Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS)

Greetings,

* Bruce Momjian (bruce@momjian.us) wrote:
> On Tue, Jul  9, 2019 at 08:01:35AM -0400, Joe Conway wrote:
> > On 7/9/19 6:07 AM, Peter Eisentraut wrote:
> > > On 2019-07-08 18:09, Joe Conway wrote:
> > >> In my mind, and in practice to a
> > >> large extent, a postgres tablespace == a unique mount point.
> > > 
> > > But a critical difference is that in file systems, a separate mount
> > > point has its own journal.
> > 
> > While it would be ideal to have separate WAL, and even separate shared
> > buffer pools, per tablespace, I think that is too much complexity for
> > the first implementation and we could have a single separate key for all
> > WAL for now. 

I agree that all of that isn't necessary for an initial implementation,
I was rather trying to lay out how we could improve on this in the
future and why having the keying done at a tablespace level makes sense
initially because we can then potentially move forward with further
segregation to improve the situation.  I do believe it's also useful in
its own right, to be clear, just not as nice since a compromised backend
could still get access to data in shared buffers that it really
shouldn't be able to, even broadly, see.

> Agreed.  I have thought about this some more.  There is certainly value
> in layered security, so if something gets violated, it doesn't open the
> whole system.  However, I think the layering has to be done at the right
> levels, and I think you want levels that have clear boundaries, like IP
> filtering or monitoring.  Placing a boundary inside the database seems
> much too complex a level to be effective.  Using separate encrypted and
> unencrypted clusters and allowing the encrypted cluster to query the
> unencrypted clusters using FDWs does seem like good layering, though the
> FDW queries might leak information.

Using FDWs simply isn't a solution to this, for a few different reasons-
the first is that our solution to authentication for FDWs is to store
passwords in our catalog tables, but an FDW table also doesn't behave
like a regular table in many important cases.

> > The main thing I don't think we want is e.g. a 50TB
> > database with everything encrypted with a single key -- for the reasons
> > previously stated.
> 
> Yes, I think we need to research in which cases the nonce must be
> random, and how much key space the secret+nonce gives us.

Agreed on both.

Thanks,

Stephen