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Fix batching for P-256 (#154) 

fix batch for P-256: use little endian encoding; increase NAF size
This commit is contained in:
Conrado Gouvea 2022-10-27 01:34:57 -03:00 committed by GitHub
parent 0bbce1059a
commit 3b497100c0
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 9 additions and 13 deletions
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14
frost-core/src/scalar_mul.rs
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@ -10,7 +10,7 @@ use crate::{Ciphersuite, Element, Field, Group, Scalar};
/// A trait for transforming a scalar generic over a ciphersuite to a non-adjacent form (NAF).
pub trait NonAdjacentForm<C: Ciphersuite> {
fn non_adjacent_form(&self, w: usize) -> [i8; 256];
fn non_adjacent_form(&self, w: usize) -> [i8; 257];
}
impl<C> NonAdjacentForm<C> for Scalar<C>
@ -24,8 +24,7 @@ where
/// # Safety
///
/// The full scalar field MUST fit in 256 bits in this implementation.
/// Assumes that a little-endian representations of the scalar in NAF work.
fn non_adjacent_form(&self, w: usize) -> [i8; 256] {
fn non_adjacent_form(&self, w: usize) -> [i8; 257] {
// required by the NAF definition
debug_assert!(w >= 2);
// required so that the NAF digits fit in i8
@ -34,11 +33,12 @@ where
use byteorder::{ByteOrder, LittleEndian};
// Safety: assumes a scalar that fits in 256 bits.
let mut naf = [0i8; 256];
// The length of the NAF is at most one more than the bit length.
let mut naf = [0i8; 257];
let mut x_u64 = [0u64; 5];
LittleEndian::read_u64_into(
<<C::Group as Group>::Field>::serialize(self).as_ref(),
<<C::Group as Group>::Field>::little_endian_serialize(self).as_ref(),
&mut x_u64[0..4],
);
@ -47,7 +47,7 @@ where
let mut pos = 0;
let mut carry = 0;
while pos < 256 {
while pos < 257 {
// Construct a buffer of bits of the scalar, starting at bit `pos`
let u64_idx = pos / 64;
let bit_idx = pos % 64;
@ -149,7 +149,7 @@ where
let mut r = <C::Group>::identity();
for i in (0..256).rev() {
for i in (0..257).rev() {
let mut t = r + r;
for (naf, lookup_table) in nafs.iter().zip(lookup_tables.iter()) {

8
frost-p256/tests/frost.rs
View File

@ -16,18 +16,14 @@ fn check_sign_with_dkg() {
frost_core::tests::check_sign_with_dkg::<P256Sha256, _>(rng);
}
// TODO: re-enable after batch is changed to work with big-endian scalars
// #[test]
#[allow(unused)]
#[test]
fn check_batch_verify() {
let rng = thread_rng();
frost_core::tests::batch::batch_verify::<P256Sha256, _>(rng);
}
// TODO: re-enable after batch is changed to work with big-endian scalars
// #[test]
#[allow(unused)]
#[test]
fn check_bad_batch_verify() {
let rng = thread_rng();