openethereum/ethkey/src/extended.rs

// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

//! Extended keys

use secret::Secret;
use Public;
use bigint::hash::{H256, FixedHash};
pub use self::derivation::Error as DerivationError;

/// Represents label that can be stored as a part of key derivation
pub trait Label {
	/// Length of the data that label occupies
	fn len() -> usize;

	/// Store label data to the key derivation sequence
	/// Must not use more than `len()` bytes from slice
	fn store(&self, target: &mut [u8]);
}

impl Label for u32 {
	fn len() -> usize { 4 }

	fn store(&self, target: &mut [u8]) {
		use byteorder::{BigEndian, ByteOrder};

		BigEndian::write_u32(&mut target[0..4], *self);
	}
}

/// Key derivation over generic label `T`
pub enum Derivation<T: Label> {
	/// Soft key derivation (allow proof of parent)
	Soft(T),
	/// Hard key derivation (does not allow proof of parent)
	Hard(T),
}

impl From<u32> for Derivation<u32> {
	fn from(index: u32) -> Self {
		if index < (2 << 30) {
			Derivation::Soft(index)
		}
		else {
			Derivation::Hard(index)
		}
	}
}

impl Label for H256 {
	fn len() -> usize { 32 }

	fn store(&self, target: &mut [u8]) {
		self.copy_to(&mut target[0..32]);
	}
}

/// Extended secret key, allows deterministic derivation of subsequent keys.
pub struct ExtendedSecret {
	secret: Secret,
	chain_code: H256,
}

impl ExtendedSecret {
	/// New extended key from given secret and chain code.
	pub fn with_code(secret: Secret, chain_code: H256) -> ExtendedSecret {
		ExtendedSecret {
			secret: secret,
			chain_code: chain_code,
		}
	}

	/// New extended key from given secret with the random chain code.
	pub fn new_random(secret: Secret) -> ExtendedSecret {
		ExtendedSecret::with_code(secret, H256::random())
	}

	/// New extended key from given secret.
	/// Chain code will be derived from the secret itself (in a deterministic way).
	pub fn new(secret: Secret) -> ExtendedSecret {
		let chain_code = derivation::chain_code(*secret);
		ExtendedSecret::with_code(secret, chain_code)
	}

	/// Derive new private key
	pub fn derive<T>(&self, index: Derivation<T>) -> ExtendedSecret where T: Label {
		let (derived_key, next_chain_code) = derivation::private(*self.secret, self.chain_code, index);

		let derived_secret = Secret::from_slice(&*derived_key)
			.expect("Derivation always produced a valid private key; qed");

		ExtendedSecret::with_code(derived_secret, next_chain_code)
	}

	/// Private key component of the extended key.
	pub fn secret(&self) -> &Secret {
		&self.secret
	}
}

/// Extended public key, allows deterministic derivation of subsequent keys.
pub struct ExtendedPublic {
	public: Public,
	chain_code: H256,
}

impl ExtendedPublic {
	/// New extended public key from known parent and chain code
	pub fn new(public: Public, chain_code: H256) -> Self {
		ExtendedPublic { public: public, chain_code: chain_code }
	}

	/// Create new extended public key from known secret
	pub fn from_secret(secret: &ExtendedSecret) -> Result<Self, DerivationError> {
		Ok(
			ExtendedPublic::new(
				derivation::point(**secret.secret())?,
				secret.chain_code.clone(),
			)
		)
	}

	/// Derive new public key
	/// Operation is defined only for index belongs [0..2^31)
	pub fn derive<T>(&self, index: Derivation<T>) -> Result<Self, DerivationError> where T: Label {
		let (derived_key, next_chain_code) = derivation::public(self.public, self.chain_code, index)?;
		Ok(ExtendedPublic::new(derived_key, next_chain_code))
	}

	pub fn public(&self) -> &Public {
		&self.public
	}
}

pub struct ExtendedKeyPair {
	secret: ExtendedSecret,
	public: ExtendedPublic,
}

impl ExtendedKeyPair {
	pub fn new(secret: Secret) -> Self {
		let extended_secret = ExtendedSecret::new(secret);
		let extended_public = ExtendedPublic::from_secret(&extended_secret)
			.expect("Valid `Secret` always produces valid public; qed");
		ExtendedKeyPair {
			secret: extended_secret,
			public: extended_public,
		}
	}

	pub fn with_code(secret: Secret, public: Public, chain_code: H256) -> Self {
		ExtendedKeyPair {
			secret: ExtendedSecret::with_code(secret, chain_code.clone()),
			public: ExtendedPublic::new(public, chain_code),
		}
	}

	pub fn with_secret(secret: Secret, chain_code: H256) -> Self {
		let extended_secret = ExtendedSecret::with_code(secret, chain_code);
		let extended_public = ExtendedPublic::from_secret(&extended_secret)
			.expect("Valid `Secret` always produces valid public; qed");
		ExtendedKeyPair {
			secret: extended_secret,
			public: extended_public,
		}
	}

	pub fn with_seed(seed: &[u8]) -> Result<ExtendedKeyPair, DerivationError> {
		let (master_key, chain_code) = derivation::seed_pair(seed);
		Ok(ExtendedKeyPair::with_secret(
			Secret::from_slice(&*master_key).map_err(|_| DerivationError::InvalidSeed)?,
			chain_code,
		))
	}

	pub fn secret(&self) -> &ExtendedSecret {
		&self.secret
	}

	pub fn public(&self) -> &ExtendedPublic {
		&self.public
	}

	pub fn derive<T>(&self, index: Derivation<T>) -> Result<Self, DerivationError> where T: Label {
		let derived = self.secret.derive(index);

		Ok(ExtendedKeyPair {
			public: ExtendedPublic::from_secret(&derived)?,
			secret: derived,
		})
	}
}

// Derivation functions for private and public keys
// Work is based on BIP0032
// https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
mod derivation {

	use rcrypto::hmac::Hmac;
	use rcrypto::mac::Mac;
	use rcrypto::sha2::Sha512;
	use bigint::hash::{H512, H256, FixedHash};
	use bigint::prelude::{U256, U512, Uint};
	use secp256k1;
	use secp256k1::key::{SecretKey, PublicKey};
	use SECP256K1;
	use keccak;
	use super::{Label, Derivation};

	#[derive(Debug)]
	pub enum Error {
		InvalidHardenedUse,
		InvalidPoint,
		MissingIndex,
		InvalidSeed,
	}

	// Deterministic derivation of the key using secp256k1 elliptic curve.
	// Derivation can be either hardened or not.
	// For hardened derivation, pass u32 index at least 2^31 or custom Derivation::Hard(T) enum
	//
	// Can panic if passed `private_key` is not a valid secp256k1 private key
	// (outside of (0..curve_n()]) field
	pub fn private<T>(private_key: H256, chain_code: H256, index: Derivation<T>) -> (H256, H256) where T: Label {
		match index {
			Derivation::Soft(index) => private_soft(private_key, chain_code, index),
			Derivation::Hard(index) => private_hard(private_key, chain_code, index),
		}
	}

	fn hmac_pair(data: &[u8], private_key: H256, chain_code: H256) -> (H256, H256) {
		let private: U256 = private_key.into();

		// produces 512-bit derived hmac (I)
		let mut hmac = Hmac::new(Sha512::new(), &*chain_code);
		let mut i_512 = [0u8; 64];
		hmac.input(&data[..]);
		hmac.raw_result(&mut i_512);

		// left most 256 bits are later added to original private key
		let hmac_key: U256 = H256::from_slice(&i_512[0..32]).into();
		// right most 256 bits are new chain code for later derivations
		let next_chain_code = H256::from(&i_512[32..64]);

		let child_key = private_add(hmac_key, private).into();
		(child_key, next_chain_code)
	}

	// Can panic if passed `private_key` is not a valid secp256k1 private key
	// (outside of (0..curve_n()]) field
	fn private_soft<T>(private_key: H256, chain_code: H256, index: T) -> (H256, H256) where T: Label {
		let mut data = vec![0u8; 33 + T::len()];

		let sec_private = SecretKey::from_slice(&SECP256K1, &*private_key)
			.expect("Caller should provide valid private key");
		let sec_public = PublicKey::from_secret_key(&SECP256K1, &sec_private)
			.expect("Caller should provide valid private key");
		let public_serialized = sec_public.serialize_vec(&SECP256K1, true);

		// curve point (compressed public key) --  index
		//             0.33                    --  33..end
		data[0..33].copy_from_slice(&public_serialized);
		index.store(&mut data[33..]);

		hmac_pair(&data, private_key, chain_code)
	}

	// Deterministic derivation of the key using secp256k1 elliptic curve
	// This is hardened derivation and does not allow to associate
	// corresponding public keys of the original and derived private keys
	fn private_hard<T>(private_key: H256, chain_code: H256, index: T) -> (H256, H256) where T: Label {
		let mut data: Vec<u8> = vec![0u8; 33 + T::len()];
		let private: U256 = private_key.into();

		// 0x00 (padding) -- private_key --  index
		//  0             --    1..33    -- 33..end
		private.to_big_endian(&mut data[1..33]);
		index.store(&mut data[33..(33 + T::len())]);

		hmac_pair(&data, private_key, chain_code)
	}

	fn private_add(k1: U256, k2: U256) -> U256 {
		let sum = U512::from(k1) + U512::from(k2);
		modulo(sum, curve_n())
	}

	// todo: surely can be optimized
	fn modulo(u1: U512, u2: U256) -> U256 {
		let dv = u1 / U512::from(u2);
		let md = u1 - (dv * U512::from(u2));
		md.into()
	}

	// returns n (for mod(n)) for the secp256k1 elliptic curve
	// todo: maybe lazy static
	fn curve_n() -> U256 {
		H256::from_slice(&secp256k1::constants::CURVE_ORDER).into()
	}

	pub fn public<T>(public_key: H512, chain_code: H256, derivation: Derivation<T>) -> Result<(H512, H256), Error> where T: Label {
		let index = match derivation {
			Derivation::Soft(index) => index,
			Derivation::Hard(_) => { return Err(Error::InvalidHardenedUse); }
		};

		let mut public_sec_raw = [0u8; 65];
		public_sec_raw[0] = 4;
		public_sec_raw[1..65].copy_from_slice(&*public_key);
		let public_sec = PublicKey::from_slice(&SECP256K1, &public_sec_raw).map_err(|_| Error::InvalidPoint)?;
		let public_serialized = public_sec.serialize_vec(&SECP256K1, true);

		let mut data = vec![0u8; 33 + T::len()];
		// curve point (compressed public key) --  index
		//             0.33                    --  33..end
		data[0..33].copy_from_slice(&public_serialized);
		index.store(&mut data[33..(33 + T::len())]);

		// HMAC512SHA produces [derived private(256); new chain code(256)]
		let mut hmac = Hmac::new(Sha512::new(), &*chain_code);
		let mut i_512 = [0u8; 64];
		hmac.input(&data[..]);
		hmac.raw_result(&mut i_512);

		let new_private = H256::from(&i_512[0..32]);
		let new_chain_code = H256::from(&i_512[32..64]);

		// Generated private key can (extremely rarely) be out of secp256k1 key field
		if curve_n() <= new_private.clone().into() { return Err(Error::MissingIndex); }
		let new_private_sec = SecretKey::from_slice(&SECP256K1, &*new_private)
			.expect("Private key belongs to the field [0..CURVE_ORDER) (checked above); So initializing can never fail; qed");
		let mut new_public = PublicKey::from_secret_key(&SECP256K1, &new_private_sec)
			.expect("Valid private key produces valid public key");

		// Adding two points on the elliptic curves (combining two public keys)
		new_public.add_assign(&SECP256K1, &public_sec)
			.expect("Addition of two valid points produce valid point");

		let serialized = new_public.serialize_vec(&SECP256K1, false);

		Ok((
			H512::from(&serialized[1..65]),
			new_chain_code,
		))
	}

	fn sha3(slc: &[u8]) -> H256 {
		keccak::Keccak256::keccak256(slc).into()
	}

	pub fn chain_code(secret: H256) -> H256 {
		// 10,000 rounds of sha3
		let mut running_sha3 = sha3(&*secret);
		for _ in 0..99999 { running_sha3 = sha3(&*running_sha3); }
		running_sha3
	}

	pub fn point(secret: H256) -> Result<H512, Error> {
		let sec = SecretKey::from_slice(&SECP256K1, &*secret)
			.map_err(|_| Error::InvalidPoint)?;
		let public_sec = PublicKey::from_secret_key(&SECP256K1, &sec)
			.map_err(|_| Error::InvalidPoint)?;
		let serialized = public_sec.serialize_vec(&SECP256K1, false);
		Ok(H512::from(&serialized[1..65]))
	}

	pub fn seed_pair(seed: &[u8]) -> (H256, H256) {
		let mut hmac = Hmac::new(Sha512::new(), b"Bitcoin seed");
		let mut i_512 = [0u8; 64];
		hmac.input(seed);
		hmac.raw_result(&mut i_512);

		let master_key = H256::from_slice(&i_512[0..32]);
		let chain_code = H256::from_slice(&i_512[32..64]);

		(master_key, chain_code)
	}
}

#[cfg(test)]
mod tests {
	use super::{ExtendedSecret, ExtendedPublic, ExtendedKeyPair};
	use secret::Secret;
	use std::str::FromStr;
	use bigint::hash::{H128, H256};
	use super::{derivation, Derivation};

	fn master_chain_basic() -> (H256, H256) {
		let seed = H128::from_str("000102030405060708090a0b0c0d0e0f")
			.expect("Seed should be valid H128")
			.to_vec();

		derivation::seed_pair(&*seed)
	}

	fn test_extended<F>(f: F, test_private: H256) where F: Fn(ExtendedSecret) -> ExtendedSecret {
		let (private_seed, chain_code) = master_chain_basic();
		let extended_secret = ExtendedSecret::with_code(Secret::from_slice(&*private_seed).unwrap(), chain_code);
		let derived = f(extended_secret);
		assert_eq!(**derived.secret(), test_private);
	}

	#[test]
	fn smoky() {
		let secret = Secret::from_str("a100df7a048e50ed308ea696dc600215098141cb391e9527329df289f9383f65").unwrap();
		let extended_secret = ExtendedSecret::with_code(secret.clone(), 0u64.into());

		// hardened
		assert_eq!(&**extended_secret.secret(), &*secret);
		assert_eq!(&**extended_secret.derive(2147483648.into()).secret(), &"0927453daed47839608e414a3738dfad10aed17c459bbd9ab53f89b026c834b6".into());
		assert_eq!(&**extended_secret.derive(2147483649.into()).secret(), &"44238b6a29c6dcbe9b401364141ba11e2198c289a5fed243a1c11af35c19dc0f".into());

		// normal
		assert_eq!(&**extended_secret.derive(0.into()).secret(), &"bf6a74e3f7b36fc4c96a1e12f31abc817f9f5904f5a8fc27713163d1f0b713f6".into());
		assert_eq!(&**extended_secret.derive(1.into()).secret(), &"bd4fca9eb1f9c201e9448c1eecd66e302d68d4d313ce895b8c134f512205c1bc".into());
		assert_eq!(&**extended_secret.derive(2.into()).secret(), &"86932b542d6cab4d9c65490c7ef502d89ecc0e2a5f4852157649e3251e2a3268".into());

		let extended_public = ExtendedPublic::from_secret(&extended_secret).expect("Extended public should be created");
		let derived_public = extended_public.derive(0.into()).expect("First derivation of public should succeed");
		assert_eq!(&*derived_public.public(), &"f7b3244c96688f92372bfd4def26dc4151529747bab9f188a4ad34e141d47bd66522ff048bc6f19a0a4429b04318b1a8796c000265b4fa200dae5f6dda92dd94".into());

		let keypair = ExtendedKeyPair::with_secret(
			Secret::from_str("a100df7a048e50ed308ea696dc600215098141cb391e9527329df289f9383f65").unwrap(),
			064.into(),
		);
		assert_eq!(&**keypair.derive(2147483648u32.into()).expect("Derivation of keypair should succeed").secret().secret(), &"edef54414c03196557cf73774bc97a645c9a1df2164ed34f0c2a78d1375a930c".into());
	}

	#[test]
	fn h256_soft_match() {
		let secret = Secret::from_str("a100df7a048e50ed308ea696dc600215098141cb391e9527329df289f9383f65").unwrap();
		let derivation_secret = H256::from_str("51eaf04f9dbbc1417dc97e789edd0c37ecda88bac490434e367ea81b71b7b015").unwrap();

		let extended_secret = ExtendedSecret::with_code(secret.clone(), 0u64.into());
		let extended_public = ExtendedPublic::from_secret(&extended_secret).expect("Extended public should be created");

		let derived_secret0 = extended_secret.derive(Derivation::Soft(derivation_secret));
		let derived_public0 = extended_public.derive(Derivation::Soft(derivation_secret)).expect("First derivation of public should succeed");

		let public_from_secret0 = ExtendedPublic::from_secret(&derived_secret0).expect("Extended public should be created");

		assert_eq!(public_from_secret0.public(), derived_public0.public());
	}

	#[test]
	fn h256_hard() {
		let secret = Secret::from_str("a100df7a048e50ed308ea696dc600215098141cb391e9527329df289f9383f65").unwrap();
		let derivation_secret = H256::from_str("51eaf04f9dbbc1417dc97e789edd0c37ecda88bac490434e367ea81b71b7b015").unwrap();
		let extended_secret = ExtendedSecret::with_code(secret.clone(), 1u64.into());

		assert_eq!(&**extended_secret.derive(Derivation::Hard(derivation_secret)).secret(), &"2bc2d696fb744d77ff813b4a1ef0ad64e1e5188b622c54ba917acc5ebc7c5486".into());
	}

	#[test]
	fn match_() {
		let secret = Secret::from_str("a100df7a048e50ed308ea696dc600215098141cb391e9527329df289f9383f65").unwrap();
		let extended_secret = ExtendedSecret::with_code(secret.clone(), 1.into());
		let extended_public = ExtendedPublic::from_secret(&extended_secret).expect("Extended public should be created");

		let derived_secret0 = extended_secret.derive(0.into());
		let derived_public0 = extended_public.derive(0.into()).expect("First derivation of public should succeed");

		let public_from_secret0 = ExtendedPublic::from_secret(&derived_secret0).expect("Extended public should be created");

		assert_eq!(public_from_secret0.public(), derived_public0.public());
	}

	#[test]
	fn test_seeds() {
		let seed = H128::from_str("000102030405060708090a0b0c0d0e0f")
			.expect("Seed should be valid H128")
			.to_vec();

		/// private key from bitcoin test vector
		/// xprv9wTYmMFdV23N2TdNG573QoEsfRrWKQgWeibmLntzniatZvR9BmLnvSxqu53Kw1UmYPxLgboyZQaXwTCg8MSY3H2EU4pWcQDnRnrVA1xe8fs
		let test_private = H256::from_str("e8f32e723decf4051aefac8e2c93c9c5b214313817cdb01a1494b917c8436b35")
			.expect("Private should be decoded ok");

		let (private_seed, _) = derivation::seed_pair(&*seed);

		assert_eq!(private_seed, test_private);
	}

	#[test]
	fn test_vector_1() {
		/// xprv9uHRZZhk6KAJC1avXpDAp4MDc3sQKNxDiPvvkX8Br5ngLNv1TxvUxt4cV1rGL5hj6KCesnDYUhd7oWgT11eZG7XnxHrnYeSvkzY7d2bhkJ7
		/// H(0)
		test_extended(
			|secret| secret.derive(2147483648.into()),
			H256::from_str("edb2e14f9ee77d26dd93b4ecede8d16ed408ce149b6cd80b0715a2d911a0afea")
				.expect("Private should be decoded ok")
		);
	}

	#[test]
	fn test_vector_2() {
		/// xprv9wTYmMFdV23N2TdNG573QoEsfRrWKQgWeibmLntzniatZvR9BmLnvSxqu53Kw1UmYPxLgboyZQaXwTCg8MSY3H2EU4pWcQDnRnrVA1xe8fs
		/// H(0)/1
		test_extended(
			|secret| secret.derive(2147483648.into()).derive(1.into()),
			H256::from_str("3c6cb8d0f6a264c91ea8b5030fadaa8e538b020f0a387421a12de9319dc93368")
				.expect("Private should be decoded ok")
		);
	}
}