[adgjlsfhk1]

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.

[phicoh]

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.

[FiloSottile]

> from a classical security point of view PQC cannot be trusted

[citation needed]

https://words.filippo.io/crqc-timeline/#fn:lattices

[Tyyps]

Just a little selections of recent attacks on a few post quantum assumptions:

Isogenie/SIDH: https://eprint.iacr.org/2022/975

Lattices: https://eprint.iacr.org/2023/1460

Classical McEliece: https://eprint.iacr.org/2024/1193

Saying that you can trust blindly PQ assumptions is a very dangerous take.

[tptacek]

I don't think you said (or cited) what you think you said.

Leaving aside that you actually didn't cite a lattice attack paper, the "dual attack" on lattice cryptography is older than P-256 was when Curve25519 was adopted to replace it. It's a model attack, going all the way back to Regev. It is to MLKEM what algebraic attacks were (are?) to AES.

You know you're in trouble in these discussions when someone inevitably cites SIDH. SIDH has absolutely nothing to do with lattices; in fact, it has basically nothing to do with any other form of cryptography. It was a wildly novel approach that attracted lots of attention because it took a form that was pin-compatible with existing asymmetric encryption (unlike MLKEM, which provides only a KEM).

People who bring up SIDH in lattice discussions are counting on non-cryptography readers not to know that lattice cryptography is quite old and extremely well studied; it was a competitor to elliptic curves for the successor to RSA.

With that established: what exactly is the point you think those three links make in this discussion? What did you glean by reading those three papers?

[ramchip]

He's obviously not saying that you can "trust blindly" any PQ algorithm out there, just that there are some that have appeared robust over many years of analysis.

[Tyyps]

He is assessing that the risk of seeing a quantum computer break dlog cryptography is stronger than the risk of having post quantum assumptions broken, in particular for lattices.

One can always debate but we have seen more post quantum assumptions break during the last 15 years than we have seen concrete progress in practical quantum factorisation (I'm not talking about the theory).

[cyberax]

It's purely a matter of _potential_ issues. The research on lattice-based crypto is still young compared to EC/RSA. Side channels, hardware bugs, unexpected research breakthroughs all can happen.

And there are no downsides to adding regular classical encryption. The resulting secret will be at least as secure as the _most_ secure algorithm.

The overhead of additional signatures and keys is also not that large compared to regular ML-KEM secrets.

[tptacek]

No it's not. This is the wrong argument. It's telling how many people trying to make a big stink out of non-hybrid PQC don't even get what the real argument is.

[cyberax]

?

I'm not entirely sure what's the problem?

[tptacek]

It's definitely not that "The research on lattice-based crypto is still young compared to EC/RSA."

[FiloSottile]

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.

[adgjlsfhk1]

All of those are costs are at least as high for non-hybrid. The spec and API are just as easy to design (because we have really good and simple ECC libraries), and the bikeshedding and bickering will be a lot less if people stop trying to force pure PQC algorithms that lots of people see as incredibly risky for incredibly little benefit.