xmr: step 03 review

src/apps/monero/protocol/signing/step_03_inputs_permutation.py

@@ -1,32 +1,39 @@
 """
-Set permutation on the inputs - sorted by key image on host.
+Inputs in transaction need to be sorted by their key image, otherwise the
+transaction is rejected. The sorting is done on host and then sent here in
+the MoneroTransactionInputsPermutationRequest message.
+
+The message contains just a simple array where each item stands for the
+input's position in the transaction.
+
+We do not do the actual sorting here (we do not store the complete input
+data anyway, so we can't) we just save the array to the state and use
+it later when needed.
 """
 
 from .state import State
 
 from apps.monero.layout.confirms import transaction_step
-from apps.monero.xmr import common
 
 
-async def tsx_inputs_permutation(state: State, permutation):
-    """
-    Set permutation on the inputs - sorted by key image on host.
-    """
+async def tsx_inputs_permutation(state: State, permutation: list):
     from trezor.messages.MoneroTransactionInputsPermutationAck import (
         MoneroTransactionInputsPermutationAck
     )
 
     await transaction_step(state.ctx, state.STEP_PERM)
 
-    _tsx_inputs_permutation(state, permutation)
-
-    return MoneroTransactionInputsPermutationAck()
-
-
-def _tsx_inputs_permutation(state: State, permutation):
     """
     Set permutation on the inputs - sorted by key image on host.
     """
     state.source_permutation = permutation
-    common.check_permutation(permutation)
+    _check_permutation(permutation)
     state.current_input_index = -1
+
+    return MoneroTransactionInputsPermutationAck()
+
+
+def _check_permutation(permutation):
+    for n in range(len(permutation)):
+        if n not in permutation:
+            raise ValueError("Invalid permutation")

src/apps/monero/xmr/common.py

@@ -9,31 +9,5 @@ def ct_equal(a, b):
     return monero.ct_equals(a, b)
 
 
-def check_permutation(permutation):
-    for n in range(len(permutation)):
-        if n not in permutation:
-            raise ValueError("Invalid permutation")
-
-
-def apply_permutation(permutation, swapper):
-    """
-    Apply permutation from idx. Used for in-place permutation application with swapper.
-    Ported from Monero.
-    :param permutation:
-    :param swapper: function(x,y)
-    :return:
-    """
-    check_permutation(permutation)
-    perm = list(permutation)
-    for i in range(len(perm)):
-        current = i
-        while i != perm[current]:
-            nxt = perm[current]
-            swapper(current, nxt)
-            perm[current] = current
-            current = nxt
-        perm[current] = current
-
-
 def is_empty(inp):
     return inp is None or len(inp) == 0