fix(bip137): align recid with the script type

CHANGELOG.md

@@ -13,6 +13,7 @@ Switch from the pure-Python urtypes and foundation-ur-py packages to the new uUR
 - Replace custom quirc (library to decode QR codes from images) with k_quirc
 - Fix default theme contrast failures for Light, CypherPink, network
   indicators, and Amigo info panels
+- Check for recids in BIP-137 message signing
 
 # Changelog 26.04.0 - April 2025
 

src/krux/bip137.py

@@ -0,0 +1,76 @@
+# The MIT License (MIT)
+
+# Copyright (c) 2021-2026 Krux contributors
+
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+P2PKH_UNCOMPRESSED_HEADER = 27
+P2PKH_HEADER = 31
+P2SH_P2WPKH_HEADER = 35
+P2WPKH_HEADER = 39
+MESSAGE_MAGIC = b"\x18Bitcoin Signed Message:\n"
+RECID_OFFSET = P2PKH_HEADER - P2PKH_UNCOMPRESSED_HEADER
+
+
+def message_commitment(message):
+    """Double-SHA256 commitment over the BIP-137 magic"""
+    from embit import compact
+
+    try:
+        import uhashlib as hashlib
+    except ImportError:
+        import hashlib
+
+    # BIP137 commitment message:
+    # `SHA256(SHA256(MAGIC // varint // message))`
+    varint = compact.to_bytes(len(message))
+    _message = MESSAGE_MAGIC + varint + message
+    return hashlib.sha256(hashlib.sha256(_message).digest()).digest()
+
+
+def build_header(raw_sig, script_type, compressed=True):
+    """Build header byte from raw signature and script_type"""
+    # Avoid some unexpected header
+    rsig = raw_sig[0]
+    if not P2PKH_UNCOMPRESSED_HEADER <= rsig <= P2PKH_HEADER + 3:
+        raise ValueError("Invalid sig header: %d" % rsig)
+
+    # grab the 2 least significant bits as recId
+    # and normalize with a minimum p2pkh (uncompressed) flag
+    recid = (raw_sig[0] - P2PKH_UNCOMPRESSED_HEADER) & 3
+
+    if script_type == "p2sh-p2wpkh":
+        return P2SH_P2WPKH_HEADER + recid
+    if script_type == "p2wpkh":
+        return P2WPKH_HEADER + recid
+
+    return (
+        P2PKH_UNCOMPRESSED_HEADER
+        + recid
+        + (0 if not compressed and script_type == "p2pkh" else RECID_OFFSET)
+    )
+
+
+def sign(message, key, derivation, script_type="p2pkh", compressed=True):
+    """Sign a BIP137 `message` with `key` at `derivation` for some `script_type`"""
+    commitment = message_commitment(message)
+    raw_sig = key.sign_at(derivation, commitment)
+    header = build_header(raw_sig, script_type, compressed)
+    sig = bytes([header]) + raw_sig[1:]
+    return (commitment, sig)

src/krux/pages/home_pages/sign_message_ui.py

@@ -20,7 +20,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-from embit import bip32, compact, script
+from embit import bip32, script
 from embit.networks import NETWORKS
 import hashlib
 import binascii
@@ -133,7 +133,8 @@ def get_bitcoin_address(self, derivation_path, script_type=""):
         return addr
 
     def _sign_at_address(self, message, derivation_str, address=""):
-        """Signs a message at a derived Bitcoin address"""
+        """Signs a BIP137 message at a derived Bitcoin address"""
+        from krux import bip137
 
         derivation = bip32.parse_path(derivation_str)
         self._display_message_sign_prompt(
@@ -143,15 +144,8 @@ def _sign_at_address(self, message, derivation_str, address=""):
         if not self.prompt(t("Sign?"), BOTTOM_PROMPT_LINE):
             return None
 
-        message_hash = hashlib.sha256(
-            hashlib.sha256(
-                b"\x18Bitcoin Signed Message:\n"
-                + compact.to_bytes(len(message))
-                + message
-            ).digest()
-        ).digest()
-
-        sig = self.ctx.wallet.key.sign_at(derivation, message_hash)
+        script_type = self.get_script_type_from_path(derivation_str) or "p2pkh"
+        _, sig = bip137.sign(message, self.ctx.wallet.key, derivation, script_type)
         self._display_signature(base_encode(sig, 64))
         return sig
 
@@ -234,6 +228,8 @@ def _sign_at_address_from_sd(self, data):
 
     def sign_standard_message(self, data):
         """Signs a standard message"""
+        from krux import bip137
+
         message_hash, is_raw_hash = self._compute_message_hash(data)
         if message_hash is None:
             return ""
@@ -248,6 +244,8 @@ def sign_standard_message(self, data):
             )
             if not self.prompt(t("Proceed?"), BOTTOM_PROMPT_LINE):
                 return ""
+        else:
+            message_hash = bip137.message_commitment(data)
 
         self.ctx.display.clear()
         self.ctx.display.draw_centered_text(
@@ -257,7 +255,13 @@ def sign_standard_message(self, data):
         if not self.prompt(t("Sign?"), BOTTOM_PROMPT_LINE):
             return ""
 
-        sig = self.ctx.wallet.key.sign(message_hash).serialize()
+        key = self.ctx.wallet.key
+        if is_raw_hash:
+            sig = key.sign(message_hash).serialize()
+        else:
+            _, sig = bip137.sign(
+                data, key, bip32.parse_path(key.derivation), key.script_type
+            )
         self._display_signature(base_encode(sig, 64))
         return sig
 

tests/pages/home_pages/test_sign_message_ui.py

@@ -68,7 +68,7 @@ def test_sign_message(mocker, m5stickv, tdata):
                 BUTTON_ENTER,  # Hex Public Key Text
                 BUTTON_ENTER,  # PK QR code
             ],
-            "MEQCIHKmpv1+vgPpFTN0JXjyrMK2TtLHVeJJ2TydPYmEt0RnAiBJVt/Y61ef5VlWjG08zf92AeF++BWdYm1Yd9IEy2cSqA==",
+            "KNDYjnAavccLPKVJ7u6RjWs9n2NzN+kHc8MHrrUiQRq9TEoXa3UAbwsjESNCi7wcAZ9Vw1N7K+ujZzasgEgsvL0=",
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",
             None,
         ),
@@ -86,7 +86,7 @@ def test_sign_message(mocker, m5stickv, tdata):
                 BUTTON_ENTER,  # Hex Public Key Text
                 BUTTON_ENTER,  # PK QR code
             ],
-            "MEQCIEHpCMfQ+5mBAOH//OCxF6iojpVtIS6G7X+3r3qB/0CaAiAkbjW2SGrPLvju+O05yH2x/4EKL2qlkdWnquiVkUY3jQ==",
+            "KIyFNagItWNotujcQQ7AoXLO90ndVEmsQvXeJbaTnFKufb2eq+G1RKvxRw+eR887Rn0UgqAKyrji4GQQYGfxvkw=",
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",
             None,
         ),
@@ -167,11 +167,11 @@ def test_sign_message(mocker, m5stickv, tdata):
                 BUTTON_PAGE_PREV,  # Move to "Go"
                 BUTTON_ENTER,  # Press "Go" (saved pubkey to SD)
             ],
-            "MEQCIHKmpv1+vgPpFTN0JXjyrMK2TtLHVeJJ2TydPYmEt0RnAiBJVt/Y61ef5VlWjG08zf92AeF++BWdYm1Yd9IEy2cSqA==",  # 4 base64 for display_qr_codes / print_qr_prompt
+            "KNDYjnAavccLPKVJ7u6RjWs9n2NzN+kHc8MHrrUiQRq9TEoXa3UAbwsjESNCi7wcAZ9Vw1N7K+ujZzasgEgsvL0=",  # 4 base64 for display_qr_codes / print_qr_prompt
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",  # 5 pubkey for display_qr_codes / print_qr_prompt
             # 6 SD file
             binascii.b2a_base64(
-                "MEQCIHKmpv1+vgPpFTN0JXjyrMK2TtLHVeJJ2TydPYmEt0RnAiBJVt/Y61ef5VlWjG08zf92AeF++BWdYm1Yd9IEy2cSqA==".encode(
+                "KNDYjnAavccLPKVJ7u6RjWs9n2NzN+kHc8MHrrUiQRq9TEoXa3UAbwsjESNCi7wcAZ9Vw1N7K+ujZzasgEgsvL0=".encode(
                     "utf-8"
                 ),
                 newline=False,
@@ -206,7 +206,6 @@ def test_sign_message(mocker, m5stickv, tdata):
             with patch(
                 "builtins.open", new=get_mock_open({"/sd/signed-message.sig": case[6]})
             ) as mock_file:
-
                 # function being tested
                 home.sign_message()
 
@@ -263,7 +262,7 @@ def test_sign_message_invalid_derivations(mocker, m5stickv, tdata):
             ],
             "signmessage m84h ascii:hello",
             "m84h",
-            "MEQCIA7DCCFox6tQqC3GE9a5IMvm8cVu1Zh6OWcUE1gls77gAiAzLncevU9FFJRvG83ahSJ8hISimgtSSdRHye2rmijwlg==",
+            "J7jAswueRmlhh64HDmfIuVvo5pcMMgBYdSCXAnMh2NQsQUwYkyI1O8G0F/8ChIiOz2pfCiQwE0FfOXWTAtMsMDE=",
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",
         ),
         (
@@ -278,7 +277,7 @@ def test_sign_message_invalid_derivations(mocker, m5stickv, tdata):
             ],
             "signmessage m/8xh/0/0 ascii:hello",
             "m/8xh/0/0",
-            "MEQCIDL/XdIRF+v0wnN/JDOu2XYMTYqJaAyjuIDdSG4E/909AiASARSc1zfJsvUKC6MDQlM3E2lrkTx3iYfpJUWRZy/Vpg==",
+            "JwdAF2MY6uglo4E3Wxbbi9G6NyrEna4LyYBsUueJg8yoLQm39BHDJ+ulgRhXl2RI/BManG05oTmRyXOqjDfDrs0=",
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",
         ),
         (  # 2 - QR invalid (empty segment)
@@ -293,15 +292,13 @@ def test_sign_message_invalid_derivations(mocker, m5stickv, tdata):
             ],
             "signmessage m//0 ascii:hello",
             "m//0",
-            "MEQCIDx4K8atJhGiaFdCCsgaUqFv22ncJ3AFHczFsNLZmbcGAiBuQdB5/pztOHjyQt0DKmuMKo799raQuRrXMVKK69ELjQ==",
+            "J0yYgnVLwEditYd+QwmJrXqFRplrBqfUfUHOpAF4m+EEW9MYf4BVp/SWPujLDYfQKWxbpRPVZdaYuyGm77bNSsE=",
             "02707a62fdacc26ea9b63b1c197906f56ee0180d0bcf1966e1a2da34f5f3a09a9b",
         ),
     ]
 
-    n = 0
-    for case in cases:
+    for n, case in enumerate(cases):
         print("Case: ", n)
-        n = 0
 
         # A mainnet wallet
         wallet = Wallet(tdata.SINGLESIG_SIGNING_KEY)
@@ -372,7 +369,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             False,
             "a test message with a colon ':' character.",
             "3. bc1qgl5…3cn3",  # bc1qgl5vlg0zdl7yvprgxj9fevsc6q6x5dmcyk3cn3
-            "IN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
+            "KN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
         ),
         (  # 1 - Sign P2WPKH Testnet
             [
@@ -387,7 +384,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             False,
             "A test message.",
             "3. tb1qynp…m5km",
-            "ILc30ti8OPSpCtzfj7sNnftANBCuVpyRX7pnM3iAgOk9F9IUtnXNPus0+MF12y5HKYHAB6IVYr66sLmL3Vi3oEE=",
+            "KLc30ti8OPSpCtzfj7sNnftANBCuVpyRX7pnM3iAgOk9F9IUtnXNPus0+MF12y5HKYHAB6IVYr66sLmL3Vi3oEE=",
         ),
         (  # 2 - Sign P2TR Mainnet
             [
@@ -432,7 +429,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             False,
             "a test message with a colon ':' character.",
             "3. 38CahkV…sEAN",
-            "HyH8898c2S6eF8hTPGhRqLC6UQrJrhw/fdguBeFG0cCrOFkbG8TCVURXOgxXaEV93vrFlHyxNGEvL10IcsLtvvI=",
+            "IyH8898c2S6eF8hTPGhRqLC6UQrJrhw/fdguBeFG0cCrOFkbG8TCVURXOgxXaEV93vrFlHyxNGEvL10IcsLtvvI=",
         ),
         (  # 5 - Sign P2WPKH Mainnet - Save to SD card
             [
@@ -449,7 +446,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             True,  # Sign to SD
             "A test message.",
             "3. bc1qgl5…3cn3",
-            "IN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
+            "KN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
         ),
         (  # 6 - Sign P2WPKH Mainnet - Load from and save to SD card
             [
@@ -468,7 +465,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             True,  # Sign to SD
             "A test message.",
             "3. bc1qgl5…3cn3",
-            "IN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
+            "KN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
         ),
         (  # 7 - Sign empty - Load from and save to SD card
             [
@@ -488,7 +485,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
             True,  # Sign to SD
             "A test message.",
             "3. bc1qgl…cn3",
-            "IN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
+            "KN/4LmcGRaI5sgvBP2mrTXQFvD6FecXd8La03SixPabsb/255ElRGTcXhicT3KFsNJbfQ9te909ZXeKMaqUcaPM=",
         ),
     ]
     case_count = 0
@@ -532,7 +529,7 @@ def test_sign_message_at_address(mocker, m5stickv, tdata):
 
         if case[2] != b"":
             ctx.display.draw_hcentered_text.assert_has_calls(
-                [mocker.call("Message:", 10, theme.highlight_color)]
+                [mocker.call("Message:", mocker.ANY, theme.highlight_color)]
             )
             ctx.display.draw_hcentered_text.assert_has_calls(
                 [mocker.call(case[4], mocker.ANY, max_lines=10)]
@@ -577,20 +574,12 @@ def test_load_from_sd_card(mocker, m5stickv, tdata):
 
     ctx = create_ctx(mocker, btn_seq, wallet)
     sign_msg = SignMessage(ctx)
-
-    # test sign at address with binary content (it can't be decoded to UTF8 and it is not sign to address)
-    sign_msg._sign_at_address_from_sd(file_content) == None
-
-    # mock load of file
+    assert sign_msg._sign_at_address_from_sd(file_content) is None
     sign_msg._load_message = lambda: (file_content, FORMAT_NONE, filename)
 
     mocker.spy(sign_msg, "_export_signature")
     mocker.spy(sign_msg, "_export_to_qr")
-
-    # Successful sign a binary (that can't be decoded) from sd card
     sign_msg.sign_message()
-
-    # Assert signature sucessfully exported to QR
     sign_msg._export_signature.assert_called()
     sign_msg._export_to_qr.assert_called()