shuffle transaction inputs and outputs

Change strategy regarding transaction inputs/outputs ordering. The node shuffles inputs and outputs, while Electrum was sorting them in a deterministic order. Both strategies are viable ways of improving user privacy, but the randomization helps also users of other wallets. If most wallets apply randomization, then the few wallets that don't will stand out less. It will be difficult to guess if a simple transaction (one or two inputs, two outputs) that matches some sorting rules did it intentionnaly or by random luck.

electrumabc/transaction.py

@@ -24,6 +24,7 @@
 # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 import hashlib
+import random
 import struct
 import warnings
 from typing import Optional, Tuple, Union
@@ -780,10 +781,9 @@ def serialize_input(self, txin, script, estimate_size=False):
             s += bitcoin.int_to_hex(txin["value"], 8)
         return s
 
-    def BIP_LI01_sort(self):
-        # See https://github.com/kristovatlas/rfc/blob/master/bips/bip-li01.mediawiki
-        self._inputs.sort(key=lambda i: (i["prevout_hash"], i["prevout_n"]))
-        self._outputs.sort(key=lambda o: (o[2], self.pay_script(o[1])))
+    def shuffle_inputs_outputs(self):
+        random.shuffle(self._inputs)
+        random.shuffle(self._outputs)
 
     def serialize_output(self, output):
         output_type, addr, amount = output

electrumabc/wallet.py

@@ -209,7 +209,7 @@ def sweep(
     tx = Transaction.from_io(
         inputs, outputs, locktime=locktime, sign_schnorr=sign_schnorr
     )
-    tx.BIP_LI01_sort()
+    tx.shuffle_inputs_outputs()
     tx.sign(keypairs)
     return tx
 
@@ -2160,8 +2160,7 @@ def fee_estimator(size):
         if sats_per_byte > 100:
             raise ExcessiveFee()
 
-        # Sort the inputs and outputs deterministically
-        tx.BIP_LI01_sort()
+        tx.shuffle_inputs_outputs()
         # Timelock tx to current height.
         locktime = 0
         if config.is_current_block_locktime_enabled():
@@ -2440,7 +2439,7 @@ def cpfp(self, tx, fee, sign_schnorr=None, enable_current_block_locktime=True):
         locktime = 0
         if enable_current_block_locktime:
             locktime = self.get_local_height()
-        # note: no need to call tx.BIP_LI01_sort() here - single input/output
+        # note: no need to call tx.shuffle_inputs_outputs here - single input/output
         return Transaction.from_io(
             inputs, outputs, locktime=locktime, sign_schnorr=sign_schnorr
         )