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Constant-time field inversion

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WARNING: THIS IS NOT ACTUALLY CONSTANT TIME YET!

The jubjub and bls12_381 crates will replace our constant-time usages,
but we NEED to fix ff_derive because other users will expect it to
implement the Field trait correctly.
This commit is contained in:
Jack Grigg
2019-05-14 14:18:37 +01:00
parent e85a9f309f
commit 40749da9a7
25 changed files with 243 additions and 221 deletions
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10
zcash_primitives/src/jubjub/tests.rs
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@@ -234,7 +234,9 @@ fn test_get_for<E: JubjubEngine>(params: &E::Params) {
let y = E::Fr::random(rng);
let sign = rng.next_u32() % 2 == 1;
if let Some(mut p) = edwards::Point::<E, _>::get_for_y(y, sign, params) {
let p = edwards::Point::<E, _>::get_for_y(y, sign, params);
if bool::from(p.is_some()) {
let mut p = p.unwrap();
assert!(p.to_xy().0.into_repr().is_odd() == sign);
p = p.negate();
assert!(edwards::Point::<E, _>::get_for_y(y, !sign, params).unwrap() == p);
@@ -328,7 +330,7 @@ fn test_jubjub_params<E: JubjubEngine>(params: &E::Params) {
let mut tmp = *params.edwards_d();
// 1 / d is nonsquare
assert!(tmp.inverse().unwrap().legendre() == LegendreSymbol::QuadraticNonResidue);
assert!(tmp.invert().unwrap().legendre() == LegendreSymbol::QuadraticNonResidue);
// tmp = -d
tmp = tmp.neg();
@@ -337,7 +339,7 @@ fn test_jubjub_params<E: JubjubEngine>(params: &E::Params) {
assert!(tmp.legendre() == LegendreSymbol::QuadraticNonResidue);
// 1 / -d is nonsquare
assert!(tmp.inverse().unwrap().legendre() == LegendreSymbol::QuadraticNonResidue);
assert!(tmp.invert().unwrap().legendre() == LegendreSymbol::QuadraticNonResidue);
}
{
@@ -358,7 +360,7 @@ fn test_jubjub_params<E: JubjubEngine>(params: &E::Params) {
// Check the validity of the scaling factor
let mut tmp = a;
tmp.sub_assign(&params.edwards_d());
tmp = tmp.inverse().unwrap();
tmp = tmp.invert().unwrap();
tmp.mul_assign(&E::Fr::from_str("4").unwrap());
tmp = tmp.sqrt().unwrap();
assert_eq!(&tmp, params.scale());