DNSSEC, ECDHE, RSA, even SSH and all other important specifications, protocols that we rely on and advise people to use them, they use Public key infrastructure.

Question: Why do we still use, advise PKI if it's a fact (not just theory) that quantum computing will break PKI in less then 10-20 years?

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    $\begingroup$ You have some mixup of the terms here. Also, how do you know what the future of quantum computing is? $\endgroup$ – Paŭlo Ebermann Sep 12 '14 at 19:06
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    $\begingroup$ Why do you say that it's established fact that someone will have a quantum computer that can handle (say) 1000 qubits in 10-20 years??? $\endgroup$ – poncho Sep 12 '14 at 19:07
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    $\begingroup$ Also, not all public key algorithms are immediately breakable even if quantum computers become practical. $\endgroup$ – otus Sep 12 '14 at 19:12
  • $\begingroup$ People working in quantum computation (aka my colleagues) estimate the arrival date of quantum computers between 20 and 200 years from now. In other words they agree on one thing: it is beyond the predictable technological horizon ! I really do not think anyone serious think we will have a quantum computer able to break classical cryptography in the next decade. $\endgroup$ – Frédéric Grosshans Sep 15 '14 at 15:56
  • $\begingroup$ Practical quantum computing, like practical fusion power, has been "10-20 years in the future" for several decades already. Basically, in both cases, we thought we knew the theory, and that the rest would be just a simple matter of engineering. Alas, sometimes "mere engineering" turns out to be not so easy, after all. $\endgroup$ – Ilmari Karonen Sep 25 '14 at 21:30

If "it's a fact (not just theory) that quantum computing will break PKI in less then 10-20 years" then
"we still use, advise PKI" because there is only a small amount of currently existing evidence for that fact.

Specifically, there are known algorithms which can be used for PKI
that are not known to be breakable by feasible quantum adversaries.

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