The effectiveness of limiting proliferation is tied directly to the difficulty and the scarcity of the human capital involved, this is why restricting the proliferation of small arms which can be build by anyone with some machining experience is near impossible, but limiting the proliferation of say nuclear arms and technology is quite possible.
It would surprise me if the NSA (or any other agency) doesn't have a list of all or most software engineers and mathematicians which are capable of designing crypto, that mailing list isn't that big.
