keyfork-derive-util: fixup request API, publicity of ExtendedPrivateKey

keyfork-derive-util/src/extended_key/private_key.rs

@@ -29,6 +29,10 @@ pub enum Error {
     /// The algorithm used mandates hardened derivation only.
     #[error("The algorithm used mandates hardened derivation only")]
     HardenedDerivationRequired,
+
+    /// The given slice was of an inappropriate size to create a Private Key.
+    #[error("The given slice was of an inappropriate size to create a Private Key")]
+    InvalidSliceError(#[from] std::array::TryFromSliceError),
 }
 
 type Result<T, E = Error> = std::result::Result<T, E>;
@@ -41,9 +45,9 @@ type HmacSha512 = Hmac<Sha512>;
 #[derive(Clone, Serialize, Deserialize)]
 pub struct ExtendedPrivateKey<K: PrivateKey + Clone> {
     /// The internal private key data.
-    pub private_key: K,
+    private_key: K,
     depth: u8,
-    pub(crate) chain_code: ChainCode,
+    chain_code: ChainCode,
 }
 
 impl<K: PrivateKey + Clone> std::fmt::Debug for ExtendedPrivateKey<K> {
@@ -88,18 +92,42 @@ where
             .into_bytes();
         let (private_key, chain_code) = hash.split_at(KEY_SIZE / 8);
 
+        Self::new_from_parts(
+            private_key,
+            0,
+            // Checked: chain_code is always the same length, hash is static size
+            chain_code.try_into().expect("Invalid chain code length"),
+        )
+    }
+
+    pub fn new_from_parts(seed: &[u8], depth: u8, chain_code: [u8; 32]) -> Result<Self> {
         Ok(Self {
-            private_key: K::from_bytes(private_key.try_into().expect("Invalid key length")),
-            depth: 0,
-            chain_code: chain_code.try_into().expect("Invalid chain code length"),
+            private_key: K::from_bytes(seed.try_into()?),
+            depth,
+            chain_code,
         })
     }
 
+    /// Returns a reference to the [`PrivateKey`].
+    pub fn private_key(&self) -> &K {
+        &self.private_key
+    }
+
     /// Return a public key for the current [`PrivateKey`].
     pub fn public_key(&self) -> K::PublicKey {
         self.private_key.public_key()
     }
 
+    /// Returns the current depth.
+    pub fn depth(&self) -> u8 {
+        self.depth
+    }
+
+    /// Returns a copy of the current chain code.
+    pub fn chain_code(&self) -> [u8; 32] {
+        self.chain_code
+    }
+
     /// Derive a child using the given [`DerivationPath`].
     ///
     /// # Errors

keyfork-derive-util/src/path.rs

@@ -34,6 +34,14 @@ impl DerivationPath {
     pub fn iter(&self) -> impl Iterator<Item = &DerivationIndex> {
         self.path.iter()
     }
+
+    pub fn len(&self) -> usize {
+        self.path.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.path.is_empty()
+    }
 }
 
 impl std::str::FromStr for DerivationPath {

keyfork-derive-util/src/request.rs

@@ -28,19 +28,19 @@ impl DerivationAlgorithm {
             Self::Ed25519 => {
                 let key = ExtendedPrivateKey::<ed25519_dalek::SigningKey>::new(seed)?;
                 let derived_key = key.derive_path(path)?;
-                Ok(DerivationResponse {
-                    algorithm: self.clone(),
-                    data: PrivateKey::to_bytes(&derived_key.private_key).to_vec(),
-                })
+                Ok(DerivationResponse::with_algo_and_xprv(
+                    self.clone(),
+                    &derived_key,
+                ))
             }
             #[cfg(feature = "secp256k1")]
             Self::Secp256k1 => {
                 let key = ExtendedPrivateKey::<k256::SecretKey>::new(seed)?;
                 let derived_key = key.derive_path(path)?;
-                Ok(DerivationResponse {
-                    algorithm: self.clone(),
-                    data: PrivateKey::to_bytes(&derived_key.private_key).to_vec(),
-                })
+                Ok(DerivationResponse::with_algo_and_xprv(
+                    self.clone(),
+                    &derived_key,
+                ))
             }
             #[allow(unreachable_patterns)]
             _ => Err(DerivationError::Algorithm),
@@ -59,6 +59,10 @@ impl DerivationRequest {
         Self { algorithm, path }
     }
 
+    pub fn path(&self) -> &DerivationPath {
+        &self.path
+    }
+
     pub fn derive_with_mnemonic(&self, mnemonic: &Mnemonic) -> Result<DerivationResponse> {
         self.derive_with_master_seed(mnemonic.seed())
     }
@@ -72,4 +76,20 @@ impl DerivationRequest {
 pub struct DerivationResponse {
     pub algorithm: DerivationAlgorithm,
     pub data: Vec<u8>,
+    pub chain_code: [u8; 32],
+    pub depth: u8,
+}
+
+impl DerivationResponse {
+    pub fn with_algo_and_xprv<T: PrivateKey + Clone>(
+        algorithm: DerivationAlgorithm,
+        xprv: &ExtendedPrivateKey<T>,
+    ) -> Self {
+        Self {
+            algorithm,
+            data: PrivateKey::to_bytes(xprv.private_key()).to_vec(),
+            chain_code: xprv.chain_code(),
+            depth: xprv.depth(),
+        }
+    }
 }

keyfork-derive-util/src/tests.rs

@@ -62,8 +62,8 @@ fn secp256k1() {
     for (seed, chain, chain_code, private_key, public_key) in tests {
         let xkey = ExtendedPrivateKey::<SecretKey>::new(seed).unwrap();
         let derived_key = xkey.derive_path(&chain).unwrap();
-        assert_eq!(derived_key.chain_code, chain_code);
-        assert_eq!(derived_key.private_key.to_bytes().as_slice(), private_key);
+        assert_eq!(derived_key.chain_code(), chain_code);
+        assert_eq!(derived_key.private_key().to_bytes().as_slice(), private_key);
         assert_eq!(derived_key.public_key().to_bytes(), public_key);
         let request = DerivationRequest::new(DerivationAlgorithm::Secp256k1, chain);
         let response = request.derive_with_master_seed(seed.to_vec()).unwrap();
@@ -103,8 +103,8 @@ fn ed25519() {
     for (seed, chain, chain_code, private_key, public_key) in tests {
         let xkey = ExtendedPrivateKey::<SigningKey>::new(seed).unwrap();
         let derived_key = xkey.derive_path(&chain).unwrap();
-        assert_eq!(derived_key.chain_code, chain_code);
-        assert_eq!(PrivateKey::to_bytes(&derived_key.private_key), private_key);
+        assert_eq!(derived_key.chain_code(), chain_code);
+        assert_eq!(PrivateKey::to_bytes(derived_key.private_key()), private_key);
         assert_eq!(PublicKey::to_bytes(&derived_key.public_key()), public_key);
         let request = DerivationRequest::new(DerivationAlgorithm::Ed25519, chain);
         let response = request.derive_with_master_seed(seed.to_vec()).unwrap();