Merge pull request #31 from zkcrypto/release-0.1.1

Release 0.1.1

Author: ebfull

.github/workflows/ci.yml

@@ -43,8 +43,18 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: build
-          args: --verbose --release --tests
+          args: --verbose --release --tests --features endo
       - name: Run tests
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --release --features endo
+      - name: Build tests (no endomorphism)
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --verbose --release --tests
+      - name: Run tests (no endomorphism)
         uses: actions-rs/cargo@v1
         with:
           command: test

Cargo.toml

@@ -6,7 +6,7 @@ homepage = "https://github.com/zkcrypto/bls12_381"
 license = "MIT/Apache-2.0"
 name = "bls12_381"
 repository = "https://github.com/zkcrypto/bls12_381"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2018"
 
 [package.metadata.docs.rs]
@@ -30,3 +30,6 @@ groups = []
 pairings = ["groups"]
 alloc = []
 nightly = ["subtle/nightly"]
+
+# GLV patents US7110538B2 and US7995752B2 expire in September 2020.
+endo = []

README.md

@@ -13,6 +13,7 @@ This crate provides an implementation of the BLS12-381 pairing-friendly elliptic
 * `pairings` (on by default): Enables some APIs for performing pairings.
 * `alloc` (on by default): Enables APIs that require an allocator; these include pairing optimizations.
 * `nightly`: Enables `subtle/nightly` which tries to prevent compiler optimizations that could jeopardize constant time operations. Requires the nightly Rust compiler.
+* `endo`: Enables optimizations that leverage curve endomorphisms, which may run foul of patents US7110538B2 and US7995752B2 set to expire in September 2020.
 
 ## [Documentation](https://docs.rs/bls12_381)
 

RELEASES.md

@@ -1,3 +1,12 @@
+# 0.1.1
+
+Added `clear_cofactor` methods to `G1Projective` and `G2Projective`. If the crate feature `endo`
+is enabled the G2 cofactor clearing will use the curve endomorphism technique described by
+[Budroni-Pintore](https://ia.cr/2017/419). If the crate feature `endo` is _not_ enabled then
+the code will simulate the effects of the Budroni-Pintore cofactor clearing in order to keep
+the API consistent. In September 2020, when patents US7110538B2 and US7995752B2 expire, the
+endo feature will be made default. However, for now it must be explicitly enabled.
+
 # 0.1.0
 
 Initial release.

src/g2.rs

@@ -805,7 +805,7 @@ impl G2Projective {
         G2Projective::conditional_select(&res, &tmp, (!f1) & (!f2) & (!f3))
     }
 
-    fn multiply(&self, by: &[u8; 32]) -> G2Projective {
+    fn multiply(&self, by: &[u8]) -> G2Projective {
         let mut acc = G2Projective::identity();
 
         // This is a simple double-and-add implementation of point
@@ -827,6 +827,7 @@ impl G2Projective {
         acc
     }
 
+    #[cfg(feature = "endo")]
     fn psi(&self) -> G2Projective {
         // 1 / ((u+1) ^ ((q-1)/3))
         let psi_coeff_x = Fp2 {
@@ -870,6 +871,7 @@ impl G2Projective {
         }
     }
 
+    #[cfg(feature = "endo")]
     fn psi2(&self) -> G2Projective {
         // 1 / 2 ^ ((q-1)/3)
         let psi2_coeff_x = Fp2 {
@@ -895,6 +897,7 @@ impl G2Projective {
     }
 
     /// Multiply `self` by `crate::BLS_X`, using double and add.
+    #[cfg(feature = "endo")]
     fn mul_by_x(&self) -> G2Projective {
         let mut xself = G2Projective::identity();
         // NOTE: in BLS12-381 we can just skip the first bit.
@@ -918,15 +921,36 @@ impl G2Projective {
     /// This is equivalent to multiplying by $h\_\textrm{eff} = 3(z^2 - 1) \cdot
     /// h_2$, where $h_2$ is the cofactor of $\mathbb{G}\_2$ and $z$ is the
     /// parameter of BLS12-381.
+    ///
+    /// The endomorphism is only actually used if the crate feature `endo` is
+    /// enabled, and it is disabled by default to mitigate potential patent
+    /// issues.
     pub fn clear_cofactor(&self) -> G2Projective {
-        let t1 = self.mul_by_x(); // [x] P
-        let t2 = self.psi(); // psi(P)
-
-        self.double().psi2() // psi^2(2P)
-            + (t1 + t2).mul_by_x() // psi^2(2P) + [x^2] P + [x] psi(P)
-            - t1 // psi^2(2P) + [x^2 - x] P + [x] psi(P)
-            - t2 // psi^2(2P) + [x^2 - x] P + [x - 1] psi(P)
-            - self // psi^2(2P) + [x^2 - x - 1] P + [x - 1] psi(P)
+        #[cfg(feature = "endo")]
+        fn clear_cofactor(this: &G2Projective) -> G2Projective {
+            let t1 = this.mul_by_x(); // [x] P
+            let t2 = this.psi(); // psi(P)
+
+            this.double().psi2() // psi^2(2P)
+                + (t1 + t2).mul_by_x() // psi^2(2P) + [x^2] P + [x] psi(P)
+                - t1 // psi^2(2P) + [x^2 - x] P + [x] psi(P)
+                - t2 // psi^2(2P) + [x^2 - x] P + [x - 1] psi(P)
+                - this // psi^2(2P) + [x^2 - x - 1] P + [x - 1] psi(P)
+        }
+
+        #[cfg(not(feature = "endo"))]
+        fn clear_cofactor(this: &G2Projective) -> G2Projective {
+            this.multiply(&[
+                0x51, 0x55, 0xa9, 0xaa, 0x5, 0x0, 0x2, 0xe8, 0xb4, 0xf6, 0xbb, 0xde, 0xa, 0x4c,
+                0x89, 0x59, 0xa3, 0xf6, 0x89, 0x66, 0xc0, 0xcb, 0x54, 0xe9, 0x1a, 0x7c, 0x47, 0xd7,
+                0x69, 0xec, 0xc0, 0x2e, 0xb0, 0x12, 0x12, 0x5d, 0x1, 0xbf, 0x82, 0x6d, 0x95, 0xdb,
+                0x31, 0x87, 0x17, 0x2f, 0x9c, 0x32, 0xe1, 0xff, 0x8, 0x15, 0x3, 0xff, 0x86, 0x99,
+                0x68, 0xd7, 0x5a, 0x14, 0xe9, 0xa8, 0xe2, 0x88, 0x28, 0x35, 0x1b, 0xa9, 0xe, 0x6a,
+                0x4c, 0x58, 0xb3, 0x75, 0xee, 0xf2, 0x8, 0x9f, 0xc6, 0xb,
+            ])
+        }
+
+        clear_cofactor(self)
     }
 
     /// Converts a batch of `G2Projective` elements into `G2Affine` elements. This
@@ -1653,6 +1677,7 @@ fn test_is_torsion_free() {
     assert!(bool::from(G2Affine::generator().is_torsion_free()));
 }
 
+#[cfg(feature = "endo")]
 #[test]
 fn test_mul_by_x() {
     // multiplying by `x` a point in G2 is the same as multiplying by
@@ -1669,6 +1694,7 @@ fn test_mul_by_x() {
     assert_eq!(point.mul_by_x(), point * x);
 }
 
+#[cfg(feature = "endo")]
 #[test]
 fn test_psi() {
     let generator = G2Projective::generator();