lnchannel: replace `assert htlc.payment_hash==sha256(preimage)` w/ exc

asserts should not be used for security checks

electrum/lnchannel.py

@@ -1428,7 +1428,8 @@ class Channel(AbstractChannel):
         self.logger.info("settle_htlc")
         assert self.can_send_ctx_updates(), f"cannot update channel. {self.get_state()!r} {self.peer_state!r}"
         htlc = self.hm.get_htlc_by_id(REMOTE, htlc_id)
-        assert htlc.payment_hash == sha256(preimage)
+        if htlc.payment_hash != sha256(preimage):
+            raise Exception("incorrect preimage for HTLC")
         assert htlc_id not in self.hm.log[REMOTE]['settles']
         self.hm.send_settle(htlc_id)
 
@@ -1450,7 +1451,8 @@ class Channel(AbstractChannel):
         """
         self.logger.info("receive_htlc_settle")
         htlc = self.hm.get_htlc_by_id(LOCAL, htlc_id)
-        assert htlc.payment_hash == sha256(preimage)
+        if htlc.payment_hash != sha256(preimage):
+            raise RemoteMisbehaving("received incorrect preimage for HTLC")
         assert htlc_id not in self.hm.log[LOCAL]['settles']
         with self.db_lock:
             self.hm.recv_settle(htlc_id)

electrum/lnworker.py

@@ -2048,15 +2048,21 @@ class LNWallet(LNWorker):
                 return key_list
 
     def save_preimage(self, payment_hash: bytes, preimage: bytes, *, write_to_disk: bool = True):
-        assert sha256(preimage) == payment_hash
+        if sha256(preimage) != payment_hash:
+            raise Exception("tried to save incorrect preimage for payment_hash")
         self.preimages[payment_hash.hex()] = preimage.hex()
         if write_to_disk:
             self.wallet.save_db()
 
     def get_preimage(self, payment_hash: bytes) -> Optional[bytes]:
         assert isinstance(payment_hash, bytes), f"expected bytes, but got {type(payment_hash)}"
-        r = self.preimages.get(payment_hash.hex())
-        return bytes.fromhex(r) if r else None
+        preimage_hex = self.preimages.get(payment_hash.hex())
+        if preimage_hex is None:
+            return None
+        preimage_bytes = bytes.fromhex(preimage_hex)
+        if sha256(preimage_bytes) != payment_hash:
+            raise Exception("found incorrect preimage for payment_hash")
+        return preimage_bytes
 
     def get_payment_info(self, payment_hash: bytes) -> Optional[PaymentInfo]:
         """returns None if payment_hash is a payment we are forwarding"""