RSA crypto defiled again, with factoring of 768-bit keys

By Dan Goodin in San Francisco
The Register
7th January 2010

Yet another domino in the RSA encryption scheme has fallen with the announcement Thursday that cryptographers have broken 768-bit keys using the widely used public-key algorithm.

An international team of mathematicians, computer scientists and cryptographers broke the key though NFS, or number field sieve, which allowed them to deduce two prime numbers that when multiplied together generated a number with 768 bits. The discovery, which took about two-and-a-half years and hundreds of general-purpose computers, means 768-bit RSA keys can no longer be counted on to encrypt or authenticate sensitive communications.

More importantly, it means it's only a matter of another decade or so - sooner assuming there's some sort of breakthrough in NFS or some other form of mathematical factoring - until the next largest RSA key size, at
1024 bits, is similarly cracked. The accomplishment was reached on December 12.

"It's an important milestone," said Benjamin Jun, vice president of technology at security consultancy Cryptography Research. "There's indisputable evidence here that 768-bit key are not enough. It's a pretty interesting way to close out a decade."