Merge #492: Privacy improvements for direct_send()

c23808f054 Privacy improvements for direct_send() (Kristaps Kaupe)

Pull request description:

  * Shuffle order of tx inputs and outputs
  * Set locktime for best anonset (Core, Electrum)

  Also make P2EP use the same locktime code instead of copy/paste. Note that Core / Electrum does not always set current block height as locktime, at random cases it sets some older value. This code does the same.

ACKs for top commit:
  AdamISZ:
    But since I don't think that's critical at all, utACK to c23808f054

Tree-SHA512: d0fb838b4fdee8be3ce8c1f38f110655697bf77c361a00b299128e7af5da8dc82aca7b7302b610b25a9037493a97496263a83d504d04cfa88070bc0032781885

jmclient/jmclient/__init__.py

@@ -17,7 +17,7 @@ from .taker import Taker, P2EPTaker
 from .wallet import (Mnemonic, estimate_tx_fee, WalletError, BaseWallet, ImportWalletMixin,
                      BIP39WalletMixin, BIP32Wallet, BIP49Wallet, LegacyWallet,
                      SegwitWallet, SegwitLegacyWallet, UTXOManager,
-                     WALLET_IMPLEMENTATIONS)
+                     WALLET_IMPLEMENTATIONS, compute_tx_locktime)
 from .storage import (Argon2Hash, Storage, StorageError, RetryableStorageError,
                       StoragePasswordError, VolatileStorage)
 from .cryptoengine import BTCEngine, BTC_P2PKH, BTC_P2SH_P2WPKH, EngineError

jmclient/jmclient/blockchaininterface.py

@@ -388,6 +388,10 @@ class BitcoinCoreInterface(BlockchainInterface):
             return 10000
         return int(Decimal(1e8) * Decimal(estimate))
 
+    def get_current_block_height(self):
+        return self.rpc("getblockchaininfo", [])["blocks"]
+
+
 class RegtestBitcoinCoreMixin():
     """
     This Mixin provides helper functions that are used in Interface classes

jmclient/jmclient/maker.py

@@ -13,7 +13,7 @@ from binascii import unhexlify
 
 from jmbitcoin import SerializationError, SerializationTruncationError
 import jmbitcoin as btc
-from jmclient.wallet import estimate_tx_fee
+from jmclient.wallet import estimate_tx_fee, compute_tx_locktime
 from jmclient.wallet_service import WalletService
 from jmclient.configure import jm_single
 from jmbase.support import get_log, EXIT_SUCCESS, EXIT_FAILURE
@@ -605,11 +605,7 @@ class P2EPMaker(Maker):
                      "value": new_change_amount})
         new_ins = [x[1] for x in utxo.values()]
         new_ins.extend(my_utxos.keys())
-        # set locktime for best anonset (Core, Electrum) - most recent block.
-        # this call should never fail so no catch here.
-        currentblock = jm_single().bc_interface.rpc(
-            "getblockchaininfo", [])["blocks"]
-        new_tx = btc.make_shuffled_tx(new_ins, new_outs, False, 2, currentblock)
+        new_tx = btc.make_shuffled_tx(new_ins, new_outs, False, 2, compute_tx_locktime())
         new_tx_deser = btc.deserialize(new_tx)
 
         # sign our inputs before transfer

jmclient/jmclient/taker.py

@@ -16,7 +16,7 @@ from jmclient.configure import jm_single, validate_address
 from jmbase.support import get_log
 from jmclient.support import (calc_cj_fee, weighted_order_choose, choose_orders,
                               choose_sweep_orders)
-from jmclient.wallet import estimate_tx_fee
+from jmclient.wallet import estimate_tx_fee, compute_tx_locktime
 from jmclient.podle import generate_podle, get_podle_commitments, PoDLE
 from jmclient.wallet_service import WalletService
 from .output import generate_podle_error_string
@@ -1007,14 +1007,10 @@ class P2EPTaker(Taker):
         if self.my_change_addr is not None:
             self.outputs.append({'address': self.my_change_addr,
                                  'value': my_change_value})
-        # set locktime for best anonset (Core, Electrum) - most recent block.
-        # this call should never fail so no catch here.
-        currentblock = jm_single().bc_interface.rpc(
-            "getblockchaininfo", [])["blocks"]
         # As for JM coinjoins, the `None` key is used for our own inputs
         # to the transaction; this preparatory version contains only those.
         tx = btc.make_shuffled_tx(self.utxos[None], self.outputs,
-                              False, 2, currentblock)
+                              False, 2, compute_tx_locktime())
         jlog.info('Created proposed fallback tx\n' + pprint.pformat(
             btc.deserialize(tx)))
         # We now sign as a courtesy, because if we disappear the recipient

jmclient/jmclient/taker_utils.py

@@ -11,8 +11,9 @@ from jmbase import get_log, jmprint
 from .configure import jm_single, validate_address
 from .schedule import human_readable_schedule_entry, tweak_tumble_schedule,\
     schedule_to_text
-from .wallet import BaseWallet, estimate_tx_fee
-from jmbitcoin import deserialize, mktx, serialize, txhash, amount_to_str
+from .wallet import BaseWallet, estimate_tx_fee, compute_tx_locktime
+from jmbitcoin import deserialize, make_shuffled_tx, serialize, txhash,\
+    amount_to_str
 from jmbase.support import EXIT_SUCCESS
 log = get_log()
 
@@ -78,7 +79,8 @@ def direct_send(wallet_service, amount, mixdepth, destaddr, answeryes=False,
     log.info("Using a fee of : " + amount_to_str(fee_est) + ".")
     if amount != 0:
         log.info("Using a change value of: " + amount_to_str(changeval) + ".")
-    txsigned = sign_tx(wallet_service, mktx(list(utxos.keys()), outs), utxos)
+    txsigned = sign_tx(wallet_service, make_shuffled_tx(
+        list(utxos.keys()), outs, False, 2, compute_tx_locktime()), utxos)
     log.info("Got signed transaction:\n")
     log.info(pformat(txsigned))
     tx = serialize(txsigned)

jmclient/jmclient/wallet.py

@@ -7,6 +7,7 @@ import warnings
 import functools
 import collections
 import numbers
+import random
 from binascii import hexlify, unhexlify
 from datetime import datetime
 from copy import deepcopy
@@ -92,6 +93,16 @@ def estimate_tx_fee(ins, outs, txtype='p2pkh'):
         raise NotImplementedError("Txtype: " + txtype + " not implemented.")
 
 
+def compute_tx_locktime():
+    # set locktime for best anonset (Core, Electrum)
+    # most recent block or some time back in random cases
+    locktime = jm_single().bc_interface.get_current_block_height()
+    if random.randint(0, 9) == 0:
+        # P2EP requires locktime > 0
+        locktime = max(1, locktime - random.randint(0, 99))
+    return locktime
+
+
 #FIXME: move this to a utilities file?
 def deprecated(func):
     @functools.wraps(func)