Re: "WIP: Data at rest encryption" patch and, PostgreSQL 11-beta3 - Mailing list pgsql-hackers

Bruce Momjian <bruce@momjian.us> wrote:

> On Mon, Jun  3, 2019 at 12:04:54PM -0400, Robert Haas wrote:
> > 
> > What I'm talking about here is that it also has to be reasonably
> > possible to write an encryption key command that does something
> > useful.  I don't have a really clear vision for how that's going to
> > work.  Nobody wants the server, which is probably being launched by
> > pg_ctl or systemd or both, to prompt using its own stdin/stderr, but
> > the we need to think about how the prompting is actually going to
> > work.  One idea is to do it via the FEBE protocol: connect to the
> > server using libpq, issue a new command that causes the server to
> > enter COPY mode, and then send the encryption key as COPY data.
> > However, that idea doesn't really work, because we've got to be able
> > to get the key before we run recovery or reach consistency, so the
> > server won't be listening for connections at that point.  Also, we've
> > got to have a way for this to work in single-user mode, which also
> > can't listen for connections.  It's probably all fine if your
> > encryption key command is something like 'curl
> > https://my.secret.keyserver.me/sekcret.key' because then there's an
> > external server which you can just go access - but I don't quite
> > understand how you'd do interactive prompting from here.  Sorry to get
> > hung up on what may seem like a minor point, but I think it's actually
> > fairly fundamental: we've got to have a clear vision of how end-users
> > will really be able to make use of this.
> 
> pgcryptoey has an example of prompting from /dev/tty:
> 
>     http://momjian.us/download/pgcryptokey/
> 
> Look at pgcryptokey_default.sample.

It's a nice exercise of shell features but does not seem to be easily
portable, and it has some other restrictions. One is mentioned in a comment:

# Use 'pg_ctl -s' so starting dots do not interfere with password entry

I think that besides the dots, log messages can also be disturbing if logging
collector is not enabled. Another corner case might be there when user runs
pg_ctl with --no-wait option and wants to do run some other command
immediately.

I'm thinking how to teach postmaster to accept FEBE protocol connections
temporarily, just to receive the key. The user applications like pg_ctl,
initdb or pg_upgrade would retrieve the key / password from the DBA, then
start postmaster and send it the key.

Perhaps the message format should be a bit generic so that extensions like
this can use it to receive their keys too.

(The idea of an unix socket or named pipe I proposed upthread is not good
because it's harder to implement in a portable way.)

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com