In the cybersecurity world they call it Q-Day, the day when a quantum computer will be built that can break the encryption of the internet. John Thornhill and Madhumita Murgia speak to cybersecurity expert and former professional hacker Mark Carney about password cracking, and why quantum computers would be so good at it. Renowned mathematician Peter Shor recounts how he became the first person to discover that quantum computers could upturn the encryption that underpins much of the internet. Jack Hidary, boss of the quantum technology company Sandbox AQ, tells us how quantum computers already pose a threat today, even if it’s decades before one powerful enough to threaten encryption will be built. And cryptographer Dan Bernstein explains why protecting ourselves from the quantum threat might just be down to better maths.

Presented by Madhumita Murgia and John Thornhill, produced by Josh Gabert-Doyon and Edwin Lane. Executive producer is Manuela Saragosa. Sound design by Breen Turner and Samantha Giovinco. The FT’s head of audio is Cheryl Brumley.

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