Re: [bitcoindev] Re: Make pathological transactions with more than 2500 legacy signature operations non-standard

["'Antoine Poinsot' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>]

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This limit only concerns legacy signature operations. Off-chain constructions use Segwit inputs, as they would be trivially broken by txid malleability otherwise.

On Friday, July 4th, 2025 at 10:38 AM, Antoine Riard <antoine.riard@gmail.com> wrote:

> Hi Poinsot,
>
> Thanks for the collection of historical txn hitting the proposed new limit.
>
> The only long-term downside coming immediately out of mind, if the rule becomes consensus
> in the future, it's the implicit limitation it would make on the multi-party dimensions
> of off-chain constructions. In the past, I made really rough math for 1000-sized participants
> payments pools, where for the funding_tx, you have the 1000 participants contributing
> one input with one sig for each [0].
>
> In my understanding the new limit of 2500 signatures operation would make a hard-limit
> for the number of participants entering in such construction, without other tricks that
> are consuming more block space. One can note the downside on funding tx of high-order
> off-chain construction, if a max tx size consensus limit is introduced in the future.
>
> Of course, I do not deny the DoS rational of introducing the 2500 sig limit and it's
> very needed. At the same time, we should be careful of not closing too much doors for
> future off-chain constructions and long-term tx throughput scalability.
>
> I do believe, it's always technically possible in the future to introduce new opcode
> or segwit versions scripts (e.g grafroot or entroot-based pool construction), which
> wouldn't be subject to the new limit, and as such more scalable. If I'm correct, I
> think it's all about how the limit is implemented to parse current scripts to be
> spent.
>
> But it's hard to say without code available to review and reason. May I kindly note
> there is no reference implementation attached in the current BIP54 document [1]. Even,
> if it's often updated, it's always fruitful to have code under the eyes for review.
>
> This might be the kind of concern (very) far down the line...but preserving the
> evolvability of the consensus rules is a good property to care about, in my humble
> opinion.
>
> Best,
> Riard
> OTS hash: a2bb9a1faf79309b039d8ae7e0b951644ca0adb2
>
> [0] https://gnusha.org/pi/bitcoindev/CALZpt+E+eKKtOXd-8A6oThw-1i5cJ4h12TuG8tnWswqbfAnRdA@mail.gmail.com/
> [1] https://github.com/bitcoin/bips/blob/master/bip-0054.md
>
> Le mercredi 2 juillet 2025 à 09:54:33 UTC+1, Antoine Poinsot a écrit :
>
>> Hi everyone,
>>
>> To mitigate high block validation time, BIP54 proposes to make transactions which require more than
>> 2500 legacy signature operations invalid by consensus. The 2500 figure was chosen as the tightest
>> value that did not make any non-pathological currently standard transaction invalid.
>>
>> No transaction in Bitcoin's history would have both hit the BIP54 sigop limit and been standard
>> according to today's Bitcoin Core policy[^0]. But what happened in the past doesn't matter as much
>> as the fact that it is possible today to create a pathological standard transaction that is
>> BIP54-invalid.
>>
>> This opens up a major DoS vector against unupgraded miners if BIP54 ever gets activated in these
>> conditions. Therefore i propose to make such transactions non-standard and hold off activation of
>> BIP54 until we have good reasons to believe that the vast majority of the hashrate won't create a
>> block containing such a transaction.
>>
>> Doing so gives better guarantees in case BIP54 is ever considered for activation, and comes at
>> virtually no cost since these pathological transactions have never been used and serve no purpose
>> beyond increasing the cost of validation. Bitcoin Core PR #32521 implements this change, which i
>> hope to get into the upcoming 30.0 release as well as backported to previous versions.
>>
>> Best,
>> Antoine Poinsot
>>
>> [^0]: Here the full list of historical transactions that would have hit the BIP54 sigops limit:
>> - 659135664894e50040830edb516a76f704fd2be409ecd8d1ea9916c002ab28a2
>> - bea1c2b87fee95a203c5b5d9f3e5d0f472385c34cb5af02d0560aab973169683
>> - 24b16a13c972522241b65fbb83d09d4bc02ceb33487f41d1f2f620b047307179
>> - 53666009e036171b1aee099bc9cd3cb551969a53315410d13ad5390b8b4f3bd0
>> - ffc178be118bc2f9eaf016d1c942aec18441a6c5ec17c9d92d1da7962f0479f6
>> - 2f1654561297114e434c4aea5ca715e4e3f10be0be8c1c9db2b6f68ea76dae09
>> - 62fc8d091a7c597783981f00b889d72d24ad5e3e224dbe1c2a317aabef89217e
>> - d939315b180d3d73b5e316eb57a18f8137a3f5943aef21a811660d25f1080a3f
>> - 8a6bfaa78828a81147e4848372d491aa4e9048631982a670ad3a61402a4ec327
>> - 02cc78789cc070125817189ec378daa750355c8b22bbce982ed96aa549facb1f
>> - b97a16ae2e8ae2a804ed7965373b42055f811653f4628e4bef999145d4b593bc
>> - c51ffaf08188859669571f897f119b6d39ea48a9334212f554bf4927401b71f3
>> - 33ccdda65abdda8025adb03841410dda5fa8948bd38b7fbaf3fed521daf5c4d3
>> - bb41a757f405890fb0f5856228e23b715702d714d59bf2b1feb70d8b2b4e3e08
>> - ba588134ecc93fdbfa06f795c9bf7a05b09ca9ca9095659e401325d501a90363
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