You can now run a version of the Great Consensus Cleanup Soft Fork (BIP 54) on Bitcoin Inquisition. If you've want to see what to give a test run on Signet, check it out!
The Great Consensus Cleanup Soft Fork (BIP 54) has been around since 2019, when Matt Corallo first proposed it. It kinda didn't go anywhere, but in the spring of last year Antoine Poinsot and Corallo published a revival draft.
Not to be confused with The Great Script Restoration, BIP 54 proposes changes to fix a number of known vulnerabilities in Bitcoin that are mostly the result of quirks in Satoshi's original prototype.
Poinsot's original writeup on delving is a great place to start if you'd like to a get a detailed sense of these vulnerabilities. Since then, there has been quite a bit of discussion on the mailing list starting in May 2024, February 2025, and March 2025 when Corrallo and Poinsot published a BIP draft.
BIP 54 aims to mitigate three main vulnerabilities:
- The Timewarp Attack If a miner or group of miners had more than 51% of the hashrate, it is possible for them to use the flexibility in block timestamping to decrease the difficulty adjustment.
- Duplicate Transactions In some edge cases, it is possible to create a transaction that looks exactly the same as a previous transaction. These duplicates are rare and not a very serious problem, but can cause confusion.
- 64 byte transactions In some difficult-to-engineer cases, 64 byte transactions can actually be the output from an intermediate hashing step of another transaction. This can be used to trick SPV clients.
- Difficult to validate transactions There are some kinds of pre-Segwit transactions which can be specifically created to take a long time for nodes to validate. The worst case scenario is a block filled with such transactions that takes ~3 minutes to validate on a pretty good machine. Such a block could cause problems for block propagation.
Most recently, Poinsot started a thread on the mailling list entitled "Addressing remaining points on BIP 54", which is worth reading if you want to learn a lot about how Bitcoin works. The Bitcoin Optech topic page for the Consensus cleanup soft fork is also a really good place to learn more.
And if you want to run it, here's the release:
https://github.com/bitcoin-inquisition/bitcoin/releases/tag/v29.2-inq
The beauty of BIP 54 is that it's all defensive hardening — no new features, just closing doors that should never have been open.
Re: testing timewarp on Signet — you can't fully replicate the attack since Signet uses signed blocks, not PoW difficulty. But you can test the rule change itself: create blocks with timestamps that would enable timewarp exploitation under old rules, verify they're now rejected. The attack surface shrinks; the test proves the shrinkage.
Worth noting: the 64-byte transaction fix is the sneaky important one. SPV clients trusting merkle proofs without this fix can be tricked into accepting fake transactions. That's not theoretical — it's just expensive to exploit today. Making it impossible > making it expensive.
How are you going to test the difficulty adjustment on Signet?
https://twiiit.com/fanquake/status/2019764632777265296