Sender: chris@suredbits.com
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From: Chris Stewart <chris@suredbits.com>
Date: Tue, 5 Jun 2018 19:17:52 -0500
Message-ID: <CAGL6+mH3ah_e-+e0=ce0-HmkaqU1YzoGNS5JXCXDbojxpVvX8Q@mail.gmail.com>
To: Johnson Lau <jl2012@xbt.hk>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="00000000000007e473056dee19b4"
Subject: Re: [bitcoin-dev] Disallow insecure use of SIGHASH_SINGLE
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Do you have any thoughts on expanding this to SIGHASH_NONE? Perhaps someone
else on the dev list can enlighten me, but is there a current use case for
SIGHASH_NONE that would suffer from it being non standard?

-Chris


On Thu, May 31, 2018 at 1:53 PM, Johnson Lau via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> I=E2=80=99ve made a PR to add a new policy to disallow using SIGHASH_SING=
LE
> without matched output:
>
> https://github.com/bitcoin/bitcoin/pull/13360
>
> Signature of this form is insecure, as it commits to no output while user=
s
> might think it commits to one. It is even worse in non-segwit scripts,
> which is effectively SIGHASH_NOINPUT|SIGHASH_NONE, so any UTXO of the sam=
e
> key could be stolen. (It=E2=80=99s restricted to only one UTXO in segwit,=
 but it=E2=80=99s
> still like a SIGHASH_NONE.)
>
> This is one of the earliest unintended consensus behavior. Since these
> signatures are inherently unsafe, I think it does no harm to disable this
> unintended =E2=80=9Cfeature=E2=80=9D with a softfork. But since these sig=
natures are
> currently allowed, the first step is to make them non-standard.
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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<div dir=3D"ltr"><div>Do you have any thoughts on expanding this to SIGHASH=
_NONE? Perhaps someone else on the dev list can enlighten me, but is there =
a current use case for SIGHASH_NONE that would suffer from it being non sta=
ndard?</div><div><br></div><div>-Chris<br></div><br></div><div class=3D"gma=
il_extra"><br><div class=3D"gmail_quote">On Thu, May 31, 2018 at 1:53 PM, J=
ohnson Lau via bitcoin-dev <span dir=3D"ltr">&lt;<a href=3D"mailto:bitcoin-=
dev@lists.linuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.linuxfou=
ndation.org</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I=E2=80=
=99ve made a PR to add a new policy to disallow using SIGHASH_SINGLE withou=
t matched output:<br>
<br>
<a href=3D"https://github.com/bitcoin/bitcoin/pull/13360" rel=3D"noreferrer=
" target=3D"_blank">https://github.com/bitcoin/<wbr>bitcoin/pull/13360</a><=
br>
<br>
Signature of this form is insecure, as it commits to no output while users =
might think it commits to one. It is even worse in non-segwit scripts, whic=
h is effectively SIGHASH_NOINPUT|SIGHASH_NONE, so any UTXO of the same key =
could be stolen. (It=E2=80=99s restricted to only one UTXO in segwit, but i=
t=E2=80=99s still like a SIGHASH_NONE.)<br>
<br>
This is one of the earliest unintended consensus behavior. Since these sign=
atures are inherently unsafe, I think it does no harm to disable this unint=
ended =E2=80=9Cfeature=E2=80=9D with a softfork. But since these signatures=
 are currently allowed, the first step is to make them non-standard.<br>
______________________________<wbr>_________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
<wbr>linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.<wbr>org=
/mailman/listinfo/bitcoin-<wbr>dev</a><br>
</blockquote></div><br></div>

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