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Add Ristretto equality

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Henry de Valence 2017-07-23 20:45:54 -07:00 committed by Henry de Valence
parent fafdae7a60
commit 7097d8f98e
1 changed files with 21 additions and 8 deletions
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29
src/ristretto.rs
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@ -10,7 +10,7 @@
//! An implementation of Mike Hamburg's Ristretto cofactor-eliminating
//! point-compression scheme, providing a prime-order group on top of
//! a non-prime-order elliptic curve.
//! Curve25519.
//!
//! Note: this code is currently feature-gated with the `yolocrypto`
//! feature flag, because our implementation is still unfinished.
@ -43,9 +43,10 @@ use edwards::EdwardsBasepointTable;
use edwards::Identity;
use scalar::Scalar;
use subtle;
use subtle::ConditionallyAssignable;
use subtle::ConditionallyNegatable;
use subtle;
use subtle::Equal;
// ------------------------------------------------------------------------
// Compressed points
@ -187,7 +188,7 @@ impl<'de> Deserialize<'de> for RistrettoPoint {
/// A point in a prime-order group.
///
// XXX think about how this API should work
/// XXX think about how this API should work
#[derive(Copy, Clone)]
pub struct RistrettoPoint(pub ExtendedPoint);
@ -395,13 +396,25 @@ impl Identity for RistrettoPoint {
// Equality
// ------------------------------------------------------------------------
/// XXX check whether there's a simple way to do equality checking
/// with cofactor 8, not just cofactor 4, and add a CT equality function?
impl PartialEq for RistrettoPoint {
fn eq(&self, other: &RistrettoPoint) -> bool {
let self_compressed = self.compress();
let other_compressed = other.compress();
self_compressed == other_compressed
self.ct_eq(other) == 1u8
}
}
impl Equal for RistrettoPoint {
/// Test equality between two `RistrettoPoint`s.
///
/// # Returns
///
/// `1u8` if the two `RistrettoPoint`s are equal, and `0u8` otherwise.
fn ct_eq(&self, other: &RistrettoPoint) -> u8 {
let X1Y2 = &self.0.X * &other.0.Y;
let Y1X2 = &self.0.Y * &other.0.X;
let X1X2 = &self.0.X * &other.0.X;
let Y1Y2 = &self.0.Y * &other.0.Y;
X1Y2.ct_eq(&Y1X2) | X1X2.ct_eq(&Y1Y2)
}
}