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use super::*;
use hmac::NewMac;
pub const XPRV_DATA_SIZE: usize = 78;
pub const SK_PREFIX: u8 = 0u8;
#[derive(Clone)]
pub struct SecpExtPrivateKey {
depth: u8,
parent_fingerprint: Vec<u8>,
idx: u32,
chain_code: ChainCode,
sk: SecpPrivateKey,
}
impl SecpExtPrivateKey {
pub(crate) fn from_seed(seed: &[u8]) -> Self {
let mut hasher = HmacSha512::new_varkey(SLIP10_SEED_HASH_SALT).unwrap();
hasher.update(seed);
let hash_bytes = hasher.finalize().into_bytes();
let sk_bytes = &hash_bytes[..PRIVATE_KEY_SIZE];
let cc_bytes = &hash_bytes[PRIVATE_KEY_SIZE..];
let depth = 0;
let parent_fingerprint = b"\x00\x00\x00\x00".to_vec();
let idx = 0u32;
let chain_code = ChainCode::from_bytes(cc_bytes).unwrap();
let sk = SecpPrivateKey::from_bytes(sk_bytes)
.expect("We should have implemented that loop in the BIP32 specs");
Self { depth, parent_fingerprint, idx, chain_code, sk }
}
pub(crate) fn cook_new<F: Fn(&mut HmacSha512) -> ()>(&self, idx: u32, recipe: F) -> Self {
let parent = self;
let salt = &parent.chain_code.to_bytes();
let mut hasher = HmacSha512::new_varkey(salt).unwrap();
recipe(&mut hasher);
let hash_bytes = hasher.finalize().into_bytes();
let sk_bytes = &hash_bytes[..PRIVATE_KEY_SIZE];
let cc_bytes = &hash_bytes[PRIVATE_KEY_SIZE..];
let depth = parent.depth + 1;
let parent_pk = parent.neuter().public_key();
let hash = hash160(parent_pk.to_bytes());
let parent_fingerprint = Vec::from(&hash[..4]);
let chain_code = ChainCode::from_bytes(cc_bytes).unwrap();
let sk = (&parent.sk + sk_bytes)
.expect("We should have implemented that loop in the BIP32 specs");
Self { depth, parent_fingerprint, idx, chain_code, sk }
}
pub fn to_xprv(&self, version: &[u8; BIP32_VERSION_PREFIX_SIZE]) -> String {
let mut res = Vec::with_capacity(XPRV_DATA_SIZE);
res.extend_from_slice(version);
res.push(self.depth);
res.extend_from_slice(&self.parent_fingerprint);
res.extend_from_slice(&self.idx.to_be_bytes());
res.extend_from_slice(&self.chain_code.to_bytes());
res.push(SK_PREFIX);
res.extend_from_slice(&self.sk.to_bytes());
to_base58check(res)
}
pub fn from_xprv(xprv: &str, prefix: &[u8; BIP32_VERSION_PREFIX_SIZE]) -> Result<Self> {
let data = from_base58check(xprv)?;
ensure!(data.len() == XPRV_DATA_SIZE, "Length of data must be {}", XPRV_DATA_SIZE);
debug_assert_eq!(BIP32_VERSION_PREFIX_SIZE, 4);
let actual_prefix = &data[0..BIP32_VERSION_PREFIX_SIZE];
ensure!(
actual_prefix == prefix,
"Invalid network prefix found: {}",
hex::encode(actual_prefix)
);
let depth = data[4];
let parent_fingerprint = data[5..9].to_vec();
let idx = {
let mut idx_bytes = [0u8; 4];
idx_bytes.copy_from_slice(&data[9..13]);
u32::from_be_bytes(idx_bytes)
};
let chain_code = {
let chain_code_bytes = &data[13..45];
ChainCode::from_bytes(chain_code_bytes)?
};
ensure!(data[45] == SK_PREFIX, "xprv must have a private key prefixed with {}", SK_PREFIX);
let sk = {
let sk_bytes = &data[46..78];
SecpPrivateKey::from_bytes(sk_bytes)?
};
Ok(Self { depth, parent_fingerprint, idx, chain_code, sk })
}
}
impl ExtendedPrivateKey<Secp256k1> for SecpExtPrivateKey {
fn derive_normal_child(&self, idx: i32) -> Result<SecpExtPrivateKey> {
ensure!(idx >= 0, "Derivation index cannot be negative");
let idx = idx as u32;
let xprv = self.cook_new(idx, |hasher| {
hasher.update(&self.sk.public_key().to_bytes());
hasher.update(&idx.to_be_bytes());
});
Ok(xprv)
}
fn derive_hardened_child(&self, idx: i32) -> Result<SecpExtPrivateKey> {
ensure!(idx >= 0, "Derivation index cannot be negative");
let idx = 0x8000_0000u32 + idx as u32;
let xprv = self.cook_new(idx, |hasher| {
hasher.update(&[SK_PREFIX]);
hasher.update(&self.sk.to_bytes());
hasher.update(&idx.to_be_bytes());
});
Ok(xprv)
}
fn neuter(&self) -> SecpExtPublicKey {
let depth = self.depth;
let parent_fingerprint = self.parent_fingerprint.clone();
let idx = self.idx;
let chain_code = self.chain_code.clone();
let pk = self.sk.public_key();
SecpExtPublicKey { depth, parent_fingerprint, idx, chain_code, pk }
}
fn private_key(&self) -> SecpPrivateKey {
self.sk.clone()
}
}