The only question I've found right now related to post quantum crypto (PQC) is this one: Is it possible for an encryption method to exist which is impossible to crack, even using quantum computers?

However, this one gets a pass in my opinion, as it seems the question asker is unaware of the fact that PQC is a modestly sized research field nowadays.

I think that questions about PQC that clearly do not crucially require knowledge of quantum computation should be off-topic. This is primarily because specific PQC algorithms are classical algorithms and hence not quantum computing. I suppose the argument for 'quantum resistance' is a question about quantum computation, but I think this wouldn't be an essential component of most PQC questions.

More importantly, I think Cryptography is much better equipped to answer such questions, as PQC as mostly a field by Crypto people than Quantum Computing people.

So, to be short: I think questions about PQC that aren't quantum should be off-topic.

What should this site's policy be on such questions?

Not to be confused with meta question, this question is about questions that relate to 'computing', but not 'quantum'.

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    $\begingroup$ Having read this comment by Robert, as well as this answer, I think this comes under the classification of "anticipating problems before they occur in actual practice" to be honest. While I agree with what you say, this may never actually occur, so "legislating hypothetical problems" is perhaps something we should avoid whenever possible $\endgroup$
    – Mithrandir24601 Mod
    Commented Mar 15, 2018 at 21:37
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    $\begingroup$ @Mithrandir24601 That seems to be the case. Partially, at least. Part of the reason why I asked this is that I considered asking a 'pure PQC' question. But I already got my own answer while writing the question. Then I suppose this question belongs in the fridge, to keep it cold until needed. Unless someone has any good reason for other actions (such as deletion or initiating a debate), let's keep it at this for now. $\endgroup$ Commented Mar 15, 2018 at 22:06

2 Answers 2


To know whether a post quantum encryption is secure you need to know whether a quantum computer can break it. So questions about post-quantum security (beyond security against classical eavesdroppers) are equivalent to questions about efficient quantum algorithms. This is on-topic. Other questions regarding, for example, efficient implementations on classical computers, might not be on-topic, of course.

  • $\begingroup$ Not all questions on post quantum crypto are about the security wrt to quantum computers. The crypto often needs to run efficiently on a classical computer, for instance. $\endgroup$ Commented Apr 5, 2018 at 10:41
  • $\begingroup$ @Discretelizard Yes, ok, but the "post-quantum" part about it is on-topic. That's what I'm saying here. $\endgroup$
    – M. Stern
    Commented Apr 5, 2018 at 11:57
  • $\begingroup$ Not quite. It seems you state all questions about PQ security are questions about quantum computing. This is false, as we also have to check whether we can break it with classical algorithms or side-channel attacks. Hence, there are questions about the security of PQC methods that are not about quantum. $\endgroup$ Commented Apr 5, 2018 at 12:01
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    $\begingroup$ @Discretelizard Again, I'm stating that the "post-quantum" in post-quantum cryptography is about quantum computing. I expanded the answer to clarify this $\endgroup$
    – M. Stern
    Commented Apr 5, 2018 at 12:09
  • $\begingroup$ Yes, I that clarification is what I want. This is fine. $\endgroup$ Commented Apr 5, 2018 at 12:26

I've created the in one of my edits. I will tag all pqp posts. So, we will at least be able to remove stuff quickly if needed :). Note that PQP is different from quantum cryptography as the latter uses quantum computers and the former runs computations on classical computers that are expected to be difficult on quantum computers.


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