RSA-640

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In mathematics, RSA-640 is one of the RSA numbers - large semiprimes that are part of the RSA Factoring Challenge. RSA-640 has a length of 193 decimal digits. A cash prize of US$20,000 had been offered by RSA Security for a successful factorisation. On 2 November 2005, F. Bahr, M. Boehm, J. Franke and T. Kleinjung of the German Federal Agency for Information Technology Security (BSI) announced that they had factorised the number using GNFS as follows:

RSA-640 = 31074182404900437213507500358885679300373460228427275457
          20161948823206440518081504556346829671723286782437916272
          83803341547107310850191954852900733772482278352574238645
          4014691736602477652346609

RSA-640 = 16347336458092538484431338838650908598417836700330923121
          81110852389333100104508151212118167511579
        * 19008712816648221131268515739354139754718967899685154936
          66638539088027103802104498957191261465571

The computation took 5 months on 80 2.2 GHz Opteron CPUs.

RSA-200, a slightly larger number at 663 bits, was factored in May 2005 by the same team.