Quantum encryption secures high-speed data stream

"No one else is doing quantum encryption at these high speeds," said Kumar. The pair's current prototype can encrypt data moving at 250 Mbits/second, and a second-generation model that can encrypt the 2.5-Gbit/s streams typical of Internet backbones will be developed within five years, Kumar said. A quantum encryption system disclosed this week by Magiq Technologies Inc. encodes only an encryption key, not an entire data stream, at rates of 1 kbit/s. Northwestern has applied for several patents for its technology.

Magiq's encryption technology is slated to see its first real world installations in the first quarter of 2003. The approach transmits an uncrackably secure encryption key over insecure lines. In contrast, Kumar and Yuen's approach sidesteps the secure key and instead secures existing high-speed data streams using uncrackable quantum logic.

Today's encryption/decryption methods go to great lengths to scramble data that's sent over an insecure backbone, as intercepted data can conceivably be decrypted if its encryption code is cracked with the help of high-speed computers. This encryption method depends upon a secret key only known by the receiver.

But keys can be discovered by trial and error. The standard 56-bit DES encryption code can be cracked on a supercomputer in a few hours, and its next-generation successor, AES, ups the ante to a 256-bit key, but code-cracking computers are also speeding up.

Quantum key distribution (QKD) uses an uncrackable key that's sent with single-photon receivers/transmitters. Kumar pointed out that this technique is limited at present to speeds of about 1 kbit/s and a distance of about 70 kilometers. At 1 kbit/s, 256-bit encryption keys can be updated four times a second, which greatly complicates the code-cracking task. But acracker has unlimited time to work on the scrambled codes, Kumar said.

Decoding denied

To go QKD one better, Kumar and Yuen's technique uses quantum mechanics to encode the actual data being transmitted, rather than just the key. If hackers intercept the actual fiber optic transmission on the backbone, quantum physics denies them the ability to decode the data due to quantum "noise," Kumar said.

"We have succeeded in encrypting and decrypting real information using quantum cryptography. Quantum key distribution is slow and impractical for long-distance or high-speed communication, whereas ours is fit for real-world applications," he said.

Northwestern's technology applies a quantum polarization angle to each transmitted bit. If eavesdroppers try to decode the message they must transgress Heisenberg's uncertainly principle — that is, their observation of the data introduces so much quantum noise as to render the result indecipherable, according to Kumar and Yuen. However, the intended receiver can use the secret key to remove enough of the noise to decode the encrypted data.

The researchers predict real world applications within five years, probably from Northwestern's industrial partners, Telcordia Technologies Inc. (Red Bank, N.J.) and BBN Technologies (Cambridge, Mass.). Funding was provided by a five-year, $4.7 million grant from the Defense Advanced Research Projects Agency (Darpa).