Perhaps it’s not surprising that China, a country obsessed with government secrecy and control of its citizens’ online activities, seems to be so interested in the idea of quantum communications. Just last month, it launched the world’s first “quantum satellite” (which really means the world’s first regular satellite with quantum experiments on it), hoping to move quantum communications forward by a quant… well, by a large amount. Now, China is nearing completion of another major facet in its push for a quantum phone at the capital building: a 2,000-kilometer fiber-optic line for ferrying quantum encryption keys. It’s the beginning of China’s roll-out of true quantum encryption technology.
Why would China care so much about something as arcane as quantum communications? Because while countries like Russia and even China itself may make the most visible cyber-attacks in the world right now, nobody can hold a candle to the NSA‘s overall level of omniscience. They’ve compromised the internet’s physical backbone at the most critical spots — for safety, China simply has to assume that all their communications are suspect, except for those on dedicated government and military lines. Even then, there’s still innovating malware and human infiltration to worry about.
Quantum security is distinct from other forms of encryption because it doesn’t simply scale up existing barriers to be computationally more difficult to beat, but adds a new, seemingly insurmountable feature to complement regular encryption schemes: awareness. In short, quantum-encrypted messages aren’t any less likely to be intercepted than regular ones, but they have the unique ability to alert the sender that they’ve been intercepted, thus ensuring that the sender will not go on to encrypt and send the actual message, using that key. In principle, an attacker could shut down a quantum network by intercepting every key, every time, but even in that scenario the victim would at least know that this was happening, and avoid sending information over a compromised line.
To be clear: In this case the Chinese don’t have to send their communications over the quantum line, only the keys for decrypting those communications. Once that key has been successfully delivered to the intended recipient, the encrypted message vulnerable only to that key can be transmitted in whatever way they like — the internet, radio, smoke signals, whatever they want. In fact, the quantum line will almost certainly be reserved for key distribution only, while encrypted packets travel the lines of the regular old internet.
This fiber-optic cable stretches from Beijing to Shanghai, over 2,000 kilometers as mentioned. Anything over about 100 kilometers, and the photons being sent start to fade, their entanglement starts to break down, and their ability to securely ferry information reduced to essentially zero. With quantum repeaters, the keys are boosted further down the line, so they can travel real distances between real-world locations.
So long as they key is secure, modern encryption algorithms can keep attackers at bay. Quantum encryption is the first broad-based way of achieving that level of security since keys were printed on paper “one-time pads” during the Second World War. In that case, entire sections of a military would use the pads to stay coordinated on the keys needed to encrypt and decrypt messages on a particular date. Capture the pad, and they’ll just get the word out not to use it, and distribute a new one. But capture the pad without them knowing, and you’ve got the makings of a wartime breakthrough.
In the years since, the rise of online encryption has led cryptographers to focus mostly on ways to avoid having to send the key at all using so-called public key cryptography. Now, though, quantum science is making the older, more direct approach to key distribution secure enough to work once again. If the aforementioned quantum-equipped satellite leads to working space-based quantum communication, then the security of quantum key distribution (QKD) could come to just about everyone. The hope is to have a partial global network of quantum-encrypted devices by 2020, and a true one by 2030.
So, this raises an interesting question: If the satellite leads to a working successor, one that can actually distribute keys via quantum protocols, then what will be the use of this physical line? The obvious answer is that, for security, the Chinese have much better control over the physical line — but in principle, that shouldn’t matter. The principle likely means little, however, since there are already numerous ideas about how to beat quantum encryption.
We can imagine that this quantum network would at first be restricted to things like bank transfers and political communications, but eventually expand with increased throughput capacity in the key distribution pipeline. Remember that you don’t need any quantum protocol for the vast majority of the data you might want to transfer.
But this isn’t the end of China’s quantum ambitions. As with all major technological powers, China’s academics are very interested in the idea of a quantum computer. In America, we can say that the idea is receiving explicit government and even military interest — but given China’s love of secrecy, we can only speculate about how much investment quantum computers are receiving, out East. China is an aggressive offensive hacker, however, so it’s probably a safe assumption that it is at least looking into the prospect of developing computers several thousands of times faster than anything that’s come before.
The country also recently announced an alleged “quantum radar,” which uses the properties of entangled photons to determine the shape, speed, and even some material qualities of a target. It would be significantly more powerful than traditional radio-wave detection, allowing China to (it insists) see all up in the stealthiest of stealth aircraft. Just how real those claims are is open for debate, but the use of the word is notable even if it’s ultimately a bit frivolous. China is a nation in pursuit of an image as the world’s most advanced super-nation, and to continue its plan of America-like economic expansion it has to be seen as an advanced and scientifically ambitious power.
Still, quantum is more than just a cool-sounding prefix to various national projects — though it is that, too. Unfortunately, the secrecy that follows so naturally from quantum science seems to be perfectly in alignment with the way China is headed, online.
Now read: Google Brain’s neural-net AI dreams up its own encryption strategy