As you probably know, all stackexchange sites have a FAQ. What you might not know is that the community can edit part of it through their moderators. Specifically, we can edit this bit:

What kind of questions can I ask here?

Crypto - Stack Exchange is for software developers, mathematicians and others interested in cryptography.

(Actually, without the section title. We can add more sections (with new titles) here, but the part from What kinds of question should I not ask here onwards is not changeable.)

Currently, this part doesn't say much, as you can see. This is a valuable opportunity for us to have a place where our scope is defined. For example, the programmers FAQ has a lot of detail about what constitutes a good question and what does not - including a nice graphic.

So, what do we want to put in ours? I suggest an approach that goes something like this:

  1. We draft some examples in this meta question. Post your draft as an answer.
  2. We vote.
  3. We come up with a final(ish) version.
  4. Your moderators copy and paste.

Of course, I'm fully expecting this process will take time and of course, as we go along we may want to change our FAQ. I know. I just think we should get the ball rolling.

Things to consider in our FAQ:

Defining the FAQ is important. At the moment, only 7 users have close vote privileges, so it would take most of them (or a moderator) to close a question. Until such a time as it becomes about votes, the more community guidance on what we (the whole) want, the better. When it does become about votes, we have something we can all use to be consistent.

Feel free to edit this question, make suggestions for the process and of course, answer!

Also, remember we have a chat room where discussions can be had. Please feel free to join us in there!


1 Answer 1


Here's my draft of a FAQ. I've written it with the "in my head" version of our policy; feel free to debate that elsewhere and I'll update this as and when. If you want to improve it, feel free to, if you want to have a go at drafting your own version, please do that too.

What kind of questions can I ask here?

Crypto - Stack Exchange is for software developers, mathematicians and others interested in cryptography.

Cryptography Stack Exchange is for asking questions about the mathematics and properties of cryptographic systems, their analysis ("cryptanalysis") and subsidiary topics that generally make up cryptology, such as random number generation. As such, we welcome questions on topics such as:

  • Asymmetric and symmetric cryptographic algorithms.
  • Cryptographic protocols.
  • Cryptanalysis techniques.
  • Hash functions, hashing.
  • Entropy and information theory.
  • Random number generation.

Do we accept basic level/homework questions?

Yes, we do. However, please try to provide an indication of what you are not understanding/need clarification on. If you have just written out your assignment, it is highly likely your question will be closed. You might want to read this article on writing the perfect question – originally for Stack Overflow, but relevant here too.

Do we accept questions asking for cryptanalysis of your cipher (hash function, ...) design?

That depends. Questions about cipher design (yours or someone else's) are fine as long as they are precise and specific - so we encourage you to break your cipher down where possible into reasonably scoped and well focused parts, so you get well focused answers. If you post a long and complicated scheme, it is likely to run into difficulties as it is hard for one answer to address all of the potentially relevant points.

Can I get data analysed here? Can I challenge people to decode something?

No, questions like 'can you decrypt this particular piece of ciphertext' are not useful. However, if you do have specific questions about the design of a cipher, its cryptanalysis or a cryptanalytic result, these are great questions.

I'm confused as to where my question belongs; there are so many sites!

There are lots of places in the Stack Exchange network to ask your question; don't worry too much about getting it wrong, because it can always be migrated to the right place. That said, it is useful to provide a general guide here:

  • If your question is about using cryptographic software in your application, you probably need Stack Overflow.
  • If your question is about mathematics generally, without any cryptographic element, you'll get an excellent answer on Mathematics.
  • If your question is about cryptographic policy within your organisation, implementation and practical usage considerations, you probably are looking for Security.
  • If your question is about usage of a specific cryptographic software, see Super User.
  • If your question involves large amounts of research and a lot of computer science, you might find CS Theory an appropriate place to ask. Please bear in mind their FAQ and policy on non-research level questions.

I'm still stuck between Security.SE and Crypto.SE.

The rule of thumb, here, being that you should post to crypto.SE if you want to understand the internals, and to security.SE if you want to know what you should do now.

  • $\begingroup$ I made the sub-titles real titles (might need # instead of ##), added some links, Super User, crypto protocols. And some typographic changes. I think this is a version that could go life (later changes are always possible). $\endgroup$ Oct 1, 2011 at 15:04
  • $\begingroup$ @PaŭloEbermann ok; I'm in a doing mood these past few days, so I've put it live now. Everyone - feel free to propose changes and one of us will include them in the live copy. $\endgroup$
    – user46
    Oct 1, 2011 at 16:07
  • 2
    $\begingroup$ My suggestion would be to shorten the last two paragraphs significantly. As it is, the length is a bit intimidating, and most sites only include/need to include a common "if your question is about..." header and a few one-line descriptions of related sites. "Pure math, ask on Math.SE." "Coding against crypto libraries, Stack Overflow." "Crypto as a corporate security policy, ITSec.SE." Just stick to the facts, save the lengthy explanations for a meta discussion if necessary. $\endgroup$
    – Aaronaught
    Oct 1, 2011 at 16:53
  • 1
    $\begingroup$ Also, the answer to "Can I get data analysed here?" question sounds a bit terse (if accurate). You might refer back to the previous question (about the types of questions that would be useful); perhaps something like "No, questions like 'can you decrypt this particular ciphertext' are not useful. However, if you do have specific questions about the design of a cipher, those can be discussed" $\endgroup$
    – poncho
    Jan 25, 2012 at 23:48
  • $\begingroup$ @poncho good idea; have incorporated it in with a slight change. Feel free to play around with the wording :) $\endgroup$
    – user46
    Jan 25, 2012 at 23:55
  • $\begingroup$ Seems quite good. By the way, you can add a last item linking to a meta post for a more detailed faq, see this. $\endgroup$
    – Kaveh
    Feb 14, 2012 at 2:42
  • $\begingroup$ @Kaveh Interesting link, thanks :) I'm not sure how best to fit it in though, there's the FAQ tag on meta too which might suit. I'll have a think and if I have time I'll try to fit it in, then will draft an edit. $\endgroup$
    – user46
    Feb 14, 2012 at 13:35

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