linux-kernel - Re: [PATCH v5 00/21] EVM

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Message-ID: <1305896771.15245.11.camel@localhost.localdomain>
Date:	Fri, 20 May 2011 09:06:11 -0400
From:	David Safford <safford@...son.ibm.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Greg KH <greg@...ah.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...ia.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH v5 00/21] EVM

On Thu, 2011-05-19 at 21:07 -0400, Mimi Zohar wrote:
> On Fri, 2011-05-20 at 10:51 +1000, James Morris wrote:
> > On Wed, 18 May 2011, Mimi Zohar wrote:
> > 
> > > > Once we have a better understanding of what the feature does and why it
> > > > does it and how it interfaces with the user, we can start looking at
> > > > the implementation.
> > > 
> > > Much appreciated!
> > 
> > What is the status of potential users of the feature?
> > 
> > I recall that MeeGo were planning to use EVM, but they've since changed 
> > their security plans.  Do they still plan to use it?  Are any other users 
> > committing to use EVM?
> > 
> > Also -- this was raised some time back, but I can't find the discussion -- 
> > what does IMA/EVM provide over disk encryption as a protection against 
> > offline attacks?
> > 
> > - James
> 
> Dave Safford's whitepaper discusses this.
> http://downloads.sf.net/project/linux-ima/linux-ima/Integrity_overview.pdf
> 
> Mimi

The short answer is that encryption provides confidentiality, but does
not provide integrity, authenticity, or immutability. 

The easiest way to think about it is to consider a one time pad, which
provides perfect confidentiality, but is trivially bit-twiddled. Yes,
AES is better in this respect, and encrypted file systems can combine
integrity (as long as you encrypt-then-authenticate), but usually they
don't. 

If you want policy driven integrity, authenticity, and immutability,
(and we have two IBM customers wanting them this year), then you want
the combination IMA, IMA-Appraisal, EVM, and Dmitry's digital signature
extensions.

dave
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