I'm planing a question/puzzle, with pitch on the tune of

The International Stamped Time Server (ISTS) broadcasts, every minute, a time stamp integrity-protected with RSA-4096. Days after it starts operation, hackers announce they pwned it by rigging the RSA cryptoengine, and publish a valid stamp for year 9999 as a proof. That stamp couldn't have been made by the ISTS. You wrote the key generator and supervised key insertion in the cryptoengine, and must clear yourself from suspicion by finding how the hackers have proceeded.

The rest describes the ISTS, its simple signature format, its implementation, and precautions taken, including to catch malfunction of the cryptoengine or exfiltration of its content. The statement has no ciphertext or large numbers. The solution involves RSA and information theory, not IT security. There are two levels of answering: finding the general principle used, which I expect will be easy; finding how the hackers managed it that fast, and the fastest they could have made it.

Would that be on-topic?

Update: the full puzzle is on the side channel. And now on Puzzling.SE.

  • $\begingroup$ Is the solution to this puzzle instructive to possible realistic implementation errors of RSA? $\endgroup$ – SEJPM Jul 27 '18 at 14:31
  • $\begingroup$ @SEJPM: yes I guess it is. $\endgroup$ – fgrieu Jul 27 '18 at 14:36

Would that be on-topic?

My word is far from a definitive answer, but it sounds like something that would be more on topic on something like the puzzling stackexchange.

Assume we did declare it on-topic and allow it on the main site

  • Future users could see your post and be able to cite it as precedent that says such posts are in general acceptable.
    • If that created a trend, we could end up as a sort of crypto-puzzling/cryptography hybrid site.
      • If such puzzles became well established, there would then be a questionable distinction between "Solve this ciphertext" and crypto-puzzles, and the former is explicitly off-topic.

Therefore it appears that such puzzles are probably off-topic.

To keep it on crypto.stackexchange

Other sites play games in chat rooms that they create. Your puzzle is definitely something you could do in a chat room.

Of course, there is the problem that not all users have access to chat. However, it's probably fine in this case as playing a game is definitely more of a privilege than asking for help.


Personally (from a non-moderator perspective) I would say no.

Mainly because the fine line between what you are describing and what is described at the related meta question "Crypto puzzles on Crypto.SE" is rather small; if not too small to explain users why your kind would be on-topic while the other wouldn't be.

Besides that, I can only echo what Ella Rose already wrote. I'm pretty sure Puzzling.SE is a perfect home for something like that.

  • 1
    $\begingroup$ I'm uncertain that Puzzling.SE welcomes puzzles centering on RSA math and information theory, but I do understand and agree with your reservations. I'll either attempt that, or (more probably) reformulate as a clearly on-topic genuine question, and a dump of the puzzle on the side channel, which is approriate down to the name. $\endgroup$ – fgrieu Jul 31 '18 at 9:34
  • $\begingroup$ @fgrieu Sounds like a perfect plan. ;) $\endgroup$ – e-sushi Aug 1 '18 at 4:14

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