From: Greg Tonoski <greg.tonoski@gmail•com>
To: bitcoindev@googlegroups.com
Subject: Re: [bitcoindev] [BIP Proposal] Limit ScriptPubkey Size >= 520 Bytes Consensus.
Date: Wed, 8 Oct 2025 17:03:54 +0200 [thread overview]
Message-ID: <CAMHHROwJA5N=SfejF353oWFFsKVCtk5cpr9QkOv+ZcqGDFz6oA@mail.gmail.com> (raw)
In-Reply-To: <001afe1d-0282-4c68-8b1c-ebcc778f57b0@dashjr.org>
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I'm for all the consensus proposals below and would further specify:
- limiting the maximum size of the scriptPubKey of a transaction to 67
bytes (to keep supporting P2PK and avoid impacting usability/compatibility
of old, deprecated software and risk of similar corner cases); good
riddance to P2MS;
- limit the maximum size of script data pushes to 73 bytes (for the same
reason, i.e. keep supporting for P2PK input: signature with its encoding
overhead; also P2PKH) "with an exception for BIP16 redeem scripts [which
may embed multiple public keys for multisig]",
- rule out "OP_FALSE OP_IF" (CVE-2023-50428),
- discontinue P2SPAM (the one that repurposed the mnemonic OP_RETURN and
was standardized in 2014, commit a79342479f577013f2fd2573fb32585d6f4981b3
<https://github.com/bitcoinknots/bitcoin/commit/a79342479f577013f2fd2573fb32585d6f4981b3>
).
BTW I think we should also consider consensus-wise limit on the maximum
size of the so-called Witness field (3600 bytes max. by policy.h) along
with max. size (80 bytes max. by policy.h) and max. count of its items (100
by policy.h). Any suggestions, anybody?
--
Greg Tonoski
On Fri, Oct 3, 2025 at 10:09 PM Luke Dashjr <luke@dashjr•org> wrote:
> If we're going this route, we should just close all the gaps for the
> immediate future:
>
> - Limit (new) scriptPubKeys to 83 bytes or less. 34 doesn't seem terrible.
> UTXOs are a huge cost to nodes, we should always keep them as small as
> possible. Anything else can be hashed (if SHA256 is broken, we need a
> hardfork anyway).
>
> - Limit script data pushes to 256 bytes, with an exception for BIP16
> redeem scripts.
>
> - Make undefined witness/taproot versions invalid, including the annex and
> OP_SUCCESS*. To make any legitimate usage of them, we need a softfork
> anyway (see below about expiring this).
>
> - Limit taproot control block to 257 bytes (128 scripts max), or at least
> way less than it currently is. 340e36 scripts is completely unrealistic.
>
> - Make OP_IF invalid inside Tapscript. It should be unnecessary with
> taproot, and has only(?) seen abuse.
>
> We can do these all together in a temporary softfork that self-expires
> after a year or two. This would buy time to come up with longer-term
> solutions, and observe how it impacts the real world. Since it expires,
> other softforks making use of upgradable mechanisms can just wait it out
> for those mechanisms to become available again - therefore we basically
> lose nothing. (This is intended to buy us time, not as a permanent fix.)
>
> Alternatively, but much more complex, we could redesign the block weight
> metric so the above limits could be exceeded, but at a higher
> weight-per-byte; perhaps weigh data 25% more per byte beyond the expected
> size. This could also be a temporary softfork, perhaps with a rolling
> window, so future softforks could be free to lower weights should they be
> needed.
>
> Another idea might be to increase the weight based on
> coin-days-destroyed/coin-age, so rapid churn has a higher feerate than
> occasional settlements. But this risks encouraging UTXO bloat, so needs
> careful consideration to proceed further.
>
> Happy to throw together a BIP and/or code if there's community support for
> this.
>
> Luke
>
>
> On 10/2/25 16:42, 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.
> - 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?
> - Users could just create more outpoints.
>
> Thoughts?
>
> source of onchain data
> <https://github.com/portlandhodl/portlandhodl/blob/main/greater_520_pubkeys.csv>
>
> PortlandHODL
>
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next prev parent reply other threads:[~2025-10-08 16:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-02 20:42 PortlandHODL
2025-10-02 22:19 ` Andrew Poelstra
2025-10-02 22:46 ` Andrew Poelstra
2025-10-02 22:47 ` 'moonsettler' via Bitcoin Development Mailing List
2025-10-03 7:11 ` Garlo Nicon
2025-10-02 22:27 ` Brandon Black
2025-10-03 1:21 ` [bitcoindev] " /dev /fd0
2025-10-03 10:46 ` 'moonsettler' via Bitcoin Development Mailing List
2025-10-03 11:26 ` /dev /fd0
2025-10-03 13:35 ` jeremy
2025-10-03 13:59 ` Andrew Poelstra
2025-10-03 14:18 ` /dev /fd0
2025-10-03 14:59 ` Andrew Poelstra
2025-10-03 16:15 ` Anthony Towns
2025-10-05 9:59 ` Guus Ellenkamp
2025-10-03 13:21 ` [bitcoindev] " Peter Todd
2025-10-03 16:52 ` 'moonsettler' via Bitcoin Development Mailing List
2025-10-03 15:42 ` Anthony Towns
2025-10-03 20:02 ` Luke Dashjr
2025-10-03 20:52 ` /dev /fd0
2025-10-04 23:12 ` jeremy
2025-10-05 10:59 ` Luke Dashjr
2025-10-08 15:03 ` Greg Tonoski [this message]
2025-10-08 18:15 ` Keagan McClelland
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