code: function zSecretKeyToSpendingKey(a_sk, zcSpendingKeyHash) {
    zcSpendingKeyHash = zcSpendingKeyHash || zconfig.mainnet.zcSpendingKeyHash;
  
    const buf = Buffer.from(zcSpendingKeyHash + a_sk, 'hex');
    return bs58check.encode(buf).toString('hex');
  }
docs: /*
  Converts the secret key to a spending key
  @param {String} a_sk (secret key)
  @param {String} zcSpendingKeyHash (secret key hash,optional)
  @return {Sting} sk (spending key)