From owner-freebsd-security  Mon Apr 16 13: 3: 7 2001
Delivered-To: freebsd-security@freebsd.org
Received: from caligula.anu.edu.au (caligula.anu.edu.au [150.203.224.42])
	by hub.freebsd.org (Postfix) with ESMTP
	id 1DC4037B42C; Mon, 16 Apr 2001 13:02:59 -0700 (PDT)
	(envelope-from avalon@caligula.anu.edu.au)
Received: (from avalon@localhost)
	by caligula.anu.edu.au (8.9.3/8.9.3) id GAA09062;
	Tue, 17 Apr 2001 06:02:42 +1000 (EST)
From: Darren Reed <avalon@coombs.anu.edu.au>
Message-Id: <200104162002.GAA09062@caligula.anu.edu.au>
Subject: Re: non-random IP IDs
To: kris@obsecurity.org (Kris Kennaway)
Date: Tue, 17 Apr 2001 06:02:42 +1000 (Australia/ACT)
Cc: avalon@coombs.anu.edu.au (Darren Reed),
	kris@obsecurity.org (Kris Kennaway),
	silby@silby.com (Mike Silbersack),
	newsletter@marktroberts.com (Mark T Roberts),
	freebsd-security@FreeBSD.ORG, net@FreeBSD.ORG
In-Reply-To: <20010416120630.C10023@xor.obsecurity.org> from "Kris Kennaway" at Apr 16, 2001 12:06:30 PM
X-Mailer: ELM [version 2.5 PL1]
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-security@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org

In some mail from Kris Kennaway, sie said:
> 
> 
> --TYecfFk8j8mZq+dy
> Content-Type: text/plain; charset=us-ascii
> Content-Disposition: inline
> 
> On Tue, Apr 17, 2001 at 04:36:15AM +1000, Darren Reed wrote:
> 
> > You should optimize it for mod being 2^n-1 (or make that a requirement).
> 
> I'm afraid I don't have time to look at this right now.  Perhaps it
> can be revisited (the sysctl defaults to off for now), or Niels Provos
> may be interested in the idea.

Basically it means '% mod' -> '& mod' and call it with a 2^n-1 number.

> > Also, drop the HTONS statements, they no longer make sense.  Before ip_id
> > was a counter and so it made sense (sorta) to change its byte ordering to
> > network.  Now it's just a random number so there is no longer any need.
> 
> Well, it still has wrapping properties like a network-order counter,
> i.e. the algorithm attempts to order the output so that it doesn't
> wrap within the segment lifetime.  That would be lost without using
> HTONS.

You're confusing properties of the local number and some opaque bits in
a packet being sent over the 'net.

Darren

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-security" in the body of the message