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

[Chad Perrin]

On Mon, Apr 14, 2008 at 05:34:25PM -0600, James DeWitt wrote:
> On Monday 14 April 2008 4:26:06 pm Chad Perrin wrote:
> > On Mon, Apr 14, 2008 at 01:09:26AM -0600, Sean Reifschneider wrote:
> > > >Unfortunately, the harsh truth is that both /dev/random and /dev/urandom
> > > >are flawed.  They're PRNGs -- they do not provide *true* random numbers.
> > >
> > > /dev/random on Linux is *NOT* simply a PRNG.  Which is why it took nearly
> > > a day to gather enough entropy for 1.6MB worth of /dev/random output. See
> > > the comments at the top of the /dev/random driver source for information
> > > about how it collects entropy, or it's approximation of it.
> >
> > The reason it took so long involved collecting seed data.  Whether or not
> > you consider it a PRNG really depends on whether you consider the number
> > generating algorithm to qualify something as a PRNG, regardless of
> > seeding behavior.
> 
> Interesting.  Please explain the algorithm that Linux uses for /dev/random 

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.

-- 
CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
Isaac Asimov: "Part of the inhumanity of the computer is that, once it is
completely programmed and working smoothly, it is completely honest."
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