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by timthelion 3320 days ago
If I had a quantum computer that was capable of breaking RSA, I wouldn't tell anyone. The whole point is to be able to spy on people, and you wouldn't be able to do that if everyone knew that RSA was broken.

I don't know if quantum computers exist, but I'm sure once they do, the people who build them will keep them secret.
3 comments
jcranmer 3320 days ago
A high-end desktop is better at simulating quantum computers than any that we've ever built [1]. The best quantum computers achieve about 10 qubits. Furthermore, quantum operations are slower than classical operations. A classical computer can do a 64-bit operation (depending on clock speed) in ~0.25ns, a quantum computer takes about 5ns. Also, quantum computers don't scale like classical computers. 2 classical computers can solve twice as many problems or problems twice as hard, while 2 quantum computers can only solve twice as many problems.

The hard part is hardware, and you need the minimum number of qubits to be of any use to breaking RSA. That number is on the order of O(N^2), where N is the number of bits--so you need qubits on the order of hundreds of thousands if not millions. Where the state of the art is around 10.

[1] D-Wave is approaching this equivalency, for certain definitions of quantum computers.

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badosu 3320 days ago
> I don't know if quantum computers exist, but I'm sure once they do, the people who build them will keep them secret.

They not only do exist but have already successfully factorized low magnitude numbers [0]. The question is if an agency with a high enough budget, secrecy and highly qualified personnel did not already scale up the reliability and capacity of existing technology.

[0]: https://en.wikipedia.org/wiki/Shor's_algorithm

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2bluesc 3320 days ago
> I don't know if quantum computers exist, but I'm sure once they do, the people who build them will keep them secret.

Probably right. UNLESS it's a private company and it's losing bids from government agencies that would otherwise pay for silence. And in this case, you could assume two quantum computer designs exist and the loser is now looking for new markets/customers.

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