Merge bitcoin#28025: test: refactor: deduplicate legacy ECDSA signing for tx inputs

5cf4427 test: refactor: deduplicate legacy ECDSA signing for tx inputs (Sebastian Falbesoner)

Pull request description:

  There are several instances in functional tests and the framework (MiniWallet, feature_block.py, p2p_segwit.py) where we create a legacy ECDSA signature for a certain transaction's input by doing the following steps:

  1. calculate the `LegacySignatureHash` with the desired sighash type
  2. create the actual digital signature by calling `ECKey.sign_ecdsa` on the signature message hash calculated above
  3. put the DER-encoded result as CScript data push into tx input's scriptSig

  Create a new helper `sign_input_legacy` which hides those details and takes only the necessary parameters (tx, input index, relevant scriptPubKey, private key, sighash type [SIGHASH_ALL by default]). For further convenience, the signature is prepended to already existing data-pushes in scriptSig, in order to avoid rehashing the transaction after calling the new signing function.

ACKs for top commit:
  dimitaracev:
    ACK `5cf4427`
  achow101:
    ACK 5cf4427
  pinheadmz:
    ACK 5cf4427

Tree-SHA512: 8f0e4fb2c3e0f84fac5dbc4dda87973276242b0f628034272a7f3e45434c1e17dd1b26a37edfb302dcaf380dbfe98b0417391ace5e0ac9720155d8fba702031e

Author: achow101

test/functional/feature_block.py

@@ -42,8 +42,7 @@
     OP_INVALIDOPCODE,
     OP_RETURN,
     OP_TRUE,
-    SIGHASH_ALL,
-    SignatureHash,
+    sign_input,
 )
 from test_framework.script_util import (
     script_to_p2sh_script,
@@ -551,12 +550,8 @@ def run_test(self):
             # second input is corresponding P2SH output from b39
             tx.vin.append(CTxIn(COutPoint(b39.vtx[i].sha256, 0), b''))
             # Note: must pass the redeem_script (not p2sh_script) to the signature hash function
-            (sighash, err) = SignatureHash(redeem_script, tx, 1, SIGHASH_ALL)
-            sig = self.coinbase_key.sign_ecdsa(sighash) + bytes(bytearray([SIGHASH_ALL]))
-            scriptSig = CScript([sig, redeem_script])
-
-            tx.vin[1].scriptSig = scriptSig
-            tx.rehash()
+            tx.vin[1].scriptSig = CScript([redeem_script])
+            sign_input(tx, 1, redeem_script, self.coinbase_key)
             new_txs.append(tx)
             lastOutpoint = COutPoint(tx.sha256, 0)
 
@@ -1354,8 +1349,7 @@ def sign_tx(self, tx, spend_tx):
         if (scriptPubKey[0] == OP_TRUE):  # an anyone-can-spend
             tx.vin[0].scriptSig = CScript()
             return
-        (sighash, err) = SignatureHash(spend_tx.vout[0].scriptPubKey, tx, 0, SIGHASH_ALL)
-        tx.vin[0].scriptSig = CScript([self.coinbase_key.sign_ecdsa(sighash) + bytes(bytearray([SIGHASH_ALL]))])
+        sign_input(tx, 0, spend_tx.vout[0].scriptPubKey, self.coinbase_key)
 
     def create_and_sign_transaction(self, spend_tx, value, script=CScript([OP_TRUE])):
         tx = self.create_tx(spend_tx, 0, value, script)

test/functional/test_framework/script.py

@@ -666,6 +666,17 @@ def SignatureHash(script, txTo, inIdx, hashtype):
 
     return (hash, None)
 
+def sign_input(tx, input_index, input_scriptpubkey, privkey, sighash_type=SIGHASH_ALL):
+    """Add legacy ECDSA signature for a given transaction input. Note that the signature
+       is prepended to the scriptSig field, i.e. additional data pushes necessary for more
+       complex spends than P2PK (e.g. pubkey for P2PKH) can be already set before."""
+    (sighash, err) = SignatureHash(input_scriptpubkey, tx, input_index, sighash_type)
+    assert err is None
+    der_sig = privkey.sign_ecdsa(sighash)
+    tx.vin[input_index].scriptSig = bytes(CScript([der_sig + bytes([sighash_type])])) + tx.vin[input_index].scriptSig
+    tx.rehash()
+
+
 class TestFrameworkScript(unittest.TestCase):
     def test_bn2vch(self):
         self.assertEqual(bn2vch(0), bytes([]))

test/functional/test_framework/wallet.py

@@ -30,10 +30,9 @@
 )
 from test_framework.script import (
     CScript,
-    SignatureHash,
     OP_TRUE,
     OP_NOP,
-    SIGHASH_ALL,
+    sign_input,
 )
 from test_framework.script_util import (
     key_to_p2pk_script,
@@ -134,18 +133,16 @@ def scan_tx(self, tx):
 
     def sign_tx(self, tx, fixed_length=True):
         if self._mode == MiniWalletMode.RAW_P2PK:
-            (sighash, err) = SignatureHash(CScript(self._scriptPubKey), tx, 0, SIGHASH_ALL)
-            assert err is None
             # for exact fee calculation, create only signatures with fixed size by default (>49.89% probability):
             # 65 bytes: high-R val (33 bytes) + low-S val (32 bytes)
-            # with the DER header/skeleton data of 6 bytes added, this leads to a target size of 71 bytes
-            der_sig = b''
-            while not len(der_sig) == 71:
-                der_sig = self._priv_key.sign_ecdsa(sighash)
+            # with the DER header/skeleton data of 6 bytes added, plus 2 bytes scriptSig overhead
+            # (OP_PUSHn and SIGHASH_ALL), this leads to a scriptSig target size of 73 bytes
+            tx.vin[0].scriptSig = b''
+            while not len(tx.vin[0].scriptSig) == 73:
+                tx.vin[0].scriptSig = b''
+                sign_input(tx, 0, self._scriptPubKey, self._priv_key)
                 if not fixed_length:
                     break
-            tx.vin[0].scriptSig = CScript([der_sig + bytes(bytearray([SIGHASH_ALL]))])
-            tx.rehash()
         elif self._mode == MiniWalletMode.RAW_OP_TRUE:
             for i in range(len(tx.vin)):
                 tx.vin[i].scriptSig = CScript([OP_NOP] * 24)  # pad to identical size