theseus/bundled-addons/bchwallet/lib/keys.js

// HD key tree for the wallet. Root = 32 bytes from api.vault.derive treated as
// a BIP32 master seed; account = m/44'/145'/0' (BCH, SLIP-44). Branch 0 is
// receive, branch 1 is change. Private keys never leave this module except
// through sign() / signRecoverable() for a specific entry.
module.exports = function makeKeys({ HDKey, secp256k1, sha256, ripemd160, cashaddr }) {
  const hash160 = (b) => ripemd160(sha256(b));
  const p2pkhScript = (h160) => Uint8Array.from([0x76, 0xa9, 0x14, ...h160, 0x88, 0xac]);
  const p2shScript = (h160) => Uint8Array.from([0xa9, 0x14, ...h160, 0x87]);
  const toHex = (b) => Array.from(b, (x) => x.toString(16).padStart(2, "0")).join("");
  // electrum scripthash: sha256(script), byte-reversed, hex.
  const scripthash = (script) => toHex(sha256(script).slice().reverse());

  class WalletKeys {
    constructor(root32, accountPath, prefix) {
      this.prefix = prefix;
      this.accountPath = accountPath;
      this._account = HDKey.fromMasterSeed(root32).derive(accountPath);
      this._branch = [this._account.deriveChild(0), this._account.deriveChild(1)];
      this._cache = new Map();   // "branch/index" -> entry
    }
    get xpub() { return this._account.publicExtendedKey; }
    // Revealed only on explicit user action in Settings (show recovery info).
    get xprv() { return this._account.privateExtendedKey; }
    entry(branch, index) {
      const k = branch + "/" + index;
      let e = this._cache.get(k);
      if (!e) {
        const node = this._branch[branch].deriveChild(index);
        const h160 = hash160(node.publicKey);
        const script = p2pkhScript(h160);
        e = {
          branch, index, path: this.accountPath + "/" + branch + "/" + index,
          publicKey: node.publicKey, h160, script, scriptHex: toHex(script),
          scripthash: scripthash(script),
          address: cashaddr.encode(this.prefix, 0, h160),
          _node: node,
        };
        this._cache.set(k, e);
      }
      return e;
    }
    findByScriptHex(scriptHex) {
      for (const e of this._cache.values()) if (e.scriptHex === scriptHex) return e;
      return null;
    }
    // ECDSA over a 32-byte digest, DER-encoded, low-S (BCH consensus rule).
    sign(entry, digest32) {
      return secp256k1.sign(digest32, entry._node.privateKey, { prehash: false, lowS: true, format: "der" });
    }
    // 65-byte BIP-137 signature: [27 + recid + 4 (compressed)] || r || s.
    signRecoverable(entry, digest32) {
      const sig = secp256k1.sign(digest32, entry._node.privateKey, { prehash: false, lowS: true, format: "recovered" });
      const out = new Uint8Array(65);
      out[0] = 27 + sig[0] + 4;
      out.set(sig.subarray(1), 1);
      return out;
    }
    wipe() {
      for (const e of this._cache.values()) { try { e._node.wipePrivateData(); } catch {} }
      this._cache.clear();
      for (const b of this._branch) { try { b.wipePrivateData(); } catch {} }
      try { this._account.wipePrivateData(); } catch {}
    }
  }
  return { WalletKeys, hash160, p2pkhScript, p2shScript, scripthash, toHex };
};