A team of researchers has successfully factored a 232-digit number into its two composite prime-number factors, but too late to claim a $50,000 prize once attached to the achievement. The number, RSA-768, was part of a cryptography challenge that technically ended in 2007 that had been sponsored by RSA Laboratories, a prominent computer-security firm. RSA-768, so named because its binary representation is 768 bits long, is the largest number from the now-defunct challenge to be cracked. Thorsten Kleinjung of the Swiss Federal Institute of Technology in Lausanne, Switzerland, and his colleagues announced their result and posted to the Cryptology ePrint.Public key encryption works because it's easy to multiply two large numbers together, but very hard to calculate the factors of a large number. Doing so is largely a brute force process taking an enormous amount of computing power.