Quantum cryptography would allow banks and their clients to verify each other's information without having to know them

Entangled photons to secure future digital transactions

An international research team has demonstrated how to secure online financial transactions and ATM withdrawals using quantum cryptography.

The latest experiment, described in the Nature Communications journal, took place at the Centre for Quantum Technologies (CQT) of the National University of Singapore and the Institute for Quantum Computing (IQC) at the University of Waterloo, Canada.

In the demonstration the researchers have used the so-called quantum-entangled photons to share information between two parties, while complying with stringent restrictions typical for financial operations.

“I expect that quantum technologies will gradually become integrated with existing devices such as smartphones, allowing us to do things like identify ourselves securely or generate encryption keys,” said Stephanie Wehner, the study’s principal investigator from the CQT.

The two parties involved in the information exchange – dubbed Alice and Bob – have managed to exchange 1,366 bits of information. The whole transaction took three minutes and followed the 1-2 random oblivious transfer protocol (ROT).

This cryptographic protocol requires Alice to have two sets of information. Bob requests access to one of those sets while Alice has to be able to transmit the correct one to him without being told which one he requested. At the same time, Bob is not allowed to learn anything about the unrequested set.

Quantum-entangled photons allow doing just that while the information exchange between them cannot be broken by computational power. The security of the process is limited only by the time during which the two parties involved can store the quantum information – in this case – the shorter the better.

To commence the information exchange, Alice generates pairs of entangled photons, measures one of each pair and sends the other to Bob to measure. Bob chooses which photons he wants to learn about, dividing his data accordingly without revealing his picks to Alice. Both then wait for a length of time chosen such that any attempt to store quantum information about the photons is likely to fail. To complete the oblivious transfer, Alice then tells Bob which measurements she made and they both process their data in set ways that ensure the result is correct and secure within a pre-agreed margin of error.

“We did the experiment with big and bulky optics taking metres of space, but you can well imagine this technology being shrunk down to sit happily next to classical processing circuits on a small little microchip,” said IQC researcher Chris Erven “The field of integrated quantum optics has been progressing in leaps and bounds, and most of the key pieces required to implement ROT have already been successfully demonstrated in integrated setups a few millimetres in size.”

Mastering the ROT protocol is the first stepping stone toward more complex quantum cryptography applications. “Oblivious transfer is a basic building block that you can stack together, like lego, to make something more fantastic,” Wehner said.

The researchers believe the quantum entangled photons could one day allow safer operations involving credit or debit cards as the user won’t have to insert their PIN into any third party device but use his or her own trusted phone instead. The phone would than generate the quantum data and carry out information exchange with, for example, an ATM.

Ultimately, the aim is to implement a scheme that can check if the user’s account number and PIN matches the bank’s records without either of them having to disclose the login details to each other.

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