fix: consistently serialize signer (#334)

- serialize the signer in base58 both as Value and as the signer embedded
in the SignedPod json data field.
- Implement serialization/deserialization for Signature

src/backends/plonky2/primitives/ec/schnorr.rs

@@ -20,16 +20,18 @@ use plonky2::{
     plonk::circuit_builder::CircuitBuilder,
 };
 use rand::rngs::OsRng;
+use serde::{Deserialize, Deserializer, Serialize, Serializer};
 
 use super::curve::Point;
 use crate::{
     backends::plonky2::{
         circuits::common::CircuitBuilderPod,
+        deserialize_bytes,
         primitives::ec::{
             bits::{BigUInt320Target, CircuitBuilderBits},
             curve::{CircuitBuilderElliptic, PointTarget, WitnessWriteCurve, GROUP_ORDER},
         },
-        Error,
+        serialize_bytes, Error,
     },
     middleware::RawValue,
 };
@@ -76,6 +78,28 @@ impl Signature {
     }
 }
 
+impl Serialize for Signature {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let signature_b64 = serialize_bytes(&self.as_bytes());
+        serializer.serialize_str(&signature_b64)
+    }
+}
+
+impl<'de> Deserialize<'de> for Signature {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let signature_b64 = String::deserialize(deserializer)?;
+        let signature_bytes =
+            deserialize_bytes(&signature_b64).map_err(serde::de::Error::custom)?;
+        Signature::from_bytes(&signature_bytes).map_err(serde::de::Error::custom)
+    }
+}
+
 /// Targets for Schnorr signature over ecGFp5.
 #[derive(Clone, Debug)]
 pub struct SignatureTarget {

src/backends/plonky2/signedpod.rs

@@ -7,7 +7,6 @@ use serde::{Deserialize, Serialize};
 
 use crate::{
     backends::plonky2::{
-        deserialize_bytes,
         error::{Error, Result},
         primitives::{
             ec::{
@@ -16,7 +15,6 @@ use crate::{
             },
             merkletree::MerkleTree,
         },
-        serialize_bytes,
     },
     middleware::{
         containers::Dictionary, AnchoredKey, Hash, Key, Params, Pod, PodId, PodSigner, PodType,
@@ -76,8 +74,8 @@ pub struct SignedPod {
 
 #[derive(Serialize, Deserialize)]
 struct Data {
-    signer: String,
+    signer: Point,
-    signature: String,
+    signature: Signature,
     kvs: Dictionary,
 }
 
@@ -93,27 +91,10 @@ fn dummy() -> SignedPod {
 impl SignedPod {
     pub(crate) fn deserialize(id: PodId, data: serde_json::Value) -> Result<Box<dyn Pod>> {
         let data: Data = serde_json::from_value(data)?;
-        let signer_bytes = deserialize_bytes(&data.signer)?;
-        let signature_bytes = deserialize_bytes(&data.signature)?;
-
-        if signer_bytes.len() != 40 {
-            return Err(Error::custom(
-                "Invalid byte encoding of signed POD signer.".to_string(),
-            ));
-        }
-        if signature_bytes.len() != 80 {
-            return Err(Error::custom(
-                "Invalid byte encoding of signed POD signature.".to_string(),
-            ));
-        }
-
-        let signer = Point::from_bytes_into_subgroup(&signer_bytes)?;
-        let signature = Signature::from_bytes(&signature_bytes)?;
-
         Ok(Box::new(Self {
             id,
-            signature,
+            signature: data.signature,
-            signer,
+            signer: data.signer,
             dict: data.kvs,
         }))
     }
@@ -189,16 +170,9 @@ impl Pod for SignedPod {
     }
 
     fn serialize_data(&self) -> serde_json::Value {
-        let signer = serialize_bytes(
-            &self
-                .signer
-                .as_bytes_from_subgroup()
-                .expect("Signer public key must lie in EC subgroup."),
-        );
-        let signature = serialize_bytes(&self.signature.as_bytes());
         serde_json::to_value(Data {
-            signer,
+            signer: self.signer,
-            signature,
+            signature: self.signature.clone(),
             kvs: self.dict.clone(),
         })
         .expect("serialization to json")