Quantum Secure Communication


Image: Deputy Prime Minister DPM Heng Swee Keat at the Quantum Networks Experience Centre tour.

Written by Jane Lo, Singapore Correspondent.

Since the birth of quantum theory at the turn of the 20th century, much research has been advanced in the study of quantum phenomena, leading to many applications we are familiar with in our daily lives, such as the semi-conductors powering our phones or the lasers operating our printers.

Of huge interest to security professionals are the developments in the recent decades of “quantum computers” and “quantum cryptography” which introduce significant implications for the way we secure our digital communication and data today.

There is the Shor’s algorithm, notable for its exponential speedup in factoring and thus breaking the encryption framework underpinning today’s digital infrastructure. Another is the BB84 protocol, frequently cited as a pioneering work in Quantum Key Distribution (QKD) – one of the most important protocols to secure communication and data.

The ground-breaking discoveries expose the vulnerability of our digital infrastructure to quantum threats, on one hand.

On the other hand, they also highlight the potential of harnessing quantum properties to harden our network, where QKD is seen as playing an important role.

Since the proposal of the BB84 protocol, QKD has been actively developed in theoretical and practical implementation.

To find out about the latest developments in Singapore, we attended the 16 November 2022 launch of Southeast Asia’s first quantum centre – Quantum Networks Experience Centre (“QNEX”) – that explores and prototypes terrestrial and space-based QKD solutions.

Housed in the offices of SpeQtral – Singapore-based Quantum Communications company, QNEX is a partnership between SpeQtral and Toshiba Digital Solutions Corporation.

Besides Singapore, the aim is also to actively promote the adoption of quantum-secure communication in Southeast Asia.

Here are some take-aways from our tour.

What is Quantum Computing?

Quantum computers exploit quantum mechanical phenomena.

In contrast to conventional computers, quantum computers are based on qubits instead of bits as the smallest memory unit. A Qubit can take on a multitude of states – different than a bit.

Notably, quantum computers will be able to solve certain problems in much less time than conventional computers, using quantum algorithms, such as Shor and Grover.

What are some quantum threats?

The ability to factor at speeds using Shor’s quantum algorithm would compromise the way we protect the confidentiality and integrity of digital communications with Public Key Infrastructure (PKI).

To do a one-off exchange of secured information, two remote parties can easily pre-agree the secret keys to encrypt and decrypt the messages.

However, this manual effort to agree the keys beforehand is clearly not scalable for continuous exchange of information.

This is where PKI comes in. By using mathematical algorithms to generate secret keys, PKI allows for information to be exchanged securely between parties who are geographically separated – such as when we use Whatsapp to communicate.

But, with the speedup introduced by Shor’s quantum algorithm, quantum computers will break such mathematical algorithms to reverse engineer the secret keys.

What is one example?

One popular example cited is the signature scheme which verifies Bitcoin’s ownership.

Comprising of a public-private key pair, the scheme could be broken by a sufficiently large quantum computer using Shor’s quantum algorithm. In other words, the secret key corresponding to a given public key can be computed very quickly.

How plausible are these quantum threats?

A recent University of Sussex, UK study estimates that it would take about 1.9 billion qubits to crack Bitcoin’s encryption in 10 minutes [1].

With the latest IBM quantum computer boasting “only” 400 qubits plus [2], it seems our digital infrastructure will remain safe from quantum attacks in the near future.

A matter of when, but not if

While “when” is disputable, there is no question that quantum technologies will change today’s digital world as we know it.

Alarms have been raised that hackers are harvesting (recording) sensitive communication and information, to decrypt for the day when quantum computers arrive.

With an eye on this “quantum future”, researchers focus their efforts on designing quantum-resistant encryption systems. The aim is to implement such approaches early enough to protect data that needs long-term security.

One such approach is to search for mathematical problems that will remain difficult for a quantum computer to break.

Another is developing quantum hardware for encryption. In this area, much progress has been achieved in implementing QKD.

Developing hardware for QKD

Instead of relying on mathematics, QKD relies on the foundations of quantum mechanics to distribute keys to trusted parties.

While quantum computers to break today’s PKI are still at the early stages of research, there are already working prototypes of quantum-resistant hardware for QKD.

Generation one QKD – single-photon technology BB84 – had already been demonstrated in test-case scenarios such as online voting and bank transfers, where commercial suppliers include Quintessence, Toshiba.

This technology exploits properties of photons (particles that transmit light) to transmit data for secure sharing of a key between a sender and a receiver.

To steal the key would require knowing the photon properties – which due to quantum physics law, is impossible without changing the properties’ behaviour and alerting both trusted parties to the attempted hack.

QKD challenges and quantum entanglement

However, the fragile nature of the phenomena makes it hard to work over long distances. The best optical fibers can carry these photons to 200 kilometers before light absorption makes the process impossible.

An advanced form of QKD achieves this with quantum entanglement – where two particles behave like one regardless of distance apart.

Here, a satellite transmits the entangled photon pair to two separate ground stations, thereby providing a key for secured communication for the two communicating parties (albeit with losses – but less so than observed in fibre optics).

At SpeQtral, for example, the founders and collaborators have demonstrated a compact entanglement quantum light source on the quantum satellite mission in 2019, and will further demonstrate quantum communication in 2024/2025.

What’s next?

Since the publication of the QKD protocol BB84 in 1984, it has been almost four decades of development in QKD.

Ground-breaking work using entangled quantum states [3] gained further profile with the recent Nobel Prize award to three researchers in this area, and will no doubt inspire further breakthroughs in quantum-based security.

Some may be encouraged that the award affirms that quantum entanglement is real and in accordance with the Quantum Theory – and more intriguingly, that “quantum teleportation” will one day become a practical reality.

Indeed, a paper published this year unveiled research from teleporting quantum information across three remote sites [4].

This work offers a tantalising glimpse into the prospect of quantum network and quantum internet – and that one day, teleportation, while not quite the Star Trek style, will become synonymous with how we communicate and exchange information, and how we secure such information.

[1] https://www.newscientist.com/article/2305646-quantum-computers-are-a-million-times-too-small-to-hack-bitcoin/
[2] https://newsroom.ibm.com/2022-11-09-IBM-Unveils-400-Qubit-Plus-Quantum-Processor-and-Next-Generation-IBM-Quantum-System-Two
[3] https://www.nobelprize.org/prizes/physics/2022/press-release/


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