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 <87leymuiu8.fsf@rustcorp.com.au>
In-Reply-To: <87leymuiu8.fsf@rustcorp.com.au>
From: Jeremy Rubin <jeremy.l.rubin@gmail.com>
Date: Mon, 7 Feb 2022 20:34:30 -0800
Message-ID: <CAD5xwhgP2_51Dvar0f1tsMrCXZ61W9-HnLgR45D-54Oc7-X1ag@mail.gmail.com>
To: Rusty Russell <rusty@rustcorp.com.au>, 
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="0000000000005733ef05d77a3c84"
Subject: Re: [bitcoin-dev] TXHASH + CHECKSIGFROMSTACKVERIFY in lieu of CTV
	and ANYPREVOUT
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Rusty,

Note that this sort of design introduces recursive covenants similarly to
how I described above.

Whether that is an issue or not precluding this sort of design or not, I
defer to others.

Best,

Jeremy


On Mon, Feb 7, 2022 at 7:57 PM Rusty Russell via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Russell O'Connor via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
> writes:
> > Given the overlap in functionality between CTV and ANYPREVOUT, I think it
> > makes sense to decompose their operations into their constituent pieces
> and
> > reassemble their behaviour programmatically.  To this end, I'd like to
> > instead propose OP_TXHASH and OP_CHECKSIGFROMSTACKVERIFY.
> >
> > OP_TXHASH would pop a txhash flag from the stack and compute a (tagged)
> > txhash in accordance with that flag, and push the resulting hash onto the
> > stack.
>
> It may be worth noting that OP_TXHASH can be further decomposed into
> OP_TX (and OP_TAGGEDHASH, or just reuse OP_SHA256).
>
> OP_TX would place the concatenated selected fields onto the stack
> (rather than hashing them) This is more compact for some tests
> (e.g. testing tx version for 2 is "OP_TX(version) 1 OP_EQUALS" vs
> "OP_TXHASH(version) 012345678...aabbccddeeff OP_EQUALS"), and also range
> testing (e.g amount less than X or greater than X, or less than 3 inputs).
>
> > I believe the difficulties with upgrading TXHASH can be mitigated by
> > designing a robust set of TXHASH flags from the start.  For example
> having
> > bits to control whether (1) the version is covered; (2) the locktime is
> > covered; (3) txids are covered; (4) sequence numbers are covered; (5)
> input
> > amounts are covered; (6) input scriptpubkeys are covered; (7) number of
> > inputs is covered; (8) output amounts are covered; (9) output
> scriptpubkeys
> > are covered; (10) number of outputs is covered; (11) the tapbranch is
> > covered; (12) the tapleaf is covered; (13) the opseparator value is
> > covered; (14) whether all, one, or no inputs are covered; (15) whether
> all,
> > one or no outputs are covered; (16) whether the one input position is
> > covered; (17) whether the one output position is covered; (18) whether
> the
> > sighash flags are covered or not (note: whether or not the sighash flags
> > are or are not covered must itself be covered).  Possibly specifying
> which
> > input or output position is covered in the single case and whether the
> > position is relative to the input's position or is an absolute position.
>
> These easily map onto OP_TX, "(1) the version is pushed as u32, (2) the
> locktime is pushed as u32, ...".
>
> We might want to push SHA256() of scripts instead of scripts themselves,
> to reduce possibility of DoS.
>
> I suggest, also, that 14 (and similarly 15) be defined two bits:
> 00 - no inputs
> 01 - all inputs
> 10 - current input
> 11 - pop number from stack, fail if >= number of inputs or no stack elems.
>
> Cheers,
> Rusty.
> _______________________________________________
> 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 class=3D"gmail_default" style=3D"font-family:arial,he=
lvetica,sans-serif;font-size:small;color:#000000"></div><div><div dir=3D"lt=
r" class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div dir=3D=
"ltr"><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,san=
s-serif;font-size:small;color:rgb(0,0,0)">Rusty,</div><div class=3D"gmail_d=
efault" style=3D"font-family:arial,helvetica,sans-serif;font-size:small;col=
or:rgb(0,0,0)"><br></div><div class=3D"gmail_default" style=3D"font-family:=
arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">Note that this=
 sort of design introduces recursive covenants similarly to how I described=
 above.</div><div class=3D"gmail_default" style=3D"font-family:arial,helvet=
ica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class=3D"gm=
ail_default" style=3D"font-family:arial,helvetica,sans-serif;font-size:smal=
l;color:rgb(0,0,0)">Whether that is an issue or not precluding this sort of=
 design or not, I defer to others.</div><br></div><div dir=3D"ltr"><div cla=
ss=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif;font-s=
ize:small;color:rgb(0,0,0)">Best,</div><div class=3D"gmail_default" style=
=3D"font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)=
"><br></div><div class=3D"gmail_default" style=3D"font-family:arial,helveti=
ca,sans-serif;font-size:small;color:rgb(0,0,0)">Jeremy</div><br></div></div=
></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail=
_attr">On Mon, Feb 7, 2022 at 7:57 PM Rusty Russell via bitcoin-dev &lt;<a =
href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.lin=
uxfoundation.org</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" =
style=3D"margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:s=
olid;border-left-color:rgb(204,204,204);padding-left:1ex">Russell O&#39;Con=
nor via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation=
.org" target=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a>&gt; write=
s:<br>
&gt; Given the overlap in functionality between CTV and ANYPREVOUT, I think=
 it<br>
&gt; makes sense to decompose their operations into their constituent piece=
s and<br>
&gt; reassemble their behaviour programmatically.=C2=A0 To this end, I&#39;=
d like to<br>
&gt; instead propose OP_TXHASH and OP_CHECKSIGFROMSTACKVERIFY.<br>
&gt;<br>
&gt; OP_TXHASH would pop a txhash flag from the stack and compute a (tagged=
)<br>
&gt; txhash in accordance with that flag, and push the resulting hash onto =
the<br>
&gt; stack.<br>
<br>
It may be worth noting that OP_TXHASH can be further decomposed into<br>
OP_TX (and OP_TAGGEDHASH, or just reuse OP_SHA256).<br>
<br>
OP_TX would place the concatenated selected fields onto the stack<br>
(rather than hashing them) This is more compact for some tests<br>
(e.g. testing tx version for 2 is &quot;OP_TX(version) 1 OP_EQUALS&quot; vs=
<br>
&quot;OP_TXHASH(version) 012345678...aabbccddeeff OP_EQUALS&quot;), and als=
o range<br>
testing (e.g amount less than X or greater than X, or less than 3 inputs).<=
br>
<br>
&gt; I believe the difficulties with upgrading TXHASH can be mitigated by<b=
r>
&gt; designing a robust set of TXHASH flags from the start.=C2=A0 For examp=
le having<br>
&gt; bits to control whether (1) the version is covered; (2) the locktime i=
s<br>
&gt; covered; (3) txids are covered; (4) sequence numbers are covered; (5) =
input<br>
&gt; amounts are covered; (6) input scriptpubkeys are covered; (7) number o=
f<br>
&gt; inputs is covered; (8) output amounts are covered; (9) output scriptpu=
bkeys<br>
&gt; are covered; (10) number of outputs is covered; (11) the tapbranch is<=
br>
&gt; covered; (12) the tapleaf is covered; (13) the opseparator value is<br=
>
&gt; covered; (14) whether all, one, or no inputs are covered; (15) whether=
 all,<br>
&gt; one or no outputs are covered; (16) whether the one input position is<=
br>
&gt; covered; (17) whether the one output position is covered; (18) whether=
 the<br>
&gt; sighash flags are covered or not (note: whether or not the sighash fla=
gs<br>
&gt; are or are not covered must itself be covered).=C2=A0 Possibly specify=
ing which<br>
&gt; input or output position is covered in the single case and whether the=
<br>
&gt; position is relative to the input&#39;s position or is an absolute pos=
ition.<br>
<br>
These easily map onto OP_TX, &quot;(1) the version is pushed as u32, (2) th=
e<br>
locktime is pushed as u32, ...&quot;.<br>
<br>
We might want to push SHA256() of scripts instead of scripts themselves,<br=
>
to reduce possibility of DoS.<br>
<br>
I suggest, also, that 14 (and similarly 15) be defined two bits:<br>
00 - no inputs<br>
01 - all inputs<br>
10 - current input<br>
11 - pop number from stack, fail if &gt;=3D number of inputs or no stack el=
ems.<br>
<br>
Cheers,<br>
Rusty.<br>
_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
</blockquote></div>

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