>Make it into a 1024 bit key, the minimum you need for real security,
I couldn't let this pass. With our current knowledge, 1024 is
about the maximum useful RSA key size, not the minimum. 512
bits is plenty for most uses. It is roughly where DES was 15
years ago: perhaps NSA can afford to break it but no one else
can. If you're worried about NSA, 640 bits is entirely
adequate unless they know some mathematics the rest of us
don't.
I think it's safe to assume that NSA does indeed know more math. Remember
that they'll permit 512-bit RSA to be exported easily. That, to me,
speaks volumes...
Where the cutoff is, I couldn't say, but I assume they left themselves
some margin.