partial impl. of @dipunm's feedback in issue SeedSigner#43

* Cannot SeedXOR against a seed's inversion.
* Cannot SeedXOR against a seed w/ passphrase.

src/seedsigner/models/seed.py

@@ -114,14 +114,17 @@ def get_xpub(self, wallet_path: str = '/', network: str = SettingsConstants.MAIN
         return embit_utils.get_xpub(seed_bytes=self.seed_bytes, derivation_path=wallet_path, embit_network=SettingsConstants.map_network_to_embit(network))
 
     def seed_xor(self, other):
-        if len(self.mnemonic_list) != len(other.mnemonic_list):
+        def xor_bytes(a, b):
+            return bytes(i^j for i, j in zip(a, b))
+        self_entropy = bip39.mnemonic_to_bytes(self.mnemonic_str)
+        other_entropy = bip39.mnemonic_to_bytes(other.mnemonic_str)
+        if len(self_entropy) != len(other_entropy):
             raise Exception("XOR requires seeds of similar mnemonic length!")
-        if self.mnemonic_list == other.mnemonic_list:
+        if self_entropy == other_entropy:
             raise Exception("You may not XOR a seed with itself.")
-        new_entropy = bytes(i^j for i,j in zip(
-            bip39.mnemonic_to_bytes(self.mnemonic_str),
-            bip39.mnemonic_to_bytes(other.mnemonic_str)
-        ))
+        if self_entropy == xor_bytes(other_entropy, b'\xff'*len(other_entropy)):
+            raise Exception("You may not XOR a seed with its inversion.")
+        new_entropy = xor_bytes(self_entropy, other_entropy)
         self._mnemonic = bip39.mnemonic_from_bytes(new_entropy).split()
         self._generate_seed()
 

src/seedsigner/views/seed_views.py

@@ -221,7 +221,10 @@ def run(self):
             button_data.append(PASSPHRASE)
 
         if self.settings.get_value(SettingsConstants.SETTING__SEED_XOR) == SettingsConstants.OPTION__ENABLED \
-        and len([x for x in self.controller.storage.seeds if len(x.mnemonic_list) == len(self.seed.mnemonic_list)]):
+        and len([x for x in self.controller.storage.seeds 			# todo: in 3 places, make it just 1
+                 if len(x.mnemonic_list) == len(self.seed.mnemonic_list) \
+                 and x.mnemonic_list != self.seed.mnemonic_list \
+                 and len(x.passphrase) == 0]):
             button_data.append(SEED_XOR)
 
         selected_menu_num = seed_screens.SeedFinalizeScreen(
@@ -309,7 +312,10 @@ def __init__(self):
         self.seed = self.controller.storage.get_pending_seed()
 
     def run(self):
-        seeds = [x for x in self.controller.storage.seeds if len(x.mnemonic_list) == len(self.seed.mnemonic_list)]
+        seeds = [x for x in self.controller.storage.seeds 			# todo: in many places, make it just 1
+                 if len(x.mnemonic_list) == len(self.seed.mnemonic_list) \
+                 and x.mnemonic_list != self.seed.mnemonic_list \
+                 and len(x.passphrase) == 0]
         title = "Seed XOR"
         text = "Select seed to XOR"
         button_data = []
@@ -337,7 +343,10 @@ class SeedXORApplyView(View):
     def __init__(self, seed_num: int = None):
         super().__init__()
         self.seed = self.controller.storage.get_pending_seed()
-        seeds = [x for x in self.controller.storage.seeds if len(x.mnemonic_list) == len(self.seed.mnemonic_list)]
+        seeds = [x for x in self.controller.storage.seeds 			# todo: in many places, make it just 1
+                 if len(x.mnemonic_list) == len(self.seed.mnemonic_list) \
+                 and x.mnemonic_list != self.seed.mnemonic_list \
+                 and len(x.passphrase) == 0]
         if seed_num is not None:
             self.other = seeds[seed_num]