[cryptography] urandom vs random

Thor Lancelot Simon tls at panix.com
Sat Aug 17 00:36:44 EDT 2013


On Fri, Aug 16, 2013 at 10:33:11PM -0400, shawn wilson wrote:
> On Fri, Aug 16, 2013 at 10:01 PM, James A. Donald <jamesd at echeque.com> wrote:
> > At startup, likely to be short of entropy.
> >
> 
> > If /dev/urandom seeded at startup, and then seeded no further, bad, but not
> > very bad.
> >
> > If /dev/urandom seeded at startup from /dev/random, then should block at
> > startup.
> >
> > If /dev/urandom never blocks, bad.  Should block at startup waiting to
> > receive 160 bits from /dev/random, and never block again.
> >
> 
> I don't follow this - I understand why lack of entropy should block
> urandom but, why shouldn't it block on a running system that
> <low_bound?

Please explain what it means, exactly, to reduce the amount of
entropy in the system in question.

Emphasis on "exactly".

Thor


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