[dm-crypt] How to compress LUKS v2 header?

[dm-crypt] How to compress LUKS v2 header?

[Julio Cesar Faracco - jfaracco@br.ibm.com]

Hi all,

I'm trying to compress a LUKS v2 header file, but I'm not seeing any
sensible reduction.
I'm using `cryptsetup luksHeaderBackup /dev/sda2 --header-backup-file /tmp/backup.header`
I used ZIP and GZIP, but I got 0% of reduction of `backup.header`. :-(
Do you have any suggestions of what algorithm should be used to
compress this type of file?

Thanks!

--     
Julio  Cesar Faracco

Re: [dm-crypt] How to compress LUKS v2 header?

[Michael Kjörling]

On 26 Dec 2019 20:20 +0000, from jfaracco@br.ibm.com (Julio Cesar Faracco - jfaracco@br.ibm.com):
> I'm using `cryptsetup luksHeaderBackup /dev/sda2 --header-backup-file /tmp/backup.header`
> I used ZIP and GZIP, but I got 0% of reduction of `backup.header`. :-(
> Do you have any suggestions of what algorithm should be used to
> compress this type of file?

Why are you trying to compress the header backup in the first place?

As a general rule, encrypted data (such as the parts of the LUKS
header that aren't already random by design) does not compress well;
if data that has been encrypted can be compressed to any notable
degree, that usually means the encryption is somehow flawed, because
it's leaving patterns in the encrypted data. Properly encrypted data
should look completely random, which means that there's very little,
if anything, for compression utilities to find reducible patterns in.

-- 
Michael Kjörling • https://michael.kjorling.se • michael@kjorling.se
 “Remember when, on the Internet, nobody cared that you were a dog?”

Re: [dm-crypt] How to compress LUKS v2 header?

[Arno Wagner]

Hi,

compressing the anti-forensic stripes would require breaking some 
pretty impressive crypto. In short, for all practical purposes,
compression is impossible.

Regards,
Arno

On Thu, Dec 26, 2019 at 21:20:44 CET, Julio Cesar Faracco - jfaracco@br.ibm.com wrote:
> Hi all,
> 
> I'm trying to compress a LUKS v2 header file, but I'm not seeing any
> sensible reduction.
> I'm using `cryptsetup luksHeaderBackup /dev/sda2 --header-backup-file /tmp/backup.header`
> I used ZIP and GZIP, but I got 0% of reduction of `backup.header`. :-(
> Do you have any suggestions of what algorithm should be used to
> compress this type of file?
> 
> Thanks!
> 
> --     
> Julio  Cesar Faracco
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
> https://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

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier

Re: [dm-crypt] How to compress LUKS v2 header?

[Julio Cesar Faracco - jfaracco@br.ibm.com]

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Hi guys!

Thanks for your answers and sorry to send a lots of cloned emails.
I got issues to send for some reason.

Anyway, we have a lab here and we usually save the backup header for security reasons.
But after moving to LUKS v2 from v1, header increased from ~1MB to ~22MB.

We would not like to remove some important features introduced by v2.

--     
Julio  Cesar Faracco

From: dm-crypt <dm-crypt-bounces@saout.de> on behalf of Arno Wagner <arno@wagner.name>
Sent: Friday, December 27, 2019 6:30 AM
To: dm-crypt@saout.de
Subject: [EXTERNAL] Re: [dm-crypt] How to compress LUKS v2 header?
    
Hi,

compressing the anti-forensic stripes would require breaking some 
pretty impressive crypto. In short, for all practical purposes,
compression is impossible.

Regards,
Arno

On Thu, Dec 26, 2019 at 21:20:44 CET, Julio Cesar Faracco - jfaracco@br.ibm.com wrote:
> Hi all,
> 
> I'm trying to compress a LUKS v2 header file, but I'm not seeing any
> sensible reduction.
> I'm using `cryptsetup luksHeaderBackup /dev/sda2 --header-backup-file /tmp/backup.header`
> I used ZIP and GZIP, but I got 0% of reduction of `backup.header`. :-(
> Do you have any suggestions of what algorithm should be used to
> compress this type of file?
> 
> Thanks!
> 
> --     
> Julio  Cesar Faracco
> _______________________________________________
> dm-crypt mailing list
> dm-crypt@saout.de
>  https://urldefense.proofpoint.com/v2/url?u=https-3A__www.saout.de_mailman_listinfo_dm-2Dcrypt&d=DwICAg&c=jf_iaSHvJObTbx-siA1ZOg&r=ZRo7ioNm6-KW9XMwc8-3Aqc6TBVFd8_9yk27A36m0u0&m=UHeTRaj2fJOS8eofLbCuddNDYr5YBFfte5x52g8cOh0&s=whK0QtntH0C5Yob4nwEPjwFCu8n7NZirV09FpwE_pbg&e=

-- 
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

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier
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