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correct point subtraction

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This commit is contained in:
Nicholas Ward 2022-02-14 11:03:44 -08:00
parent f77192ef66
commit e88564ce5e
1 changed files with 22 additions and 10 deletions
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32
plonky2/src/gadgets/curve_windowed_mul.rs
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@ -1,16 +1,19 @@
use std::marker::PhantomData;
use num::BigUint;
use plonky2_field::extension_field::Extendable;
use plonky2_field::field_types::Field;
use crate::curve::curve_types::Curve;
use crate::curve::curve_types::{Curve, CurveScalar};
use crate::gadgets::arithmetic_u32::U32Target;
use crate::gadgets::biguint::BigUintTarget;
use crate::gadgets::curve::AffinePointTarget;
use crate::gadgets::nonnative::NonNativeTarget;
use crate::hash::hash_types::RichField;
use crate::hash::keccak::KeccakHash;
use crate::iop::target::{BoolTarget, Target};
use crate::plonk::circuit_builder::CircuitBuilder;
use crate::plonk::config::{GenericHashOut, Hasher};
const WINDOW_SIZE: usize = 4;
@ -85,9 +88,20 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
p: &AffinePointTarget<C>,
n: &NonNativeTarget<C::ScalarField>,
) -> AffinePointTarget<C> {
let mut result = self.constant_affine_point(C::GENERATOR_AFFINE);
let mut to_subtract = self.constant_affine_point(C::GENERATOR_AFFINE);
let mut to_subtract_grows = self._true();
let hash_0 = KeccakHash::<25>::hash(&[F::ZERO], false);
let hash_0_scalar = C::ScalarField::from_biguint(BigUint::from_bytes_le(
&GenericHashOut::<F>::to_bytes(&hash_0),
));
let starting_point = CurveScalar(hash_0_scalar) * C::GENERATOR_PROJECTIVE;
let starting_point_multiplied = {
let mut cur = starting_point;
for _ in 0..C::ScalarField::BITS {
cur = cur.double();
}
cur
};
let mut result = self.constant_affine_point(starting_point.to_affine());
let precomputation = self.precompute_window(p);
let zero = self.zero();
@ -96,20 +110,18 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
let m = C::ScalarField::BITS / WINDOW_SIZE;
for i in (0..m).rev() {
result = self.curve_repeated_double(&result, WINDOW_SIZE);
let to_subtract_increased = self.curve_repeated_double(&to_subtract, WINDOW_SIZE);
to_subtract =
self.if_affine_point(to_subtract_grows, &to_subtract_increased, &to_subtract);
let window = windows[i];
let to_add = self.random_access_curve_points(window, precomputation.clone());
let is_zero = self.is_equal(window, zero);
to_subtract_grows = self.and(to_subtract_grows, is_zero);
let should_add = self.not(is_zero);
result = self.curve_conditional_add(&result, &to_add, should_add);
}
let to_subtract = self.constant_affine_point(starting_point_multiplied.to_affine());
let to_add = self.curve_neg(&to_subtract);
result = self.curve_add(&result, &to_add);
result
}
}