Merge bitcoin/bitcoin#28154: test: refactor: deduplicate segwitv0 ECDSA signing for tx inputs

83d7cfd5429b0be7755bc48145032956f5f56dae test: refactor: deduplicate segwitv0 ECDSA signing for tx inputs (Sebastian Falbesoner)

Pull request description:

  This PR is a simple follow-up for #28025. It introduces a `signing_input_segwitv0` helper in order to deduplicate the following steps needed to create a segwitv0 ECDSA signature:
  1. calculate the `SegwitV0SignatureHash` 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 (plus sighash byte) at the bottom of the witness stack

ACKs for top commit:
  achow101:
    ACK 83d7cfd5429b0be7755bc48145032956f5f56dae
  pinheadmz:
    code review ACK at 83d7cfd5429b0be7755bc48145032956f5f56dae

Tree-SHA512: b8e55409ddc9ddb14cfc06daeb4730d7750a4632f175f88dcac6ec4d216e71fd4a7eee325a64d6ebba3b33be50bcd30c2de7400f834c01abb67e52840d9823b6

2 files changed, 18 insertions, 11 deletions

diff --git a/test/functional/p2p_segwit.py b/test/functional/p2p_segwit.py
index cfc177574f..b398ef51e1 100755
--- a/test/functional/p2p_segwit.py
+++ b/test/functional/p2p_segwit.py
@@ -70,9 +70,9 @@ from test_framework.script import (
     SIGHASH_ANYONECANPAY,
     SIGHASH_NONE,
     SIGHASH_SINGLE,
-    SegwitV0SignatureHash,
     hash160,
     sign_input_legacy,
+    sign_input_segwitv0,
 )
 from test_framework.script_util import (
     key_to_p2pk_script,
@@ -121,10 +121,8 @@ def subtest(func):
 
 def sign_p2pk_witness_input(script, tx_to, in_idx, hashtype, value, key):
     """Add signature for a P2PK witness script."""
-    tx_hash = SegwitV0SignatureHash(script, tx_to, in_idx, hashtype, value)
-    signature = key.sign_ecdsa(tx_hash) + chr(hashtype).encode('latin-1')
-    tx_to.wit.vtxinwit[in_idx].scriptWitness.stack = [signature, script]
-    tx_to.rehash()
+    tx_to.wit.vtxinwit[in_idx].scriptWitness.stack = [script]
+    sign_input_segwitv0(tx_to, in_idx, script, value, key, hashtype)
 
 def test_transaction_acceptance(node, p2p, tx, with_witness, accepted, reason=None):
     """Send a transaction to the node and check that it's accepted to the mempool
@@ -1476,11 +1474,9 @@ class SegWitTest(BitcoinTestFramework):
         tx2.vin.append(CTxIn(COutPoint(tx.sha256, 0), b""))
         tx2.vout.append(CTxOut(tx.vout[0].nValue - 1000, script_wsh))
         script = keyhash_to_p2pkh_script(pubkeyhash)
-        sig_hash = SegwitV0SignatureHash(script, tx2, 0, SIGHASH_ALL, tx.vout[0].nValue)
-        signature = key.sign_ecdsa(sig_hash) + b'\x01'  # 0x1 is SIGHASH_ALL
         tx2.wit.vtxinwit.append(CTxInWitness())
-        tx2.wit.vtxinwit[0].scriptWitness.stack = [signature, pubkey]
-        tx2.rehash()
+        tx2.wit.vtxinwit[0].scriptWitness.stack = [pubkey]
+        sign_input_segwitv0(tx2, 0, script, tx.vout[0].nValue, key)
 
         # Should fail policy test.
         test_transaction_acceptance(self.nodes[0], self.test_node, tx2, True, False, 'non-mandatory-script-verify-flag (Using non-compressed keys in segwit)')
@@ -1676,11 +1672,13 @@ class SegWitTest(BitcoinTestFramework):
         tx2.vout.append(CTxOut(tx.vout[0].nValue, CScript([OP_TRUE])))
 
         script = keyhash_to_p2pkh_script(pubkeyhash)
-        sig_hash = SegwitV0SignatureHash(script, tx2, 0, SIGHASH_ALL, tx.vout[0].nValue)
-        signature = key.sign_ecdsa(sig_hash) + b'\x01'  # 0x1 is SIGHASH_ALL
+        tx2.wit.vtxinwit.append(CTxInWitness())
+        sign_input_segwitv0(tx2, 0, script, tx.vout[0].nValue, key)
+        signature = tx2.wit.vtxinwit[0].scriptWitness.stack.pop()
 
         # Check that we can't have a scriptSig
         tx2.vin[0].scriptSig = CScript([signature, pubkey])
+        tx2.rehash()
         block = self.build_next_block()
         self.update_witness_block_with_transactions(block, [tx, tx2])
         test_witness_block(self.nodes[0], self.test_node, block, accepted=False,
diff --git a/test/functional/test_framework/script.py b/test/functional/test_framework/script.py
index 78f58cf11f..17a954cb22 100644
--- a/test/functional/test_framework/script.py
+++ b/test/functional/test_framework/script.py
@@ -699,6 +699,15 @@ def sign_input_legacy(tx, input_index, input_scriptpubkey, privkey, sighash_type
     tx.vin[input_index].scriptSig = bytes(CScript([der_sig + bytes([sighash_type])])) + tx.vin[input_index].scriptSig
     tx.rehash()
 
+def sign_input_segwitv0(tx, input_index, input_scriptpubkey, input_amount, privkey, sighash_type=SIGHASH_ALL):
+    """Add segwitv0 ECDSA signature for a given transaction input. Note that the signature
+       is inserted at the bottom of the witness stack, i.e. additional witness data
+       needed (e.g. pubkey for P2WPKH) can already be set before."""
+    sighash = SegwitV0SignatureHash(input_scriptpubkey, tx, input_index, sighash_type, input_amount)
+    der_sig = privkey.sign_ecdsa(sighash)
+    tx.wit.vtxinwit[input_index].scriptWitness.stack.insert(0, der_sig + bytes([sighash_type]))
+    tx.rehash()
+
 # TODO: Allow cached hashPrevouts/hashSequence/hashOutputs to be provided.
 # Performance optimization probably not necessary for python tests, however.
 # Note that this corresponds to sigversion == 1 in EvalScript, which is used