Re: "WIP: Data at rest encryption" patch and, PostgreSQL 11-beta3

On Fri, Apr 5, 2019 at 11:22 AM Antonin Houska <ah(at)cybertec(dot)at> wrote:
> > Wouldn't Tom's proposal to use a stream cipher fix all this?
>
> Yes it would make the extra alignment unnecessary, but our solution tries to
> meet specific requirements of disk encryption. Stream cipher appears to be
> incompatible with these requirements:
>
> https://en.wikipedia.org/wiki/Disk_encryption_theory

Hmm. Well, I don't know what to do about that, but I think this patch
is going to be facing an uphill battle if the encrypted and
unencrypted WAL formats use different alignment.

> Currently we try to use the CBC-ESSIV mode. It's worth to mention that in this
> mode, if the page is encrypted twice and if the plain data in the encryption
> block N (i.e. block of 16 bytes) changes before the 2nd encryption, the
> encrypted data will only change in blocks >= N. So the problem of losing
> already flushed WAL records should not happen.

Well, this is just a question of alignment. If WAL records are at
least 16-byte aligned, then it should be fine. But I have a feeling
they may just be MAXALIGN'd.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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