Hi, This approach was discussed last year when evaluating the best way to mitigate DoS blocks in terms of gains compared to confiscatory surface. Limiting the size of created scriptPubKeys is not a sufficient mitigation on its own, and has a non-trivial confiscatory surface.
One of the goal of BIP54 is to address objections to Matt's earlier proposal, notably the (in my opinion reasonable) confiscation concerns voiced by Russell O'Connor. Limiting the size of scriptPubKeys would in this regard be moving in the opposite direction. Various approaches of limiting the size of spent scriptPubKeys were discussed, in forms that would mitigate the confiscatory surface, to adopt in addition to (what eventually became) the BIP54 sigops limit. However i decided against including this additional measure in BIP54 because: - of the inherent complexity of the discussed schemes, which would make it hard to reason about constructing transactions spending legacy inputs, and equally hard to evaluate the reduction of the confiscatory surface; - more importantly, there is steep diminishing returns to piling on more mitigations. The BIP54 limit on its own prevents an externally-motivated attacker from *unevenly* stalling the network for dozens of minutes, and a revenue-maximizing miner from regularly stalling its competitions for dozens of seconds, at a minimized cost in confiscatory surface. Additional mitigations reduce the worst case validation time by a smaller factor at a higher cost in terms of confiscatory surface. It "feels right" to further reduce those numbers, but it's less clear what the tangible gains would be. Furthermore, it's always possible to get the biggest bang for our buck in a first step and going the extra mile in a later, more controversial, soft fork. I previously floated the idea of a "cleanup v2" in private discussions, and i think besides a reduction of the maximum scriptPubKey size it should feature a consensus-enforced maximum transaction size for the reasons stated here: https://delvingbitcoin.org/t/non-confiscatory-transaction-weight-limit/1732/8. I wouldn't hold my breath on such a "cleanup v2", but it may be useful to have it documented somewhere. I'm trying to not go into much details regarding which mitigations were considered in designing BIP54, because they are tightly related to the design of various DoS blocks. But i'm always happy to rehash the decisions made there and (re-)consider alternative approaches on the semi-private Delving thread [0] dedicated to this purpose. Feel free to ping me to get access if i know you. Best, Antoine Poinsot [0]: https://delvingbitcoin.org/t/worst-block-validation-time-inquiry/711 On Friday, October 17th, 2025 at 1:12 PM, Brandon Black <[email protected]> wrote: > > > On 2025-10-16 (Thu) at 00:06:41 +0000, Greg Maxwell wrote: > > > But also given that there are essentially no violations and no reason to > > expect any I'm not sure the proposal is worth time relative to fixes of > > actual moderately serious DOS attack issues. > > > I believe this limit would also stop most (all?) of PortlandHODL's > DoSblocks without having to make some of the other changes in GCC. I > think it's worthwhile to compare this approach to those proposed by > Antoine in solving these DoS vectors. > > Best, > > --Brandon > > -- > You received this message because you are subscribed to the Google Groups > "Bitcoin Development Mailing List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/aPJ3w6bEoaye3WJ6%40console. -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/OAoV-Uev9IosyhtUCyeIhclsVq-xUBZgGFROALaCKZkEFRNWSqbfDsVyiXnZ8B1TxKpfxmaULuwe4WpGHLI_iMdvPr5B0gM0nDvlwrKjChc%3D%40protonmail.com.
