I disagree for the following reasons:
- I think Cryptography as a subject covers a wide range of disciplines. An explanation of RSA is impossible without understanding Number Theory. The basis for AES is rooted in Abstract Algebra (Finite Fields specifically), questions on which are if anywhere more appropriate to math.se and mathoverflow. I think however that there are additional points to be made on such subjects in the context of a cryptographic environment which in the context of other domains might be seen as unnecessary.
- There is some pretext for duplicate subset proposals. All of these sites: https://askubuntu.com/, https://unix.stackexchange.com/, http://dba.stackexchange.com/https://dba.stackexchange.com/, http://serverfault.com, http://superuser.com technically share common ground, they just have different focus.
- From @AviD's comment, "I would say this should be more in the direction of research / theoretical / conceptual / algorithmical / mathy parts of crypto". I don't take that to mean solely research level questions - I take it to mean the full spectrum from research level to basic questions (but well asked ones, of course) are on-topic. From the CSTheory FAQ these kind of questions are considered too basic there.
- I think rather than taking a pre-emptive action against a potential community, we should allow the site a chance to stand or fall on its own merits. It may well be that this community does not achieve critical mass in any case. After all commitment is not necessarily a measure of quality participation.
I suggest hanging fire here. There is a fairly large overlap between the two communities and that could be seen in a negative light (removing potential questions from CSTheory) but it could also be positive. I expect CSTheory, Math, ITSec and StackOverflow would be the obvious migration routes for questions and I imagine there'll be a subset of the userbase who are members of all three.