On Wed, Jul 31, 2019 at 04:58:49PM +0900, Masahiko Sawada wrote:
> On Wed, Jul 31, 2019 at 3:29 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> >
> > For WAL encryption, before flushing WAL we encrypt whole 8k WAL page
> > and then write only the encrypted data of the new WAL record using
> > pg_pwrite() rather than write whole encrypted page. So each time we
> > encrypt 8k WAL page we end up with encrypting different data with the
> > same key+nonce but since we don't write to the disk other than space
> > where we actually wrote WAL records it's not a problem. Is that right?
>
> Hmm that's incorrect. We always write an entire 8k WAL page even if we
> write a few WAl records into a page. It's bad because we encrypt
> different pages with the same key+IV, but we cannot change IV for each
> WAL writes as we end up with changing also
> already-flushed-WAL-records. So we might need to change the WAL write
> so that it write only WAL records we actually wrote.
Uh, I don't understand. We use the LSN to write the 8k page, and we use
a different nonce scheme for the WAL. The LSN changes each time the
page is modified. The 8k page in the WAL is encrypted just like the rest
of the WAL.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
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