From: Milan Broz Subject: Re: [PATCH] dm-crypt: disable block encryption with arc4 Date: Tue, 26 Jan 2010 11:48:55 +0100 Message-ID: <4B5EC897.5050102@redhat.com> References: <4B5DE54F.7050206@redhat.com> <20100126092234.GA3304@Chamillionaire.breakpoint.cc> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: Mikulas Patocka , dm-devel@redhat.com, Alasdair G Kergon , linux-crypto@vger.kernel.org To: Sebastian Andrzej Siewior Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49214 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751559Ab0AZKtU (ORCPT ); Tue, 26 Jan 2010 05:49:20 -0500 In-Reply-To: <20100126092234.GA3304@Chamillionaire.breakpoint.cc> Sender: linux-crypto-owner@vger.kernel.org List-ID: On 01/26/2010 10:22 AM, Sebastian Andrzej Siewior wrote: > * Milan Broz | 2010-01-25 19:39:11 [+0100]: >> On 01/25/2010 07:29 PM, Mikulas Patocka wrote: >>> When using arc4 to encrypt a block device, the resulting device is >>> unreliable. It reads garbage. That's because arc4 is a stream cipher, if >>> you write something, it advances its state and if you attempt to decrypt >>> the same sector, it uses new state that is different. >>> >>> This patch disables the use of arc4 on block devices. >> >> arc4 again. it is simply not a block cipher:-) >> >> This should be solved inside cryptoAPI and not blacklist it in dm-crypt, >> see that thread >> http://article.gmane.org/gmane.linux.kernel.cryptoapi/3441 > > I some how remember Herbert saying to test for block size > 1. Wouldn't > this be acceptable to block all stream cipher in one go? yes, I think it is better. (...and I just forgot to add that test to dm-crypt after that suggestion.) Milan