linux-kernel - Re: [RFC PATCH 0/2] TPM derived keys

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Date: Tue, 14 May 2024 17:45:49 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Ignat Korchagin" <ignat@...udflare.com>
Cc: "James Bottomley" <James.Bottomley@...senpartnership.com>, "Mimi Zohar"
 <zohar@...ux.ibm.com>, "David Howells" <dhowells@...hat.com>, "Paul Moore"
 <paul@...l-moore.com>, "James Morris" <jmorris@...ei.org>,
 <serge@...lyn.com>, <linux-integrity@...r.kernel.org>,
 <keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <kernel-team@...udflare.com>
Subject: Re: [RFC PATCH 0/2] TPM derived keys

On Tue May 14, 2024 at 5:41 PM EEST, Ignat Korchagin wrote:
> On Tue, May 14, 2024 at 3:00 PM Jarkko Sakkinen <jarkko@...nel.org> wrote:
> >
> > On Tue May 14, 2024 at 4:11 PM EEST, Ignat Korchagin wrote:
> > > For example, a cheap NAS box with no internal storage (disks connected
> > > externally via USB). We want:
> > >   * disks to be encrypted and decryptable only by this NAS box
> >
> > So how this differs from LUKS2 style, which also systemd supports where
> > the encryption key is anchored to PCR's? If I took hard drive out of my
> > Linux box, I could not decrypt it in another machine because of this.
>
> It differs with the fact that the disk has a clearly identifiable
> LUKS2 header, which tells an adversary that this is a disk with some
> data that is encrypted. With derived keys and plain dm-crypt mode
> there is no LUKS header, so it is not possible to tell if it is an
> encrypted disk or a disk with just random data. Additionally, if I
> accidentally wipe the sector with the LUKS2 header - all my data is
> lost (because the data encryption key from the header is lost). With
> derived keys I can always decrypt at least some data, if the disk is
> available.

I figured most of this out myself and sent a follow-up but yeah thnaks
for confirming my toughts. I get this part now.

Follow-ups to my follow-up...

BR, Jarkko