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Document dalek-ff-group

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Removes from_canonical_bytes, which is offered by from_repr, and 
from_bytes_mod_order, which frequently leads to security issues.

Removes the pointless Compressed type.

Adds From u8/u16/u32 as they're pleasant.
This commit is contained in:
Luke Parker 2022-07-09 02:01:22 -04:00
parent 5942492519
commit a4cd1755a5
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GPG key ID: F9F1386DB1E119B6
1 changed files with 20 additions and 34 deletions
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54
crypto/dalek-ff-group/src/lib.rs
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@ -32,6 +32,7 @@ use dalek::{
use ff::{Field, PrimeField, FieldBits, PrimeFieldBits};
use group::{Group, GroupEncoding, prime::PrimeGroup};
// Convert a boolean to a Choice in a *presumably* constant time manner
fn choice(value: bool) -> Choice {
let bit = value as u8;
debug_assert_eq!(bit | 1, 1);
@ -119,24 +120,19 @@ macro_rules! math {
}
}
/// Wrapper around the dalek Scalar type
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub struct Scalar(pub DScalar);
deref_borrow!(Scalar, DScalar);
math!(Scalar, Scalar, Scalar);
impl Scalar {
pub fn from_canonical_bytes(bytes: [u8; 32]) -> Option<Scalar> {
DScalar::from_canonical_bytes(bytes).map(|x| Self(x))
}
pub fn from_bytes_mod_order(bytes: [u8; 32]) -> Scalar {
Self(DScalar::from_bytes_mod_order(bytes))
}
/// Perform wide reduction on a 64-byte array to create a Scalar without bias
pub fn from_bytes_mod_order_wide(bytes: &[u8; 64]) -> Scalar {
Self(DScalar::from_bytes_mod_order_wide(bytes))
}
/// Derive a Scalar without bias from a digest via wide reduction
pub fn from_hash<D: Digest<OutputSize = U64>>(hash: D) -> Scalar {
let mut output = [0u8; 64];
output.copy_from_slice(&hash.finalize());
@ -174,6 +170,18 @@ impl Field for Scalar {
fn pow_vartime<S: AsRef<[u64]>>(&self, _exp: S) -> Self { unimplemented!() }
}
impl From<u8> for Scalar {
fn from(a: u8) -> Scalar { Self(DScalar::from(a)) }
}
impl From<u16> for Scalar {
fn from(a: u16) -> Scalar { Self(DScalar::from(a)) }
}
impl From<u32> for Scalar {
fn from(a: u32) -> Scalar { Self(DScalar::from(a)) }
}
impl From<u64> for Scalar {
fn from(a: u64) -> Scalar { Self(DScalar::from(a)) }
}
@ -205,7 +213,7 @@ impl PrimeFieldBits for Scalar {
fn char_le_bits() -> FieldBits<Self::ReprBits> {
let mut bytes = (Scalar::zero() - Scalar::one()).to_repr();
bytes[0] += 1;
debug_assert_eq!(Scalar::from_bytes_mod_order(bytes), Scalar::zero());
debug_assert_eq!(DScalar::from_bytes_mod_order(bytes), DScalar::zero());
bytes.into()
}
}
@ -219,12 +227,12 @@ macro_rules! dalek_group {
$Table: ident,
$DTable: ident,
$Compressed: ident,
$DCompressed: ident,
$BASEPOINT_POINT: ident,
$BASEPOINT_TABLE: ident
) => {
/// Wrapper around the dalek Point type. For Ed25519, this is restricted to the prime subgroup
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub struct $Point(pub $DPoint);
deref_borrow!($Point, $DPoint);
@ -271,28 +279,8 @@ macro_rules! dalek_group {
impl PrimeGroup for $Point {}
pub struct $Compressed(pub $DCompressed);
deref_borrow!($Compressed, $DCompressed);
impl $Compressed {
pub fn new(y: [u8; 32]) -> $Compressed {
Self($DCompressed(y))
}
pub fn decompress(&self) -> Option<$Point> {
self.0.decompress().map(|x| $Point(x))
}
pub fn to_bytes(&self) -> [u8; 32] {
self.0.to_bytes()
}
}
impl $Point {
pub fn compress(&self) -> $Compressed {
$Compressed(self.0.compress())
}
}
/// Wrapper around the dalek Table type, offering efficient multiplication against the
/// basepoint
pub struct $Table(pub $DTable);
deref_borrow!($Table, $DTable);
pub const $BASEPOINT_TABLE: $Table = $Table(constants::$BASEPOINT_TABLE);
@ -312,7 +300,6 @@ dalek_group!(
EdwardsBasepointTable,
DEdwardsBasepointTable,
CompressedEdwardsY,
DCompressedEdwards,
ED25519_BASEPOINT_POINT,
@ -327,7 +314,6 @@ dalek_group!(
RistrettoBasepointTable,
DRistrettoBasepointTable,
CompressedRistretto,
DCompressedRistretto,
RISTRETTO_BASEPOINT_POINT,