From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael K. Edwards" Subject: Re: Extensible hashing and RCU Date: Tue, 20 Feb 2007 12:03:04 -0800 Message-ID: References: <200702191913.08125.dada1@cosmosbay.com> <200702201738.19590.dada1@cosmosbay.com> <20070220165907.GB24930@2ka.mipt.ru> <200702201820.27095.dada1@cosmosbay.com> <20070220175550.GB26961@2ka.mipt.ru> <20070220181217.GA3401@2ka.mipt.ru> <20070220194409.GB5590@2ka.mipt.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "Eric Dumazet" , "David Miller" , akepner@sgi.com, linux@horizon.com, netdev@vger.kernel.org, bcrl@kvack.org To: "Evgeniy Polyakov" Return-path: Received: from nz-out-0506.google.com ([64.233.162.225]:10038 "EHLO nz-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965195AbXBTUDF (ORCPT ); Tue, 20 Feb 2007 15:03:05 -0500 Received: by nz-out-0506.google.com with SMTP id s1so2033423nze for ; Tue, 20 Feb 2007 12:03:04 -0800 (PST) In-Reply-To: <20070220194409.GB5590@2ka.mipt.ru> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2/20/07, Evgeniy Polyakov wrote: > How I like personal insults - it is always fun to read about myself from > people who never knew me :) On this occasion, I did not set out to insult you. I set out to suggest an explanation for why cooler and grayer heads than mine are not falling over themselves to merge your designs into the mainline kernel. Did I succeed? > I just shown a problem in jenkins hash - it is not how to find a > differnet input for the same output - it is a _law_ which allows to > break a hash. You will add some constant, and that law will be turned > into something different (getting into account what was written, it will > end up with the same law). Correct. That's called a "weak hash", and Jenkins is known to be a thoroughly weak hash. That's why you never, ever use it without a salt, and you don't let an attacker inspect the hash output either. > Using jenkins hash is equal to the situation, when part of you hash > chains will be 5 times longer than median square value, with XOR one > there is no such distribution. Show us the numbers. Salt properly this time to reduce the artifacts that come of applying a weak hash to a poor PRNG, and histogram your results. If you don't get a Poisson distribution you probably don't know how to use gnuplot either. :-) > Added somthing into permutations will not endup in different > distribution, since it is permutations which are broken, not its result > (which can be xored with something). I can't parse this. Care to try again? Cheers, - Michael