Subject: Re: [bitcoindev] CTV + CSFS: a letter

From: Peter Todd <[email-masked]>
Date: Fri, 20 Jun 2025 14:28:28 +0000

On Wed, Jun 11, 2025 at 11:33:35AM -0400, Greg Sanders wrote:
> It clearly can be a liability if the relative utility of CTV is damaged by
> a possible future change, even non-consensus ones, some of which are
> already being deployed with non-zero miner support such as
> https://x.com/PortlandHODL/status/1921350395424563572 . This could have led
> to legitimate usage of CTV being trivially DoS'able. Good news is there are
> practical if not beautiful mitigations to this that don't involve annex
> commitment. See https://github.com/bitcoin/bitcoin/pull/32453 and
> https://github.com/petertodd/bitcoin/pull/10 for some relevant details.

Note that in this example the "mitigation" is simply enforcing what is optimal
for miners: mining annexes only when the annexes are required for the
transaction to be valid.

A miner who had allowed standard annexes who was *not* mining CTV transactions
because of a large uncommitted annex is just unnecessarily losing money. They
could easily take that exact transaction, remove the uncommitted annex, and
earn a bit more money. In much the same way that a miner can always do
themselves unnecessary harm by disabling the clean-stack check, and then
failing to mine perfectly valid transactions that would be more profitable if
the extraneous stack elements were removed (modulo non-segwit cases with
high-fee child transactions of course).

It may be a good idea for CTV to commit to annexes. But this issue isn't a
reason to do so.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org

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