X-Loop: openpgp.net
From: "Tim May" <[EMAIL PROTECTED]>
> >Speaking of which - does anybody have any hints on how to determine the
> >entropy of an input string? [Needed in Yarrow, and so far I don't know
how
> >to do it - my implementation multiplies the length of the input string
(in
> >bits) with a constant, which is way too "crude".]
>
> Easy method: run the string through a standard compression algorithm,
> e.g., Lempel-Ziv. To the extent it compresses, it's not random,
> i.e., it has less entropy per bit than a random string would have.
I've read about that; however, I'm talking about very short strings here -
like 128 bits.
> In other words, one cannot say that there is not some _compression_
> (shorter description) of a string of bits.
Yep. Got that.
> Despite this, a rough measure of the _apparent_ entropy is to run the
> string, or image, or whatever, through a compressor.
Ahem. I think I'll go with a combination here - I'll try to find a
compressor suitable for small bit strings, let the source also indicate the
maximum entropy, and maybe multiply the minimum of those two with a
constant. At least I don't make the "1 bit of source = 1 bit of entropy"
mistake...
Mark
