Implement correct `did:key` format

We weren't including the *multicodec* bytes previously.
This is now tested against some test vectors from the spec.

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>

radicle/src/crypto.rs

@@ -131,6 +131,8 @@ pub enum PublicKeyError {
     InvalidLength(usize),
     #[error("invalid multibase string: {0}")]
     Multibase(#[from] multibase::Error),
+    #[error("invalid multicodec prefix, expected {0:?}")]
+    Multicodec([u8; 2]),
     #[error("invalid key: {0}")]
     InvalidKey(#[from] ed25519::Error),
 }
@@ -198,8 +200,21 @@ impl TryFrom<&[u8]> for PublicKey {
 }
 
 impl PublicKey {
+    /// Multicodec key type for Ed25519 keys.
+    pub const MULTICODEC_TYPE: [u8; 2] = [0xED, 0x1];
+
+    /// Encode public key in human-readable format.
+    ///
+    /// We use the format specified by the DID `key` method, which is described as:
+    ///
+    /// `did:key:MULTIBASE(base58-btc, MULTICODEC(public-key-type, raw-public-key-bytes))`
+    ///
     pub fn to_human(&self) -> String {
-        multibase::encode(multibase::Base::Base58Btc, self.0.deref())
+        let mut buf = [0; 2 + ed25519::PublicKey::BYTES];
+        buf[..2].copy_from_slice(&Self::MULTICODEC_TYPE);
+        buf[2..].copy_from_slice(self.0.deref());
+
+        multibase::encode(multibase::Base::Base58Btc, &buf)
     }
 }
 
@@ -208,12 +223,14 @@ impl FromStr for PublicKey {
 
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         let (_, bytes) = multibase::decode(s)?;
-        let array: [u8; 32] = bytes
-            .try_into()
-            .map_err(|v: Vec<u8>| PublicKeyError::InvalidLength(v.len()))?;
-        let key = ed25519::PublicKey::new(array);
 
-        Ok(Self(key))
+        if let Some(bytes) = bytes.strip_prefix(&Self::MULTICODEC_TYPE) {
+            let key = ed25519::PublicKey::from_slice(bytes)?;
+
+            Ok(Self(key))
+        } else {
+            Err(PublicKeyError::Multicodec(Self::MULTICODEC_TYPE))
+        }
     }
 }
 
@@ -246,4 +263,12 @@ mod test {
 
         assert_eq!(input, decoded);
     }
+
+    #[test]
+    fn test_encode_decode() {
+        let input = "z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK";
+        let key = PublicKey::from_str(input).unwrap();
+
+        assert_eq!(key.to_string(), input);
+    }
 }

radicle/src/identity.rs

@@ -117,4 +117,19 @@ mod test {
         let json = serde_json::to_string(&did).unwrap();
         assert_eq!(format!("\"{}\"", did), json);
     }
+
+    #[test]
+    fn test_did_encode_decode() {
+        let input = "did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK";
+        let Did(key) = Did::decode(input).unwrap();
+
+        assert_eq!(Did::from(key).encode(), input);
+    }
+
+    #[test]
+    fn test_did_vectors() {
+        Did::decode("did:key:z6MkiTBz1ymuepAQ4HEHYSF1H8quG5GLVVQR3djdX3mDooWp").unwrap();
+        Did::decode("did:key:z6MkjchhfUsD6mmvni8mCdXHw216Xrm9bQe2mBH1P5RDjVJG").unwrap();
+        Did::decode("did:key:z6MknGc3ocHs3zdPiJbnaaqDi58NGb4pk1Sp9WxWufuXSdxf").unwrap();
+    }
 }

radicle/src/ssh.rs

@@ -53,7 +53,8 @@ pub mod fmt {
 
         #[test]
         fn test_key() {
-            let pk = PublicKey::from_str("zF4VJZgNEeL1niWmKu1NtT1B4ZyGpjACyhs2VEZvtsws5").unwrap();
+            let pk =
+                PublicKey::from_str("z6MktWkM9vcfysWFq1c2aaLjJ6j4PYYg93TLPswR4qtuoAeT").unwrap();
 
             assert_eq!(
                 key(&pk),
@@ -63,8 +64,8 @@ pub mod fmt {
 
         #[test]
         fn test_fingerprint() {
-            let pk = PublicKey::from_str("zF4VJZgNEeL1niWmKu1NtT1B4ZyGpjACyhs2VEZvtsws5").unwrap();
-
+            let pk =
+                PublicKey::from_str("z6MktWkM9vcfysWFq1c2aaLjJ6j4PYYg93TLPswR4qtuoAeT").unwrap();
             assert_eq!(
                 fingerprint(&pk),
                 "SHA256:gE/Ty4fuXzww49lcnNe9/GI0L7xSEQdFp/v9tOjFwB4"
@@ -360,7 +361,7 @@ mod test {
     fn test_agent_encoding_remove() {
         use std::str::FromStr;
 
-        let pk = PublicKey::from_str("zF4VJZgNEeL1niWmKu1NtT1B4ZyGpjACyhs2VEZvtsws5").unwrap();
+        let pk = PublicKey::from_str("z6MktWkM9vcfysWFq1c2aaLjJ6j4PYYg93TLPswR4qtuoAeT").unwrap();
         let expected = [
             0, 0, 0, 56, // Message length
             18, // Message type (remove identity)
@@ -387,7 +388,7 @@ mod test {
     fn test_agent_encoding_sign() {
         use std::str::FromStr;
 
-        let pk = PublicKey::from_str("zF4VJZgNEeL1niWmKu1NtT1B4ZyGpjACyhs2VEZvtsws5").unwrap();
+        let pk = PublicKey::from_str("z6MktWkM9vcfysWFq1c2aaLjJ6j4PYYg93TLPswR4qtuoAeT").unwrap();
         let expected = [
             0, 0, 0, 73, // Message length
             13, // Message type (sign request)