linux-kernel - Re: Why does reading from /dev/urandom deplete entropy so much?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 4 Dec 2007 18:49:40 +0000 (UTC)
From:	Russ Dill <Russ.Dill@....edu>
To:	linux-kernel@...r.kernel.org
Subject:  Re: Why does reading from /dev/urandom deplete entropy so much?

Marc Haber <mh+linux-kernel <at> zugschlus.de> 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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/