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Use GroupEncoding instead of Curve's from_slice/to_bytes

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Increases usage of standardization while expanding dalek_ff_group.

Closes https://github.com/serai-dex/serai/issues/26 by moving 
dfg::EdwardsPoint to only be for the prime subgroup.
This commit is contained in:
Luke Parker
2022-06-28 01:25:26 -04:00
parent ac17645fc8
commit 3de7a76051
14 changed files with 141 additions and 178 deletions
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50
crypto/frost/src/curve/mod.rs
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@@ -4,7 +4,7 @@ use thiserror::Error;
use rand_core::{RngCore, CryptoRng};
use group::{ff::PrimeField, Group, GroupOps};
use group::{ff::PrimeField, Group, GroupOps, prime::PrimeGroup};
#[cfg(any(test, feature = "dalek"))]
mod dalek;
@@ -42,7 +42,7 @@ pub trait Curve: Clone + Copy + PartialEq + Eq + Debug {
// This is available via G::Scalar yet `C::G::Scalar` is ambiguous, forcing horrific accesses
type F: PrimeField;
/// Group element type
type G: Group<Scalar = Self::F> + GroupOps;
type G: Group<Scalar = Self::F> + GroupOps + PrimeGroup;
/// Precomputed table type
type T: Mul<Self::F, Output = Self::G>;
@@ -99,23 +99,31 @@ pub trait Curve: Clone + Copy + PartialEq + Eq + Debug {
// that is on them
#[allow(non_snake_case)]
fn G_len() -> usize;
/// Field element from slice. Preferred to be canonical yet does not have to be
// Required due to the lack of standardized encoding functions provided by ff/group
// While they do technically exist, their usage of Self::Repr breaks all potential library usage
// without helper functions like this
#[allow(non_snake_case)]
fn F_from_slice(slice: &[u8]) -> Result<Self::F, CurveError>;
/// Group element from slice. Must require canonicity or risks differing binding factors
#[allow(non_snake_case)]
fn G_from_slice(slice: &[u8]) -> Result<Self::G, CurveError>;
/// Obtain a vector of the byte encoding of F
#[allow(non_snake_case)]
fn F_to_bytes(f: &Self::F) -> Vec<u8>;
/// Obtain a vector of the byte encoding of G
#[allow(non_snake_case)]
fn G_to_bytes(g: &Self::G) -> Vec<u8>;
}
/// Field element from slice
#[allow(non_snake_case)]
pub(crate) fn F_from_slice<F: PrimeField>(slice: &[u8]) -> Result<F, CurveError> {
let mut encoding = F::Repr::default();
encoding.as_mut().copy_from_slice(slice);
let point = Option::<F>::from(F::from_repr(encoding)).ok_or(CurveError::InvalidScalar)?;
if point.to_repr().as_ref() != slice {
Err(CurveError::InvalidScalar)?;
}
Ok(point)
}
/// Group element from slice
#[allow(non_snake_case)]
pub(crate) fn G_from_slice<G: PrimeGroup>(slice: &[u8]) -> Result<G, CurveError> {
let mut encoding = G::Repr::default();
encoding.as_mut().copy_from_slice(slice);
let point = Option::<G>::from(G::from_bytes(&encoding)).ok_or(CurveError::InvalidPoint)?;
// Ban the identity, per the FROST spec, and non-canonical points
if (point.is_identity().into()) || (point.to_bytes().as_ref() != slice) {
Err(CurveError::InvalidPoint)?;
}
Ok(point)
}