Re: [bitcoindev] Update on the Great Consensus Cleanup Revival

["'Antoine Poinsot' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>]

I laid out my reasoning for increasing the grace period to 7200 on the Consensus Cleanup Delving
thread [0]. TL;DR: there is marginal safety benefits to doing so and virtually no cost (it only
increases the worst case block rate from ~0.1% to ~0.65%). So on balance i concluded it was
preferable to err on the safe side.

I chose to go with mandating nLockTime be set in coinbase transactions to the height of the block
they are included in minus 1 because it has marginal benefits in addition to ensuring coinbase
transactions can't be duplicate (retrieving / proving the block height more efficiently), and the
feedback i got from miners both publicly [1] and privately was that none of the options presented
significantly more challenge for them.

Antoine

[0] https://delvingbitcoin.org/t/great-consensus-cleanup-revival/710/66
[1] https://groups.google.com/g/bitcoinminingdev/c/qyrPzU1WKSI/m/uzxS5jG0AwAJ



On Thursday, February 6th, 2025 at 4:34 PM, Murch <murch@murch.one> wrote:

> 
> 
> Thank you for the update and your work on the Great Consensus Cleanup. I
> am looking forward to reading your BIP, and would hope that you could
> share here or in the BIP’s Rationale what convinced you to change the
> grace period from 600 seconds to 7200 seconds and how the nLockTime of
> height-1 won out.
> 
> Cheers,
> Murch
> 
> On 2025-02-05 13:09, 'Antoine Poinsot' via Bitcoin Development Mailing
> List wrote:
> 
> > Hi everyone,
> > 
> > A bit over a year ago i started working on revisiting the 2019 Great Consensus Cleanup proposal from
> > Matt Corallo [0]. His proposal included:
> > - making <=64 bytes transactions invalid to fix merkle tree weaknesses;
> > - making non-pushonly scriptSigs, FindAndDelete matches, OP_CODESEPARATOR and non-standard sighash
> > types fail script validation to mitigate the worst case block validation time;
> > - restrict the nTime field of the first block in each difficulty adjustment interval to be no less
> > than 600 seconds lower than the previous block's;
> > 
> > I set out to research the impact of each of the vulnerabilities this intended to patch, the
> > alternative fixes possible for each and finally if there was any other protocol bug fix we'd want to
> > include if we went through the considerable effort of soft forking Bitcoin already.
> > 
> > Later in March i shared some first findings on Delving [1] and advertized the effort on this mailing
> > list [2]. I also created a companion thread on Delving, kept private, to discuss the details of the
> > worst case block validation time [3]. As one would expect due to the larger design space available
> > to fix this issue, this private thread is where most of the discussion would happen. Thank you to
> > everyone who contributed feedback, insights, ideas and argumented opinions on the different issues
> > all along the process.
> > 
> > Now i would like to update the broader Bitcoin development community on the outcome of this effort.
> > I believe a Consensus Cleanup proposal should include the following.
> > - A fix for vulnerabilities surrounding the use of timestamps in the difficulty adjustment
> > algorithm. In particular, a fix for the timewarp attack with a 7200 seconds grace period as well
> > as a fix for the Murch-Zawy attack [4] by making invalid any difficulty adjustment period with a
> > negative duration.
> > - A fix for long block validation times with a minimal "confiscation surface", by introducing a
> > per-transaction limit on the number of legacy sigops in the inputs.
> > - A fix for merkle tree weaknesses by making transactions which serialize to exactly 64 bytes
> > invalid.
> > - A fix for duplicate transactions to supplement BIP34 in order to avoid resuming unnecessary BIP30
> > validation in the future. This is achieved by mandating the nLockTime field of coinbase
> > transaction to be set to the height of their block minus 1.
> > 
> > I have started drafting a BIP draft with the detailed specs for this.
> > 
> > Antoine Poinsot
> > 
> > [0] https://github.com/TheBlueMatt/bips/blob/7f9670b643b7c943a0cc6d2197d3eabe661050c2/bip-XXXX.mediawiki
> > [1] https://delvingbitcoin.org/t/great-consensus-cleanup-revival/710
> > [2] https://groups.google.com/g/bitcoindev/c/CAfm7D5ppjo/m/bYJ3BiOuAAAJ
> > [3] https://delvingbitcoin.org/t/worst-block-validation-time-inquiry/711
> > [4] https://delvingbitcoin.org/t/zawy-s-alternating-timestamp-attack/1062#variant-on-zawys-attack-2
> 
> 
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