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Add root_of_unity to dalek-ff-group

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Also adds a few more tests.

All functions are now implemented.
This commit is contained in:
Luke Parker
2022-12-15 20:33:58 -05:00
parent b8db677d4c
commit 256d920835
3 changed files with 104 additions and 15 deletions
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46
crypto/dalek-ff-group/src/lib.rs
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@@ -285,7 +285,7 @@ impl PrimeField for Scalar {
const CAPACITY: u32 = 252;
fn from_repr(bytes: [u8; 32]) -> CtOption<Self> {
let scalar = DScalar::from_canonical_bytes(bytes);
// TODO: This unwrap_or isn't constant time, yet do we have an alternative?
// TODO: This unwrap_or isn't constant time, yet we don't exactly have an alternative...
CtOption::new(Scalar(scalar.unwrap_or_else(DScalar::zero)), choice(scalar.is_some()))
}
fn to_repr(&self) -> [u8; 32] {
@@ -300,7 +300,11 @@ impl PrimeField for Scalar {
2u64.into()
}
fn root_of_unity() -> Self {
unimplemented!()
const ROOT: [u8; 32] = [
212, 7, 190, 235, 223, 117, 135, 190, 254, 131, 206, 66, 83, 86, 240, 14, 122, 194, 193, 171,
96, 109, 61, 125, 231, 129, 121, 224, 16, 115, 74, 9,
];
Scalar::from_repr(ROOT).unwrap()
}
}
@@ -449,6 +453,44 @@ dalek_group!(
RISTRETTO_BASEPOINT_TABLE
);
#[test]
fn test_s() {
// "This is the number of leading zero bits in the little-endian bit representation of
// `modulus - 1`."
let mut s = 0;
for b in (Scalar::zero() - Scalar::one()).to_le_bits() {
if b {
break;
}
s += 1;
}
assert_eq!(s, Scalar::S);
}
#[test]
fn test_root_of_unity() {
// "It can be calculated by exponentiating `Self::multiplicative_generator` by `t`, where
// `t = (modulus - 1) >> Self::S`."
let t = Scalar::zero() - Scalar::one();
let mut bytes = t.to_repr();
for _ in 0 .. Scalar::S {
bytes[0] >>= 1;
for b in 1 .. 32 {
// Shift the dropped but down a byte
bytes[b - 1] |= (bytes[b] & 1) << 7;
// Shift the byte
bytes[b] >>= 1;
}
}
let t = Scalar::from_repr(bytes).unwrap();
assert_eq!(Scalar::multiplicative_generator().pow(t), Scalar::root_of_unity());
assert_eq!(
Scalar::root_of_unity().pow(Scalar::from(2u64).pow(Scalar::from(Scalar::S))),
Scalar::one()
);
}
#[test]
fn test_sqrt() {
assert_eq!(Scalar::zero().sqrt().unwrap(), Scalar::zero());