/// Depending on the `EccChip` implementation, this may either witness the scalar
/// immediately, or delay witnessing until its first use in [`NonIdentityPoint::mul`].
pub fn new(
chip: EccChip,
mut layouter: impl Layouter<C::Base>,
value: Option<C::Scalar>,
) -> Result<Self, Error> {
let scalar = chip.witness_scalar_var(&mut layouter, value);
scalar.map(|inner| ScalarVar { chip, inner })
}
}
impl<C: CurveAffine, EccChip: BaseFitsInScalarInstructions<C> + UtilitiesInstructions<C::Base>>
ScalarVar<C, EccChip>
{
/// Constructs a scalar from an existing base-field element.
pub fn from_base(
chip: EccChip,
mut layouter: impl Layouter<C::Base>,
base: &EccChip::Var,
) -> Result<Self, Error> {
let scalar = chip.scalar_var_from_base(&mut layouter, base);
scalar.map(|inner| ScalarVar { chip, inner })
}
}
/// A full-width element of the given elliptic curve's scalar field, to be used for fixed-base scalar mul.
#[derive(Debug)]
pub struct ScalarFixed<C: CurveAffine, EccChip: EccInstructions<C>> {
@ -268,10 +301,10 @@ impl<C: CurveAffine, EccChip: EccInstructions<C>> NonIdentityPoint<C, EccChip> {
pub fn mul(
&self,
mut layouter: impl Layouter<C::Base>,
by: &EccChip::ScalarVar,
by: ScalarVar<C, EccChip>,
) -> Result<(Point<C, EccChip>, ScalarVar<C, EccChip>), Error> {
self.chip
.mul(&mut layouter, by, &self.inner.clone())
.mul(&mut layouter, &by.inner, &self.inner.clone())
.map(|(point, scalar)| {
(
Point {

26
halo2_gadgets/src/ecc/chip/mul.rs
View File

@ -483,7 +483,7 @@ pub mod tests {
ecc::{
chip::{EccChip, EccPoint},
tests::TestFixedBases,
BaseFitsInScalarInstructions, EccInstructions, NonIdentityPoint, Point,
EccInstructions, NonIdentityPoint, Point, ScalarVar,
},
utilities::UtilitiesInstructions,
};
@ -525,8 +525,12 @@ pub mod tests {
column,
Some(scalar_val),
)?;
let scalar = chip.scalar_var_from_base(&mut layouter, &scalar)?;
p.mul(layouter.namespace(|| "random [a]B"), &scalar)?
let scalar = ScalarVar::from_base(
chip.clone(),
layouter.namespace(|| "ScalarVar from_base"),
&scalar,
)?;
p.mul(layouter.namespace(|| "random [a]B"), scalar)?
};
constrain_equal_non_id(
chip.clone(),
@ -544,8 +548,12 @@ pub mod tests {
let (result, _) = {
let scalar =
chip.load_private(layouter.namespace(|| "zero"), column, Some(scalar_val))?;
let scalar = chip.scalar_var_from_base(&mut layouter, &scalar)?;
p.mul(layouter.namespace(|| "[0]B"), &scalar)?
let scalar = ScalarVar::from_base(
chip.clone(),
layouter.namespace(|| "ScalarVar from_base"),
&scalar,
)?;
p.mul(layouter.namespace(|| "[0]B"), scalar)?
};
if let Some(is_identity) = result.inner().is_identity() {
assert!(is_identity);
@ -558,8 +566,12 @@ pub mod tests {
let (result, _) = {
let scalar =
chip.load_private(layouter.namespace(|| "-1"), column, Some(scalar_val))?;
let scalar = chip.scalar_var_from_base(&mut layouter, &scalar)?;
p.mul(layouter.namespace(|| "[-1]B"), &scalar)?
let scalar = ScalarVar::from_base(
chip.clone(),
layouter.namespace(|| "ScalarVar from_base"),
&scalar,
)?;
p.mul(layouter.namespace(|| "[-1]B"), scalar)?
};
constrain_equal_non_id(
chip,