Merge pull request #5494 from SomberNight/tx_signing_perf_20190708

transaction: segwit input signing was doing quadratic hashing

electrum/transaction.py

@@ -86,6 +86,12 @@ class TxOutputHwInfo(NamedTuple):
     script_type: str
 
 
+class BIP143SharedTxDigestFields(NamedTuple):
+    hashPrevouts: str
+    hashSequence: str
+    hashOutputs: str
+
+
 class BCDataStream(object):
     """Workalike python implementation of Bitcoin's CDataStream class."""
 
@@ -958,7 +964,18 @@ class Transaction:
         s += script
         return s
 
-    def serialize_preimage(self, txin_index: int) -> str:
+    def _calc_bip143_shared_txdigest_fields(self) -> BIP143SharedTxDigestFields:
+        inputs = self.inputs()
+        outputs = self.outputs()
+        hashPrevouts = bh2u(sha256d(bfh(''.join(self.serialize_outpoint(txin) for txin in inputs))))
+        hashSequence = bh2u(sha256d(bfh(''.join(int_to_hex(txin.get('sequence', 0xffffffff - 1), 4) for txin in inputs))))
+        hashOutputs = bh2u(sha256d(bfh(''.join(self.serialize_output(o) for o in outputs))))
+        return BIP143SharedTxDigestFields(hashPrevouts=hashPrevouts,
+                                          hashSequence=hashSequence,
+                                          hashOutputs=hashOutputs)
+
+    def serialize_preimage(self, txin_index: int, *,
+                           bip143_shared_txdigest_fields: BIP143SharedTxDigestFields = None) -> str:
         nVersion = int_to_hex(self.version, 4)
         nHashType = int_to_hex(1, 4)  # SIGHASH_ALL
         nLocktime = int_to_hex(self.locktime, 4)
@@ -966,9 +983,11 @@ class Transaction:
         outputs = self.outputs()
         txin = inputs[txin_index]
         if self.is_segwit_input(txin):
-            hashPrevouts = bh2u(sha256d(bfh(''.join(self.serialize_outpoint(txin) for txin in inputs))))
-            hashSequence = bh2u(sha256d(bfh(''.join(int_to_hex(txin.get('sequence', 0xffffffff - 1), 4) for txin in inputs))))
-            hashOutputs = bh2u(sha256d(bfh(''.join(self.serialize_output(o) for o in outputs))))
+            if bip143_shared_txdigest_fields is None:
+                bip143_shared_txdigest_fields = self._calc_bip143_shared_txdigest_fields()
+            hashPrevouts = bip143_shared_txdigest_fields.hashPrevouts
+            hashSequence = bip143_shared_txdigest_fields.hashSequence
+            hashOutputs = bip143_shared_txdigest_fields.hashOutputs
             outpoint = self.serialize_outpoint(txin)
             preimage_script = self.get_preimage_script(txin)
             scriptCode = var_int(len(preimage_script) // 2) + preimage_script
@@ -1129,6 +1148,7 @@ class Transaction:
 
     def sign(self, keypairs) -> None:
         # keypairs:  (x_)pubkey -> secret_bytes
+        bip143_shared_txdigest_fields = self._calc_bip143_shared_txdigest_fields()
         for i, txin in enumerate(self.inputs()):
             pubkeys, x_pubkeys = self.get_sorted_pubkeys(txin)
             for j, (pubkey, x_pubkey) in enumerate(zip(pubkeys, x_pubkeys)):
@@ -1142,14 +1162,15 @@ class Transaction:
                     continue
                 _logger.info(f"adding signature for {_pubkey}")
                 sec, compressed = keypairs.get(_pubkey)
-                sig = self.sign_txin(i, sec)
+                sig = self.sign_txin(i, sec, bip143_shared_txdigest_fields=bip143_shared_txdigest_fields)
                 self.add_signature_to_txin(i, j, sig)
 
         _logger.info(f"is_complete {self.is_complete()}")
         self.raw = self.serialize()
 
-    def sign_txin(self, txin_index, privkey_bytes) -> str:
-        pre_hash = sha256d(bfh(self.serialize_preimage(txin_index)))
+    def sign_txin(self, txin_index, privkey_bytes, *, bip143_shared_txdigest_fields=None) -> str:
+        pre_hash = sha256d(bfh(self.serialize_preimage(txin_index,
+                                                       bip143_shared_txdigest_fields=bip143_shared_txdigest_fields)))
         privkey = ecc.ECPrivkey(privkey_bytes)
         sig = privkey.sign_transaction(pre_hash)
         sig = bh2u(sig) + '01'