Re: Internal key management system

On Thu, Mar 19, 2020 at 11:42:36PM +0900, Masahiko Sawada wrote:
> On Thu, 19 Mar 2020 at 22:00, Bruce Momjian <bruce@momjian.us> wrote:
> >
> > On Thu, Mar 19, 2020 at 06:32:57PM +0900, Masahiko Sawada wrote:
> > > On Thu, 19 Mar 2020 at 15:59, Masahiko Sawada
> > > > I understand that your idea is to include fixed length string to the
> > > > 256 bit key in order to separate key space. But if we do that, I think
> > > > that the key strength would actually be the same as the strength of
> > > > weaker key length, depending on how we have the fixed string. I think
> > > > if we want to have multiple key spaces, we need to derive keys from the
> > > > master key using KDF.
> > >
> > > Or we can simply generate a different encryption key for block
> > > encryption. Therefore we will end up with having two encryption keys
> > > inside database. Maybe we can discuss this after the key manager has
> > > been introduced.
> >
> > I know Sehrope liked derived keys so let's get his feedback on this.  We
> > might want to have two keys anyway for key rotation purposes.
> >
>
> Agreed. Maybe we can derive a key for the use of wrap and unwrap SQL
> interface by like HKDF(MK, 'USER_KEY:') or HKDF(KM, 'USER_KEY:' ||
> system_identifier).

Well, the issue is if the user can control the user key, there is might be
a way to make the user key do nothing.