# How can one calculate the estimated RSA key life based on Moore's law?

How can someone estimate the number of years needed to factor an RSA key based on the advancement of technology if followed Moore's law?

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An estimation based on Moore's law and current integer factorization is not a realistic estimate (and probably it will state something like thousands of years for RSA 2048). The reason is that having a more powerful computer does not matter much, when compared to finding a more efficient factoring algorithm. The general number sieve is the best algorithm we know, but a better algorithm might be found in the near future (or not). Also, there are approaches to optimize various aspects of the GNS, like polynomial selecation, which might speed up the process compared to today's method. –  tylo Oct 21 '13 at 17:19

and either invert the formula or use newtons approximation.

as for the offset to work on:

http://en.wikipedia.org/wiki/RSA_numbers

the number RSA 1024 appears to not have been factorized, but many companies already moved on to 2048 or even 4096.

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Unfortunately this answer links to a Wikipedia page with an incorrect formula: it confuses the number of bits of a number and its natural logarithm; and it misses an $o(1)$ term. The correct formula is here. –  fgrieu Oct 20 '13 at 10:27