Boy Scouts have been sending Morse code with flashlights for years, but Hughes used a special technique for his message: quantum cryptography. It works by exploiting a tenet of quantum physics–that the mere act of observing always changes that which is observed. To eavesdrop on a quantum message is to change the message’s content, immediately signaling the intrusion like an alarm bell. Even if some high-tech Captain Midnight had been watching, it would have been impossible for him to decode the message without Hughes’s being aware of it.
Quantum cryptography is now emerging from the lab and into the realm of real technology. Is such ironclad protection overkill? After all, standard “crypto” requires would-be hackers to crunch some gigantic numbers, which can take thousands of years even with the fastest computers. But it’s probably not safe to rest on these laurels. Quantum computers now on the drawing board could trim the time these code-breaking calculations take down to a matter of months, weeks–maybe even minutes or seconds. Nobody yet knows how to build a full-scale quantum computer, but if somebody figures it out, suddenly the need for quantum crypto would be urgent.
Quantum cryptography would end the encryption arms race once and for all. No matter how fast computers get, they could never be fast enough because the act of spying would corrupt the data, foiling the spy. To understand how this works requires a brief foray into the weird world of quantum physics. Light, according to this view, is made up of tiny particles called photons. Each photon possesses certain characteristics that can be used to represent information, like the ones and zeros of computers. Hughes and other cryptographers prefer to use polarization. They send a string of photons representing a “key”–a number that serves to unlock subsequent messages. To figure out what the key is, the person who receives the photons runs each one through a filter, which allows only one of four types of polarized photons through, yielding a string different from the original one. The sender and receiver then compare their photon strings in such a way that doesn’t disclose what they are, but still allows the receiver to deduce what the key is. An eavesdropper, though, would ruin the photons, which the receiver would readily discover.
By the time Hughes picked up on the idea, it had bounced among several physicists. Stephen Wiesner, a student at Columbia University, proposed the concept in 1969, but no journal would publish it. His classmate Charles Bennett was intrigued and about 10 years later found himself chatting with a colleague, Gilles Brassard, at a conference in Puerto Rico. Brassard and Bennett collaborated on the first blueprint for sending quantum-cryptographic messages and eventually got around to rigging up an experiment: two boxes connected by a foot of optical fiber exchanged quantum-encoded photons. (Hughes modified this experiment for satellites–sending the photons through the air instead of an optical fiber.) In 1999 a group of entrepreneurs formed MagiQ Technologies, based in New York City, to come up with a commercial product.
The MagiQ product is called Navajo, after the Native American code breakers who used the Navajo language to send encrypted messages for the U.S. military in World War II. MagiQ has distributed the device, which sends quantum-cryptographic keys over an optical fiber, to some telecommunications and financial-services companies on a trial basis. The firm plans to make it available by the end of the year at $50,000 a unit. Andrew Hammond, MagiQ’s VP of marketing and business development, predicts that the quantum-cryptography market will grow from $500 million next year to $1 billion in three years.
Navajo is somewhat limited–because it’s sensitive to background noise, it requires a dedicated fiber-optic line and, even so, works only over distances of 30 miles or less. But distance won’t be a limitation for long. University of Geneva physicist Nicolas Gisin recently set the record for transmitting quantum data–67 kilometers over optical fibers from Geneva to Lausanne. Gisin’s Geneva-based start-up, ID Quantique, is readying a quantum-cryptography unit that works over 60 kilometers. Gisin expects the product to appeal to those who “value their security very highly,” like banks, embassies and government agencies. Intelligence agencies are also following developments. The rest of us don’t need to worry–yet.
