From owner-freebsd-hackers@FreeBSD.ORG Mon Nov 24 15:57:43 2003 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id E416316A4CF; Mon, 24 Nov 2003 15:57:43 -0800 (PST) Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.126.187]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9A14E43FAF; Mon, 24 Nov 2003 15:57:42 -0800 (PST) (envelope-from se@freebsd.org) Received: from [212.227.126.206] (helo=mrelayng.kundenserver.de) by moutng.kundenserver.de with esmtp (Exim 3.35 #1) id 1AOQaL-0001QB-00; Tue, 25 Nov 2003 00:57:41 +0100 Received: from [80.132.232.172] (helo=Gatekeeper.FreeBSD.org) by mrelayng.kundenserver.de with asmtp (Exim 3.35 #1) id 1AOQaK-0004j3-00; Tue, 25 Nov 2003 00:57:41 +0100 Received: from StefanEsser.FreeBSD.org (StefanEsser [10.0.0.1]) by Gatekeeper.FreeBSD.org (Postfix) with ESMTP id 0A0B35F18; Tue, 25 Nov 2003 00:57:38 +0100 (CET) Received: by StefanEsser.FreeBSD.org (Postfix, from userid 200) id 910621E95; Tue, 25 Nov 2003 00:57:38 +0100 (CET) Date: Tue, 25 Nov 2003 00:57:38 +0100 From: Stefan =?iso-8859-1?Q?E=DFer?= To: Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?= Message-ID: <20031124235738.GA4107@StefanEsser.FreeBSD.org> References: <20031119003133.18473.qmail@web11404.mail.yahoo.com> <200311230019.11310.wes@softweyr.com> <20031123124620.GB1133@StefanEsser.FreeBSD.org> <200311231011.32965.wes@softweyr.com> <20031124102940.GC1168@StefanEsser.FreeBSD.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.5.1i Content-Transfer-Encoding: quoted-printable X-Provags-ID: kundenserver.de abuse@kundenserver.de auth:fa3fae9b6ca38d745862a668565919f6 cc: Rayson Ho cc: phk@freebsd.org cc: freebsd-hackers@freebsd.org Subject: Re: "secure" file flag? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Nov 2003 23:57:44 -0000 On 2003-11-24 12:20 +0100, Dag-Erling Sm=F8rgrav wrote: > Stefan E=DFer writes: > > Ok. I've also thought some about this, and I think that different med= ia > > might need different methods (i.e. MFM vs. RLL vs. PRML, but also vs.= =20 > > Flash media). >=20 > PRML is not an encoding scheme like MFM or RLL, it is an algorithm for > recovering a bitstream from a weak analog signal. Modern disks mostly > use RLL encoding. So what? PRML is not complementary to RLL. RLL is typically used=20 to mean 1,7 RLL offering a 2/3 coding, while PRML starts at 8/9=20 and current devices use up to 24/25 (i.e. 24 bits in 25 channel bits).=20 MFM can be considered a special case of RLL encoding, too, BTW ... But it's utterly irrelevant, that PRML data is written to disk as=20 an RLL encoded data stream. What matters is what can be read back=20 from the disk media (and PRML is about reading, not writing ;-) You probably don't want to claim that 1,7 RLL and a modern PRML=20 encoding can be decoded with similar effort ... And that is what this thread is about: Secure removal of data from=20 storage media. There definitely is a difference between RLL (as in=20 1,7i RLL) and modern PRML drives under this aspect. Regards, STefan