Skip to content

prf: remove small statistical bias in PRF output and speedup #9

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
tcoratger merged 2 commits into from
Nov 25, 2025
Merged

prf: remove small statistical bias in PRF output and speedup #9

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
42fb0dd
prf: optimize get_domain_element and get_randomness
tcoratger Nov 21, 2025
2920ca7
some fixes
tcoratger Nov 24, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
45 changes: 18 additions & 27 deletions src/symmetric/prf/shake_to_field.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,17 +2,14 @@ use crate::F;

use super::Pseudorandom;
use p3_field::PrimeCharacteristicRing;
use p3_field::PrimeField64;
use serde::{Serialize, de::DeserializeOwned};
use sha3::{
Shake128,
digest::{ExtendableOutput, Update, XofReader},
};

use num_bigint::BigUint;

// Number of pseudorandom bytes to generate one pseudorandom field element
const PRF_BYTES_PER_FE: usize = 8;
/// Number of pseudorandom bytes to generate one pseudorandom field element
const PRF_BYTES_PER_FE: usize = 16;

const KEY_LENGTH: usize = 32; // 32 bytes
const PRF_DOMAIN_SEP: [u8; 16] = [
Expand Down Expand Up @@ -62,19 +59,16 @@ where
// Finalize the hash process and create an XofReader
let mut xof_reader = hasher.finalize_xof();

// Buffer to store the output
let mut prf_output = vec![0u8; PRF_BYTES_PER_FE * DOMAIN_LENGTH_FE];
// Mapping bytes to field elements
std::array::from_fn(|_| {
// Buffer to store the output
let mut buf = [0u8; PRF_BYTES_PER_FE];

// Read the extended output into the buffer
xof_reader.read(&mut prf_output);
// Read the extended output into the buffer
xof_reader.read(&mut buf);

// Mapping bytes to field elements
std::array::from_fn(|i| {
let chunk_start = i * PRF_BYTES_PER_FE;
let chunk_end = chunk_start + PRF_BYTES_PER_FE;
let integer_value =
BigUint::from_bytes_be(&prf_output[chunk_start..chunk_end]) % F::ORDER_U64;
F::from_u64(integer_value.try_into().unwrap())
// Mapping bytes to a field element
F::from_u128(u128::from_be_bytes(buf))
})
}

Expand Down Expand Up @@ -109,19 +103,16 @@ where
// Finalize the hash process and create an XofReader
let mut xof_reader = hasher.finalize_xof();

// Buffer to store the output
let mut prf_output = vec![0u8; PRF_BYTES_PER_FE * DOMAIN_LENGTH_FE];
// Mapping bytes to field elements
std::array::from_fn(|_| {
// Buffer to store the output
let mut buf = [0u8; PRF_BYTES_PER_FE];

// Read the extended output into the buffer
xof_reader.read(&mut prf_output);
// Read the extended output into the buffer
xof_reader.read(&mut buf);

// Mapping bytes to field elements
std::array::from_fn(|i| {
let chunk_start = i * PRF_BYTES_PER_FE;
let chunk_end = chunk_start + PRF_BYTES_PER_FE;
let integer_value =
BigUint::from_bytes_be(&prf_output[chunk_start..chunk_end]) % F::ORDER_U64;
F::from_u64(integer_value.try_into().unwrap())
// Mapping bytes to a field element
F::from_u128(u128::from_be_bytes(buf))
})
}

Expand Down