Horton

Re: storing an explicit nonce

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Bruce Momjian <bruce@momjian.us>
Cc: Stephen Frost <sfrost@snowman.net>, Robert Haas <robertmhaas@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Tom Kincaid <tomjohnkincaid@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL Development <pgsql-hackers@postgresql.org>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Date: 2021-05-27T16:13:07Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Rethink method for assigning OIDs to the template0 and postgres DBs.

  2. pg_upgrade: Preserve database OIDs.

  3. pg_upgrade: Preserve relfilenodes and tablespace OIDs.

  4. Fix for new Boolean node

  5. Improve error handling of HMAC computations

  6. Add macro RelationIsPermanent() to report relation permanence

  7. Enhance nbtree index tuple deletion.

Hi,

On 2021-05-27 12:01:16 -0400, Bruce Momjian wrote:
> On Thu, May 27, 2021 at 08:34:51AM -0700, Andres Freund wrote:
> > On Thu, May 27, 2021, at 08:10, Bruce Momjian wrote:
> > > On Wed, May 26, 2021 at 05:11:24PM -0700, Andres Freund wrote:
> > > > On 2021-05-25 17:12:05 -0400, Bruce Momjian wrote:
> > > > > If we used a block cipher instead of a streaming one (CTR), this might
> > > > > not work because the earlier blocks can be based in the output of
> > > > > later blocks.
> > > > 
> > > > What made us choose CTR for WAL & data file encryption? I checked the
> > > > README in the patchset and the wiki page, and neither seem to discuss
> > > > that.
> > > > 
> > > > The dangers around nonce reuse, the space overhead of storing the nonce,
> > > > the fact that single bit changes in the encrypted data don't propagate
> > > > seem not great?  Why aren't we using something like XTS? It has obvious
> > > > issues as wel, but CTR's weaknesses seem at least as great. And if we
> > > > want a MAC, then we don't want CTR either.
> > > 
> > > We chose CTR because it was fast, and we could use the same method for
> > > WAL, which needs a streaming, not block, cipher.
> > 
> > The WAL is block oriented too.
> 
> Well, AES block mode only does 16-byte blocks, as far as I know, and I
> assume WAL is more granular than that.

WAL is 8kB blocks by default. We only ever write it out with at least
that granularity.


> Also, you need to know the bytes _before_ the WAL do write a new
> 16-byte block, so it seems overly complex for our usage too.

See the XTS reference. Yes, it needs the previous 16bytes, but only
within the 8kB page.

Greetings,

Andres Freund