Add global xpubs, and key derivations also for external keys
What the developer wrote
Authored by Salvatore Ingala
Add global xpubs, and key derivations also for external keys
createPsbt does not create BIP-174 compliant PSBT, as it was
written to quickly create transactions that the Bitcoin app would
accept; therefore, a lot of fields where ignored.
This improves the PSBT creation by adding more info about the
other keys, and filling the global xpubs, and setting the
transaction version to 2.
What changed, and why it matters
This commit updates a test helper script that builds Bitcoin PSBT test transactions. It makes the generated test PSBTs more standards-compliant by adding missing key origin information, global extended public keys, and setting the transaction version to 2. The change only affects test utilities, not the actual Ledger app code that runs on devices or handles real funds.
No security action required. Review as normal test-code maintenance; ensure the updated test fixtures still exercise the intended device-side PSBT validation paths.
Security signals we found
Change is confined to test utilities (test_utils/txmaker.py)
Adds BIP-174 compliance improvements to test PSBT generation
Adds fallback key origin computation for external xpubs in tests
Sets transaction version to 2 in generated test transactions
No changes to device firmware, signing, or parsing code
Evidence from the diff
The diff modifies test_utils/txmaker.py’s createPsbt/fill_inout helpers. It adds fallback key-origin derivation for external keys lacking explicit origin info (using hash160 of the root pubkey as fingerprint), populates PSBT global xpubs, fills taproot/non-taproot bip32 paths for external keys, and sets CTransaction.nVersion = 2. These are test-fixture improvements; no device-side signing or validation logic is changed.
Changed components
test_utils/txmaker.pyInspect captured patch +31 / −5
diff --git a/test_utils/txmaker.py b/test_utils/txmaker.py
index 04fb07d..9dac432 100644
--- a/test_utils/txmaker.py
+++ b/test_utils/txmaker.py
@@ -27,10 +27,8 @@ from embit.script import Script
from embit.bip32 import HDKey
from embit.bip39 import mnemonic_to_seed
-from hashlib import sha256
-
from bitcoin_client.ledger_bitcoin.embit.descriptor.miniscript import Miniscript
-from test_utils import bip0340
+from test_utils import bip0340, sha256, hash160
from test_utils.wallet_policy import DescriptorTemplate, KeyPlaceholder, PlainKeyPlaceholder, TrDescriptorTemplate, WshDescriptorTemplate, derive_plain_descriptor, tapleaf_hash
@@ -66,7 +64,7 @@ def random_p2tr() -> bytes:
"""Returns 32 random bytes. Not cryptographically secure."""
global privkey_initial
# Using non-random sequence for the sake of tests
- privkey_initial = sha256(privkey_initial).digest()
+ privkey_initial = sha256(privkey_initial)
pubkey = bip0340.point_mul(bip0340.G, int.from_bytes(privkey_initial, 'big'))
return b'\x51\x20' + (pubkey[0]).to_bytes(32, 'big')
@@ -220,6 +218,18 @@ def fill_inout(wallet_policy: WalletPolicy, inout: Union[PartiallySignedInput, P
# In BIP-388 compliant wallet policies, there will be only one tapleaf with a given key
leaf_hashes = [tapleaf_hash(leaf_script)]
+ inout.tap_bip32_paths[derived_pubkey.pubkey[1:]] = (
+ leaf_hashes, derived_key_origin)
+ else:
+ # No key origin info: treat the xpub as the root key, so compute its own fingerprint
+ # and use placeholder_der_subpath as the full derivation path.
+ fpr = hash160(root_pubkey.pubkey)[:4]
+ derived_key_origin = KeyOriginInfo(fpr, placeholder_der_subpath)
+
+ leaf_hashes = []
+ if leaf_script is not None:
+ leaf_hashes = [tapleaf_hash(leaf_script)]
+
inout.tap_bip32_paths[derived_pubkey.pubkey[1:]] = (
leaf_hashes, derived_key_origin)
else:
@@ -248,7 +258,10 @@ def fill_inout(wallet_policy: WalletPolicy, inout: Union[PartiallySignedInput, P
root_pubkey_origin.fingerprint, root_pubkey_origin.path + placeholder_der_subpath)
inout.hd_keypaths[derived_pubkey.pubkey] = derived_key_origin
-
+ else:
+ fpr = hash160(root_pubkey.pubkey)[:4]
+ derived_key_origin = KeyOriginInfo(fpr, placeholder_der_subpath)
+ inout.hd_keypaths[derived_pubkey.pubkey] = derived_key_origin
def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amounts: List[int], output_is_change: List[bool]) -> PSBT:
assert len(output_amounts) == len(output_is_change)
@@ -280,6 +293,7 @@ def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amo
psbt.version = 0
tx = CTransaction()
+ tx.nVersion = 2
tx.vin = vin
tx.vout = vout
tx.wit = CTxWitness()
@@ -298,6 +312,18 @@ def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amo
# a random P2TR output
tx.vout[i].scriptPubKey = random_p2tr()
+ # Fill the global xpub map: each root key in the wallet policy maps to its key origin info
+ for key_info_str in wallet_policy.keys_info:
+ key_origin_end_pos = key_info_str.find("]")
+ if key_origin_end_pos == -1:
+ root_pubkey = ExtendedKey.deserialize(key_info_str)
+ fpr = hash160(root_pubkey.pubkey)[:4]
+ key_origin = KeyOriginInfo(fpr, [])
+ else:
+ root_pubkey = ExtendedKey.deserialize(key_info_str[key_origin_end_pos + 1:])
+ key_origin = KeyOriginInfo.from_string(key_info_str[1:key_origin_end_pos])
+ psbt.xpub[root_pubkey.serialize()] = key_origin
+
psbt.inputs = [PartiallySignedInput(0) for _ in input_amounts]
psbt.outputs = [PartiallySignedOutput(0) for _ in output_amounts]
Why this scored 18/100
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