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Fri, 10 Apr 2026 18:28:23 -0700 (PDT) X-Received: by 2002:a05:6808:1b21:b0:466:fcbb:1673 with SMTP id 5614622812f47-4789ee0c0admr2664572b6e.17.1775870903137; Fri, 10 Apr 2026 18:28:23 -0700 (PDT) Received: by 2002:a05:690c:4c01:b0:79a:e1a5:fe7e with SMTP id 00721157ae682-7ae240f9947ms7b3; Fri, 10 Apr 2026 18:25:12 -0700 (PDT) X-Received: by 2002:a05:690c:6e09:b0:7a4:e4e5:38ba with SMTP id 00721157ae682-7af71e47939mr61817237b3.45.1775870712087; Fri, 10 Apr 2026 18:25:12 -0700 (PDT) Date: Fri, 10 Apr 2026 18:25:11 -0700 (PDT) From: Antoine Riard To: Bitcoin Development Mailing List Message-Id: <459bd81c-584f-4adf-9112-bb733d381c99n@googlegroups.com> In-Reply-To: References: <0vqF88LoOnY4GiUB4vf-MdeZpTAtR70tokS3cLwt2DX0e6_fD1X_wyhPwWEdIdm6R88AULObIU08CWsb5QfeoaM5c4yXPqN5wHyCrqMCtfQ=@protonmail.com> <6wBygQ_pK40ZpU_CMXfzIy-6LkthOmEh-xd2g9bwUl-f8w2K6G4rUWJEssE2zeJgxyipGe2GrFH9y_TUUI48asqfh7dhi9A2rl7NpWyFW1o=@proton.me> <765490aa-5df3-4619-86cc-17570b6d3e99@mattcorallo.com> Subject: Re: [bitcoindev] In defense of a PQ output type MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_79488_1531942752.1775870711675" X-Original-Sender: antoine.riard@gmail.com Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -0.5 (/) ------=_Part_79488_1531942752.1775870711675 Content-Type: multipart/alternative; boundary="----=_Part_79489_1689714362.1775870711675" ------=_Part_79489_1689714362.1775870711675 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi, Thanks for rolling up the ball forward on this topic. I'm +1 on disentangling the introduction of a PQ safe scheme from the more fuzzy idea of freezing coins based on output types. Even the idea of "freezing" coins, the goal of why is still unclear. It sounds the motivations are blurred between ensuring coins are staying in the hands of their legitimate owners, a goal I can share but I don't see how freezing help here, from the more loose idea of ensuring there is no crash in the bitcoin price vs fiat in the face of CQRC-enabled attacks, which sounds to me a pandora box. Even in this eventuality, if there is a general concern on the network disruptions that might be induced by CRQC attacks (e.g chain instability due to reorgs by competing CRQC attackers), I believe there are still intermediary technical solutions, e.g rate-limiting the number of output types that can be spent by difficulty periods to minimize the risks of disruptions, while not technically confiscating anyone coin. Back to introducing a PQ safe scheme, I don't think in this thread the question is raised to enable to secure one's coin under double classic cryptogrraphic assumption and PQ assumption, i.e "hybrid" security (more for the risk of a cryptanalysis break of any PQ safe scheme that would be introduced at the consensus-level). It might more a real engineering burden, though I believe it's giving more flexibility for technically savy bitcoin users to secure one's stack. Anyway, I think it's good to have a scheme ready early on given the development cycle to have stuff available on HW wallets and HSMs. E.g BIP32 support was added in 2018 on Gemalto's HSM i.e a mere 6 years after the standard introduction (which is not that bad given that blockchain were recents actors in the hardware industry at the time). Best, Antoine OTS hash: 6d7c2f5ab01bcdda4ec27d4c21198a9b13ce1dfd138c4a2e6dfaedee9458f6c0 Le Saturday, April 11, 2026 =C3=A0 2:06:55=E2=80=AFAM UTC+1, Hayashi a =C3= =A9crit : > Hi Conduition, Matt and Ethan > > > an ownership proof used for non-BIP32 hashed addresses > I=E2=80=99m concerned that shared xpubs could become an attack vector if = we allow=20 > ZKP of hash preimages for unused addresses (excluding P2PK/P2TR). Given= =20 > that, are there alternative methods for publishing proof of ownership tha= t=20 > we should consider? > > > It seems the current default stance is effectively "do not freeze,"=20 > because preserving the status quo is the only path if we cannot reach=20 > consensus (and if we do not chose hardfork). However, by formalizing a=20 > freezing plan=E2=80=94either through a new BIP or an amendment to BIP361= =E2=80=94I believe=20 > we gain several strategic advantages: > > *Clarity on P2MR discussion*: It would clarify the ongoing P2MR and P2TR= =20 > discussions by defining how P2TR will be treated (I personally prefer P2M= R). > > *Incentivized Migration*: Establishing a clear future plan encourages=20 > users to migrate to BIP32-hardened addresses with longer time period whic= h=20 > eventually maximize recovery. > > *Advance Planning for CRQCs*: We will not panic on the edge case scenario= =20 > that CRQCs arrive earlier than PQ signature scheme adoption or when we fi= nd=20 > out we cannot allow enough migration period after PQ signature scheme=20 > adoption (I strongly believe we also have to prepare for this future). > > While further R&D is required, we likely have sufficient information to= =20 > formalize a framework now. We can also disable or modify the defined=20 > freezing plan if the threat landscape changes significantly. > > Hayashi > 2026=E5=B9=B44=E6=9C=8811=E6=97=A5=E5=9C=9F=E6=9B=9C=E6=97=A5 8:33:54 UTC= +8 Ethan Heilman: > >> > IMO even something like P2MR's additional cost will strongly=20 >> discourage adoption. >> >> I don't agree. >> >> Over time as quantum attacks become a bigger and bigger concern for=20 >> holders, wallets will want to show that they can offer security against= =20 >> CRQCs. This is especially true for wallets focused on high value Bitcoin= =20 >> outputs. Even if someone thinks there is only a 2% chance they lose all= =20 >> their Bitcoin because of a quantum computer, that 2% chance will keep th= em=20 >> up at night. >> >> P2MR would have 17.25 more vBytes, an 11% overhead. >> >> P2TR 1 input, 2 output - key path spend. 154 vbytes >> P2MR 1 input, 2 output - spending a schnorr sig leaf of a P2MR output=20 >> with two leafs: 1. PQ sig leaf and 2. Schnorr sig leaf. 171.25 vbytes >> >> I'm stacking the deck against P2MR here. Under some circumstances P2MR= =20 >> has lower fees than P2TR. >> >> It is hard to imagine someone holding significant quantities of Bitcoin= =20 >> not wanting to pay 50 sats to ensure their Bitcoin isn't stolen by a=20 >> quantum computer. >> >> >> On Fri, Apr 10, 2026 at 7:10=E2=80=AFPM Matt Corallo =20 >> wrote: >> >>> >>> >>> On 4/10/26 1:03 PM, conduition wrote: >>> >> But as mentioned above I do not see why any addition of hash based= =20 >>> signatures to tapscript should require any kind of community consensus = on=20 >>> future disablement of insecure spend paths >>> >=20 >>> > I think Antoine's point here is that if we introduce a PQC opcode to= =20 >>> tapscript but choose NOT to deploy P2MR, and then encourage people to u= se=20 >>> that opcode in P2TR script leaves, then we are locking ourselves into t= he=20 >>> assumption that the community will later disable P2TR key-path spending= -=20 >>> otherwise those addresses will be compromised by a CRQC and the PQC lea= f=20 >>> script is useless. >>> >>> Right, but you cut my quote off and appear to be responding to a point = I=20 >>> didn't make? The very next=20 >>> few words that you cut were "not only is it a likely prerequisite for a= n=20 >>> alternative output type".=20 >>> Yes, we have to figure out what kind of output type we want, whether=20 >>> P2MR (360), P2TRv2 or just=20 >>> P2TR. There are strong arguments for each. But none of that has any=20 >>> bearing on whether we add hash=20 >>> based signatures to tapscript. We have to add hash based signatures to= =20 >>> tapscript first no matter=20 >>> what output type we want! >>> >>> >> Adding a PQ output type which no one will use (eg one where use of= =20 >>> the hash-based signature is mandatory, which drives fees up hugely and = has=20 >>> all the drawbacks you mention) is not a risk mitigation strategy - it d= oes=20 >>> not materially allow for any migration and doesn't accomplish much of= =20 >>> anything. But as mentioned above I do not see why any addition of hash= =20 >>> based signatures to tapscript >>> >=20 >>> > I don't think anyone is suggesting deployment of an output type with= =20 >>> mandatory hash-based signatures. That would be borderline unusable for= =20 >>> anyone but large companies and wealthy elites. >>> >=20 >>> > Every decent proposal I've seen has suggested using PQC in tandem wit= h=20 >>> ECC across multiple tapscript leaves, whether in some bastardized varia= nt=20 >>> of P2TR, or in BIP360's P2MR. >>> >>> IMO even something like P2MR's additional cost will strongly discourage= =20 >>> adoption. We have a very=20 >>> long history with Bitcoin wallets not only refusing to adopt new=20 >>> features but actively making some=20 >>> of the worst possible design decisions from a Bitcoin PoV. IMO we shoul= d=20 >>> very strongly not give them=20 >>> any excuse, even if that's just fees. >>> >>> Matt >>> >>> --=20 >>> You received this message because you are subscribed to the Google=20 >>> Groups "Bitcoin Development Mailing List" group. >>> To unsubscribe from this group and stop receiving emails from it, send= =20 >>> an email to bitcoindev+...@googlegroups.com. >>> >> To view this discussion visit=20 >>> https://groups.google.com/d/msgid/bitcoindev/765490aa-5df3-4619-86cc-17= 570b6d3e99%40mattcorallo.com >>> . >>> >> --=20 You received this message because you are subscribed to the Google Groups "= Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/= 459bd81c-584f-4adf-9112-bb733d381c99n%40googlegroups.com. ------=_Part_79489_1689714362.1775870711675 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi,

Thanks for rolling up the ball forward on this topic.
<= br />I'm +1 on disentangling the introduction of a PQ safe scheme from
the more fuzzy idea of freezing coins based on output types.

Ev= en the idea of "freezing" coins, the goal of why is still unclear.
It = sounds the motivations are blurred between ensuring coins are
staying = in the hands of their legitimate owners, a goal I can share
but I don'= t see how freezing help here, from the more loose idea of
ensuring the= re is no crash in the bitcoin price vs fiat in the face
of CQRC-enable= d attacks, which sounds to me a pandora box.

Even in this eventu= ality, if there is a general concern on the network
disruptions that m= ight be induced by CRQC attacks (e.g chain instability
due to reorgs b= y competing CRQC attackers), I believe there are still
intermediary te= chnical solutions, e.g rate-limiting the number of output
types that c= an be spent by difficulty periods to minimize the risks of
disruptions= , while not technically confiscating anyone coin.

Back to introd= ucing a PQ safe scheme, I don't think in this thread
the question is r= aised to enable to secure one's coin under double
classic cryptogrraph= ic assumption and PQ assumption, i.e "hybrid"
security (more for the r= isk of a cryptanalysis break of any PQ safe
scheme that would be intro= duced at the consensus-level). It might
more a real engineering burden= , though I believe it's giving more
flexibility for technically savy b= itcoin users to secure one's stack.

Anyway, I think it's good to= have a scheme ready early on given
the development cycle to have stuf= f available on HW wallets and
HSMs. E.g BIP32 support was added in 201= 8 on Gemalto's HSM i.e a
mere 6 years after the standard introduction = (which is not that
bad given that blockchain were recents actors in th= e hardware
industry at the time).

Best,
Antoine
O= TS hash: 6d7c2f5ab01bcdda4ec27d4c21198a9b13ce1dfd138c4a2e6dfaedee9458f6c0
Le Saturday, April 11, 2026 =C3=A0 2:06:55=E2=80=AFAM UTC+1, Hayashi a =C3= =A9crit=C2=A0:
2026=E5=B9=B44=E6=9C=8811=E6=97=A5=E5=9C=9F=E6=9B=9C=E6=97= =A5 8:33:54 UTC+8 Ethan Heilman:
=
>=C2=A0 IMO even something like P2MR's additional cost will strongly discourage= adoption.

I don't agree.

Over tim= e as quantum attacks become a bigger and bigger concern for holders, wallet= s will want to show that they can offer security against CRQCs. This is esp= ecially true for wallets focused on high value Bitcoin outputs. Even if som= eone thinks there is only a 2% chance they lose all their Bitcoin because o= f a quantum computer, that 2% chance will keep them up at night.

P2M= R would have 17.25 more vBytes, an 11% overhead.

P2TR 1 input, 2 out= put - key path spend. 154 vbytes
P2MR=20 1 input, 2 output - spending a=C2=A0schnorr sig leaf of a P2MR output with = two leafs: 1. PQ sig leaf and 2. Schnorr sig leaf.=C2=A0171.25 vbytes
I'm stacking the deck against=C2=A0P2MR here. Under some circumstance= s P2MR has lower fees than P2TR.

It is hard to imagine someone holdi= ng significant quantities of Bitcoin not wanting to pay 50 sats=C2=A0to ens= ure their Bitcoin isn't stolen by a quantum computer.


=
On Fri, Apr 10, 2026 at 7:10=E2=80=AFPM Matt Corallo= <lf-l...@mattcorallo.com> wrote:


On 4/10/26 1:03 PM, conduition wrote:
>> But as mentioned above I do not see why any addition of hash based= signatures to tapscript should require any kind of community consensus on = future disablement of insecure spend paths
>
> I think Antoine's point here is that if we introduce a PQC opcode = to tapscript but choose NOT to deploy P2MR, and then encourage people to us= e that opcode in P2TR script leaves, then we are locking ourselves into the= assumption that the community will later disable P2TR key-path spending - = otherwise those addresses will be compromised by a CRQC and the PQC leaf sc= ript is useless.

Right, but you cut my quote off and appear to be responding to a point I di= dn't make? The very next
few words that you cut were "not only is it a likely prerequisite for = an alternative output type".
Yes, we have to figure out what kind of output type we want, whether P2MR (= 360), P2TRv2 or just
P2TR. There are strong arguments for each. But none of that has any bearing= on whether we add hash
based signatures to tapscript. We have to add hash based signatures to taps= cript first no matter
what output type we want!

>> Adding a PQ output type which no one will use (eg one where use of= the hash-based signature is mandatory, which drives fees up hugely and has= all the drawbacks you mention) is not a risk mitigation strategy - it does= not materially allow for any migration and doesn't accomplish much of = anything. But as mentioned above I do not see why any addition of hash base= d signatures to tapscript
>
> I don't think anyone is suggesting deployment of an output type wi= th mandatory hash-based signatures. That would be borderline unusable for a= nyone but large companies and wealthy elites.
>
> Every decent proposal I've seen has suggested using PQC in tandem = with ECC across multiple tapscript leaves, whether in some bastardized vari= ant of P2TR, or in BIP360's P2MR.

IMO even something like P2MR's additional cost will strongly discourage= adoption. We have a very
long history with Bitcoin wallets not only refusing to adopt new features b= ut actively making some
of the worst possible design decisions from a Bitcoin PoV. IMO we should ve= ry strongly not give them
any excuse, even if that's just fees.

Matt

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