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Comment by f33d5173 | Hacker News Reader

You don't need to keep shrinking features. Brute forcing is highly parallel; to break a key within a certain time frame all you need is a large enough quantity of chips. While it's in the realm of science fiction today, in a few centuries we might have nanorobots that can tile the entire surface of mars with processors. That would get you enough orders of magnitude of additional compute to break a 128 bit key. 256 bit would probably still be out though.

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Classical brute force is embarrassingly parallel, but Grover's algorithm (the quantum version) isn't. To the extent you parallelize it, you lose the quantum advantage, which means that to speed it up by a factor of N, you need N^2 processors. The article discusses this in detail, and calculates that "This means we’ll need 140 trillion quantum circuits of 724 logical qubits each operating in parallel for 10 years to break AES-128 with Grover’s."

So then why is quantum always touted as being able to possibly beat AES ?

Because some people make their living from the vague possibly it might work one day. It's the cold fusion of computing.

Is it possible you are confusing AES with RSA?

I've heard a lot about Shor's algorithm breaking RSA, but this article on hackernews is the first I've heard anyone discuss quantum attacks for AES. Then again, I am in quantum computing not cryptography, maybe different circles have different discussions.

Is it? I've generally understood that most symmetric cryptography like AES is safe. QC only gives exponential speedups on some specific problems. The most is that naively you might want to double your keysize to get the same protection, something that the article points out is unecessary because that naive approach assumes that QC is like classical computing but with extra magic, as opposed to having its own tradeoffs.

The power and heat are the issues for that, though. Think about how much energy and heat are used/generated in the chips we have now. If we tiled out those chips to be 20 orders of magnitude larger… where is the heat going to go, and where is the energy coming from?

In my example I had imagined that your nanobots would also create solar panels and radiators for the chips you were tiling the surface of mars with. This is why it needs to be done on the surface instead of underground somewhere.

By the time you built this machine, someone could just bump to 256 bit AES and you suddenly need a billion Marses covered in chips.

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