Problem with /dev/random? - new question.

akonstam at trinity.edu akonstam at trinity.edu
Mon May 17 16:19:38 UTC 2004


On Thu, May 13, 2004 at 05:55:03PM -0400, Kent Borg wrote:
> On Thu, May 13, 2004 at 02:26:08PM -0700, Vladimir G. Ivanovic wrote:
> > I am not logged in remotely but locally. I've had a "cat /dev/random"
> > running in a GNOME Terminal tab (window) now for several hours while I
> > read mail & surfed.
> 
> Eeek!
> 
> One of the problems with /dev/random (as opposed to /dev/urandom) is
> that any user can read it, drain all the entropy, and prevent others
> from getting any.  As a test it can be interesting, but don't do that
> otherwise.  (Don't forget an extra cat left running on a different
> console.)
> 
> Kill the cat.  cd to /proc/sys/kernel/random and look around.
> Specifically, cat entropy_avail.  I am guessing you will see nothing.
> Now cat a few bytes into /dev/random and cat entropy_avail again.  Did
> any show up?  If so, then things are as I expect, you need to tell
> your mouse and keyboard and other devices to contribute entropy.  I
> would have to start searching through kernel sources and googling to
> find out how.
> 
> -kb, the Kent who has run off the end of his immediate knowledge.
> 
> 
> P.S.  Did you do a standard install?  What strange things have you
> done?  (Compile your own kernel?  Mess with boot initializations?)

I have only just had a chance to try the above and found the
following:
1. cat entropy_avail returned 4096
2. I cat-ed a small file into /dev/random. The cat just went on with
random characters on screen until I hit crtl-C. 
3.  cat entropy_avail returned 177

This is not what you said would happen and I am at a loss what this
all means. Any clarification?
-- 
-------------------------------------------
Aaron Konstam
Computer Science
Trinity University
One Trinity Place.
San Antonio, TX 78212-7200

telephone: (210)-999-7484
email:akonstam at trinity.edu





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