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Researchers Demonstrate Unbreakable Quantum Cryptography

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The way we secure digital transactions could soon change. Theorists at the Centre for Quantum Technologies (CQT) at the National University of Singapore, Stephanie Wehner and Nelly Ng, teamed up with researchers at the Institute for Quantum Computing at the University of Waterloo, Canada, to demonstrate a form of quantum cryptography.

The experiments performed deployed quantum-entangled photons in such a way that one party, dubbed Alice, could share information with a second party, dubbed Bob, while meeting stringent restrictions. Specifically, Alice has two sets of information. Bob requests access to one or the other, and Alice must be able to send it to him without knowing which set he’s asked for. Bob must also learn nothing about the unrequested set. This is a protocol known as 1-2 random oblivious transfer (ROT).  In cryptography, the problem of providing a secure way for two mutually distrustful parties to interact is known as ‘two-party secure computation.’

Stephanie Wehner (Principal Investigator, Centre for Quantum Technologies, National University of Singapore): 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.

ROT is a starting point for more complicated schemes that have applications, for example, in secure identification.  

Today, taking money out of an ATM requires that you put in a card and type in your PIN. You trust the bank’s machine with your personal data. But what if you don’t trust the machine? You might instead type your PIN into your trusted phone, then let your phone do secure quantum identification with the ATM (see artist’s impression). Ultimately, the aim is to implement a scheme that can check if your account number and PIN matches the bank’s records without either you or the bank having to disclose the login details to each other.

Unlike protocols for ROT that use only classical physics, the security of the quantum protocol cannot be broken by computational power. Even if the attacker had a quantum computer, the protocol would remain secure.

[Image courtesy: University of Waterloo]

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