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From: WTShaw on 7 Apr 2010 04:09
On Apr 6, 6:31 am, Maaartin <grajc...(a)seznam.cz> wrote:
> On Apr 6, 12:56 pm, David Eather <eat...(a)tpg.com.au> wrote:
>
> > I think shannon also pointed out that the amount of entropy also depends
> > on the length of text - the entropy dropping as the text get longer.
>
> This all should be no problem as there's a lot of text available, so
> you can hash a couple of kilobytes to 128 bits. But a publicly known
> text can be no source of entropy, can it? Hashing the title page of a
> fixed internet newspaper could be enough, but for what purpose can I
> use it? Surely not as a secret key, since the attacker knows it. Maybe
> as a nonce, but for the nonce using a counter could be better (e.g.,
> Salsa20 needs just a unique nonce, for CBC an encrypted counter works,
> right?). Pls give me an example, where using an internet text as a
> entropy source is advantageous.

In search of randomness, the essence of disorder perhaps, entropy, you
are trying to find that which is worth nothing. Go to the store and
ask for a big bag to hold all the entropy you can find and inquire to
the price of nothing? How about lots of nothing? So, you had better
be prepared to pay for the bag. In collecting what you consider
randomness, you have consciously excluded what had value according to
some test and your collection gives whatever you have found some value
and therefore it is no long random even if it ever was.

I can take a few letters, not necessarily words, and squeeze lots of
order from them and add more with a few simple manipulations to just
about any level desired. That is because characters that have
individual ranking in some sort of system have meaning in themselves
in any collection. Language is alive so looking for death there is
counterproductive.


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