It is relevant to note that BIP 117 makes an insecure form of CODESEPARATOR delegation possible, which could be made secure if some sort of CHECKSIGFROMSTACK opcode is added at a later point in time. It is not IMHO a very elegant way to achieve delegation, however, so I hope that one way or another this could be resolved quickly so it doesn’t hold up either one of those valuable additions.

I have no objections to making them nonstandard, or even to make them invalid if someone with a better grasp of history can attest that CODESEPARATOR was known to be entirely useless before the introduction of P2SH—not the same as saying it was useless, but that it was widely known to not accomplish what a early-days script author might think it was doing—and the UTXO set contains no scriptPubKeys making use of the opcode, even from the early days. Although a small handful could be special cased, if they exist.

On Nov 27, 2017, at 8:33 AM, Matt Corallo <lf-lists@mattcorallo.com> wrote:

I strongly disagree here - we don't only soft-fork out transactions that
are "fundamentally insecure", that would be significantly too
restrictive. We have generally been willing to soft-fork out things
which clearly fall outside of best-practices, especially rather
"useless" fields in the protocol eg soft-forking behavior into OP_NOPs,
soft-forking behavior into nSequence, etc.

As a part of setting clear best-practices, making things non-standard is
the obvious step, though there has been active discussion of
soft-forking out FindAndDelete and OP_CODESEPARATOR for years now. I
obviously do not claim that we should be proposing a soft-fork to
blacklist FindAndDelete and OP_CODESEPARATOR usage any time soon, and
assume that it would take at least a year or three from when it was made
non-standard to when a soft-fork to finally remove them was proposed.
This should be more than sufficient time for folks using such weird (and
largely useless) parts of the protocol to object, which should be
sufficient to reconsider such a soft-fork.

Independently, making them non-standard is a good change on its own, and
if nothing else should better inform discussion about the possibility of
anyone using these things.

Matt

On 11/15/17 14:54, Mark Friedenbach via bitcoin-dev wrote:
As good of an idea as it may or may not be to remove this feature from
the code base, actually doing so would be crossing a boundary that we
have not previously been willing to do except under extraordinary
duress. The nature of bitcoin is such that we do not know and cannot
know what transactions exist out there pre-signed and making use of
these features.

It may be a good idea to make these features non standard to further
discourage their use, but I object to doing so with the justification of
eventually disabling them for all transactions. Taking that step has the
potential of destroying value and is something that we have only done in
the past either because we didn’t understand forks and best practices
very well, or because the features (now disabled) were fundamentally
insecure and resulted in other people’s coins being vulnerable. This
latter concern does not apply here as far as I’m aware.

On Nov 15, 2017, at 8:02 AM, Johnson Lau via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org
<mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:

In https://github.com/bitcoin/bitcoin/pull/11423 I propose to
make OP_CODESEPARATOR and FindAndDelete in non-segwit scripts non-standard

I think FindAndDelete() is one of the most useless and complicated
functions in the script language. It is omitted from segwit (BIP143),
but we still need to support it in non-segwit scripts. Actually,
FindAndDelete() would only be triggered in some weird edge cases like
using out-of-range SIGHASH_SINGLE.

Non-segwit scripts also use a FindAndDelete()-like function to remove
OP_CODESEPARATOR from scriptCode. Note that in BIP143, only executed
OP_CODESEPARATOR are removed so it doesn’t have the
FindAndDelete()-like function. OP_CODESEPARATOR in segwit scripts are
useful for Tumblebit so it is not disabled in this proposal

By disabling both, it guarantees that scriptCode serialized inside
SignatureHash() must be constant

If we use a softfork to remove FindAndDelete() and OP_CODESEPARATOR
from non-segwit scripts, we could completely remove FindAndDelete()
from the consensus code later by whitelisting all blocks before the
softfork block. The first step is to make them non-standard in the
next release.


 
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