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

Greetings,

* Bruce Momjian (bruce@momjian.us) wrote:
> On Mon, Jul  8, 2019 at 11:18:01AM -0400, Joe Conway wrote:
> > On 7/8/19 10:19 AM, Bruce Momjian wrote:
> > > When people are asking for multiple keys (not just for key rotation),
> > > they are asking to have multiple keys that can be supplied by users only
> > > when they need to access the data.  Yes, the keys are always in the
> > > datbase, but the feature request is that they are only unlocked when the
> > > user needs to access the data.  Obviously, that will not work for
> > > autovacuum when the encryption is at the block level.
> > 
> > > If the key is always unlocked, there is questionable security value of
> > > having multiple keys, beyond key rotation.
> > 
> > That is not true. Having multiple keys also allows you to reduce the
> > amount of data encrypted with a single key, which is desirable because:
> > 
> > 1. It makes cryptanalysis more difficult
> > 2. Puts less data at risk if someone gets "lucky" in doing brute force
> 
> What systems use multiple keys like that?  I know of no website that
> does that.  Your arguments seem hypothetical.  What is your goal here?

Not sure what the reference to 'website' is here, but one doesn't get
certificates for TLS/SSL usage that aren't time-bounded, and when it
comes to the actual on-the-wire encryption that's used, that's a
symmetric key that's generated on-the-fly for every connection.

Wouldn't the fact that they generate a different key for every
connection be a pretty clear indication that it's a good idea to use
multiple keys and not use the same key over and over..?

Of course, we can discuss if what websites do with over-the-wire
encryption is sensible to compare to what we want to do in PG for
data-at-rest, but then we shouldn't be talking about what websites do,
it'd make more sense to look at other data-at-rest encryption systems
and consider what they're doing.

Thanks,

Stephen