Fix signmessage to be Electrum-compatible

Verification of message signatures against segwit addresses
is not currently functional/possible in Core, and additionally
the signing function used for messages in jmbitcoin, derived
from coincurve, was not compatible with Electrum either.
This commit uses the functionality in python-bitcointx's
signmessage module, and now the wallet method `signmessage`
creates signatures on messages against segwit addresses that
are verifiable in Electrum.
Test cases of p2sh and native are added.

jmbitcoin/jmbitcoin/__init__.py

@@ -27,10 +27,12 @@ from bitcointx.core import (x, b2x, b2lx, lx, COutPoint, CTxOut, CTxIn,
                             coins_to_satoshi, satoshi_to_coins)
 from bitcointx.core.key import KeyStore
 from bitcointx.wallet import (P2SHCoinAddress, P2SHCoinAddressError,
-                              P2WPKHCoinAddress, P2WPKHCoinAddressError)
+                              P2WPKHCoinAddress, P2WPKHCoinAddressError,
+                              CBitcoinKey)
 from bitcointx.core.script import (CScript, OP_0, SignatureHash, SIGHASH_ALL,
                                    SIGVERSION_WITNESS_V0, CScriptWitness)
 from bitcointx.core.psbt import (PartiallySignedTransaction, PSBT_Input,
                                  PSBT_Output)
+from bitcointx.signmessage import SignMessage
 from .blocks import get_transactions_in_block
 

jmclient/jmclient/cryptoengine.py

@@ -218,13 +218,19 @@ class BTCEngine(object):
     @staticmethod
     def sign_message(privkey, message):
         """
+        Note: only (currently) used for manual
+        signing of text messages by keys,
+        *not* used in Joinmarket communication protocol.
         args:
             privkey: bytes
             message: bytes
         returns:
             base64-encoded signature
         """
-        return btc.ecdsa_sign(message, privkey, True, False)
+        # note: only supported on mainnet
+        assert get_network() == "mainnet"
+        k = btc.CBitcoinKey(BTCEngine.privkey_to_wif(privkey))
+        return btc.SignMessage(k, btc.BitcoinMessage(message)).decode("ascii")
 
     @classmethod
     def script_to_address(cls, script):

jmclient/jmclient/wallet_utils.py

@@ -1052,7 +1052,17 @@ def wallet_dumpprivkey(wallet, hdpath):
     return wallet.get_wif_path(path)  # will raise exception on invalid path
 
 
-def wallet_signmessage(wallet, hdpath, message):
+def wallet_signmessage(wallet, hdpath, message, out_str=True):
+    """ Given a wallet, a BIP32 HD path (as can be output
+    from the display method) and a message string, returns
+    a base64 encoded signature along with the corresponding
+    address and message.
+    If `out_str` is True, returns human readable representation,
+    otherwise returns tuple of (signature, message, address).
+    """
+    if not get_network() == "mainnet":
+        return "Error: message signing is only supported on mainnet."
+
     msg = message.encode('utf-8')
 
     if not hdpath:
@@ -1062,8 +1072,12 @@ def wallet_signmessage(wallet, hdpath, message):
 
     path = wallet.path_repr_to_path(hdpath)
     sig = wallet.sign_message(msg, path)
-    retval = "Signature: {}\nTo verify this in Bitcoin Core".format(sig)
-    return retval + " use the RPC command 'verifymessage'"
+    addr = wallet.get_address_from_path(path)
+    if not out_str:
+        return (sig, message, addr)
+    return ("Signature: {}\nMessage: {}\nAddress: {}\n"
+    "To verify this in Electrum use Tools->Sign/verify "
+    "message.".format(sig, message, addr))
 
 def wallet_signpsbt(wallet_service, psbt):
     if not psbt:

jmclient/test/test_walletutils.py

@@ -1,7 +1,39 @@
+import pytest
+from jmbitcoin import select_chain_params
+from jmclient import (SegwitLegacyWallet, SegwitWallet, get_network,
+                      jm_single, VolatileStorage, load_test_config)
+from jmclient.wallet_utils import (bip32pathparse, WalletView,
+                                   WalletViewAccount, WalletViewBranch,
+                                   WalletViewEntry, wallet_signmessage)
 
-from jmclient.wallet_utils import bip32pathparse, WalletView, \
-    WalletViewAccount, WalletViewBranch, WalletViewEntry
-
+# The below signatures have all been verified against Electrum 4.0.9:
+@pytest.mark.parametrize('seed, hdpath, walletcls, message, sig, addr', [
+    [b"\x01"*16, "m/84'/0'/0'/0/0", SegwitWallet, "hello",
+     "IOLk6ct/8aKtvTNnEAc+xojIWKv5FOwnzHGcnHkTJJwRBAyhrZ2ZyB0Re+dKS4SEav3qgjQeqMYRm+7mHi4sFKA=",
+     "bc1qq53d9372u8d50jfd5agq9zv7m7zdnzwducuqgz"],
+    [b"\x01"*16, "m/49'/0'/0'/0/0", SegwitLegacyWallet, "hello",
+     "HxVaQuXyBpl1UKutiusJjeLfKHwJYBzUiWuu6hEbmNFeSZGt/mbXKJ071ANR1gvdICbS/AnEa2RKDq9xMd/nU8s=",
+     "3AdTcqdoLHFGNq6znkahJDT41u65HAwiRv"],
+    [b"\x02"*16, "m/84'/0'/2'/1/0", SegwitWallet, "sign me",
+     "IA/V5DG7u108aNzCnpNPHqfrJAL8pF4GQ0sSqpf4Vlg5UWizauXzh2KskoD6Usl13hzqXBi4XDXl7Xxo5z6M298=",
+     "bc1q8mm69xs740sr0l2umrhmpl4ewhxfudxg2zvjw5"],
+    [b"\x02"*16, "m/49'/0'/2'/1/0", SegwitLegacyWallet, "sign me",
+     "H4cAtoE+zL+Mr+U8jm9DiYxZlym5xeZM3mcgymLz+TF4YYr4lgnM8qTZhFwlK4izcPaLuF27LFEoGJ/ltleIHUI=",
+     "3Qan1D4Vcy1yMGHfR9j7szDuC8QxSFVScA"],
+])
+def test_signmessage(seed, hdpath, walletcls, message, sig, addr):
+    load_test_config()
+    jm_single().config.set('BLOCKCHAIN', 'network', 'mainnet')
+    select_chain_params("bitcoin/mainnet")
+    storage = VolatileStorage()
+    walletcls.initialize(
+        storage, get_network(), entropy=seed, max_mixdepth=3)
+    wallet = walletcls(storage)
+    s, m, a = wallet_signmessage(wallet, hdpath, message,
+                                        out_str=False)
+    assert (s, m, a) == (sig, message, addr)
+    jm_single().config.set("BLOCKCHAIN", "network", "testnet")
+    select_chain_params("bitcoin/regtest")
 
 def test_bip32_pathparse():
     assert bip32pathparse("m/2/1/0017")