Fix Scalar Serde implementation

Author: daxpedda

ed448-goldilocks/src/edwards/scalar.rs

@@ -297,7 +297,7 @@ mod test {
         let res = serde_bare::to_vec(&EdwardsScalar::TWO_INV);
         assert!(res.is_ok());
         let sb = res.unwrap();
-        assert_eq!(sb.len(), 57);
+        assert_eq!(sb.len(), 58);
 
         let res = serde_bare::from_slice::<EdwardsScalar>(&sb);
         assert!(res.is_ok());

ed448-goldilocks/src/field/scalar.rs

@@ -430,7 +430,7 @@ impl<C: CurveWithScalar> serdect::serde::Serialize for Scalar<C> {
     where
         S: serdect::serde::Serializer,
     {
-        serdect::slice::serialize_hex_lower_or_bin(&self.to_bytes(), s)
+        serdect::slice::serialize_hex_lower_or_bin(&self.to_repr(), s)
     }
 }
 
@@ -441,7 +441,7 @@ impl<'de, C: CurveWithScalar> serdect::serde::Deserialize<'de> for Scalar<C> {
         D: serdect::serde::Deserializer<'de>,
     {
         let mut buffer = ScalarBytes::<C>::default();
-        serdect::array::deserialize_hex_or_bin(&mut buffer[..56], d)?;
+        serdect::array::deserialize_hex_or_bin(&mut buffer, d)?;
         Option::from(Self::from_canonical_bytes(&buffer)).ok_or(serdect::serde::de::Error::custom(
             "scalar was not canonically encoded",
         ))

ed448-goldilocks/src/lib.rs

@@ -100,12 +100,12 @@ impl PointCompression for Ed448 {
 
 impl FieldBytesEncoding<Ed448> for U448 {
     fn decode_field_bytes(field_bytes: &Ed448FieldBytes) -> Self {
-        U448::from_le_slice(field_bytes)
+        U448::from_le_slice(&field_bytes[..56])
     }
 
     fn encode_field_bytes(&self) -> Ed448FieldBytes {
         let mut data = Ed448FieldBytes::default();
-        data.copy_from_slice(&self.to_le_byte_array()[..]);
+        data[..56].copy_from_slice(&self.to_le_byte_array());
         data
     }
 }