Merge bitcoin#26341: test: add BIP158 false-positive element check in rpc_scanblocks.py

fa54d30 test: check for false-positives in rpc_scanblocks.py (Sebastian Falbesoner)
3bca6cd test: add compact block filter (BIP158) helper routines (Sebastian Falbesoner)
25ee74d test: add SipHash implementation for generic data in Python (Sebastian Falbesoner)

Pull request description:

  This PR adds a fixed false-positive element check to the functional test rpc_scanblocks.py by using a pre-calculated scriptPubKey that collides with the regtest genesis block's coinbase output. Note that determining a BIP158 false-positive at runtime would also be possible, but take too long (we'd need to create and check ~800k output scripts on average, which took at least 2 minutes on average on my machine).

  The introduced check is related to issue bitcoin#26322 and more concretely inspired by PR bitcoin#26325 which introduces an "accurate" mode that filters out these false-positives. The introduced cryptography routines (siphash for generic data) and helpers (BIP158 ranged hash calculation, relevant scriptPubKey per block determination) could potentially also be useful for more tests in the future that involve compact block filters.

ACKs for top commit:
  achow101:
    ACK fa54d30

Tree-SHA512: c6af50864146028228d197fb022ba2ff24d1ef48dc7d171bccfb21e62dd50ac80db5fae0c53f5d205edabd48b3493c7aa2040f628a223e68df086ec2243e5a93

Co-authored-by: Andrew Chow <github@achow101.com>

Author: knst

test/functional/rpc_scanblocks.py

@@ -3,6 +3,10 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test the scanblocks RPC call."""
+from test_framework.blockfilter import (
+    bip158_basic_element_hash,
+    bip158_relevant_scriptpubkeys,
+)
 from test_framework.messages import COIN
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -70,6 +74,28 @@ def run_test(self):
         assert(blockhash in node.scanblocks(
             "start", [{"desc": f"pkh({parent_key}/*)", "range": [0, 100]}], height)['relevant_blocks'])
 
+        # check that false-positives are included in the result now; note that
+        # finding a false-positive at runtime would take too long, hence we simply
+        # use a pre-calculated one that collides with the regtest genesis block's
+        # coinbase output and verify that their BIP158 ranged hashes match
+        genesis_blockhash = node.getblockhash(0)
+        genesis_spks = bip158_relevant_scriptpubkeys(node, genesis_blockhash)
+        assert_equal(len(genesis_spks), 1)
+        genesis_coinbase_spk = list(genesis_spks)[0]
+        false_positive_spk = bytes.fromhex("1400000000000000000000000000000000000ad23b")
+
+        genesis_coinbase_hash = bip158_basic_element_hash(genesis_coinbase_spk, 1, genesis_blockhash)
+        false_positive_hash = bip158_basic_element_hash(false_positive_spk, 1, genesis_blockhash)
+        assert_equal(genesis_coinbase_hash, false_positive_hash)
+
+        assert(genesis_blockhash in node.scanblocks(
+            "start", [{"desc": f"raw({genesis_coinbase_spk.hex()})"}], 0, 0)['relevant_blocks'])
+        assert(genesis_blockhash in node.scanblocks(
+            "start", [{"desc": f"raw({false_positive_spk.hex()})"}], 0, 0)['relevant_blocks'])
+
+        # TODO: after an "accurate" mode for scanblocks is implemented (e.g. PR #26325)
+        # check here that it filters out the false-positive
+
         # test node with disabled blockfilterindex
         assert_raises_rpc_error(-1, "Index is not enabled for filtertype basic",
                                 self.nodes[1].scanblocks, "start", [f"addr({addr_1})"])