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RE: `Random' seed.
Matt Blaze <[email protected]> wrote:
>Here's my current favorite quick-and-dirty true-random-in-software
generator.
>Use at own risk and read the comments carefully...
[...]
> * Physically random numbers (very nearly uniform)
> * D. P. Mitchell
> * Modified by Matt Blaze 2/95
[...]
> * WARNING: depending on the particular platform, truerand() output may
> * be biased or correlated. In general, you can expect about 16 bits of
> * "pseudo-entropy" out of each 32 bit word returned by truerand(),
> * but it may not be uniformly diffused.
While this comment provides some general information, it does not give the
expected entropy in the form of testable assumptions. A first step in this
direction is to provide the entropy series used to arrive at the 16 bit per
32 bit word estimate. The second step, as I recommended last week (RE: RNG
Resource FAQ... on 9/22), is to provide a concise argument drawn directly
from the mathematical weaknesses of the entropy series. In that post, I
posed the following four criteria because they address the mathematical
(theoretical) weaknesses of the entropy series, while using a vocabulary
that should be sensible to a rigorous designer:
1) The states exist and can be identified.
2) The number of states n is known.
3) The index value i uniquely identifies a state.
4) The function P_i is known and well-behaved.
In this way, an analyst can review both the entropy series itself, and a
_concise_ statement of the criteria under which the series is defined (i.e.
when the 4 mathematical weaknesses have been appropriately addressed), and
the argument "why" has been scrutinized against the code or proposed design.
dvw