Subject: Re: [bitcoindev] Relax OP_RETURN standardness restrictions

From: "Jason Hughes (wk057)" <[email-masked]>
Date: Mon, 28 Apr 2025 09:20:14 -0700 (PDT)

I was asked to take my comments to the mailing list, so here we go.

First, see my comments on Github PR #32359:
- https://github.com/bitcoin/bitcoin/pull/32359#issuecomment-2835467933
- https://github.com/bitcoin/bitcoin/pull/32359#issuecomment-2835638919
- https://github.com/bitcoin/bitcoin/pull/32359#issuecomment-2834012756

Next, I'll once again point out relevant history for those just tuning in:

OP_RETURN was only made standard in a limited size to encourage less 
harmful data carrying in Bitcoin. Attackers were using harmful methods of 
data carrying in unspendable UTXOs, and so a way to inject a small amount 
of data was TOLERABLE over this harmful UTXO bloat that.  That mostly 
worked, and such practices were quickly minimized. This remained the case 
for about a decade without significant issue. Bitcoin is not file storage, 
and this was known to developers at that time.  Sadly, eventually an 
exploit called 'inscriptions' happened which blew the cap off of the size 
limitation of arbitrary data storage... and to make matters worse, 
developers refused to patch the exploit or otherwise enforce the decade old 
limit on arbitrary data size. If that wasn't bad enough, exploiters get a 
75% discount on transaction fees.

With that history in mind, removing limits on OP_RETURN standardness size 
is pointless. Relaxing OP_RETURN size limits without dealing with the 
inscriptions exploit means no one will use this for anything besides 
attacking the network with the worst possible data. There's little to no 
incentive to use OP_RETURN for data storage when using the 'inscriptions' 
exploit costs 4x less in transactions. What's the point of having a 
"standard" way to store arbitrary data if the exploit method is 4x cheaper? 
And the nonstandard version of the exploit allows 4x the data?

Further, the inscriptions exploit currently requires chunking the data 
between PUSH opcodes, meaning an on-disk analysis doesn't actually directly 
reveal the underlying data the injector intended.  I can still run 
something like "photorec" on my system and not have to sift through 
thousands of 'inscriptions'. Removing the size limit on OP_RETURN breaks 
this happenstance obfuscation that has saved us to-date. After this change, 
when data is recovered from a full node system, whatever some anonymous 
person decided to stuff into an OP_RETURN will be serialized in plaintext 
directly on disk. For the low price of a few sats per byte, an attacker can 
now directly poison the storage of every full node runner.

If you can't imagine the harm this will do to the ecosystem, let me paint 
some pictures for you:

First, there's the obvious. Everyone running a node will now be guaranteed 
to "posses and distribute" content that is likely illegal in their 
jurisdiction. Not only are you storing this as a full node runner, you're 
serving it to others. Hooray. /s

Next, there's less obvious abuses. For example, let's say I want to 
distribute malware. Well, might as well just store it in an OP_RETURN. 
Then, any time I compromise a system with a Bitcoin node I know my malware 
is directly on their system in a mostly predetermined spot already and I 
don't even need to retrieve it from elsewhere! And, even better, my malware 
can use the Bitcoin P2P network itself to distribute itself. Just find a 
willing full node, grab the block it's in. Thanks for the boost, node 
runners!

Worse, in order to actually participate in the network, everyone MUST 
download all of this data from others (who must host it for you), process 
it, and generally must host it for others to do the same. The network can't 
survive with 100% pruned nodes. I think too many users nowadays don't 
understand that running a full node is the ONLY way to actually participate 
in Bitcoin.

It's bad enough that chunked partly-obfuscated things exist on the systems 
of full node runners today. It'll be even worse if that's unrestricted with 
the removal of such limits.

As I said in my Github comment: This is far more than a small technical 
change. This is a fundamental change to the nature of what the Bitcoin 
network itself is in its entirety. Ten years ago, developers of the 
reference implementation knew this, and acted in the best interest of 
Bitcoin itself. Today, too many developers don't understand this duty.

That may sound like hyperbole, but it really isn't. If this change is 
merged into Bitcoin Core, and Bitcoin Core then continues to be the 
reference implementation... Bitcoin as we know it changes forever in the 
most fundamental way imaginable: The reference implementation explicitly 
turning the Bitcoin network into an arbitrary data storage system, instead 
of evolving it as a decentralized currency.

That's not Bitcoin anymore, and we might as well give up on Bitcoin ever 
being a thing if this is the path chosen.  There are very few paths that 
lead to a worthless Bitcoin, and this is probably in the top 3 worst 
options.

I can't understate this. It's one thing to refuse to act when faced with an 
attack/exploit/etc.  That takes actual courage and conviction to do what's 
right for the ecosystem... and I _almost_ can't fault the current batch of 
devs for not having that courage.  However, it's another to openly make 
sweeping changing to the ecosystem in an effort to make such things 
acceptable.

Have the courage to reject this type of thing for the sake of the overall 
project.

JH
aka wk057
aka wizkid057
On Saturday, April 26, 2025 at 8:50:59 AM UTC-4 Pieter Wuille wrote:

> On Saturday, April 26th, 2025 at 7:45 AM, Luke Dashjr <[email-masked]> 
> wrote:
>
> > That's nonsense. They were and continue to be very effective, even with
> > only a small amount of adoption. Further, mining centralization and
>
> Standardness rules have definitely been effective in the past, if we go 
> far enough back in time. But back then:
>
> * There were far less financial incentives to bypass them. Standardness 
> adds inconvenience to people developing infrastructure on top, which can 
> nudge in another direction. But I don't see how million-dollar (or more) 
> business incentives would be thwarted by the need to communicate with 
> miners directly (see below). These incentives will only increase as the 
> subsidy dwindles.
>
> * There was far more reason for rules of this kind; the network was small 
> and far less valuable, and there were significant concerns about increased 
> node operation cost with a quickly-growing blockchain. With blocks 
> consistently full for most of the time for years now, even at times without 
> so-called "spam", that concern just does not exist; nodes will be 
> processing the same amount of transaction data anyway. I think I share 
> Luke's feelings around non-financially-relevant transactions on-chain, but 
> given sufficient demand for block space anyway, there just is no need to 
> discriminate.
>
> > pools denying miners options has been the biggest barrier to that
> > adoption. There is no significant financial impact either, that's just
> > FUD; miners using the fixed and improved spam filters have in fact
> > earned significantly more than miners using Core.
>
> I am doubtful of this claim, and would like to see evidence of it.
>
> > It would be a pain, but it is definitely viable. Thankfully, policy
> > works just fine for spam filtration, and can be adapted much quicker.
>
> Nobody is required to adopt policy, and I think you're burying your head 
> in the sand if you believe even in a world with more decentralized 
> hashpower, miners/hashers would voluntarily choose to disregard 
> transactions that pay a significant fee, if the potential gains from 
> accepting them exceed the cost of building infrastructure to bypass 
> whatever policy exists.
>
> Bitcoin users do have a means to deny usage of the chain to truly damaging 
> use: consensus changes. Those are not optional, apply to everyone equally, 
> do not create incentives for bypass, and - and I believe that is a good 
> thing - can only be adopted with very wide agreement.
>
> > > b) centralisation
> > 
> > No, this is more FUD.
>
> The **entire** reason why Bitcoin uses PoW, as opposed to using a 
> traditional consensus system with a federation of block-builders, is to 
> avoid censorship. If anyone dislikes the choices current miners make in 
> what transactions they accept, they can - without asking anyone for 
> permission - join the set of miners, and earn a proportional piece of the 
> pie. While it is the case that today mining power is quite concentrated in 
> a number of businesses, the set of such businesses can, and has, changed 
> over time. This is a very valuable property.
>
> Part of the puzzle to make that permissionlessness of mining work is 
> access to fee-paying transactions from the public. If sufficient economic 
> demand exist for transactions that the public network denies, miners and 
> creators of such transaction will develop transaction rails that bypass 
> that network.
>
> If it comes to a point where that economic demand is so high that miners 
> need to rely on private transaction rails to realistically compete, I feel 
> we'd be giving up on one of the most valuable properties the network has. I 
> realize this is a slipstreamery-slope argument, but it is already 
> happening, and once the rails are ubiquitous, it will be very hard to go 
> back to a public network.
>
> ---
>
> Because of all these reasons, Concept ACK on relaxing the OP_RETURN 
> limits, including removing them entirely. I have been a strong proponent of 
> these limits in the past, and I'm not happy with seeing the demand for 
> those transactions. But I also recognize the reality that that demand 
> exists, and the alternative of pushing that demand to bypass the public 
> network is far more damaging.
>
> I will add that I am not in favor of relaxing many other standardness 
> rules in Bitcoin Core, such as transaction sizes and other resource 
> limitations. These have significant impact on the public's ability to 
> verify and relay transactions, and reason about incentive compatibility 
> while doing so. Significant and sustained economic demand for such 
> transactions may at some point too mean the policy needs to be revised to 
> avoid an even worse outcome, but I'm hopeful that is not the case. However, 
> these arguments do not apply to OP_RETURN limits, which don't serve an 
> objective harm reduction beyond a subjective "that isn't what you should be 
> using the chain for".
>
> -- 
> Pieter
>
>

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