From mboxrd@z Thu Jan 1 00:00:00 1970 From: Milan Broz Subject: Re: [PATCH 2/2] dm-crypt: Add TCW IV mode for old CBC TCRYPT containers. Date: Mon, 28 Oct 2013 17:58:35 +0100 Message-ID: <526E97BB.2080604@gmail.com> References: <1382275000-10660-1-git-send-email-gmazyland@gmail.com> <1382275000-10660-2-git-send-email-gmazyland@gmail.com> <20131028160849.GB25212@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20131028160849.GB25212@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer Cc: dm-devel@redhat.com List-Id: dm-devel.ids On 28.10.2013 17:08, Mike Snitzer wrote: > What does TCW mean? How does it relate to CBC? > - Is TCW mode: "CBC mode with some additional tweaks"? Yes, as said in previous mail, it is just shortcut. > >> While TCRYPT CBC mode is legacy and is known to be vulnerable >> to some watermarking attacks (e.g. revealing of hidden disk >> existence) it can be still useful to mount old containers >> without using 3rd party software or for independent forensic >> analysis of such containers. > > Now you're switching back to referring to "TCRYPT CBC mode". What > happened to "TCW mode"? I am talking about implementation in general, not dmcrypt specific one. It is still the same mode of course. >> There is also second key used for "whitening" of sectors. >> Whitening key is xored with sector number and mixed using >> CRC32 and resulting value is applied to whole sector. >> (Detailed calculation is in Truecrypt documentation for version < 4.1 >> and will be also described on dmcrypt site.) > > Can you add a pointer to the Truecrypt documentation for < 4.1? I am afraid they removed all old documentation from site. (but search google e.g. for truecrypt-3.1a-user-guide.pdf or some similar version which use CBC mode, whitening and IV generator is described there as well) > Or a pointer to the dmcrypt site documentation? Description is not yet there (once it is in kernel I will add it) but link is referenced even from kernel Documentation http://code.google.com/p/cryptsetup/wiki/DMCrypt (and yes, seems that IV generators need better description there) Thanks, Milan