On Mon, Oct 14, 2019 at 3:42 PM Antonin Houska <ah@cybertec.at> wrote:
>
> Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> > On Wed, Oct 9, 2019 at 3:57 PM Antonin Houska <ah@cybertec.at> wrote:
> > >
> > > Moon, Insung <tsukiwamoon.pgsql@gmail.com> wrote:
> > >
> > > v04-0011-Make-buffile.c-aware-of-encryption.patch in [1] changes buffile.c so
> > > that data is read and written in 8kB blocks if encryption is enabled. In order
> > > to record the IV per block, the computation of the buffer position within the
> > > file would have to be adjusted somehow. I can check it soon but not in the
> > > next few days.
> >
> > As far as I read the patch the nonce consists of pid, counter and
> > block number where the counter is the number incremented each time of
> > creating a BufFile. Therefore it could happen to rewrite the buffer
> > data with the same nonce and key, which is bad.
>
> This patch was written before the requirement on non-repeating IV was raiesed,
> and it does not use the AES-CTR mode. I mentioned it here because it reads /
> writes data in 8kB blocks.
>
> > So I think we can have the rewrite counter of the block in the each 8k
> > block header. And then the nonce consists of block number within a
> > segment file (4 bytes), temp file counter (8 bytes), rewrite counter
> > (2 bytes) and CTR mode counter (2 bytes). And then if we have a
> > single-use encryption key per backend processes I guess we can
> > guarantee the uniqueness of the combination of key and nonce.
>
> Since the segment size is 1 GB, the segment cosists of 2^17 blocks, so 4 bytes
> will not be utilized.
>
> As for the "CTR mode counter", consider that it gets incremented once per 16
> bytes of input. So even if BLCKSZ is 32 kB, we need no more than 11 bits for
> this counter.
>
> If these two parts become smaller, we can perhaps increase the size of the
> "rewrite counter".
Yeah I designed it to make implementation easier but we can increase
the size of the rewrite counter to 3 bytes while the block number uses
3 bytes.
Regards,
--
Masahiko Sawada