Merge

lib/src/lightwallet/extended_key.rs

@@ -0,0 +1,127 @@
+use ring::{
+    digest,
+    hmac::{SigningContext, SigningKey},
+};
+use lazy_static::lazy_static;
+use secp256k1::{PublicKey, Secp256k1, SecretKey, SignOnly, VerifyOnly, Error};
+
+lazy_static! {
+    static ref SECP256K1_SIGN_ONLY: Secp256k1<SignOnly> = Secp256k1::signing_only();
+    static ref SECP256K1_VERIFY_ONLY: Secp256k1<VerifyOnly> = Secp256k1::verification_only();
+}
+/// Random entropy, part of extended key.
+type ChainCode = Vec<u8>;
+
+
+const HARDENED_KEY_START_INDEX: u32 = 2_147_483_648; // 2 ** 31
+
+/// KeyIndex indicates the key type and index of a child key.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum KeyIndex {
+    /// Normal key, index range is from 0 to 2 ** 31 - 1
+    Normal(u32),
+    /// Hardened key, index range is from 2 ** 31 to 2 ** 32 - 1
+    Hardened(u32),
+}
+
+impl KeyIndex {
+    
+    /// Check index range.
+    pub fn is_valid(self) -> bool {
+        match self {
+            KeyIndex::Normal(i) => i < HARDENED_KEY_START_INDEX,
+            KeyIndex::Hardened(i) => i >= HARDENED_KEY_START_INDEX,
+        }
+    }
+
+    /// Generate Hardened KeyIndex from normalize index value.
+    pub fn hardened_from_normalize_index(i: u32) -> Result<KeyIndex, Error> {
+        if i < HARDENED_KEY_START_INDEX {
+            Ok(KeyIndex::Hardened(HARDENED_KEY_START_INDEX + i))
+        } else {
+            Ok(KeyIndex::Hardened(i))
+        }
+    }
+
+    /// Generate KeyIndex from raw index value.
+    pub fn from_index(i: u32) -> Result<Self, Error> {
+        if i < HARDENED_KEY_START_INDEX {
+            Ok(KeyIndex::Normal(i))
+        } else {
+            Ok(KeyIndex::Hardened(i))
+        }
+    }
+}
+
+impl From<u32> for KeyIndex {
+    fn from(index: u32) -> Self {
+        KeyIndex::from_index(index).expect("KeyIndex")
+    }
+}
+
+
+/// ExtendedPrivKey is used for child key derivation.
+/// See [secp256k1 crate documentation](https://docs.rs/secp256k1) for SecretKey signatures usage.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ExtendedPrivKey {
+    pub private_key: SecretKey,
+    pub chain_code: ChainCode,
+}
+
+
+impl ExtendedPrivKey {
+    
+    /// Generate an ExtendedPrivKey from seed
+    pub fn with_seed(seed: &[u8]) -> Result<ExtendedPrivKey, Error> {
+        let signature = {
+            let signing_key = SigningKey::new(&digest::SHA512, b"Bitcoin seed");
+            let mut h = SigningContext::with_key(&signing_key);
+            h.update(&seed);
+            h.sign()
+        };
+        let sig_bytes = signature.as_ref();
+        let (key, chain_code) = sig_bytes.split_at(sig_bytes.len() / 2);
+        let private_key = SecretKey::from_slice(key)?;
+        Ok(ExtendedPrivKey {
+            private_key,
+            chain_code: chain_code.to_vec(),
+        })
+    }
+
+    fn sign_hardended_key(&self, index: u32) -> ring::hmac::Signature {
+        let signing_key = SigningKey::new(&digest::SHA512, &self.chain_code);
+        let mut h = SigningContext::with_key(&signing_key);
+        h.update(&[0x00]);
+        h.update(&self.private_key[..]);
+        h.update(&index.to_be_bytes());
+        h.sign()
+    }
+
+    fn sign_normal_key(&self, index: u32) -> ring::hmac::Signature {
+        let signing_key = SigningKey::new(&digest::SHA512, &self.chain_code);
+        let mut h = SigningContext::with_key(&signing_key);
+        let public_key = PublicKey::from_secret_key(&SECP256K1_SIGN_ONLY, &self.private_key);
+        h.update(&public_key.serialize());
+        h.update(&index.to_be_bytes());
+        h.sign()
+    }
+
+    /// Derive a child key from ExtendedPrivKey.
+    pub fn derive_private_key(&self, key_index: KeyIndex) -> Result<ExtendedPrivKey, Error> {
+        if !key_index.is_valid() {
+            return Err(Error::InvalidTweak);
+        }
+        let signature = match key_index {
+            KeyIndex::Hardened(index) => self.sign_hardended_key(index),
+            KeyIndex::Normal(index) => self.sign_normal_key(index),
+        };
+        let sig_bytes = signature.as_ref();
+        let (key, chain_code) = sig_bytes.split_at(sig_bytes.len() / 2);
+        let mut private_key = SecretKey::from_slice(key)?;
+        private_key.add_assign(&self.private_key[..])?;
+        Ok(ExtendedPrivKey {
+            private_key,
+            chain_code: chain_code.to_vec(),
+        })
+    }
+}