pycoin学习笔记(6) 对交易签名的源码简析(PayToAddressScript)

（个人学习用，可能理解上存在谬误）

上篇中，签名的步骤如下，

solver = build_hash160_lookup([exponent])
signed_new_tx = unsigned_new_tx.sign(solver)

对于pycoin是如何完成交易签名的，很有必要从其源码中进行研究

    def sign(self, hash160_lookup, hash_type=None, **kwargs):
        """
        Sign a standard transaction.
        hash160_lookup:
            A dictionary (or another object with .get) where keys are hash160 and
            values are tuples (secret exponent, public_pair, is_compressed) or None
            (in which case the script will obviously not be signed).
        """
        if hash_type is None:
            hash_type = self.SIGHASH_ALL #1
        self.check_unspents() #2
        for idx, tx_in in enumerate(self.txs_in):
            if self.is_signature_ok(idx) or tx_in.is_coinbase():
                continue
            try:
                if self.unspents[idx]:
                    self.sign_tx_in(
                        hash160_lookup, idx, self.unspents[idx].script, hash_type=hash_type, **kwargs)#3
            except SolvingError:
                pass

        return self

大致流程：

1）先检查是否交易输入都有其对应的锁定脚本（#2处）

2）逐个对未签名过的交易输入进行签名操作（#3处)

#1处，将hash_type默认设为SIGHASH_ALL,这也是目前最主流的方式，具体细节可自行搜索

继续进入sign_tx_in方法：

    def sign_tx_in(self, hash160_lookup, tx_in_idx, tx_out_script, hash_type=None, **kwargs):
        if hash_type is None:
            hash_type = self.SIGHASH_ALL
        r = self.solve(hash160_lookup, tx_in_idx, tx_out_script,
                       hash_type=hash_type, **kwargs) #1
        if isinstance(r, bytes):
            self.txs_in[tx_in_idx].script = r #2
        else:
            self.txs_in[tx_in_idx].script = r[0] #3
            self.set_witness(tx_in_idx, r[1])

在#1处调用solve进行签名，返回解锁脚本。然后在#2处将解锁脚本设置入相应的交易输入TxIn的script字段中，完成了对该交易输入的签名。

#3处涉及到segwit相关的东西，不深入研究了

继续跟进solve

    def solve(self, hash160_lookup, tx_in_idx, tx_out_script, ha