Greetings,
* Ryan Lambert (ryan@rustprooflabs.com) wrote:
> > What I think Tomas is getting at here is that we don't write a page only
> > once.
>
> > A nonce of tableoid+pagenum will only be unique the first time we write
> > out that page. Seems unlikely that we're only going to be writing these
> > pages once though- what we need is a nonce that's unique for *every
> > write* of the 8k page, isn't it? As every write of the page is going to
> > be encrypting something new.
>
> > With sufficient randomness, we can at least be more likely to have a
> > unique nonce for each 8K write. Including the LSN seems like it'd be a
> > possible alternative.
>
> Agreed. I know little of the inner details about the LSN but what I read
> in [1] sounds encouraging in addition to tableoid + pagenum.
>
> [1] https://www.postgresql.org/docs/current/datatype-pg-lsn.html
Yes, but it's still something that we'd have to store somewhere- the
actual LSN of the page is going to be in the 8K block.
Unless we decide that we can pull the LSN *out* of the 8K block and
store it unencrypted, and then store the *rest* of the block
encrypted... That might also allow things like backup software to work
on these encrypted data files for page-level backups without needing
access to the key and that'd be pretty neat.
Of course, as with anything, the more data you expose, the higher the
overall risk that someone can figure out some meaning from it. Still,
if the idea was that we'd use the LSN in this way, then it'd need to be
stored unencrypted regardless...
Thanks,
Stephen
