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Message-ID: <CAHmME9pip1w3fYKKZ==RUYss+GZmQ1w3kjT4Lgvkxi_=SyK+wg@mail.gmail.com>
Date: Fri, 16 Dec 2016 23:23:59 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Netdev <netdev@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>,
Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, David Laight <David.Laight@...lab.com>,
Ted Tso <tytso@....edu>, Hannes Frederic Sowa <hannes@...essinduktion.org>,
Linus Torvalds <torvalds@...ux-foundation.org>, Eric Biggers <ebiggers3@...il.com>,
Tom Herbert <tom@...bertland.com>, George Spelvin <linux@...encehorizons.net>,
Vegard Nossum <vegard.nossum@...il.com>, Andi Kleen <ak@...ux.intel.com>,
"David S. Miller" <davem@...emloft.net>,
Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: [PATCH v6 3/5] random: use SipHash in place of MD5
Hi Andy,
> Agreed. A simpler contruction would be:
>
> chaining++;
> output = H(chaining, secret);
>
> And this looks a whole lot like Ted's ChaCha20 construction.
In that simpler construction with counter-based secret rekeying and in
Ted's ChaCha20 construction, the issue is that every X hits, there's a
call to get_random_bytes, which has variable performance and entropy
issues. Doing it my way with it being time based, in the event that
somebody runs ` :(){ :|:& };:`, system performance doesn't suffer
because ASLR is making repeated calls to get_random_bytes every 128 or
so process creations. In the time based way, the system performance
will not suffer.
Jason
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