Subject: Re: [bitcoindev] [BIP Proposal] Limit ScriptPubkey Size >= 520 Bytes Consensus.

From: "'moonsettler' via Bitcoin Development Mailing List" <[email-masked]>
Date: Fri, 03 Oct 2025 16:52:51 +0000

> NACK, for exactly this reason. It's hard to predict what kind of math will be
> needed in the future for future signature algorithms. With taproot, we include
> bare pubkeys in scriptPubKeys for a good reason. It's quite possible that we'll
> want to do something similar with >520byte pubkeys for some future signature
> 
> algorithm (e.g. quantum hard) or some other difficult to predict technical
> upgrade (the spendableness of scriptPubKeys with >520bytes isn't relevant to
> 
> this discussion).

No matter how large a pubkey script you need, you can just delegate to the
witness if you have a cryptographically secure hash function.

Hard to even imagine needing anywhere near 4096 bits for that.

The going assumption for quantum algos is they could halve the bit strength of
a hash function, but SHA512 seems quiet robust even under worst assumptions.
And it's not enough to find ANY collision for a script or some Merkle root.

Putting the unlocking conditions into the UTXO set does not seem like a healthy
idea to me anyhow.

BR,
moonsettler

PS:
No hard opinion on temporary vs final restrictions. I wouldn't worry about it.

Sent with Proton Mail secure email.

On Friday, October 3rd, 2025 at 5:51 PM, Peter Todd <[email-masked]> wrote:

> On Thu, Oct 02, 2025 at 01:42:06PM -0700, PortlandHODL wrote:
> 
> > Proposing: Softfork to after (n) block height; the creation of outpoints
> > with greater than 520 bytes in the ScriptPubkey would be consensus invalid.
> > 
> > This is my gathering of information per BIP 0002
> > 
> > After doing some research into the number of outpoints that would have
> > violated the proposed rule there are exactly 169 outpoints. With only 8
> > being non OP_RETURN. I think after 15 years and not having discovered use
> > for 'large' ScriptPubkeys; the reward for not invalidating them at the
> > consensus level is lower than the risk of their abuse.
> > 
> > -
> > *Reasons for *
> > - Makes DoS blocks likely impossible to create that would have any
> > sufficient negative impact on the network.
> 
> 
> Further restricting v0 scripts is sufficient to achieve this goal. We do not
> need to actually prohibit >520 byte pushes.
> 
> > - Leaves enough room for hooks long term
> > - Would substantially reduce the divergence between consensus and
> > relay policy
> > - Incredibly little use onchain as evidenced above.
> > - Could possibly reduce codebase complexity. Legacy Script is largely
> > considered a mess though this isn't a complete disablement it should reduce
> > the total surface that is problematic.
> > - Would make it harder to use the ScriptPubkey as a 'large'
> > datacarrier.
> > - Possible UTXO set size bloat reduction.
> > 
> > - *Reasons Against *
> > - Bitcoin could need it in the future? Quantum?
> 
> 
> NACK, for exactly this reason. It's hard to predict what kind of math will be
> needed in the future for future signature algorithms. With taproot, we include
> bare pubkeys in scriptPubKeys for a good reason. It's quite possible that we'll
> want to do something similar with >520byte pubkeys for some future signature
> 
> algorithm (e.g. quantum hard) or some other difficult to predict technical
> upgrade (the spendableness of scriptPubKeys with >520bytes isn't relevant to
> 
> this discussion).
> 
> > - Users could just create more outpoints.
> 
> 
> The second reason for my NACK. It makes no significant difference whether or
> not data is contiguous or split across multiple outputs. All the same concerns
> about arbitrary data ("spam") exist and will continue to be argued over even if
> we do a soft-fork to prohibit this. All we'll done is have used up valuable dev
> and political resources.
> 
> --
> https://petertodd.org 'peter'[:-1]@petertodd.org
> 
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