answers.py

'''
# tag::exercise4[]
==== Exercise 4

Create a testnet transaction that sends 60% of a single UTXO to `mwJn1YPMq7y5F8J3LkC5Hxg9PHyZ5K4cFv`. The remaining amount minus fees should go back to your own change address. This should be a one-input, two-output pass:[<span class="keep-together">transaction</span>].

You can broadcast the transaction at https://blockstream.info/testnet/tx/push[].
# end::exercise4[]
# tag::answer4[]
>>> from ecc import PrivateKey
>>> from helper import decode_base58, SIGHASH_ALL
>>> from script import p2pkh_script, Script
>>> from tx import TxIn, TxOut, Tx
>>> prev_tx = bytes.fromhex('75a1c4bc671f55f626dda1074c7725991e6f68b8fcefcfca7\
b64405ca3b45f1c')
>>> prev_index = 1
>>> target_address = 'miKegze5FQNCnGw6PKyqUbYUeBa4x2hFeM'
>>> target_amount = 0.01
>>> change_address = 'mzx5YhAH9kNHtcN481u6WkjeHjYtVeKVh2'
>>> change_amount = 0.009
>>> secret = 8675309
>>> priv = PrivateKey(secret=secret)
>>> tx_ins = []
>>> tx_ins.append(TxIn(prev_tx, prev_index))
>>> tx_outs = []
>>> h160 = decode_base58(target_address)
>>> script_pubkey = p2pkh_script(h160)
>>> target_satoshis = int(target_amount*100000000)
>>> tx_outs.append(TxOut(target_satoshis, script_pubkey))
>>> h160 = decode_base58(change_address)
>>> script_pubkey = p2pkh_script(h160)
>>> change_satoshis = int(change_amount*100000000)
>>> tx_outs.append(TxOut(change_satoshis, script_pubkey))
>>> tx_obj = Tx(1, tx_ins, tx_outs, 0, testnet=True)
>>> print(tx_obj.sign_input(0, priv))
True
>>> print(tx_obj.serialize().hex())
01000000011c5fb4a35c40647bcacfeffcb8686f1e9925774c07a1dd26f6551f67bcc4a1750100\
00006b483045022100a08ebb92422b3599a2d2fcdaa11f8f807a66ccf33e7f4a9ff0a3c51f1b1e\
c5dd02205ed21dfede5925362b8d9833e908646c54be7ac6664e31650159e8f69b6ca539012103\
935581e52c354cd2f484fe8ed83af7a3097005b2f9c60bff71d35bd795f54b67ffffffff024042\
0f00000000001976a9141ec51b3654c1f1d0f4929d11a1f702937eaf50c888ac9fbb0d00000000\
001976a914d52ad7ca9b3d096a38e752c2018e6fbc40cdf26f88ac00000000

# end::answer4[]
# tag::exercise5[]
==== Exercise 5

Advanced: Get some more testnet coins from a testnet faucet and create a two-input, one-output transaction. One input should be from the faucet, the other should be from the previous exercise; the output can be your own address.

You can broadcast the transaction at https://blockstream.info/testnet/tx/push[].
# end::exercise5[]
# tag::answer5[]
>>> from ecc import PrivateKey
>>> from helper import decode_base58, SIGHASH_ALL
>>> from script import p2pkh_script, Script
>>> from tx import TxIn, TxOut, Tx
>>> prev_tx_1 = bytes.fromhex('11d05ce707c1120248370d1cbf5561d22c4f83aeba04367\
92c82e0bd57fe2a2f')
>>> prev_index_1 = 1
>>> prev_tx_2 = bytes.fromhex('51f61f77bd061b9a0da60d4bedaaf1b1fad0c11e65fdc74\
4797ee22d20b03d15')
>>> prev_index_2 = 1
>>> target_address = 'mwJn1YPMq7y5F8J3LkC5Hxg9PHyZ5K4cFv'
>>> target_amount = 0.0429
>>> secret = 8675309
>>> priv = PrivateKey(secret=secret)
>>> tx_ins = []
>>> tx_ins.append(TxIn(prev_tx_1, prev_index_1))
>>> tx_ins.append(TxIn(prev_tx_2, prev_index_2))
>>> tx_outs = []
>>> h160 = decode_base58(target_address)
>>> script_pubkey = p2pkh_script(h160)
>>> target_satoshis = int(target_amount*100000000)
>>> tx_outs.append(TxOut(target_satoshis, script_pubkey))
>>> tx_obj = Tx(1, tx_ins, tx_outs, 0, testnet=True)
>>> print(tx_obj.sign_input(0, priv))
True
>>> print(tx_obj.sign_input(1, priv))
True
>>> print(tx_obj.serialize().hex())
01000000022f2afe57bde0822c793604baae834f2cd26155bf1c0d37480212c107e75cd0110100\
00006a47304402204cc5fe11b2b025f8fc9f6073b5e3942883bbba266b71751068badeb8f11f03\
64022070178363f5dea4149581a4b9b9dbad91ec1fd990e3fa14f9de3ccb421fa5b26901210393\
5581e52c354cd2f484fe8ed83af7a3097005b2f9c60bff71d35bd795f54b67ffffffff153db020\
2de27e7944c7fd651ec1d0fab1f1aaed4b0da60d9a1b06bd771ff651010000006b483045022100\
b7a938d4679aa7271f0d32d83b61a85eb0180cf1261d44feaad23dfd9799dafb02205ff2f366dd\
d9555f7146861a8298b7636be8b292090a224c5dc84268480d8be1012103935581e52c354cd2f4\
84fe8ed83af7a3097005b2f9c60bff71d35bd795f54b67ffffffff01d0754100000000001976a9\
14ad346f8eb57dee9a37981716e498120ae80e44f788ac00000000

# end::answer5[]
'''


from unittest import TestCase

from helper import (
    encode_varint,
    hash256,
    int_to_little_endian,
    SIGHASH_ALL,
)
from script import Script
from tx import Tx, TxIn


'''
# tag::exercise1[]
==== Exercise 1

Write the `sig_hash` method for the `Tx` class.
# end::exercise1[]
'''


# tag::answer1[]
def sig_hash(self, input_index):
    s = int_to_little_endian(self.version, 4)
    s += encode_varint(len(self.tx_ins))
    for i, tx_in in enumerate(self.tx_ins):
        if i == input_index:
            s += TxIn(
                prev_tx=tx_in.prev_tx,
                prev_index=tx_in.prev_index,
                script_sig=tx_in.script_pubkey(self.testnet),
                sequence=tx_in.sequence,
            ).serialize()
        else:
            s += TxIn(
                prev_tx=tx_in.prev_tx,
                prev_index=tx_in.prev_index,
                sequence=tx_in.sequence,
            ).serialize()
    s += encode_varint(len(self.tx_outs))
    for tx_out in self.tx_outs:
        s += tx_out.serialize()
    s += int_to_little_endian(self.locktime, 4)
    s += int_to_little_endian(SIGHASH_ALL, 4)
    h256 = hash256(s)
    return int.from_bytes(h256, 'big')
# end::answer1[]


'''
# tag::exercise2[]
==== Exercise 2

Write the `verify_input` method for the `Tx` class. You will want to use the `TxIn.script_pubkey`, `Tx.sig_hash`, and `Script.evaluate` methods.
# end::exercise2[]
'''


# tag::answer2[]
def verify_input(self, input_index):
    tx_in = self.tx_ins[input_index]
    script_pubkey = tx_in.script_pubkey(testnet=self.testnet)
    z = self.sig_hash(input_index)
    combined = tx_in.script_sig + script_pubkey
    return combined.evaluate(z)
# end::answer2[]


'''
# tag::exercise3[]
==== Exercise 3

Write the `sign_input` method for the `Tx` class.
# end::exercise3[]
'''


# tag::answer3[]
def sign_input(self, input_index, private_key):
    z = self.sig_hash(input_index)
    der = private_key.sign(z).der()
    sig = der + SIGHASH_ALL.to_bytes(1, 'big')
    sec = private_key.point.sec()
    self.tx_ins[input_index].script_sig = Script([sig, sec])
    return self.verify_input(input_index)
# end::answer3[]


class ChapterTest(TestCase):

    def test_apply(self):
        Tx.sig_hash = sig_hash
        Tx.verify_input = verify_input
        Tx.sign_input = sign_input