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Date:	Tue, 4 Dec 2007 18:49:40 +0000 (UTC)
From:	Russ Dill <>
Subject:  Re: Why does reading from /dev/urandom deplete entropy so much?

Marc Haber <mh+linux-kernel <at>> writes:

> While debugging Exim4's GnuTLS interface, I recently found out that
> reading from /dev/urandom depletes entropy as much as reading from
> /dev/random would. This has somehow surprised me since I have always
> believed that /dev/urandom has lower quality entropy than /dev/random,
> but lots of it.
> This also means that I can "sabotage" applications reading from
> /dev/random just by continuously reading from /dev/urandom, even not
> meaning to do any harm.

An application either needs to be cryptographically secure, or it doesn't. If it
doesn't, then just use /dev/urandom to seed a PRNG.

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