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From: "Russell O'Connor" <roconnor@blockstream.com>
Date: Sat, 11 Feb 2023 09:40:38 -0500
Message-ID: <CAMZUoKm3OJ4DVCnpGk+CfJGnMMnuJqsqNMr-sJh53Rx99wj9CA@mail.gmail.com>
To: Anthony Towns <aj@erisian.com.au>,
"Russell O'Connor via bitcoin-dev" <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="000000000000a0d2d805f46d994f"
Subject: Re: [bitcoin-dev] Unenforceable fee obligations in multiparty
protocols with Taproot inputs
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Yes. If you would otherwise sign the tapleaf, then I would recommend also
signing the entire tapbranch.
On Sat, Feb 11, 2023 at 12:15 AM Anthony Towns <aj@erisian.com.au> wrote:
> On 9 February 2023 12:04:16 am AEST, Russell O'Connor via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
> >The fix for the bug is to sign the entire tapbranch instead of the
> tapleaf.
> >
> >On Wed., Feb. 8, 2023, 04:35 Michael Folkson, <
> michaelfolkson@protonmail.com>
> >wrote:
> >
> >> Hi Andrew
> >>
> >> > There is a bug in Taproot that allows the same Tapleaf to be repeated
> >> multiple times in the same Taproot, potentially at different Taplevels
> >> incurring different Tapfee rates.
> >> >
> >> > The countermeasure is that you should always know the entire Taptree
> >> when interacting with someone's Tapspend.
> >>
> >> I wouldn't say it is a "bug" unless there is a remedy for the bug that
> >> wasn't (and retrospectively should have been) included in the Taproot
> >> design. In retrospect and assuming you could redesign the Taproot
> consensus
> >> rules again today would you prevent spending from a valid P2TR address
> if a
> >> repeated Tapleaf hash was used to prove that a spending path was
> embedded
> >> in a Taproot tree? That's the only thing I can think of to attempt to
> >> remedy this "bug" and it would only be a partial protection as proving a
> >> spending path exists within a Taproot tree only requires a subset of the
> >> Tapleaf hashes.
> >>
> >> I only point this out because there seems to be a push to find "bugs"
> and
> >> "accidental blowups" in the Taproot design currently. No problem with
> this
> >> if there are any, they should definitely be highlighted and discussed if
> >> they do exist. The nearest to a possible inferior design decision thus
> far
> >> that I'm aware of is x-only pubkeys in BIP340 [0].
> >>
> >> Thanks
> >> Michael
> >>
> >> [0]:
> >>
> https://btctranscripts.com/london-bitcoin-devs/2022-08-11-tim-ruffing-musig2/#a-retrospective-look-at-bip340
> >>
> >> --
> >> Michael Folkson
> >> Email: michaelfolkson at protonmail.com
> >> Keybase: michaelfolkson
> >> PGP: 43ED C999 9F85 1D40 EAF4 9835 92D6 0159 214C FEE3
> >>
> >> ------- Original Message -------
> >> On Tuesday, February 7th, 2023 at 18:35, Russell O'Connor via
> bitcoin-dev <
> >> bitcoin-dev@lists.linuxfoundation.org> wrote:
> >>
> >> There is a bug in Taproot that allows the same Tapleaf to be repeated
> >> multiple times in the same Taproot, potentially at different Taplevels
> >> incurring different Tapfee rates.
> >>
> >> The countermeasure is that you should always know the entire Taptree
> when
> >> interacting with someone's Tapspend.
> >>
> >>
> >> On Tue, Feb 7, 2023 at 1:10 PM Andrew Poelstra via bitcoin-dev <
> >> bitcoin-dev@lists.linuxfoundation.org> wrote:
> >>
> >>>
> >>> Some people highlighted some minor problems with my last email:
> >>>
> >>> On Tue, Feb 07, 2023 at 01:46:22PM +0000, Andrew Poelstra via
> bitcoin-dev
> >>> wrote:
> >>> >
> >>> > <snip>
> >>> >
> >>> > [1] https://bitcoin.sipa.be/miniscript/
> >>> > [2] In Taproot, if you want to prevent signatures migrating to
> another
> >>> > branch or within a branch, you can use the CODESEPARATOR opcode
> >>> > which was redisegned in Taproot for exactly this purpose... we
> >>> > really did about witness malleation in its design!
> >>>
> >>> In Taproot the tapleaf hash is always covered by the signature (though
> >>> not in some ANYONECANPAY proposals) so you can never migrate signatures
> >>> between tapbranches.
> >>>
> >>> I had thought this was the case, but then I re-confused myself by
> >>> reading BIP 341 .... which has much of the sighash specified, but not
> >>> all of it! The tapleaf hash is added in BIP 342.
> >>>
> >>> >
> >>> > If you want to prevent signatures from moving around *within* a
> >>> > branch,
> >>> >
> >>>
> >>> And this sentence I just meant to delete :)
> >>>
> >>>
> >>> --
> >>> Andrew Poelstra
> >>> Director of Research, Blockstream
> >>> Email: apoelstra at wpsoftware.net
> >>> Web: https://www.wpsoftware.net/andrew
> >>>
> >>> The sun is always shining in space
> >>> -Justin Lewis-Webster
> >>>
> >>> _______________________________________________
> >>> bitcoin-dev mailing list
> >>> bitcoin-dev@lists.linuxfoundation.org
> >>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> >>>
> >>
> >>
>
> Is this something that should be fixed in bip118 signatures then?
>
> Cheers,
> aj
> --
> Sent from my phone.
>
--000000000000a0d2d805f46d994f
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div>Yes.=C2=A0 If you would otherwise sign the tapleaf, t=
hen I would recommend also signing the entire tapbranch.</div><div><br></di=
v><div><br></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" clas=
s=3D"gmail_attr">On Sat, Feb 11, 2023 at 12:15 AM Anthony Towns <<a href=
=3D"mailto:aj@erisian.com.au">aj@erisian.com.au</a>> wrote:<br></div><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-lef=
t:1px solid rgb(204,204,204);padding-left:1ex">On 9 February 2023 12:04:16 =
am AEST, Russell O'Connor via bitcoin-dev <<a href=3D"mailto:bitcoin=
-dev@lists.linuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.linuxfo=
undation.org</a>> wrote:<br>
>The fix for the bug is to sign the entire tapbranch instead of the tapl=
eaf.<br>
><br>
>On Wed., Feb. 8, 2023, 04:35 Michael Folkson, <<a href=3D"mailto:mic=
haelfolkson@protonmail.com" target=3D"_blank">michaelfolkson@protonmail.com=
</a>><br>
>wrote:<br>
><br>
>> Hi Andrew<br>
>><br>
>> > There is a bug in Taproot that allows the same Tapleaf to be =
repeated<br>
>> multiple times in the same Taproot, potentially at different Taple=
vels<br>
>> incurring different Tapfee rates.<br>
>> ><br>
>> > The countermeasure is that you should always know the entire =
Taptree<br>
>> when interacting with someone's Tapspend.<br>
>><br>
>> I wouldn't say it is a "bug" unless there is a remed=
y for the bug that<br>
>> wasn't (and retrospectively should have been) included in the =
Taproot<br>
>> design. In retrospect and assuming you could redesign the Taproot =
consensus<br>
>> rules again today would you prevent spending from a valid P2TR add=
ress if a<br>
>> repeated Tapleaf hash was used to prove that a spending path was e=
mbedded<br>
>> in a Taproot tree? That's the only thing I can think of to att=
empt to<br>
>> remedy this "bug" and it would only be a partial protect=
ion as proving a<br>
>> spending path exists within a Taproot tree only requires a subset =
of the<br>
>> Tapleaf hashes.<br>
>><br>
>> I only point this out because there seems to be a push to find &qu=
ot;bugs" and<br>
>> "accidental blowups" in the Taproot design currently. No=
problem with this<br>
>> if there are any, they should definitely be highlighted and discus=
sed if<br>
>> they do exist. The nearest to a possible inferior design decision =
thus far<br>
>> that I'm aware of is x-only pubkeys in BIP340 [0].<br>
>><br>
>> Thanks<br>
>> Michael<br>
>><br>
>> [0]:<br>
>> <a href=3D"https://btctranscripts.com/london-bitcoin-devs/2022-08-=
11-tim-ruffing-musig2/#a-retrospective-look-at-bip340" rel=3D"noreferrer" t=
arget=3D"_blank">https://btctranscripts.com/london-bitcoin-devs/2022-08-11-=
tim-ruffing-musig2/#a-retrospective-look-at-bip340</a><br>
>><br>
>> --<br>
>> Michael Folkson<br>
>> Email: michaelfolkson at <a href=3D"http://protonmail.com" rel=3D"=
noreferrer" target=3D"_blank">protonmail.com</a><br>
>> Keybase: michaelfolkson<br>
>> PGP: 43ED C999 9F85 1D40 EAF4 9835 92D6 0159 214C FEE3<br>
>><br>
>> ------- Original Message -------<br>
>> On Tuesday, February 7th, 2023 at 18:35, Russell O'Connor via =
bitcoin-dev <<br>
>> <a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D=
"_blank">bitcoin-dev@lists.linuxfoundation.org</a>> wrote:<br>
>><br>
>> There is a bug in Taproot that allows the same Tapleaf to be repea=
ted<br>
>> multiple times in the same Taproot, potentially at different Taple=
vels<br>
>> incurring different Tapfee rates.<br>
>><br>
>> The countermeasure is that you should always know the entire Taptr=
ee when<br>
>> interacting with someone's Tapspend.<br>
>><br>
>><br>
>> On Tue, Feb 7, 2023 at 1:10 PM Andrew Poelstra via bitcoin-dev <=
;<br>
>> <a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D=
"_blank">bitcoin-dev@lists.linuxfoundation.org</a>> wrote:<br>
>><br>
>>><br>
>>> Some people highlighted some minor problems with my last email=
:<br>
>>><br>
>>> On Tue, Feb 07, 2023 at 01:46:22PM +0000, Andrew Poelstra via =
bitcoin-dev<br>
>>> wrote:<br>
>>> ><br>
>>> > <snip><br>
>>> ><br>
>>> > [1] <a href=3D"https://bitcoin.sipa.be/miniscript/" rel=
=3D"noreferrer" target=3D"_blank">https://bitcoin.sipa.be/miniscript/</a><b=
r>
>>> > [2] In Taproot, if you want to prevent signatures migrati=
ng to another<br>
>>> > branch or within a branch, you can use the CODESEPARATOR =
opcode<br>
>>> > which was redisegned in Taproot for exactly this purpose.=
.. we<br>
>>> > really did about witness malleation in its design!<br>
>>><br>
>>> In Taproot the tapleaf hash is always covered by the signature=
(though<br>
>>> not in some ANYONECANPAY proposals) so you can never migrate s=
ignatures<br>
>>> between tapbranches.<br>
>>><br>
>>> I had thought this was the case, but then I re-confused myself=
by<br>
>>> reading BIP 341 .... which has much of the sighash specified, =
but not<br>
>>> all of it! The tapleaf hash is added in BIP 342.<br>
>>><br>
>>> ><br>
>>> > If you want to prevent signatures from moving around *wit=
hin* a<br>
>>> > branch,<br>
>>> ><br>
>>><br>
>>> And this sentence I just meant to delete :)<br>
>>><br>
>>><br>
>>> --<br>
>>> Andrew Poelstra<br>
>>> Director of Research, Blockstream<br>
>>> Email: apoelstra at <a href=3D"http://wpsoftware.net" rel=3D"n=
oreferrer" target=3D"_blank">wpsoftware.net</a><br>
>>> Web: <a href=3D"https://www.wpsoftware.net/andrew" rel=3D"nore=
ferrer" target=3D"_blank">https://www.wpsoftware.net/andrew</a><br>
>>><br>
>>> The sun is always shining in space<br>
>>> -Justin Lewis-Webster<br>
>>><br>
>>> _______________________________________________<br>
>>> bitcoin-dev mailing list<br>
>>> <a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" targe=
t=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.linuxfounda=
tion.org/mailman/listinfo/bitcoin-dev</a><br>
>>><br>
>><br>
>><br>
<br>
Is this something that should be fixed in bip118 signatures then?<br>
<br>
Cheers,<br>
aj<br>
-- <br>
Sent from my phone.<br>
</blockquote></div>
--000000000000a0d2d805f46d994f--
|
