[dm-crypt] Filling a disk with random data - question

[dm-crypt] Filling a disk with random data - question

[Cpp]

Hello,

I noticed a lot of online articles recommend to overwrite your hard
disk with random data before creating an encryption volume on it.
Normally this is done by:

# dd if=/dev/urandom of=/dev/sda bs=4096

This will of course take a while, and there is also the badblocks
alternative. However recently I've seen another approach that uses an
encrypted (non-luks) container that is later filled with blank data.
It's said that this approach is much faster than the urandom method
above. I haven't used this yet, so I hope I got the command line
right:

# cryptsetup -c aes-xts-plain64 -h sha512 -s 512 -d /dev/urandom open
/dev/sda --type plain cryptroot
# dd if=/dev/zero of=/dev/mapper/cryptroot bs=4096

My question is are there any serious drawbacks of using this method in
place of the urandom one?


Best regards!

Re: [dm-crypt] Filling a disk with random data - question

[.. ink ..]

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On Mon, Mar 17, 2014 at 2:55 PM, Cpp <tzornik@gmail.com> wrote:



> My question is are there any serious drawbacks of using this method in
> place of the urandom one?
>
>
I do not know of any drawbacks and i also use cryptsetup to fill up hard
drives with
random data or when creating encrypted container files because i too find
it to be faster
than /dev/urandom.

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Re: [dm-crypt] Filling a disk with random data - question

[Arno Wagner]

On Mon, Mar 17, 2014 at 19:55:05 CET, Cpp wrote:
> Hello,
> 
> I noticed a lot of online articles recommend to overwrite your hard
> disk with random data before creating an encryption volume on it.
> Normally this is done by:
> 
> # dd if=/dev/urandom of=/dev/sda bs=4096

This is slooooooooooow.... ;-)
 
> This will of course take a while, and there is also the badblocks
> alternative. However recently I've seen another approach that uses an
> encrypted (non-luks) container that is later filled with blank data.
> It's said that this approach is much faster than the urandom method
> above. 

I came up with that when I had to securely wipe 50 disks 
a few years ago. Other people may have had a similar idea.

> I haven't used this yet, so I hope I got the command line
> right:
> 
> # cryptsetup -c aes-xts-plain64 -h sha512 -s 512 -d /dev/urandom open
> /dev/sda --type plain cryptroot

Make ist easier on you, the defaults are really quite enough: 

# cryptsetup create -d /dev/urandom /dev/sda cryptroot

> # dd if=/dev/zero of=/dev/mapper/cryptroot bs=4096

And you can get a progress meter like this:

# dd_rescue -w /dev/zero /dev/mapper/cryptroot

or like this

# cat /dev/zero | wcs > /dev/mapper/cryptroot

(uses my sream-meter "wcs" from:  http://www.tansi.org/tools/index.html)
 
> My question is are there any serious drawbacks of using this method in
> place of the urandom one?

None. 

Arno
-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
A good decision is based on knowledge and not on numbers. -  Plato

Re: [dm-crypt] Filling a disk with random data - question

[Robert Nichols]

On 03/17/2014 09:33 PM, Arno Wagner wrote:
> On Mon, Mar 17, 2014 at 19:55:05 CET, Cpp wrote:
>> # cryptsetup -c aes-xts-plain64 -h sha512 -s 512 -d /dev/urandom open
>> /dev/sda --type plain cryptroot
>
> Make ist easier on you, the defaults are really quite enough:
>
> # cryptsetup create -d /dev/urandom /dev/sda cryptroot
>
>> # dd if=/dev/zero of=/dev/mapper/cryptroot bs=4096
>
>> My question is are there any serious drawbacks of using this method in
>> place of the urandom one?
>
> None.

Glad to hear it, since I've been doing that all along.  If you happen
to be doing this with an old cryptsetup, you want to select an IV
that does not repeat on a large volume.  This, for example would be
a poor choice (from cryptsetup 1.1.3):

   Default compiled-in device cipher parameters:
       plain: aes-cbc-plain, Key: 256 bits, Password hashing: ripemd160

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

Re: [dm-crypt] Filling a disk with random data - use a hige bs= to speed it up

[Chris Drake]

Hi Robert,

Remember to use a sensible bs= parameter on "dd" - maybe bs=8225280
instead of bs=4096 - writing one-block-at-a-time (bs=4096) would take
*days* (weeks even!) to fill a modern large drive!

Kind Regards,
Chris Drake
p.s. 8225280 is one whole track on older drives.

Wednesday, March 19, 2014, 8:20:47 AM, you wrote:

RN> On 03/17/2014 09:33 PM, Arno Wagner wrote:
>> On Mon, Mar 17, 2014 at 19:55:05 CET, Cpp wrote:
>>> # cryptsetup -c aes-xts-plain64 -h sha512 -s 512 -d /dev/urandom open
>>> /dev/sda --type plain cryptroot
>>
>> Make ist easier on you, the defaults are really quite enough:
>>
>> # cryptsetup create -d /dev/urandom /dev/sda cryptroot
>>
>>> # dd if=/dev/zero of=/dev/mapper/cryptroot bs=4096
>>
>>> My question is are there any serious drawbacks of using this method in
>>> place of the urandom one?
>>
>> None.

RN> Glad to hear it, since I've been doing that all along.  If you happen
RN> to be doing this with an old cryptsetup, you want to select an IV
RN> that does not repeat on a large volume.  This, for example would be
RN> a poor choice (from cryptsetup 1.1.3):

RN>    Default compiled-in device cipher parameters:
RN>        plain: aes-cbc-plain, Key: 256 bits, Password hashing: ripemd160

Re: [dm-crypt] Filling a disk with random data - question

[Arno Wagner]

Just added this to the Wiki-Version of the FAQ as Item 2.19, if 
anybody wants to have a look and comment.

Arno


On Tue, Mar 18, 2014 at 03:33:51 CET, Arno Wagner wrote:
> On Mon, Mar 17, 2014 at 19:55:05 CET, Cpp wrote:
> > Hello,
> > 
> > I noticed a lot of online articles recommend to overwrite your hard
> > disk with random data before creating an encryption volume on it.
> > Normally this is done by:
> > 
> > # dd if=/dev/urandom of=/dev/sda bs=4096
> 
> This is slooooooooooow.... ;-)
>  
> > This will of course take a while, and there is also the badblocks
> > alternative. However recently I've seen another approach that uses an
> > encrypted (non-luks) container that is later filled with blank data.
> > It's said that this approach is much faster than the urandom method
> > above. 
> 
> I came up with that when I had to securely wipe 50 disks 
> a few years ago. Other people may have had a similar idea.
> 
> > I haven't used this yet, so I hope I got the command line
> > right:
> > 
> > # cryptsetup -c aes-xts-plain64 -h sha512 -s 512 -d /dev/urandom open
> > /dev/sda --type plain cryptroot
> 
> Make ist easier on you, the defaults are really quite enough: 
> 
> # cryptsetup create -d /dev/urandom /dev/sda cryptroot
> 
> > # dd if=/dev/zero of=/dev/mapper/cryptroot bs=4096
> 
> And you can get a progress meter like this:
> 
> # dd_rescue -w /dev/zero /dev/mapper/cryptroot
> 
> or like this
> 
> # cat /dev/zero | wcs > /dev/mapper/cryptroot
> 
> (uses my sream-meter "wcs" from:  http://www.tansi.org/tools/index.html)
>  
> > My question is are there any serious drawbacks of using this method in
> > place of the urandom one?
> 
> None. 
> 
> Arno
> -- 
> Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
> GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
> ----
> A good decision is based on knowledge and not on numbers. -  Plato
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
A good decision is based on knowledge and not on numbers. -  Plato

Re: [dm-crypt] Filling a disk with random data - question

[.. ink ..]

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On Thu, Apr 10, 2014 at 11:15 AM, Arno Wagner <arno@wagner.name> wrote:

> Just added this to the Wiki-Version of the FAQ as Item 2.19, if
> anybody wants to have a look and comment.
>
> Arno
>
>
Your example uses a syntax that is marked as being "obsolete" in the man
page.

There is an error in your example as that syntax expects the device to be
the last argument,not the mapper path.Your example fail with the following
error:

[root@mtz ink]# cryptsetup create -d /dev/urandom /dev/loop0  to_be_wiped
Device to_be_wiped doesn't exist or access denied.
[root@mtz ink]#

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Re: [dm-crypt] Filling a disk with random data - question

[Arno Wagner]

Thanks, fixed.

Arno

On Thu, Apr 10, 2014 at 17:50:20 CEST, .. ink .. wrote:
> On Thu, Apr 10, 2014 at 11:15 AM, Arno Wagner <arno@wagner.name> wrote:
> 
> > Just added this to the Wiki-Version of the FAQ as Item 2.19, if
> > anybody wants to have a look and comment.
> >
> > Arno
> >
> >
> Your example uses a syntax that is marked as being "obsolete" in the man
> page.
> 
> There is an error in your example as that syntax expects the device to be
> the last argument,not the mapper path.Your example fail with the following
> error:
> 
> [root@mtz ink]# cryptsetup create -d /dev/urandom /dev/loop0  to_be_wiped
> Device to_be_wiped doesn't exist or access denied.
> [root@mtz ink]#

> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt


-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
A good decision is based on knowledge and not on numbers. -  Plato