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use crate::{hash_to_curve::hash_to_curve, CRHError, CRH};
use snarkvm_curves::{AffineCurve, ProjectiveCurve};
use snarkvm_fields::{ConstraintFieldError, Field, ToConstraintField};
use snarkvm_utilities::{FromBytes, ToBytes};
use std::{
borrow::Cow,
fmt::Debug,
io::{Read, Result as IoResult, Write},
};
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct PedersenCRH<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> {
pub bases: Vec<Vec<G>>,
}
impl<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> CRH
for PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE>
{
type Output = G::Affine;
type Parameters = Vec<Vec<G>>;
fn setup(message: &str) -> Self {
Self::bases(message).into()
}
fn hash_bits(&self, input: &[bool]) -> Result<Self::Output, CRHError> {
if input.len() > WINDOW_SIZE * NUM_WINDOWS {
return Err(CRHError::IncorrectInputLength(input.len(), WINDOW_SIZE, NUM_WINDOWS));
}
let mut padded_input = Cow::Borrowed(input);
if padded_input.len() < WINDOW_SIZE * NUM_WINDOWS {
padded_input.to_mut().resize(WINDOW_SIZE * NUM_WINDOWS, false);
}
if self.bases.len() != NUM_WINDOWS {
return Err(CRHError::IncorrectParameterSize(
self.bases[0].len(),
self.bases.len(),
WINDOW_SIZE,
NUM_WINDOWS,
));
}
let result = padded_input
.chunks(WINDOW_SIZE)
.zip(&self.bases)
.map(|(bits, powers)| {
let mut encoded = G::zero();
for (bit, base) in bits.iter().zip(powers.iter()) {
if *bit {
encoded += base;
}
}
encoded
})
.fold(G::zero(), |a, b| a + b);
Ok(result.into_affine())
}
fn parameters(&self) -> &Self::Parameters {
&self.bases
}
}
impl<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE> {
fn bases(message: &str) -> Vec<Vec<G>> {
let mut bases = Vec::with_capacity(NUM_WINDOWS);
for index in 0..NUM_WINDOWS {
let indexed_message = format!("{} at {}", message, index);
let (generator, _, _) = hash_to_curve::<G::Affine>(&indexed_message);
let mut base = generator.into_projective();
let mut powers = Vec::with_capacity(WINDOW_SIZE);
for _ in 0..WINDOW_SIZE {
powers.push(base);
base.double_in_place();
}
bases.push(powers);
}
bases
}
}
impl<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> From<Vec<Vec<G>>>
for PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE>
{
fn from(bases: Vec<Vec<G>>) -> Self {
Self { bases }
}
}
impl<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> ToBytes
for PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE>
{
fn write_le<W: Write>(&self, mut writer: W) -> IoResult<()> {
(self.bases.len() as u32).write_le(&mut writer)?;
for base in &self.bases {
(base.len() as u32).write_le(&mut writer)?;
for g in base {
g.write_le(&mut writer)?;
}
}
Ok(())
}
}
impl<G: ProjectiveCurve, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize> FromBytes
for PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE>
{
#[inline]
fn read_le<R: Read>(mut reader: R) -> IoResult<Self> {
let num_bases: u32 = FromBytes::read_le(&mut reader)?;
let mut bases = Vec::with_capacity(num_bases as usize);
for _ in 0..num_bases {
let base_len: u32 = FromBytes::read_le(&mut reader)?;
let mut base = Vec::with_capacity(base_len as usize);
for _ in 0..base_len {
let g: G = FromBytes::read_le(&mut reader)?;
base.push(g);
}
bases.push(base);
}
Ok(Self { bases })
}
}
impl<F: Field, G: ProjectiveCurve + ToConstraintField<F>, const NUM_WINDOWS: usize, const WINDOW_SIZE: usize>
ToConstraintField<F> for PedersenCRH<G, NUM_WINDOWS, WINDOW_SIZE>
{
#[inline]
fn to_field_elements(&self) -> Result<Vec<F>, ConstraintFieldError> {
Ok(Vec::new())
}
}
