Improve points being used in data structures

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "curve25519-dalek"
-version = "0.21.0"
+version = "1.0.0-pre.0"
 authors = ["Isis Lovecruft <[email protected]>",
            "Henry de Valence <[email protected]>"]
 readme = "README.md"
@@ -45,7 +45,7 @@ rand = { version = "0.5", default-features = false }
 byteorder = { version = "^1.2.3", default-features = false, features = ["i128"] }
 digest = { version = "0.8", default-features = false }
 clear_on_drop = "=0.2.3"
-subtle = { version = "1", default-features = false }
+subtle = { version = "2.0.0-pre.0", default-features = false }
 serde = { version = "1.0", optional = true }
 packed_simd = { version = "0.3.0", features = ["into_bits"], optional = true }
 
@@ -54,7 +54,7 @@ rand = { version = "0.5", default-features = false }
 byteorder = { version = "^1.2.3", default-features = false, features = ["i128"] }
 digest = { version = "0.8", default-features = false }
 clear_on_drop = "=0.2.3"
-subtle = { version = "1", default-features = false }
+subtle = { version = "2.0.0-pre.0", default-features = false }
 serde = { version = "1.0", optional = true }
 packed_simd = { version = "0.3.0", features = ["into_bits"], optional = true }
 
@@ -78,3 +78,4 @@ avx2_backend = ["nightly", "u64_backend", "packed_simd"]
 # into the build script. Then, the build.rs emits the stage2_build
 # feature before the main-stage compilation.
 stage2_build = []
+

README.md

@@ -45,7 +45,7 @@ make doc-internal
 To import `curve25519-dalek`, add the following to the dependencies section of
 your project's `Cargo.toml`:
 ```toml
-curve25519-dalek = "0.21"
+curve25519-dalek = "1.0.0-pre.0"
 ```
 Then import the crate as:
 ```rust,no_run

src/backend/avx2/edwards.rs

@@ -38,7 +38,7 @@ use core::convert::From;
 use core::ops::{Add, Neg, Sub};
 
 use subtle::Choice;
-use subtle::ConditionallyAssignable;
+use subtle::ConditionallySelectable;
 
 use edwards;
 use scalar_mul::window::{LookupTable, NafLookupTable5, NafLookupTable8};
@@ -76,8 +76,12 @@ impl From<ExtendedPoint> for edwards::EdwardsPoint {
     }
 }
 
-impl ConditionallyAssignable for ExtendedPoint {
-    fn conditional_assign(&mut self, other: &ExtendedPoint, choice: Choice) {
+impl ConditionallySelectable for ExtendedPoint {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        ExtendedPoint(FieldElement32x4::conditional_select(&a.0, &b.0, choice))
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
         self.0.conditional_assign(&other.0, choice);
     }
 }
@@ -209,8 +213,12 @@ impl Identity for CachedPoint {
     }
 }
 
-impl ConditionallyAssignable for CachedPoint {
-    fn conditional_assign(&mut self, other: &CachedPoint, choice: Choice) {
+impl ConditionallySelectable for CachedPoint {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        CachedPoint(FieldElement32x4::conditional_select(&a.0, &b.0, choice))
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
         self.0.conditional_assign(&other.0, choice);
     }
 }

src/backend/avx2/field.rs

@@ -144,15 +144,37 @@ pub enum Shuffle {
 pub struct FieldElement32x4(pub(crate) [u32x8; 5]);
 
 use subtle::Choice;
-use subtle::ConditionallyAssignable;
+use subtle::ConditionallySelectable;
 
-impl ConditionallyAssignable for FieldElement32x4 {
-    fn conditional_assign(&mut self, other: &FieldElement32x4, choice: Choice) {
+impl ConditionallySelectable for FieldElement32x4 {
+    fn conditional_select(
+        a: &FieldElement32x4,
+        b: &FieldElement32x4,
+        choice: Choice,
+    ) -> FieldElement32x4 {
         let mask = (-(choice.unwrap_u8() as i32)) as u32;
         let mask_vec = u32x8::splat(mask);
-        for i in 0..5 {
-            self.0[i] = self.0[i] ^ (mask_vec & (self.0[i] ^ other.0[i]));
-        }
+        FieldElement32x4([
+            a.0[0] ^ (mask_vec & (a.0[0] ^ b.0[0])),
+            a.0[1] ^ (mask_vec & (a.0[1] ^ b.0[1])),
+            a.0[2] ^ (mask_vec & (a.0[2] ^ b.0[2])),
+            a.0[3] ^ (mask_vec & (a.0[3] ^ b.0[3])),
+            a.0[4] ^ (mask_vec & (a.0[4] ^ b.0[4])),
+        ])
+    }
+
+    fn conditional_assign(
+        &mut self,
+        other: &FieldElement32x4,
+        choice: Choice,
+    ) {
+        let mask = (-(choice.unwrap_u8() as i32)) as u32;
+        let mask_vec = u32x8::splat(mask);
+        self.0[0] ^= mask_vec & (self.0[0] ^ other.0[0]);
+        self.0[1] ^= mask_vec & (self.0[1] ^ other.0[1]);
+        self.0[2] ^= mask_vec & (self.0[2] ^ other.0[2]);
+        self.0[3] ^= mask_vec & (self.0[3] ^ other.0[3]);
+        self.0[4] ^= mask_vec & (self.0[4] ^ other.0[4]);
     }
 }
 

src/backend/u32/field.rs

@@ -16,13 +16,13 @@
 //! of signed limbs.
 
 use core::fmt::Debug;
+use core::ops::Neg;
 use core::ops::{Add, AddAssign};
-use core::ops::{Sub, SubAssign};
 use core::ops::{Mul, MulAssign};
-use core::ops::Neg;
+use core::ops::{Sub, SubAssign};
 
-use subtle::ConditionallyAssignable;
 use subtle::Choice;
+use subtle::ConditionallySelectable;
 
 /// A `FieldElement32` represents an element of the field
 /// \\( \mathbb Z / (2\^{255} - 19)\\).
@@ -219,11 +219,50 @@ impl<'a> Neg for &'a FieldElement32 {
     }
 }
 
-impl ConditionallyAssignable for FieldElement32 {
+impl ConditionallySelectable for FieldElement32 {
+    fn conditional_select(
+        a: &FieldElement32,
+        b: &FieldElement32,
+        choice: Choice,
+    ) -> FieldElement32 {
+        FieldElement32([
+            u32::conditional_select(&a.0[0], &b.0[0], choice),
+            u32::conditional_select(&a.0[1], &b.0[1], choice),
+            u32::conditional_select(&a.0[2], &b.0[2], choice),
+            u32::conditional_select(&a.0[3], &b.0[3], choice),
+            u32::conditional_select(&a.0[4], &b.0[4], choice),
+            u32::conditional_select(&a.0[5], &b.0[5], choice),
+            u32::conditional_select(&a.0[6], &b.0[6], choice),
+            u32::conditional_select(&a.0[7], &b.0[7], choice),
+            u32::conditional_select(&a.0[8], &b.0[8], choice),
+            u32::conditional_select(&a.0[9], &b.0[9], choice),
+        ])
+    }
+
     fn conditional_assign(&mut self, other: &FieldElement32, choice: Choice) {
-        for i in 0..10 {
-            self.0[i].conditional_assign(&other.0[i], choice);
-        }
+        self.0[0].conditional_assign(&other.0[0], choice);
+        self.0[1].conditional_assign(&other.0[1], choice);
+        self.0[2].conditional_assign(&other.0[2], choice);
+        self.0[3].conditional_assign(&other.0[3], choice);
+        self.0[4].conditional_assign(&other.0[4], choice);
+        self.0[5].conditional_assign(&other.0[5], choice);
+        self.0[6].conditional_assign(&other.0[6], choice);
+        self.0[7].conditional_assign(&other.0[7], choice);
+        self.0[8].conditional_assign(&other.0[8], choice);
+        self.0[9].conditional_assign(&other.0[9], choice);
+    }
+
+    fn conditional_swap(a: &mut FieldElement32, b: &mut FieldElement32, choice: Choice) {
+        u32::conditional_swap(&mut a.0[0], &mut b.0[0], choice);
+        u32::conditional_swap(&mut a.0[1], &mut b.0[1], choice);
+        u32::conditional_swap(&mut a.0[2], &mut b.0[2], choice);
+        u32::conditional_swap(&mut a.0[3], &mut b.0[3], choice);
+        u32::conditional_swap(&mut a.0[4], &mut b.0[4], choice);
+        u32::conditional_swap(&mut a.0[5], &mut b.0[5], choice);
+        u32::conditional_swap(&mut a.0[6], &mut b.0[6], choice);
+        u32::conditional_swap(&mut a.0[7], &mut b.0[7], choice);
+        u32::conditional_swap(&mut a.0[8], &mut b.0[8], choice);
+        u32::conditional_swap(&mut a.0[9], &mut b.0[9], choice);
     }
 }
 

src/backend/u64/field.rs

@@ -12,13 +12,13 @@
 //! limbs with \\(128\\)-bit products.
 
 use core::fmt::Debug;
+use core::ops::Neg;
 use core::ops::{Add, AddAssign};
-use core::ops::{Sub, SubAssign};
 use core::ops::{Mul, MulAssign};
-use core::ops::Neg;
+use core::ops::{Sub, SubAssign};
 
-use subtle::ConditionallyAssignable;
 use subtle::Choice;
+use subtle::ConditionallySelectable;
 
 /// A `FieldElement64` represents an element of the field
 /// \\( \mathbb Z / (2\^{255} - 19)\\).
@@ -209,11 +209,35 @@ impl<'a> Neg for &'a FieldElement64 {
     }
 }
 
-impl ConditionallyAssignable for FieldElement64 {
+impl ConditionallySelectable for FieldElement64 {
+    fn conditional_select(
+        a: &FieldElement64,
+        b: &FieldElement64,
+        choice: Choice,
+    ) -> FieldElement64 {
+        FieldElement64([
+            u64::conditional_select(&a.0[0], &b.0[0], choice),
+            u64::conditional_select(&a.0[1], &b.0[1], choice),
+            u64::conditional_select(&a.0[2], &b.0[2], choice),
+            u64::conditional_select(&a.0[3], &b.0[3], choice),
+            u64::conditional_select(&a.0[4], &b.0[4], choice),
+        ])
+    }
+
+    fn conditional_swap(a: &mut FieldElement64, b: &mut FieldElement64, choice: Choice) {
+        u64::conditional_swap(&mut a.0[0], &mut b.0[0], choice);
+        u64::conditional_swap(&mut a.0[1], &mut b.0[1], choice);
+        u64::conditional_swap(&mut a.0[2], &mut b.0[2], choice);
+        u64::conditional_swap(&mut a.0[3], &mut b.0[3], choice);
+        u64::conditional_swap(&mut a.0[4], &mut b.0[4], choice);
+    }
+
     fn conditional_assign(&mut self, other: &FieldElement64, choice: Choice) {
-        for i in 0..5 {
-            self.0[i].conditional_assign(&other.0[i], choice);
-        }
+        self.0[0].conditional_assign(&other.0[0], choice);
+        self.0[1].conditional_assign(&other.0[1], choice);
+        self.0[2].conditional_assign(&other.0[2], choice);
+        self.0[3].conditional_assign(&other.0[3], choice);
+        self.0[4].conditional_assign(&other.0[4], choice);
     }
 }
 

src/constants.rs

@@ -129,12 +129,13 @@ mod test {
         }
     }
 
+    /// Test that SQRT_M1 is the positive square root of -1
     #[test]
-    /// Test that SQRT_M1 is a square root of -1
     fn test_sqrt_minus_one() {
         let minus_one = FieldElement::minus_one();
         let sqrt_m1_sq = &constants::SQRT_M1 * &constants::SQRT_M1;
         assert_eq!(minus_one,  sqrt_m1_sq);
+        assert_eq!(constants::SQRT_M1.is_negative().unwrap_u8(), 0);
     }
 
     #[test]
@@ -143,8 +144,6 @@ mod test {
         let (was_nonzero_square, invsqrt_m1) = minus_one.invsqrt();
         assert_eq!(was_nonzero_square.unwrap_u8(), 1u8);
         let sign_test_sqrt  = &invsqrt_m1 * &constants::SQRT_M1;
-        // XXX it seems we have flipped the sign relative to
-        // the invsqrt function?
         assert_eq!(sign_test_sqrt, minus_one);
     }
 

src/curve_models/mod.rs

@@ -124,15 +124,15 @@
 #![allow(non_snake_case)]
 
 use core::fmt::Debug;
-use core::ops::{Add, Sub, Neg};
+use core::ops::{Add, Neg, Sub};
 
-use subtle::ConditionallyAssignable;
 use subtle::Choice;
+use subtle::ConditionallySelectable;
 
 use constants;
 
-use field::FieldElement;
 use edwards::EdwardsPoint;
+use field::FieldElement;
 use traits::ValidityCheck;
 
 // ------------------------------------------------------------------------
@@ -204,7 +204,7 @@ use traits::Identity;
 
 impl Identity for ProjectivePoint {
     fn identity() -> ProjectivePoint {
-        ProjectivePoint{
+        ProjectivePoint {
             X: FieldElement::zero(),
             Y: FieldElement::one(),
             Z: FieldElement::one(),
@@ -268,18 +268,34 @@ impl ValidityCheck for ProjectivePoint {
 // Constant-time assignment
 // ------------------------------------------------------------------------
 
-impl ConditionallyAssignable for ProjectiveNielsPoint {
-    fn conditional_assign(&mut self, other: &ProjectiveNielsPoint, choice: Choice) {
+impl ConditionallySelectable for ProjectiveNielsPoint {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        ProjectiveNielsPoint {
+            Y_plus_X: FieldElement::conditional_select(&a.Y_plus_X, &b.Y_plus_X, choice),
+            Y_minus_X: FieldElement::conditional_select(&a.Y_minus_X, &b.Y_minus_X, choice),
+            Z: FieldElement::conditional_select(&a.Z, &b.Z, choice),
+            T2d: FieldElement::conditional_select(&a.T2d, &b.T2d, choice),
+        }
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
         self.Y_plus_X.conditional_assign(&other.Y_plus_X, choice);
         self.Y_minus_X.conditional_assign(&other.Y_minus_X, choice);
         self.Z.conditional_assign(&other.Z, choice);
         self.T2d.conditional_assign(&other.T2d, choice);
     }
 }
 
-impl ConditionallyAssignable for AffineNielsPoint {
-    fn conditional_assign(&mut self, other: &AffineNielsPoint, choice: Choice) {
-        // PreComputedGroupElementCMove()
+impl ConditionallySelectable for AffineNielsPoint {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        AffineNielsPoint {
+            y_plus_x: FieldElement::conditional_select(&a.y_plus_x, &b.y_plus_x, choice),
+            y_minus_x: FieldElement::conditional_select(&a.y_minus_x, &b.y_minus_x, choice),
+            xy2d: FieldElement::conditional_select(&a.xy2d, &b.xy2d, choice),
+        }
+    }
+
+    fn conditional_assign(&mut self, other: &Self, choice: Choice) {
         self.y_plus_x.conditional_assign(&other.y_plus_x, choice);
         self.y_minus_x.conditional_assign(&other.y_minus_x, choice);
         self.xy2d.conditional_assign(&other.xy2d, choice);
@@ -296,7 +312,7 @@ impl ProjectivePoint {
     ///
     /// This costs \\(3 \mathrm M + 1 \mathrm S\\).
     pub fn to_extended(&self) -> EdwardsPoint {
-        EdwardsPoint{
+        EdwardsPoint {
             X: &self.X * &self.Z,
             Y: &self.Y * &self.Z,
             Z: self.Z.square(),
@@ -311,7 +327,7 @@ impl CompletedPoint {
     ///
     /// This costs \\(3 \mathrm M \\).
     pub fn to_projective(&self) -> ProjectivePoint {
-        ProjectivePoint{
+        ProjectivePoint {
             X: &self.X * &self.T,
             Y: &self.Y * &self.Z,
             Z: &self.Z * &self.T,
@@ -323,7 +339,7 @@ impl CompletedPoint {
     ///
     /// This costs \\(4 \mathrm M \\).
     pub fn to_extended(&self) -> EdwardsPoint {
-        EdwardsPoint{
+        EdwardsPoint {
             X: &self.X * &self.T,
             Y: &self.Y * &self.Z,
             Z: &self.Z * &self.T,