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China’s New Satellite Will Test An Un-Hackable Encryption System
published during a waning crescent moon.
08/01/2016

New Satellite

The Quantum Space Satellite under construction at the Shanghai Engineering Center for Microsatellites (part of the Chinese Academy of Sciences). Credit: Xinhua/Cai Yang

By the end of this summer, China is expected to launch the Quantum Science Satellite—a space project that could revolutionize how we encrypt and send sensitive information by harnessing the spooky features of quantum mechanics.

One of the most basic tools of cryptography is something called a cryptologic key. Though there are many different approaches, the unifying theme behind all of them is the creation of a secret set of random numbers that use complex algorithms to transform information into a math problem that is too intense to be solved without first knowing those numbers. The “weakest link” of such a system, however, is the fact that the security of the information depends on how private that secret key remains—and that is something subject to plenty of potential human error.

But what if you had a secret key that ceases to exist when a third party attempts to view it? That’s where an esoteric area of physics called quantum entanglement comes into play. Quantum mechanics describes atomic and subatomic scale particles as existing in quantum states—a collection of properties including things like spin direction, location, velocity, polarity, etc. A fundamental tenet of quantum mechanics is that measuring the properties of a quantum system inherently changes those properties.

New Satellite

The Chinese Academy of Sciences’ quantum simulation laboratory. Credit: Xinhua/Cai Yang

“Are you horizontally or vertically polarized?”

Two quantum systems can become ‘entangled,’ meaning that when measuring the property of a particle in one system, the other system changes or reacts in turn (this is a counterintuitive mathematical consequence of quantum mechanics that turns out to exist in real life). For the purposes of this story, let’s focus only on the light-creating particles/waves called photons and their property of polarization, the direction the wave propagates.

“Neither [photon] carries any polarization on its own,” Anton Zeilinger, an Austrian quantum physicist and one of the primary QSS mission scientists, told NOW.SPACE. “But when you ask one of them, ‘Are you horizontally or vertically polarized?’, it gives you a random answer. Then the other one, no matter how far it is away, is instantly projected […] into the same state.” In theory, it doesn’t matter where in the universe either of the two photons is measured.

One of the primary goals of the QSS will be to use this weird property to simultaneously create a unique and secret cryptologic key between two distant locations. You can think of the key as a series of ones and zeros, with each one or zero corresponding to horizontal or vertical polarization. Each one or zero comes from the measurement of a single entangled photon pair. You measure it once, and if all is well, it should be identical on the other side. You can repeat this with as many photons as you want. “If you use entanglement, the key does not have to be transported from A to B,” Zeilinger explained, “It comes into existence at both places simultaneously.”

New Satellite

The “quantum entanglement source” that will generate entangled photons in space.  Credit:Xinhua/Cai Yang

The real genius of the system, though, is that if a third party were observing the creation of this key, that act alone would break the correlation between the entangled protons because the act of observing the quantum system will change it. The key will not match, making it immediately clear to the two people on either end of the key creation process that the system had been compromised.

This weirdness, even without the launch of the QSS, is far from merely theoretical. Zeilinger, and his former doctoral student, Jian-Wei Pan (now a scientist at the Chinese Academy of Sciences), have spent the better part of the last two decades observing this effect with entangled photons over ever increasing distances between Earth-based stations. The teams demonstrated that even when photos are separated by distances of well over 100km, measuring the polarity of one of them forced the photon at the other end to match its polarity. Pan, who invited his former boss Zeilinger to collaborate on the project, is the lead scientist behind the Quantum Space Telescope.

“Unless quantum mechanics is false,” he told me, “you can’t break it.”

But beaming entangled photons between two points on Earth becomes nearly impossible over longer distances due to the light-absorbing nature of fiber optic cables or, alternatively, the noise created by all the particles and light in the atmosphere. If you really want to go wild, you need to use the vacuum of space. Prior to the QSS, Zeilinger and Pan’s experiments showed that a signal could propagate far enough to be transported from the ground to a satellite in space. Now they just need to put a satellite into orbit that creates entangled photons (a process that involves shining a laser into a specific kind of crystal, Zeilinger said) and then see if quantum entanglement holds up over even longer distances.

“There are some people who believe that if you go further away, this kind of spooky action ceases to work,” Zeilinger explained.  “I don’t believe that, but some people think that might be the case.”

If the Quantum Science Satellite proves to be a success, then it would be the first step in creating a network of satellites capable of generating private encryption keys between two parties anywhere on Earth; by turning what was once the weakest link in encrypted data transmission into the most unbreakable part, this cryptologic key portion of the system system is literally unhackable.”

I asked Caltech professor of quantum information science, Fernando Brandao, for a second opinion on how hard such a system would be to hack:

“Unless quantum mechanics is false,” he told me, “you can’t break it.”