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Date: Sat, 19 Feb 2011 12:11:12 -0700
From: Nicolas Bock <nicolasbock@gmail.com>
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Subject: Re: [dm-crypt] LUKS and LVM
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On 02/19/11 11:17, Jonas Meurer wrote:
> Hey Milan,
> 
> On 19/02/2011 Milan Broz wrote:
>> On 02/19/2011 05:46 PM, Nicolas Bock wrote:
>>> Why use random data to overwrite? Shouldn't /dev/zero be enough since
>>> the crypto should produce good randomness on disk?
>>
>> Then you can distinguish between used blocks ("random noise") and
>> unused blocks (remains zeroed).
>>
>> So filling with zero guarantees that old data are wiped, but also
>> leaks info which blocks were overwritten later.
> 
> If I got Arno right, he, first setups a plain dm-crypt device for the
> to-be-encrypted partition, and then fills the encrypted device with
> random data. In this case it should be enough to fill the encrypted
> device with zeros, shouldn't it?

That's how I understood Arno's email too. The zeros will be written as
"random noise" to disk since they go through the cipher first. I could
see though that the extra paranoid would use a random source :)

nick
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