ACM has named Charles H. Bennett and Gilles Brassard as the recipients of the 2025 ACM A.M. Turing Award for their essential role in establishing the foundations of quantum information science and transforming secure communication and computing.
* An accessible news excerpt via CNN science [1]
Years before emails, internet banking, cloud servers and cryptocurrency wallets, two scientists devised a way to keep secrets perfectly safe and indecipherable to eavesdropping outsiders.
Their 1984 work depended on the hidden, counterintuitive world of quantum physics, which governs the way the world works at the smallest, subatomic scale, rather than complex but theoretically breakable mathematical codes to secure data.
The insights of Charles Bennett, an American physicist who is a fellow at IBM Research, and Gilles Brassard, a Canadian computer scientist and professor at the University of Montreal, have since transformed cryptography and computing. The pair received the A.M. Turing Award on Wednesday for their groundbreaking work on quantum key cryptography.
Really curious, not a critique: apart from the idea of the possibility of intrusion detection due to the quantum nature of the communication link, what is special about the protocol that is mentioned?
> Bennett and Brassard, with Ethan Bernstein and Umesh Vazirani, showed that in black-box setting, quantum computers would require big-omega(sqrt(n)) queries to search n entries, matching Grover's algorithm. For some reason, the popular press rarely covers these results that limit the power of quantum computing.
This is mentioned almost as a footnote, but to (layman) me seems much more important than QKD, especially from a comp sci perspective instead of a physics perspective.
Not sure what is going on in QC world; With this ACM prize it has become even more murky.
As Sabine Hossenfelder (Theoretical Physicist) points out, companies to do with QC are seeing a surge in investments and marketing. It is as if somebody knows something that the "common public" doesn't - https://www.youtube.com/watch?v=gBTS7JZTyZY
I don't know enough about the science/technology to form an opinion but have recently started down the path of trying to understand it - https://news.ycombinator.com/item?id=46599807
As a young grad student, I remember going to a talk by Bennett where he explained how a Quantum Computer allows manipulation in a 2^N dimensional hilbert space, while the outputs measurements give you only N bits of information. The trick is to somehow encode the result in the final N bits.
I felt this was a much better layman explanation of what a quantum computer does than simply saying a quantum computer runs all possible paths in parallel.
I don't want to take anything away from Bennett and Brassard, but I'd like someone to spare a word for poor Stephen Wiesner, who invented the earliest quantum information-distribution protocols as far back as the 1960s and published them before Bennett and Brassard. He also invented Oblivious Transfer (OT) which is required for multi-party computation -- although his was a quantum protocol that demonstrated some of the ideas behind QKD, not the classical protocol we call OT today [1].* Weisner was an inspiration for Bennett and Brassard, who then realized more useful systems.
While obviously this takes nothing away from BB's many later contributions (and they have extensively credited him), it's just a reminder of the randomness that goes with scientific credit. Since my PhD thesis was on OT, I like to remind people of Wiesner. He deserves a lot more credit than he gets!
* I suppose if you're a real theoretician, since OT implies MPC and MPC implies all cryptography, then perhaps Wiesner's OT implies everything that BB did subsequently. I'm not sure any of that is true (and I've since checked with an LLM and there are some no-go theorems from the 1990s that block it, so that's super interesting.)
Actually you can't compose quantum crypto protocols like you can classical ones - the composed protocol needs a new security analysis. Entanglement across protocols often kills the composition!
Interestingly (to me!) it took a while in the 90’s/early 00’s for the community to realise that there are distinct questions:
Question A: Does there exist a set of target states and measurements that implement the task
Question B: Can mistrustful parties find a communication protocol that securely (from their perspective) create/implement those states/measurments.
An example where the answer to A is “no” is fully secure oblivious transfer. There were a bunch of misguided papers trying to find communication protocols for OT, but they were doomed from the start!
An example where the answer to A is “yes" but to B is “no” is strong coin flipping. And an example where the answer to both is “yes” is weak coin flipping. (See Carlos Mochon’s magnus opus arxiv 0711.4114 for the coin flipping examples).
I first articulated the distinction between A and B quant-ph/0202143 but left the proof about OT and Question A as an exercise to the reader! Roger Colbeck in arxiv 0708.2843 provided a simple proof and elucidated the whole situation a lot I think.
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[ 2.9 ms ] story [ 39.4 ms ] threadACM has named Charles H. Bennett and Gilles Brassard as the recipients of the 2025 ACM A.M. Turing Award for their essential role in establishing the foundations of quantum information science and transforming secure communication and computing.
* An accessible news excerpt via CNN science [1]
Years before emails, internet banking, cloud servers and cryptocurrency wallets, two scientists devised a way to keep secrets perfectly safe and indecipherable to eavesdropping outsiders.
Their 1984 work depended on the hidden, counterintuitive world of quantum physics, which governs the way the world works at the smallest, subatomic scale, rather than complex but theoretically breakable mathematical codes to secure data.
The insights of Charles Bennett, an American physicist who is a fellow at IBM Research, and Gilles Brassard, a Canadian computer scientist and professor at the University of Montreal, have since transformed cryptography and computing. The pair received the A.M. Turing Award on Wednesday for their groundbreaking work on quantum key cryptography.
[0] https://www.acm.org/media-center/2026/march/turing-award-202...
[1] https://edition.cnn.com/2026/03/18/science/quantum-key-crypt...
Congratulations to Charles Bennett and Gilles Brassard.
This is mentioned almost as a footnote, but to (layman) me seems much more important than QKD, especially from a comp sci perspective instead of a physics perspective.
There is some interesting work being done, but it will never match the excessive hype. =3
"The Genius of Computing with Light"
https://www.youtube.com/watch?v=rbxcd9gaims
Time will tell.
As Sabine Hossenfelder (Theoretical Physicist) points out, companies to do with QC are seeing a surge in investments and marketing. It is as if somebody knows something that the "common public" doesn't - https://www.youtube.com/watch?v=gBTS7JZTyZY
I don't know enough about the science/technology to form an opinion but have recently started down the path of trying to understand it - https://news.ycombinator.com/item?id=46599807
I felt this was a much better layman explanation of what a quantum computer does than simply saying a quantum computer runs all possible paths in parallel.
I did see Gilles' lunch talks though, it was really insightful!
While obviously this takes nothing away from BB's many later contributions (and they have extensively credited him), it's just a reminder of the randomness that goes with scientific credit. Since my PhD thesis was on OT, I like to remind people of Wiesner. He deserves a lot more credit than he gets!
* I suppose if you're a real theoretician, since OT implies MPC and MPC implies all cryptography, then perhaps Wiesner's OT implies everything that BB did subsequently. I'm not sure any of that is true (and I've since checked with an LLM and there are some no-go theorems from the 1990s that block it, so that's super interesting.)
[1] https://dl.acm.org/doi/10.1145/1008908.1008920
Interestingly (to me!) it took a while in the 90’s/early 00’s for the community to realise that there are distinct questions:
Question A: Does there exist a set of target states and measurements that implement the task
Question B: Can mistrustful parties find a communication protocol that securely (from their perspective) create/implement those states/measurments.
An example where the answer to A is “no” is fully secure oblivious transfer. There were a bunch of misguided papers trying to find communication protocols for OT, but they were doomed from the start!
An example where the answer to A is “yes" but to B is “no” is strong coin flipping. And an example where the answer to both is “yes” is weak coin flipping. (See Carlos Mochon’s magnus opus arxiv 0711.4114 for the coin flipping examples).
I first articulated the distinction between A and B quant-ph/0202143 but left the proof about OT and Question A as an exercise to the reader! Roger Colbeck in arxiv 0708.2843 provided a simple proof and elucidated the whole situation a lot I think.