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

On Sat, 2 Nov 2019 at 21:33, Antonin Houska <ah(at)cybertec(dot)at> wrote:

> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> > On Tue, Aug 6, 2019 at 10:36 AM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> > Seems reasonable (not that I am an encryption expert).
> >
> > > For WAL, we effectively create a 16MB bitstream, though we can create
> it
> > > in parts as needed. (Creating it in parts is easier in CTR mode.) The
> > > nonce is the segment number, but each 16-byte chunk uses a different
> > > counter. Therefore, even if you are encrypting the same 8k page
> several
> > > times in the WAL, the 8k page would be different because of the LSN
> (and
> > > other changes), and the bitstream you encrypt/XOR it with would be
> > > different because the counter would be different for that offset in the
> > > WAL.
> >
> > But, if you encrypt the same WAL page several times, the LSN won't
> > change, because a WAL page doesn't have an LSN on it, and if it did,
> > it wouldn't be changing, because an LSN is just a position within the
> > WAL stream, so any given byte on any given WAL page always has the
> > same LSN, whatever it is.
> >
> > And if the counter value changed on re-encryption, I don't see how
> > we'd know what counter value to use when decrypting. There's no way
> > for the code that is decrypting to know how many times the page got
> > rewritten as it was being filled.
> >
> > Please correct me if I'm being stupid here.
>
> In my implementation (I haven't checked whether Masahiko Sawada changed
> this
> in his patch) I avoided repeated encryption of different data using the
> same
> key+IV by omitting the unused part of the WAL page from encryption. Already
> written records can be encrypted repeatedly because they do not change.
>
>
Yeah my patch doesn't change this part. IV for WAL encryption consists of
the segment file number, page offset within segment file and the counter
for CTR cipher mode.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/>
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