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So earlier I decided to close this question based on several factors. I chose too localised, because I don't think such a question really benefits anyone as it stands.

This raised the question in my mind, so I'm proactively asking in the general case - do we want challenge questions ("please try to decrypt/analyse/tell me something about this?") here? If so, is there anything we should require of them?

I personally don't think these sorts of questions work on StackExchange, but it's not up to me.

So, what do we think? This will go some way to defining our scope and helping us write the FAQ and will help guide future decisions.

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These questions tend to plague unmoderated discussion sites about crypto, and they're almost always bad questions. I think any question of the form “here's a bunch of bytes, how do I break them” should be summarily closed. This blanket ban could be mentioned in the FAQ.

I'll cite somewhat similar examples on other Stack Exchange sites as precedents:

  • On Science Fiction and Fantasy, we have a specific ban on “genre classification” questions (is X science fiction?). The reason for this ban is that these questions are pretty uniformly bad (the answer is yes or no depending on who you ask, for uniformly uninteresting reasons).
  • On Programmers, there are specific question types that are considered unwelcome, such as “what language should I learn?” (where in 99.99% of cases there's no better answer than “whatever you like”) or “what salary should I ask for?” (where in 99% of cases any answer would be completely specific to the asker's case).

This would be a ban on questions that are specifically about identifying a crypto system from a given bunch of bytes.

Questions about cryptanalysis techniques are obviously welcome here, even including questions such as this (not a great question because the asker didn't come back with more information, but still a good fit for the site). A couple of signs this question is OK are that it doesn't have or need a byte dump, and that there's a specific story behind it.

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  • $\begingroup$ Removed the somewhat strong wording as this Q/A may be linked to to explain why questions are off topic. $\endgroup$
    – Maarten Bodewes Mod
    Commented Apr 29, 2019 at 9:00
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For any modern algorithm, one can't see anything else from a byte dump than

  • the encoding used (Base64 in this example), and
  • the length of the output. (From this one can guess at the hash function family, or the block size of a block cipher.)

So the only ways there would anything doable would be with classical ciphers, but even then, it is not really a useful question (for anyone but the asker).

So, closing as too localized seems fine for these types of question.

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