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Correct decoding identity for embedwards25519/secq256k1

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This commit is contained in:
Luke Parker
2025-01-29 23:01:45 -05:00
parent 2bc880e372
commit 315d4fb356
4 changed files with 14 additions and 6 deletions
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5
crypto/evrf/secq256k1/src/point.rs
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@@ -192,6 +192,7 @@ impl Group for Point {
Point { x: FieldElement::ZERO, y: FieldElement::ONE, z: FieldElement::ZERO }
}
fn generator() -> Self {
// Point with the lowest valid x-coordinate
Point {
x: FieldElement::from_repr(
hex_literal::hex!("0000000000000000000000000000000000000000000000000000000000000001")
@@ -334,8 +335,10 @@ impl GroupEncoding for Point {
// If this the identity, set y to 1
let y =
CtOption::conditional_select(&y, &CtOption::new(FieldElement::ONE, 1.into()), is_identity);
// If this the identity, set y to 1 and z to 0 (instead of 1)
let z = <_>::conditional_select(&FieldElement::ONE, &FieldElement::ZERO, is_identity);
// Create the point if we have a y solution
let point = y.map(|y| Point { x, y, z: FieldElement::ONE });
let point = y.map(|y| Point { x, y, z });
let not_negative_zero = !(is_identity & sign);
// Only return the point if it isn't -0 and the sign byte wasn't malleated