hardware wallets: wizard no longer requests xpub at path "m"

This was done to calculate the bip32 root fingerprint but it broke
the digitalbitbox. The keystore already had a different way to get
the root fingerprint for existing wallets, specifically handling this
case; the code in base_wizard used when creating new wallets was
duplicating that code originally and was then forgotten to be updated.
Now these codepaths are unified.

closes #5816

electrum/base_wizard.py

@@ -418,21 +418,23 @@ class BaseWizard(Logger):
 
     def on_hw_derivation(self, name, device_info, derivation, xtype):
         from .keystore import hardware_keystore
+        devmgr = self.plugins.device_manager
         try:
             xpub = self.plugin.get_xpub(device_info.device.id_, derivation, xtype, self)
-            root_xpub = self.plugin.get_xpub(device_info.device.id_, 'm', 'standard', self)
+            client = devmgr.client_by_id(device_info.device.id_)
+            if not client: raise Exception("failed to find client for device id")
+            root_fingerprint = client.request_root_fingerprint_from_device()
         except ScriptTypeNotSupported:
             raise  # this is handled in derivation_dialog
         except BaseException as e:
             self.logger.exception('')
             self.show_error(e)
             return
-        xfp = BIP32Node.from_xkey(root_xpub).calc_fingerprint_of_this_node().hex().lower()
         d = {
             'type': 'hardware',
             'hw_type': name,
             'derivation': derivation,
-            'root_fingerprint': xfp,
+            'root_fingerprint': root_fingerprint,
             'xpub': xpub,
             'label': device_info.label,
         }

electrum/keystore.py

@@ -709,11 +709,7 @@ class Hardware_KeyStore(KeyStore, Xpub):
     def opportunistically_fill_in_missing_info_from_device(self, client: 'HardwareClientBase'):
         assert client is not None
         if self._root_fingerprint is None:
-            # digitalbitbox (at least) does not reveal xpubs corresponding to unhardened paths
+            self._root_fingerprint = client.request_root_fingerprint_from_device()
-            # so ask for a direct child, and read out fingerprint from that:
-            child_of_root_xpub = client.get_xpub("m/0'", xtype='standard')
-            root_fingerprint = BIP32Node.from_xkey(child_of_root_xpub).fingerprint.hex().lower()
-            self._root_fingerprint = root_fingerprint
             self.is_requesting_to_be_rewritten_to_wallet_file = True
         if self.label != client.label():
             self.label = client.label()

electrum/plugins/hw_wallet/plugin.py

@@ -175,6 +175,13 @@ class HardwareClientBase:
     def get_xpub(self, bip32_path: str, xtype) -> str:
         raise NotImplementedError()
 
+    def request_root_fingerprint_from_device(self) -> str:
+        # digitalbitbox (at least) does not reveal xpubs corresponding to unhardened paths
+        # so ask for a direct child, and read out fingerprint from that:
+        child_of_root_xpub = self.get_xpub("m/0'", xtype='standard')
+        root_fingerprint = BIP32Node.from_xkey(child_of_root_xpub).fingerprint.hex().lower()
+        return root_fingerprint
+
 
 def is_any_tx_output_on_change_branch(tx: PartialTransaction) -> bool:
     return any([txout.is_change for txout in tx.outputs()])