mirror of https://github.com/zcash/halo2.git
193 lines
6.4 KiB
Rust
193 lines
6.4 KiB
Rust
use std::collections::HashSet;
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use super::NonIdentityEccPoint;
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use halo2_proofs::{
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circuit::Region,
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plonk::{Advice, Column, ConstraintSystem, Constraints, Error, 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, Copy, Debug, Eq, PartialEq)]
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pub struct Config {
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q_add_incomplete: Selector,
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// x-coordinate of P in P + Q = R
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pub x_p: Column<Advice>,
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// y-coordinate of P in P + Q = R
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pub y_p: Column<Advice>,
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// x-coordinate of Q or R in P + Q = R
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pub x_qr: Column<Advice>,
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// y-coordinate of Q or R in P + Q = R
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pub y_qr: Column<Advice>,
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}
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impl Config {
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pub(super) fn configure(
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meta: &mut ConstraintSystem<pallas::Base>,
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x_p: Column<Advice>,
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y_p: Column<Advice>,
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x_qr: Column<Advice>,
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y_qr: Column<Advice>,
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) -> Self {
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meta.enable_equality(x_p);
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meta.enable_equality(y_p);
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meta.enable_equality(x_qr);
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meta.enable_equality(y_qr);
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let config = Self {
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q_add_incomplete: meta.selector(),
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x_p,
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y_p,
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x_qr,
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y_qr,
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};
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config.create_gate(meta);
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config
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}
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pub(crate) fn advice_columns(&self) -> HashSet<Column<Advice>> {
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[self.x_p, self.y_p, self.x_qr, self.y_qr]
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.into_iter()
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.collect()
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}
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fn create_gate(&self, meta: &mut ConstraintSystem<pallas::Base>) {
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// https://p.z.cash/halo2-0.1:ecc-incomplete-addition
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meta.create_gate("incomplete addition", |meta| {
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let q_add_incomplete = meta.query_selector(self.q_add_incomplete);
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let x_p = meta.query_advice(self.x_p, Rotation::cur());
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let y_p = meta.query_advice(self.y_p, Rotation::cur());
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let x_q = meta.query_advice(self.x_qr, Rotation::cur());
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let y_q = meta.query_advice(self.y_qr, Rotation::cur());
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let x_r = meta.query_advice(self.x_qr, Rotation::next());
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let y_r = meta.query_advice(self.y_qr, Rotation::next());
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// (x_r + x_q + x_p)⋅(x_p − x_q)^2 − (y_p − y_q)^2 = 0
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let poly1 = {
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(x_r.clone() + x_q.clone() + x_p.clone())
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* (x_p.clone() - x_q.clone())
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* (x_p.clone() - x_q.clone())
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- (y_p.clone() - y_q.clone()).square()
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};
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// (y_r + y_q)(x_p − x_q) − (y_p − y_q)(x_q − x_r) = 0
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let poly2 = (y_r + y_q.clone()) * (x_p - x_q.clone()) - (y_p - y_q) * (x_q - x_r);
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Constraints::with_selector(q_add_incomplete, [("x_r", poly1), ("y_r", poly2)])
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});
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}
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pub(super) fn assign_region(
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&self,
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p: &NonIdentityEccPoint,
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q: &NonIdentityEccPoint,
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offset: usize,
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region: &mut Region<'_, pallas::Base>,
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) -> Result<NonIdentityEccPoint, Error> {
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// Enable `q_add_incomplete` selector
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self.q_add_incomplete.enable(region, offset)?;
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// Handle exceptional cases
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let (x_p, y_p) = (p.x.value(), p.y.value());
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let (x_q, y_q) = (q.x.value(), q.y.value());
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x_p.zip(y_p)
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.zip(x_q)
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.zip(y_q)
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.error_if_known_and(|(((x_p, y_p), x_q), y_q)| {
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// P is point at infinity
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(x_p.is_zero_vartime() && y_p.is_zero_vartime())
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// Q is point at infinity
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|| (x_q.is_zero_vartime() && y_q.is_zero_vartime())
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// x_p = x_q
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|| (x_p == x_q)
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})?;
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// Copy point `p` into `x_p`, `y_p` columns
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p.x.copy_advice(|| "x_p", region, self.x_p, offset)?;
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p.y.copy_advice(|| "y_p", region, self.y_p, offset)?;
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// Copy point `q` into `x_qr`, `y_qr` columns
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q.x.copy_advice(|| "x_q", region, self.x_qr, offset)?;
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q.y.copy_advice(|| "y_q", region, self.y_qr, offset)?;
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// Compute the sum `P + Q = R`
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let r = x_p
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.zip(y_p)
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.zip(x_q)
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.zip(y_q)
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.map(|(((x_p, y_p), x_q), y_q)| {
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{
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// λ = (y_q - y_p)/(x_q - x_p)
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let lambda = (y_q - y_p) * (x_q - x_p).invert();
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// x_r = λ^2 - x_p - x_q
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let x_r = lambda.square() - x_p - x_q;
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// y_r = λ(x_p - x_r) - y_p
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let y_r = lambda * (x_p - x_r) - y_p;
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(x_r, y_r)
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}
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});
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// Assign the sum to `x_qr`, `y_qr` columns in the next row
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let x_r = r.map(|r| r.0);
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let x_r_var = region.assign_advice(|| "x_r", self.x_qr, offset + 1, || x_r)?;
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let y_r = r.map(|r| r.1);
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let y_r_var = region.assign_advice(|| "y_r", self.y_qr, offset + 1, || y_r)?;
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let result = NonIdentityEccPoint::from_coordinates_unchecked(x_r_var, y_r_var);
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Ok(result)
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}
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}
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#[cfg(test)]
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pub mod tests {
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use group::Curve;
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use halo2_proofs::{
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circuit::{Layouter, Value},
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plonk::Error,
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};
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use pasta_curves::pallas;
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use crate::ecc::{EccInstructions, NonIdentityPoint};
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#[allow(clippy::too_many_arguments)]
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pub fn test_add_incomplete<
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EccChip: EccInstructions<pallas::Affine> + Clone + Eq + std::fmt::Debug,
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>(
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chip: EccChip,
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mut layouter: impl Layouter<pallas::Base>,
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p_val: pallas::Affine,
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p: &NonIdentityPoint<pallas::Affine, EccChip>,
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q_val: pallas::Affine,
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q: &NonIdentityPoint<pallas::Affine, EccChip>,
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p_neg: &NonIdentityPoint<pallas::Affine, EccChip>,
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test_errors: bool,
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) -> Result<(), Error> {
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// P + Q
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{
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let result = p.add_incomplete(layouter.namespace(|| "P + Q"), q)?;
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let witnessed_result = NonIdentityPoint::new(
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chip,
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layouter.namespace(|| "witnessed P + Q"),
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Value::known((p_val + q_val).to_affine()),
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)?;
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result.constrain_equal(layouter.namespace(|| "constrain P + Q"), &witnessed_result)?;
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}
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if test_errors {
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// P + P should return an error
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p.add_incomplete(layouter.namespace(|| "P + P"), p)
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.expect_err("P + P should return an error");
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// P + (-P) should return an error
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p.add_incomplete(layouter.namespace(|| "P + (-P)"), p_neg)
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.expect_err("P + (-P) should return an error");
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}
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Ok(())
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}
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}
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