Subject: RE: [bitcoindev] Consensus Cleanup BIP draft

From: <[email-masked]>
Date: Fri, 28 Mar 2025 15:53:51 -0400

Hi Jeremy,

> I'm also personally strongly against removing 64-byte transactions. It's a wart
> in how transactions work, and future upgrades (especially around tx
> programmability) might integrate very poorly with this kind of edge condition.

I tend to agree. This kind of discontinuity always comes back to bite eventually. That concern should not be dismissed so casually.

But more to the point, it does not solve any of the problems that were originally provided as justification, apart from making it slightly simpler to implement an SPV wallet (no need to get the coinbase tx). This was discussed at very great length here and on delving by myself and others, and I believe that it was fully accepted that the only justification is this SPV question. There are no issues of security or performance for any code, and not even a code simplification for a node. It's a new consensus rule that creates this discontinuity - only to make an SPV wallet very slightly easier to implement. There is no other benefit whatsoever. I want to emphasize this because in the discussion it still seems that people may be holding on to the idea that it provides some other benefit - it doesn't. If people agree that this is a worthwhile trade, I'm not going to lose any sleep over it. But I don't like seeing arguments about consensus being based on implementation details - especially when they are flawed. It feels very much to me that this is what got this issue going (the several rejected arguments about node performance and simplification), and may be in part what's still driving it.

I ACK the single activation concept, but don't accept that a rule should be deployed that would not stand on its own justification.

Also, I do appreciate the work that Antoine and others have done on the set of issues overall.

Best,
Eric

> On Thursday, March 27, 2025 at 3:36:13 PM UTC-4 Antoine Poinsot wrote:
> 
> 
> 	Hi Chris,
> 
> 	As i already explained on this very list 2 months ago [0], i don't find
> the argument for splitting my BIP convincing. On the contrary i think it would
> be counterproductive as it would create more churn, invite bikeshedding and
> overall impede progress on this proposal.
> 
> 
> 		we've successfully activated multiple BIPs within a single soft
> fork in the past—e.g., BIP141 and BIP143 in Segwit, as well as BIP341,
> BIP342, and BIP343 in Taproot.
> 
> 
> 
> 	Those BIPs had much more content to them. The specifications of the
> Consensus Cleanup is trivial in comparison: they fit in less than a dozen lines of
> text when described in details. Splitting them in 4 different BIPs with a single or
> a couple lines of specifications would just introduce unnecessary overhead.
> 
> 
> 		if one of the proposed changes turns out to be controversial,
> we could remove it without holding up the rest of the improvements.
> 
> 
> 
> 	First of all, i do not expect to remove any of the mitigations from the
> BIP at this stage. The fact that each of these mitigations was researched and
> discussed at length by multiple people over the past year gives me confidence
> to move forward with every single one of those. Otherwise i would not have
> proposed this BIP in the first place.
> 
> 	Now, even if somehow we should drop one of the mitigations from
> the proposal, having them in separate BIPs does not make that any easier.
> 
> 
> 		More active contributors to the project may have stronger
> opinions on the best approach there.
> 
> 
> 
> 	Yes.
> 
> 	Best,
> 	Antoine
> 
> 
> 	[0]
> https://gnusha.org/pi/bitcoindev/mm_NvE4votqtjm455I3AmdrLOTzwgfFpq
> btbFFNy0Zf2PywGt220MXfn76it60q_kbnS9Rw97cv6XzqogNgQMfIXi6-
> HdOnamw7tUrMtmXc=@protonmail.com
> 
> 	On Thursday, March 27th, 2025 at 6:46 AM, Chris Stewart
> <[email-masked]> wrote:
> 
> 
> 		Hi Antoine,
> 
> 		First off, concept ACK. My concerns are procedural rather than
> objections to the individual security fixes themselves.
> 
> 		The "Great Consensus Cleanup" is a fantastic brand for
> communicating these protocol changes to non-technical users. However, since
> this is a technical forum and we are producing BIPs intended for technical
> audiences, I believe we should document these changes in separate BIPs.
> 
> 		The proposed security fixes are largely unrelated from a
> technical standpoint:
> 
> 		1.	Timewarp attack mitigation
> 
> 		2.	Worst-case block validation constraints
> 
> 		3.	Disallowing 64-byte transactions
> 
> 		4.	Avoiding duplicate transactions
> 
> 		We should absolutely retain the "Great Consensus Cleanup"
> branding while independently documenting each security enhancement.
> 
> 		A common concern I’ve heard about splitting this BIP is that
> deploying soft forks is difficult, so all changes should be bundled together.
> While soft fork deployment is indeed challenging, we've successfully activated
> multiple BIPs within a single soft fork in the past—e.g., BIP141 and BIP143 in
> Segwit, as well as BIP341, BIP342, and BIP343 in Taproot. If the community
> reaches consensus, we can still deploy all these changes together, even if they
> are documented separately.
> 
> 		This approach also provides flexibility: if one of the proposed
> changes turns out to be controversial, we could remove it without holding up
> the rest of the improvements. Additionally, once these fixes are deployed,
> there will likely be significant research and documentation to incorporate, and
> maintaining independent BIPs will make it easier to manage that growth.
> 
> 		I do see merit in implementing all the security fixes in a single
> PR for Bitcoin Core. More active contributors to the project may have stronger
> opinions on the best approach there.
> 
> 
> 
> 		-Chris
> 
> 
> ________________________________
> 
> 
> 
> 
> 
> 		On Wed, Mar 26, 2025 at 1:23 PM 'Antoine Poinsot' via
> Bitcoin Development Mailing List <[email-masked]> wrote:
> 
> 
> 			Hi everyone,
> 
> 			About two months ago i shared an update on this list
> about my (and others', really) work on the
> 			Consensus Cleanup [0]. I am now ready to share a BIP
> draft for a Consensus Cleanup soft fork.
> 
> 			The BIP draft can be found here:
> https://github.com/darosior/bips/blob/consensus_cleanup/bip-cc.md
> 
> 			It includes the following fixes:
> 			- a restriction on the timestamp of the first and last
> blocks of a difficulty adjustment period to
> 			address the Timewarp and Murch-Zawy attacks;
> 			- a limit on the number of legacy signature operations
> that may be executed in validating a single
> 			transaction to address long block validation times;
> 			- making 64 bytes transactions invalid to address
> weaknesses in the block Merkle tree construction;
> 			- mandating coinbase transactions be timelocked to
> their block height to prevent future transaction
> 			duplication without resorting to BIP30 validation.
> 
> 			This BIP draws on the 2019 Great Consensus Cleanup
> proposal from Matt Corallo [1]. A number of
> 			people contributed ideas, testing, data or useful
> discussions. This includes Ava Chow, Matt Corallo,
> 			Mark Erhardt, Brian Groll, David A. Harding, Sjors
> Provoost, Anthony Towns, Greg Sanders, Chris
> 			Stewart, Eric Voskuil, @0xb10c and others.
> 
> 			Antoine Poinsot
> 
> 			[0]
> https://gnusha.org/pi/bitcoindev/jiyMlvTX8BnG71f75SqChQZxyhZDQ65kldc
> ugeIDJVJsvK4hadCO3GT46xFc7_cUlWdmOCG0B_WIz0HAO5ZugqYTuX5qxnN
> LRBn3MopuATI=@protonmail.com
> 			[1]
> https://github.com/TheBlueMatt/bips/blob/7f9670b643b7c943a0cc6d2197
> d3eabe661050c2/bip-XXXX.mediawiki
> 
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