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

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Message-ID: <54C4C65A.2020403@ahsoftware.de>
Date:	Sun, 25 Jan 2015 11:32:58 +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 03:43 schrieb Alexander Holler:
> 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

That's wrong, of course it should read "and signed modules".

> - 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) ;)

By the way, I still remember the time when people learned that if they 
delete a file on a FAT file system, it isn't really gone. Afterwards all 
kinds of device-shredding software and hardware appeared.

But instead of fixing that broken design, now, around 30 years later, 
this stupid and broken design is almost part of any storage and filesystem.

And even worse, because storage is nowadays often fixed to device (no 
floppy anymore you can easily destroy), it often has become almost 
impossible to really delete stuff on devices.
E.g. how do you overwrite an eMMC which is soldered, without the 
possibility to boot from something else in order to launch the shredding 
software?

So we are now at the point that the only way to keep some information 
private (forever) is to not store it on any computer.

How crazy or userfriendly is that?

Regards,

Alexander Holler


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