Say that I have a theoretical computer security question - such as 'what if a 2046 bit processor exists. what would the impact on modern cryptography with 2046 bit keys be?' or 'if we decreased the latency in TOR by using geographically closer relay nodes what would the impact be?'- where should they be asked?
We have a theoretical computer science site, the crypto site and here. None of which seem to really quite fit the bill.
The Tor question is answerable, but isn't a security question, so you could try asking it over on SuperUser.
The crypto one likewise doesn't sound like a security question.
Theoretical security questions are welcome here, as long as they are applicable to a real world environment, and are answerable.
At least the Tor question should be either on the Tor site, or here on the main site. Indeed, it is a question about traffic analysis and correlation of data, which seems more on-topic on security.SE than on crypto.SE. Of course we can argue that cs.SE or crypto.SE seem related, but that's the lot of most questions on security.SE: when there is security and computers are involved, Computer Science and cryptography are never too far away.
The other one (the 2046-bit question) would be better on StackOverflow because it only calls for a generic answer which explains that the "size" of a processor is a pure question of performance (existing computers have no trouble using 2046-bit value right now; having registers with that size may just speed up operations a bit, but not significantly). Although I could engage in a discussion comparing password cracking performance on a GPU and on a CPU with SIMD instructions (a 2048-bit register would allow for 64 32-bit operations in parallel)(a good GPU would still win, though).
To sum up, I see nothing wrong in theoretical questions per se. We answer theoretical questions all the time. Answers tend to have a "practical viewpoint" (for instance, when talking about 256-bit encryption, a security.SE answer will often explain why that's overkill in practice) but theory of security is still on-topic. Which does not prevent any particular question from being off-topic, not because it is about theory, but because it is about theory of something which is not information security.
