NUS researchers make new progress in quantum communication attack defense technology

Quantum Key Distribution (QKD) is a secure communication method that uses quantum encryption of information. While QKD’s security is in principle unbreakable, attackers can still steal important information if not implemented properly. These are called side-channel attacks, where attackers exploit weaknesses in the setup of information systems to eavesdrop on the exchange of secret keys.

Researchers at the National University of Singapore (NUS) have developed two methods, one theoretical and one experimental, to ensure that QKD communications cannot be attacked in this way. The first is an ultra-secure cryptographic protocol that can be deployed in any communication network that requires long-term security. The second is a first-of-its-kind device that protects the QKD system from intense light pulses by creating a power threshold.

“Rapid advances in quantum computing and algorithmic research mean we can no longer take today’s most powerful security software for granted. Our two new approaches promise to secure the information we use for banking, healthcare and other critical infrastructure and data storage The system is resistant to any potential future attack,” said Charles Lim, Assistant Professor at the Department of Electrical and Computer Engineering at the National University of Singapore. and the Center for Quantum Technology, which leads the two research projects.

Future-proof quantum communication protocols

Typically, in QKD, two measurement setups are used – one for generating keys and one for testing the integrity of the channel. In a paper published in the journal Nature Communications on May 17, 2021, the NUS team shows that with their new protocol, users can generate a set of keys from two randomly selected key generation settings instead of one A secret key is generated in the setup to independently test each other’s encryption devices. The researchers demonstrated that introducing an additional set of key generation measurements for users could make it harder for eavesdroppers to steal information.

“This is a simple variant of the original protocol that pioneered the field, but it can only be solved now due to major developments in mathematical tools,” said Professor Valerio Scarani, one of the inventors of such methods and the field one’s business Patner. – The author of the paper. He is from the Department of Physics and the Centre for Quantum Technology at the National University of Singapore.

Compared to the original “device-independent” QKD protocol, the new protocol is easier to set up and is more tolerant of noise and loss. It also provides users with the highest level of security allowed by quantum communication and enables them to independently verify their own key generation devices.

With the team’s setup, all information systems built with “device independent” QKD are free from misconfiguration and misimplementation. “Our approach makes data safe from attackers even if they have unlimited quantum computing power. This approach enables truly secure information systems, eliminates all side-channel attacks, and allows end users to easily and confidently monitor their Implement security,” explained Assistant Professor Lim.

First-of-its-kind quantum power limiter

In effect, quantum cryptography uses pulses of very low light intensity to exchange data over untrusted networks. Quantum effects can be used to securely distribute keys, generate truly random numbers, and even create mathematically unforgeable banknotes.

However, experiments have shown that intense light pulses can be injected into a quantum cryptosystem to breach its security. This side-channel attack strategy uses the way the injected bright light is reflected to the external environment to reveal the secrets kept in the quantum cryptosystem.

In a new paper published in PRX Quantum on July 7, 2021, researchers at the National University of Singapore report the first optical device they have developed to solve this problem. It confines the energy of incident light based on the thermal light defocusing effect. The researchers exploited the fact that the energy of the intense light changed the refractive index of the transparent plastic material embedded in the device, thereby emitting a portion of the light out of the quantum channel. This enforces the power limit threshold.

The NUS team’s power limiter can be seen as the optical equivalent of an electric fuse, except it’s reversible and doesn’t burn when the energy threshold is breached. It is highly cost-effective and can be easily manufactured using off-the-shelf components. It also does not require any power supply, so it can easily be added to any quantum cryptosystem to strengthen its implementation security.

Assistant Professor Lin added: “If we are to use quantum secure communication for the quantum internet of the future, we must bridge the gap between the theory and practice of quantum secure communication. We do this holistically – on the one hand, we More practical quantum protocols are designed, and on the other hand, we designed quantum devices that are very consistent with the mathematical models assumed by the protocol. In doing so, we can significantly close the gap.”

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