Date: Tue, 17 Jul 2001 22:39:49 -0500 (CDT) From: Mike Silbersack <silby@silby.com> To: Kris Kennaway <kris@obsecurity.org> Cc: <freebsd-arch@FreeBSD.ORG> Subject: Re: TCP Initial Sequence Numbers: We need to talk Message-ID: <20010717223135.F3744-100000@achilles.silby.com> In-Reply-To: <20010717202901.A89611@xor.obsecurity.org>
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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
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