A new study from researchers at the Institute for Quantum Computing (IQC) at the University of Waterloo marks an important step in certifying Quantum Key Distribution (QKD) devices, crucial to enabling secure quantum communication technology.
QKD allows users to share keys that are secure and unknown to any potential eavesdropper. These keys can be used to secure critical communications. Part of what makes it powerful is that it uses the properties of quantum mechanics - like superposition and entanglement - to provide security against eavesdropping. An attempted attack can disturb those quantum states, alerting users to the presence of a malicious attacking party.
But the guarantee of security is only as good as the mathematical proof that establishes it. Just as medical devices need to be approved before they can be used, mathematical proofs for QKD also need to be verified through careful, third-party evaluation of the underlying mathematics.
The research group led by Dr. Norbert Lütkenhaus, executive director of IQC and professor in the Department of Physics and Astronomy, looked at one of the most common methods for sharing quantum encrypted keys and analyzed the mathematical proofs that provide evidence that the method is secure.
"We looked at papers from the 1990s to today on mathematical security proofs, but found they are of varying level of rigor and use different assumptions and leave out different technical steps," says Devashish Tupkary, PhD student at IQC and the Department of Physics and Astronomy, and lead author of the study. "At some point, academia and industry will need a certifiable proof and our paper is an important first step towards that."
This work is part of the multi-phase project Qu-Gov, overseen by Germany's federal Ministry of Finance, funded by the Bundesdruckerei GmbH, a German federal technology company that provides cybersecurity and digital solutions. The project's end goal is to develop a verifiable security proof that can be evaluated by third parties and serve as a foundation for certifying QKD systems.
To that end, the IQC team distilled its findings into a comprehensive review paper that explains the mathematics behind these proofs, highlights common mistakes and overlooked gaps, and outlines the steps needed to reach a self-contained proof that can be evaluated by third parties.
"We value the joint theoretical research with the experts at IQC aiming at a rigorous mathematical proof for QKD security," says Dr. Holger Eble, innovation department of Bundesdruckerei. "As a German federal technology company, it is a fundamental task for us to evaluate the security of new technologies such as quantum technologies. Our research results constitute an essential building block for the envisaged certification of QKD by the Federal Office for Information Security (BSI)."
Lütkenhaus says that the Canadian government actively funds QKD research and follows the development of the field with interest.
"This research, funded by Bundesdruckerei GmbH, has the potential to set the standard for secure quantum cryptography globally and shows how Canada's quantum talent benefits research and development worldwide," Lütkenhaus says.
Dr. Michele Mosca, IQC faculty and professor in the Department of Combinatorics and Optimization at Waterloo, says quantum cryptography certification is crucial to protecting online information.
"As we enter the era with quantum and artificial intelligence technologies, our cyber defences must be resilient against rapid advances in code breaking," Mosca says. "Certification of quantum cryptography solutions, supported by security analysis, is a critical part of harnessing the emerging quantum band of communication to create a more resilient digital economy."
IQC's group says that, looking ahead, more work needs to be done. Working on QKD proofs is theoretical by nature, but the keys are transmitted by laser or other hardware. Tupkary says the collaborative nature of experimental and theoretical researchers at IQC provides the ideal setting for this research.
"There is a mismatch between working on theoretical proofs and what happens in the lab: how the laser and detector work, potential imperfections, errors and noise fluctuations," Tupkary says. "Our research group has a critical mass of people whose expertise bridges these differences, which is rare. There are many groups globally that do excellent work, but we are in that sweet spot of depth and breadth of knowledge."
