Encoding of G1/G2 elements in compressed or uncompressed form.

Cargo.toml

@@ -11,3 +11,4 @@ repository = "https://github.com/ebfull/pairing"
 
 [dependencies]
 rand = "0.3"
+byteorder = "1.1"

src/bls12_381/ec.rs

@@ -4,7 +4,9 @@ macro_rules! curve_impl {
         $affine:ident,
         $prepared:ident,
         $basefield:ident,
-        $scalarfield:ident
+        $scalarfield:ident,
+        $uncompressed:ident,
+        $compressed:ident
     ) => {
         #[derive(Copy, Clone, PartialEq, Eq, Debug)]
         pub struct $affine {
@@ -98,6 +100,8 @@ macro_rules! curve_impl {
             type Base = $basefield;
             type Prepared = $prepared;
             type Projective = $projective;
+            type Uncompressed = $uncompressed;
+            type Compressed = $compressed;
 
             fn zero() -> Self {
                 $affine {
@@ -563,10 +567,190 @@ macro_rules! curve_impl {
 
 pub mod g1 {
     use rand::{Rand, Rng};
-    use super::super::{Fq, Fr, FrRepr};
-    use ::{CurveProjective, CurveAffine, PrimeField, PrimeFieldRepr, Field, BitIterator};
+    use super::super::{Fq, Fr, FrRepr, FqRepr};
+    use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint};
 
-    curve_impl!(G1, G1Affine, G1Prepared, Fq, Fr);
+    curve_impl!(G1, G1Affine, G1Prepared, Fq, Fr, G1Uncompressed, G1Compressed);
+
+    pub struct G1Uncompressed([u8; 96]);
+
+    impl AsRef<[u8]> for G1Uncompressed {
+        fn as_ref(&self) -> &[u8] {
+            &self.0
+        }
+    }
+
+    impl AsMut<[u8]> for G1Uncompressed {
+        fn as_mut(&mut self) -> &mut [u8] {
+            &mut self.0
+        }
+    }
+
+    impl EncodedPoint for G1Uncompressed {
+        type Affine = G1Affine;
+
+        fn empty() -> Self { G1Uncompressed([0; 96]) }
+        fn size() -> usize { 96 }
+        fn into_affine_unchecked(&self) -> Result<G1Affine, ()> {
+            use byteorder::{ReadBytesExt, BigEndian};
+
+            let mut x = FqRepr([0; 6]);
+            let mut y = FqRepr([0; 6]);
+
+            {
+                let mut reader = &self.0[..];
+
+                for b in x.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+
+                for b in y.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+            }
+
+            Ok(G1Affine {
+                x: Fq::from_repr(x)?,
+                y: Fq::from_repr(y)?,
+                infinity: false
+            })
+        }
+        fn from_affine(affine: G1Affine) -> Result<Self, ()> {
+            use byteorder::{WriteBytesExt, BigEndian};
+
+            if affine.is_zero() {
+                return Err(())
+            }
+
+            let mut res = Self::empty();
+
+            {
+                let mut writer = &mut res.0[..];
+
+                for digit in affine.x.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+
+                for digit in affine.y.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+            }
+
+            Ok(res)
+        }
+    }
+
+    pub struct G1Compressed([u8; 48]);
+
+    impl AsRef<[u8]> for G1Compressed {
+        fn as_ref(&self) -> &[u8] {
+            &self.0
+        }
+    }
+
+    impl AsMut<[u8]> for G1Compressed {
+        fn as_mut(&mut self) -> &mut [u8] {
+            &mut self.0
+        }
+    }
+
+    impl EncodedPoint for G1Compressed {
+        type Affine = G1Affine;
+
+        fn empty() -> Self { G1Compressed([0; 48]) }
+        fn size() -> usize { 48 }
+        fn into_affine_unchecked(&self) -> Result<G1Affine, ()> {
+            use byteorder::{ReadBytesExt, BigEndian};
+
+            // Create a copy of this representation.
+            let mut copy = self.0;
+
+            if copy[0] & (1 << 7) == 0 {
+                // Distinguisher bit isn't set.
+                return Err(())
+            }
+
+            // Determine if the intended y coordinate must be greater
+            // lexicographically.
+            let greatest = copy[0] & (1 << 6) != 0;
+
+            // Unset the two most significant bits.
+            copy[0] &= 0x3f;
+
+            let mut x = FqRepr([0; 6]);
+
+            {
+                let mut reader = &copy[..];
+
+                for b in x.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+            }
+
+            // Interpret as Fq element.
+            let x = Fq::from_repr(x)?;
+
+            // Compute x^3 + b
+            let mut x3b = x;
+            x3b.square();
+            x3b.mul_assign(&x);
+            x3b.add_assign(&G1Affine::get_coeff_b());
+
+            // Attempt to compute y
+            match x3b.sqrt() {
+                Some(y) => {
+                    let mut negy = y;
+                    negy.negate();
+
+                    // Get the parity of the sqrt we found.
+                    let parity = y.into_repr() > negy.into_repr();
+
+                    Ok(G1Affine {
+                        x: x,
+                        y: if parity == greatest { y } else { negy },
+                        infinity: false
+                    })
+                },
+                None => {
+                    // Point must not be on the curve.
+                    Err(())
+                }
+            }
+        }
+        fn from_affine(affine: G1Affine) -> Result<Self, ()> {
+            use byteorder::{WriteBytesExt, BigEndian};
+
+            if affine.is_zero() {
+                return Err(())
+            }
+
+            let mut res = Self::empty();
+
+            {
+                let mut writer = &mut res.0[..];
+
+                for digit in affine.x.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+            }
+
+            // Distinguish this from an uncompressed element.
+            res.0[0] |= 1 << 7; // Set highest bit.
+
+            {
+                let mut negy = affine.y;
+                negy.negate();
+
+                // If the correct y coordinate is the largest (lexicographically),
+                // the bit should be set.
+                if affine.y.into_repr() > negy.into_repr() {
+                    res.0[0] |= 1 << 6; // Set second highest bit.
+                }
+            }
+
+            Ok(res)
+        }
+    }
 
     impl G1Affine {
         fn get_generator() -> Self {
@@ -629,9 +813,6 @@ pub mod g1 {
         }
     }
 
-    #[cfg(test)]
-    use super::super::{FqRepr};
-
     #[test]
     fn g1_generator() {
         use ::SqrtField;
@@ -880,10 +1061,226 @@ pub mod g1 {
 
 pub mod g2 {
     use rand::{Rand, Rng};
-    use super::super::{Fq2, Fr, FrRepr};
-    use ::{CurveProjective, CurveAffine, PrimeField, PrimeFieldRepr, Field, BitIterator};
+    use super::super::{Fq2, Fr, Fq, FrRepr, FqRepr};
+    use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint};
 
-    curve_impl!(G2, G2Affine, G2Prepared, Fq2, Fr);
+    curve_impl!(G2, G2Affine, G2Prepared, Fq2, Fr, G2Uncompressed, G2Compressed);
+
+    pub struct G2Uncompressed([u8; 192]);
+
+    impl AsRef<[u8]> for G2Uncompressed {
+        fn as_ref(&self) -> &[u8] {
+            &self.0
+        }
+    }
+
+    impl AsMut<[u8]> for G2Uncompressed {
+        fn as_mut(&mut self) -> &mut [u8] {
+            &mut self.0
+        }
+    }
+
+    impl EncodedPoint for G2Uncompressed {
+        type Affine = G2Affine;
+
+        fn empty() -> Self { G2Uncompressed([0; 192]) }
+        fn size() -> usize { 192 }
+        fn into_affine_unchecked(&self) -> Result<G2Affine, ()> {
+            use byteorder::{ReadBytesExt, BigEndian};
+
+            let mut x_c1 = FqRepr([0; 6]);
+            let mut x_c0 = FqRepr([0; 6]);
+            let mut y_c1 = FqRepr([0; 6]);
+            let mut y_c0 = FqRepr([0; 6]);
+
+            {
+                let mut reader = &self.0[..];
+
+                for b in x_c1.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+
+                for b in x_c0.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+
+                for b in y_c1.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+
+                for b in y_c0.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+            }
+
+            Ok(G2Affine {
+                x: Fq2 {
+                    c0: Fq::from_repr(x_c0)?,
+                    c1: Fq::from_repr(x_c1)?
+                },
+                y: Fq2 {
+                    c0: Fq::from_repr(y_c0)?,
+                    c1: Fq::from_repr(y_c1)?
+                },
+                infinity: false
+            })
+        }
+        fn from_affine(affine: G2Affine) -> Result<Self, ()> {
+            use byteorder::{WriteBytesExt, BigEndian};
+
+            if affine.is_zero() {
+                return Err(())
+            }
+
+            let mut res = Self::empty();
+
+            {
+                let mut writer = &mut res.0[..];
+
+                for digit in affine.x.c1.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+
+                for digit in affine.x.c0.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+
+                for digit in affine.y.c1.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+
+                for digit in affine.y.c0.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+            }
+
+            Ok(res)
+        }
+    }
+
+    pub struct G2Compressed([u8; 96]);
+
+    impl AsRef<[u8]> for G2Compressed {
+        fn as_ref(&self) -> &[u8] {
+            &self.0
+        }
+    }
+
+    impl AsMut<[u8]> for G2Compressed {
+        fn as_mut(&mut self) -> &mut [u8] {
+            &mut self.0
+        }
+    }
+
+    impl EncodedPoint for G2Compressed {
+        type Affine = G2Affine;
+
+        fn empty() -> Self { G2Compressed([0; 96]) }
+        fn size() -> usize { 96 }
+        fn into_affine_unchecked(&self) -> Result<G2Affine, ()> {
+            use byteorder::{ReadBytesExt, BigEndian};
+
+            // Create a copy of this representation.
+            let mut copy = self.0;
+
+            if copy[0] & (1 << 7) == 0 {
+                // Distinguisher bit isn't set.
+                return Err(())
+            }
+
+            // Determine if the intended y coordinate must be greater
+            // lexicographically.
+            let greatest = copy[0] & (1 << 6) != 0;
+
+            // Unset the two most significant bits.
+            copy[0] &= 0x3f;
+
+            let mut x_c1 = FqRepr([0; 6]);
+            let mut x_c0 = FqRepr([0; 6]);
+
+            {
+                let mut reader = &copy[..];
+
+                for b in x_c1.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+
+                for b in x_c0.0.iter_mut().rev() {
+                    *b = reader.read_u64::<BigEndian>().unwrap();
+                }
+            }
+
+            // Interpret as Fq element.
+            let x = Fq2 {
+                c0: Fq::from_repr(x_c0)?,
+                c1: Fq::from_repr(x_c1)?
+            };
+
+            // Compute x^3 + b
+            let mut x3b = x;
+            x3b.square();
+            x3b.mul_assign(&x);
+            x3b.add_assign(&G2Affine::get_coeff_b());
+
+            // Attempt to compute y
+            match x3b.sqrt() {
+                Some(y) => {
+                    let mut negy = y;
+                    negy.negate();
+
+                    // Get the parity of the sqrt we found.
+                    let parity = y > negy;
+
+                    Ok(G2Affine {
+                        x: x,
+                        y: if parity == greatest { y } else { negy },
+                        infinity: false
+                    })
+                },
+                None => {
+                    // Point must not be on the curve.
+                    Err(())
+                }
+            }
+        }
+        fn from_affine(affine: G2Affine) -> Result<Self, ()> {
+            use byteorder::{WriteBytesExt, BigEndian};
+
+            if affine.is_zero() {
+                return Err(())
+            }
+
+            let mut res = Self::empty();
+
+            {
+                let mut writer = &mut res.0[..];
+
+                for digit in affine.x.c1.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+
+                for digit in affine.x.c0.into_repr().as_ref().iter().rev() {
+                    writer.write_u64::<BigEndian>(*digit).unwrap();
+                }
+            }
+
+            // Distinguish this from an uncompressed element.
+            res.0[0] |= 1 << 7; // Set highest bit.
+
+            {
+                let mut negy = affine.y;
+                negy.negate();
+
+                // If the correct y coordinate is the largest (lexicographically),
+                // the bit should be set.
+                if affine.y > negy {
+                    res.0[0] |= 1 << 6; // Set second highest bit.
+                }
+            }
+
+            Ok(res)
+        }
+    }
 
     impl G2Affine {
         fn get_generator() -> Self {
@@ -948,9 +1345,6 @@ pub mod g2 {
         pub(crate) infinity: bool
     }
 
-    #[cfg(test)]
-    use super::super::{Fq, FqRepr};
-
     #[test]
     fn g2_generator() {
         use ::SqrtField;
@@ -965,14 +1359,12 @@ pub mod g2 {
             rhs.add_assign(&G2Affine::get_coeff_b());
 
             if let Some(y) = rhs.sqrt() {
-                let yrepr = y.c1.into_repr();
                 let mut negy = y;
                 negy.negate();
-                let negyrepr = negy.c1.into_repr();
-
+                
                 let p = G2Affine {
                     x: x,
-                    y: if yrepr < negyrepr { y } else { negy },
+                    y: if y < negy { y } else { negy },
                     infinity: false
                 };
 

src/bls12_381/fq2.rs

@@ -1,7 +1,9 @@
 use rand::{Rng, Rand};
-use ::{Field, SqrtField};
+use ::{Field, SqrtField, PrimeField};
 use super::fq::{Fq, FROBENIUS_COEFF_FQ2_C1, NEGATIVE_ONE};
 
+use std::cmp::Ordering;
+
 /// An element of F_{q^2}, represented by c0 + c1 * u.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Fq2 {
@@ -9,6 +11,24 @@ pub struct Fq2 {
     pub c1: Fq
 }
 
+impl Ord for Fq2 {
+    #[inline(always)]
+    fn cmp(&self, other: &Fq2) -> Ordering {
+        match self.c1.into_repr().cmp(&other.c1.into_repr()) {
+            Ordering::Greater => Ordering::Greater,
+            Ordering::Less => Ordering::Less,
+            Ordering::Equal => self.c0.into_repr().cmp(&other.c0.into_repr())
+        }
+    }
+}
+
+impl PartialOrd for Fq2 {
+    #[inline(always)]
+    fn partial_cmp(&self, other: &Fq2) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
 impl Fq2 {
     /// Multiply this element by the cubic and quadratic nonresidue 1 + u.
     pub fn mul_by_nonresidue(&mut self) {
@@ -157,6 +177,30 @@ impl SqrtField for Fq2 {
     }
 }
 
+#[test]
+fn test_fq2_ordering() {
+    let mut a = Fq2 {
+        c0: Fq::zero(),
+        c1: Fq::zero()
+    };
+
+    let mut b = a.clone();
+
+    assert!(a.cmp(&b) == Ordering::Equal);
+    b.c0.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Less);
+    a.c0.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Equal);
+    b.c1.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Less);
+    a.c0.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Less);
+    a.c1.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Greater);
+    b.c0.add_assign(&Fq::one());
+    assert!(a.cmp(&b) == Ordering::Equal);
+}
+
 #[test]
 fn test_fq2_basics() {
     assert_eq!(Fq2 { c0: Fq::zero(), c1: Fq::zero() }, Fq2::zero());

src/bls12_381/mod.rs

@@ -5,11 +5,14 @@ mod fq6;
 mod fq12;
 mod ec;
 
+#[cfg(test)]
+mod tests;
+
 pub use self::fr::{Fr, FrRepr};
 pub use self::fq::{Fq, FqRepr};
 pub use self::fq2::Fq2;
 pub use self::fq12::Fq12;
-pub use self::ec::{G1, G2, G1Affine, G2Affine, G1Prepared, G2Prepared};
+pub use self::ec::{G1, G2, G1Affine, G2Affine, G1Prepared, G2Prepared, G1Uncompressed, G2Uncompressed, G1Compressed, G2Compressed};
 
 use super::{Engine, CurveAffine, Field, BitIterator};
 

src/bls12_381/tests/mod.rs

@@ -0,0 +1,48 @@
+use super::*;
+use ::*;
+
+fn test_vectors<G: CurveProjective, E: EncodedPoint<Affine=G::Affine>>(expected: &[u8])
+{
+    let mut e = G::one();
+
+    let mut v = vec![];
+    {
+        let mut expected = expected;
+        for _ in 0..1000 {
+            let e_affine = e.to_affine();
+            let encoded = E::from_affine(e_affine).unwrap();
+            v.extend_from_slice(encoded.as_ref());
+
+            let mut decoded = E::empty();
+            decoded.as_mut().copy_from_slice(&expected[0..E::size()]);
+            expected = &expected[E::size()..];
+            let decoded = decoded.into_affine().unwrap();
+            assert_eq!(e_affine, decoded);
+
+            e.add_assign(&G::one());
+        }
+    }
+
+    assert_eq!(&v[..], expected);
+}
+
+#[test]
+fn test_g1_uncompressed_vectors() {
+    test_vectors::<G1, G1Uncompressed>(include_bytes!("g1_uncompressed_test_vectors.dat"));
+}
+
+#[test]
+fn test_g1_compressed_vectors() {
+    test_vectors::<G1, G1Compressed>(include_bytes!("g1_compressed_test_vectors.dat"));
+}
+
+#[test]
+fn test_g2_uncompressed_vectors() {
+    test_vectors::<G2, G2Uncompressed>(include_bytes!("g2_uncompressed_test_vectors.dat"));
+}
+
+#[test]
+fn test_g2_compressed_vectors() {
+    test_vectors::<G2, G2Compressed>(include_bytes!("g2_compressed_test_vectors.dat"));
+}
+

src/lib.rs

@@ -5,6 +5,7 @@
 extern crate test;
 
 extern crate rand;
+extern crate byteorder;
 
 #[cfg(test)]
 pub mod tests;
@@ -151,6 +152,8 @@ pub trait CurveAffine: Copy +
     type Base: SqrtField;
     type Projective: CurveProjective<Affine=Self, Scalar=Self::Scalar>;
     type Prepared: Clone + Send + Sync + 'static;
+    type Uncompressed: EncodedPoint<Affine=Self>;
+    type Compressed: EncodedPoint<Affine=Self>;
 
     /// Returns the additive identity.
     fn zero() -> Self;
@@ -176,6 +179,56 @@ pub trait CurveAffine: Copy +
 
     /// Converts this element into its affine representation.
     fn to_projective(&self) -> Self::Projective;
+
+    /// Converts this element into its compressed encoding, so long as it's not
+    /// the point at infinity.
+    fn to_compressed(&self) -> Result<Self::Compressed, ()> {
+        <Self::Compressed as EncodedPoint>::from_affine(*self)
+    }
+
+    /// Converts this element into its uncompressed encoding, so long as it's not
+    /// the point at infinity.
+    fn to_uncompressed(&self) -> Result<Self::Uncompressed, ()> {
+        <Self::Uncompressed as EncodedPoint>::from_affine(*self)
+    }
+}
+
+/// An encoded elliptic curve point, which should essentially wrap a `[u8; N]`.
+pub trait EncodedPoint: Sized +
+                        Send +
+                        Sync +
+                        AsRef<[u8]> +
+                        AsMut<[u8]> +
+                        'static
+{
+    type Affine: CurveAffine;
+
+    /// Creates an empty representation.
+    fn empty() -> Self;
+
+    /// Returns the number of bytes consumed by this representation.
+    fn size() -> usize;
+
+    /// Converts an `EncodedPoint` into a `CurveAffine` element,
+    /// if the point is valid.
+    fn into_affine(&self) -> Result<Self::Affine, ()> {
+        let affine = self.into_affine_unchecked()?;
+
+        if affine.is_valid() {
+            Ok(affine)
+        } else {
+            Err(())
+        }
+    }
+
+    /// Converts an `EncodedPoint` into a `CurveAffine` element,
+    /// without checking if it's a valid point. Caller must be careful
+    /// when using this, as misuse can violate API invariants.
+    fn into_affine_unchecked(&self) -> Result<Self::Affine, ()>;
+
+    /// Creates an `EncodedPoint` from an affine point, as long as the
+    /// point is not the point at infinity.
+    fn from_affine(affine: Self::Affine) -> Result<Self, ()>;
 }
 
 /// This trait represents an element of a field.

src/tests/curve.rs

@@ -1,6 +1,6 @@
 use rand::{SeedableRng, XorShiftRng, Rand};
 
-use ::{CurveProjective, CurveAffine, Field};
+use ::{CurveProjective, CurveAffine, Field, EncodedPoint};
 
 pub fn curve_tests<G: CurveProjective>()
 {
@@ -59,6 +59,7 @@ pub fn curve_tests<G: CurveProjective>()
     random_negation_tests::<G>();
     random_transformation_tests::<G>();
     random_wnaf_tests::<G>();
+    random_encoding_tests::<G::Affine>();
 }
 
 fn random_wnaf_tests<G: CurveProjective>() {
@@ -291,3 +292,29 @@ fn random_transformation_tests<G: CurveProjective>() {
         assert_eq!(v, expected_v);
     }
 }
+
+fn random_encoding_tests<G: CurveAffine>()
+{
+    assert!(G::zero().to_compressed().is_err());
+    assert!(G::zero().to_uncompressed().is_err());
+
+    let mut rng = XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
+
+    for _ in 0..1000 {
+        let mut r = G::Projective::rand(&mut rng).to_affine();
+
+        let uncompressed = r.to_uncompressed().unwrap();
+        let de_uncompressed = uncompressed.into_affine().unwrap();
+        assert_eq!(de_uncompressed, r);
+
+        let compressed = r.to_compressed().unwrap();
+        let de_compressed = compressed.into_affine().unwrap();
+        assert_eq!(de_compressed, r);
+
+        r.negate();
+
+        let compressed = r.to_compressed().unwrap();
+        let de_compressed = compressed.into_affine().unwrap();
+        assert_eq!(de_compressed, r);
+    }
+}