Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data

From: Yael Tiomkin <yaelt@google.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Martin Ross <mross@pobox.com>,
	corbet@lwn.net, dhowells@redhat.com, jejb@linux.ibm.com,
	jmorris@namei.org, keyrings@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-integrity@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-security-module <linux-security-module@vger.kernel.org>,
	serge@hallyn.com, Mimi Zohar <zohar@linux.ibm.com>
Subject: Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data
Date: Wed, 26 Jan 2022 15:56:44 -0500	[thread overview]
Message-ID: <CAKoutNsaHNriobnsQ1X0Qfs=K+YN3JvfhTBnQqPL01AvjRm5EA@mail.gmail.com> (raw)
In-Reply-To: <YfFf8fvsDm8lQJgJ@iki.fi>

On Wed, Jan 26, 2022 at 9:51 AM Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> On Wed, Jan 26, 2022 at 04:47:22PM +0200, Jarkko Sakkinen wrote:
> > On Tue, Jan 18, 2022 at 01:26:05PM -0500, Martin Ross wrote:
> > > Hi Jarkko,
> > >
> > > I have been working with Yael on this project so I thought I might add
> > > a bit of background here around the use case that this series of
> > > patches is trying to address.
> > >
> > > At a high level we are trying to provide users of encryption that have
> > > key management hierarchies a better tradeoff between security and
> > > availability.  For available and performance reasons master keys often
> > > need to be released (or derived/wrapped keys created) outside of a KMS
> > > to clients (which may in turn further wrap those keys in a series of
> > > levels).  What we are trying to do is provide a mechanism where the
> > > wrapping/unwrapping of these keys is not dependent on a remote call at
> > > runtime.  e.g.  To unwrap a key if you are using AWS KMS or Google
> > > Service you need to make an RPC.  In practice to defend against
> > > availability or performance issues, designers end up building their
> > > own kms and effectively encrypting everything with a DEK.  The DEK
> > > encrypts same set as the master key thereby eliminating the security
> > > benefit of keeping the master key segregated in the first place.
>
> Mainly this part (would be enough to explain why it is there).
>
> BR, Jarkko

Hi Jarkko,

As for the commit message, WDYT about the following:

KEYS: encrypted: Instantiate key with user-provided decrypted data

For availability and performance reasons master keys often need to be
released outside of a KMS to clients. It would be beneficial to provide a
mechanism where the wrapping/unwrapping of DEKs is not dependent
on a remote call at runtime yet security is not (or only minimally) compromised.
Master keys could be securely stored in the Kernel and be used to wrap/unwrap
keys from userspace.

The encrypted.c class supports instantiation of encrypted keys with
either an already-encrypted key material, or by generating new key
material based on random numbers. This patch defines a new datablob
format: [<format>] <master-key name> <decrypted data length>
<decrypted data> that allows to inject and encrypt user-provided
decrypted data.

I want to make sure we're on the same page before publishing a new version.

Thanks,
Yael