tiny-hderive 0.3.0

use secp256k1::{SecretKey, PublicKey};
use base58::FromBase58;
use sha2::Sha512;
use hmac::{Hmac, Mac};
use memzero::Memzero;
use std::ops::Deref;
use std::str::FromStr;
use std::fmt;

use crate::bip44::{ChildNumber, IntoDerivationPath};
use crate::Error;

#[derive(Clone, PartialEq, Eq)]
pub struct Protected(Memzero<[u8; 32]>);

impl<Data: AsRef<[u8]>> From<Data> for Protected {
    fn from(data: Data) -> Protected {
        let mut buf = [0u8; 32];

        buf.copy_from_slice(data.as_ref());

        Protected(Memzero::from(buf))
    }
}

impl Deref for Protected {
    type Target = [u8];

    fn deref(&self) -> &[u8] {
        self.0.as_ref()
    }
}

impl fmt::Debug for Protected {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Protected")
    }
}

#[derive(Clone, PartialEq, Eq, Debug)]
pub struct ExtendedPrivKey {
    secret_key: SecretKey,
    chain_code: Protected,
}

impl ExtendedPrivKey {
    /// Attempts to derive an extended private key from a path.
    pub fn derive<Path>(seed: &[u8], path: Path) -> Result<ExtendedPrivKey, Error>
    where
        Path: IntoDerivationPath,
    {
        let mut hmac: Hmac<Sha512> = Hmac::new_varkey(b"Bitcoin seed").expect("seed is always correct; qed");
        hmac.input(seed);

        let result = hmac.result().code();
        let (secret_key, chain_code) = result.split_at(32);

        let mut sk = ExtendedPrivKey {
            secret_key: SecretKey::parse_slice(secret_key).map_err(Error::Secp256k1)?,
            chain_code: Protected::from(chain_code),
        };

        for child in path.into()?.as_ref() {
            sk = sk.child(*child)?;
        }

        Ok(sk)
    }

    pub fn secret(&self) -> [u8; 32] {
        self.secret_key.serialize()
    }

    pub fn child(&self, child: ChildNumber) -> Result<ExtendedPrivKey, Error> {
        let mut hmac: Hmac<Sha512> = Hmac::new_varkey(&self.chain_code)
            .map_err(|_| Error::InvalidChildNumber)?;

        if child.is_normal() {
            hmac.input(&PublicKey::from_secret_key(&self.secret_key).serialize_compressed()[..]);
        } else {
            hmac.input(&[0]);
            hmac.input(&self.secret_key.serialize()[..]);
        }

        hmac.input(&child.to_bytes());

        let result = hmac.result().code();
        let (secret_key, chain_code) = result.split_at(32);

        let mut secret_key = SecretKey::parse_slice(&secret_key).map_err(Error::Secp256k1)?;
        secret_key.tweak_add_assign(&self.secret_key).map_err(Error::Secp256k1)?;

        Ok(ExtendedPrivKey {
            secret_key,
            chain_code: Protected::from(&chain_code)
        })
    }
}

impl FromStr for ExtendedPrivKey {
    type Err = Error;

    fn from_str(xprv: &str) -> Result<ExtendedPrivKey, Error> {
        let data = xprv.from_base58().map_err(|_| Error::InvalidExtendedPrivKey)?;

        if data.len() != 82 {
            return Err(Error::InvalidExtendedPrivKey);
        }

        Ok(ExtendedPrivKey {
            chain_code: Protected::from(&data[13..45]),
            secret_key: SecretKey::parse_slice(&data[46..78]).map_err(|e| Error::Secp256k1(e))?
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bip39::{Mnemonic, Language, Seed};
    use ethsign::SecretKey;

    #[test]
    fn bip39_to_address() {
        let phrase = "panda eyebrow bullet gorilla call smoke muffin taste mesh discover soft ostrich alcohol speed nation flash devote level hobby quick inner drive ghost inside";

        let expected_secret_key = b"\xff\x1e\x68\xeb\x7b\xf2\xf4\x86\x51\xc4\x7e\xf0\x17\x7e\xb8\x15\x85\x73\x22\x25\x7c\x58\x94\xbb\x4c\xfd\x11\x76\xc9\x98\x93\x14";
        let expected_address: &[u8] = b"\x63\xF9\xA9\x2D\x8D\x61\xb4\x8a\x9f\xFF\x8d\x58\x08\x04\x25\xA3\x01\x2d\x05\xC8";

        let mnemonic = Mnemonic::from_phrase(phrase, Language::English).unwrap();
        let seed = Seed::new(&mnemonic, "");

        let account = ExtendedPrivKey::derive(seed.as_bytes(), "m/44'/60'/0'/0/0").unwrap();

        assert_eq!(expected_secret_key, &account.secret(), "Secret key is invalid");

        let secret_key = SecretKey::from_raw(&account.secret()).unwrap();
        let public_key = secret_key.public();

        assert_eq!(expected_address, public_key.address(), "Address is invalid");

        // Test child method
        let account = ExtendedPrivKey::derive(seed.as_bytes(), "m/44'/60'/0'/0").unwrap().child(ChildNumber::from_str("0").unwrap()).unwrap();

        assert_eq!(expected_secret_key, &account.secret(), "Secret key is invalid");

        let secret_key = SecretKey::from_raw(&account.secret()).unwrap();
        let public_key = secret_key.public();

        assert_eq!(expected_address, public_key.address(), "Address is invalid");
    }
}