Received-SPF: pass (google.com: domain of linux-kernel+bounces-178856-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
Mime-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=UTF-8
Date: Tue, 14 May 2024 18:26:14 +0300
Message-Id: <D19H0UVF3R0O.3N4GLZWFRZ2DO@kernel.org>
Cc: "James Bottomley" <James.Bottomley@hansenpartnership.com>, "Mimi Zohar"
 <zohar@linux.ibm.com>, "David Howells" <dhowells@redhat.com>, "Paul Moore"
 <paul@paul-moore.com>, "James Morris" <jmorris@namei.org>,
 <serge@hallyn.com>, <linux-integrity@vger.kernel.org>,
 <keyrings@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
 <kernel-team@cloudflare.com>
Subject: Re: [RFC PATCH 0/2] TPM derived keys
From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Jarkko Sakkinen" <jarkko@kernel.org>, "Ignat Korchagin"
 <ignat@cloudflare.com>
References: <20240503221634.44274-1-ignat@cloudflare.com>
 <CALrw=nGhgRrhJ5mWWC6sV2WYWoijvD9WgFzMfOe6mHmqnza-Hw@mail.gmail.com>
 <D18XXJ373C2V.2M6AOMKD1B89W@kernel.org>
 <CALrw=nHGLN=dn3fbyAcXsBufw0tAWUT1PKVHDK5RZkHcdd3CUw@mail.gmail.com>
 <D19CUF0H9Q3S.3L5Y5S9553S5@kernel.org>
 <CALrw=nEZ07U9VhbGsnpchOYw1icUZCnuoHHXkJLzhFqSPe9_fQ@mail.gmail.com>
 <D19F74M6B8UC.2VEOOZHGOS87V@kernel.org>
 <D19FUGDA2CUO.16EF7U9ZEZ4SD@kernel.org>
 <D19GWXHYP2VC.1OY7BOW5LNXVF@kernel.org>
In-Reply-To: <D19GWXHYP2VC.1OY7BOW5LNXVF@kernel.org>

On Tue May 14, 2024 at 6:21 PM EEST, Jarkko Sakkinen wrote:
> On Tue May 14, 2024 at 5:30 PM EEST, Jarkko Sakkinen wrote:
> > On Tue May 14, 2024 at 5:00 PM EEST, Jarkko Sakkinen 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 connec=
ted
> > > > 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 whe=
re
> > > 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.
> >
> > Maybe you could replace the real LUKS2 header with a dummy LUKS2
> > header, which would need to be able the describe "do not use this" and
> > e.g. SHA256 of the actual header. And then treat the looked up header a=
s
> > the header when the drive is mounted.
> >
> > LUKS2 would also need to be able to have pre-defined (e.g. kernel
> > command-line or bootconfig) small internal storage, which would be
> > also encrypted with TPM's PRCs containing an array of LUKS2 header
> > and then look up that with SHA256 as the key.
> >
> > Without knowing LUKS2 implementation to me these do not sound reaching
> > the impossible engineer problems so maybe this would be worth of
> > investigating...
>
> Or why you could not just encrypt the whole header with another key
> that is only in that device? Then it would appear as random full
> length.
>
> I.e. unsealing
>
> 1. Decrypt LUKS2 header with TPM2 key
> 2. Use the new resulting header as it was in the place of encrypted
>    stored to the external drive.
> 3. Decrypt key from the LUK2S header etc.

Maybe something like:

1. Asymmetric for LUKS2 (just like it is)
2. Additional symmetric key, which is created as non-migratable and stored
   to the TPM2 chip. This deciphers the header, i.e. takes the random
   away.

BR, Jarkko