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

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Message-ID: <YfzHb9K5wZciy5um@iki.fi>
Date:   Fri, 4 Feb 2022 08:27:59 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Yael Tiomkin <yaelt@...gle.com>
Cc:     Martin Ross <mross@...ox.com>, corbet@....net, dhowells@...hat.com,
        jejb@...ux.ibm.com, jmorris@...ei.org, keyrings@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module <linux-security-module@...r.kernel.org>,
        serge@...lyn.com, Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided
 decrypted data

On Wed, Jan 26, 2022 at 03:56:44PM -0500, Yael Tiomkin wrote:
> On Wed, Jan 26, 2022 at 9:51 AM Jarkko Sakkinen <jarkko@...nel.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

It looks really good.

/Jarkko