Crunching Internet security codes.

The so-called RSA encryption scheme is widely used to safeguard credit card numbers and other information transmitted across the Internet. To unscramble intercepted data, a snoop's computer must factor a large number into its two prime-number components. If the number is large enough, this task is prohibitively time-consuming (SN: 10/3/98, p. 217). A team of researchers has now demonstrated that numbers consisting of 155 decimal digits (or 512 bits), typically used for securing commercial Internet transactions, no longer provide adequate protection.

Using a worldwide network of computers and a sophisticated mathematical technique called the Number Field Sieve, Herman te Riele of the National Research Institute for Mathematics and Computer Science (CWI) in Amsterdam and his coworkers succeeded in factoring a 155-digit number into two 78-digit primes. The effort took 5 months on 300 personal computers and a Cray 916 supercomputer.

Although such a feat is currently beyond the capability of an ordinary snooper's computer, projected increases in computer speed could make it feasible in 2 or 3 years. Companies involved in Internet commerce are already considering the possibility of switching to RSA schemes requiring as many as 309 decimal digits (1,024 bits).