Customizable serialization for SWCurveConfig and TECurveConfig (#467)

Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>

Author: alexander-zw

CHANGELOG.md

@@ -144,6 +144,8 @@
 - [\#430](https://github.com/arkworks-rs/algebra/pull/430) (`ark-ec`) Add functionality for mapping a field element to a curve element for hash-to-curve.
 - [\#440](https://github.com/arkworks-rs/algebra/pull/440) (`ark-ff`) Add a method to construct a field element from an element of the underlying base prime field.
 - [\#446](https://github.com/arkworks-rs/algebra/pull/446) (`ark-ff`) Add `CyclotomicMultSubgroup` trait and impl for extension fields
+- [\#467](https://github.com/arkworks-rs/algebra/pull/467) (`ark-ec`)
+    - Move implementation of `serialize_with_mode()`, `deserialize_with_mode()`, and `serialized_size()` into `{SW,TE}CurveConfig` to allow customization.
 
 ### Improvements
 

ec/src/models/short_weierstrass/affine.rs

@@ -1,6 +1,5 @@
 use ark_serialize::{
-    CanonicalDeserialize, CanonicalDeserializeWithFlags, CanonicalSerialize,
-    CanonicalSerializeWithFlags, Compress, SerializationError, Valid, Validate,
+    CanonicalDeserialize, CanonicalSerialize, Compress, SerializationError, Valid, Validate,
 };
 use ark_std::{
     borrow::Borrow,
@@ -125,7 +124,7 @@ impl<P: SWCurveConfig> Affine<P> {
     ///
     /// The results are sorted by lexicographical order.
     /// This means that, if `P::BaseField: PrimeField`, the results are sorted as integers.
-    fn get_ys_from_x_unchecked(x: P::BaseField) -> Option<(P::BaseField, P::BaseField)> {
+    pub fn get_ys_from_x_unchecked(x: P::BaseField) -> Option<(P::BaseField, P::BaseField)> {
         // Compute the curve equation x^3 + Ax + B.
         // Since Rust does not optimise away additions with zero, we explicitly check
         // for that case here, and avoid multiplication by `a` if possible.
@@ -186,6 +185,7 @@ impl<P: SWCurveConfig> Zeroize for Affine<P> {
 }
 
 impl<P: SWCurveConfig> Distribution<Affine<P>> for Standard {
+    /// Generates a uniformly random instance of the curve.
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Affine<P> {
         loop {
@@ -344,38 +344,18 @@ impl<P: SWCurveConfig> From<Projective<P>> for Affine<P> {
 }
 
 impl<P: SWCurveConfig> CanonicalSerialize for Affine<P> {
-    #[allow(unused_qualifications)]
     #[inline]
     fn serialize_with_mode<W: Write>(
         &self,
-        mut writer: W,
+        writer: W,
         compress: ark_serialize::Compress,
     ) -> Result<(), SerializationError> {
-        let (x, y, flags) = match self.infinity {
-            true => (
-                P::BaseField::zero(),
-                P::BaseField::zero(),
-                SWFlags::infinity(),
-            ),
-            false => (self.x, self.y, self.to_flags()),
-        };
-
-        match compress {
-            Compress::Yes => x.serialize_with_flags(writer, flags),
-            Compress::No => {
-                x.serialize_with_mode(&mut writer, compress)?;
-                y.serialize_with_flags(&mut writer, flags)
-            },
-        }
+        P::serialize_with_mode(self, writer, compress)
     }
 
     #[inline]
     fn serialized_size(&self, compress: Compress) -> usize {
-        let zero = P::BaseField::zero();
-        match compress {
-            Compress::Yes => zero.serialized_size_with_flags::<SWFlags>(),
-            Compress::No => zero.compressed_size() + zero.serialized_size_with_flags::<SWFlags>(),
-        }
+        P::serialized_size(compress)
     }
 }
 
@@ -390,47 +370,12 @@ impl<P: SWCurveConfig> Valid for Affine<P> {
 }
 
 impl<P: SWCurveConfig> CanonicalDeserialize for Affine<P> {
-    #[allow(unused_qualifications)]
     fn deserialize_with_mode<R: Read>(
-        mut reader: R,
+        reader: R,
         compress: Compress,
         validate: Validate,
     ) -> Result<Self, SerializationError> {
-        let (x, y, flags) = match compress {
-            Compress::Yes => {
-                let (x, flags): (_, SWFlags) =
-                    CanonicalDeserializeWithFlags::deserialize_with_flags(reader)?;
-                match flags {
-                    SWFlags::PointAtInfinity => (Self::identity().x, Self::identity().y, flags),
-                    _ => {
-                        let is_positive = flags.is_positive().unwrap();
-                        let (y, neg_y) = Self::get_ys_from_x_unchecked(x)
-                            .ok_or(SerializationError::InvalidData)?;
-                        if is_positive {
-                            (x, y, flags)
-                        } else {
-                            (x, neg_y, flags)
-                        }
-                    },
-                }
-            },
-            Compress::No => {
-                let x: P::BaseField =
-                    CanonicalDeserialize::deserialize_with_mode(&mut reader, compress, validate)?;
-                let (y, flags): (_, SWFlags) =
-                    CanonicalDeserializeWithFlags::deserialize_with_flags(&mut reader)?;
-                (x, y, flags)
-            },
-        };
-        if flags.is_infinity() {
-            Ok(Self::identity())
-        } else {
-            let point = Self::new_unchecked(x, y);
-            if let Validate::Yes = validate {
-                point.check()?;
-            }
-            Ok(point)
-        }
+        P::deserialize_with_mode(reader, compress, validate)
     }
 }
 

ec/src/models/short_weierstrass/group.rs

@@ -96,6 +96,7 @@ impl<P: SWCurveConfig> Hash for Projective<P> {
 }
 
 impl<P: SWCurveConfig> Distribution<Projective<P>> for Standard {
+    /// Generates a uniformly random instance of the curve.
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Projective<P> {
         loop {
@@ -504,21 +505,19 @@ impl<P: SWCurveConfig> From<Affine<P>> for Projective<P> {
 }
 
 impl<P: SWCurveConfig> CanonicalSerialize for Projective<P> {
-    #[allow(unused_qualifications)]
     #[inline]
     fn serialize_with_mode<W: Write>(
         &self,
         writer: W,
         compress: Compress,
     ) -> Result<(), SerializationError> {
         let aff = Affine::<P>::from(*self);
-        aff.serialize_with_mode(writer, compress)
+        P::serialize_with_mode(&aff, writer, compress)
     }
 
     #[inline]
     fn serialized_size(&self, compress: Compress) -> usize {
-        let aff = Affine::<P>::from(*self);
-        aff.serialized_size(compress)
+        P::serialized_size(compress)
     }
 }
 
@@ -540,13 +539,12 @@ impl<P: SWCurveConfig> Valid for Projective<P> {
 }
 
 impl<P: SWCurveConfig> CanonicalDeserialize for Projective<P> {
-    #[allow(unused_qualifications)]
     fn deserialize_with_mode<R: Read>(
         reader: R,
         compress: Compress,
         validate: Validate,
     ) -> Result<Self, SerializationError> {
-        let aff = Affine::<P>::deserialize_with_mode(reader, compress, validate)?;
+        let aff = P::deserialize_with_mode(reader, compress, validate)?;
         Ok(aff.into())
     }
 }

ec/src/models/short_weierstrass/mod.rs

@@ -1,3 +1,9 @@
+use ark_serialize::{
+    CanonicalDeserialize, CanonicalDeserializeWithFlags, CanonicalSerialize,
+    CanonicalSerializeWithFlags, Compress, SerializationError, Valid, Validate,
+};
+use ark_std::io::{Read, Write};
+
 use ark_ff::fields::Field;
 
 use crate::{AffineRepr, Group};
@@ -98,4 +104,87 @@ pub trait SWCurveConfig: super::CurveConfig {
 
         res
     }
+
+    /// If uncompressed, serializes both x and y coordinates as well as a bit for whether it is
+    /// infinity. If compressed, serializes x coordinate with two bits to encode whether y is
+    /// positive, negative, or infinity.
+    #[inline]
+    fn serialize_with_mode<W: Write>(
+        item: &Affine<Self>,
+        mut writer: W,
+        compress: ark_serialize::Compress,
+    ) -> Result<(), SerializationError> {
+        let (x, y, flags) = match item.infinity {
+            true => (
+                Self::BaseField::zero(),
+                Self::BaseField::zero(),
+                SWFlags::infinity(),
+            ),
+            false => (item.x, item.y, item.to_flags()),
+        };
+
+        match compress {
+            Compress::Yes => x.serialize_with_flags(writer, flags),
+            Compress::No => {
+                x.serialize_with_mode(&mut writer, compress)?;
+                y.serialize_with_flags(&mut writer, flags)
+            },
+        }
+    }
+
+    /// If `validate` is `Yes`, calls `check()` to make sure the element is valid.
+    fn deserialize_with_mode<R: Read>(
+        mut reader: R,
+        compress: Compress,
+        validate: Validate,
+    ) -> Result<Affine<Self>, SerializationError> {
+        let (x, y, flags) = match compress {
+            Compress::Yes => {
+                let (x, flags): (_, SWFlags) =
+                    CanonicalDeserializeWithFlags::deserialize_with_flags(reader)?;
+                match flags {
+                    SWFlags::PointAtInfinity => (
+                        Affine::<Self>::identity().x,
+                        Affine::<Self>::identity().y,
+                        flags,
+                    ),
+                    _ => {
+                        let is_positive = flags.is_positive().unwrap();
+                        let (y, neg_y) = Affine::<Self>::get_ys_from_x_unchecked(x)
+                            .ok_or(SerializationError::InvalidData)?;
+                        if is_positive {
+                            (x, y, flags)
+                        } else {
+                            (x, neg_y, flags)
+                        }
+                    },
+                }
+            },
+            Compress::No => {
+                let x: Self::BaseField =
+                    CanonicalDeserialize::deserialize_with_mode(&mut reader, compress, validate)?;
+                let (y, flags): (_, SWFlags) =
+                    CanonicalDeserializeWithFlags::deserialize_with_flags(&mut reader)?;
+                (x, y, flags)
+            },
+        };
+        if flags.is_infinity() {
+            Ok(Affine::<Self>::identity())
+        } else {
+            let point = Affine::<Self>::new_unchecked(x, y);
+            if let Validate::Yes = validate {
+                point.check()?;
+            }
+            Ok(point)
+        }
+    }
+
+    #[inline]
+    fn serialized_size(compress: Compress) -> usize {
+        let zero = Self::BaseField::zero();
+        match compress {
+            Compress::Yes => zero.serialized_size_with_flags::<SWFlags>(),
+            Compress::No => zero.compressed_size() + zero.serialized_size_with_flags::<SWFlags>(),
+        }
+    }
 }

ec/src/models/twisted_edwards/affine.rs

@@ -1,6 +1,5 @@
 use ark_serialize::{
-    CanonicalDeserialize, CanonicalDeserializeWithFlags, CanonicalSerialize,
-    CanonicalSerializeWithFlags, Compress, SerializationError, Valid, Validate,
+    CanonicalDeserialize, CanonicalSerialize, Compress, SerializationError, Valid, Validate,
 };
 use ark_std::{
     borrow::Borrow,
@@ -260,6 +259,7 @@ impl<P: TECurveConfig> Default for Affine<P> {
 }
 
 impl<P: TECurveConfig> Distribution<Affine<P>> for Standard {
+    /// Generates a uniformly random instance of the curve.
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Affine<P> {
         loop {
@@ -301,30 +301,18 @@ impl<P: TECurveConfig> From<Projective<P>> for Affine<P> {
     }
 }
 impl<P: TECurveConfig> CanonicalSerialize for Affine<P> {
-    #[allow(unused_qualifications)]
     #[inline]
     fn serialize_with_mode<W: Write>(
         &self,
-        mut writer: W,
+        writer: W,
         compress: ark_serialize::Compress,
     ) -> Result<(), SerializationError> {
-        let flags = TEFlags::from_x_coordinate(self.x);
-        match compress {
-            Compress::Yes => self.y.serialize_with_flags(writer, flags),
-            Compress::No => {
-                self.x.serialize_uncompressed(&mut writer)?;
-                self.y.serialize_uncompressed(&mut writer)
-            },
-        }
+        P::serialize_with_mode(self, writer, compress)
     }
 
     #[inline]
     fn serialized_size(&self, compress: Compress) -> usize {
-        let zero = P::BaseField::zero();
-        match compress {
-            Compress::Yes => zero.serialized_size_with_flags::<TEFlags>(),
-            Compress::No => self.x.uncompressed_size() + self.y.uncompressed_size(),
-        }
+        P::serialized_size(compress)
     }
 }
 
@@ -339,35 +327,12 @@ impl<P: TECurveConfig> Valid for Affine<P> {
 }
 
 impl<P: TECurveConfig> CanonicalDeserialize for Affine<P> {
-    #[allow(unused_qualifications)]
     fn deserialize_with_mode<R: Read>(
-        mut reader: R,
+        reader: R,
         compress: Compress,
         validate: Validate,
     ) -> Result<Self, SerializationError> {
-        let (x, y) = match compress {
-            Compress::Yes => {
-                let (y, flags): (_, TEFlags) =
-                    CanonicalDeserializeWithFlags::deserialize_with_flags(reader)?;
-                let (x, neg_x) =
-                    Self::get_xs_from_y_unchecked(y).ok_or(SerializationError::InvalidData)?;
-                if flags.is_negative() {
-                    (neg_x, y)
-                } else {
-                    (x, y)
-                }
-            },
-            Compress::No => {
-                let x: P::BaseField = CanonicalDeserialize::deserialize_uncompressed(&mut reader)?;
-                let y: P::BaseField = CanonicalDeserialize::deserialize_uncompressed(&mut reader)?;
-                (x, y)
-            },
-        };
-        let point = Self::new_unchecked(x, y);
-        if let Validate::Yes = validate {
-            point.check()?;
-        }
-        Ok(point)
+        P::deserialize_with_mode(reader, compress, validate)
     }
 }
 

ec/src/models/twisted_edwards/group.rs

@@ -82,6 +82,7 @@ impl<P: TECurveConfig> Hash for Projective<P> {
 }
 
 impl<P: TECurveConfig> Distribution<Projective<P>> for Standard {
+    /// Generates a uniformly random instance of the curve.
     #[inline]
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Projective<P> {
         loop {
@@ -430,13 +431,12 @@ impl<P: TECurveConfig> CanonicalSerialize for Projective<P> {
         compress: Compress,
     ) -> Result<(), SerializationError> {
         let aff = Affine::<P>::from(*self);
-        aff.serialize_with_mode(writer, compress)
+        P::serialize_with_mode(&aff, writer, compress)
     }
 
     #[inline]
     fn serialized_size(&self, compress: Compress) -> usize {
-        let aff = Affine::<P>::from(*self);
-        aff.serialized_size(compress)
+        P::serialized_size(compress)
     }
 }
 
@@ -464,7 +464,7 @@ impl<P: TECurveConfig> CanonicalDeserialize for Projective<P> {
         compress: Compress,
         validate: Validate,
     ) -> Result<Self, SerializationError> {
-        let aff = Affine::<P>::deserialize_with_mode(reader, compress, validate)?;
+        let aff = P::deserialize_with_mode(reader, compress, validate)?;
         Ok(aff.into())
     }
 }