How the NSA is cracking encryption

The National Security Agency is bypassing encrypted Internet connections because the encryption data is all the same, researchers posited this week. It has long been believed the NSA had a way to bypass common types of encryption, but its methods haven't been known.

"There have been rumors for years that the NSA can decrypt a significant fraction of encrypted Internet traffic," Alex Halderman and Nadia Heninger wrote in a study Wednesday. "The key is, somewhat ironically, Diffie-Hellman key exchange, an algorithm that we and many others have advocated as a defense against mass surveillance."

Along with twelve co-authors, Heninger and Halderman presented their research on the topic in a paper this week.

In short, the Diffie-Hellman method uses the same data, called a "prime," to encrypt connections. When it was created, the researchers wrote, "There seemed to be no reason why everyone couldn't just use the same prime, and, in fact, many applications tend to use standardized or hard-coded primes." The problem with that, they said, is that "an adversary can perform a single enormous computation to 'crack' a particular prime, then easily break any individual connection."

In the past, that wasn't considered a problem. "For the most common strength of Diffie-Hellman (1024 bits), it would cost a few hundred million dollars to build a machine," the researchers said, and would be a feat "not seen since the Enigma cryptanalysis during World War II."