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Comment by aruss | Hacker News Reader

That's right, symmetric encryption is fine. You're also right that protocols that rely on factoring or discrete log (more generally, any hidden subgroup problem) will be broken by quantum computers. However, this still means symmetric encryption is in trouble; namely in that we still need a post-quantum method for exchanging keys, otherwise symmetric ciphers will be virtually useless.

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How about hashing - in particular wrt key derivation? Does anyone have some insight there? Is it likely passphrase+salt+stretching might be in danger from quantum attacks? (I also wonder if DNA/RNA based biologic computing (or computing inspired by biology) might somehow change things around in terms of guessing passwords or look for hash collision...)

Hashing is in a similar position in that we just need to increase the size. Biological computing is (AFAIK) irrelevant to the speedups provided by quantum mechanics.

> Hashing is in a similar position in that we just need to increase the size.

Size of hash, or number of iterations? Or either? And will it still be "convenient security" available for those that "only" have classical computers? (ie: is will be get away with "small" increases in size, and get to keep (some of) our current speed)?

> Biological computing is (AFAIK) irrelevant to the speedups provided by quantum mechanics.

I didn't think otherwise. But they might be relevant to combinatorial problems, and so relevant to security?

There are some quantum key distribution protocols[1], though they still have their faults.

[1](https://en.wikipedia.org/wiki/Quantum_key_distribution)

Based on what I've read, QKD requires a out of band shared secret to authenticate and rule out an active man in the middle. Given that I don't see the point at all.

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