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Implement CTEq for FieldElement.

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Isis Lovecruft 2017-02-21 02:36:50 +00:00
parent 5308fef210
commit b1afdf5204
Failed to extract signature
1 changed files with 17 additions and 5 deletions
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22
src/field.rs
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@ -24,8 +24,10 @@ use core::ops::{Index, IndexMut};
use core::cmp::{Eq, PartialEq}; use core::cmp::{Eq, PartialEq};
use core::ops::Neg; use core::ops::Neg;
use util::arrays_equal_ct;
use util::byte_is_nonzero; use util::byte_is_nonzero;
use util::CTAssignable; use util::CTAssignable;
use util::CTEq;
/// FieldElements are represented as an array of ten "Limbs", which are radix /// FieldElements are represented as an array of ten "Limbs", which are radix
/// 25.5, that is, each Limb of a FieldElement alternates between being /// 25.5, that is, each Limb of a FieldElement alternates between being
@ -40,6 +42,7 @@ pub type Limb = i32;
#[derive(Copy, Clone)] #[derive(Copy, Clone)]
pub struct FieldElement(pub [Limb; 10]); pub struct FieldElement(pub [Limb; 10]);
impl Eq for FieldElement {}
impl PartialEq for FieldElement { impl PartialEq for FieldElement {
/// Test equality between two FieldElements by converting them to bytes. /// Test equality between two FieldElements by converting them to bytes.
/// ///
@ -48,10 +51,10 @@ impl PartialEq for FieldElement {
/// This comparison is *not* constant time. It could easily be /// This comparison is *not* constant time. It could easily be
/// made to be, but the main use of an `Eq` implementation is for /// made to be, but the main use of an `Eq` implementation is for
/// branching, so it seems pointless. /// branching, so it seems pointless.
/// //
/// XXX it would be good to encode constant-time considerations // XXX it would be good to encode constant-time considerations
/// (no data flow from secret information) into Rust's type // (no data flow from secret information) into Rust's type
/// system. // system.
fn eq(&self, other: &FieldElement) -> bool { fn eq(&self, other: &FieldElement) -> bool {
let self_bytes = self.to_bytes(); let self_bytes = self.to_bytes();
let other_bytes = other.to_bytes(); let other_bytes = other.to_bytes();
@ -63,7 +66,16 @@ impl PartialEq for FieldElement {
} }
} }
impl Eq for FieldElement {} impl CTEq for FieldElement {
/// Test equality between two `FieldElement`s by converting them to bytes.
///
/// # Returns
///
/// `1u8` if the two `FieldElement`s are equal, and `0u8` otherwise.
fn ct_eq(&self, other: &FieldElement) -> u8 {
arrays_equal_ct(&self.to_bytes(), &other.to_bytes())
}
}
impl Debug for FieldElement { impl Debug for FieldElement {
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result { fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {