Merge bitcoin/bitcoin#30352: policy: Add PayToAnchor(P2A), `OP_1 <0x4e73>` as a standard output script for spending

75648cea5a9032b3d388cbebacb94d908e08924e test: add P2A ProduceSignature coverage (Greg Sanders)
7998ce6b20fba62c022228355907b612ba6692e1 Add release note for P2A output feature (Greg Sanders)
71c9b02a04742eeecab14aae4697b1a3eb51ff7f test: add P2A coverage for decodescript (Greg Sanders)
1349e9ec1558484f2912a2444c410170fcec8745 test: Add anchor mempool acceptance test (Greg Sanders)
9d892099378b2ad5f52220403bdeae43c61d6955 policy: stop 3rd party wtxid malleability of anchor spend (Greg Sanders)
b60aaf8b239978947d2b0e3f56e7d8a4092d7570 policy: make anchor spend standard (Greg Sanders)
455fca86cfada1823aa28615b5683f9dc73dbb9a policy: Add OP_1 <0x4e73> as a standard output type (Greg Sanders)

Pull request description:

  This is a sub-feature taken out of the original proposal for ephemeral anchors #30239

  This PR makes *spending* of `OP_1 <0x4e73>` (i.e. `bc1pfeessrawgf`) standard. Creation of this output type is already standard.

  Any future witness output types are considered relay-standard to create, but not to spend. This preserves upgrade hooks, such as a completely new output type for a softfork such as BIP341.  It also gives us a bit of room to use a new output type for policy uses.

  This particular sized witness program has no other known use-cases (https://bitcoin.stackexchange.com/a/110664/17078), s it affords insufficient cryptographic security for a secure commitment to data, such as a script or a public key. This makes this type of output "keyless", or unauthenticated.

  As a witness program, the `scriptSig` of the input MUST be blank, by BIP141. This helps ensure txid-stability of the spending transaction, which may be required for smart contracting wallets. If we do not use segwit, a miner can simply insert an `OP_NOP` in the `scriptSig` without effecting the result of program execution.

  An additional relay restriction is to disallow non-empty witness data, which an adversary may use to penalize the "honest" transactor when RBF'ing the transaction due to the incremental fee requirement of RBF rules.

  The intended use-case for this output type is to "anchor" the transaction with a spending child to bring exogenous CPFP fees into the transaction package, encouraging the inclusion of the package in a block. The minimal size of creation and spending of this output makes it an attractive contrast to outputs like `p2sh(OP_TRUE)` and `p2wsh(OP_TRUE)` which
  are significantly larger in vbyte terms.

  Combined with TRUC transactions which limits the size of child transactions significantly, this is an attractive option for presigned transactions that need to be fee-bumped after the fact.

ACKs for top commit:
  sdaftuar:
    utACK 75648cea5a9032b3d388cbebacb94d908e08924e
  theStack:
    re-ACK 75648cea5a9032b3d388cbebacb94d908e08924e
  ismaelsadeeq:
    re-ACK 75648cea5a9032b3d388cbebacb94d908e08924e via [diff](https://github.com/bitcoin/bitcoin/compare/e7ce6dc070c0319cbb868d41cadd836b2e6ca9db..75648cea5a9032b3d388cbebacb94d908e08924e)
  glozow:
    ACK 75648cea5a9032b3d388cbebacb94d908e08924e
  tdb3:
    ACK 75648cea5a9032b3d388cbebacb94d908e08924e

Tree-SHA512: d529de23d20857e6cdb40fa611d0446b49989eaafed06c28280e8fd1897f1ed8d89a4eabbec1bbf8df3d319910066c3dbbba5a70a87ff0b2967d5205db32ad1e

1 files changed, 3 insertions, 0 deletions

diff --git a/test/functional/test_framework/script_util.py b/test/functional/test_framework/script_util.py
index 855f3b8cf5..938183ece4 100755
--- a/test/functional/test_framework/script_util.py
+++ b/test/functional/test_framework/script_util.py
@@ -8,6 +8,7 @@ import unittest
 from test_framework.script import (
     CScript,
     OP_0,
+    OP_1,
     OP_15,
     OP_16,
     OP_CHECKMULTISIG,
@@ -42,6 +43,8 @@ assert MIN_PADDING == 5
 DUMMY_MIN_OP_RETURN_SCRIPT = CScript([OP_RETURN] + ([OP_0] * (MIN_PADDING - 1)))
 assert len(DUMMY_MIN_OP_RETURN_SCRIPT) == MIN_PADDING
 
+PAY_TO_ANCHOR = CScript([OP_1, bytes.fromhex("4e73")])
+
 def key_to_p2pk_script(key):
     key = check_key(key)
     return CScript([key, OP_CHECKSIG])