Merge bitcoin/bitcoin#25595: Verify PSBT inputs rather than check for fields being empty

e133264c5b1f72e94dcb9cebd85cdb523fcf8070 Add test for PSBT input verification (Greg Sanders)
d25699280af1ea45bebc884f63a10da7ea275ef9 Verify PSBT inputs rather than check for fields being empty (Greg Sanders)

Pull request description:

  In a few keys spots, PSBT finality is checked by looking for non-empty witness data.

  This complicates a couple things:
  1) Empty data can be valid in certain cases
  2) User may be passed bogus final data by a counterparty during PSBT work happening, and end up with incorrect signatures that they may not be able to check in other contexts if the UTXO doesn't exist yet in chain/mempool, timelocks, etc.

  On the whole I think these heavier checks are worth it in case someone is actually assuming the signatures are correct if our API is saying so.

ACKs for top commit:
  achow101:
    ACK e133264c5b1f72e94dcb9cebd85cdb523fcf8070

Tree-SHA512: 9de4fbb0be1257b081781f5df908fd55666e3acd5c4e36beb3b3f2f5a6aed69ff77068c44cde6127e159e773293fd9ced4c0bb47e693969f337e74dc8af030da

1 files changed, 14 insertions, 0 deletions

diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 1fe3b21542..3b78a7d095 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -27,8 +27,10 @@ from test_framework.psbt import (
     PSBT_IN_SHA256,
     PSBT_IN_HASH160,
     PSBT_IN_HASH256,
+    PSBT_IN_WITNESS_UTXO,
     PSBT_OUT_TAP_TREE,
 )
+from test_framework.script import CScript, OP_TRUE
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_approx,
@@ -852,6 +854,18 @@ class PSBTTest(BitcoinTestFramework):
         assert_raises_rpc_error(-8, "PSBTs not compatible (different transactions)", self.nodes[0].combinepsbt, [psbt1, psbt2])
         assert_equal(self.nodes[0].combinepsbt([psbt1, psbt1]), psbt1)
 
+        self.log.info("Test that PSBT inputs are being checked via script execution")
+        acs_prevout = CTxOut(nValue=0, scriptPubKey=CScript([OP_TRUE]))
+        tx = CTransaction()
+        tx.vin = [CTxIn(outpoint=COutPoint(hash=int('dd' * 32, 16), n=0), scriptSig=b"")]
+        tx.vout = [CTxOut(nValue=0, scriptPubKey=b"")]
+        psbt = PSBT()
+        psbt.g = PSBTMap({PSBT_GLOBAL_UNSIGNED_TX: tx.serialize()})
+        psbt.i = [PSBTMap({bytes([PSBT_IN_WITNESS_UTXO]) : acs_prevout.serialize()})]
+        psbt.o = [PSBTMap()]
+        assert_equal(self.nodes[0].finalizepsbt(psbt.to_base64()),
+            {'hex': '0200000001dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd0000000000000000000100000000000000000000000000', 'complete': True})
+
 
 if __name__ == '__main__':
     PSBTTest().main()