def create_payment_tx(self, deposit_tx, redeem_script, merchant_public_key,
customer_public_key, amount, fee):
# Find P2SH output index in deposit_tx
deposit_utxo_index = deposit_tx.output_index_for_address(
redeem_script.hash160())
# Look up deposit amount
deposit_amount = deposit_tx.outputs[deposit_utxo_index].value - fee
# Build unsigned payment transaction
script_sig = Script()
inp = TransactionInput(deposit_tx.hash, deposit_utxo_index, script_sig,
0xffffffff)
out1 = TransactionOutput(
amount, Script.build_p2pkh(merchant_public_key.hash160()))
out2 = TransactionOutput(
deposit_amount - amount,
Script.build_p2pkh(customer_public_key.hash160()))
payment_tx = Transaction(1, [inp], [out1, out2], 0x0)
# Sign payment transaction
public_key = redeem_script.customer_public_key
private_key = self.get_private_for_public(public_key)
sig = payment_tx.get_signature_for_input(0, Transaction.SIG_HASH_ALL,
private_key, redeem_script)[0]
# Update input script sig
script_sig = Script([
sig.to_der() + utils.pack_compact_int(Transaction.SIG_HASH_ALL),
'OP_1',
bytes(redeem_script)
])
payment_tx.inputs[0].script = script_sig
return payment_tx
def write_ew_message(msg):
"""Write a message to the blockchain."""
print("write_ew_message({})" % msg)
# Create a bitcoin script object with our message
if len(msg) > 72:
raise Exception('Message is too long and may not be accepted.')
msg = "EW " + msg
message_script = Script('OP_RETURN 0x{}'.format(utils.bytes_to_str(msg.encode())))
# Define the fee we're willing to pay for the tx
tx_fee = 11000
# Get the first UTXO from our set that can cover the fee
utxo = None
for utxo_addr, utxos in wallet.get_utxos().items():
for u in utxos:
if u.value > tx_fee:
utxo = u
break
if utxo:
break
if not utxo:
raise Exception('No UTXOs available to pay for the transaction.')
# Build the transaction inputs (there is only one, but Transaction expects a list)
inputs = [TransactionInput(outpoint=utxo.transaction_hash,
outpoint_index=utxo.outpoint_index,
script=utxo.script,
sequence_num=0xffffffff)]
outputs = []
# Build one output with our custom message script
outputs.append(TransactionOutput(value=0, script=message_script))
# Build another output to pay the UTXO money back to one of our addresses
_, change_key_hash = utils.address_to_key_hash(wallet._accounts[0].get_next_address(True))
outputs.append(TransactionOutput(value=utxo.value - tx_fee,
script=Script.build_p2pkh(change_key_hash)))
# Build an unsigned transaction object
txn = Transaction(version=Transaction.DEFAULT_TRANSACTION_VERSION,
inputs=inputs,
outputs=outputs,
lock_time=0
)
# Sign the transaction with the correct private key
private_key = wallet.get_private_key(utxo_addr)
txn.sign_input(input_index=0,
hash_type=Transaction.SIG_HASH_ALL,
private_key=private_key,
sub_script=utxo.script
)
# Broadcast the transaction
tx = wallet.broadcast_transaction(txn.to_hex())
return tx
def receive_payment(self, deposit_txid, payment_tx):
"""Receive and process a payment within the channel.
The customer makes a payment in the channel by sending the merchant a
half-signed payment transaction. The merchant signs the other half of
the transaction and saves it in its records (but does not broadcast it
or send it to the customer). The merchant responds with 200 to verify
that the payment was handled successfully.
Args:
deposit_txid (string): string representation of the deposit
transaction hash. This is used to look up the payment channel.
payment_tx (string): half-signed payment transaction from a
customer.
Returns:
(string): payment transaction id
"""
# Parse payment channel `payment` parameters
payment_tx = Transaction.from_hex(payment_tx)
# Get channel and addresses related to the deposit
channel = self._db.pc.lookup(deposit_txid)
if not channel:
raise PaymentChannelNotFoundError('Related channel not found.')
# Get merchant public key information from payment channel
merchant_public_key = PublicKey.from_hex(channel.merchant_pubkey)
# Verify that redeem script contains the merchant public key
redeem_script = PaymentChannelRedeemScript.from_bytes(payment_tx.inputs[0].script[-1])
if redeem_script.merchant_public_key.to_hex() != merchant_public_key.to_hex():
raise BadTransactionError('Invalid merchant pubkey.')
# Verify that the payment has a valid signature from the customer
txn_copy = payment_tx._copy_for_sig(0, Transaction.SIG_HASH_ALL, redeem_script)
msg_to_sign = bytes(Hash.dhash(bytes(txn_copy) + pack_u32(Transaction.SIG_HASH_ALL)))
sig = Signature.from_der(payment_tx.inputs[0].script[0][:-1])
if not redeem_script.customer_public_key.verify(msg_to_sign, sig, False):
raise BadTransactionError('Invalid payment signature.')
# Verify the length of the script is what we expect
if len(payment_tx.inputs[0].script) != 3:
raise BadTransactionError('Invalid payment channel transaction structure.')
# Verify the script template is valid for accepting a merchant signature
if (not Script.validate_template(payment_tx.inputs[0].script, [bytes, 'OP_1', bytes]) and
not Script.validate_template(payment_tx.inputs[0].script, [bytes, 'OP_TRUE', bytes])):
raise BadTransactionError('Invalid payment channel transaction structure.')
# Verify that the payment channel is ready
if channel.state == ChannelSQLite3.CONFIRMING:
confirmed = self._blockchain.check_confirmed(channel.deposit_txid)
if confirmed:
self._db.pc.update_state(channel.deposit_txid, ChannelSQLite3.READY)
else:
raise ChannelClosedError('Payment channel not ready.')
elif channel.state == ChannelSQLite3.CLOSED:
raise ChannelClosedError('Payment channel closed.')
# Verify that payment is made to the merchant public key
index = payment_tx.output_index_for_address(merchant_public_key.hash160())
if index is None:
raise BadTransactionError('Payment must pay to merchant pubkey.')
# Verify that both payments are not below the dust limit
for output_index, output in enumerate(payment_tx.outputs):
if output.value < PaymentServer.DUST_LIMIT:
# Payment to merchant is less than dust limit
if output_index == index:
raise BadTransactionError(
'Initial payment must be greater than {}.'.format(PaymentServer.DUST_LIMIT))
# Payment to customer is less than dust limit
else:
raise BadTransactionError(
'Payment channel balance is not large enough to make payment.')
# Validate that the payment is more than the last one
new_pmt_amt = payment_tx.outputs[index].value
if new_pmt_amt <= channel.last_payment_amount:
raise BadTransactionError('Payment must be greater than 0.')
# Verify that the transaction has adequate fees
net_pmt_amount = sum([d.value for d in payment_tx.outputs])
deposit_amount = channel.amount
fee = deposit_amount - net_pmt_amount
if fee < PaymentServer.MIN_TX_FEE:
raise BadTransactionError('Payment must have adequate fees.')
# Recreate redeem script from merchant side
redeem_script_copy = PaymentChannelRedeemScript(
merchant_public_key,
redeem_script.customer_public_key,
channel.expires_at)
if redeem_script.to_hex() != redeem_script_copy.to_hex():
raise BadTransactionError('Invalid redeem script.')
# Recreate customer payment from merchant side
payment_tx_copy = self._wallet.create_unsigned_payment_tx(
channel.deposit_tx, redeem_script, new_pmt_amt, fee)
# Recreate signed input script using signature from customer
hash_type = pack_compact_int(Transaction.SIG_HASH_ALL)
signed_input_script = Script(
[sig.to_der() + hash_type, "OP_1", bytes(redeem_script)])
payment_tx_copy.inputs[0].script = signed_input_script
if payment_tx.to_hex() != payment_tx_copy.to_hex():
raise BadTransactionError('Invalid payment channel transaction structure.')
# Update the current payment transaction
self._db.pc.update_payment(deposit_txid, payment_tx_copy, new_pmt_amt)
self._db.pmt.create(deposit_txid, payment_tx_copy, new_pmt_amt - channel.last_payment_amount)
return str(payment_tx_copy.hash)
