Currently we have two quantum related tags:

I suggest replacing by or . It should be removed from questions which involve post quantum schemes like NTRU but are not about how secure they are against attackers using quantum computers.

I'd replace by , since that makes the difference between it and breaking crypto using quantum computers clear.

  • 1
    $\begingroup$ I'd say the idea behind those being different is that PQ-Crypto talks about schemes that are secure in a quantum world, whereas quantum-crypto uses quantum computers to do crypto (see quantum key exchange). I think we should leave PQ-Crypto as is as well as q-crypto, because there may be other schemes than the standard (plain) key-exchange. $\endgroup$
    – SEJPM
    Jun 28, 2015 at 16:20
  • $\begingroup$ If we want to keep post-quantum-cryptography, another option might be to just rename quantum-cryptography to quantum-computers (which I agree is a better name) and create a new tag for quantum-key-exchange (or should it be quantum-key-distribution?); out of the 31 questions currently tagged with quantum-cryptography, only 5 also have key-exchange. $\endgroup$ Jun 17, 2016 at 7:44
  • $\begingroup$ We could also do with a tag for BB84. Anyone? $\endgroup$
    – Paul Uszak
    Jul 28, 2017 at 21:23
  • $\begingroup$ I've completely skipped the meta discussion and introduced a quantum-cryptanalysis tag. I'll start a meta-discussion about that though. $\endgroup$
    – Maarten Bodewes Mod
    Aug 15, 2018 at 21:29

3 Answers 3


I think (PQC from here on) is the most logical tag for questions about that subject (algorithms and primitives resistant to quantum computers) and should remain.

However, separate from that there probably ought to be a (QC, could alternatively be called ) tag for questions like this or this that are specifically about the capabilities of quantum computers or quantum algorithms and not specifically about quantum computer resistance.

I.e. have the tag PQC for questions about "quantum computer resistance" and the tag QC for anything else to do with quantum computers and algorithms. There's nothing wrong with overlap or one tag being a subset of another, that's normal and there are enough questions to warrant a specific PQC tag.

I have no opinion on the other replacement suggestion. I think the second suggestion is a good one.

  • $\begingroup$ I completely agree that the post-quantum-cryptography tag should remain. Maybe an interesting new tag could be quantum-cryptanalysis, for those questions about quantum algorithms for breaking crypto schemes. See blog.cr.yp.to/20160516-quantum.html $\endgroup$
    – cygnusv
    Jun 16, 2016 at 7:59

I don't think it's necessary to have separate tags for and .

Questions which are about a post quantum scheme, but only mention quantum computing is passing if at all, neither tag adds much value. e.g. Fractal Merkle Traversal or Implementations of Ntru TLS (the latter might be off-topic anyways).

Once we rule out those questions, becomes a subset of . The boundaries between questions about PQC and CQ is rather fluid, for example should questions like Is SRP post-quantum secure? be tagged with PQC or just CQ?


I suggested the following edit to the tag:

"Quantum cryptography describes the use of quantum mechanical effects to perform cryptographic tasks, this method is alternatively known as quantum communication. These terms are interchangeable in most literature. This is not to be confused with quantum computing."

I believe the current tag now reads: "Quantum cryptography describes the use of quantum mechanical effects to perform cryptographic tasks or to break cryptographic systems. In particular quantum cryptography handles the aspects of quantum communication and quantum computation."

I have an issue with this, because quantum cryptography does not deal with breaking any encryption schemes. Breaking encryption is only done by quantum computing.

Quantum computing and quantum communication are two distinct areas requiring distinct, and unique, hardware in order to operate.

I do not think the quantum cryptography tag should mention quantum computing at all.

I also disagree with Codes' answer. I think keeping pqc and qc separate will help people answering know if they need to address any component of quantum computing, or can write their answer focusing only on the pqc field.

I also disagree that quantum cryptography be replaced by QKD. That would significantly narrow the tag. I think the goal of Codes suggestion about changing quantum crypto with QKD was to segment it from quantum computing, but we don't need to change quantum crypto to QKD in order to do that.

I don't think quantum computing or cryptanalysis should be mentioned in the quantum crypto tag, because both of those are distinctly different from quantum cryptography.


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