[NCLUG] My attempts using /dev/random...

[Chad Perrin]

On Tue, Apr 15, 2008 at 02:25:00AM -0600, James DeWitt wrote:
> On Monday 14 April 2008 8:47:33 pm Chad Perrin wrote:
> >
> > overview:
> >
> >   http://en.wikipedia.org/wiki//dev/random#Linux
> >
> > In short, /dev/random and /dev/urandom use the same algorithm, except
> > that when /dev/urandom "runs out of entropy" bit it just starts over on
> > what it already has -- and when /dev/random runs out, it waits until it
> > gets more.  What each of them uses to "generate entropy" is whatever
> > activity is going on at the time on the computer -- keystrokes, I/O
> > operations, et cetera.  This is generally quite more than sufficient for
> > cryptographic purposes (which is about as stringent as requirements are
> > going to get in our everyday lives), but in some theoretical academic
> > sense a case could be made for a lot of the "entropy" generated in this
> > manner being pseudo-deterministic in a lot of cases.  Unless the NSA has
> > some serious blue-sky prediction stuff going on that the only the most
> > paranoid of us might imagine, though, the effective difference between
> > system-generated "entropy" and what you could get from quantum events is
> > negligible.
> 
> That is not quite what the source says. It makes a sharper distinction between
> the quality of the random numbers from /dev/random and /dev/urandom.
> 
> "
>  * The two other interfaces are two character devices /dev/random and
>  * /dev/urandom.  /dev/random is suitable for use when very high
>  * quality randomness is desired (for example, for key generation or
>  * one-time pads), as it will only return a maximum of the number of
>  * bits of randomness (as estimated by the random number generator)
>  * contained in the entropy pool.
>  *
>  * The /dev/urandom device does not have this limit, and will return
>  * as many bytes as are requested.  As more and more random bytes are
>  * requested without giving time for the entropy pool to recharge,
>  * this will result in random numbers that are merely cryptographically
>  * strong.  For many applications, however, this is acceptable.
> "
> Looking through the docs and code, I can't see how the system entropy
> pool could be considered just random seeds. 

Tell me, then -- what *is* the system entropy pool, and how do you think
it differs functionally from random seeds?

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
Anonymous: "Eat your crow early, while it's young and tender.  Don't wait
until it's old and tough."
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