Whenever you make an online purchase, sensitive information such as your payment card number is sent to the merchant. To prevent such data from being obtained by a hacker, it is necessary to ‘lock’ it before sending it through an encryption process. Then, if the merchant has a ‘key’ corresponding to the one used to lock your information, it can then be unlocked, or decrypted.

Cracking an encrypted message is not impossible, it just takes an incredibly long time—millions of years even if you use the world’s fastest supercomputer. But you can count on quantum computing to turn the tables. Encryptions could be broken in mere seconds—posing a real threat to many critical security infrastructures if no countermeasures are taken. Therefore, it is of utmost importance that cybersecurity technologies continue to evolve, especially vis-à-vis the context of the rapid rise of online transactions across the world. 

Enter quantum key distribution (QKD), a quantum-based encryption solution. Senior Researcher Dr Wang Chao and Assistant Professor Dr Charles Lim from the College of Design and Engineering, NUS are polishing up QKD to give communications security a major shot in the arm.

QKD leverages the properties of quantum mechanics to securely encrypt information. “It offers a robust and long-term solution to the key exchange problem. Through the measurement and exchange of single photons, a pair of identical and secret random keys are distributed between users,” explained Wang. “The main advantage of QKD is that its channel security is mathematically unbreakable, which makes it an ideal candidate for securing sensitive data.”

Long-distance, attack-proof quantum communications

While the security of QKD is ironclad, however, flawed implementation of the quantum system could still render it susceptible to malicious attacks—perfecting this aspect has historically been a tough nut to crack. In particular, attackers can exploit faults in the system setup to eavesdrop on the exchange of secret keys.

To that end, the duo and their colleagues have successfully demonstrated, for the first time, a QKD-based network that is not just secure even if users are unfamiliar with the underlying quantum devices, but also capable of creating quality entanglement between two devices separated by a long distance apart—a tremendous feat of surmounting two major challenges at once.

Based on device-independent QKD (DIQKD), the network is underpinned by a protocol containing two sets of key-generating measurements for the users, in contrast to traditional protocols which typically have just one. As a result, the team’s protocol is less prone to disturbances, which greatly lowers the chances of eavesdropping.

“DIQKD is the pinnacle of secure key exchange and could change how we manage risks and trust in communication networks,” said Lim, who is now on a two-year no pay leave to JPMorgan as the investment bank’s global head for quantum communications and cryptography. “We have also proven that the system is viable over long distances through a careful balance between entanglement quality, generation rate, and system noise—an essential step towards large-scale quantum networks.”