[john_nl]

I'm also curious where the 30x comes from. If cost is indeed the square of key size I would expect:

  Cost(1024) = (1024*x)^2
  Cost(2048) = (2048*x)^2 = (2*1024*x)^2 = 4 * (1024*x)^2

Which is a 4x increase in cost, not 30x.

[illumin8]

Cube, not square. Also, implementation matters.

2^3, or 8 times more expensive.