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

On Fri, Jul 5, 2019 at 04:10:04PM -0400, Bruce Momjian wrote:
> On Fri, Jul 5, 2019 at 03:46:28PM -0400, Alvaro Herrera wrote:
> > On 2019-Jul-05, Bruce Momjian wrote:
> >
> > > What people really want with more-granular-than-cluster encryption is
> > > the ability to supply their passphrase key _when_ they want to access
> > > their data, and then leave and be sure their data is secure from
> > > decryption. That will not be possible since the WAL will be encrypted
> > > and any replay of it will need their passphrase key to unlock it, or the
> > > entire system will be unrecoverable.
> >
> > I'm not sure I understand why WAL replay needs the passphrase to work.
> > Why isn't the data saved in WAL already encrypted, which can be applied
> > as raw bytes to each data block, without needing to decrypt anything?
> > Only if somebody wants to interpret the bytes they need the passphrase,
> > no?
>
> Uh, well, you have the WAL record, and you want to write it to an 8k
> page. You have to read the 8k page from disk into shared buffers, and
> you have to decrypt the 8k page to do that, right? We aren't going to
> store 8k pages encrypted in shared buffers, right?
>
> If you did want to do that, or wanted to write them to disk without
> decrypting the 8k page, it still would not work since AES is a 16-byte
> encryption cipher. I don't think we can break 8k pages up into 16-byte
> chunks and be sure we can just place data into those 16-byte boundaries.

I am not sure I was clear in describing this. If you want to copy data
directly from WAL to the 8k pages, you have to use either block mode or
streaming mode for both 8k pages and WAL. If you use block mode, then
changing any data on the pages will change all encrypted storage in the
same pages after the change, and computing WAL will require 16-byte
boundries. If you use streaming mode, you have to compute the proper
stream at the point in the 8k pages where you are changing the row. My
point is that in neither case can you just encrypt for the row for WAL
and assume it can be placed in an 8k pages. Neither option seems
desirable.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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