mirror of https://github.com/zcash/orchard.git
345 lines
11 KiB
Rust
345 lines
11 KiB
Rust
use halo2_gadgets::ecc::chip::EccPoint;
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use halo2_proofs::{
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circuit::{AssignedCell, Chip, Layouter, Value},
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plonk::{self, Advice, Column, ConstraintSystem, Constraints, Expression, Selector},
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poly::Rotation,
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};
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use pasta_curves::pallas;
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#[derive(Clone, Debug)]
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pub(in crate::circuit) struct MuxConfig {
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choice: Column<Advice>,
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left: Column<Advice>,
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right: Column<Advice>,
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out: Column<Advice>,
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q_mux: Selector,
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}
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/// A chip implementing a multiplexer on a single row.
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///
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/// out = if (choice == 0) {left} else {right}
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///
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/// `choice` must be constrained to {0, 1} separately.
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#[derive(Clone, Debug)]
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pub(in crate::circuit) struct MuxChip {
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config: MuxConfig,
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}
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impl Chip<pallas::Base> for MuxChip {
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type Config = MuxConfig;
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type Loaded = ();
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fn config(&self) -> &Self::Config {
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&self.config
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}
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fn loaded(&self) -> &Self::Loaded {
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&()
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}
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}
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impl MuxChip {
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pub(in crate::circuit) fn configure(
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meta: &mut ConstraintSystem<pallas::Base>,
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choice: Column<Advice>,
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left: Column<Advice>,
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right: Column<Advice>,
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out: Column<Advice>,
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) -> MuxConfig {
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let q_mux = meta.selector();
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meta.create_gate("Field element multiplexer", |meta| {
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let q_mux = meta.query_selector(q_mux);
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let choice = meta.query_advice(choice, Rotation::cur());
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let left = meta.query_advice(left, Rotation::cur());
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let right = meta.query_advice(right, Rotation::cur());
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let out = meta.query_advice(out, Rotation::cur());
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let one = Expression::Constant(pallas::Base::one());
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let should_be_zero = (one - choice.clone()) * left + choice * right - out;
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Constraints::with_selector(q_mux, Some(should_be_zero))
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});
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MuxConfig {
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choice,
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left,
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right,
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out,
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q_mux,
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}
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}
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pub(in crate::circuit) fn construct(config: MuxConfig) -> Self {
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Self { config }
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}
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}
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/// An instruction set for multiplexing two points.
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pub(crate) trait MuxInstructions {
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/// Constraints `MUX(choice, left, right)` and returns the selected point.
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fn mux(
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&self,
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layouter: impl Layouter<pallas::Base>,
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choice: &AssignedCell<pallas::Base, pallas::Base>,
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left: &EccPoint,
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right: &EccPoint,
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) -> Result<EccPoint, plonk::Error>;
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}
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impl MuxInstructions for MuxChip {
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fn mux(
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&self,
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mut layouter: impl Layouter<pallas::Base>,
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choice: &AssignedCell<pallas::Base, pallas::Base>,
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left: &EccPoint,
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right: &EccPoint,
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) -> Result<EccPoint, plonk::Error> {
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let x_cell = layouter.assign_region(
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|| "mux x",
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|mut region| {
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self.config.q_mux.enable(&mut region, 0)?;
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choice.copy_advice(|| "copy choice", &mut region, self.config.choice, 0)?;
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left.x()
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.copy_advice(|| "copy left_x", &mut region, self.config.left, 0)?;
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right
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.x()
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.copy_advice(|| "copy right_x", &mut region, self.config.right, 0)?;
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let out_val = (Value::known(pallas::Base::one()) - choice.value())
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* left.x().value()
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+ choice.value() * right.x().value();
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region.assign_advice(|| "out x", self.config.out, 0, || out_val)
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},
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)?;
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let y_cell = layouter.assign_region(
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|| "mux y",
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|mut region| {
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self.config.q_mux.enable(&mut region, 0)?;
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choice.copy_advice(|| "copy choice", &mut region, self.config.choice, 0)?;
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left.y()
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.copy_advice(|| "copy left_y", &mut region, self.config.left, 0)?;
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right
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.y()
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.copy_advice(|| "copy right_y", &mut region, self.config.right, 0)?;
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let out_val = (Value::known(pallas::Base::one()) - choice.value())
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* left.y().value()
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+ choice.value() * right.y().value();
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region.assign_advice(|| "out y", self.config.out, 0, || out_val)
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},
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)?;
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Ok(EccPoint::from_coordinates_unchecked(
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x_cell.into(),
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y_cell.into(),
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))
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::circuit::gadget::mux_chip::{MuxChip, MuxConfig, MuxInstructions};
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use crate::{circuit::gadget::assign_free_advice, circuit::K, constants::OrchardFixedBases};
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use halo2_gadgets::{
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ecc::{
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chip::{EccChip, EccConfig},
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Point,
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},
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utilities::lookup_range_check::LookupRangeCheckConfig,
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};
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use group::{cofactor::CofactorCurveAffine, Curve, Group};
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use halo2_proofs::{
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circuit::{Layouter, SimpleFloorPlanner, Value},
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dev::MockProver,
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plonk::{Advice, Circuit, Column, ConstraintSystem, Error, Instance},
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};
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use pasta_curves::arithmetic::CurveAffine;
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use pasta_curves::{pallas, EpAffine};
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use rand::rngs::OsRng;
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#[test]
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fn test_mux_chip() {
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#[derive(Clone, Debug)]
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pub struct MyConfig {
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primary: Column<Instance>,
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advice: Column<Advice>,
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mux_config: MuxConfig,
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ecc_config: EccConfig<OrchardFixedBases>,
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}
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#[derive(Default)]
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struct MyCircuit {
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left_point: Value<EpAffine>,
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right_point: Value<EpAffine>,
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choice: Value<pallas::Base>,
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}
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impl Circuit<pallas::Base> for MyCircuit {
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type Config = MyConfig;
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type FloorPlanner = SimpleFloorPlanner;
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fn without_witnesses(&self) -> Self {
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Self::default()
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}
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fn configure(meta: &mut ConstraintSystem<pallas::Base>) -> Self::Config {
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let advices = [
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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meta.advice_column(),
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];
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for advice in advices.iter() {
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meta.enable_equality(*advice);
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}
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// Instance column used for public inputs
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let primary = meta.instance_column();
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meta.enable_equality(primary);
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let mux_config =
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MuxChip::configure(meta, advices[0], advices[1], advices[2], advices[3]);
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let table_idx = meta.lookup_table_column();
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let table_range_check_tag = meta.lookup_table_column();
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let lagrange_coeffs = [
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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meta.fixed_column(),
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];
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meta.enable_constant(lagrange_coeffs[0]);
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let range_check = LookupRangeCheckConfig::configure(
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meta,
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advices[9],
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table_idx,
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table_range_check_tag,
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);
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let ecc_config = EccChip::<OrchardFixedBases>::configure(
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meta,
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advices,
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lagrange_coeffs,
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range_check,
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);
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MyConfig {
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primary,
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advice: advices[0],
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mux_config,
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ecc_config,
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}
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}
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fn synthesize(
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&self,
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config: Self::Config,
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mut layouter: impl Layouter<pallas::Base>,
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) -> Result<(), Error> {
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// Construct a MUX chip
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let mux_chip = MuxChip::construct(config.mux_config);
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// Construct an ECC chip
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let ecc_chip = EccChip::construct(config.ecc_config);
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// Assign left point
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let left_point = Point::new(
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ecc_chip.clone(),
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layouter.namespace(|| "left point"),
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self.left_point.map(|left_point| left_point),
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)?;
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// Assign right point
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let right_point = Point::new(
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ecc_chip,
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layouter.namespace(|| "right point"),
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self.right_point.map(|right_point| right_point),
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)?;
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// Assign choice
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let choice = assign_free_advice(
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layouter.namespace(|| "choice"),
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config.advice,
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self.choice,
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)?;
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// Apply mux
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let result = mux_chip.mux(
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layouter.namespace(|| "MUX"),
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&choice,
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left_point.inner(),
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right_point.inner(),
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)?;
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// Check equality with instance
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layouter.constrain_instance(result.x().cell(), config.primary, 0)?;
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layouter.constrain_instance(result.y().cell(), config.primary, 1)
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}
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}
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// Test different circuits
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let mut circuits = vec![];
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let mut instances = vec![];
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for choice in [false, true] {
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let choice_value = if choice {
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pallas::Base::one()
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} else {
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pallas::Base::zero()
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};
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for left_point in [
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pallas::Point::identity().to_affine(),
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pallas::Point::random(OsRng).to_affine(),
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] {
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for right_point in [
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pallas::Point::identity().to_affine(),
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pallas::Point::random(OsRng).to_affine(),
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] {
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circuits.push(MyCircuit {
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left_point: Value::known(left_point),
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right_point: Value::known(right_point),
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choice: Value::known(choice_value),
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});
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let expected_output = if choice { right_point } else { left_point };
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let (expected_x, expected_y) = if bool::from(expected_output.is_identity()) {
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(pallas::Base::zero(), pallas::Base::zero())
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} else {
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let coords = expected_output.coordinates().unwrap();
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(*coords.x(), *coords.y())
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};
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instances.push([[expected_x, expected_y]]);
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}
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}
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}
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for (circuit, instance) in circuits.iter().zip(instances.iter()) {
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let prover = MockProver::<pallas::Base>::run(
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K,
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circuit,
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instance.iter().map(|p| p.to_vec()).collect(),
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)
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.unwrap();
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assert_eq!(prover.verify(), Ok(()));
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}
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}
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}
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