From: "'ArmchairCryptologist' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>
To: "bitcoindev@googlegroups.com" <bitcoindev@googlegroups.com>
Subject: Re: [bitcoindev] Aligning privacy incentives in P2MR
Date: Fri, 26 Jun 2026 09:27:09 +0000 [thread overview]
Message-ID: <2UBm2dVIs3jNHvlZtgXA_7Pfa09T6bK0BBkpvEZUMV8CNgeOwpG87vmUZ9vEnn0TQIfag2uIbiViizuDaND9UljX9LdDqHYXgJhTlW7OGqs=@protonmail.com> (raw)
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In my humble opinion, I think the preference for P2MR vs P2TRv2 for users would largely boil down to whether or not someone is a long-term holder, or someone who actively makes frequent transactions on the network.
On one hand, if I were a self-reliant long-term holder of significant assets (which I may or may not be), I would be reluctant to use P2TRv2 for this, since the funds would always be fully exposed to CRQCs until such a time EC spending is disabled by a third party, which may or may not happen in time.
On the other, if I were making frequent transactions on the network (which I may or may not do), I would be reluctant to use P2MR for this due to the additional transaction cost, which would be wasteful before CRQCs exist - and especially considering that they might never exist.
As such, unless someone were to come up with a different scheme that has the best of both worlds, I feel like the discussion should be more along the lines of "one, or possibly both if it is beneficial" rather than "we have to pick just one no matter what".
Personally, using the ideas Pieter Wuille presented in the other thread, my preference would be to add both:
- P2TRv2 using one or both of the Tripwire and Miner Lockdown triggers (P2TRv2-T / P2TRv2-ML / P2TRv2-T-ML) to emergency-disable EC spending, while still leaving the ability to disable it with a soft fork, for frequent transactors and people who trust miners to act responsibly.
- P2MR (plain), with EC spending only disabled with a soft fork, for the self-reliant holders who know (how) to not expose their EC public key and want full control over their funds.
This would leave EC spending available for P2MR while it is still in the "danger zone" and after it has been initially disabled for P2TRv2, but when/if EC spending is considered by the developers to be completely broken, a follow-up soft fork would disable it for both address types.
I feel like this should be worth the trade-offs of easier wallet fingerprinting as well as the increase in implementation complexity and long-term maintenance cost - but then again, I'm not the one paying that cost, and the people who will might disagree.
--
Best,ArmchairCryptologist
On Thursday, June 25th, 2026 at 12:35 AM, Anthony Derbidge <aderb001@gmail.com> wrote:
> I agree with the core point that Bitcoin’s post-quantum transition cannot rely primarily on self-reliance. If the migration requires most users to understand Q-Day timing, keep EC spend paths secret, or react quickly under pressure, then it is unlikely to protect Bitcoin as a system. The safer path needs to be low-friction and close to the default experience long before the threat becomes urgent.
>
> That is why a "Later" style strategy seems compelling: ordinary users can opt into a future migration path without immediately adopting restrictive post-quantum workflows, while consensus can still act when the risk becomes concrete. Bitcoin mainnet should remain simple and conservative, while more complex identity, recovery, coordination, and enhanced post-quantum workflows can exist in optional Bitcoin-aligned layers rather than the base layer.
>
> Systems such as Lightning and ProofnetBTC can experiment with those optional workflows and recovery models while continuing to settle to Bitcoin, allowing innovation without requiring the Bitcoin mainnet itself to absorb that additional complexity.
>
> Best,
> Anthony D.
>
> On Wed, Jun 24, 2026 at 3:50 PM 'Antoine Poinsot' via Bitcoin Development Mailing List <bitcoindev@googlegroups.com> wrote:
>
>> Hi AJ,
>>
>>> There are three main variations to this, I think:
>>>
>>> [...]
>>>
>>> Self-reliance: Q-day goes from maybe to definitely faster than consensus
>>> changes can be coordinated, and the only reason people's funds remain
>>> safe is that they can (and do) keep the quantum-vulnerable spend
>>> paths secret.
>>
>> I think that scenario may only result in a successful migration if the vast
>> majority of users have updated their workflows to keep said quantum vulnerable
>> paths secret.
>>
>> This may only happen if the vast majority of users either:
>> 1. have preemptively updated their workflows during the "maybe" period;
>> 2. react promptly enough (within weeks? a couple months?) to migrate all their wealth.
>>
>> Option (1) is utterly implausible. As Pieter explained in his email, we can't
>> expect users to adopt workflows radically at odds with how they use Bitcoin
>> today in response to a (still --at the time they need to migrate) speculative
>> threat.
>>
>> I believe Bitcoin is successful precisely because users are not required to be
>> active bitcoiners and pay close attention to avoid losing their funds. A
>> substantial share of users value and rely on this property, and therefore Option
>> (2) is likewise implausible.
>>
>> Therefore i don't think the "Self-reliance" variation can result in a successful
>> migration.
>>
>>> As far as I can see, only having P2TRv2 addresses would rule out the "self-reliance" path here.
>>>
>>> Picking when Q-day will occur, either individually for determining
>>> your own security posture, or collectively for organising a consensus
>>> change seems very difficulty: it involves evaluating both complex state
>>> of the art physics research, but also estimating the covert abilities
>>> of national governments and the incentives to attack bitcoin prior to
>>> revealing their capabilities. To me, that doesn't bode well for a smooth
>>> and fast deployment of a consensus change in advance of problems occuring.
>>
>> Yes. P2TRv2 optimizes for the "Later dominant" path at the expense of the
>> "self-reliance" path. I think this is good, because our best (only?) shot at
>> fully migrating large amounts of users is to provide them with a virtually free
>> way to opt into a future consensus-triggered migration.
>>
>> The follow-up step does not require predicting with precision the day on which
>> an attack would be set up, but to be done before a CRQC could realistically
>> threaten Bitcoin. Definitely not a piece of cake, but not infeasible. In fact if
>> P2TRv2 does become the Schelling point for PQ migration, i would be more
>> concerned about the follow-up step happening too soon rather than too late.
>>
>> Of course, if a full CRQC is built in secret, with no reliable information about
>> the progress getting out whatsoever, and subsequently starts attacking Bitcoin
>> overnight, then this migration strategy would fail. But so would any other
>> migration strategy!
>>
>>> It's possible that general carelessness on behalf of users would also
>>> rule out the effectiveness of a self-reliance approach: if only the most
>>> conscientious 1% of users make use of P2MR securely, that might secure 10%
>>> of funds, but having 90% of the bitcoin supply crash probably wouldn't be
>>> very valuable either.
>>
>> For what it’s worth, while the supply at risk matters, i think the primary
>> metric we should optimize for is the share of users at risk. Widespread,
>> indiscriminate theft would fatally undermine trust in Bitcoin, whereas more
>> concentrated sweeps (such as that of early, presumed-lost coins) *could* cause
>> severe price shocks without necessarily destroying confidence in the system
>> itself.
>>
>>> > > Theorycrafting for a second here. It's reasonable to conjecture fee
>>> > > rates will be much higher post-Q-day, and thus P2MR's 32 byte advantage
>>> > > over P2TRv2 will yield significant savings for end-users in absolute
>>> > > terms. If fee rates inflate 10x higher after Q-day, then 8 vbytes becomes
>>> > > significant (100 sats per spend or more).
>>>
>>> I don't think that is the right way to look at. 8vb/input is about
>>> an additional 14% today (vs a taproot key-path spend), but with the
>>> post-quantum signatures we have available now that's likely to reduce
>>> to ~7% (SHRINCS) or ~1% (winternitz).
>>
>> Yes. Also, our goal here is to mitigate the risk that a CRQC materializes by
>> providing a path for Bitcoin to survive it. We shouldn't take the risk for a
>> certainty and shift the goal to designing the best possible PQ-Bitcoin. This can
>> be done if/when it becomes clearer that CRQCs will become a reality.
>>
>>> > FWIW, I don't think the P2TRv2 EC-disabling fork needs to be timed
>>> > perfectly. The expectation should be just that it happens before Q-day,
>>> > and when it looks inevitable or the fear about that is large enough.
>>>
>>> FWIW, I would define "timed perfectly" precisely as "EC disabling
>>> fork happens before Q-day". Maybe allowing some additional months of
>>> EC-efficiency would be a win while not taking out too much migration time,
>>> but for me "perfection" here means "no one who upgraded lost money via
>>> quantum-related vulnerabilities".
>>
>> I don't think that's a good definition of "timed perfectly". By your definition,
>> EC could be disabled from the get-go, Bitcoin's migration would spectacularly
>> fail because very few users switched to the new output type, and it would still
>> be "timed perfectly". :)
>>
>> I would define "timed perfectly" as maximizing the number of migrated users
>> without any of them losing money to a CRQC. But it's not quite the right
>> definition, because there is also probably an aspect of not doing it
>> prematurely, i.e. in the scenario where the CRQC threat never materializes, no
>> P2TRv2 user is forced to use heavily restrictive PQ worklows.
>>
>>> Correct me if I'm mistaken, but I think P2TRv2 is preferable only in the
>>> "Later-dominant" scenario, and only to the degree that it's slightly
>>> cheaper prior to Q-day.
>>
>> From the perspective that a successful migration hinges on virtually all users
>> opting into a (full) migration to CRQC-safe workflows, this difference in costs
>> is material. Especially since users would presumably need to opt in long before
>> we know whether CRQCs will become a reality anytime soon.
>>
>>> My (cynical?) view is the only people who will adopt either P2TRv2 or
>>> P2MR prior to NoEC-day being schedule will be people who are willign
>>> to use those features in a quantum-safe way -- that is, keeping their
>>> EC pubkeys secret, and only revealing those EC pubkeys to spend them
>>> immediately, prior to NoEC-day.
>>
>> How can this apply to P2TRv2, where EC pubkeys are always public?
>>
>> I think i disagree that most users of P2MR, were it made available, would treat
>> their EC public keys as secrets. But more importantly, the whole point of
>> P2TRv2, or more generally of what Pieter labels "Later" type strategies, is
>> precisely to avoid imposing on individual users the costs of treating their
>> public keys as secrets. P2TRv2 (compared to other "Later" options) also ensures
>> that using it is no more costly than using any other available output type.
>> Together, these properties may make users who are not yet particularly
>> concerned, or are simply unaware, indifferent to opting in: they bear the
>> additional costs only if the CRQC threat materializes and are no worse off if it
>> does not.
>>
>>> > This focus on allowing individual users the ability to safeguard their
>>> > coins just feels like a red herring: [...]
>>>
>>> While I appreciate your point, I also feel that "allowing individual
>>> users the ability to safeguard their coins" is pretty close to the entire
>>> point of Bitcoin. :)
>>
>> Cherry-picking this part of Pieter's sentence does not do it justice. Of course
>> we all agree about this. But as he says in the part you left out, not addressing
>> this issue as a systemic one is exactly how we lose that property: "I'm not
>> worried about my own coins being stolen. I'm worried about (fear of) a CRQC
>> undermining trust in the currency as a whole, or through a fear-driven consensus
>> change the ecosystem destroying its own values beforehand."
>>
>>> having a consistent push that every single wallet/service that doesn't deprecate every current
>>> address type is a danger to the entire ecosystem, even absent widespread agreement on when/if
>>> Q-day will happen. Arguably that would be easier to agree on if the incremental cost of EC spend
>>> paths in P2TRv2 prior to NoEC-day/Q-day versus current spend paths is near to zero, rather than up
>>> to ~14% per input.
>>
>> Yes, that's essentially the case for P2TRv2.
>>
>> Best,
>> Antoine
>>
>> On Thursday, June 18th, 2026 at 1:09 AM, Anthony Towns <aj@erisian.com.au> wrote:
>>
>>> On Tue, Jun 16, 2026 at 08:09:08PM +0000, Pieter Wuille wrote:
>>> > I want to first correct a potential misunderstanding here, because
>>> > I realize the terms "Later" and "Never" aren't very descriptive. They
>>> > are specifically about an expected and relied-upon expectation that an
>>> > EC-disabling fork will happen that at least applies to the output type
>>> > itself, in time. "Later" is the expectation that such a disabling will
>>> > happen after the output type is introduced, but still in time (so, before
>>> > Q-day). Outputs without a strong expectation that their EC paths/opcodes
>>> > will be disabled, or not in time, I classify under "Never".
>>>
>>> > I believe here you're instead arguing for P2MR ("Merkle-Never")
>>> > over all "Later" options. That was my previous point: I think (solely)
>>> > having "Never" output types like P2MR is just utterly insufficient for
>>> > any worthwhile migration. It's so incompatible with today's workflows
>>> > that it either won't be adopted, or (possibly inadvertently) adopted
>>> > in an insecure fashion. Yes, it gives people the option to safeguard
>>> > their own coins, but to me that's disaster recovery territory - I think
>>> > we ought to prioritize maximizing the chances for saving the currency
>>> > as a whole in case Q-day comes, not a small subset of individual users'
>>> > coins. P2MR (alone) doesn't really achieve much in that regard in my view,
>>> > thus we at least need something of the "Later" class in addition.
>>>
>>> I'm not sure I follow/agree with the logic here. I think the general idea
>>> is:
>>>
>>> 1) we create some new address types that allow post-quantum spending, but
>>> also allow efficient quantum-vulnerable spending that can be used prior
>>> to Q-day
>>>
>>> 2) many people migrate to these new address types
>>>
>>> 3) Q-day arrives
>>>
>>> 4) all spending goes via the post-quantum paths, and everyone's funds are
>>> safe
>>>
>>> There are three main variations to this, I think:
>>>
>>> Later-dominant: towards the end of (2) but prior to (3), the
>>> quantum-vulnerable spend paths are disabled in a predictable, planned
>>> manner, preventing coin theft, but not disrupting active usage
>>> significantly (or not disrupting it any more than the proximity of
>>> Q-day already is).
>>>
>>> Self-reliance: Q-day goes from maybe to definitely faster than consensus
>>> changes can be coordinated, and the only reason people's funds remain
>>> safe is that they can (and do) keep the quantum-vulnerable spend
>>> paths secret.
>>>
>>> Disaster-recovery: neither the "predictable/planned consensus change" of
>>> Later nor the "everyone takes responsiblity for their own funds"
>>> works, and the only way to avoid a large percentage of bitcoin
>>> becoming a reward for quantum research is to replace EC spend paths
>>> with a ZK proof of knowledge of a BIP32 seed or similar, requiring
>>> a hard fork. Such a hard fork would be certain to be controversial
>>> ("why at this height: I received a payment five blocks after //
>>> my funds were stolen by a quantum attacker five blocks earlier //
>>> why are only BIP32 funds recoverable not scheme X"), but if no other
>>> approach works, might still be the ultimately outcome.
>>>
>>> > So the point here was just: if you already accept the need for a "Later"
>>> > output type (= one with builtin-in EC disabling expected from the start),
>>> > P2TRv2 is preferable over P2MR+ED, because:
>>>
>>> As far as I can see, only having P2TRv2 addresses would rule out the
>>> "self-reliance" path here.
>>>
>>> Picking when Q-day will occur, either individually for determining
>>> your own security posture, or collectively for organising a consensus
>>> change seems very difficulty: it involves evaluating both complex state
>>> of the art physics research, but also estimating the covert abilities
>>> of national governments and the incentives to attack bitcoin prior to
>>> revealing their capabilities. To me, that doesn't bode well for a smooth
>>> and fast deployment of a consensus change in advance of problems occuring.
>>>
>>> It's possible that general carelessness on behalf of users would also
>>> rule out the effectiveness of a self-reliance approach: if only the most
>>> conscientious 1% of users make use of P2MR securely, that might secure 10%
>>> of funds, but having 90% of the bitcoin supply crash probably wouldn't be
>>> very valuable either. But even then, that may make the "disaster-recovery"
>>> approach less problematic, by ensuring the 1%/10% who were conscientious
>>> can avoid being part of the "my funds were stolen by a quantum attacker"
>>> contingent, eg.
>>>
>>> > > Theorycrafting for a second here. It's reasonable to conjecture fee
>>> > > rates will be much higher post-Q-day, and thus P2MR's 32 byte advantage
>>> > > over P2TRv2 will yield significant savings for end-users in absolute
>>> > > terms. If fee rates inflate 10x higher after Q-day, then 8 vbytes becomes
>>> > > significant (100 sats per spend or more).
>>>
>>> I don't think that is the right way to look at. 8vb/input is about
>>> an additional 14% today (vs a taproot key-path spend), but with the
>>> post-quantum signatures we have available now that's likely to reduce
>>> to ~7% (SHRINCS) or ~1% (winternitz). So, post-Q-day, by dropping 32B,
>>> you're only getting an expected savings in fees / increase in block
>>> capacity on that order of magnitude, ie: 1%-7%. That's nice to have,
>>> for sure, but doesn't compare to introducing a new address type that
>>> puts the PQ sigs in an extension block, or one that uses ZK proofs to
>>> do cross-input or cross-transaction signature aggregation, eg. So a 32B
>>> witness overhead for an unused/unusable key-path post-Q-day doesn't seem
>>> very relevant to me.
>>>
>>> > FWIW, I don't think the P2TRv2 EC-disabling fork needs to be timed
>>> > perfectly. The expectation should be just that it happens before Q-day,
>>> > and when it looks inevitable or the fear about that is large enough.
>>>
>>> FWIW, I would define "timed perfectly" precisely as "EC disabling
>>> fork happens before Q-day". Maybe allowing some additional months of
>>> EC-efficiency would be a win while not taking out too much migration time,
>>> but for me "perfection" here means "no one who upgraded lost money via
>>> quantum-related vulnerabilities".
>>>
>>> One reason I'm doubtful is that I think for some the "it looks inevitable"
>>> threshold has already been crossed, eg:
>>>
>>> >> So let me attempt to partially fill the silence, similarly to what
>>> >> Scott Aaronson did in his April 29 post. Given everything I know,
>>> >> including scary non-public information, I now put the odds of qday by
>>> >> 2032 at 50%. 10% by 2030.
>>>
>>> >> IMO a good target date for migration is 2029, roughly 3.5 years
>>> >> out. 2029 happens to be the date selected by Google, Cloudflare, and
>>> >> the Ethereum Foundation.
>>>
>>> https://x.com/drakefjustin/status/2061793725299224676
>>>
>>> >> So, here it is: if quantum computers start breaking cryptography a
>>> >> few years from now, don’t you dare come to this blog and tell me that
>>> >> I failed to warn you. This post is your warning. Please start switching
>>> >> to quantum-resistant encryption, and urge your company or organization
>>> >> or blockchain or standards body to do the same.
>>>
>>> https://scottaaronson.blog/?p=9718
>>>
>>> Personally, that leaves me at a minimum very skeptical of the utility
>>> of introducing either P2MR or P2TRv2 (etc) approaches that don't also
>>> introduce a quantum-safe spending path on day one.
>>>
>>> > First a meta-point here: the reason I like separating the discussion into different dimensions than just "P2TRv2 vs P2MR" is because there are more options than those two, and not every argument applies to the same separation into two classes. Let me list them explicitly here, roughly in decreasing order of how strongly I feel about them:
>>> > - We need at least a "Later" option for meaningful migration, i.e. P2TRv2 or P2MR+ED.
>>> > - Within the "Later" option, P2TRv2 is preferable.
>>> > - A "Later" option benefits from being the only PQC migration strategy, making it a Schelling point.
>>>
>>> Correct me if I'm mistaken, but I think P2TRv2 is preferable only in the
>>> "Later-dominant" scenario, and only to the degree that it's slightly
>>> cheaper prior to Q-day. If it were the only available option, that would
>>> increase the risk of loss involved with both the other approaches. (I
>>> don't think P2TRv2 is meaningfully more private than P2MR in the way
>>> taproot v1 is, as presumably you'd only adopt that address format if
>>> you wanted to have a post-quantum script path)
>>>
>>> > > You'd have to convince everyone to deploy and then adopt P2TRv2 today under the public knowledge that it is insecure and their coins are more likely to be stolen. That's a hard sell.
>>> >
>>> > > How does one pitch P2TRv2 to users? "It will be quantum secure one day we promise because everyone is incentivized to fix it later as Bitcoin will die if we don't."
>>> > >
>>> > > How do you pitch P2MR? "It's quantum secure if you use it correctly."
>>> > To me, the pitch is "Bitcoin can only remain valuable if we mostly/all migrate." for both. P2TRv2 is just much easier to adopt, because P2MR (or any "Never" output type) fundamentally requires many users to change their workflows entirely.
>>>
>>> Let's call NoEC-day the earlier of activation of a soft-fork disabling
>>> EC-spends on P2MR/P2TRv2 or Q-day. NoEC-day to some extent is presumably
>>> equal to "the day the bitcoin ecosystem has finally agreed that CRQCs
>>> are inevitable".
>>>
>>> My (cynical?) view is the only people who will adopt either P2TRv2 or
>>> P2MR prior to NoEC-day being schedule will be people who are willign
>>> to use those features in a quantum-safe way -- that is, keeping their
>>> EC pubkeys secret, and only revealing those EC pubkeys to spend them
>>> immediately, prior to NoEC-day. In that view, the EC-spend-paths of such
>>> coins prior to NoEC-day are only an opportunistic "make spends cheaper"
>>> shortcut, they don't allow the funds to be used in lightning channels
>>> or to let your wallet be audited via sharing an xpub or anything similar.
>>>
>>> Perhaps I'm wrong: it's my opinion, not a technical fact; it's possible
>>> that lightning software could get an upgrade to generate post-quantum
>>> signatures for channel commitments or HTLC claims, I just think it's
>>> pretty unlikely that that will happen at a meaningful scale when everyone
>>> has much more immediate and less theoretical things to work on prior to
>>> NoEC-day, especially when the efficiency/performance of such changes is
>>> likely to be very low.
>>>
>>> > This focus on allowing individual users the ability to safeguard their
>>> > coins just feels like a red herring: [...]
>>>
>>> While I appreciate your point, I also feel that "allowing individual
>>> users the ability to safeguard their coins" is pretty close to the entire
>>> point of Bitcoin. :)
>>>
>>> > In either case, I consider anything that requires hardcoding
>>> > specific wallet designs (BIP32 or otherwise) into Bitcoin's consensus
>>> > rules (and only allowing those coins to survive) to be squarely in
>>> > disaster-recovery land. It feels like embracing arbitrariness, and
>>> > giving up on the permissionlessness that makes Bitcoin interesting -
>>> > if the community shows it can get consensus on effectively burning
>>> > coins except those that match a whitelist, it feels hard to maintain
>>> > censorship-freeness as a value, even if the whitelist includes most of
>>> > the (active) coins. That is of course not to say such techniques aren't
>>> > interesting to work on, but to me, their place is in disaster recovery
>>> > scenarios to save what's left, after Q-day, if migration attempts were
>>> > unsuccessful. In such a setting, I think we're already in effectively an
>>> > altcoin-with-UTXO-bootstrapped-from-Bitcoin territory, and a (possibly
>>> > growing) set of ways to recover burned coins can be hardforked in.
>>>
>>> Just for the record, I think the above is an accurate description of the
>>> "disaster-recovery" scenario above: the "quantum-safe" hard-fork variant
>>> of bitcoin would be fairly described as a utxo-bootstrapped altcoin,
>>> would compete in the market with the "quantum-unsafe" bitcoin that
>>> existing nodes would continue to follow, and possibly there would be
>>> many slightly varying such altcoins competing with each other, eg on
>>> exactly what height the utxo snapshot was taken or what coins become
>>> spendable. It would not be a fun time for holders of affected utxos.
>>>
>>> > My impression is that your approach is to have an answer for many
>>> > possible futures, including ones where Q-day arrives within just a few
>>> > years.
>>>
>>> "The key of strategy... is not to choose a path to victory, but to choose
>>> so that all paths lead to a victory."
>>>
>>> -- https://tvtropes.org/pmwiki/pmwiki.php/Main/XanatosGambit
>>>
>>> > But optimizing for disaster-recovery also means reducing the
>>> > chances of preserving Bitcoin as we know it in the scenarios where a
>>> > successful migration is still possible. And if Q-day does arrive that
>>> > soon, I don't see what we can do today that would preserve Bitcoin in
>>> > a form we care about anyway. By accepting that, we can focus on the
>>> > futures where our choices today can still materially improve the outcome.
>>>
>>> Preserving bitcoin as a personally-possessible inflation resistant
>>> store of value seems both possible and worth caring about, even if other
>>> constraints means that many people can't afford to personally hold it
>>> (and have to go through ETFs/exchanges/banks) and that it can't be used
>>> for day-to-day transactions. Would be very disappointing if true, and
>>> even given Q-day in a few years I expect we could do better than just
>>> that, but it doesn't feel like a throw-in-the-towel event to me.
>>>
>>> > > Essentially yes though, I expect the majority of holders will probably
>>> > > migrate to PQ addresses via rescue protocols, either on Bitcoin or a fork
>>> > > thereof. Even if we can't come to consensus and deploy a new output type,
>>> > > we'll still be able to rescue most coins. It's just that we'd have nowhere
>>> > > to rescue them to, so we ought to make PQ wallets available soon, so we're
>>> > > not in a rush to build them later when we need them. If a PQ wallet can
>>> > > use cheap EC signatures while they're still trustworthy, all the better
>>>
>>> FWIW, that's my guess on how things would play out if the near-term Q-day
>>> timelines I've seen (ie, 2029 to 2035) match reality. I hope that's
>>> pessimistic (either because the Q-day timelines are bad estimates, or
>>> because migration happens in a more orderly fashion), but I guess we'll
>>> see. I don't rate my ability to evaluate Q-day predictions very highly.
>>>
>>> > - A (not-quite-CR)-QC breaks 128-bit ECDLP, say.
>>>
>>> I'm not in a position to judge, but the google paper claims:
>>>
>>> "Indeed, if a leading quantum architecture encounters and overcomes
>>> all its scaling challenges before producing a device able to
>>> solve (for example) 32-bit ECDLP, then there may be little time
>>> between the breaking of 32-bit ECDLP and the breaking of 256-bit
>>> ECDLP. Furthermore, the community should not expect to see published
>>> demonstrations of the most advanced quantum error-correction
>>> architectures and quantum algorithms deployed to cryptanalytic
>>> problems. Thus, a successful public demonstration of Shor’s
>>> algorithm on a 32-bit elliptic curve should not be seen as a wake-up
>>> call to adopt PQC as much as a potential signal that PQC adoption
>>> has already failed."
>>>
>>> and places the required tiffoli gates and logical qubits for a 32-bit
>>> break at about (300k, 200) vs (10M, 600) for 128-bit or (80M, 1100)
>>> for 256-bit.
>>>
>>> > Of course, if you believe it's the only possible future, I understand
>>> > you'd come to a different conclusion. But is it really? Do you think
>>> > this isn't a plausible future:
>>>
>>> > - A P2TRv2 type (let's leave aside whether P2MR or P2QR gets added too) gets introduced in the next few years, with hash-based PQC opcodes.
>>> > - Over the course of the next decade or so, it gets adopted by practically all active users.
>>>
>>> I think it might be better to look at that scenario in a more fine-grained
>>> way? I think your "Late-ish" scenario is:
>>>
>>> 1) P2TRv2 (or whatever) is introduced
>>> 2) Some PQ opcodes get enabled, allowing expensive but PQ-safe spend-paths
>>> via those outputs
>>> 3) P2PK, P2PKH, P2WPKH, P2WSH, P2TR all become obsolete in favour of P2TRv2,
>>> but EC spend paths continue to be what's used in practice.
>>> 4) Some better PQ solutions become available, allowing cheap PQ-safe spend-paths
>>> 5) Everyone switches from EC paths to the new PQ paths.
>>> 6) NoEC-day happens, but no one is impacted.
>>>
>>> I think your "Soon-ish" scenario differs as of step (4):
>>>
>>> 4) NoEC-day happens. Massive disruption because the "what's used in practice"
>>> path breaks, but everything is recoverable.
>>> 5) Post-quantum approaches get even higher priority
>>>
>>> I'm skeptical of step 3 here; and would expect to see something more like:
>>>
>>> 3') Only a small proportion of users (ie, the most conscientious/fearful)
>>> switch to P2TRv2 with most preferring to stick with what works
>>>
>>> That has no real impact on the Late-ish scenario, but changes the Soon-ish
>>> scenario to either:
>>>
>>> 4'a) NoEC-day happens substantially before Q-day; people hurry to migrate
>>> to P2TRv2, but it mostly works.
>>>
>>> or
>>>
>>> 4'b) NoEC-day happens essentially at the same time as Q-day; coins get
>>> stolen and we hit the disaster-recovery scenario.
>>>
>>> Perhaps the difference between (3') and (3) playing out in reality
>>> is just having nearly everyone agree that the upgrade is essential,
>>> and rather than leaving it to self-interest/market-dynamics, having a
>>> consistent push that every single wallet/service that doesn't deprecate
>>> every current address type is a danger to the entire ecosystem, even
>>> absent widespread agreement on when/if Q-day will happen. Arguably that
>>> would be easier to agree on if the incremental cost of EC spend paths
>>> in P2TRv2 prior to NoEC-day/Q-day versus current spend paths is near to
>>> zero, rather than up to ~14% per input.
>>>
>>> Cheers,
>>> aj
>>>
>>
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next prev parent reply other threads:[~2026-06-26 9:42 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-03 23:12 [bitcoindev] Aligning privacy incentives in P2MR 'conduition' via Bitcoin Development Mailing List
2026-06-05 19:56 ` 'Antoine Poinsot' via Bitcoin Development Mailing List
2026-06-05 22:52 ` 'conduition' via Bitcoin Development Mailing List
2026-06-06 4:29 ` Pieter Wuille
2026-06-06 19:33 ` 'conduition' via Bitcoin Development Mailing List
2026-06-10 3:00 ` Pieter Wuille
2026-06-12 4:43 ` 'conduition' via Bitcoin Development Mailing List
2026-06-16 20:09 ` Pieter Wuille
2026-06-18 5:09 ` Anthony Towns
2026-06-19 0:30 ` 'conduition' via Bitcoin Development Mailing List
2026-06-19 0:38 ` 'conduition' via Bitcoin Development Mailing List
2026-06-22 11:33 ` waxwing/ AdamISZ
2026-06-24 20:24 ` 'Antoine Poinsot' via Bitcoin Development Mailing List
2026-06-24 22:00 ` Anthony Derbidge
2026-06-25 15:24 ` Alex
2026-06-26 9:27 ` 'ArmchairCryptologist' via Bitcoin Development Mailing List [this message]
2026-06-26 16:11 ` 'conduition' via Bitcoin Development Mailing List
2026-06-06 22:12 ` Boris Nagaev
2026-06-06 17:52 ` 'Hayashi' via Bitcoin Development Mailing List
2026-06-13 15:33 ` [bitcoindev] " 'conduition' via Bitcoin Development Mailing List
[not found] <Q8YTY1ArMzia7tRvcZ5v769WPxCMxAl=5F0rUy-byOBjBcTd4HXj7IB7Yt4gxLbKqk7EXFWy-PuGB6QtI28qRjE5Vob-l44UmBH6L8aXInoSk=3D@proton.me>
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[not found] ` <=5Fz6=5FJUmphCkUYvI6gemSFMD9Sb=5FrDL03IQbtZQCNlk6pmioGEQBir=5FgMyZCfticFa8Ttfc0xoFHdxR07=5FMNuAfBu8do=5Fh5IDf2apVk1w1BM=3D@wuille.net>
[not found] ` <E2-B=5FJaZeZg3tFHhiGcp-Mitl34-=5FuxcTVga5ogSMKOfeCvjHuzox7EXNw6GdlC4ggEIehP2elA3xnmvBSvIMnNu-QSHqGW81MzvD8BKRRI=3D@proton.me>
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