The first thing to know about RSA is that no one knows for certain that it is secure. Or more specifically, no one knows for sure that factoring is a difficult problem, which is the assumption that RSA rests upon. In fact, no one knows for sure that factoring is the fastest way to break RSA. Then again, no one knows for sure whether P = NP, which largely amounts to the same thing. While theoretical certainty about the strength of RSA remains elusive, the same uncertainty applies to the most basic assumptions of computational complexity theory (i.e. P = NP). The security of RSA rests on assumptions that are made by almost all serious mathematicians. But for now it is one of those unproven theorems that mathematicians believe without formal proof.