There isn’t yet a universal quantum computer big enough to break the widely used public key encryption systems, such as RSA, that secure everyday online information exchanges. Nor does anyone know when there will be. But with many predicting a significant breakthrough this decade, companies and governments are racing to launch cryptographic solutions so they can claim a stake in what is expected to be a billion-dollar market.

Public key encryption is based on the assumption that factoring integers – whole numbers – with several hundred or more digits is practically impossible. An algorithm known as Shors showed that a quantum computer could meet the challenge, however, allowing bad actors to decrypt information and spy on communications without detection. And they wouldn’t even need a phishing email to do it. What’s more, governments are increasingly concerned about the risk of ‘harvest and decrypt later attacks’, whereby an adversary steals sensitive...

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