[dm-crypt] dm-crypt Digest, Vol 27, Issue 2

Yaron Sheffer yaronf at gmx.com
Thu Sep 1 15:30:23 CEST 2011

Hi Arno,

Encryption of data-at-rest in the public cloud is not "pointless", it is 
yet another layer of security. Just as people encrypt their laptops even 
though they are password protected.

The cloud provider does not have access to "everything", certainly not 
when we're talking about data at rest, where the keys may have come and 
gone months ago but the data is still there. Moreover, the cloud 
provider is not the only or the most important threat. By the way, I am 
not claiming that the permission system is broken.

Attacks on encrypted data are no harder or more expensive in the cloud 
than on physical disks. If you parallelize things, your throughput is 
limited by the disks physical access, just as for "real" disks.

This is a solution for a very real problem. But I don't want to go 
commercial again...


On 09/01/2011 02:38 PM, dm-crypt-request at saout.de wrote:

Message: 2
Date: Thu, 1 Sep 2011 13:27:24 +0200
From: Arno Wagner<arno at wagner.name>
To: dm-crypt at saout.de
Subject: Re: [dm-crypt] Blog post on FDE and integrity protection
Message-ID:<20110901112724.GB4617 at tansi.org>
Content-Type: text/plain; charset=us-ascii

Disk encryption in a non-private cloud is pretty pointless.
The cloud provider can access everything. An attacker should
reliably be kept from accessing your storage, otherwise you are
screwed anyways. I know, people are doing this, but they are
kidding themselves.

For your EBS scenario, true, block-level encryption
can be done, but it is irrelevant. Encryption is not the
right way to fix a broken cloud permission system. Critical
encrypted data should never be decrypted in the cloud. It
is just not secure. On the other hand, attacks that
manipulate encrypted images are not relevant for lower
security requirements, as they are very hard (expensive)
to do.

This makes integtity protection of encrypted data in the cloud
a complete non-issue. This is a solution without a problem.


On Thu, Sep 01, 2011 at 01:51:38PM +0300, Yaron Sheffer wrote:

>> Hi Arno,
>> Thank you for reviewing my post. Please see my comments below.
>> Thanks,
>>      Yaron
>>> Message: 3
>>> Date: Wed, 31 Aug 2011 23:29:40 +0200
>>> From: Arno Wagner<arno at wagner.name>
>>> To: dm-crypt at saout.de
>>> Subject: Re: [dm-crypt] Blog post on FDE and integrity protection
>>> Message-ID:<20110831212940.GB25013 at tansi.org>
>>> Content-Type: text/plain; charset=us-ascii
>>> Commercial, for sure. It combines fragments from well-known
>>> facts and marketing speech. And it has not understood the
>>> problem, advertizing for SAN/cloud services, where storage is
>>> not block-based but file-based.
>> The most commonly used public cloud is Amazon WS. This cloud offers
>> two storage possibilities, S3 which is object ("file") storage, and
>> EBS which is block storage, and is exposed to the application as a
>> disk volume. The post is about EBS, sorry if that wasn't clear.
>>> I should also note to anyone contemplating "solution" 3
>>> that RAID1 does not read both devices on read access,
>>> and inconsistencies will only show up if you or your
>>> distro does RAID consistency checks.
>> This is correct, thanks.
>>> And of course the whole article does not apply to the
>>> SAN/cloud setting in the first place, as the attack
>>> scenario is for an unmapped encrypted filesystem and
>>> an attacker getting write access to that, i.e. the
>>> encrypted raw (block) view needs to be exported to
>>> the attacker. I do not see how that would be done in the
>>> SAN/Cloud setting. These do their own filesystem
>>> and block encryption must be done below the FS layer,
>>> there is no way around that.
>> The attack scenario is for someone who has access (possibly limited
>> access) to your cloud account to detach your EBS volume from its
>> current virtual server, attach it to a different server, and then
>> modify the (encrypted) storage. This is all completely doable and
>> actually standard procedure on AWS.
>>> Arno
>>> On Wed, Aug 31, 2011 at 04:25:51PM +0200, Heinz Diehl wrote:
>>>> On 31.08.2011, Yaron Sheffer wrote:

More information about the dm-crypt mailing list