def is_any_tx_output_on_change_branch(tx: Transaction):
if not tx.output_info:
return False
for o in tx.outputs():
info = tx.output_info.get(o.address)
if info is not None:
if info.address_index[0] == 1:
return True
return False
def build_psbt(self, tx: Transaction, wallet=None, xfp=None):
# Render a PSBT file, for upload to Coldcard.
#
if xfp is None:
# need fingerprint of MASTER xpub, not the derived key
xfp = self.ckcc_xfp
inputs = tx.inputs()
if 'prev_tx' not in inputs[0]:
# fetch info about inputs, if needed?
# - needed during export PSBT flow, not normal online signing
assert wallet, 'need wallet reference'
wallet.add_hw_info(tx)
# wallet.add_hw_info installs this attr
assert tx.output_info is not None, 'need data about outputs'
# Build map of pubkey needed as derivation from master, in PSBT binary format
# 1) binary version of the common subpath for all keys
# m/ => fingerprint LE32
# a/b/c => ints
base_path = pack('<I', xfp)
for x in self.get_derivation()[2:].split('/'):
if x.endswith("'"):
x = int(x[:-1]) | 0x80000000
else:
x = int(x)
base_path += pack('<I', x)
# 2) all used keys in transaction
subkeys = {}
derivations = self.get_tx_derivations(tx)
for xpubkey in derivations:
pubkey = xpubkey_to_pubkey(xpubkey)
# assuming depth two, non-harded: change + index
aa, bb = derivations[xpubkey]
assert 0 <= aa < 0x80000000
assert 0 <= bb < 0x80000000
subkeys[bfh(pubkey)] = base_path + pack('<II', aa, bb)
for txin in inputs:
if txin['type'] == 'coinbase':
self.give_error("Coinbase not supported")
if txin['type'] in ['p2sh', 'p2wsh-p2sh', 'p2wsh']:
self.give_error('No support yet for inputs of type: ' +
txin['type'])
# Construct PSBT from start to finish.
out_fd = io.BytesIO()
out_fd.write(b'psbt\xff')
def write_kv(ktype, val, key=b''):
# serialize helper: write w/ size and key byte
out_fd.write(my_var_int(1 + len(key)))
out_fd.write(bytes([ktype]) + key)
if isinstance(val, str):
val = bfh(val)
out_fd.write(my_var_int(len(val)))
out_fd.write(val)
# global section: just the unsigned txn
class CustomTXSerialization(Transaction):
@classmethod
def input_script(cls, txin, estimate_size=False):
return ''
unsigned = bfh(
CustomTXSerialization(
tx.serialize()).serialize_to_network(witness=False))
write_kv(PSBT_GLOBAL_UNSIGNED_TX, unsigned)
# end globals section
out_fd.write(b'\x00')
# inputs section
for txin in inputs:
if Transaction.is_segwit_input(txin):
utxo = txin['prev_tx'].outputs()[txin['prevout_n']]
spendable = txin['prev_tx'].serialize_output(utxo)
write_kv(PSBT_IN_WITNESS_UTXO, spendable)
else:
write_kv(PSBT_IN_NON_WITNESS_UTXO, str(txin['prev_tx']))
pubkeys, x_pubkeys = tx.get_sorted_pubkeys(txin)
pubkeys = [bfh(k) for k in pubkeys]
for k in pubkeys:
write_kv(PSBT_IN_BIP32_DERIVATION, subkeys[k], k)
if txin['type'] == 'p2wpkh-p2sh':
assert len(
pubkeys
) == 1, 'can be only one redeem script per input'
pa = hash_160(k)
assert len(pa) == 20
write_kv(PSBT_IN_REDEEM_SCRIPT, b'\x00\x14' + pa)
out_fd.write(b'\x00')
# outputs section
for o in tx.outputs():
# can be empty, but must be present, and helpful to show change inputs
# wallet.add_hw_info() adds some data about change outputs into tx.output_info
if o.address in tx.output_info:
# this address "is_mine" but might not be change (I like to sent to myself)
output_info = tx.output_info.get(o.address)
index, xpubs = output_info.address_index, output_info.sorted_xpubs
if index[0] == 1 and len(index) == 2:
# it is a change output (based on our standard derivation path)
assert len(xpubs) == 1 # not expecting multisig
xpubkey = xpubs[0]
# document its bip32 derivation in output section
aa, bb = index
assert 0 <= aa < 0x80000000
assert 0 <= bb < 0x80000000
deriv = base_path + pack('<II', aa, bb)
pubkey = bfh(self.get_pubkey_from_xpub(xpubkey, index))
write_kv(PSBT_OUT_BIP32_DERIVATION, deriv, pubkey)
if output_info.script_type == 'p2wpkh-p2sh':
pa = hash_160(pubkey)
assert len(pa) == 20
write_kv(PSBT_OUT_REDEEM_SCRIPT, b'\x00\x14' + pa)
out_fd.write(b'\x00')
return out_fd.getvalue()