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pub use crate::crh::pedersen_parameters::PedersenSize;
use crate::{
crh::{PedersenCRH, PedersenCRHParameters},
errors::CRHError,
traits::CRH,
};
use snarkvm_curves::Group;
use snarkvm_fields::{errors::ConstraintFieldError, traits::to_field_vec::ToConstraintField, Field, PrimeField};
use snarkvm_utilities::{biginteger::biginteger::BigInteger, bytes_to_bits};
use rand::Rng;
#[cfg(feature = "parallel")]
use rayon::prelude::*;
pub const BOWE_HOPWOOD_CHUNK_SIZE: usize = 3;
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct BoweHopwoodPedersenCRH<G: Group, S: PedersenSize> {
pub parameters: PedersenCRHParameters<G, S>,
}
impl<G: Group, S: PedersenSize> BoweHopwoodPedersenCRH<G, S> {
pub fn create_generators<R: Rng>(rng: &mut R) -> Vec<Vec<G>> {
let mut generators = Vec::with_capacity(S::NUM_WINDOWS);
for _ in 0..S::NUM_WINDOWS {
let mut generators_for_segment = Vec::with_capacity(S::WINDOW_SIZE);
let mut base = G::rand(rng);
for _ in 0..S::WINDOW_SIZE {
generators_for_segment.push(base);
for _ in 0..4 {
base.double_in_place();
}
}
generators.push(generators_for_segment);
}
generators
}
}
impl<G: Group, S: PedersenSize> CRH for BoweHopwoodPedersenCRH<G, S> {
type Output = G;
type Parameters = PedersenCRHParameters<G, S>;
const INPUT_SIZE_BITS: usize = PedersenCRH::<G, S>::INPUT_SIZE_BITS;
fn setup<R: Rng>(rng: &mut R) -> Self {
fn calculate_num_chunks_in_segment<F: PrimeField>() -> usize {
let upper_limit = F::modulus_minus_one_div_two();
let mut c = 0;
let mut range = F::BigInteger::from(2_u64);
while range < upper_limit {
range.muln(4);
c += 1;
}
c
}
let maximum_num_chunks_in_segment = calculate_num_chunks_in_segment::<G::ScalarField>();
if S::WINDOW_SIZE > maximum_num_chunks_in_segment {
panic!(
"Bowe-Hopwood hash must have a window size resulting in scalars < (p-1)/2, \
maximum segment size is {}",
maximum_num_chunks_in_segment
);
}
let time = start_timer!(|| format!(
"BoweHopwoodPedersenCRH::Setup: {} segments of {} 3-bit chunks; {{0,1}}^{{{}}} -> G",
S::NUM_WINDOWS,
S::WINDOW_SIZE,
S::WINDOW_SIZE * S::NUM_WINDOWS * BOWE_HOPWOOD_CHUNK_SIZE
));
let bases = Self::create_generators(rng);
end_timer!(time);
let parameters = Self::Parameters::from(bases);
Self { parameters }
}
fn hash(&self, input: &[u8]) -> Result<Self::Output, CRHError> {
let eval_time = start_timer!(|| "BoweHopwoodPedersenCRH::Eval");
if (input.len() * 8) > S::WINDOW_SIZE * S::NUM_WINDOWS {
return Err(CRHError::IncorrectInputLength(
input.len(),
S::WINDOW_SIZE,
S::NUM_WINDOWS,
));
}
let mut input_bytes = input;
let mut padded_input_bytes = vec![];
if (input.len() * 8) < S::WINDOW_SIZE * S::NUM_WINDOWS {
padded_input_bytes.extend_from_slice(input_bytes);
padded_input_bytes.resize((S::WINDOW_SIZE * S::NUM_WINDOWS) / 8, 0u8);
input_bytes = padded_input_bytes.as_slice();
}
let mut padded_input = Vec::with_capacity(input_bytes.len());
let input = bytes_to_bits(input_bytes);
let input_len = input_bytes.len() * 8;
padded_input.extend(input);
if input_len % BOWE_HOPWOOD_CHUNK_SIZE != 0 {
let current_length = input_len;
padded_input.resize(
current_length + BOWE_HOPWOOD_CHUNK_SIZE - current_length % BOWE_HOPWOOD_CHUNK_SIZE,
false,
);
}
assert_eq!(padded_input.len() % BOWE_HOPWOOD_CHUNK_SIZE, 0);
assert_eq!(
self.parameters.bases.len(),
S::NUM_WINDOWS,
"Incorrect pp of size {:?} for window params {:?}x{:?}x{}",
self.parameters.bases.len(),
S::WINDOW_SIZE,
S::NUM_WINDOWS,
BOWE_HOPWOOD_CHUNK_SIZE,
);
for bases in self.parameters.bases.iter() {
assert_eq!(bases.len(), S::WINDOW_SIZE);
}
assert_eq!(BOWE_HOPWOOD_CHUNK_SIZE, 3);
let mapping = cfg_chunks!(padded_input, S::WINDOW_SIZE * BOWE_HOPWOOD_CHUNK_SIZE)
.zip(&self.parameters.bases)
.map(|(segment_bits, segment_generators)| {
cfg_reduce!(
cfg_chunks!(segment_bits, BOWE_HOPWOOD_CHUNK_SIZE)
.zip(segment_generators)
.map(|(chunk_bits, generator)| {
let mut encoded = *generator;
if chunk_bits[0] {
encoded += generator;
}
if chunk_bits[1] {
encoded += &generator.double();
}
if chunk_bits[2] {
encoded = encoded.neg();
}
encoded
}),
G::zero,
|a, b| a + &b
)
});
let result = cfg_reduce!(mapping, G::zero, |a, b| a + &b);
end_timer!(eval_time);
Ok(result)
}
fn parameters(&self) -> &Self::Parameters {
&self.parameters
}
}
impl<G: Group, S: PedersenSize> From<PedersenCRHParameters<G, S>> for BoweHopwoodPedersenCRH<G, S> {
fn from(parameters: PedersenCRHParameters<G, S>) -> Self {
Self { parameters }
}
}
impl<F: Field, G: Group + ToConstraintField<F>, S: PedersenSize> ToConstraintField<F> for BoweHopwoodPedersenCRH<G, S> {
#[inline]
fn to_field_elements(&self) -> Result<Vec<F>, ConstraintFieldError> {
self.parameters.to_field_elements()
}
}