From: Mark Friedenbach <mark@friedenbach.org>
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Date: Wed, 15 Nov 2017 09:54:17 -1000
Message-Id: <081A517B-B730-43AB-9D4E-4F696EFD91A3@friedenbach.org>
References: <53A587C3-DAC1-4055-875F-96B61717ACE6@xbt.hk>
In-Reply-To: <53A587C3-DAC1-4055-875F-96B61717ACE6@xbt.hk>
To: Johnson Lau <jl2012@xbt.hk>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Making OP_CODESEPARATOR and FindAndDelete in
	non-segwit scripts non-standard
Precedence: list


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As good of an idea as it may or may not be to remove this feature from the c=
ode base, actually doing so would be crossing a boundary that we have not pr=
eviously 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 discour=
age 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 d=
estroying value and is something that we have only done in the past either b=
ecause we didn=E2=80=99t understand forks and best practices very well, or b=
ecause the features (now disabled) were fundamentally insecure and resulted i=
n other people=E2=80=99s coins being vulnerable. This latter concern does no=
t apply here as far as I=E2=80=99m aware.

> On Nov 15, 2017, at 8:02 AM, Johnson Lau via bitcoin-dev <bitcoin-dev@list=
s.linuxfoundation.org> wrote:
>=20
> In https://github.com/bitcoin/bitcoin/pull/11423 I propose to make OP_CODE=
SEPARATOR and FindAndDelete in non-segwit scripts non-standard
>=20
> I think FindAndDelete() is one of the most useless and complicated functio=
ns in the script language. It is omitted from segwit (BIP143), but we still n=
eed to support it in non-segwit scripts. Actually, FindAndDelete() would onl=
y be triggered in some weird edge cases like using out-of-range SIGHASH_SING=
LE.
>=20
> Non-segwit scripts also use a FindAndDelete()-like function to remove OP_C=
ODESEPARATOR from scriptCode. Note that in BIP143, only executed OP_CODESEPA=
RATOR are removed so it doesn=E2=80=99t have the FindAndDelete()-like functi=
on. OP_CODESEPARATOR in segwit scripts are useful for Tumblebit so it is not=
 disabled in this proposal
>=20
> By disabling both, it guarantees that scriptCode serialized inside Signatu=
reHash() must be constant
>=20
> If we use a softfork to remove FindAndDelete() and OP_CODESEPARATOR from n=
on-segwit scripts, we could completely remove FindAndDelete() from the conse=
nsus code later by whitelisting all blocks before the softfork block. The fi=
rst step is to make them non-standard in the next release.
>=20
>=20
> =20
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=3D=
utf-8"></head><body dir=3D"auto">As good of an idea as it may or may not be t=
o remove this feature from the code base, actually doing so&nbsp;would be cr=
ossing a boundary that we have not previously been willing to do except unde=
r extraordinary duress. The nature of bitcoin is such that we do not know an=
d cannot know what transactions exist out there pre-signed and making use of=
 these features.<div><br></div><div>It may be a good idea to make these feat=
ures non standard to further discourage their use, but I object to doing so w=
ith the justification of eventually disabling them for all transactions. Tak=
ing that step has the potential of destroying value and is something that we=
 have only done in the past either because we didn=E2=80=99t understand fork=
s and best practices very well, or because the features (now disabled) were f=
undamentally insecure and resulted in other people=E2=80=99s coins being vul=
nerable. This latter concern does not apply here as far as I=E2=80=99m aware=
.<br><div><br>On Nov 15, 2017, at 8:02 AM, Johnson Lau via bitcoin-dev &lt;<=
a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.li=
nuxfoundation.org</a>&gt; wrote:<br><br></div><blockquote type=3D"cite"><div=
><meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Dutf-8">In=
&nbsp;<a href=3D"https://github.com/bitcoin/bitcoin/pull/11423" class=3D"">h=
ttps://github.com/bitcoin/bitcoin/pull/11423</a>&nbsp;I propose to make&nbsp=
;OP_CODESEPARATOR and FindAndDelete in non-segwit scripts non-standard<div c=
lass=3D""><br class=3D""></div><div class=3D"">I think FindAndDelete() is on=
e of the most useless and complicated functions in the script language. It i=
s omitted from segwit (BIP143), but we still need to support it in non-segwi=
t scripts. Actually, FindAndDelete() would only be triggered in some weird e=
dge cases like using out-of-range SIGHASH_SINGLE.</div><div class=3D""><br c=
lass=3D""></div><div class=3D"">Non-segwit scripts also use a FindAndDelete(=
)-like function to remove OP_CODESEPARATOR from scriptCode. Note that in BIP=
143, only executed OP_CODESEPARATOR are removed so it doesn=E2=80=99t have t=
he FindAndDelete()-like function. OP_CODESEPARATOR in segwit scripts are use=
ful for Tumblebit so it is not disabled in this proposal</div><div class=3D"=
"><br class=3D""></div><div class=3D"">By disabling both, it guarantees that=
 scriptCode serialized inside SignatureHash() must be constant</div><div cla=
ss=3D""><br class=3D""></div><div class=3D"">If we use a softfork to remove =
FindAndDelete() and OP_CODESEPARATOR from non-segwit scripts, we could compl=
etely remove FindAndDelete() from the consensus code later by whitelisting a=
ll blocks before the softfork block. The first step is to make them non-stan=
dard in the next release.</div><div class=3D""><br class=3D""></div><div cla=
ss=3D""><br class=3D""></div><div class=3D"">&nbsp;</div></div></blockquote>=
<blockquote type=3D"cite"><div><span>_______________________________________=
________</span><br><span>bitcoin-dev mailing list</span><br><span><a href=3D=
"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.linuxfounda=
tion.org</a></span><br><span><a href=3D"https://lists.linuxfoundation.org/ma=
ilman/listinfo/bitcoin-dev">https://lists.linuxfoundation.org/mailman/listin=
fo/bitcoin-dev</a></span><br></div></blockquote></div></body></html>=

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