Scientists Work On Quantum Code

Relying on the principles of uncertainty underlying quantum mechanics, Harvard researchers recently established the first experimental secure network that, when perfected, should make it impossible for hackers to gain unauthorized access to documents shared electronically.

The system, called a quantum network, could not be intercepted without alerting the intended recipient of an electronic message, project researcher John M. Myers said.

McKay Professor of Applied Physics and Professor of Physics Tai T. Wu, the head of the Harvard lab experimenting with the quantum code key system, was on vacation and could not be reached for comment.

The quantum network involves the signaling of weak light impulses between two locations. Any message would be accompanied by a scrambled key that would be encoded by the sender and decoded by the recipient. The message could only be accessed if the code were successfully unscrambled.

Once the weak light impulses reached their destination, the sender and receiver would compare elements of their decoded keys to make sure they were identical, Myers said. He said a tenet of quantum physics would make this comparison the essential factor that would make the quantum code key a successful encoding system.

The Heisenberg uncertainty principle states that if a person observes particles in a specific state, then the person must have altered the state of those particles merely by having observed them.

Unlike strong light, weak light would be subject to the constrains of the Heisenberg uncertainty principle because of the low levels of energy involved, Myers said.

Myers said the Heisenberg Uncertainly Principle implied that a hacker could not steal a key encoded in weak light waves en route to its destination without altering the key itself.

He said two parties using a quantum key code would be sure that their key was not intercepted en route if the keys were identical. Conversely, the parties would know not to activate their keys—which in turn would open the message protected by the key—if there were discrepancies between the sender and recipient.

“The peculiar security offered by a quantum key distribution is security against undetected eavesdropping on the key,” Myers said.

Myers added that the Heisenberg Uncertainty Principle guaranteed that a hacker could not steal the same code that would ultimately be received.

Myers said the quantum code key would be an improvement over current number-based encryption systems.

Present electronic coding systems rely on large numbers that are extremely difficult to factor and therefore impossible to hack using present technology.

But Myers said there is no theoretical reason that the numbers could not be decoded in the future with improved number-factoring programs.

“If some student in the hills of India figures out how to do that in a hurry, then the cryptography used to send banking information over the internet is no longer secure,” Myers said.

Despite the theoretical advantages of the quantum key code, Myers said researchers had to ensure the quantum network would be as secure as the equations suggest it should be.

“The equation says there is no way anybody can eavesdrop on this without causing errors you can detect,” Myers said. “That’s a very hard thing to test because maybe I can come in and not [be able to hack the system without being detected], but how do I know there isn’t someone smarter than I am?”

Myers said researchers have been intrigued by the possibility of an encryption network using weak light since a 1984 scientific paper broached the possibility of such an impregnable system. He added that Harvard has been working on making the quantum code key a reality since 2001.

In June, a network connecting Harvard, Boston University and BBN Technologies—a Fresh Pond company that helped invent the internet—was created.

Myers said the system—which because of high costs would likely only be utilized by the government—is not yet complete.

He said the researchers hope to be able to squeeze all the materials needed for the quantum network into a box small enough to be placed in a sewer.

He added that the current optic fibers along which the weak light impulses are sent would only allow for two locations a maximum of 60 miles apart to communicate securely. Myers said this barrier could be overcome either with improved optic wiring, or by finding a way to send the weak light to a satellite.

Myers said the researchers hope to hope to have the system up and running by the year 2012.

—Staff writer Alan J. Tabak can be reached at tabak@fas.harvard.edu.