Factoring large numbers is hard. Unfortunately for algorithm designers, it is getting easier. Even worse, it is getting easier faster than mathematicians expected. In 1976 Richard Guy wrote: “I shall be surprised if anyone regularly factors numbers of size 10^80 without special form during the present century”. In 1977 Ron Rivest said that factoring a 125-digit number would take 40 quadrillion years. In 1994 a 129-digit number was factored. If there is any lesson in all this, it is that making predictions is foolish.引自 Chapter 7 : Key Length
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