[bitcoin-dev] OP_CODESEPARATOR Re: BIP Proposal: The Great Consensus Cleanup

[Matt Corallo]

Aside from the complexity issues here, note that for a user to be adversely affect, they probably have to have pre-signed lock-timed transactions. Otherwise, in the crazy case that such a user exists, they should have no problem claiming the funds before activation of a soft-fork (and just switching to the swgwit equivalent, or some other equivalent scheme). Thus, adding additional restrictions like tx size limits will equally break txn.

> On Mar 8, 2019, at 14:12, Sjors Provoost <sjors at sprovoost.nl> wrote:
> 
> 
>> (1) It has been well documented again and again that there is desire to remove OP_CODESEPARATOR, (2) it is well-documented OP_CODESEPARATOR in non-segwit scripts represents a rather significant vulnerability in Bitcoin today, and (3) lots of effort has gone into attempting to find practical use-cases for OP_CODESEPARATOR's specific construction, with no successes as of yet. I strongly, strongly disagree that the highly-unlikely remote possibility that someone created something before which could be rendered unspendable is sufficient reason to not fix a vulnerability in Bitcoin today.
>> 
>>> I suggest an alternative whereby the execution of OP_CODESEPARATOR increases the transactions weight suitably as to temper the vulnerability caused by it.  Alternatively there could be some sort of limit (maybe 1) on the maximum number of OP_CODESEPARATORs allowed to be executed per script, but that would require an argument as to why exceeding that limit isn't reasonable.
>> 
>> You could equally argue, however, that any such limit could render some moderately-large transaction unspendable, so I'm somewhat skeptical of this argument. Note that OP_CODESEPARATOR is non-standard, so getting them mined is rather difficult in any case.
> 
> Although I'm not a fan of extra complicity, just to explore these two ideas a bit further.
> 
> What if such a transaction:
> 
> 1. must have one input; and
> 2. must be smaller than 400 vbytes; and
> 3. must spend from a UTXO older than fork activation
> 
> Adding such a contextual check seems rather painful, perhaps comparable to nLockTime. Anything more specific than the above, e.g. counting the number of OP_CODESEPARATOR calls, seems like guess work.
> 
> Transaction weight currently doesn't consider OP codes, it only considers if bytes are part of the witness. Changing that to something more akin to Ethereums gas pricing sounds too complicated to even consider.
> 
> 
> I would also like to believe that whoever went through the trouble of using OP_CODESEPARATOR reads this list.
> 
> Sjors
>