It should be noted that if indeed there has not remained much time until a usable quantum computer will become available, the priority is the deployment of FIPS 203 (ML-KEM) for the establishment of the secret session keys that are used in protocols like TLS or SSH.
ML-KEM is intended to replace the traditional and the elliptic-curve variant of the Diffie-Hellman algorithm for creating a shared secret value.
When FIPS 203, i.e. ML-KEM is not used, adversaries may record data transferred over the Internet and they might become able to decrypt the data after some years.
On the other hand, there is much less urgency to replace the certificates and the digital signature methods that are used today, because in most cases it would not matter if someone would become able to forge them in the future, because they cannot go in the past to use that for authentication.
The only exception is when there would exist some digital documents that would completely replace some traditional paper documents that have legal significance, like some documents proving ownership of something, which would be digitally signed, so forging them in the future could be useful for somebody, in which case a future-proof signing method would make sense for them.
OpenSSH, OpenSSL and many other cryptographic libraries and applications already support FIPS 203 (ML-KEM), so it could be easily deployed, at least for private servers and clients, without also replacing the existing methods used for authentication, e.g. certificates, where using post-quantum signing methods would add a lot of overhead, due to much bigger certificates.
That was my position until last year, and pretty much a consensus in the industry.
What changed is that the new timeline might be so tight that (accounting for specification, rollout, and rotation time) the time to switch authentication has also come.
ML-KEM deployment is tangentially touched on in the article because it's both uncontroversial and underway, but:
> This is not the article I wanted to write. I’ve had a pending draft for months now explaining we should ship PQ key exchange now, but take the time we still have to adapt protocols to larger signatures, because they were all designed with the assumption that signatures are cheap. That other article is now wrong, alas: we don’t have the time if we need to be finished by 2029 instead of 2035.
> For key exchange, the migration to ML-KEM is going well enough but: 1. Any non-PQ key exchange should now be considered a potential active compromise, worthy of warning the user like OpenSSH does, because it’s very hard to make sure all secrets transmitted over the connection or encrypted in the file have a shorter shelf life than three years. [...]
You comment is essentially the premise of the other article.
I agree with you that one must prepare for the transition to post-quantum signatures, so that when it becomes necessary the transition can be done immediately.
However that does not mean that the switch should really be done as soon as it is possible, because it would add unnecessary overhead.
This could be done by distributing a set of post-quantum certificates, while continuing to allow the use of the existing certificates. When necessary, the classic certificates could be revoked immediately.
> I agree with you that one must prepare for the transition to post-quantum signatures, so that when it becomes necessary the transition can be done immediately.
Personally, my reading between the lines on this subject as a non-expert is that we in the public might not know when post-quantum cryptography is necessary until quite a while after it is necessary.
Prior to the public-key cryptography revolution, the state of the art in cryptography was locked inside state agencies. Since then, public cryptographic research has been ahead or even with state work. One obvious tell was all the attempts to force privately-operated cryptographic schemes to open doors to the government via e.g. the Clipper chip and other appeals to magical key escrow.
A whole generation of cryptographers grew up in this world. Quantum cryptography might change things back. We know what papers say from Google and other companies. Who knows what is happening inside the NSA or military facilities?
It seems that with quantum cryptography we are back to physics, and the government does secret physics projects really well. This paragraph really stood out to me:
> Scott Aaronson tells us that the “clearest warning that [he] can offer in public right now about the urgency of migrating to post-quantum cryptosystems” is a vague parallel with how nuclear fission research stopped happening in public between 1939 and 1940.
As a practical matter, revocation on the Web is handled mostly by centrally distributed revocation lists (CRLsets, CRLite, etc. [0]), so all you really need is:
(1) A PQ-secure way of getting the CRLs to the browser vendors.
(2) a PQ-secure update channel.
Neither of these require broad scale deployment.
However, the more serious problem is that if you have a setting where most servers do not have PQ certificates, then disabling the non-PQ certificates means that lots of servers can't do secure connections at all. This obviously causes a lot of breakage and, depending on the actual vulnerability of the non-PQ algorithms, might not be good for security either, especially if people fall back to insecure HTTP.
Indeed, in an open system like the WebPKI it's fine in theory to only make the central authority PQ, but then you have the ecosystem adoption issue. In a closed system, you don't have the adoption issue, but the benefit to making only the central authority PQ is likely to be a lot smaller, because it might actually be the only authority. In both cases, you need to start moving now and gain little from trying to time the switchover.
> In both cases, you need to start moving now and gain little from trying to time the switchover.
There are a number of "you"s here, including:
- The SDOs specifying the algorithms (IETF mostly)
- CABF adding the algorithms to the Baseline Requirements so they can be used in the WebPKI
- The HSM vendors adding support for the algorithms
- CAs adding PQ roots
- Browsers accepting them
- Sites deploying them
This is a very long supply line and the earlier players do indeed need to make progress. I'm less sure how helpful it is for individual sites to add PQ certificates right now. As long as clients will still accept non-PQ algorithms for those sites, there isn't much security benefit so most of what you are doing is getting some experience for when you really need it. There are obvious performance reasons not to actually have most of your handshakes use PQ certificates until you really have to.
Yeah, that's an audience mismatch, this article is for "us." End users of cryptography, including website operators and passkey users (https://news.ycombinator.com/item?id=47664744) can't do much right now, because "we" still need to finish our side.
> The only exception is when there would exist some digital documents that would completely replace some traditional paper documents that have legal significance, like some documents proving ownership of something, which would be digitally signed, so forging them in the future could be useful for somebody, in which case a future-proof signing method would make sense for them.
This very much exists. In particular, the cryptographic timestamps that are supposed to protect against future tampering are themselves currently using RSA or EC.
This is a good take, there's really not much to argue about.
>[...] the availability of HPKE hybrid recipients, which blocked on the CFRG, which took almost two years to select a stable label string for X-Wing (January 2024) with ML-KEM (August 2024), despite making precisely no changes to the designs. The IETF should have an internal post-mortem on this, but I doubt we’ll see one
My kingdom for a standards body that discusses and resolves process issues.
I think the anti-hybrid argument the article makes is clearly wrong. Even if CRQCs existed today, we still should be using hybrid algorithms because even once CRQCs exist, they will be slow, expensive, and power hungry for at least a decade. The hybrid algorithms at a minimum make the cost of any attack ~$1M, which is way better than half of the PQC algorithms that made it to the 3rd stage of the PQC competition (2 of them can be broken on a laptop)
> [CRQCs] will be slow, expensive, and power hungry for at least a decade
How could you know that? What if it was 5 years? 1 year? 6 months?
I predict there will be an insane global pivot once Q-day arrives. No nation wants to invest billions in science fiction. Every nation wants to invest billions in a practical reality of being able to read everyone's secrets.
The absolute low end of cost of a QC is the cost of an MRI machine ~100k-400k (cost of cooling the computer to super low temps). Sure we expect QCs to get faster and cheaper over time, but putting 100% faith in the security of the PQC algorithms seems like a bad idea with no upside.
It is the paradox of PQC: from a classical security point of view PQC cannot be trusted (except for hash-based algorithms which are not very practical). So to get something we can trust we need hybrid. However, the premise for introducing PQC in the first place is that quantum computers can break classical public key crypto, so hybrid doesn't provide any benefit over pure PQC.
Yes, the sensible thing to do is hybrid. But that does assume that either PQC cannot be broken by classical computers or that quantum computers will be rare or expensive enough that they don't break your classical public key crypto.
We can disagree on the tradeoff, but if you see no upside, you are missing the velocity cost of the specification work, the API design, and the implementation complexity. Plus the annoying but real social cost of all the bikeshedding and bickering.
> “Doesn’t the NSA lie to break our encryption?” No, the NSA has never intentionally jeopardized US national security with a non-NOBUS backdoor, and there is no way for ML-KEM and ML-DSA to hide a NOBUS backdoor.
The most concrete issue for me, as highlighted by djb, is that when the NSA insists against hybrids, vendors like telecommunications companies will handwrite poor implementations of ML-KEM to save memory/CPU time etc. for their constrained hardware that will have stacks of timing side channels for the NSA to break. Meanwhile X25519 has standard implementations that don't have such issues already deployed, which the NSA presumably cannot break (without spending $millions per key with a hypothetical quantum attack, a lot more expensive than side channels).
> The most concrete issue for me, as highlighted by djb, is that when the NSA insists against hybrids
The fact that only NSA does that and they really have no convincing arguments seems like the biggest reason why the wider internet should only roll out hybrids. Then possibly wait decades for everything to mature and then reconsider plain modes of operation.
Thus succeeding at making the telecommunications vendors used for Top Secret US national security data less secure, the obvious goal of the US National Security Agency, and the only reason they wouldn't use the better cryptography designed by Dr. Bernstein. /s
Truly, truly can't understand why anyone finds this line of reasoning plausible. (Before anyone yells Dual_EC_DRBG, that was a NOBUS backdoor, which is an argument against the NSA promoting mathematically broken cryptography, if anything.)
Timing side channels don't matter to ephemeral ML-KEM key exchanges, by the way. It's really hard to implement ML-KEM wrong. It's way easier to implement ECDH wrong, and remember that in this hypothetical you need to compare to P-256, not X25519, because US regulation compliance is the premise.
(I also think these days P-256 is fine, but that is a different argument.)
What surprises me is how non-linear this argument is. For a classical attack on, for example RSA, it is very easy to a factor an 8-bit composite. It is a bit harder to factor a 64-bit composite. For a 256-bit composite you need some tricky math, etc. And people did all of that. People didn't start out speculating that you can factor a 1024-bit composite and then one day out of the blue somebody did it.
The weird thing we have right now is that quantum computers are absolutely hopeless doing anything with RSA and as far as I know, nobody even tried EC. And that state of the art has not moved much in the last decade.
And then suddenly, in a few years there will be a quantum computer that can break all of the classical public key crypto that we have.
This kind of stuff might happen in a completely new field. But people have been working on quantum computers for quite a while now.
If this is easy enough that in a few years you can have a quantum computer that can break everything then people should be able to build something in a lab that breaks RSA 256. I'd like to see that before jumping to conclusions on how well this works.
> Sure, papers about an abacus and a dog are funny and can make you look smart and contrarian on forums. But that’s not the job, and those arguments betray a lack of expertise. As Scott Aaronson said:
> Once you understand quantum fault-tolerance, asking “so when are you going to factor 35 with Shor’s algorithm?” becomes sort of like asking the Manhattan Project physicists in 1943, “so when are you going to produce at least a small nuclear explosion?”
To summarize, the hard part of scalable quantum computation is error correction. Without it, you can't factorize essentially anything. Once you get any practical error correction, the distance between 32-bit RSA and 2048-bit RSA is small. Similarly to how the hard part is to cause a self-sustaining fissile chain reaction, and once you do making the bomb bigger is not the hard part.
This is what the experts know, and why they tell us of the timelines they do. We'd do better not to dismiss them by being smug about our layperson's understanding of their progress curve.
The thing is, producing the right isotopes of uranium is mostly a linear process. It goes faster as you scale up of course, but each day a reactor produces a given amount. If you double the number of reactors you produce twice as much, etc.
There is no such equivalent for qubits or error correction. You can't say, we produce this much extra error correction per day so we will hit the target then and then.
There is also something weird in the graph in https://bas.westerbaan.name/notes/2026/04/02/factoring.html. That graph suggests that even with the best error correction in the graph, it is impossible to factor RSA-4 with less then 10^4 qubits. Which seems very odd. At the same time, Scott Aaronson wrote: "you actually can now factor 6- or 7-digit numbers with a QC". Which in the graph suggests that error rate must be very low already or quantum computers with an insane number of qubits exist.
You can already factor a 6 digit number with a QC, but not with an algorithm that scales polynomially. The graph linked is for optimized variants of Shor's algorithm.
We are stretching the metaphor thin, but surely the progress towards an atomic bomb was not measured only in uranium production, in the same way that the progress towards a QC is not measured only in construction time of the machine.
At the theory level, there were only theories, then a few breakthroughs, then some linear production time, then a big boom.
> Something doesn't add up here.
Please consider it might be your (and my) lack of expertise in the specific sub-field. (I do realize I am saying this on Hacker News.)
The Manhattan Project scientists actually did this before anybody broke ground at Los Alamos. It was called the Chicago Pile. And if the control rods were removed and the SCRAM disabled, it absolutely would have created a "small nuclear explosion" in the middle of a major university campus.
Given the level of hype and how long it's been going on, I think it's totally reasonable for the wider world to ask the quantum crypto-breaking people to build a Chicago Pile first.
The argument to skip hybrid keys sounds dangerous to me.
These algorithms are not widely deployed and thus real world tested at all. If there is a simple flaw, suddenly any cheap crawler pwns you while you tried to protect against state actors.
Building out a supercomputer capable of breaking cryptography is exactly the kind of thing I expect governments to be working on now. It is referenced in the article, but the analogy to the Manhattan Project is clear.
Prior to 1940 it was known that clumping enough fissile material together could produce an explosion. There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.
I say this because there’s a meme that governments are cooking up exotic technologies behind closed doors which I personally tend to doubt.
This is almost perfect analogy to the MP though. We know exactly what could happen if we clumped enough qubits together. There are hard engineering challenges of actually doing so, and governments are pretty good at clumping dollars together when they want to.
> There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.
FWIW, constructing a weapon with highly enriched uranium is, relatively, simple. At the time, the choice was made to use a gun-type weapon that shot a projectile of highly enriched uranium into a a "target" of highly enriched uranium. The scientists were so sure it would work that the design didn't necessitate a live test. This was "little boy", which was eventually dropped on Hiroshima.
Fat Man utilized plutonium which required an implosion to compress the fissile material that would set off the chain reaction. This is a much more complex undertaking, but it's much more efficient. Namely, you need much less fissile material, and more of that fissile material is able to participate in the chain reaction. This design is what allows for nuclear tipped missiles. The same principles can be applied to a U-235 based weapon as well.
The implosion based design is super interesting to read about. One memorable aspect is that the designers realized that applying a tamper of uranium (U-238) around the fissile material allows for significant improvement in yield. The chain reaction is exponential, so the few extra nanoseconds that the uranium keeps the fissile material together leads to significant increase in yield.
The Manhattan project employed some significant % of all of America. A project of that scale will likely never happen again.
It was also about far more than the science. It was about industrializing the entire production process and creating industrial capability that simply did not exist before.
Does quantum computing need that though? We don't suddenly need a large, unique supply chain for these computers. We don't need to dig up the qubits and refine them. Testing doesn't blow up the computer.
I don’t know why the author likes AES 128 so badly. AES 256 adds little additional cost, and protects against store now decrypt later attacks (and situations like: “my opinion suddenly changed in few months”). The industry standard and general recommendation for quantum resistant symmetric encryption is using 256 bit keys, so just follow that. Every time he comes up with all sorts of arguments that AES 128 is good.
Age should be using 256 bit file keys, and default to PC keys in asymmetric mode.
> The industry standard and general recommendation for quantum resistant symmetric encryption is using 256 bit keys
It simply is not. NIST and BSI specifically recommend all of AES-128, AES-196, and AES-256 in their post-quantum guidance. All of my industry peers I have discussed this with agree that AES-128 is fine for post-quantum security. It's a LinkedIn meme at best, and a harmful one at that.
My opinion changed on the timeline of CRQC. There is no timeline in which CRQC are theorized to become a threat to symmetric encryption.
he pretty explicitly states that AES 128 is not in any imminent danger and mandating a switch to 256 would distract from the actual thing he thinks needs to happen.
So why argue about whether AES-256 is worth it if we can just literally replace those 3 characters and be done with the upgrade? This was the smart move already in 2001 when Shor's algorithm was known and computers fast enough that we don't notice the difference. At least to me, it seems like less bikeshedding will be done if we abandon AES-128 and don't have to deal with all the people left wondering if that's truly ok
Then again, something something md5. 'Just replace those bytes with sha256()' is apparently also hard. But it's a lot easier than digging into different scenarios under which md5 might still be fine and accepting that use-case, even if only for new deployments
You can’t just throw “Grover’s algorithm is difficult to parallelize” etc. It’s not same as implementation, especially when it gets to quantum computers. It’s very specialized.
Yeah, sounds like it's time to take this very seriously. Sobering article to read, practical and to the point on risk posture. One brief paragraph though that I think deserves extra emphasis and I don't see in the comments here yet:
>In symmetric encryption, we don’t need to do anything, thankfully
This is valuable because it does offer a non-scalable but very important extra layer that a lot of us will be able to implement in a few important places today, or could have for awhile even. A lot of people and organizations here may have some critical systems where they can make a meat-space-man-power vs security trade by virtue of pre-shared keys and symmetric encryption instead of the more convenient and scalable normal pki. For me personally the big one is WireGuard, where as of a few years ago I've been able to switch the vast majority of key site-to-site VPNs to using PSKs. This of course requires out of band, ie, huffing it on over to every single site, and manually sharing every single profile via direct link in person vs conveniently deployable profiles. But for certain administrative capability where the magic circle in our case isn't very large this has been doable, and it gives some leeway there as any traffic being collected now or in the future will be worthless without actual direct hardware compromise.
That doesn't diminish the importance of PQE and industry action in the slightest and it can't scale to everything, but you may have software you're using capable of adding a symmetric layer today without any other updates. Might be worth considering as part of low hanging immediate fruit for critical stuff. And maybe in general depending on organization and threat posture might be worth imagining a worst-case scenario world where symmetric and OTP is all we have that's reliable over long time periods and how we'd deal with that. In principle sneakernetting around gigabytes or even terabytes of entropy securely and a hardware and software stack that automatically takes care of the rough edges should be doable but I don't know of any projects that have even started around that idea.
PQE is obviously the best outcome, we ""just"" switch albeit with a lot of increase compute and changed assumptions in protocols pain, but we're necessarily going to be leaning on a lot of new math and systems that won't have had the tires kicked nearly as long as all conventional ones have. I guess it's all feeling real now.
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f*d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
Slightly off-topic but: Does anyone know what the Signal developers plan on doing there to replace SGX? I mean it's not like outside observers haven't been looking very critically at SGX usage in Signal for years (which the Signal devs have ignored), but this does seem to put additional pressure on them.
What is the consequence on e.g. Yubikeys (or say the Android Keystore)? Do I understand correctly that those count as "signature algorithms" and are a little less at risk than "full TEEs" because there is no "store now, decrypt later" for authentication?
E.g. can I use my Yubikey with FIDO2 for SSH together with a PQ encryption, such that I am safe from "store now, decrypt later", but can still use my Yubikey (or Android Keystore, for that matter)?
This article is more aimed at those specifying and implementing WebAuthN and SSH, than at those using them.
They/we need to migrate those protocols to PQ now, so that you all can start migrating to PQ keys in time, including the long tail of users that will not rotate their keys and hardware the moment the new algorithms are supported.
For example, it might be too late to get anything into Debian for it to be in oldstable when the CRQCs come!
> This article is more aimed at those specifying and implementing WebAuthN and SSH, than at those using them.
Sure, I'm just trying to understand the consequences of that. Felt great to finally have secure elements on smartphones and laptops (or Yubikeys), protecting against the OS being compromised (i.e. "you access my OS, but at least you can't steal my keys").
I was wondering if PQ meant that when it becomes reality, we just get back to a world where if our OS is compromised, then our keys get compromised, too. Or if there is a middle ground in the threat model, e.g. "it's okay to keep using your Yubikey, because an attacker would need to have physical access to your key, specialised hardware AND access to a quantum computer in order to break it". Versus "you can stop bothering about security keys because with "store now, decrypt later", everything you do today with your security keys will anyway get broken with quantum computers eventually".
If you are doing authentication with those hardware keys, you will probably be fine, if we do our job fast enough. Apple's Secure Enclave already supports some PQ signatures (although annoyingly not ML-DSA-44 apparently?) and I trust Yubico is working on it.
If you are doing encryption, then you do have reason to worry, and there aren't great options right now. For example if you are using age you should switch to hybrid software ML-KEM-768 + hardware P-256 keys as soon as they are available (https://github.com/str4d/age-plugin-yubikey/pull/215). This might be a scenario in which hybrids provide some protection, so that an attacker will need to compromise both your OS and have a CRQC. In the meantime, depending on your threat model and the longevity of your secrets (and how easily they can rotated in 1-2 years), it might make sense to switch to software PQ keys.
If you are doing a post-quantum key exchange and only authenticating with the Yubikey, then you are safe from after-the-fact attacks. Well, as long as the PQ key exchange holds up, and I am personally not as optimistic about that as I’d like to be.
> If you are doing a post-quantum key exchange and only authenticating with the Yubikey, then you are safe from after-the-fact attacks.
Let me rephrase it to see if I understand correctly: so it is fine to keep using my security keys today for authentication (e.g. FIDO2?), but everything else should use PQ algorithm because the actual data transfers can be stored now and decrypted later.
Meaning that today (and for a few years), my Yubikey still protects me from my key being stolen when my OS is compromised.
Looking forward to a PQ yubikey rev. I would buy a box of them today so I could start experimenting!
Another challenge of the transition is how much silicon we have yet to even implement. Smart cards? Mobile acceleration/offloading? We're at the mercy of vendors.
Is this also true for other TPM/snitching/DRM chips out there? IE will every existing device eventually become jailbreakable in the future or will we unfortunately not even get that benefit from all this?
The new thing here seems to be the use of the neutral atom technique. Supposedly we are up to 96 entangled qubits for a second or two based on neutral atoms.
Shouldn't that be enough capability to factor 15 using Shor's?
What do you recomend as reading material for someone that was in college a while ago (before AE modes got popular) to get up to speed with the new PQ developments?
If you want something book-shaped, the 2nd edition of Serious Cryptography is updated to when the NIST standards were near-final drafts, and has a nice chapter on post-quantum cryptography.
If you want something that includes details on how they were deployed, I'm afraid that's all very recent and I don't have good references.
Ethereum is way more complex than let's say Bitcoin and all parts are affected. This is not just the "signature scheme".
The fact that the signature size is multiplied by ~10 will greatly affect things like blockspace (what I guess is even more a problem with Bitcoin !)
Also they are the only blockchain I believe that put an emphasis on allowing large number of validators to run on very modest hardware (in the ballpark of a RPI, N100 or phone).
My understanding is they will need to pack it with a larger upgrade to solve all those problems, the so called zkVM/leanVM roadmap.
And then there are the L2 that are an integral part of the ecosystem.
So this is the greatest upgrade ever made on Ethereum, pretty much full rewrite, larger than the transition to proof of stake.
I remember before the Proof of Stake migration they were planning to redo the EVM too (with something WASM based at the time) but they had to abandon their plan. Now it seems there is no choice but to do it.
Adding new signature schemes to bitcoin is relatively trivial and has been done previously (today Bitcoin supports both schnorr and ecdsa signatures).
Existing PQ standards have signatures with the wrong efficiency tradeoffs for usage in Bitcoin-- large signatures that are durable against a lot of use and supports fast signing, while for Bitcoin signature+key size is critical, keys should be close to single use, and signing time is irrelevant.
To the extent that I've seen any opposition related to this isn't only been in related to schemes that were to inefficient or related to proposals to confiscate the assets of people not adopting the proponent's scheme (which immediately raises concerns about backdoors and consent).
Claims that there is no development are as far as I can tell are just backscatter from a massive fraud scheme that is ongoing (actually, at least two distinct cons with an almost identical script). There are criminal fraudsters out seeking investments in a scheme to raise money to build a quantum computer and steal Bitcoins. One of them reportedly has raised funds approaching a substantial fraction of a billion dollars from victims. For every one sucker they convince to give them money, they probably create 99 others people panicked about it (since believing it'll work is a pre-req to handing over your money).
They're a pretty bad stopgap: https://bas.westerbaan.name/notes/2026/04/02/factoring.html. Going to RSA-32000 only buys you ~a year once QCs can factor RSA-2048. In order to get a standard that would resist quantum attacks for realistic time, we would need MB to GB keys at least (see https://eprint.iacr.org/2017/351.pdf for a hilarious post-quantum RSA attempt that used terabyte size keys)
No, and even if we could, it would require a migration of approaching the same difficulty of a migration to PQ, at which point why not just migrate to PQ
I was in this field a while back, and I always found it baffling that anyone ever believed in the earlier large estimates for the size of a quantum computer needed to run Shor's algorithm. For a working quantum computer, Shor's algorithm is about as difficult as modular exponentiation or elliptic curve scalar multiplication: if it can compute or verify signatures or encrypt or decrypt, then it can compute discrete logs. To break keys of a few hundred bits, you need a few hundred qubits plus not all that much overhead. And the error correction keeps improving all the time.
Also...
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f**d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
This part is embarrassing. We’ve had hash-based signatures that are plenty good for this for years and inspire more confidence for long-term security than the lattice schemes. Sure, the private keys are bigger. So what?
We will also need some clean way to upgrade WebAuthn keys, and WebAuthn key management currently massively sucks.
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f*d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
compare to SGX, a more critical impacted component is TPM chip, secured/measured boot depends on TPM, and cost of replacing all servers and OS ...
This would also be a good time for certain governments to knowingly push broken PQ KE standards while there is a panicked rush to get PQ tech in place.
Remember that the entities most likely to heed those governments recommendations are those providing services to said government and its military.
I feel like the NSA pushing a (definitely misguided and obviously later exploited by adversaries) NOBUS backdoor has poorly percolated into the collective consciousness, missing the NOBUS part entirely.
IMO the idea that NSA only uses NOBUS backdoors is obviously false (see for example DES's 56 bit key size). The NSA is perfectly capable of publicly calling for an insecure algorithm and then having secret documentation to not use it for anything important.
DES is the algorithms that was secretly modified by the NSA to protect it against differential cryptanalysis. Capping a key size is hardly a "backdoor."
Also, that was the time of export ciphers and Suite A vs Suite B, which were very explicit about there being different algorithms for US NatSec vs. everything else. This time there's only CNSA 2.0, which is pure ML-KEM and ML-DSA.
So no, there is no history of the NSA pushing non-NOBUS backdoors into NatSec algorithms.
In fairness, that was from 1975. I don't particularly trust the NSA, but i dont think things they did half a century ago is a great way to extrapolate their current interests.
The first and most obvious target will be Bitcoin. It’s market cap today is $1.4T. That’s a gigantic reward for any state actor or entity with the resources and budget to break it.
Does this mean Bitcoin is going to $0? Absolutely not, it’s just going to take the community organizing and putting in the gigantic effort to make the changes. Frankly I’m not personally clear if that means all existing cold wallets need to be flashed/replaced? All existing Bitcoin miner software needs to be updated? All existing Bitcoin node software needs to be updated?
This seems like something uniquely suited to the startup ecosystem. I.e. offering PQ Encryption Migration as a Service. PQ algorithms exist and now theres a large lift required to get them into the tech with substantial possible value.
… really? This is simultaneously so far down in the plumbing and extremely resistant to measuring the impact of, I can’t imagine anyone building a company off of this that’s not already deep in the weeds (lookin’ at you, WolfSSL).
The idea that a startup would be competitive in the VC “the only thing that matters are the feels” environment seems crazy to me.
Yeah... I spent the 90s working for RSADSI and Certicom implementing algorithms. Crypto is a vitamin, not an aspirin. Hardly anyone is capable of properly assessing risk in general, much less the technical world of information risk management. Telling someone they should pay you money to reduce the impact of something that may or may not happen in the future is not a sales win.
So... In 2013 I was working for Mozilla adding TLS 1.1 and 1.2 support into Firefox. It turns out that some of the extensions common in 1.1, in some instances caused PDUs to grow beyond 16k (or maybe it was 32k, can't remember.). This caused middle boxes to barf. Sure, they shouldn't barf, but they did. We discovered the problem (or rather one of our users discovered the problem) by increasing the key size on server and client certs to push PDU sizes over the limit.
At the very least, you want to start using hybrid legacy / pqc algorithms so engineers at Cisco will know not to limit key sizes in PDUs to 128 bytes.
A few points here:
There is already very wide use of PQ algorithms in the Web context [0], which is the most problematic one because clients need to be able to connect to any site and there's no real coordination between sites and clients. So we're exercising the middleboxes already.
The incident you're thinking of doesn't sound familiar. None of the extensions in 1.1 really were that big, though of course certs can get that big if you work hard enough. Are you perhaps thinking instead of the 256-511 byte ClientHello issue addressed ion [1]
Oh hey Eric. I think I was wrong saying it was 1.1. It was a middlebox that ignored max fragment negotiation, which I think was introduced in 1.2. IIRC, the middlebox claimed to support it for 1.2 connections, but silently failed by blackholing the connection. They eventually crafted a fix, but it was an annoying year waiting for network operators to upgrade the firmware on their routers.
In rebuttal, Peter Gutmann seems to think the progress towards quantum computing devices which can break commonly used public key crypto systems is not moving especially quickly: https://eprint.iacr.org/2025/1237
>and a rebuttal to it from an expert in the field.
while i agree with filippo, the way you worded this makes me think that you may not be aware that gutmann is also an expert in the field. so, if you are giving filippo weight because he is an expert, it is worth giving some amount to gutmann as well.
I apologize if I flippantly dismissed the fact that experts disagree. That was not my intention. I was trying to point out that OP does address the referenced counter-point post specifically.
>Sorry if I flippantly dismissed the fact that experts disagree!
i dont really get your reply/insincere apology.
if you are going to bother mentioning filippo's expertise in the first place, its just weird to frame it the way you did. that is how someone would typically dismiss some random blogger with an appeal to authority. but if both people are authorities, it doesnt make sense.
if you already knew, than my comment can be context for future readers that dont and might just dismiss gutmann as a non-expert getting rebutted by an expert.
If only we had a technology where an author could specify a unique identifier and name of another author's paper. Something that could cite a different paper and link to it.
Is that even a rebuttal? Seems like just a dismissal without any substance. I expect in 10 years the predictions will be wrong, kind of like Y2K all over again.
> This paper presents implementations that match and, where possible, exceed current quantum factorisation records using a VIC-20 8-bit home computer from 1981, an abacus, and a dog.
From the link:
> Sure, papers about an abacus and a dog are funny and can make you look smart and contrarian on forums. But that’s not the job, and those arguments betray a lack of expertise[1]. As Scott Aaronson said[2]:
> > Once you understand quantum fault-tolerance, asking “so when are you going to factor 35 with Shor’s algorithm?” becomes sort of like asking the Manhattan Project physicists in 1943, “so when are you going to produce at least a small nuclear explosion?”
It should be noted that if indeed there has not remained much time until a usable quantum computer will become available, the priority is the deployment of FIPS 203 (ML-KEM) for the establishment of the secret session keys that are used in protocols like TLS or SSH.
ML-KEM is intended to replace the traditional and the elliptic-curve variant of the Diffie-Hellman algorithm for creating a shared secret value.
When FIPS 203, i.e. ML-KEM is not used, adversaries may record data transferred over the Internet and they might become able to decrypt the data after some years.
On the other hand, there is much less urgency to replace the certificates and the digital signature methods that are used today, because in most cases it would not matter if someone would become able to forge them in the future, because they cannot go in the past to use that for authentication.
The only exception is when there would exist some digital documents that would completely replace some traditional paper documents that have legal significance, like some documents proving ownership of something, which would be digitally signed, so forging them in the future could be useful for somebody, in which case a future-proof signing method would make sense for them.
OpenSSH, OpenSSL and many other cryptographic libraries and applications already support FIPS 203 (ML-KEM), so it could be easily deployed, at least for private servers and clients, without also replacing the existing methods used for authentication, e.g. certificates, where using post-quantum signing methods would add a lot of overhead, due to much bigger certificates.
That was my position until last year, and pretty much a consensus in the industry.
What changed is that the new timeline might be so tight that (accounting for specification, rollout, and rotation time) the time to switch authentication has also come.
ML-KEM deployment is tangentially touched on in the article because it's both uncontroversial and underway, but:
> This is not the article I wanted to write. I’ve had a pending draft for months now explaining we should ship PQ key exchange now, but take the time we still have to adapt protocols to larger signatures, because they were all designed with the assumption that signatures are cheap. That other article is now wrong, alas: we don’t have the time if we need to be finished by 2029 instead of 2035.
> For key exchange, the migration to ML-KEM is going well enough but: 1. Any non-PQ key exchange should now be considered a potential active compromise, worthy of warning the user like OpenSSH does, because it’s very hard to make sure all secrets transmitted over the connection or encrypted in the file have a shorter shelf life than three years. [...]
You comment is essentially the premise of the other article.
I agree with you that one must prepare for the transition to post-quantum signatures, so that when it becomes necessary the transition can be done immediately.
However that does not mean that the switch should really be done as soon as it is possible, because it would add unnecessary overhead.
This could be done by distributing a set of post-quantum certificates, while continuing to allow the use of the existing certificates. When necessary, the classic certificates could be revoked immediately.
> I agree with you that one must prepare for the transition to post-quantum signatures, so that when it becomes necessary the transition can be done immediately.
Personally, my reading between the lines on this subject as a non-expert is that we in the public might not know when post-quantum cryptography is necessary until quite a while after it is necessary.
Prior to the public-key cryptography revolution, the state of the art in cryptography was locked inside state agencies. Since then, public cryptographic research has been ahead or even with state work. One obvious tell was all the attempts to force privately-operated cryptographic schemes to open doors to the government via e.g. the Clipper chip and other appeals to magical key escrow.
A whole generation of cryptographers grew up in this world. Quantum cryptography might change things back. We know what papers say from Google and other companies. Who knows what is happening inside the NSA or military facilities?
It seems that with quantum cryptography we are back to physics, and the government does secret physics projects really well. This paragraph really stood out to me:
> Scott Aaronson tells us that the “clearest warning that [he] can offer in public right now about the urgency of migrating to post-quantum cryptosystems” is a vague parallel with how nuclear fission research stopped happening in public between 1939 and 1940.
Planning now on a fast upgrade later, is planning on discovering all of the critical bugs after it is too late to do much about them.
Things need to be rolled out in advance of need, so that you can get a do-again in case there proves to be a need.
How do you do revocation or software updates securely if your current signature algorithm is compromised?
As a practical matter, revocation on the Web is handled mostly by centrally distributed revocation lists (CRLsets, CRLite, etc. [0]), so all you really need is:
(1) A PQ-secure way of getting the CRLs to the browser vendors. (2) a PQ-secure update channel.
Neither of these require broad scale deployment.
However, the more serious problem is that if you have a setting where most servers do not have PQ certificates, then disabling the non-PQ certificates means that lots of servers can't do secure connections at all. This obviously causes a lot of breakage and, depending on the actual vulnerability of the non-PQ algorithms, might not be good for security either, especially if people fall back to insecure HTTP.
See: https://educatedguesswork.org/posts/pq-emergency/ and https://www.chromium.org/Home/chromium-security/post-quantum...
[0] The situation is worse for Apple.
Indeed, in an open system like the WebPKI it's fine in theory to only make the central authority PQ, but then you have the ecosystem adoption issue. In a closed system, you don't have the adoption issue, but the benefit to making only the central authority PQ is likely to be a lot smaller, because it might actually be the only authority. In both cases, you need to start moving now and gain little from trying to time the switchover.
> In both cases, you need to start moving now and gain little from trying to time the switchover.
There are a number of "you"s here, including:
- The SDOs specifying the algorithms (IETF mostly)
- CABF adding the algorithms to the Baseline Requirements so they can be used in the WebPKI
- The HSM vendors adding support for the algorithms
- CAs adding PQ roots
- Browsers accepting them
- Sites deploying them
This is a very long supply line and the earlier players do indeed need to make progress. I'm less sure how helpful it is for individual sites to add PQ certificates right now. As long as clients will still accept non-PQ algorithms for those sites, there isn't much security benefit so most of what you are doing is getting some experience for when you really need it. There are obvious performance reasons not to actually have most of your handshakes use PQ certificates until you really have to.
If your HSM vendor isn't actively working on/have a release date for GA PQ, you should probably get a new vendor.
Yeah, that's an audience mismatch, this article is for "us." End users of cryptography, including website operators and passkey users (https://news.ycombinator.com/item?id=47664744) can't do much right now, because "we" still need to finish our side.
> The only exception is when there would exist some digital documents that would completely replace some traditional paper documents that have legal significance, like some documents proving ownership of something, which would be digitally signed, so forging them in the future could be useful for somebody, in which case a future-proof signing method would make sense for them.
This very much exists. In particular, the cryptographic timestamps that are supposed to protect against future tampering are themselves currently using RSA or EC.
Yes, though we do know how to solve this problem by using hash-based timestamping systems. See: https://link.springer.com/article/10.1007/BF00196791
Of course, the modern version of this is putting the timestamp and a hash of the signature on the blockchain.
This is a good take, there's really not much to argue about.
>[...] the availability of HPKE hybrid recipients, which blocked on the CFRG, which took almost two years to select a stable label string for X-Wing (January 2024) with ML-KEM (August 2024), despite making precisely no changes to the designs. The IETF should have an internal post-mortem on this, but I doubt we’ll see one
My kingdom for a standards body that discusses and resolves process issues.
I think the anti-hybrid argument the article makes is clearly wrong. Even if CRQCs existed today, we still should be using hybrid algorithms because even once CRQCs exist, they will be slow, expensive, and power hungry for at least a decade. The hybrid algorithms at a minimum make the cost of any attack ~$1M, which is way better than half of the PQC algorithms that made it to the 3rd stage of the PQC competition (2 of them can be broken on a laptop)
Is it?
Your reasoning relies on this being true:
> [CRQCs] will be slow, expensive, and power hungry for at least a decade
How could you know that? What if it was 5 years? 1 year? 6 months?
I predict there will be an insane global pivot once Q-day arrives. No nation wants to invest billions in science fiction. Every nation wants to invest billions in a practical reality of being able to read everyone's secrets.
The absolute low end of cost of a QC is the cost of an MRI machine ~100k-400k (cost of cooling the computer to super low temps). Sure we expect QCs to get faster and cheaper over time, but putting 100% faith in the security of the PQC algorithms seems like a bad idea with no upside.
It is the paradox of PQC: from a classical security point of view PQC cannot be trusted (except for hash-based algorithms which are not very practical). So to get something we can trust we need hybrid. However, the premise for introducing PQC in the first place is that quantum computers can break classical public key crypto, so hybrid doesn't provide any benefit over pure PQC.
Yes, the sensible thing to do is hybrid. But that does assume that either PQC cannot be broken by classical computers or that quantum computers will be rare or expensive enough that they don't break your classical public key crypto.
> from a classical security point of view PQC cannot be trusted
[citation needed]
https://words.filippo.io/crqc-timeline/#fn:lattices
We can disagree on the tradeoff, but if you see no upside, you are missing the velocity cost of the specification work, the API design, and the implementation complexity. Plus the annoying but real social cost of all the bikeshedding and bickering.
I missed you at the most recent CRFG meeting.
> “Doesn’t the NSA lie to break our encryption?” No, the NSA has never intentionally jeopardized US national security with a non-NOBUS backdoor, and there is no way for ML-KEM and ML-DSA to hide a NOBUS backdoor.
The most concrete issue for me, as highlighted by djb, is that when the NSA insists against hybrids, vendors like telecommunications companies will handwrite poor implementations of ML-KEM to save memory/CPU time etc. for their constrained hardware that will have stacks of timing side channels for the NSA to break. Meanwhile X25519 has standard implementations that don't have such issues already deployed, which the NSA presumably cannot break (without spending $millions per key with a hypothetical quantum attack, a lot more expensive than side channels).
> The most concrete issue for me, as highlighted by djb, is that when the NSA insists against hybrids
The fact that only NSA does that and they really have no convincing arguments seems like the biggest reason why the wider internet should only roll out hybrids. Then possibly wait decades for everything to mature and then reconsider plain modes of operation.
Thus succeeding at making the telecommunications vendors used for Top Secret US national security data less secure, the obvious goal of the US National Security Agency, and the only reason they wouldn't use the better cryptography designed by Dr. Bernstein. /s
Truly, truly can't understand why anyone finds this line of reasoning plausible. (Before anyone yells Dual_EC_DRBG, that was a NOBUS backdoor, which is an argument against the NSA promoting mathematically broken cryptography, if anything.)
Timing side channels don't matter to ephemeral ML-KEM key exchanges, by the way. It's really hard to implement ML-KEM wrong. It's way easier to implement ECDH wrong, and remember that in this hypothetical you need to compare to P-256, not X25519, because US regulation compliance is the premise.
(I also think these days P-256 is fine, but that is a different argument.)
What surprises me is how non-linear this argument is. For a classical attack on, for example RSA, it is very easy to a factor an 8-bit composite. It is a bit harder to factor a 64-bit composite. For a 256-bit composite you need some tricky math, etc. And people did all of that. People didn't start out speculating that you can factor a 1024-bit composite and then one day out of the blue somebody did it.
The weird thing we have right now is that quantum computers are absolutely hopeless doing anything with RSA and as far as I know, nobody even tried EC. And that state of the art has not moved much in the last decade.
And then suddenly, in a few years there will be a quantum computer that can break all of the classical public key crypto that we have.
This kind of stuff might happen in a completely new field. But people have been working on quantum computers for quite a while now.
If this is easy enough that in a few years you can have a quantum computer that can break everything then people should be able to build something in a lab that breaks RSA 256. I'd like to see that before jumping to conclusions on how well this works.
See https://bas.westerbaan.name/notes/2026/04/02/factoring.html and https://scottaaronson.blog/?p=9665#comment-2029013 which are linked to in the first section of the article.
> Sure, papers about an abacus and a dog are funny and can make you look smart and contrarian on forums. But that’s not the job, and those arguments betray a lack of expertise. As Scott Aaronson said:
> Once you understand quantum fault-tolerance, asking “so when are you going to factor 35 with Shor’s algorithm?” becomes sort of like asking the Manhattan Project physicists in 1943, “so when are you going to produce at least a small nuclear explosion?”
To summarize, the hard part of scalable quantum computation is error correction. Without it, you can't factorize essentially anything. Once you get any practical error correction, the distance between 32-bit RSA and 2048-bit RSA is small. Similarly to how the hard part is to cause a self-sustaining fissile chain reaction, and once you do making the bomb bigger is not the hard part.
This is what the experts know, and why they tell us of the timelines they do. We'd do better not to dismiss them by being smug about our layperson's understanding of their progress curve.
The thing is, producing the right isotopes of uranium is mostly a linear process. It goes faster as you scale up of course, but each day a reactor produces a given amount. If you double the number of reactors you produce twice as much, etc.
There is no such equivalent for qubits or error correction. You can't say, we produce this much extra error correction per day so we will hit the target then and then.
There is also something weird in the graph in https://bas.westerbaan.name/notes/2026/04/02/factoring.html. That graph suggests that even with the best error correction in the graph, it is impossible to factor RSA-4 with less then 10^4 qubits. Which seems very odd. At the same time, Scott Aaronson wrote: "you actually can now factor 6- or 7-digit numbers with a QC". Which in the graph suggests that error rate must be very low already or quantum computers with an insane number of qubits exist.
Something doesn't add up here.
You can already factor a 6 digit number with a QC, but not with an algorithm that scales polynomially. The graph linked is for optimized variants of Shor's algorithm.
We are stretching the metaphor thin, but surely the progress towards an atomic bomb was not measured only in uranium production, in the same way that the progress towards a QC is not measured only in construction time of the machine.
At the theory level, there were only theories, then a few breakthroughs, then some linear production time, then a big boom.
> Something doesn't add up here.
Please consider it might be your (and my) lack of expertise in the specific sub-field. (I do realize I am saying this on Hacker News.)
> produce at least a small nuclear explosion
The Manhattan Project scientists actually did this before anybody broke ground at Los Alamos. It was called the Chicago Pile. And if the control rods were removed and the SCRAM disabled, it absolutely would have created a "small nuclear explosion" in the middle of a major university campus.
Given the level of hype and how long it's been going on, I think it's totally reasonable for the wider world to ask the quantum crypto-breaking people to build a Chicago Pile first.
https://en.wikipedia.org/wiki/Chicago_Pile-1
TIL about the Chicago Pile! (I don't know enough about the physics to tell if it could have indeed exploded.)
> On 2 December 1942
https://en.wikipedia.org/wiki/Chicago_Pile-1
> on July 16, 1945
https://en.wikipedia.org/wiki/Trinity_(nuclear_test)
Two years and a half. This is still a good metaphor for "once you can make a small one, the large one is not far at all."
What? No. No matter what anybody did with the Chicago Pile, it would never have produced a small version of a nuclear detonation.
His article specifically mentions that the threat is with the public key exchange, not the encryption that happens after the key exchange.
IIRC the largest number factored still remains 21
The argument to skip hybrid keys sounds dangerous to me. These algorithms are not widely deployed and thus real world tested at all. If there is a simple flaw, suddenly any cheap crawler pwns you while you tried to protect against state actors.
Building out a supercomputer capable of breaking cryptography is exactly the kind of thing I expect governments to be working on now. It is referenced in the article, but the analogy to the Manhattan Project is clear.
Prior to 1940 it was known that clumping enough fissile material together could produce an explosion. There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.
I say this because there’s a meme that governments are cooking up exotic technologies behind closed doors which I personally tend to doubt.
This is almost perfect analogy to the MP though. We know exactly what could happen if we clumped enough qubits together. There are hard engineering challenges of actually doing so, and governments are pretty good at clumping dollars together when they want to.
> There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.
FWIW, constructing a weapon with highly enriched uranium is, relatively, simple. At the time, the choice was made to use a gun-type weapon that shot a projectile of highly enriched uranium into a a "target" of highly enriched uranium. The scientists were so sure it would work that the design didn't necessitate a live test. This was "little boy", which was eventually dropped on Hiroshima.
Fat Man utilized plutonium which required an implosion to compress the fissile material that would set off the chain reaction. This is a much more complex undertaking, but it's much more efficient. Namely, you need much less fissile material, and more of that fissile material is able to participate in the chain reaction. This design is what allows for nuclear tipped missiles. The same principles can be applied to a U-235 based weapon as well.
The implosion based design is super interesting to read about. One memorable aspect is that the designers realized that applying a tamper of uranium (U-238) around the fissile material allows for significant improvement in yield. The chain reaction is exponential, so the few extra nanoseconds that the uranium keeps the fissile material together leads to significant increase in yield.
https://en.wikipedia.org/wiki/Little_Boy
https://en.wikipedia.org/wiki/Fat_Man
The Manhattan project employed some significant % of all of America. A project of that scale will likely never happen again.
It was also about far more than the science. It was about industrializing the entire production process and creating industrial capability that simply did not exist before.
My comment was not limited to the U.S. government.
And the Manhattan Project cost $30B in today’s money. Compared with some of the numbers Congress has allocated recently, I’d call that a bargain.
Does quantum computing need that though? We don't suddenly need a large, unique supply chain for these computers. We don't need to dig up the qubits and refine them. Testing doesn't blow up the computer.
I don’t know why the author likes AES 128 so badly. AES 256 adds little additional cost, and protects against store now decrypt later attacks (and situations like: “my opinion suddenly changed in few months”). The industry standard and general recommendation for quantum resistant symmetric encryption is using 256 bit keys, so just follow that. Every time he comes up with all sorts of arguments that AES 128 is good.
Age should be using 256 bit file keys, and default to PC keys in asymmetric mode.
> The industry standard and general recommendation for quantum resistant symmetric encryption is using 256 bit keys
It simply is not. NIST and BSI specifically recommend all of AES-128, AES-196, and AES-256 in their post-quantum guidance. All of my industry peers I have discussed this with agree that AES-128 is fine for post-quantum security. It's a LinkedIn meme at best, and a harmful one at that.
My opinion changed on the timeline of CRQC. There is no timeline in which CRQC are theorized to become a threat to symmetric encryption.
he pretty explicitly states that AES 128 is not in any imminent danger and mandating a switch to 256 would distract from the actual thing he thinks needs to happen.
So why argue about whether AES-256 is worth it if we can just literally replace those 3 characters and be done with the upgrade? This was the smart move already in 2001 when Shor's algorithm was known and computers fast enough that we don't notice the difference. At least to me, it seems like less bikeshedding will be done if we abandon AES-128 and don't have to deal with all the people left wondering if that's truly ok
Then again, something something md5. 'Just replace those bytes with sha256()' is apparently also hard. But it's a lot easier than digging into different scenarios under which md5 might still be fine and accepting that use-case, even if only for new deployments
Because you cannot "just literally replace those 3 characters and be done with the upgrade".
How would he know? Did he publish papers on it?
You can’t just throw “Grover’s algorithm is difficult to parallelize” etc. It’s not same as implementation, especially when it gets to quantum computers. It’s very specialized.
Yeah, sounds like it's time to take this very seriously. Sobering article to read, practical and to the point on risk posture. One brief paragraph though that I think deserves extra emphasis and I don't see in the comments here yet:
>In symmetric encryption, we don’t need to do anything, thankfully
This is valuable because it does offer a non-scalable but very important extra layer that a lot of us will be able to implement in a few important places today, or could have for awhile even. A lot of people and organizations here may have some critical systems where they can make a meat-space-man-power vs security trade by virtue of pre-shared keys and symmetric encryption instead of the more convenient and scalable normal pki. For me personally the big one is WireGuard, where as of a few years ago I've been able to switch the vast majority of key site-to-site VPNs to using PSKs. This of course requires out of band, ie, huffing it on over to every single site, and manually sharing every single profile via direct link in person vs conveniently deployable profiles. But for certain administrative capability where the magic circle in our case isn't very large this has been doable, and it gives some leeway there as any traffic being collected now or in the future will be worthless without actual direct hardware compromise.
That doesn't diminish the importance of PQE and industry action in the slightest and it can't scale to everything, but you may have software you're using capable of adding a symmetric layer today without any other updates. Might be worth considering as part of low hanging immediate fruit for critical stuff. And maybe in general depending on organization and threat posture might be worth imagining a worst-case scenario world where symmetric and OTP is all we have that's reliable over long time periods and how we'd deal with that. In principle sneakernetting around gigabytes or even terabytes of entropy securely and a hardware and software stack that automatically takes care of the rough edges should be doable but I don't know of any projects that have even started around that idea.
PQE is obviously the best outcome, we ""just"" switch albeit with a lot of increase compute and changed assumptions in protocols pain, but we're necessarily going to be leaning on a lot of new math and systems that won't have had the tires kicked nearly as long as all conventional ones have. I guess it's all feeling real now.
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f*d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
Slightly off-topic but: Does anyone know what the Signal developers plan on doing there to replace SGX? I mean it's not like outside observers haven't been looking very critically at SGX usage in Signal for years (which the Signal devs have ignored), but this does seem to put additional pressure on them.
Signal uses SGX for features every other mainstream E2E messenger does in serverside plaintext.
What is the consequence on e.g. Yubikeys (or say the Android Keystore)? Do I understand correctly that those count as "signature algorithms" and are a little less at risk than "full TEEs" because there is no "store now, decrypt later" for authentication?
E.g. can I use my Yubikey with FIDO2 for SSH together with a PQ encryption, such that I am safe from "store now, decrypt later", but can still use my Yubikey (or Android Keystore, for that matter)?
This article is more aimed at those specifying and implementing WebAuthN and SSH, than at those using them.
They/we need to migrate those protocols to PQ now, so that you all can start migrating to PQ keys in time, including the long tail of users that will not rotate their keys and hardware the moment the new algorithms are supported.
For example, it might be too late to get anything into Debian for it to be in oldstable when the CRQCs come!
> This article is more aimed at those specifying and implementing WebAuthN and SSH, than at those using them.
Sure, I'm just trying to understand the consequences of that. Felt great to finally have secure elements on smartphones and laptops (or Yubikeys), protecting against the OS being compromised (i.e. "you access my OS, but at least you can't steal my keys").
I was wondering if PQ meant that when it becomes reality, we just get back to a world where if our OS is compromised, then our keys get compromised, too. Or if there is a middle ground in the threat model, e.g. "it's okay to keep using your Yubikey, because an attacker would need to have physical access to your key, specialised hardware AND access to a quantum computer in order to break it". Versus "you can stop bothering about security keys because with "store now, decrypt later", everything you do today with your security keys will anyway get broken with quantum computers eventually".
If you are doing authentication with those hardware keys, you will probably be fine, if we do our job fast enough. Apple's Secure Enclave already supports some PQ signatures (although annoyingly not ML-DSA-44 apparently?) and I trust Yubico is working on it.
If you are doing encryption, then you do have reason to worry, and there aren't great options right now. For example if you are using age you should switch to hybrid software ML-KEM-768 + hardware P-256 keys as soon as they are available (https://github.com/str4d/age-plugin-yubikey/pull/215). This might be a scenario in which hybrids provide some protection, so that an attacker will need to compromise both your OS and have a CRQC. In the meantime, depending on your threat model and the longevity of your secrets (and how easily they can rotated in 1-2 years), it might make sense to switch to software PQ keys.
Thanks a lot, that helps!
> This might be a scenario in which hybrids provide some protection, so that an attacker will need to compromise both your OS and have a CRQC.
Did you mean "your OS and have a CRQC" here, or "your Yubikey and have a CRQC"?
Your Yubikey itself is doomed.
If you are doing a post-quantum key exchange and only authenticating with the Yubikey, then you are safe from after-the-fact attacks. Well, as long as the PQ key exchange holds up, and I am personally not as optimistic about that as I’d like to be.
> If you are doing a post-quantum key exchange and only authenticating with the Yubikey, then you are safe from after-the-fact attacks.
Let me rephrase it to see if I understand correctly: so it is fine to keep using my security keys today for authentication (e.g. FIDO2?), but everything else should use PQ algorithm because the actual data transfers can be stored now and decrypted later.
Meaning that today (and for a few years), my Yubikey still protects me from my key being stolen when my OS is compromised.
Correct?
Looking forward to a PQ yubikey rev. I would buy a box of them today so I could start experimenting!
Another challenge of the transition is how much silicon we have yet to even implement. Smart cards? Mobile acceleration/offloading? We're at the mercy of vendors.
Is this also true for other TPM/snitching/DRM chips out there? IE will every existing device eventually become jailbreakable in the future or will we unfortunately not even get that benefit from all this?
So this is the exciting paper:
* https://arxiv.org/pdf/2603.28627
The new thing here seems to be the use of the neutral atom technique. Supposedly we are up to 96 entangled qubits for a second or two based on neutral atoms.
Shouldn't that be enough capability to factor 15 using Shor's?
I wonder, what is the impact of this to widely deployed smartcards like credit cards / EID passports?
Aren't they relying on asymmetrical signing aswell?
Yes. They will need to switch, so that hardware needs to be swapped out
This is exactly how customers who do threat modeling see PQC. HN can armchair QB this all they want, the real money is moving fast to migrate.
The analogy to a small atomic bomb is on point.
What do you recomend as reading material for someone that was in college a while ago (before AE modes got popular) to get up to speed with the new PQ developments?
If you want something book-shaped, the 2nd edition of Serious Cryptography is updated to when the NIST standards were near-final drafts, and has a nice chapter on post-quantum cryptography.
If you want something that includes details on how they were deployed, I'm afraid that's all very recent and I don't have good references.
We'll know it's been cracked when all the lost Bitcoins start to move.
No, it will likely be a state actor who reaches it first, who will never give away such a capability so easily
The bitcoins won't move until the technology is commoditized (ie well past mainstream usage by the government.)
Having PQ and your adversaries not knowing is far more valuable than the few hundred billion you could get from cracking (and tanking) BTC.
Yep, I was looking into it and from what I understand:
- There is a dark outlook on Bitcoin as the community and devs can't seem to coordinate. Especially on what to do with the "Satoshi coins"
- Ethereum has a hard but clear path (pretty much full rewrite) with a roadmap [0]
- The highly optimized "fast chains" (Solana & co) are in a lot of trouble too.
It would be funny if Bitcoin the asset end up migrating to Ethereum as another erc20 token
- [0] https://pq.ethereum.org/
> pretty much full rewrite
This is far from my understanding. Changing out this signature scheme is hard work, but doesn't require a rewrite of the VM.
Ethereum is way more complex than let's say Bitcoin and all parts are affected. This is not just the "signature scheme".
The fact that the signature size is multiplied by ~10 will greatly affect things like blockspace (what I guess is even more a problem with Bitcoin !)
Also they are the only blockchain I believe that put an emphasis on allowing large number of validators to run on very modest hardware (in the ballpark of a RPI, N100 or phone).
My understanding is they will need to pack it with a larger upgrade to solve all those problems, the so called zkVM/leanVM roadmap.
And then there are the L2 that are an integral part of the ecosystem.
So this is the greatest upgrade ever made on Ethereum, pretty much full rewrite, larger than the transition to proof of stake. I remember before the Proof of Stake migration they were planning to redo the EVM too (with something WASM based at the time) but they had to abandon their plan. Now it seems there is no choice but to do it.
Adding new signature schemes to bitcoin is relatively trivial and has been done previously (today Bitcoin supports both schnorr and ecdsa signatures).
Existing PQ standards have signatures with the wrong efficiency tradeoffs for usage in Bitcoin-- large signatures that are durable against a lot of use and supports fast signing, while for Bitcoin signature+key size is critical, keys should be close to single use, and signing time is irrelevant.
To the extent that I've seen any opposition related to this isn't only been in related to schemes that were to inefficient or related to proposals to confiscate the assets of people not adopting the proponent's scheme (which immediately raises concerns about backdoors and consent).
There is active development for PQ signature standards tailored to Bitcoin's needs, e.g. https://delvingbitcoin.org/t/shrimps-2-5-kb-post-quantum-sig... and I think progress looks pretty reasonable.
Claims that there is no development are as far as I can tell are just backscatter from a massive fraud scheme that is ongoing (actually, at least two distinct cons with an almost identical script). There are criminal fraudsters out seeking investments in a scheme to raise money to build a quantum computer and steal Bitcoins. One of them reportedly has raised funds approaching a substantial fraction of a billion dollars from victims. For every one sucker they convince to give them money, they probably create 99 others people panicked about it (since believing it'll work is a pre-req to handing over your money).
noob question: can't we just use longer classical keys, at least as a stop gap?
They're a pretty bad stopgap: https://bas.westerbaan.name/notes/2026/04/02/factoring.html. Going to RSA-32000 only buys you ~a year once QCs can factor RSA-2048. In order to get a standard that would resist quantum attacks for realistic time, we would need MB to GB keys at least (see https://eprint.iacr.org/2017/351.pdf for a hilarious post-quantum RSA attempt that used terabyte size keys)
No, and even if we could, it would require a migration of approaching the same difficulty of a migration to PQ, at which point why not just migrate to PQ
I was in this field a while back, and I always found it baffling that anyone ever believed in the earlier large estimates for the size of a quantum computer needed to run Shor's algorithm. For a working quantum computer, Shor's algorithm is about as difficult as modular exponentiation or elliptic curve scalar multiplication: if it can compute or verify signatures or encrypt or decrypt, then it can compute discrete logs. To break keys of a few hundred bits, you need a few hundred qubits plus not all that much overhead. And the error correction keeps improving all the time.
Also...
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f**d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
This part is embarrassing. We’ve had hash-based signatures that are plenty good for this for years and inspire more confidence for long-term security than the lattice schemes. Sure, the private keys are bigger. So what?
We will also need some clean way to upgrade WebAuthn keys, and WebAuthn key management currently massively sucks.
> Trusted Execution Environments (TEEs) like Intel SGX and AMD SEV-SNP and in general hardware attestation are just f*d. All their keys and roots are not PQ and I heard of no progress in rolling out PQ ones, which at hardware speeds means we are forced to accept they might not make it, and can’t be relied upon.
compare to SGX, a more critical impacted component is TPM chip, secured/measured boot depends on TPM, and cost of replacing all servers and OS ...
This would also be a good time for certain governments to knowingly push broken PQ KE standards while there is a panicked rush to get PQ tech in place.
Remember that the entities most likely to heed those governments recommendations are those providing services to said government and its military.
I feel like the NSA pushing a (definitely misguided and obviously later exploited by adversaries) NOBUS backdoor has poorly percolated into the collective consciousness, missing the NOBUS part entirely.
See https://keymaterial.net/2025/11/27/ml-kem-mythbusting/ for whether the current standards can hide NOBUS backdoors. It talks about ML-KEM, but all recent standards I read look like this.
IMO the idea that NSA only uses NOBUS backdoors is obviously false (see for example DES's 56 bit key size). The NSA is perfectly capable of publicly calling for an insecure algorithm and then having secret documentation to not use it for anything important.
DES is the algorithms that was secretly modified by the NSA to protect it against differential cryptanalysis. Capping a key size is hardly a "backdoor."
Also, that was the time of export ciphers and Suite A vs Suite B, which were very explicit about there being different algorithms for US NatSec vs. everything else. This time there's only CNSA 2.0, which is pure ML-KEM and ML-DSA.
So no, there is no history of the NSA pushing non-NOBUS backdoors into NatSec algorithms.
> see for example DES's 56 bit key size
In fairness, that was from 1975. I don't particularly trust the NSA, but i dont think things they did half a century ago is a great way to extrapolate their current interests.
Which governments are you thinking of?
RemindMe! 3 years "impending doom"
The first and most obvious target will be Bitcoin. It’s market cap today is $1.4T. That’s a gigantic reward for any state actor or entity with the resources and budget to break it.
Does this mean Bitcoin is going to $0? Absolutely not, it’s just going to take the community organizing and putting in the gigantic effort to make the changes. Frankly I’m not personally clear if that means all existing cold wallets need to be flashed/replaced? All existing Bitcoin miner software needs to be updated? All existing Bitcoin node software needs to be updated?
This seems like something uniquely suited to the startup ecosystem. I.e. offering PQ Encryption Migration as a Service. PQ algorithms exist and now theres a large lift required to get them into the tech with substantial possible value.
… really? This is simultaneously so far down in the plumbing and extremely resistant to measuring the impact of, I can’t imagine anyone building a company off of this that’s not already deep in the weeds (lookin’ at you, WolfSSL).
The idea that a startup would be competitive in the VC “the only thing that matters are the feels” environment seems crazy to me.
Yeah... I spent the 90s working for RSADSI and Certicom implementing algorithms. Crypto is a vitamin, not an aspirin. Hardly anyone is capable of properly assessing risk in general, much less the technical world of information risk management. Telling someone they should pay you money to reduce the impact of something that may or may not happen in the future is not a sales win.
> Traveling back from an excellent AtmosphereConf 2026, I saw my first aurora, from the north-facing window of a Boeing 747.
Given the author's "safety first" stance on pqc, it seems a bit incongruent to continue to fly to conferences...
There is always a price to encryption. The cost goes up the more you have to cater to different and older encryptions while supporting the latest.
Why do we "need to ship"? 1,000 qubit quantum computers are still decades away at this point
So... In 2013 I was working for Mozilla adding TLS 1.1 and 1.2 support into Firefox. It turns out that some of the extensions common in 1.1, in some instances caused PDUs to grow beyond 16k (or maybe it was 32k, can't remember.). This caused middle boxes to barf. Sure, they shouldn't barf, but they did. We discovered the problem (or rather one of our users discovered the problem) by increasing the key size on server and client certs to push PDU sizes over the limit.
At the very least, you want to start using hybrid legacy / pqc algorithms so engineers at Cisco will know not to limit key sizes in PDUs to 128 bytes.
A few points here: There is already very wide use of PQ algorithms in the Web context [0], which is the most problematic one because clients need to be able to connect to any site and there's no real coordination between sites and clients. So we're exercising the middleboxes already.
The incident you're thinking of doesn't sound familiar. None of the extensions in 1.1 really were that big, though of course certs can get that big if you work hard enough. Are you perhaps thinking instead of the 256-511 byte ClientHello issue addressed ion [1]
[0] https://blog.cloudflare.com/pq-2025/ [1] https://datatracker.ietf.org/doc/html/rfc7685
Oh hey Eric. I think I was wrong saying it was 1.1. It was a middlebox that ignored max fragment negotiation, which I think was introduced in 1.2. IIRC, the middlebox claimed to support it for 1.2 connections, but silently failed by blackholing the connection. They eventually crafted a fix, but it was an annoying year waiting for network operators to upgrade the firmware on their routers.
In rebuttal, Peter Gutmann seems to think the progress towards quantum computing devices which can break commonly used public key crypto systems is not moving especially quickly: https://eprint.iacr.org/2025/1237
That's not a rebuttal. The post references the paper and a rebuttal to it from an expert in the field.
>and a rebuttal to it from an expert in the field.
while i agree with filippo, the way you worded this makes me think that you may not be aware that gutmann is also an expert in the field. so, if you are giving filippo weight because he is an expert, it is worth giving some amount to gutmann as well.
I apologize if I flippantly dismissed the fact that experts disagree. That was not my intention. I was trying to point out that OP does address the referenced counter-point post specifically.
>Sorry if I flippantly dismissed the fact that experts disagree!
i dont really get your reply/insincere apology.
if you are going to bother mentioning filippo's expertise in the first place, its just weird to frame it the way you did. that is how someone would typically dismiss some random blogger with an appeal to authority. but if both people are authorities, it doesnt make sense.
if you already knew, than my comment can be context for future readers that dont and might just dismiss gutmann as a non-expert getting rebutted by an expert.
Damn. It's like I insulted Vault.
Also, I went over Filippo's post again and still can't see where it references the Gutmann / Neuhaus paper. Are we talking about the same post?
From Filippo's post: "Sure, papers about an abacus and a dog are funny and can make you look smart and contrarian on forums."
If only we had a technology where an author could specify a unique identifier and name of another author's paper. Something that could cite a different paper and link to it.
Is that even a rebuttal? Seems like just a dismissal without any substance. I expect in 10 years the predictions will be wrong, kind of like Y2K all over again.
From the abstract:
> This paper presents implementations that match and, where possible, exceed current quantum factorisation records using a VIC-20 8-bit home computer from 1981, an abacus, and a dog.
From the link:
> Sure, papers about an abacus and a dog are funny and can make you look smart and contrarian on forums. But that’s not the job, and those arguments betray a lack of expertise[1]. As Scott Aaronson said[2]:
> > Once you understand quantum fault-tolerance, asking “so when are you going to factor 35 with Shor’s algorithm?” becomes sort of like asking the Manhattan Project physicists in 1943, “so when are you going to produce at least a small nuclear explosion?”
[1]: https://bas.westerbaan.name/notes/2026/04/02/factoring.html
[2]: https://scottaaronson.blog/?p=9665#comment-2029013
Yes, this is why I invested in QRL crypto. With lates updates and no T1 exchange it looks like a good opportunity to grow.