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Merge pull request #226 from ebfull/faster-equality

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Check the equality of `EdwardsPoint`s in the projective coordinates
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Henry de Valence 2019-05-21 08:50:32 -07:00 committed by GitHub
commit 23ca520ac2
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1 changed files with 8 additions and 1 deletions
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src/edwards.rs
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@ -394,7 +394,14 @@ impl ConditionallySelectable for EdwardsPoint {
impl ConstantTimeEq for EdwardsPoint {
fn ct_eq(&self, other: &EdwardsPoint) -> Choice {
self.compress().ct_eq(&other.compress())
// We would like to check that the point (X/Z, Y/Z) is equal to
// the point (X'/Z', Y'/Z') without converting into affine
// coordinates (x, y) and (x', y'), which requires two inversions.
// We have that X = xZ and X' = x'Z'. Thus, x = x' is equivalent to
// (xZ)Z' = (x'Z')Z, and similarly for the y-coordinate.
(&self.X * &other.Z).ct_eq(&(&other.X * &self.Z))
& (&self.Y * &other.Z).ct_eq(&(&other.Y * &self.Z))
}
}