Decode multibase value when parsing did:key

Cargo.lock

@@ -446,6 +446,12 @@ dependencies = [
  "alloc-stdlib",
 ]
 
+[[package]]
+name = "bs58"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "771fe0050b883fcc3ea2359b1a96bcfbc090b7116eae7c3c512c7a083fdf23d3"
+
 [[package]]
 name = "bumpalo"
 version = "3.6.1"
@@ -1681,6 +1687,7 @@ dependencies = [
  "ammonia",
  "anyhow",
  "base64",
+ "bs58",
  "chrono",
  "clap",
  "comrak",

Cargo.toml

@@ -21,6 +21,8 @@ ammonia = "3.2.0"
 anyhow = "1.0.58"
 # Used for working with RSA keys, HTTP signatures and file uploads
 base64 = "0.13.0"
+# Used to decode base58btc
+bs58 = "0.4.0"
 # Used for working with dates
 chrono = { version = "0.4.22", features = ["serde"] }
 # Used to build admin CLI tool

src/identity/did_key.rs

@@ -10,7 +10,45 @@ const DID_KEY_RE: &str = r"did:key:(?P<key>z[a-km-zA-HJ-NP-Z1-9]+)";
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct DidKey {
-    pub key: String,
+    pub key: Vec<u8>,
+}
+
+#[derive(thiserror::Error, Debug)]
+enum MultibaseError {
+    #[error("invalid base string")]
+    InvalidBaseString,
+
+    #[error("unknown base")]
+    UnknownBase,
+
+    #[error(transparent)]
+    DecodeError(#[from] bs58::decode::Error),
+}
+
+/// Decodes multibase base58 (bitcoin) value
+/// https://github.com/multiformats/multibase
+fn decode_multibase_base58btc(value: &str)
+    -> Result<Vec<u8>, MultibaseError>
+{
+    let base = value.chars().next()
+        .ok_or(MultibaseError::InvalidBaseString)?;
+    // z == base58btc
+    // https://github.com/multiformats/multibase#multibase-table
+    if base.to_string() != "z" {
+        return Err(MultibaseError::UnknownBase);
+    };
+    let encoded_data = &value[base.len_utf8()..];
+    let data = bs58::decode(encoded_data)
+        .with_alphabet(bs58::Alphabet::BITCOIN)
+        .into_vec()?;
+    Ok(data)
+}
+
+fn encode_multibase_base58btc(value: &[u8]) -> String {
+    let result = bs58::encode(value)
+        .with_alphabet(bs58::Alphabet::BITCOIN)
+        .into_string();
+    format!("z{}", result)
 }
 
 impl FromStr for DidKey {
@@ -19,16 +57,17 @@ impl FromStr for DidKey {
     fn from_str(value: &str) -> Result<Self, Self::Err> {
         let did_key_re = Regex::new(DID_KEY_RE).unwrap();
         let caps = did_key_re.captures(value).ok_or(DidParseError)?;
-        let did_key = Self {
-            key: caps["key"].to_string(),
-        };
+        let key = decode_multibase_base58btc(&caps["key"])
+            .map_err(|_| DidParseError)?;
+        let did_key = Self { key };
         Ok(did_key)
     }
 }
 
 impl fmt::Display for DidKey {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let did_str = format!("did:key:{}", self.key);
+        let encoded_key = encode_multibase_base58btc(&self.key);
+        let did_str = format!("did:key:{}", encoded_key);
         write!(formatter, "{}", did_str)
     }
 }
@@ -41,6 +80,7 @@ mod tests {
     fn test_did_key_string_conversion() {
         let did_str = "did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK";
         let did_key: DidKey = did_str.parse().unwrap();
+        assert_eq!(did_key.key.len(), 34); // Ed25519 public key
         assert_eq!(did_key.to_string(), did_str);
     }
 }