Charles H. Bennett and Gilles Brassard have spent four decades proving that the laws of physics make better locks than mathematics. Earlier this week, the Association for Computing Machinery agreed, awarding the pair the 2025 A.M. Turing Award — and its $1 million prize — for founding the field of quantum information science.

The centrepiece of their work is a 1984 protocol called BB84, a method for two parties to generate a shared encryption key using individual photons of light. The trick: any attempt to intercept the photons disturbs them, instantly alerting both sides to an eavesdropper. Security is not a matter of computational difficulty — it is a consequence of quantum mechanics itself.

Why Now

When Bennett and Brassard first demonstrated BB84 in a lab in 1989, the signal travelled 30 centimetres. Today, quantum key distribution systems operate over more than 1,000 kilometres. More urgently, the conventional encryption protecting bank transfers, medical records, and government communications faces a looming threat: sufficiently powerful quantum computers could crack it using Peter Shor’s 1994 factoring algorithm.

As Brassard put it, “Shor’s algorithm made our idea unavoidable.”

That convergence — quantum computers advancing from theory toward engineering reality while classical encryption grows more vulnerable — is precisely why the Turing committee acted now. ACM President Yannis Ioannidis said their work “expanded the boundaries of computing and set in motion decades of discovery across disciplines.”

Bennett, a physicist at IBM, and Brassard, a computer scientist at the Université de Montréal, also co-invented quantum teleportation in 1993, establishing entanglement as a practical resource for transmitting quantum information. Scott Aaronson, a leading complexity theorist, noted they were pioneers “since before quantum computing was even a field.”

For ordinary internet users, the significance is concrete: the encryption shielding your data today has an expiry date. Bennett and Brassard wrote the physics-based replacement.

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