impl ConditionallySelectable for Field

Cargo.toml

@@ -21,6 +21,7 @@ byteorder = "1"
 ff = { version = "0.6", path = "../ff", features = ["derive"] }
 group = { version = "0.6", path = "../group" }
 rand_core = "0.5"
+subtle = "2.2.1"
 
 [dev-dependencies]
 rand_xorshift = "0.2"

src/bls12_381/fq12.rs

@@ -4,6 +4,7 @@ use super::fq6::Fq6;
 use ff::Field;
 use rand_core::RngCore;
 use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
+use subtle::{Choice, ConditionallySelectable};
 
 /// An element of Fq12, represented by c0 + c1 * w.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -40,6 +41,15 @@ impl Fq12 {
     }
 }
 
+impl ConditionallySelectable for Fq12 {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Fq12 {
+            c0: Fq6::conditional_select(&a.c0, &b.c0, choice),
+            c1: Fq6::conditional_select(&a.c1, &b.c1, choice),
+        }
+    }
+}
+
 impl Neg for Fq12 {
     type Output = Self;
 

src/bls12_381/fq2.rs

@@ -3,6 +3,7 @@ use ff::{Field, SqrtField};
 use rand_core::RngCore;
 use std::cmp::Ordering;
 use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
+use subtle::{Choice, ConditionallySelectable};
 
 /// An element of Fq2, represented by c0 + c1 * u.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -54,6 +55,15 @@ impl Fq2 {
     }
 }
 
+impl ConditionallySelectable for Fq2 {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Fq2 {
+            c0: Fq::conditional_select(&a.c0, &b.c0, choice),
+            c1: Fq::conditional_select(&a.c1, &b.c1, choice),
+        }
+    }
+}
+
 impl Neg for Fq2 {
     type Output = Self;
 

src/bls12_381/fq6.rs

@@ -3,6 +3,7 @@ use super::fq2::Fq2;
 use ff::Field;
 use rand_core::RngCore;
 use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
+use subtle::{Choice, ConditionallySelectable};
 
 /// An element of Fq6, represented by c0 + c1 * v + c2 * v^(2).
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -100,6 +101,16 @@ impl Fq6 {
     }
 }
 
+impl ConditionallySelectable for Fq6 {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Fq6 {
+            c0: Fq2::conditional_select(&a.c0, &b.c0, choice),
+            c1: Fq2::conditional_select(&a.c1, &b.c1, choice),
+            c2: Fq2::conditional_select(&a.c2, &b.c2, choice),
+        }
+    }
+}
+
 impl Neg for Fq6 {
     type Output = Self;