fix SignatureShare and Identifier serialization

frost-core/src/identifier.rs

@@ -17,7 +17,10 @@ use crate::{
 #[derive(Copy, Clone, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(feature = "serde", serde(bound = "C: Ciphersuite"))]
-#[cfg_attr(feature = "serde", serde(transparent))]
+// We use these to add a validation step since zero scalars should cause an
+// error when deserializing.
+#[cfg_attr(feature = "serde", serde(try_from = "SerializableScalar<C>"))]
+#[cfg_attr(feature = "serde", serde(into = "SerializableScalar<C>"))]
 pub struct Identifier<C: Ciphersuite>(SerializableScalar<C>);
 
 impl<C> Identifier<C>
@@ -68,6 +71,28 @@ where
     }
 }
 
+#[cfg(feature = "serde")]
+impl<C> TryFrom<SerializableScalar<C>> for Identifier<C>
+where
+    C: Ciphersuite,
+{
+    type Error = Error<C>;
+
+    fn try_from(s: SerializableScalar<C>) -> Result<Self, Self::Error> {
+        Self::new(s.0)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<C> From<Identifier<C>> for SerializableScalar<C>
+where
+    C: Ciphersuite,
+{
+    fn from(i: Identifier<C>) -> Self {
+        i.0
+    }
+}
+
 impl<C> Eq for Identifier<C> where C: Ciphersuite {}
 
 impl<C> Debug for Identifier<C>

frost-core/src/round2.rs

@@ -13,8 +13,10 @@ use crate::{
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(feature = "serde", serde(bound = "C: Ciphersuite"))]
 #[cfg_attr(feature = "serde", serde(deny_unknown_fields))]
-#[cfg_attr(feature = "serde", serde(transparent))]
 pub struct SignatureShare<C: Ciphersuite> {
+    /// Serialization header
+    #[getter(skip)]
+    pub(crate) header: Header<C>,
     /// This participant's signature over the message.
     pub(crate) share: SerializableScalar<C>,
 }
@@ -27,6 +29,7 @@ where
         scalar: <<<C as Ciphersuite>::Group as Group>::Field as Field>::Scalar,
     ) -> Self {
         Self {
+            header: Header::default(),
             share: SerializableScalar(scalar),
         }
     }
@@ -40,6 +43,7 @@ where
     /// Deserialize [`SignatureShare`] from bytes
     pub fn deserialize(bytes: &[u8]) -> Result<Self, Error<C>> {
         Ok(Self {
+            header: Header::default(),
             share: SerializableScalar::deserialize(bytes)?,
         })
     }