Date: Tue, 13 Jun 2017 13:01:32 -0400
From: Stephen Frost <sfrost@snowman.net>
To: Bruce Momjian <bruce@momjian.us>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	Ants Aasma <ants.aasma@eesti.ee>,
	Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: WIP: Data at rest encryption
Message-ID: <20170613170132.GH3151@tamriel.snowman.net>
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Bruce,

* Bruce Momjian (bruce@momjian.us) wrote:
> On Tue, Jun 13, 2017 at 12:23:01PM -0400, Stephen Frost wrote:
> > > Of course, if the
> > > key stored in the database is visible to someone using the operating
> > > system, we really haven't added much/any security --- I guess my point
> > > is that the OS easily can hide the key from the database, but the
> > > database can't easily hide the key from the operating system.
> >=20
> > This is correct- the key must be available to the PostgreSQL process
> > and therefore someone with privileged access to the OS would be able to
> > retrieve the key, but that's also true of filesystem encryption.
> >=20
> > Basically, if the server is doing the encryption and you have the
> > ability to read all memory on the server then you can get the key.  Of
> > course, if you can read all memory then you can just look at shared
> > buffers and you don't really need to bother yourself with the key or
> > the encryption, and it doesn't make any difference if you're encrypting
> > in the database or in the filesystem.  That attack vector is not one
> > which this is intending to address.
>=20
> My point is that if you have the key accessible to the database server,
> both the database server and OS have access to it.  If you store it in
> the OS, only the OS has access to it.

I understand that, but that's not a particularly interesting distinction
as the database server must, necessairly, have access to the data in the
database.

> > > I have to admit we tend to avoid heavy-API solutions that are designed
> > > just to work around deployment challenges.  Commercial databases are
> > > fine in doing that, but it leads to very complex products.
> >=20
> > I'm not following what you mean here.
>=20
> By adding all-cluster encryption, we are re-implementing something the
> OS does just fine, in most cases.  We are going to have API overhead to
> do it in the database, and historically we have avoided that.

We do try to avoid the overhead of additional function calls, in places
where it matters.  As this is all about reading and writing data, the
overhead for the additional check to see if we're doing encryption or
not is unlikely to be interesting.

> > > One cool idea I have is using public encryption to store the encrypti=
on
> > > key by users who don't know the decryption key, e.g. RSA.  It would b=
e a
> > > write-only encryption option.  Not sure how useful that is, but it
> > > easily possible, and doesn't require us to keep the _encryption_ key
> > > secret, just the decryption one.
> >=20
> > The downside here is that asymmetric encryption is much more expensive
> > than symmetric encryption and that probably makes it a non-starter.  I
> > do think we'll want to support multiple encryption methods and perhaps
> > we can have an option where asymmetric encryption is used, but that's
> > not what I expect will be typically used.
>=20
> Well, usually the symetric key is stored using RSA and a symetric
> cipher is used to encrypt/decrypt the data.  I was thinking of a case
> where you encrypt a row using a symetric key, then store RSA-encrypted
> versions of the symetric key encrypted that only specific users could
> decrypt and get the key to decrypt the data.

This goes back to key management and I agree that it often makes sense
to use RSA or similar to encrypt the symmetric key, and this approach
would allow the user to do so.  That doesn't actually give you a
"write-only" encryption option though, since any user who can decrypt
the symmetric key is able to use the symmetric key for both encryption
and decryption, and someone who only has access to the RSA encryption
key can't actually encrypt the data since they can't access the
symmetric key.

Thanks!

Stephen

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