linux-kernel - Re: [PATCH v2] modsign: use shred to overwrite the private key before deleting it

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Message-ID: <54C4583A.5040505@ahsoftware.de>
Date:	Sun, 25 Jan 2015 03:43:06 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Pádraig Brady <P@...igBrady.com>,
	linux-kernel@...r.kernel.org
CC:	linux-kbuild@...r.kernel.org, Michal Marek <mmarek@...e.cz>,
	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] modsign: use shred to overwrite the private key before
 deleting it

Am 25.01.2015 um 03:13 schrieb Pádraig Brady:
> On 24/01/15 12:29, Alexander Holler wrote:
>> Am 24.01.2015 um 13:09 schrieb Alexander Holler:
>>> Am 24.01.2015 um 12:37 schrieb Alexander Holler:
>>>> Am 24.01.2015 um 11:45 schrieb Alexander Holler:
>>>>
>>>>> It uses shred, in the hope it will somedays learn how to shred stuff on
>>>>> FLASH based devices securely too, once that has become possible.
>>>>
>>>> BTW: This is a good example where technology failed to keep the needs of
>>>> users in mind.
>>>
>>> Failed completely.
>>>
>>> Since ever it's a problem for people to securely delete files on storage.
>>>
>>> Also it should be very simple to securely erase files on block based
>>> devices, people have to try cruel ways in the hope to get securely rid
>>> of files nobody else should be able to see ever again.
>>>
>>> It's almost unbelievable how completely the IT industry (including the
>>> field I'm working myself: SW) failed in regard to that since 30 years or
>>> even more.
>>
>> And it isn't such that this is a new requirement. Humans are doing such
>> since thousands of years. They use fire to get rid of paper documents
>> and even the old egypts were able to destroyed stuff on stones by using
>> simple steps. Just the IT failed completely.
>>
>> Really unbelievable.
>>
>> So, sorry if anyone got bored by this mail, but I think that really has
>> to be said and repeated.
>
> Well not failed completely, just used a different method (encryption).
>
> As for "shredding", that improves in effectiveness the lower you go.
> I.E. it's effective for the whole file system (SSD range), or whole device.

That's the usual broken way to go by adding another layer. And if you 
encrypt your whole device, it won't help if you want to delete one file. 
As long as the encrypted device is mounted and the blocks aren't 
overwritten, the stuff is still there. So your solution would end up with:

- mount encrypted device
- build kernel and secret key
- install kernel and secret key
- unmount encrypted device

That's almost the same as shredding a whole device just to securely 
delete one file, with the added complication that the encryption 
requires an authentication, which usually is very uncomfortable to do, 
at least if the authentication is somewhat secure.

Or what do you have in mind?

Sorry, but deleting a file such that it isn't readable anymore by anyone 
shouldn't be a complicated sequence of geek-stuff and all filesystem and 
storage designers should be ashamed that they haven't managed it in 
around 30 years to accomplish that simple goal. (imho) ;)

Regards,

Alexander Holler

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