def recover_tx_from_psbt(first: BasicPSBT, wallet: Abstract_Wallet) -> Transaction:
# Take a PSBT object and re-construct the Electrum transaction object.
# - does not include signatures, see merge_sigs_from_psbt
# - any PSBT in the group could be used for this purpose; all must share tx details
tx = Transaction(first.txn.hex())
tx.deserialize(force_full_parse=True)
# .. add back some data that's been preserved in the PSBT, but isn't part of
# of the unsigned bitcoin txn
tx.is_partial_originally = True
for idx, inp in enumerate(tx.inputs()):
scr = first.inputs[idx].redeem_script or first.inputs[idx].witness_script
# XXX should use transaction.py parse_scriptSig() here!
if scr:
try:
M, N, __, pubkeys, __ = parse_redeemScript_multisig(scr)
except NotRecognizedRedeemScript:
# limitation: we can only handle M-of-N multisig here
raise ValueError("Cannot handle non M-of-N multisig input")
inp['pubkeys'] = pubkeys
inp['x_pubkeys'] = pubkeys
inp['num_sig'] = M
inp['type'] = 'p2wsh' if first.inputs[idx].witness_script else 'p2sh'
# bugfix: transaction.py:parse_input() puts empty dict here, but need a list
inp['signatures'] = [None] * N
if 'prev_tx' not in inp:
# fetch info about inputs' previous txn
wallet.add_hw_info(tx)
if 'value' not in inp:
# we'll need to know the value of the outpts used as part
# of the witness data, much later...
inp['value'] = inp['prev_tx'].outputs()[inp['prevout_n']].value
return tx
def build_psbt(tx: Transaction, wallet: Abstract_Wallet):
# Render a PSBT file, for possible upload to Coldcard.
#
# TODO this should be part of Wallet object, or maybe Transaction?
if getattr(tx, 'raw_psbt', False):
_logger.info('PSBT cache hit')
return tx.raw_psbt
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
wallet.add_hw_info(tx)
# wallet.add_hw_info installs this attr
assert tx.output_info is not None, 'need data about outputs'
# Build a map of all pubkeys needed as derivation from master XFP, in PSBT binary format
# 1) binary version of the common subpath for all keys
# m/ => fingerprint LE32
# a/b/c => ints
#
# 2) all used keys in transaction:
# - for all inputs and outputs (when its change back)
# - for all keystores, if multisig
#
subkeys = {}
for ks in wallet.get_keystores():
# XFP + fixed prefix for this keystore
ks_prefix = packed_xfp_path_for_keystore(ks)
# all pubkeys needed for input signing
for xpubkey, derivation in ks.get_tx_derivations(tx).items():
pubkey = xpubkey_to_pubkey(xpubkey)
# assuming depth two, non-harded: change + index
aa, bb = derivation
assert 0 <= aa < 0x80000000 and 0 <= bb < 0x80000000
subkeys[bfh(pubkey)] = ks_prefix + pack('<II', aa, bb)
# all keys related to change outputs
for o in tx.outputs():
if o.address in tx.output_info:
# this address "is_mine" but might not be change (if I send funds to myself)
output_info = tx.output_info.get(o.address)
if not output_info.is_change:
continue
chg_path = output_info.address_index
assert chg_path[0] == 1 and len(chg_path) == 2, f"unexpected change path: {chg_path}"
pubkey = ks.derive_pubkey(True, chg_path[1])
subkeys[bfh(pubkey)] = ks_prefix + pack('<II', *chg_path)
for txin in inputs:
assert txin['type'] != 'coinbase', _("Coinbase not supported")
if txin['type'] in ['p2sh', 'p2wsh-p2sh', 'p2wsh']:
assert type(wallet) is Multisig_Wallet
# 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)
if type(wallet) is Multisig_Wallet:
# always put the xpubs into the PSBT, useful at least for checking
for xp, ks in zip(wallet.get_master_public_keys(), wallet.get_keystores()):
ks_prefix = packed_xfp_path_for_keystore(ks)
write_kv(PSBT_GLOBAL_XPUB, ks_prefix, DecodeBase58Check(xp))
# 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]
if type(wallet) is Multisig_Wallet:
# always need a redeem script for multisig
scr = Transaction.get_preimage_script(txin)
if Transaction.is_segwit_input(txin):
# needed for both p2wsh-p2sh and p2wsh
write_kv(PSBT_IN_WITNESS_SCRIPT, bfh(scr))
else:
write_kv(PSBT_IN_REDEEM_SCRIPT, bfh(scr))
sigs = txin.get('signatures')
for pk_pos, (pubkey, x_pubkey) in enumerate(zip(pubkeys, x_pubkeys)):
if pubkey in subkeys:
# faster? case ... calculated above
write_kv(PSBT_IN_BIP32_DERIVATION, subkeys[pubkey], pubkey)
else:
# when an input is partly signed, tx.get_tx_derivations()
# doesn't include that keystore's value and yet we need it
# because we need to show a correct keypath...
assert x_pubkey[0:2] == 'ff', x_pubkey
for ks in wallet.get_keystores():
d = ks.get_pubkey_derivation(x_pubkey)
if d is not None:
ks_path = packed_xfp_path_for_keystore(ks, d)
write_kv(PSBT_IN_BIP32_DERIVATION, ks_path, pubkey)
break
else:
raise AssertionError("no keystore for: %s" % x_pubkey)
if txin['type'] == 'p2wpkh-p2sh':
assert len(pubkeys) == 1, 'can be only one redeem script per input'
pa = hash_160(pubkey)
assert len(pa) == 20
write_kv(PSBT_IN_REDEEM_SCRIPT, b'\x00\x14'+pa)
# optional? insert (partial) signatures that we already have
if sigs and sigs[pk_pos]:
write_kv(PSBT_IN_PARTIAL_SIG, bfh(sigs[pk_pos]), pubkey)
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 (if I send funds to myself)
output_info = tx.output_info.get(o.address)
if output_info.is_change:
pubkeys = [bfh(i) for i in wallet.get_public_keys(o.address)]
# Add redeem/witness script?
if type(wallet) is Multisig_Wallet:
# always need a redeem script for multisig cases
scr = bfh(multisig_script([bh2u(i) for i in sorted(pubkeys)], wallet.m))
if output_info.script_type == 'p2wsh-p2sh':
write_kv(PSBT_OUT_WITNESS_SCRIPT, scr)
write_kv(PSBT_OUT_REDEEM_SCRIPT, b'\x00\x20' + sha256(scr))
elif output_info.script_type == 'p2wsh':
write_kv(PSBT_OUT_WITNESS_SCRIPT, scr)
elif output_info.script_type == 'p2sh':
write_kv(PSBT_OUT_REDEEM_SCRIPT, scr)
else:
raise ValueError(output_info.script_type)
elif output_info.script_type == 'p2wpkh-p2sh':
# need a redeem script when P2SH is used to wrap p2wpkh
assert len(pubkeys) == 1
pa = hash_160(pubkeys[0])
write_kv(PSBT_OUT_REDEEM_SCRIPT, b'\x00\x14' + pa)
# Document change output's bip32 derivation(s)
for pubkey in pubkeys:
sk = subkeys[pubkey]
write_kv(PSBT_OUT_BIP32_DERIVATION, sk, pubkey)
out_fd.write(b'\x00')
# capture for later use
tx.raw_psbt = out_fd.getvalue()
return tx.raw_psbt