elliptic-curve: expose AffineCoordinates::y

elliptic-curve/src/dev.rs

@@ -473,6 +473,14 @@ impl AffineCoordinates for AffinePoint {
         unimplemented!();
     }
 
+    fn y(&self) -> FieldBytes {
+        unimplemented!();
+    }
+
+    fn x_is_odd(&self) -> Choice {
+        unimplemented!();
+    }
+
     fn y_is_odd(&self) -> Choice {
         unimplemented!();
     }

elliptic-curve/src/point.rs

@@ -22,12 +22,18 @@ pub type ProjectivePoint<C> = <C as CurveArithmetic>::ProjectivePoint;
 /// Access to the affine coordinates of an elliptic curve point.
 // TODO: use zkcrypto/group#30 coordinate API when available
 pub trait AffineCoordinates {
-    /// Field element representation.
+    /// Field element representation with curve-specific serialization/endianness.
     type FieldRepr: AsRef<[u8]>;
 
     /// Get the affine x-coordinate as a serialized field element.
     fn x(&self) -> Self::FieldRepr;
 
+    /// Get the affine y-coordinate as a serialized field element.
+    fn y(&self) -> Self::FieldRepr;
+
+    /// Is the affine x-coordinate odd?
+    fn x_is_odd(&self) -> Choice;
+
     /// Is the affine y-coordinate odd?
     fn y_is_odd(&self) -> Choice;
 }