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[2a00:1450:4864:20::12c]) by gmr-mx.google.com with ESMTPS id 5b1f17b1804b1-455edeb6b25si2105245e9.2.2025.07.14.11.52.31 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Jul 2025 11:52:31 -0700 (PDT) Received-SPF: pass (google.com: domain of jameson.lopp@gmail.com designates 2a00:1450:4864:20::12c as permitted sender) client-ip=2a00:1450:4864:20::12c; Received: by mail-lf1-x12c.google.com with SMTP id 2adb3069b0e04-553ba7f11cbso4694039e87.1 for ; Mon, 14 Jul 2025 11:52:31 -0700 (PDT) X-Gm-Gg: ASbGncuxbdrm0yT6+MGDgIT5Loaa4p9bXOStlbugVFlUF70vgtfMgx5hNaIT/wv1o5z gV81ptPY37fc218nFGttX2TUsg3YBZuR7FENZk/lq15ZD+YHpkoNOz+PWLGbUfreQY1zqoigolr 6K/JrlSIGU6wFjKYgmLNkGymWZ9rW9XlUFqVFsmQnakLzrP9lTltXk3JH5b0rqOJisOz6i3mGv4 30Q194= X-Received: by 2002:a05:6512:110d:b0:554:f74b:789e with SMTP id 2adb3069b0e04-55a04633397mr4485634e87.43.1752519150697; Mon, 14 Jul 2025 11:52:30 -0700 (PDT) MIME-Version: 1.0 References: <37ed2e5d-34cd-4391-84b8-5bcc6d42c617n@googlegroups.com> <4d9ce13e-466d-478b-ab4d-00404c80d620n@googlegroups.com> In-Reply-To: <4d9ce13e-466d-478b-ab4d-00404c80d620n@googlegroups.com> From: Jameson Lopp Date: Mon, 14 Jul 2025 14:52:17 -0400 X-Gm-Features: Ac12FXysF7q1eRvH1psP0knynQcNjsy6RLPkeGUIbVXKJe-HDLJ3zyIokpgOYfA Message-ID: Subject: Re: [bitcoindev] Re: A Post Quantum Migration Proposal To: Antoine Riard Cc: Bitcoin Development Mailing List Content-Type: multipart/alternative; boundary="0000000000007083180639e82939" X-Original-Sender: jameson.lopp@gmail.com X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@gmail.com header.s=20230601 header.b=nqJZcprW; spf=pass (google.com: domain of jameson.lopp@gmail.com designates 2a00:1450:4864:20::12c as permitted sender) smtp.mailfrom=jameson.lopp@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com; dara=pass header.i=@googlegroups.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 (/) --0000000000007083180639e82939 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Jul 14, 2025 at 10:09=E2=80=AFAM Antoine Riard wrote: > Hi Jameson, > > Thanks for your thoughts on this complex subject. > > First and foremost, I think your following statement: "Never before has > Bitcoin faced > an existential threat to its cryptographic primitives" is very myopic, > given that > cryptanalysts and number theorists are making progress every year in thei= r > works, and > each bitcoin cryptographic primitive has been and is constantly analyzed > to uncover > potential weaknesses. > > So in my view the quantum threat is a bit less specific that the image > you're painting > of it. Even if go all to upgrade to lattices-based schemes, we have no > certainty that > novels flaws won't be found, one can just go to see the modifications of > the NIST-approved > schemes in between their rounds of selection that we'll never reach > something like > "self-sovereign peace of mind"...Unless we start to forbid people of > practicing the > art of mathematics, practice which has been ongoing since Euclide and > Pythagore... > > I do concede that quantum is a bit different, as after all new physics > paradigm > do not happen often (Heisenberg published in the 20s iirc), though that's > in my > view the flaw of your reasoning as you're assuming some "post-quantum" > upgraded > state where bitcoin, as a community and a network, would be definitely > safe from > advances in applied science. At minima, in my understanding, you're > arguing this > time is different to justify extra-ordinary technical measures never seen > before, > namely the freezing of "vulnerable" coins. > > Correct, this time is different in that we're not talking about vague unknown weaknesses. Rather, we're talking about a known algorithm that makes breaking cryptographic primitives orders of magnitude cheaper. The unknown becomes the rate at which advancements in quantum computing will be achieved, which is concerning given the funding going into pushing said advancements forward. > I'm worried this is opening a Pandora box, where we would introduce a > precedent > that it is legitimate as a community to technicaly confiscate some coins > of users, > without their _consents_, for extra-ordinary reasons. That's opening a > worms of > shenanigans in the future...There is no guarantee that this precedent won= 't > be leveraged in the future by any group of entities to justify future > upgrades > eroding one of the "fundamental property" you're yourself deeming as > valuable. > > This is a fair fear, though the counterpoint is that it is legitimate for the community to protect itself against security threats. It just so happens that both viewpoints can be valid. This is especially worrying as if I'm understanding you correctly you're > justifying > this position as that somehow we should protect the price of the currency > as an end > in itself (i.e "Beyond its impact on price, ..."). It's unclear the price > of bitcoin > versus what fiat or hard asset (e.g oil) you have in mind. And in anyway, > as far > as I know, none of the bitcoin devs is seating on the board of the FED, > the ECB > or the BoJ... > > To put it simply, even if a quantum attacker can tomorrow starts to steal > vulnerable coins, 1 BTC will be always equal to 1 BTC. Full stop. In my > humble > opinion, let's not introduce the idea that, we, as a community of > stakeholders > and developers we have a positive "fiduciary" duty to act to maintain the > price > of bitcoin in some "monetary snake" with another class of assets... > > Protocol developers have no fiduciary duty to bitcoin holders. I wouldn't argue they have any duty whatsoever to users. Bitcoin is not (yet) a unit of account. The ecosystem does not run on 1 BTC =3D 1 BTC. The purchasing power of satoshis is very much relevant to the health and sustainability of the ecosystem at its current level. I would not claim that "devs must do something" - rather, I believe that the incentives of other groups I outlined will roughly align them with my thinking. That's also the problem with game theory, all the matrices of analysis are > based on some scale of utilitarism. See Von Neuman's Theory of Games, the > section on "The Notion of Utility". My subjective appreciation of the val= ue > of my coins might not be your subjective appreication of the value of you= r > coins. > > Now I do understand the perspective of the institutional holders, the > exchanges, > the custodians or any other industry providers, who might be in the full > uncertainty > about their business responsibilities in case of a quantum threat > affecting their > custodied coins. But, first legally speaking there is something call > "force majeure" > and in view of the quantum threat, which is a risk discussed far beyond > the bitcoin > industry, they should be able to shield themselves behind that. Secondly, > if there > is any futute upgrade "opt-in" only path a la BIP360, you can move your > funds or > the ones under custody under a PQC scheme like Dilthium or Falcon and be > good > without caring about what the others users are doing. Thirdly, if you're > an actor > in the industry like Coinbase and you're deeply concerned about how > extended maelstrom > on the price might affect the viability of your operations, it is unclear > to me why > you don't call MunichRe or any other company like that tomorrow to craft > and be > covered by specific insurance on quantum threats... > > Agreed that companies may be legally protected from lawsuits. Not sure about the insurance angle, though I'd see that as a one time payout that could very well come at the expense of said business ceasing operations. I suspect few businesses would be happy with that. Unfortunately I don't think opt-in security suffices in this situation. Human nature is to procrastinate and if the incentives are insufficient to motivate mass migration to quantum secure schemes, Q-Day will be quite unpleasant. > To be frank, all those considerations on how "I cannot see how the > currency can > maintain any value at all in such a setting", is a strong red flag of low > time > preferences. It's not like we're used to strong volatility in bitcoin wit= h > the > almost 2 decades of operations of the network. In my view, it's more a > hint of > very high-exposition by some to a single class of asset, i.e bitcoin, > rather than wise > diversification... And a push to sacrify a "fundamental property" i.e > "conservatism" > in view of short-term concerns (i.e the stability of the currency price > along > a period of few years). > > Bitcoin has many inviolable properties and some of them are actually in conflict with each other. Conservatism and property rights are clearly on the table in this matter. But shouldn't one of Bitcoin's fundamental properties be the fact that it can be upgraded? That it can respond to new challenges and threats? Beyond just the quantum computing issue, I expect the above to create continued conflict between ossifiers and developers over the long term. Do not get me wrong, I'm certainly not of the school "let's reward quantum > attackers". Leveraging techical superiority and employing CRQRC to steal > vulnerable coins would be clearly a theft. But ethically, the best we can > do is > to have an opt-in upgrade path and be pro-active, by education and > outreach, > to have the maximum of coin owners upgrading to non-vulnerable addresses > types. > Then show the level of "fortitude" or "endurance" as a community in face > of price > fluctuations for a while, while seeing regularly old P2PK coins hacked. > Marcus > Aurelius can be bought for few bucks in most of decent libraries... > > Beware the blurry line between stoicism and apathy. How well will it play out if we can say "well, we could have stopped a massive threat but chose not to, because we were confident the system would survive." The alternative path is "we saw a threat coming and the community collaborated to neutralize it before massive harm occurred." Both scenarios show resilience. Which evokes greater confidence? I'm definitely on the "no old coins confiscation" position you're > underlighting: > > "I don't see why old coins should be confiscated. The better option is to > let > those with quantum computers free up old coins. While this might have an > inflationary impact on bitcoin's price, to use a turn of phrase, the > inflation > is transitory. Those with low time preference should support returning lo= st > coins to circulation". > > Notwhitstanding that I disagree with your position, one can only apprecia= te > the breadth and depth with which you're gathering and articulating all th= e > elements on this complex problem. > > Best, > Antoine > OTS hash: c064b43047bf3036faf098b5ac8e74930df63d25629f590a419522297940282= 6 > Le lundi 14 juillet 2025 =C3=A0 00:53:34 UTC+1, Tadge Dryja a =C3=A9crit = : > >> Hi >> >> While I generally agree that "freeze" beats "steal", and that a lot of >> lead time is good, I don't think this plan is viable. >> To me the biggest problem is that it ties activation of a PQ output type >> to *de*activation of EC output types. That would mean that someone who >> wants to keep using all the great stuff in libsecp256k1 should try to >> prevent BIP360 from being activated. >> >> Sure, there can be risks from CRQCs. But this proposal would go the >> other direction, disabling important functionality and even destroying >> coins preemptively, in anticipation of something that may never happen. >> >> Also, how do you define "quantum-vulnerable UTXO"? Would any P2PKH, or >> P2WPKH output count? Or only P2PKH / P2WPKH outputs where the public ke= y >> is already known? I can understand disabling spends from known-pubkey >> outputs, but for addresses where the public key has never been revealed, >> commit/reveal schemes (like the one I posted about & am working on a >> follow-up post for) should safely let people spend from those outputs >> indefinitely. >> >> With no evidence of a QRQC, I can see how there would be people who'd sa= y >> "We might never really know if a CRQC exists, so we need to disable EC >> spends out of caution" and others who'd say "Don't disable EC spends, si= nce >> that's destroying coins", and that could be a persistent disagreement. = But >> I hope if we did in fact have a proof that a CRQC has broken secp256k1, >> there would be significant agreement on freezing known-pubkey EC outputs= . >> >> -Tadge >> On Saturday, July 12, 2025 at 8:46:09=E2=80=AFPM UTC-4 Jameson Lopp wrot= e: >> >>> Building upon my earlier essay against allowing quantum recovery of >>> bitcoin >>> I >>> wish to formalize a proposal after several months of discussions. >>> >>> This proposal does not delve into the multitude of issues regarding pos= t >>> quantum cryptography and trade-offs of different schemes, but rather is >>> meant to specifically address the issues of incentivizing adoption and >>> migration of funds *after* consensus is established that it is prudent >>> to do so. >>> >>> As such, this proposal requires P2QRH as described in BIP-360 or >>> potential future proposals. >>> Abstract >>> >>> This proposal follows the implementation of post-quantum (PQ) output >>> type (P2QRH) and introduces a pre-announced sunset of legacy ECDSA/Schn= orr >>> signatures. It turns quantum security into a private incentive: fail to >>> upgrade and you will certainly lose access to your funds, creating a >>> certainty where none previously existed. >>> >>> - >>> >>> Phase A: Disallows sending of any funds to quantum-vulnerable >>> addresses, hastening the adoption of P2QRH address types. >>> - >>> >>> Phase B: Renders ECDSA/Schnorr spends invalid, preventing all >>> spending of funds in quantum-vulnerable UTXOs. This is triggered by = a >>> well-publicized flag-day roughly five years after activation. >>> - >>> >>> Phase C (optional): Pending further research and demand, a separate >>> BIP proposing a fork to allow recovery of legacy UTXOs through ZK pr= oof of >>> possession of BIP-39 seed phrase. >>> >>> Motivation >>> >>> We seek to secure the value of the UTXO set and minimize incentives for >>> quantum attacks. This proposal is radically different from any in Bitco= in=E2=80=99s >>> history just as the threat posed by quantum computing is radically >>> different from any other threat in Bitcoin=E2=80=99s history. Never be= fore has >>> Bitcoin faced an existential threat to its cryptographic primitives. A >>> successful quantum attack on Bitcoin would result in significant econom= ic >>> disruption and damage across the entire ecosystem. Beyond its impact on >>> price, the ability of miners to provide network security may be >>> significantly impacted. >>> >>> - >>> >>> Accelerating quantum progress. >>> - >>> >>> NIST ratified three production-grade PQ signature schemes in >>> 2024; academic road-maps now estimate a cryptographically-relevan= t quantum >>> computer as early as 2027-2030. [McKinsey >>> >>> ] >>> - >>> >>> Quantum algorithms are rapidly improving >>> - >>> >>> The safety envelope is shrinking by dramatic increases in >>> algorithms even if the pace of hardware improvements is slower. A= lgorithms >>> are improving up to 20X >>> , >>> lowering the theoretical hardware requirements for breaking class= ical >>> encryption. >>> - >>> >>> Bitcoin=E2=80=99s exposed public keys. >>> - >>> >>> Roughly 25% of all bitcoin have revealed a public key on-chain; >>> those UTXOs could be stolen with sufficient quantum power. >>> - >>> >>> We may not know the attack is underway. >>> - >>> >>> Quantum attackers could compute the private key for known public >>> keys then transfer all funds weeks or months later, in a covert b= leed to >>> not alert chain watchers. Q-Day may be only known much later if t= he attack >>> withholds broadcasting transactions in order to postpone revealin= g their >>> capabilities. >>> - >>> >>> Private keys become public. >>> - >>> >>> Assuming that quantum computers are able to maintain their >>> current trajectories and overcome existing engineering obstacles,= there is >>> a near certain chance that all P2PK (and other outputs with expos= ed >>> pubkeys) private keys will be found and used to steal the funds. >>> - >>> >>> Impossible to know motivations. >>> - >>> >>> Prior to a quantum attack, it is impossible to know the >>> motivations of the attacker. An economically motivated attacker = will try >>> to remain undetected for as long as possible, while a malicious a= ttacker >>> will attempt to destroy as much value as possible. >>> - >>> >>> Upgrade inertia. >>> - >>> >>> Coordinating wallets, exchanges, miners and custodians >>> historically takes years. >>> - >>> >>> The longer we postpone migration, the harder it becomes to >>> coordinate wallets, exchanges, miners, and custodians. A clear, t= ime-boxed >>> pathway is the only credible defense. >>> - >>> >>> Coordinating distributed groups is more prone to delay, even if >>> everyone has similar motivations. Historically, Bitcoin has been = slow to >>> adopt code changes, often taking multiple years to be approved. >>> >>> Benefits at a Glance >>> >>> - >>> >>> Resilience: Bitcoin protocol remains secure for the foreseeable >>> future without waiting for a last-minute emergency. >>> - >>> >>> Certainty: Bitcoin users and stakeholders gain certainty that a plan >>> is both in place and being implemented to effectively deal with the = threat >>> of quantum theft of bitcoin. >>> - >>> >>> Clarity: A single, publicized timeline aligns the entire ecosystem >>> (wallets, exchanges, hardware vendors). >>> - >>> >>> Supply Discipline: Abandoned keys that never migrate become >>> unspendable, reducing supply, as Satoshi described >>> . >>> >>> Specification >>> >>> Phase >>> >>> What Happens >>> >>> Who Must Act >>> >>> Time Horizon >>> >>> Phase A - Disallow spends to legacy script types >>> >>> Permitted sends are from legacy scripts to P2QRH scripts >>> >>> Everyone holding or accepting BTC. >>> >>> 3 years after BIP-360 implementation >>> >>> Phase B =E2=80=93 Disallow spends from quantum vulnerable outputs >>> >>> At a preset block-height, nodes reject transactions that rely on >>> ECDSA/Schnorr keys. >>> >>> Everyone holding or accepting BTC. >>> >>> 2 years after Phase A activation. >>> >>> Phase C =E2=80=93 Re-enable spends from quantum vulnerable outputs via = ZK Proof >>> >>> Users with frozen quantum vulnerable funds and a HD wallet seed phrase >>> can construct a quantum safe ZK proof to recover funds. >>> >>> Users who failed to migrate funds before Phase B. >>> >>> TBD pending research, demand, and consensus. >>> Rationale >>> >>> - >>> >>> Even if Bitcoin is not a primary initial target of a >>> cryptographically relevant quantum computer, widespread knowledge th= at such >>> a computer exists and is capable of breaking Bitcoin=E2=80=99s crypt= ography will >>> damage faith in the network . >>> - >>> >>> An attack on Bitcoin may not be economically motivated - an attacker >>> may be politically or maliciously motivated and may attempt to destr= oy >>> value and trust in Bitcoin rather than extract value. There is no w= ay to >>> know in advance how, when, or why an attack may occur. A defensive >>> position must be taken well in advance of any attack. >>> - >>> >>> Bitcoin=E2=80=99s current signatures (ECDSA/Schnorr) will be a tanta= lizing >>> target: any UTXO that has ever exposed its public key on-chain (roug= hly 25 >>> % of all bitcoin) could be stolen by a cryptographically relevant qu= antum >>> computer. >>> - >>> >>> Existing Proposals are Insufficient. >>> 1. >>> >>> Any proposal that allows for the quantum theft of =E2=80=9Clost= =E2=80=9D bitcoin >>> is creating a redistribution dilemma. There are 3 types of propos= als: >>> 1. >>> >>> Allow anyone to steal vulnerable coins, benefitting those who >>> reach quantum capability earliest. >>> 2. >>> >>> Allow throttled theft of coins, which leads to RBF battles and >>> ultimately miners subsidizing their revenue from lost coins. >>> 3. >>> >>> Allow no one to steal vulnerable coins. >>> - >>> >>> Minimizes attack surface >>> 1. >>> >>> By disallowing new spends to quantum vulnerable script types, we >>> minimize the attack surface with each new UTXO. >>> 2. >>> >>> Upgrades to Bitcoin have historically taken many years; this will >>> hasten and speed up the adoption of new quantum resistant script = types. >>> 3. >>> >>> With a clear deadline, industry stakeholders will more readily >>> upgrade existing infrastructure to ensure continuity of services. >>> - >>> >>> Minimizes loss of access to funds >>> 1. >>> >>> If there is sufficient demand and research proves possible, >>> submitting a ZK proof of knowledge of a BIP-39 seed phrase corres= ponding to >>> a public key hash or script hash would provide a trustless means = for legacy >>> outputs to be spent in a quantum resistant manner, even after the= sunset. >>> >>> >>> Stakeholder >>> >>> Incentive to Upgrade >>> >>> Miners >>> >>> =E2=80=A2 Larger size PQ signatures along with incentive for users to m= igrate >>> will create more demand for block space and thus higher fees collected = by >>> miners. >>> >>> =E2=80=A2 Post-Phase B, non-upgraded miners produce invalid blocks. >>> >>> =E2=80=A2 A quantum attack on Bitcoin will significantly devalue both t= heir >>> hardware and Bitcoin as a whole. >>> >>> Institutional Holders >>> >>> =E2=80=A2 Fiduciary duty: failing to act to prevent a quantum attack on= Bitcoin >>> would violate the fiduciary duty to shareholders. >>> >>> =E2=80=A2 Demonstrating Bitcoin=E2=80=99s ability to effectively mitiga= te emerging >>> threats will prove Bitcoin to be an investment grade asset. >>> >>> Exchanges & Custodians >>> >>> =E2=80=A2 Concentrated risk: a quantum hack could bankrupt them overnig= ht. >>> >>> =E2=80=A2 Early migration is cheap relative to potential losses, potent= ial >>> lawsuits over improper custody and reputational damage. >>> >>> Everyday Users >>> >>> =E2=80=A2 Self-sovereign peace of mind. >>> >>> =E2=80=A2 Sunset date creates a clear deadline and incentive to improve= their >>> security rather than an open-ended =E2=80=9Csome day=E2=80=9D that invi= tes procrastination. >>> >>> Attackers >>> >>> =E2=80=A2 Economic incentive diminishes as sunset nears, stolen coins c= annot be >>> spent after Q-day. >>> >>> Key Insight: As mentioned earlier, the proposal turns quantum security >>> into a private incentive to upgrade. >>> >>> This is not an offensive attack, rather, it is defensive: our thesis is >>> that the Bitcoin ecosystem wishes to defend itself and its interests >>> against those who would prefer to do nothing and allow a malicious acto= r to >>> destroy both value and trust. >>> >>> >>> "Lost coins only make everyone else's coins worth slightly more. Think >>>> of it as a donation to everyone." - Satoshi Nakamoto >>> >>> >>> If true, the corollary is: >>> >>> >>> "Quantum recovered coins only make everyone else's coins worth less. >>>> Think of it as a theft from everyone." >>> >>> >>> The timelines that we are proposing are meant to find the best balance >>> between giving ample ability for account owners to migrate while >>> maintaining the integrity of the overall ecosystem to avoid catastrophi= c >>> attacks. >>> >>> Backward Compatibility >>> >>> As a series of soft forks, older nodes will continue to operate without >>> modification. Non-upgraded nodes, however, will consider all post-quant= um >>> witness programs as anyone-can-spend scripts. They are strongly encoura= ged >>> to upgrade in order to fully validate the new programs. >>> >>> Non-upgraded wallets can receive and send bitcoin from non-upgraded and >>> upgraded wallets until Phase A. After Phase A, they can no longer recei= ve >>> from any other wallets and can only send to upgraded wallets. After Ph= ase >>> B, both senders and receivers will require upgraded wallets. Phase C wo= uld >>> likely require a loosening of consensus rules (a hard fork) to allow >>> vulnerable funds recovery via ZK proofs. >>> >> -- > 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 > email to bitcoindev+unsubscribe@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/4d9ce13e-466d-478b-ab4d-0040= 4c80d620n%40googlegroups.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/= CADL_X_f3sDECRUosNaXyez3F_inKjJAWm%3DESm3DSLCKD4JV7yA%40mail.gmail.com. --0000000000007083180639e82939 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Mon, Jul 14,= 2025 at 10:09=E2=80=AFAM Antoine Riard <antoine.riard@gmail.com> wrote:
Hi Jameson,

Thanks for your thoug= hts on this complex subject.

First and foremost, I think your follow= ing statement: "Never before has Bitcoin faced
an existential threa= t to its cryptographic primitives" is very myopic, given that
crypt= analysts and number theorists are making progress every year in their works= , and
each bitcoin cryptographic primitive has been and is constantly an= alyzed to uncover
potential weaknesses.

So in my view the quantum= threat is a bit less specific that the image you're painting
of it.= Even if go all to upgrade to lattices-based schemes, we have no certainty = that
novels flaws won't be found, one can just go to see the modific= ations of the NIST-approved
schemes in between their rounds of selection= that we'll never reach something like
"self-sovereign peace of= mind"...Unless we start to forbid people of practicing the
art of = mathematics, practice which has been ongoing since Euclide and Pythagore...=

I do concede that quantum is a bit different, as after all new phys= ics paradigm
do not happen often (Heisenberg published in the 20s iirc),= though that's in my
view the flaw of your reasoning as you're a= ssuming some "post-quantum" upgraded
state where bitcoin, as a= community and a network, would be definitely safe from
advances in appl= ied science. At minima, in my understanding, you're arguing this
tim= e is different to justify extra-ordinary technical measures never seen befo= re,
namely the freezing of "vulnerable" coins.


Correct, this time is different in that we're = not talking about vague unknown weaknesses. Rather, we're talking about= a known algorithm that makes breaking cryptographic primitives orders of m= agnitude cheaper.

The unknown becomes the rate at = which advancements in quantum computing will be achieved, which is concerni= ng given the funding going into pushing said advancements forward.
=C2=A0
I'm wor= ried this is opening a Pandora box, where we would introduce a precedentthat it is legitimate as a community to technicaly confiscate some coins o= f users,
without their _consents_, for extra-ordinary reasons. That'= ;s opening a worms of
shenanigans in the future...There is no guarantee = that this precedent won't
be leveraged in the future by any group of= entities to justify future upgrades
eroding one of the "fundamenta= l property" you're yourself deeming as valuable.


This is a fair fear, though the counterpoint is that= it is legitimate for the community to protect itself against security thre= ats. It just so happens that both viewpoints can be valid.

This is especially wo= rrying as if I'm understanding you correctly you're justifying
t= his position as that somehow we should protect the price of the currency as= an end
in itself (i.e "Beyond its impact on price, ..."). It&= #39;s unclear the price of bitcoin
versus what fiat or hard asset (e.g o= il) you have in mind. And in anyway, as far
as I know, none of the bitco= in devs is seating on the board of the FED, the ECB
or the BoJ...
To put it simply, even if a quantum attacker can tomorrow starts to steal<= br>vulnerable coins, 1 BTC will be always equal to 1 BTC. Full stop. In my = humble
opinion, let's not introduce the idea that, we, as a communit= y of stakeholders
and developers we have a positive "fiduciary"= ; duty to act to maintain the price
of bitcoin in some "monetary sn= ake" with another class of assets...


Protocol developers have no fiduciary duty to bitcoin holders. I wou= ldn't argue they have any duty whatsoever=C2=A0to users.

=
Bitcoin is not (yet) a unit of account. The ecosystem does not r= un on 1 BTC =3D 1 BTC. The purchasing power of satoshis is very much releva= nt to the health and sustainability of the ecosystem at its current level.<= /div>

I would not claim that "devs must do somethin= g" - rather, I believe that the incentives of other groups I outlined = will roughly align them with my thinking.

That's also the problem with game = theory, all the matrices of analysis are
based on some scale of utilitar= ism. See Von Neuman's Theory of Games, the
section on "The Noti= on of Utility". My subjective appreciation of the value
of my coins= might not be your subjective appreication of the value of your
coins.
Now I do understand the perspective of the institutional holders, the= exchanges,
the custodians or any other industry providers, who might be= in the full uncertainty
about their business responsibilities in case o= f a quantum threat affecting their
custodied coins. But, first legally s= peaking there is something call "force majeure"
and in view of= the quantum threat, which is a risk discussed far beyond the bitcoin
in= dustry, they should be able to shield themselves behind that. Secondly, if = there
is any futute upgrade "opt-in" only path a la BIP360, yo= u can move your funds or
the ones under custody =C2=A0under a PQC scheme= like Dilthium or Falcon and be good
without caring about what the other= s users are doing. Thirdly, if you're an actor
in the industry like = Coinbase and you're deeply concerned about how extended maelstrom
on= the price might affect the viability of your operations, it is unclear to = me why
you don't call MunichRe or any other company like that tomorr= ow to craft and be
covered by specific insurance on quantum threats...
Agreed that companies may be legally protected from= lawsuits. Not sure about the insurance angle, though I'd see that as a= one time payout that=C2=A0could very=C2=A0well come at the expense of said= business ceasing operations. I suspect few businesses would be happy with = that.

Unfortunately I don't think opt-in secur= ity suffices in this situation. Human nature is to procrastinate and if the= incentives are insufficient to motivate mass migration to quantum secure s= chemes, Q-Day will be quite=C2=A0unpleasant.
=C2=A0
To be frank, all those considerat= ions on how "I cannot see how the currency can
maintain any value a= t all in such a setting", is a strong red flag of low time
preferen= ces. It's not like we're used to strong volatility in bitcoin with = the
almost 2 decades of operations of the network. In my view, it's = more a hint of
very high-exposition by some to a single class of asset, = i.e bitcoin, rather than wise
diversification... And a push to sacrify a= "fundamental property" i.e "conservatism"
in view o= f short-term concerns (i.e the stability of the currency price along
a p= eriod of few years).


Bitcoin has ma= ny inviolable properties and some of them are actually in conflict with eac= h other. Conservatism and property rights are clearly on the table in this = matter.

But shouldn't one of Bitcoin's fun= damental properties be the fact that it can be upgraded? That it can respon= d to new challenges and threats?

Beyond just the q= uantum computing issue, I expect the above to create continued conflict bet= ween ossifiers and developers over the long term.

Do not get me wrong, I'm c= ertainly not of the school "let's reward quantum
attackers"= ;. Leveraging techical superiority and employing CRQRC to steal
vulnerab= le coins would be clearly a theft. But ethically, the best we can do is
= to have an opt-in upgrade path and be pro-active, by education and outreach= ,
to have the maximum of coin owners upgrading to non-vulnerable address= es types.
Then show the level of "fortitude" or "enduranc= e" as a community in face of price
fluctuations for a while, while = seeing regularly old P2PK coins hacked. Marcus
Aurelius can be bought fo= r few bucks in most of decent libraries...


Beware the blurry line between stoicism and apathy.

<= /div>
How well will it play out if we can say "well, we could have= stopped a massive threat but chose not to, because we were confident the s= ystem would survive."

The alternative path is= "we saw a threat coming and the community collaborated to neutralize = it before massive harm occurred."

Both scenar= ios show resilience. Which evokes greater confidence?

<= blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-l= eft:1px solid rgb(204,204,204);padding-left:1ex">I'm definitely on the = "no old coins confiscation" position you're underlighting:
"I don't see why old coins should be confiscated. The better = option is to let
those with quantum computers free up old coins. While t= his might have an
inflationary impact on bitcoin's price, to use a t= urn of phrase, the inflation
is transitory. Those with low time preferen= ce should support returning lost
coins to circulation".

Notw= hitstanding that I disagree with your position, one can only appreciate
= the breadth and depth with which you're gathering and articulating all = the
elements on this complex problem.

Best,
Antoine
OTS has= h: c064b43047bf3036faf098b5ac8e74930df63d25629f590a4195222979402826
Le lundi 14 j= uillet 2025 =C3=A0 00:53:34 UTC+1, Tadge Dryja a =C3=A9crit=C2=A0:
Hi =C2=A0

While = I generally agree that "freeze" beats "steal", and that= a lot of lead time is good, I don't think this plan is viable.
To m= e the biggest problem is that it ties activation of a PQ output type to *de= *activation of EC output types.=C2=A0 That would mean that someone who want= s to keep using all the great stuff in libsecp256k1 should try to prevent B= IP360 from being activated.

Sure, there can be risks from CRQCs.=C2= =A0 But this proposal would go the other direction, disabling important fun= ctionality and even destroying coins preemptively, in anticipation of somet= hing that may never happen.

Also, how do you define "quantum-vu= lnerable UTXO"?=C2=A0 Would any P2PKH, or P2WPKH output count?=C2=A0 O= r only P2PKH / P2WPKH outputs where the public key is already known?=C2=A0 = I can understand disabling spends from known-pubkey outputs, but for addres= ses where the public key has never been revealed, commit/reveal schemes (li= ke the one I posted about & am working on a follow-up post for) should = safely let people spend from those outputs indefinitely.

With no evi= dence of a QRQC, I can see how there would be people who'd say "We= might never really know if a CRQC exists, so we need to disable EC spends = out of caution" and others who'd say "Don't disable EC sp= ends, since that's destroying coins", and that could be a persiste= nt disagreement.=C2=A0 But I hope if we did in fact have a proof that a CRQ= C has broken secp256k1, there would be significant agreement on freezing kn= own-pubkey EC outputs.

-Tadge
On Saturday, July 12, 2025= at 8:46:09=E2=80=AFPM UTC-4 Jameson Lopp wrote:

Building upon my = earlier essay against allowing quantum recove= ry of bitcoin I wish to formalize a proposa= l after several months of discussions.

This proposal does not de= lve into the multitude of issues regarding post quantum cryptography and tr= ade-offs of different schemes, but rather is meant to specifically address = the issues of incentivizing adoption and migration of funds af= ter consensus is established that it is pru= dent to do so.

As such, this proposal requires P2QRH as described in BIP-360 or potenti= al future proposals.

Abstract

This proposal follows the implementation of post-quantum (PQ) output ty= pe (P2QRH) and introduces a pre-announced sunset of legacy ECDSA/Schnorr si= gnatures. It turns quantum security into a private incentive: fail to upgrade and you will cer= tainly lose access to your funds, creating a certainty where none previousl= y existed.=C2=A0

    <= li dir=3D"ltr" style=3D"list-style-type:disc;font-size:11pt;font-family:&qu= ot;Courier New",monospace;color:rgb(0,0,0);background-color:transparen= t;font-variant-numeric:normal;font-variant-east-asian:normal;font-variant-a= lternates:normal;vertical-align:baseline;white-space:pre-wrap">

    Phase A: Disallows sending of any funds to quantum-vulnerable address= es, hastening the adoption of P2QRH address types.

  • Phase B: Renders ECDSA/Schnorr spends invalid, preventing all spending of f= unds in quantum-vulnerable UTXOs. This is triggered by a well-publicized fl= ag-day roughly five years after activation.

  • Phase C (optional): Pending further research and demand, a separate BIP proposing a = fork to allow recovery of legacy UTXOs through ZK proof of possession of BI= P-39 seed phrase.=C2=A0=C2=A0

Motivation

We seek to s= ecure the value of the UTXO set <= span style=3D"font-size:11pt;font-family:"Courier New",monospace;= color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;f= ont-variant-east-asian:normal;font-variant-alternates:normal;vertical-align= :baseline">and minimize incentives for quantum attacks. This proposal is ra= dically different from any in Bitcoin=E2=80=99s history just as the threat = posed by quantum computing is radically different from any other threat in = Bitcoin=E2=80=99s history.=C2=A0 Never before has Bitcoin faced an existent= ial threat to its cryptographic primitives. A successful quantum attack on = Bitcoin would result in significant economic disruption and damage across t= he entire ecosystem. Beyond its impact on price, the ability of miners to p= rovide network security may be significantly impacted.=C2=A0=C2=A0

  • Accelerating quantum progress.=C2=A0

    • NIST ratified three production-= grade PQ signature schemes in 2024; academic road-maps now estimate a crypt= ographically-relevant quantum computer as early as 2027-2030. [McKinsey]

  • Quantum algorithms are rapidly improving

    • The safety envelope is shrinking = by dramatic increases in algorithms even if the pace of hardware improvemen= ts is slower. Algorithms are improving up to 20X, lowering the theoretical hardware requirements= for breaking classical encryption.

  • Bitcoin=E2=80=99s exposed public keys.=C2=A0

    • Roughly 25% of all= bitcoin have revealed a public key on-chain; those UTXOs could be stolen w= ith sufficient quantum power.=C2=A0=C2=A0

  • We may not know t= he attack is underway.=C2=A0

    • Qua= ntum attackers could compute the private key for known public keys then tra= nsfer all funds weeks or months later, in a covert bleed to not alert chain= watchers. Q-Day may be only known much later if the attack withholds broad= casting transactions in order to postpone revealing their capabilities.

  • Private= keys become public.=C2=A0

    • Assuming that quantum computers are able to maintain their current = trajectories and overcome existing engineering obstacles, there is a near c= ertain chance that all P2PK (and other outputs with exposed pubkeys) privat= e keys will be found and used to steal the funds.

  • =

    Impossible to know motivation= s.=C2=A0

    • Prior to a= quantum attack, it is impossible to know the motivations of the attacker.= =C2=A0 An economically motivated attacker will try to remain undetected for= as long as possible, while a malicious attacker will attempt to destroy as= much value as possible.=C2=A0=C2=A0

  • Upgrade inertia.=C2=A0

      • <= li dir=3D"ltr" style=3D"list-style-type:circle;font-size:11pt;font-family:&= quot;Courier New",monospace;color:rgb(0,0,0);background-color:transpar= ent;font-variant-numeric:normal;font-variant-east-asian:normal;font-variant= -alternates:normal;vertical-align:baseline;white-space:pre-wrap">

      Coordinating wallets, exchanges, miners= and custodians historically takes years.

    • The longer we postpone migration, the= harder it becomes to coordinate wallets, exchanges, miners, and custodians= . A clear, time-boxed pathway is the only credible defense.

      • =

    • Coordinating distr= ibuted groups is more prone to delay, even if everyone has similar motivati= ons. Historically, Bitcoin has been slow to adopt code changes, often takin= g multiple years to be approved.

Benefits at a Glance

  • Resilience: Bitcoin protoc= ol remains secure for the foreseeable future without waiting for a last-min= ute emergency.

  • Certainty: Bitcoin = users and stakeholders gain certainty that a plan is both in place and bein= g implemented to effectively deal with the threat of quantum theft of bitco= in.=C2=A0=C2=A0

  • Clarity: A single,= publicized timeline aligns the entire ecosystem (wallets, exchanges, hardw= are vendors).

  • Supply Discipline: = Abandoned keys that never migrate become unspendable, reducing supply, as Satoshi described.=C2=A0=C2=A0

Specification

= =

Phase

What Happens<= /p>

Who Must Act

Time= Horizon

Phase A - Disallow spends to legacy script types

Permitted sends are from leg= acy scripts to P2QRH scripts

Everyone holding or accepting BTC.

3 years after BIP-360 implementation

Phase B =E2=80=93 Dis= allow spends from quantum vulnerable outputs

At a preset block-height, nod= es reject transactions that rely on ECDSA/Schnorr keys.=C2=A0

Everyone holding or accepting BTC.

2 years after = Phase A activation.

Phase C = =E2=80=93 Re-enable spends from quantum vulnerable outpu= ts via ZK Proof

Users with frozen quantum vulnerable funds and a HD wallet= seed phrase can construct a quantum safe ZK proof to recover funds.=

Users= who failed to migrate funds before Phase B.

TBD pending research, demand,= and consensus.

Rationale

  • Even if Bitc= oin is not a primary initial target of a cryptographically relevant quantum= computer, widespread knowledge that such a computer exists and is capable = of breaking Bitcoin=E2=80=99s cryptography will damage faith in the network= .=C2=A0

  • An attack on Bitcoin may not be economically motivated - an attacker may= be politically or maliciously motivated and may attempt to destroy value a= nd trust in Bitcoin rather than extract value.=C2=A0 There is no way to kno= w in advance how, when, or why an attack may occur.=C2=A0 A defensive posit= ion must be taken well in advance of any attack.=C2=A0=C2=A0

  • Bitcoin=E2=80=99s cu= rrent signatures (ECDSA/Schnorr) will be a tantalizing target: any UTXO tha= t has ever exposed its public key on-chain (roughly 25 % of all bitcoin) co= uld be stolen by a cryptographically relevant quantum computer.

    <= /li>

  • Existing Proposals are Insufficient.=C2=A0= =C2=A0

    1. Any proposal that al= lows for the quantum theft of =E2=80=9Clost=E2=80=9D bitcoin is creating a = redistribution dilemma. There are 3 types of proposals:

      1. Allow anyone to steal vulnerable coins, benefi= tting those who reach quantum capability earliest.

      2. Allow throttled theft= of coins, which leads to RBF battles and ultimately miners subsidizing the= ir revenue from lost coins.

      3. Allow no one to steal vulnerable coins.=

  • Minimizes attack surface

    1. By disallowing new spends to quantum vulnerable script types, = we minimize the attack surface with each new UTXO.=C2=A0=C2=A0

    2. <= p dir=3D"ltr" style=3D"line-height:1.38;text-align:justify;margin-top:0pt;m= argin-bottom:0pt" role=3D"presentation">Upgrades to= Bitcoin have historically taken many years; this will hasten and speed up = the adoption of new quantum resistant script types.=C2=A0

      3. With a clear dea= dline, industry stakeholders will more readily upgrade existing infrastruct= ure to ensure continuity of services.=C2=A0=C2=A0

  • =

    Minimizes = loss of access to funds=C2=A0

    1. If there is sufficient demand and research proves possible, submitting = a ZK proof of knowledge of a BIP-39 seed phrase corresponding to a public = key hash or script hash would provide a trustless means for legacy outputs = to be spent in a quantum resistant manner, even after the sunset.=C2=A0=C2= =A0


Stakeholder

Incentive to Upgrade

<= /td>

Miners

=E2=80=A2 Larger size PQ s= ignatures along with incentive for users to migrate will create more demand= for block space and thus higher fees collected by miners.

=E2=80=A2 Post-Phase B, non-upgraded miners produce invalid blocks.

=E2=80=A2 A quantum attack on Bitcoin will significant= ly devalue both their hardware and Bitcoin as a whole.=C2=A0

Institutional Holders

=E2=80=A2 Fiduciary d= uty: failing to act to prevent a quantum attack on Bitcoin would violate th= e fiduciary duty to shareholders.=C2=A0=C2=A0

=E2=80= =A2 Demonstrating Bitcoin=E2=80=99s ability to effectively mitigate emergin= g threats will prove Bitcoin to be an investment grade asset.

Exchanges & Custodians

=E2=80=A2 Conce= ntrated risk: a quantum hack could bankrupt them overnight.

=E2=80=A2 Early migration is cheap relative to potential losses, pot= ential lawsuits over improper custody and reputational damage.

Everyday Users

=E2=80=A2 Self-sovereign p= eace of mind.

=E2=80=A2 Sunset date creates a clear d= eadline and incentive to improve their security rather than an open-ended = =E2=80=9Csome day=E2=80=9D that invites procrastination.

Attackers

=E2=80=A2 Economic incentive dim= inishes as sunset nears, stolen coins cannot be spent after Q-day.

Key Insight: As mentioned earlier, the proposal = turns quantum security into a private = incentive to upgrade.=C2=A0=C2=A0

This is not an offensive attack, rather, it is defensive: our thesis is th= at the Bitcoin ecosystem wishes to defend itself and its interests against = those who would prefer to do nothing and allow a malicious actor to destroy= both value and trust.=C2=A0=C2=A0


"Lost coins only make everyone else's coins worth= slightly more. Think of it as a donation to everyone." - Satoshi Naka= moto

If true, the corollary is:


"Quantum recovered co= ins only make everyone else's coins worth less. Think of it as a theft = from everyone."

The timelines that = we are proposing are meant to find the best balance between giving ample ab= ility for account owners to migrate while maintaining the integrity of the = overall ecosystem to avoid catastrophic attacks.=C2=A0=C2=A0


=

Backward Compatibility

As a series of = soft forks, older nodes will continue to operate without modification. Non-= upgraded nodes, however, will consider all post-quantum witness programs as= anyone-can-spend scripts. They are strongly encouraged to upgrade in order= to fully validate the new programs.


Non-upgraded= wallets can receive and send bitcoin from non-upgraded and upgraded wallet= s until Phase A. After Phase A, they can no longer receive from any other w= allets and can only send to upgraded wallets.=C2=A0 After Phase B, both sen= ders and receivers will require upgraded wallets.=C2=A0Phase C would likely= require a loosening of consensus rules (a hard fork) to allow vulnerable f= unds recovery via ZK proofs.

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