From owner-freebsd-hackers Wed Feb 23 12:18:26 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from spirit.jaded.net (spirit.jaded.net [216.94.113.12]) by hub.freebsd.org (Postfix) with ESMTP id 7132237B992 for ; Wed, 23 Feb 2000 12:18:22 -0800 (PST) (envelope-from dan@spirit.jaded.net) Received: (from dan@localhost) by spirit.jaded.net (8.9.3/8.9.3) id PAA01950; Wed, 23 Feb 2000 15:17:19 -0500 (EST) Date: Wed, 23 Feb 2000 15:17:18 -0500 From: Dan Moschuk To: Peter Wemm Cc: Sergey Babkin , hackers@FreeBSD.ORG Subject: Re: DeCSS Message-ID: <20000223151718.A1731@spirit.jaded.net> References: <20000223091808.979921CDF@overcee.netplex.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0i In-Reply-To: <20000223091808.979921CDF@overcee.netplex.com.au>; from peter@netplex.com.au on Wed, Feb 23, 2000 at 05:18:08PM +0800 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG | IMHO, what would be FAR better would be for things that use the Xing keys | to go away, and something else used that exploited the weaknesses of the | CSS system itself. A couple of researchers have found that CSS is *SO | PATHETICALLY WEAK* that it takes merely a few seconds on a reasonably quick | computer to break the session key for the DVD without having *any* | knowledge of the compromised Xing key. That way the MPAA and CCA can't | claim that you are using a stolen key, because you are not using any of the | 512 player keys. You are simply figuring out what the session key is. Correct! CSS is so pathetic that breaking it in runtime is quite easily accomplished. Each DVD has a disk key, which is stored in a five byte hash on the disk. The disk key is also stored encrypted with all the various player keys. The layout looks something like this: 5 byte disk key hash Disk key encrypted with player key 1 Disk key encrypted with player key 2 ... Disk key encrypted with player key n When a disk is inserted, the player decrypts the disk key with its assigned player key, then hashes it and compares it to the 5 byte hash. Since CSS is a 40bit cipher (something to do with US export regulations I'm sure), attacking the keyspace is quite trivial to do (about a complexity of 2^25). Another interesting point is that with one player key compromised, one can derive the rest of the player keys through a similar search. -- Dan Moschuk (TFreak!dan@freebsd.org) "Waste not fresh tears on old griefs." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message