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The Futility of Lava Lamps: What Random Means

loup-vaillant.fr

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Re: The Futility of Lava Lamps: What Random Means

#61
post #30

With a one-time pad being, as I understand it, the only really good encryption, I am surprised there is not a market for pairs of matched hard drives—the pair having the same "one time pad" stored on them (how you generate those numbers is left as an exercise for the company marketing them). A simple app could be used by parties on both ends of the message—an app that relies on an associated drive to act as the pad.…

One-time pad has 2 problems: (1) The key can only be used once. If you use the same key for multiple different messages it's not secure anymore. (2) The key has to be the same length as the message. With those 2 restrictions, OTP is not really that feasible for practical applications.

> (1) The key can only be used once.

Sure, and I'm contemplating something like 10 TB of random data as key (I mean hard drives are large these days).

> (2) The key has to be the same length as the message.

I thought that was just a matter of indexing through the (10 TB) of data with each message—picking up in the byte stream where you left off from your previous message.

Re: The Futility of Lava Lamps: What Random Means

#62
> And before you go on objecting that a physical true RNG remains better than a could-theoretically-be-broken CSPRNG, understand that your random output often must have no detectable bias to be secure. That means a distribution so uniform you can’t detect a bias even after analysing 2^64 samples.

Why not, actually? I would think simple and trivially auditable HW RNG with, say, only 0.9 bits of entropy per output bit (raw! no whitening) is preferable to "perfect" but fragile algorithm.

Anything that requires the randomness in practice has enough overhead so that the 90% good entropy is not a problem. Failures caused by wrong assumptions and complications are.

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