12 settembre 2010

Crittografia quantistica: Cina codifica, Norvegia crakka

Andando a spulciare nientepopodimeno che un articolo pubblicato dai ricercatori cinesi su Nature Photonics, il settimanale Time in un pezzo sulle esercitazioni militari che la Cina sta conducendo nel Mar Giallo sostiene che l'esercito cinese è a un passo da una rivoluzionaria applicazione della fotonica quantistica: la capacità di inviare (su frequenze ottiche) messaggi intrinsecamente sicuri nello spazio libero. Una tecnologia che darebbe ai militari cinesi un enorme vantaggio in termini di capacità di comunicazione e controllo.
While China has been showing off its new hardware, a potentially more important military advancement has gone largely unnoticed: In May, Chinese scientists announced a demonstration of "quantum teleportation" over 16 kilometers (10 miles), creating what Matthew Luce, a researcher at the Defense Group Inc.'s Center for Intelligence Research and Analysis, calls "secure communications guaranteed by the laws of physics." China is now at the cutting-edge of military communications, transforming the field of cryptography and spotlighting a growing communications arms race.
While the People's Liberation Army won't be beaming up objects Star Trek-style anytime soon, the new technology could greatly enhance its command and control capabilities. Scientists use machines to manipulate units of light called photons. By changing the photons' quantum states and creating a new, readable pattern not unlike Morse code, they can pass on simple messages or encryption codes. A group of researchers from Tsinghua University and the Hefei National Laboratory for Physical Sciences entangled pairs of photons — linking them so changes to one photon will be instantaneously transferred to the other. Using a high-powered blue laser (the type China appears to be investing in for its submarine fleet), they then transported the quantum information farther than anyone had done before, their paper in Nature Photonics claims.
The process is called teleportation, but the information in the message is not actually moved. Instead, changes to one photon's quantum state will be adopted instantly by the other — something Einstein famously called "spooky action at a distance." The result is akin to having two pieces of paper 10 miles apart, and as a person writes on one paper the message simultaneously appears on the other.
Why is this superior to e-mail or radio? Because, theoretically, this method "cannot be cracked or intercepted," says Luce. If the photons in the laser beam are observed by a third party, the particles themselves will be altered due to a law of physics called the Heisenberg Uncertainty Principle, which states that measuring a particle alters it. As such, the sender and receiver would be immediately informed that someone was snooping.
At the 16km distance tested, China would be able to send these secure messages from its network of satellites to units on the ground. Luce also says the choice of a blue laser — instead of an infrared one like the U.S. has been testing — was chosen with its growing submarine fleet in mind since blue lasers penetrate farther underwater. Soon, Chinese satellites could be able to communicate with submarines without them needing to surface or give away their location by breaking radio silence. This may sound like science-fiction, but quantum encryption is already used by a few banks and governments for highly sensitive information on a smaller scale. The Chinese scientists write in Nature Photonics that a quantum communication network could be "within reach of current technology on a global scale."
Siamo davvero alle soglie di una rivoluzione nel campo della crittografia? In realtà la crittografia quantistica non è una novità e il principio di "azione a distanza" (una forma di teletrasporto, anche se su scala molto limitata) su cui si basa questa nuova applicazione dei cosiddetti "entangled photons", i fotoni intrecciati, viene sperimentato in molti laboratori e ha dato vita a diverse startup commerciali. Gli scienziati cinesi affermano di essere riusciti a stabilire una connessione che non necessita di fibre ottiche o altre guide d'onda, utilizzando un particolare laser su distanze mai raggiunte prima: oltre i 16 kilometri.
Questo annuncio risaliva al mese di maggio. Ma al Time deve essere sfuggito quello, apparso sull'ultimo numero di Nature Photonics, del team norvegese che ha dimostrato, per la prima volta, che anche i sistemi di crittografia quantistica attualmente in commercio possono essere "crakkati". E adesso come risponderanno i cinesi?

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