Merge #797: Add musig string and serde support

1d8b862 Add tests for MuSig2 de/serialization (Daniel Roberts)
6100c6d Add serialization and deserialization for relevant MuSig2 types (Daniel Roberts)
c668f8e Fix `musig::ParseError` docs (Daniel Roberts)

Pull request description:

  This addresses #796 to add serialization and deserialization for musig types that make sense to transmit as part of a protocol.

  There might be an argument to also include every type with a `serialize()` but IMHO this change implements serialization for the types that that make the most sense.

  The test vectors come from https://github.com/Ademan/rust-secp256k1/tree/musig-serde-vectors because I wasn't sure if/what the licensing implications are of taking the vectors from bip-0327 (which is BSD licensed). However, they could be trivially dropped in if desired (convert to lowercase first).

  The actual implementations are heavily "borrowed" from the serialization+deserialization of `schnorr::Signature`

ACKs for top commit:
  apoelstra:
    ACK 1d8b862; successfully ran local tests

Tree-SHA512: 85fe69347b73761d1ac3c18a7496d2734d7ca5be9d819e1c0d576bfe183f1be3c1710621beee1df86b1ab78da5437cd798684801d5d1a831806702982a6ff9a3

Author: apoelstra

src/musig.rs

@@ -13,11 +13,11 @@ use std;
 
 use crate::ffi::{self, CPtr};
 use crate::{
-    schnorr, Error, Keypair, Message, PublicKey, Scalar, Secp256k1, SecretKey, Signing,
+    from_hex, schnorr, Error, Keypair, Message, PublicKey, Scalar, Secp256k1, SecretKey, Signing,
     Verification, XOnlyPublicKey,
 };
 
-/// Musig partial signature parsing errors
+/// Musig parsing errors
 #[derive(Debug, Clone, Copy, Eq, PartialEq, PartialOrd, Ord, Hash)]
 pub enum ParseError {
     /// Parse Argument is malformed. This might occur if the point is on the secp order,
@@ -222,6 +222,62 @@ impl CPtr for PartialSignature {
     fn as_mut_c_ptr(&mut self) -> *mut Self::Target { self.as_mut_ptr() }
 }
 
+impl fmt::LowerHex for PartialSignature {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for b in self.serialize() {
+            write!(f, "{:02x}", b)?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Display for PartialSignature {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
+}
+
+impl core::str::FromStr for PartialSignature {
+    type Err = ParseError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut res = [0u8; ffi::MUSIG_PART_SIG_SERIALIZED_LEN];
+        match from_hex(s, &mut res) {
+            Ok(ffi::MUSIG_PART_SIG_SERIALIZED_LEN) => PartialSignature::from_byte_array(&res),
+            _ => Err(ParseError::MalformedArg),
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl serde::Serialize for PartialSignature {
+    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        if s.is_human_readable() {
+            s.collect_str(self)
+        } else {
+            s.serialize_bytes(&self.serialize()[..])
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for PartialSignature {
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        if d.is_human_readable() {
+            d.deserialize_str(super::serde_util::FromStrVisitor::new(
+                "a hex string representing a MuSig2 partial signature",
+            ))
+        } else {
+            d.deserialize_bytes(super::serde_util::BytesVisitor::new(
+                "a raw MuSig2 partial signature",
+                |slice| {
+                    let bytes: &[u8; ffi::MUSIG_PART_SIG_SERIALIZED_LEN] =
+                        slice.try_into().map_err(|_| ParseError::MalformedArg)?;
+
+                    Self::from_byte_array(bytes)
+                },
+            ))
+        }
+    }
+}
+
 impl PartialSignature {
     /// Serialize a PartialSignature as a byte array.
     pub fn serialize(&self) -> [u8; ffi::MUSIG_PART_SIG_SERIALIZED_LEN] {
@@ -635,6 +691,62 @@ impl CPtr for PublicNonce {
     fn as_mut_c_ptr(&mut self) -> *mut Self::Target { self.as_mut_ptr() }
 }
 
+impl fmt::LowerHex for PublicNonce {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for b in self.serialize() {
+            write!(f, "{:02x}", b)?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Display for PublicNonce {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
+}
+
+impl core::str::FromStr for PublicNonce {
+    type Err = ParseError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut res = [0u8; ffi::MUSIG_PUBNONCE_SERIALIZED_LEN];
+        match from_hex(s, &mut res) {
+            Ok(ffi::MUSIG_PUBNONCE_SERIALIZED_LEN) => PublicNonce::from_byte_array(&res),
+            _ => Err(ParseError::MalformedArg),
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl serde::Serialize for PublicNonce {
+    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        if s.is_human_readable() {
+            s.collect_str(self)
+        } else {
+            s.serialize_bytes(&self.serialize()[..])
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for PublicNonce {
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        if d.is_human_readable() {
+            d.deserialize_str(super::serde_util::FromStrVisitor::new(
+                "a hex string representing a MuSig2 public nonce",
+            ))
+        } else {
+            d.deserialize_bytes(super::serde_util::BytesVisitor::new(
+                "a raw MuSig2 public nonce",
+                |slice| {
+                    let bytes: &[u8; ffi::MUSIG_PUBNONCE_SERIALIZED_LEN] =
+                        slice.try_into().map_err(|_| ParseError::MalformedArg)?;
+
+                    Self::from_byte_array(bytes)
+                },
+            ))
+        }
+    }
+}
+
 impl PublicNonce {
     /// Serialize a PublicNonce
     pub fn serialize(&self) -> [u8; ffi::MUSIG_PUBNONCE_SERIALIZED_LEN] {
@@ -696,6 +808,62 @@ impl CPtr for AggregatedNonce {
     fn as_mut_c_ptr(&mut self) -> *mut Self::Target { self.as_mut_ptr() }
 }
 
+impl fmt::LowerHex for AggregatedNonce {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for b in self.serialize() {
+            write!(f, "{:02x}", b)?;
+        }
+        Ok(())
+    }
+}
+
+impl fmt::Display for AggregatedNonce {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self, f) }
+}
+
+impl core::str::FromStr for AggregatedNonce {
+    type Err = ParseError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut res = [0u8; ffi::MUSIG_AGGNONCE_SERIALIZED_LEN];
+        match from_hex(s, &mut res) {
+            Ok(ffi::MUSIG_AGGNONCE_SERIALIZED_LEN) => AggregatedNonce::from_byte_array(&res),
+            _ => Err(ParseError::MalformedArg),
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl serde::Serialize for AggregatedNonce {
+    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
+        if s.is_human_readable() {
+            s.collect_str(self)
+        } else {
+            s.serialize_bytes(&self.serialize()[..])
+        }
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> serde::Deserialize<'de> for AggregatedNonce {
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        if d.is_human_readable() {
+            d.deserialize_str(super::serde_util::FromStrVisitor::new(
+                "a hex string representing a MuSig2 aggregated nonce",
+            ))
+        } else {
+            d.deserialize_bytes(super::serde_util::BytesVisitor::new(
+                "a raw MuSig2 aggregated nonce",
+                |slice| {
+                    let bytes: &[u8; ffi::MUSIG_AGGNONCE_SERIALIZED_LEN] =
+                        slice.try_into().map_err(|_| ParseError::MalformedArg)?;
+
+                    Self::from_byte_array(bytes)
+                },
+            ))
+        }
+    }
+}
+
 impl AggregatedNonce {
     /// Combine received public nonces into a single aggregated nonce
     ///
@@ -1520,4 +1688,21 @@ mod tests {
 
         let _agg_sig = session.partial_sig_agg(&[]);
     }
+
+    #[test]
+    fn de_serialization() {
+        const MUSIG_PUBLIC_NONCE_HEX: &str = "03f4a361abd3d50535be08421dbc73b0a8f595654ae3238afcaf2599f94e25204c036ba174214433e21f5cd0fcb14b038eb40b05b7e7c820dd21aa568fdb0a9de4d7";
+        let pubnonce: PublicNonce = MUSIG_PUBLIC_NONCE_HEX.parse().unwrap();
+
+        assert_eq!(pubnonce.to_string(), MUSIG_PUBLIC_NONCE_HEX);
+
+        const MUSIG_AGGREGATED_NONCE_HEX: &str = "0218c30fe0f567a4a9c05eb4835e2735419cf30f834c9ce2fe3430f021ba4eacd503112e97bcf6a022d236d71a9357824a2b19515f980131b3970b087cadf94cc4a7";
+        let aggregated_nonce: AggregatedNonce = MUSIG_AGGREGATED_NONCE_HEX.parse().unwrap();
+        assert_eq!(aggregated_nonce.to_string(), MUSIG_AGGREGATED_NONCE_HEX);
+
+        const MUSIG_PARTIAL_SIGNATURE_HEX: &str =
+            "289eeb2f5efc314aa6d87bf58125043c96d15a007db4b6aaaac7d18086f49a99";
+        let partial_signature: PartialSignature = MUSIG_PARTIAL_SIGNATURE_HEX.parse().unwrap();
+        assert_eq!(partial_signature.to_string(), MUSIG_PARTIAL_SIGNATURE_HEX);
+    }
 }

tests/serde.rs

@@ -4,9 +4,9 @@ extern crate bincode;
 extern crate secp256k1;
 extern crate serde_cbor;
 
+use secp256k1::{musig, PublicKey, SecretKey, XOnlyPublicKey};
 #[cfg(feature = "global-context")]
 use secp256k1::{Keypair, Secp256k1};
-use secp256k1::{PublicKey, SecretKey, XOnlyPublicKey};
 
 // Arbitrary key data.
 
@@ -35,6 +35,43 @@ static XONLY_PK_BYTES: [u8; 32] = [
     0x4a, 0xc8, 0x87, 0xfe, 0x91, 0xdd, 0xd1, 0x66,
 ];
 
+#[rustfmt::skip]
+static MUSIG_PUBLIC_NONCE_BYTES: [u8; 74] = [
+    0x42, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x03, 0xf4, 0xa3, 0x61, 0xab, 0xd3, 0xd5, 0x05,
+    0x35, 0xbe, 0x08, 0x42, 0x1d, 0xbc, 0x73, 0xb0,
+    0xa8, 0xf5, 0x95, 0x65, 0x4a, 0xe3, 0x23, 0x8a,
+    0xfc, 0xaf, 0x25, 0x99, 0xf9, 0x4e, 0x25, 0x20,
+    0x4c, 0x03, 0x6b, 0xa1, 0x74, 0x21, 0x44, 0x33,
+    0xe2, 0x1f, 0x5c, 0xd0, 0xfc, 0xb1, 0x4b, 0x03,
+    0x8e, 0xb4, 0x0b, 0x05, 0xb7, 0xe7, 0xc8, 0x20,
+    0xdd, 0x21, 0xaa, 0x56, 0x8f, 0xdb, 0x0a, 0x9d,
+    0xe4, 0xd7,
+];
+
+#[rustfmt::skip]
+static MUSIG_AGGREGATED_NONCE_BYTES: [u8; 74] = [
+    0x42, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x02, 0x18, 0xc3, 0x0f, 0xe0, 0xf5, 0x67, 0xa4,
+    0xa9, 0xc0, 0x5e, 0xb4, 0x83, 0x5e, 0x27, 0x35,
+    0x41, 0x9c, 0xf3, 0x0f, 0x83, 0x4c, 0x9c, 0xe2,
+    0xfe, 0x34, 0x30, 0xf0, 0x21, 0xba, 0x4e, 0xac,
+    0xd5, 0x03, 0x11, 0x2e, 0x97, 0xbc, 0xf6, 0xa0,
+    0x22, 0xd2, 0x36, 0xd7, 0x1a, 0x93, 0x57, 0x82,
+    0x4a, 0x2b, 0x19, 0x51, 0x5f, 0x98, 0x01, 0x31,
+    0xb3, 0x97, 0x0b, 0x08, 0x7c, 0xad, 0xf9, 0x4c,
+    0xc4, 0xa7,
+];
+
+#[rustfmt::skip]
+static MUSIG_PARTIAL_SIG_BYTES: [u8; 40] = [
+    0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x28, 0x9e, 0xeb, 0x2f, 0x5e, 0xfc, 0x31, 0x4a,
+    0xa6, 0xd8, 0x7b, 0xf5, 0x81, 0x25, 0x04, 0x3c,
+    0x96, 0xd1, 0x5a, 0x00, 0x7d, 0xb4, 0xb6, 0xaa,
+    0xaa, 0xc7, 0xd1, 0x80, 0x86, 0xf4, 0x9a, 0x99,
+];
+
 fn secret_key() -> SecretKey {
     SecretKey::from_slice(&SK_BYTES).expect("failed to create sk from slice")
 }
@@ -85,3 +122,23 @@ fn cbor() {
     // It also adds a 1-byte length prefix and a byte of metadata for the whole vector.
     assert_eq!(e.len(), 54);
 }
+
+#[test]
+fn musig() {
+    let public_nonce: musig::PublicNonce = bincode::deserialize(&MUSIG_PUBLIC_NONCE_BYTES).unwrap();
+    let ser = bincode::serialize(&public_nonce).unwrap();
+
+    assert_eq!(ser, MUSIG_PUBLIC_NONCE_BYTES);
+
+    let aggregated_nonce: musig::AggregatedNonce =
+        bincode::deserialize(&MUSIG_AGGREGATED_NONCE_BYTES).unwrap();
+    let ser = bincode::serialize(&aggregated_nonce).unwrap();
+
+    assert_eq!(ser, MUSIG_AGGREGATED_NONCE_BYTES);
+
+    let partial_sig: musig::PartialSignature =
+        bincode::deserialize(&MUSIG_PARTIAL_SIG_BYTES).unwrap();
+    let ser = bincode::serialize(&partial_sig).unwrap();
+
+    assert_eq!(ser, MUSIG_PARTIAL_SIG_BYTES);
+}