From: Richard Jones <rich@annexia.org>
To: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
Cc: kamaradclimber@gmail.com, caml-list@inria.fr
Subject: Re: [Caml-list] range of hash function
Date: Sun, 21 Feb 2010 23:10:01 +0000 [thread overview]
Message-ID: <20100221231001.GA8709@annexia.org> (raw)
In-Reply-To: <20100220.225412.98507853.garrigue@math.nagoya-u.ac.jp>
On Sat, Feb 20, 2010 at 10:54:12PM +0900, Jacques Garrigue wrote:
> Since you have the algorithm, you can predict collisions. Basically
> shifting character n by 1 is equivalent to shifting character n+1 by
> 19, so you have lots of collisions. But this hash function being
> intended for hashtables, collisions are not a problem, uniform
> distribution matters more.
I would slightly dispute your assertion that collisions are not a
problem, because of algorithmic complexity attacks:
http://www.cs.rice.edu/~scrosby/hash/CrosbyWallach_UsenixSec2003/index.html
The hash implementation used by Perl was changed to avoid this attack:
http://perl5.git.perl.org/perl.git/blob/HEAD:/perl.c#l1465
Rich.
--
Richard Jones
Red Hat
prev parent reply other threads:[~2010-02-21 23:10 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-20 8:54 Grégoire Seux
2010-02-20 10:52 ` [Caml-list] " Goswin von Brederlow
2010-02-20 12:39 ` ygrek
2010-02-20 13:54 ` Jacques Garrigue
2010-02-21 23:10 ` Richard Jones [this message]
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