Optionally pass BIP388 policy to signtx

hwilib/_cli.py

@@ -22,6 +22,7 @@
 )
 from .common import (
     AddressType,
+    BIP388Policy,
     Chain,
 )
 from .errors import (
@@ -88,7 +89,13 @@ def signmessage_handler(args: argparse.Namespace, client: HardwareWalletClient)
     return signmessage(client, message=args.message, path=args.path)
 
 def signtx_handler(args: argparse.Namespace, client: HardwareWalletClient) -> Dict[str, Union[bool, str]]:
-    return signtx(client, psbt=args.psbt)
+    policy = BIP388Policy(
+        name=args.policy_name,
+        descriptor_template=args.policy_desc,
+        keys_info=args.key,
+        hmac=args.hmac
+    )
+    return signtx(client, psbt=args.psbt, bip388_policy=policy)
 
 def wipe_device_handler(args: argparse.Namespace, client: HardwareWalletClient) -> Dict[str, bool]:
     return wipe_device(client)
@@ -161,6 +168,11 @@ def get_parser() -> HWIArgumentParser:
 
     signtx_parser = subparsers.add_parser('signtx', help='Sign a PSBT')
     signtx_parser.add_argument('psbt', help='The Partially Signed Bitcoin Transaction to sign')
+    signtx_policy_group = signtx_parser.add_argument_group("BIP388 policy")
+    signtx_policy_group.add_argument('--policy-name', help='Registered policy name')
+    signtx_policy_group.add_argument('--policy-desc', help='Registered policy descriptor template')
+    signtx_policy_group.add_argument('--key', help='Registered policy key information', action='append')
+    signtx_policy_group.add_argument('--hmac', help='Registered policy hmac, obtained via register command')
     signtx_parser.set_defaults(func=signtx_handler)
 
     getxpub_parser = subparsers.add_parser('getxpub', help='Get an extended public key')

hwilib/commands.py

@@ -52,6 +52,7 @@
 from .devices import __all__ as all_devs
 from .common import (
     AddressType,
+    BIP388Policy,
     Chain,
 )
 from .hwwclient import HardwareWalletClient
@@ -183,7 +184,11 @@ def getmasterxpub(client: HardwareWalletClient, addrtype: AddressType = AddressT
     """
     return {"xpub": client.get_master_xpub(addrtype, account).to_string()}
 
-def signtx(client: HardwareWalletClient, psbt: str) -> Dict[str, Union[bool, str]]:
+def signtx(
+    client: HardwareWalletClient,
+    psbt: str,
+    bip388_policy: Optional[BIP388Policy]
+) -> Dict[str, Union[bool, str]]:
     """
     Sign a Partially Signed Bitcoin Transaction (PSBT) with the client.
 
@@ -195,7 +200,7 @@ def signtx(client: HardwareWalletClient, psbt: str) -> Dict[str, Union[bool, str
     # Deserialize the transaction
     tx = PSBT()
     tx.deserialize(psbt)
-    result = client.sign_tx(tx).serialize()
+    result = client.sign_tx(tx, bip388_policy).serialize()
     return {"psbt": result, "signed": result != psbt}
 
 def getxpub(client: HardwareWalletClient, path: str, expert: bool = False) -> Dict[str, Any]:

hwilib/common.py

@@ -3,12 +3,17 @@
 ****************************
 """
 
+from dataclasses import dataclass
+
 import hashlib
 
 from enum import Enum
 
-from typing import Union
-
+from typing import (
+    List,
+    Optional,
+    Union,
+)
 
 class Chain(Enum):
     """
@@ -56,6 +61,15 @@ def argparse(s: str) -> Union['AddressType', str]:
         except KeyError:
             return s
 
+@dataclass
+class BIP388Policy:
+    """
+    Serialization agnostic BIP388 policy.
+    """
+    name: str
+    descriptor_template: str
+    keys_info: List[str]
+    hmac: Optional[str] = None
 
 def sha256(s: bytes) -> bytes:
     """

hwilib/devices/bitbox02.py

@@ -57,6 +57,7 @@
 )
 from ..common import (
     AddressType,
+    BIP388Policy,
     Chain,
 )
 
@@ -563,7 +564,11 @@ def display_multisig_address(
         return address
 
     @bitbox02_exception
-    def sign_tx(self, psbt: PSBT) -> PSBT:
+    def sign_tx(
+        self,
+        psbt: PSBT,
+        __: Optional[BIP388Policy],
+    ) -> PSBT:
         """
         Sign a transaction with the BitBox02.
 

hwilib/devices/coldcard.py

@@ -51,6 +51,7 @@
 )
 from ..common import (
     AddressType,
+    BIP388Policy,
     Chain,
 )
 from functools import wraps
@@ -116,7 +117,11 @@ def get_master_fingerprint(self) -> bytes:
         return struct.pack('<I', self.device.master_fingerprint)
 
     @coldcard_exception
-    def sign_tx(self, tx: PSBT) -> PSBT:
+    def sign_tx(
+        self,
+        psbt: PSBT,
+        __: Optional[BIP388Policy],
+    ) -> PSBT:
         """
         Sign a transaction with the Coldcard.
 
@@ -132,7 +137,7 @@ def sign_tx(self, tx: PSBT) -> PSBT:
 
         # For multisigs, we may need to do multiple passes if we appear in an input multiple times
         passes = 1
-        for psbt_in in tx.inputs:
+        for psbt_in in psbt.inputs:
             our_keys = 0
             for key in psbt_in.hd_keypaths.keys():
                 keypath = psbt_in.hd_keypaths[key]
@@ -143,8 +148,8 @@ def sign_tx(self, tx: PSBT) -> PSBT:
 
         for _ in range(passes):
             # Get psbt in hex and then make binary
-            tx.convert_to_v0()
-            fd = io.BytesIO(base64.b64decode(tx.serialize()))
+            psbt.convert_to_v0()
+            fd = io.BytesIO(base64.b64decode(psbt.serialize()))
 
             # learn size (portable way)
             sz = fd.seek(0, 2)
@@ -190,10 +195,10 @@ def sign_tx(self, tx: PSBT) -> PSBT:
 
             result = self.device.download_file(result_len, result_sha, file_number=1)
 
-            tx = PSBT()
-            tx.deserialize(base64.b64encode(result).decode())
+            psbt = PSBT()
+            psbt.deserialize(base64.b64encode(result).decode())
 
-        return tx
+        return psbt
 
     @coldcard_exception
     def sign_message(self, message: Union[str, bytes], keypath: str) -> str:

hwilib/devices/digitalbitbox.py

@@ -29,6 +29,7 @@
 
 from ..common import (
     AddressType,
+    BIP388Policy,
     Chain,
     hash256,
 )
@@ -387,17 +388,21 @@ def get_pubkey_at_path(self, path: str) -> ExtendedKey:
         return xpub
 
     @digitalbitbox_exception
-    def sign_tx(self, tx: PSBT) -> PSBT:
+    def sign_tx(
+        self,
+        psbt: PSBT,
+        __: Optional[BIP388Policy],
+    ) -> PSBT:
 
         # Create a transaction with all scriptsigs blanked out
-        blank_tx = tx.get_unsigned_tx()
+        blank_tx = psbt.get_unsigned_tx()
 
         # Get the master key fingerprint
         master_fp = self.get_master_fingerprint()
 
         # create sighashes
         sighash_tuples = []
-        for txin, psbt_in, i_num in zip(blank_tx.vin, tx.inputs, range(len(blank_tx.vin))):
+        for txin, psbt_in, i_num in zip(blank_tx.vin, psbt.inputs, range(len(blank_tx.vin))):
             sighash = b""
             utxo = None
             if psbt_in.witness_utxo:
@@ -493,7 +498,7 @@ def sign_tx(self, tx: PSBT) -> PSBT:
 
         # Return early if nothing to do
         if len(sighash_tuples) == 0:
-            return tx
+            return psbt
 
         for i in range(0, len(sighash_tuples), 15):
             tups = sighash_tuples[i:i + 15]
@@ -533,9 +538,9 @@ def sign_tx(self, tx: PSBT) -> PSBT:
 
             # add sigs to tx
             for tup, sig in zip(tups, der_sigs):
-                tx.inputs[tup[2]].partial_sigs[tup[3]] = sig
+                psbt.inputs[tup[2]].partial_sigs[tup[3]] = sig
 
-        return tx
+        return psbt
 
     @digitalbitbox_exception
     def sign_message(self, message: Union[str, bytes], keypath: str) -> str:

hwilib/devices/jade.py

@@ -34,6 +34,7 @@
 )
 from ..common import (
     AddressType,
+    BIP388Policy,
     Chain,
     sha256
 )
@@ -370,16 +371,21 @@ def _split_at_last_hardened_element(path: Sequence[int]) -> Tuple[Sequence[int],
     # Sign tx PSBT - newer Jade firmware supports native PSBT signing, but old firmwares require
     # mapping to the legacy 'sign_tx' structures.
     @jade_exception
-    def sign_tx(self, tx: PSBT) -> PSBT:
+    def sign_tx(
+        self,
+        psbt: PSBT,
+        __: Optional[BIP388Policy],
+    ) -> PSBT:
         """
         Sign a transaction with the Blockstream Jade.
         """
+
         # Old firmware does not have native PSBT handling - use legacy method
         if self.PSBT_SUPPORTED_FW_VERSION > self.fw_version.finalize_version():
-            return self.legacy_sign_tx(tx)
+            return self.legacy_sign_tx(psbt)
 
         # Firmware 0.1.47 (March 2023) and later support native PSBT signing
-        psbt_b64 = tx.serialize()
+        psbt_b64 = psbt.serialize()
         psbt_bytes = base64.b64decode(psbt_b64.strip())
 
         # NOTE: sign_psbt() does not use AE signatures, so sticks with default (rfc6979)

hwilib/devices/ledger.py

@@ -32,6 +32,7 @@
 from ..common import (
     AddressType,
     Chain,
+    BIP388Policy,
 )
 from .ledger_bitcoin.client import (
     createClient,
@@ -185,7 +186,11 @@ def get_pubkey_at_path(self, path: str) -> ExtendedKey:
         return ExtendedKey.deserialize(xpub_str)
 
     @ledger_exception
-    def sign_tx(self, tx: PSBT) -> PSBT:
+    def sign_tx(
+        self,
+        psbt: PSBT,
+        bip388_policy: Optional[BIP388Policy]
+    ) -> PSBT:
         """
         Sign a transaction with a Ledger device. Not all transactions can be signed by a Ledger.
 
@@ -198,6 +203,8 @@ def sign_tx(self, tx: PSBT) -> PSBT:
         For application versions 2.1.x and above:
 
         - Only keys derived with standard BIP 44, 49, 84, and 86 derivation paths are supported for single signature addresses.
+
+        BIP388: for basic descriptors this is optional, but if provided name must be empty
         """
         master_fp = self.get_master_fingerprint()
 
@@ -206,20 +213,20 @@ def legacy_sign_tx() -> PSBT:
             if not isinstance(client, LegacyClient):
                 client = LegacyClient(self.transport_client, self.chain)
             wallet = WalletPolicy("", "wpkh(@0/**)", [""])
-            legacy_input_sigs = client.sign_psbt(tx, wallet, None)
+            legacy_input_sigs = client.sign_psbt(psbt, wallet, None)
 
             for idx, pubkey, sig in legacy_input_sigs:
-                psbt_in = tx.inputs[idx]
+                psbt_in = psbt.inputs[idx]
                 psbt_in.partial_sigs[pubkey] = sig
-            return tx
+            return psbt
 
         if isinstance(self.client, LegacyClient):
             return legacy_sign_tx()
 
         # Make a deepcopy of this psbt. We will need to modify it to get signing to work,
         # which will affect the caller's detection for whether signing occured.
-        psbt2 = copy.deepcopy(tx)
-        if tx.version != 2:
+        psbt2 = copy.deepcopy(psbt)
+        if psbt.version != 2:
             psbt2.convert_to_v2()
 
         # Figure out which wallets are signing
@@ -264,6 +271,25 @@ def legacy_sign_tx() -> PSBT:
                     else:
                         continue
 
+            if bip388_policy is not None:
+                policy = WalletPolicy(
+                    name=bip388_policy.name,
+                    descriptor_template=bip388_policy.descriptor_template,
+                    keys_info=bip388_policy.keys_info
+                )
+                if policy.id not in wallets:
+                    if bip388_policy.hmac is None:
+                        raise BadArgumentError("Missing --hmac")
+                    wallets[policy.id] = (
+                        signing_priority[script_addrtype],
+                        script_addrtype,
+                        policy,
+                        bytes.fromhex(bip388_policy.hmac),
+                    )
+                continue
+
+            # No BIP388 policy provided, construct on the fly
+
             # Check if P2WSH
             if is_p2wsh(scriptcode):
                 if len(psbt_in.witness_script) == 0:
@@ -369,13 +395,13 @@ def process_origin(origin: KeyOriginInfo) -> None:
                     psbt_in.partial_sigs[pubkey] = sig
 
         # Extract the sigs from psbt2 and put them into tx
-        for sig_in, psbt_in in zip(psbt2.inputs, tx.inputs):
+        for sig_in, psbt_in in zip(psbt2.inputs, psbt.inputs):
             psbt_in.partial_sigs.update(sig_in.partial_sigs)
             psbt_in.tap_script_sigs.update(sig_in.tap_script_sigs)
             if len(sig_in.tap_key_sig) != 0 and len(psbt_in.tap_key_sig) == 0:
                 psbt_in.tap_key_sig = sig_in.tap_key_sig
 
-        return tx
+        return psbt
 
     @ledger_exception
     def sign_message(self, message: Union[str, bytes], keypath: str) -> str: