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Joseph Ashwood
> > > Because with a pRNG we can sometimes prove very important
> > > things, while with a RNG we can prove very little (we can't
> > > even prove that entropy actually exists, let alone that we
> > > can collect it).
James A. Donald:
> > Don't be silly. Of course we know that entropy exists, and we
> > can collect it.
> >
> > If a RNG runs off Johnson noise, then the ability to predict
> > its output would imply the ability to violate the second law
> > of thermodynamics. If it runs off shot noise, then the
> > ability to predict its output would disprove quantum
> > mechanics.
Joseph Ashwood
> Actually there are models that fit the universe that are
> entirely deterministic.
These models are entirely incoherent, and I would summarize them
as "God knows". And if these models allowed us to predict the
outcome of a true RNG, they would not fit the universe.
James A. Donald:
> > > > And if ofne is implementing a PRNG in software, it is
> > > > trivial to have lots of internal state (asymptotically
> > > > approaching one-time pad properties).
Joseph Ashwood
> > > The problem is not having that much internal state, but what
> > > do you do with it? Currently the best options on that front
> > > involve using block ciphers in various modes, but this has a
> > > rather small state,
> >
> > RC4 has 1684 bits of state, which should prove sufficient to
> > defeat guessing.
>
> And RC4 is far from a good RNG of any type, it's distinguishable
> from random fairly easily, and unless it's used very carefully
> it's weak. If one were to try to guess all 1684 bits it would be
> exceedingly difficult, but to start with, it's only a
> permutation so the space is much smaller, in addition the state
> itself has more attacks available
Wrong. 1684 bits of entropy. Count them.
The state is a permutation 256, which requires 2048 bits to
describe (256 *8) but contains 1684 bits of entropy, not 1684
bits.
2048 bit description, but because it is a permutation, 1684 bits
actual entropy.
--digsig
James A. Donald
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