Subject: Re: [bitcoindev] Relax OP_RETURN standardness restrictions

From: Anthony Towns <[email-masked]>
Date: Thu, 1 May 2025 02:37:49 +1000

On Tue, Apr 29, 2025 at 11:39:01PM -0600, Chris Guida wrote:
> We are under a spam attack.

Fees are under 3sat/vb; there's no attack. Excess block space is being
filled by low-value spam, but that's expected and, in a permissionless
system, unavoidable.

> This is not the first time this has happened.
> Bitcoin has endured several spam attacks in the past. They subside when
> bitcoin core devs show that they are serious about countering the attacks.

They subside when the people creating the spam realise they're wasting
money paying for fees.

Acting tough about it at best has zero effect, and at worst generates
publicity for the spammers as media and influencers gather around the
drame, making the activity more profitable.

> Unfortunately, the bitcoin core project made a misstep when it rejected
> this PR[3] from Luke-jr to filter transactions using the op_false op_if
> envelope to exploit the witness discount.

Encoding data into random protocols is a standard exercise, and doing
so in ways that are undetectable to third parties is also standard,
albeit more complicated. In a permissionless system, attempting to
filter encoded data is a losing proposition.

Well, I guess if you can convince someone to pay you by the hour to write
the filters, you've got yourself a job that will never be finished,
so really it's only a losing proposition if you ever hope to actually
succeed at it.

> Another trope from the anti-filter crowd I keep seeing is that spam
> protection is a "cat-and-mouse" game. Well, the cat won in 2014 and the
> mouse didn't come back until 2023.

Not every form of transaction spam is about jpegs or altcoins. There
were significant spam attacks on the network in 2015, see

https://en.bitcoin.it/wiki/July_2015_flood_attack
https://www.ibtimes.co.uk/coinwallet-plans-bitcoin-dust-attack-september-create-30-day-transaction-backlog-1515981
https://nyuscholars.nyu.edu/en/publications/stressing-out-bitcoin-stress-testing

eg. The spam during that time was particularly harmful, because most
wallets failed to calculate fees on a per-vbyte basis and replace-by-fee
was rarely supported, leading to many transactions getting stuck in the
mempool for weeks or months as a result.

The only sustainable way to avoid low value spam appearing on the
blockchain (whatever form that spam might take) is to prevent low value
*transactions* from appearing on the blockchain. I don't think that's
particularly desirable at this time; but it's something that could be
achieved (even on a temporary basis) by lowering the block size.

Cheers,
aj

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