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

On Fri, Aug 23, 2019 at 10:35:17AM -0400, Stephen Frost wrote:
> > Agreed.  The features of other databases are a clear source for what we
> > should consider and run through the useful/reasonable filter.
> 
> Following on from that- when other databases don't have something that
> we're thinking about implementing, maybe we should be contemplating if
> it really makes sense as a requirement for us.

Yes, that's a good point.

> Specifically in this case- I went back and tried to figure out what
> other database systems have an "encrypt EVERYTHING" option.  I didn't
> have much luck finding one though.  So I think we need to ask ourselves-
> the "check box" that we're trying to check off with TDE, do the other
> database system check that box?  If so, then it looks like the "check
> box" isn't actually "encrypt EVERYTHING", it's more along the lines of
> "make sure all regular user data is encrypted automatically" or some
> such, and that's a very different requirement, which seems to be
> answered by the other systems by having a KMS + tablespace/database
> level encryption.  We certainly shouldn't be putting a lot of effort
> into building something that is either overkill or won't be interesting
> to users due to limitations like "have to take the entire cluster
> offline to re-key it".

Well, I think they might do that to reduce encryption overhead.  I think
tests have shown that is not an issue, but we will need to test further.
I am not sure of the downside of encrypting everything, since it leaks
the least information and has a minimal user API and code impact.  What
is the value of encrypting only the user rows?  Better key control?

> Now, that KMS has to be encrypted using a master key, of course, and we
> have to make sure that it is able to survive across a crash, and it'd
> sure be nice if it was indexed.  One option for such a KMS would be
> something entirely external (which could potentially just be another PG
> database or something) but it'd be nice if we had something built-in.
> We might also want it to be replicated (or maybe we don't, as was
> discussed on the call, to allow for a replica to use an independent set
> of keys- of course that leads to issues with pg_rewind and such though).

I think the replica could use a different key for the relations, but the
WAL key would have to be the same.

> Anything built-in does seem like it'd be a fair bit of work to get it to
> address those requirements, but that does seem to be what the other
> database systems have done.  Unfortunately, their documentation doesn't
> seem to really say exactly what they've done to address that.

I do like they pgcrypto key support to be per-database so pg_dump will
dump the data encrypted, and with its locked keys.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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