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

From: Peter Todd <[email-masked]>
Date: Fri, 3 Oct 2025 13:21:38 +0000

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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