From: Roland Dreier <roland@topspin.com>
To: linux@horizon.com
Cc: ak@muc.de, arjan@infradead.org, bunk@stusta.de, chrisw@osdl.org,
davem@redhat.com, hlein@progressive-comp.com,
linux-kernel@vger.kernel.org, netdev@oss.sgi.com,
shemminger@osdl.org, Valdis.Kletnieks@vt.edu
Subject: Re: [PATCH] OpenBSD Networking-related randomization port
Date: Sat, 12 Feb 2005 16:18:14 -0800 [thread overview]
Message-ID: <527jld2tyx.fsf@topspin.com> (raw)
In-Reply-To: <20050212232518.10838.qmail@science.horizon.com> (linux@horizon.com's message of "12 Feb 2005 23:25:18 -0000")
linux> It's easy to make a smaller hash by just thowing bits away,
linux> but a block cipher is a permutation, and has to be
linux> invertible.
linux> For example, if I take a k-bit counter and encrypt it with
linux> a k-bit block cipher, the output is guaranteed not to
linux> repeat in less than 2^k steps, but the value after a given
linux> value is hard to predict.
Huh? What if my cipher consists of XOR-ing with a k-bit pattern?
That's a permutation on the set of k-bit blocks but it happens to
decompose as a product of (non-overlapping) swaps.
In general for more realistic block ciphers like DES it seems
extremely unlikely that the cipher has only a single orbit when viewed
as a permutation. I would expect a real block cipher to behave more
like a random permutation, which means that the expected number of
orbits for a k-bit cipher should be about ln(2^k) or roughly .7 * k.
- R.
next prev parent reply other threads:[~2005-02-13 0:19 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-28 17:17 [PATCH] OpenBSD Networking-related randomization port Lorenzo Hernández García-Hierro
2005-01-28 17:40 ` Adrian Bunk
2005-01-28 17:47 ` Lorenzo Hernández García-Hierro
2005-01-28 18:18 ` Stephen Hemminger
2005-01-28 18:54 ` Lorenzo Hernández García-Hierro
2005-01-28 19:09 ` Adrian Bunk
2005-01-28 18:02 ` Stephen Hemminger
2005-01-28 18:31 ` Lorenzo Hernández García-Hierro
2005-01-28 18:52 ` Stephen Hemminger
2005-01-28 18:58 ` Lorenzo Hernández García-Hierro
2005-01-28 20:34 ` Lorenzo Hernández García-Hierro
2005-01-28 20:45 ` David S. Miller
2005-01-28 21:34 ` Stephen Hemminger
2005-01-28 21:45 ` David S. Miller
2005-01-29 6:59 ` Andi Kleen
2005-01-28 20:47 ` Arjan van de Ven
2005-01-28 22:12 ` Lorenzo Hernández García-Hierro
2005-01-29 8:04 ` Arjan van de Ven
2005-01-29 8:05 ` Arjan van de Ven
2005-01-29 9:15 ` Valdis.Kletnieks
2005-01-31 16:50 ` Adrian Bunk
2005-01-31 17:23 ` Lorenzo Hernández García-Hierro
2005-01-31 20:11 ` Ingo Molnar
2005-01-31 23:27 ` linux
2005-02-12 22:29 ` Andi Kleen
2005-02-12 23:25 ` linux
2005-02-13 0:18 ` Roland Dreier [this message]
2005-02-13 1:41 ` linux
2005-02-02 17:17 ` linux
2005-02-02 17:38 ` Lorenzo Hernández García-Hierro
2005-02-03 19:51 ` Stephen Hemminger
2005-02-03 20:14 ` Lennert Buytenhek
2005-01-31 19:42 ` Valdis.Kletnieks
2005-01-31 20:03 ` Lorenzo Hernández García-Hierro
2005-02-01 23:22 ` Matt Mackall
2005-01-28 18:04 ` Jörn Engel
2005-01-28 18:07 ` Arjan van de Ven
2005-01-28 18:36 ` Lorenzo Hernández García-Hierro
2005-02-01 14:54 ` Bill Davidsen
2005-01-28 19:24 ` Horst von Brand
2005-01-29 18:16 ` Florian Weimer
2005-01-28 19:24 Hank Leininger
2005-01-29 7:24 linux
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