What a pain in the ass. This changes the `feature_cltv` functional test
to use the `MiniWallet`, an internal Pythonic wallet that produces
"signatures" consisting of several OP_NOPs in a row, so that this test
can be used when the wallet is disabled.
This means that the functions in feature_cltv which add a CLTV check and
change the locktime/sequence number no longer need to re-sign when they
change the txid, so they don't...HOWEVER, our Elements-specific
`feature_block_v4` test calls these functions with a real transaction
and depended on the re-signing behavior.
After several attempts at min-effort min-diff fixes I landed on this,
which simply sets the locktime at transaction creation and avoids having
to re-sign at all.
Also, I had to change the number of NOPs in the fake wallet code to make
a vsize assertion pass, presumably because of differences in Bitcoin/Elements
transaction serialization.
d6d2ab9845 test: MiniWallet: fix fee calculation for P2PK and check tx vsize (Sebastian Falbesoner)
ce024b1c0e test: MiniWallet: force P2PK signature to have fixed size (71 bytes) (Sebastian Falbesoner)
Pull request description:
This PR is a follow-up to #21945. It aims to both fix the fee calculation for P2PK mode transactions and enable its vsize check. Currently, the latter assumes a fixed tx length, which is fine for anyone-can-spend txs but doesn't apply to P2PK output spends due to varying DER signature size; the vsize check is therefore disabled for P2PK mode on master branch.
Creating one million DER signatures with MiniWallet shows the following distribution of sizes (smart people with better math skills probably could deduce the ratios without trying, but hey):
| DER signature size [bytes] | #occurences (ratio) |
| ------------- | ------------- |
| 71 | 498893 (49.89%) |
| 70 | 497244 (49.72%) |
| 69 | 3837 (0.38%) |
| 68 | 22 (0.0022%) |
Note that even smaller signatures are possible (for smaller R and S values with leading zero bytes), it's just that the probability decreases exponentially. Instead of choosing a large vsize check range and hoping that smaller signatures are never created (potentially leading to flaky tests), the proposed solution is ~~to limit the signature size to the two most common sizes 71 and 70 (>99.6% probability) and then accordingly only check for two vsize values; the value to be used for fee calculation is a decimal right between the two possible sizes (167.5 vbytes) and for the vsize check it's rounded down/up integer values are used.~~ to simply grind the signature to a fixed size of 71 bytes (49.89% probability, i.e. on average each call to `sign_tx()`, on average two ECC signing operations are needed).
~~The idea of grinding signatures to a fixed size (similar to https://github.com/bitcoin/bitcoin/pull/13666 which grinds to low-R values) would be counter-productive, as the signature creation in the test suite is quite expensive and this would significantly slow down tests that calculate hundreds of signatures (like e.g. feature_csv_activation.py).~~
For more about transaction sizes on different input/output types, see the following interesting article: https://medium.com/coinmonks/on-bitcoin-transaction-sizes-97e31bc9d816
ACKs for top commit:
MarcoFalke:
Concept ACK d6d2ab9845
Tree-SHA512: 011c70ee0e4adf9ba12902e4b6c411db9ae96bdd8bc810bf1d67713367998e28ea328394503371fc1f5087a819547ddaea56c073b28db893ae1c0031d7927f32
In order to enable exact fee calculation for transactions that spend
P2PK outputs in the MiniWallet, we enforce the created signatures to
have a fixed length (>49.89% probability) by default. With that it is
easier to check the created transactions vsize and avoid flaky tests
that would appear whenever the signatures R- or S-values are smaller
(due to leading zero bytes).
Note that to get the total scriptSig size one has to add another
2 bytes, as there is also the OP_PUSHx instruction on the front and
the sighash type byte on the back, leading to a final scriptSig size
of 73 bytes.
- run mempool_reorg.py even when the wallet is not compiled
- add `locktime` argument to `create_self_transfer` and `send_self_transfer`
- use more logs instead of comments
For the MiniWallet constructor, the two boolean parameters
"raw_script" and "use_p2pk" are replaced by a single parameter of the
newly introduced type MiniWalletMode (derived by enum.Enum), which can
hold the following values:
- ADDRESS_OP_TRUE
- RAW_OP_TRUE
- RAW_P2PK
Adds two new features to MiniWallet:
* The fee rate is irrelevant sometimes, so just set an arbitrary default
* The utxo to spend needs to be selected manually sometimes
