Have you ever been compelled to enter sensitive payment data on the website of an unknown merchant? Would you be willing to consign your credit card data or passwords to untrustworthy hands? Scientists from the University of Vienna have now designed an unconditionally secure system for shopping in such settings, combining modern cryptographic techniques with the fundamental properties of quantum light. We just published the demonstration of such “quantum-digital payments” in a realistic environment in Nature Communications

Digital payments have undoubtedly replaced physical banknotes in many aspects of our daily lives. Just as we expect banknotes to be, digital payments should ideally be easy to use, unique, tamper-resistant, and untraceable. Moreover, in the digital realm, they need to withstand the additional threats posed by digital attackers and data breaches. In today’s payment ecosystem, we have made strides in protecting customer data. For instance, we substitute sensitive information with sequences of random numbers. Furthermore, a classical cryptographic method or code secures the uniqueness of each transaction. However, this is not foolproof. Adversaries and merchants equipped with powerful computational resources can, in fact, crack these codes. Consequently, they can recover the customers’ private data and potentially make payments in their name

A research team led by Prof. Philip Walther from the University of Vienna has shown how the quantum properties of light particles or photons can ensure unconditional security for digital payments. In an experiment, the researchers demonstrated that malicious parties cannot duplicate or divert each transaction, and that the user’s sensitive data remains private. Tobias Guggemos says, “The quantum properties of light can protect new applications such as digital payments that are relevant in our everyday lives, and I am really impressed by this.”

For enabling absolute secure digital payments, the scientists replaced classical cryptographic techniques with a quantum protocol exploiting single photons. During the course of a classical digital payment transaction the client shares a classical code – called cryptogram – with his payment provider (e.g. a bank or credit card company). The customer, merchant, and payment provider subsequently exchange the cryptogram amongst themselves. In the demonstrated quantum protocol, the payment provider initially generates this cryptogram by transmitting specially prepared single photons to the client. Subsequently, for the payment procedure, the client measures these photons, whereby the measurement settings are contingent upon the transaction parameters. Ultimately, since no one can replicate quantum states of light, the transaction can only be executed once. This, together with the fact that any deviation of the intendent payment alters the measurement outcomes, which are verified by the payment provider, makes this digital payment unconditionally secure.

The researchers successfully implemented quantum-digital payments over an urban optical fiber link of 641m, connecting two university buildings in down-town Vienna. Digital payments currently operate within a few seconds. “At present, our protocol takes a few minutes of quantum communication to complete a transaction. This is to guarantee security in the presence of noise and losses” says Peter Schiansky, first author of the paper. “However, these time limitations are only of technological nature” adds Matthieu Bozzio, who is convinced that “we will witness that quantum-digital payments reach practical performance in the very near future”.

Original Publication: 
P. Schiansky, J. Kalb, E. Sztatecsny, M.-C. Roehsner, T. Guggemos, A. Trenti, M. Bozzio, P. Walther, “Demonstration of quantum-digital payments” Nature Communications 14, 3849 (2023)

DOI: 10.1038/s41467-023-39519-w

Fig. 1: Artistic image of digital payments secured by quantum technology (C: Christine Schiansky)