Re: [Cfrg] naive question: QC vs RC vs Moore-blip

Philip Lafrance <> Mon, 08 May 2017 18:44 UTC

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From: Philip Lafrance <>
Date: Mon, 08 May 2017 14:44:26 -0400
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To: Dan Brown <>
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Subject: Re: [Cfrg] naive question: QC vs RC vs Moore-blip
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I wanted to make a comment about the introduction of more powerful, but
classical computers.

There is a good thermodynamics argument to be made here. Even absurdly
powerful classical devices need to actually perform the bit operations.
Consider the 128 bit level of security. I'm being vague here, but I am
pretty sure if even if you assume that every operation is just a bit-flip,
then 2^{128} such operations would still take >1% of the Earth's annual
power output. Maybe I am being slightly inaccurate, but the point is that
even high powered super computers simply don't have the time or energy to
say factor secure RSA moduli (try something with 256-bits of classic
security!). This is one of the reasons that quantum computers are so
dangerous to public key crypto, they compute in a fundamentally different
way which more or less avoid the thermodynamics problem.

For this reason, I believe quantum-resistant standards are more important
for us to consider than contradictions to Moore's law. However, this is far
from the best possible argument for quantum-resistance.

-Philip Lafrance

On Mon, May 8, 2017 at 11:31 AM, Dan Brown <> wrote:

> Dear CFRG,
> Please forgive my naivety on the matters below.
> If quantum computers are realistic enough to warrant standards changes
> (now or soon), then what about other hypothetical computers, such as:
> (1) computers that can do super high-precision, as in the "real
> computation" model (or whatever variant of this model that can implement
> Shamir's algorithm to factor using super-large integers in a polynomial
> (even linear?) number of integer arithmetic steps),
> (2) sudden (single) blips exceeding the usual Moore's law (and variants)
> for future computing power (e.g. are sudden and new 100x faster transistor
> material, superconductors, photonics, less realistic than quantum
> computers)?
> I don't know the established answers, but would speculate:
> (a) quantum computers are deemed more realistic than each of (1) and (2),
> (b) model (1) is known [?] to affect all algorithms equally, so we must
> just give up on it,
> (c) most justifications for 128-bit security already include a margin of
> error for risk (2),
> (d) 256-bit security (and variants) are meant to deal with (2).
> Are these the established answers, or is there better answers?
> As a research issue, I'd like to know more about (b), if it is correct.
> I'd like to know more about (a), the why of it, but am unlikely to
> understand.
> Best regards,
> Dan Brown
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