Re: [LI] /dev/random & /dev/urandom - d..uh what is it?????

[Vimal Mathew <vml@xxxxxxxxxxxxx>]

On Wed, Jan 19, 2000 at 09:26:56AM +0700, Pankaj Mathur wrote:
> just now came across two things called /dev/random & /dev/urandom. Out of 
> curiosity I did cat for both of them and my screen was filled with all 
> garbled stuff. What are these anyway and what possible use it has on an OS?

If you have install your kernel sources, go through the comments in
/usr/src/linux/drivers/char/random.c. The comments are *very* comprehensive.
Quoting relevant parts...

<quote>
 * This routine gathers environmental noise from device drivers, etc.,
 * and returns good random numbers, suitable for cryptographic use.
 * Besides the obvious cryptographic uses, these numbers are also good
 * for seeding TCP sequence numbers, and other places where it is
 * desirable to have numbers which are not only random, but hard to
 * predict by an attacker.
<snip>
 * 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.
</quote>

--vml,
Model Engg. College,
Cochin
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