Culture

RSA200 digit number factored in encryption challenge

A team of German researchers has managed to factor a 200-digit number, marking the most complex puzzle solved to date in the closely-watched challenge created by RSA Security.

In an announcement Monday, Thorsten Kleinjung said he and his colleagues finally succeeded after trying to find factors for the "RSA200" number since December 2003. During one step, Kleinjung said, 80 2.2 GHz computers with AMD Operton processors were linked in a gigabit network.

The RSA Challenge is popular among cryptographers and computer science researchers because it indicates how expensive it is to attack messages encoded with strong encryption algorithms. (If, for instance, 768-bit keys can be factored with little effort, it may be time to switch to longer ones.)

Unfortunately for the German researchers, RSA has reformulated its challenge and now expresses numbers in bits (base 2) instead of decimal (base 10) -- it's not clear whether a prize will be awarded for a number on the old list.

The next RSA Challenge number on the current list is RSA-640 (2^640), which has about 193 digits and a cash prize of $20,000. That's a full 7 digits shorter than the RSA200 number that the German researchers already factored.

The RSA200 number is, by the way, 27,997,833,911,221,327,870,829,467,638,722,601,621,070,446,786,
955,428,537,560,009,929,326,128,400,107,609,345,671,052,955,
360,856,061,822,351,910,951,365,788,637,105,954,482,006, 576,775,098,580,557,613,579,098,734,950,144,178,863,178,946,295,
187,237,869,221,823,983.