Quantum encryption supposedly offers two parties an unhackable communications channel. Like any pioneering technology still in its infancy, we’re many steps to go before common folks like your or me can get their hands on such tech. Progress in the field, however, really is fast. American researchers report a quantum leap in data transfer encrypted in a quantum system in the order of five to 10 times faster than existing methods, allowing megabit-per-second rates. That’s fast enough to enable voice or video calls.
Whether you’re messaging friends with an encrypted app or shopping online, data is kept secure using ciphers called encryption keys. The most common method is RSA encryption, where access to data is secured with two keys. The encryption key is public and differs from the decryption key, which is kept secret. The public key, which anyone can see and use to encrypt a message, is based on the product of two large primes, and an auxiliary exponential. Multiplying two large primes to an integer is easy, but determining the original primes that make the product with no other info is very difficult. The encryption system’s reliability exploits the fact that factoring large primes takes years to do even for today’s fastest supercomputers, so protocols based on RSA have proven paramount to anything from processing payments to storing classified intelligence. RSA, however, might soon become obsolete as quantum computer systems become more stable and efficient.
Previously, scientists at MIT and the University of Innsbruck in Austria showed how to factor a prime using a quantum algorithm that calculates the prime factors of a large number vastly more efficiently than a classical computer. Their work, which employed a five-qubit machine, factored the prime 15, which is the smallest that can meaningfully demonstrate Shor’s algorithm. To decrypt a typical 1024-bit key, the same system would need thousands of qubits or simultaneous laser pulses. But all of this sounds doable in the not so distant future. Basically, quantum computers are poised to easily breach our current encryption methods. So, what’s next? Quantum encryption of course.
“We are now likely to have a functioning quantum computer that might be able to start breaking the existing cryptographic codes in the near future,” said Daniel Gauthier, a professor of physics at The Ohio State University. “We really need to be thinking hard now of different techniques that we could use for trying to secure the internet.”
Theoretically, a quantum-based encryption cannot be hacked due to inherent quirks of quantum mechanics. Since measuring matter or light instantly changes their properties, both parties that share keys are just as immediately alerted of a communication breach. One such protocol, called the Quantum key distribution (QKD), was first theorized in 1984 but its only recently that the hardware technology has caught up.
The problem is that these systems, which generally transmit keys with a weakened laser that encodes information on individual photons, can only transmit at low rates. Typically, we see data transfer in the orders of tens to hundreds of kilobits per second. Not bad if you want to send super-secure messages but way too slow for most practical applications we’re used to nowadays on the internet, like video streaming or voice calls. A solution may have been found by researchers Duke University, The Ohio State University, and Oak Ridge National Laboratory.
Their new QKD system also uses a weakened laser to encode information, but they’ve found a way to pack more information on each photon. By simply adjusting the time at which the photon is released and its phase, researchers were able to encode two bits of information per photon rather than one. Paired with high-speed detectors, this nifty tricks enabled a key transmission rate of 5 to 10 times faster than existing methods.
“It was changing these additional properties of the photon that allowed us to almost double the secure key rate that we were able to obtain if we hadn’t done that,” said Clinton Cahall, now at Ohio State University.
There are a couple of limitations we should all be aware of, though. For starters, the transmitter and receiver are as large as a computer, though that may not necessarily be a problem if you’re overly determined. Secondly, real-world applications of QKD require imperfect equipment which can open up leaks for hackers to exploit. So a theoretically unhackable quantum system can be breached if non-quantum components are vulnerable.
“All of this equipment, apart from the single-photon detectors, exist in the telecommunications industry, and with some engineering we could probably fit the entire transmitter and receiver in a box as big as a computer CPU,” Islam said.
All of these developments are incredibly exciting. Not long ago, China — the country with the world’s first operational quantum satellite — beamed entangled particles of photons to three ground stations across China, each separated by more than 1,200km. They then used this satellite to perform a quantum-encrypted video call between scientists at Xinglong, China, and colleagues in Vienna, Austria. The call lasted for about half an hour and the quality was reportedly ‘excellent’. One day, a swarm of similar satellites might power a quantum internet that’s orders of magnitude faster and more secure than it is today.