From owner-freebsd-arch Tue Jul 17 20:39:54 2001 Delivered-To: freebsd-arch@freebsd.org Received: from silby.com (cb34181-a.mdsn1.wi.home.com [24.14.173.39]) by hub.freebsd.org (Postfix) with ESMTP id E903437B406 for ; Tue, 17 Jul 2001 20:39:50 -0700 (PDT) (envelope-from silby@silby.com) Received: (qmail 3798 invoked by uid 1000); 18 Jul 2001 03:39:49 -0000 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 18 Jul 2001 03:39:49 -0000 Date: Tue, 17 Jul 2001 22:39:49 -0500 (CDT) From: Mike Silbersack To: Kris Kennaway Cc: Subject: Re: TCP Initial Sequence Numbers: We need to talk In-Reply-To: <20010717202901.A89611@xor.obsecurity.org> Message-ID: <20010717223135.F3744-100000@achilles.silby.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Tue, 17 Jul 2001, Kris Kennaway wrote: > On Tue, Jul 17, 2001 at 09:49:03PM -0500, Mike Silbersack wrote: > > > In order to meet these requirements, I propose that we use the following > > system: > > > > For SYN-ACKs: Use the value of arc4random() as our ISN. > > > > For SYNs: Use the value generated by the rfc1948 scheme, with the > > modification that the secret used in the hash be changed on a weekly > > basis. (This will break recycling for perhaps a minute a week, but it > > will ensure that the hash can not be bruteforced and also make sure that > > the system's uptime cannot be easily tracked.) > > > > Comments are appreciated. > > If you're going to implement RFC 1948, why not just implement RFC > 1948? :-) > > Kris For SYN-ACKs: RFC1948 can only increase the predictability of the returned ISN, relative to a random number generator. For SYNs: I still have this bad feeling that the hash could be brute-forced, given enough (up)time. Actually, linux's RFC1948-like implementation reseeds every 300 seconds, if I'm reading the code correctly. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message