Re: [openpgp] AEAD Chunk Size

"Neal H. Walfield" <neal@walfield.org> Fri, 29 March 2019 13:20 UTC

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Date: Fri, 29 Mar 2019 14:20:21 +0100
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From: "Neal H. Walfield" <neal@walfield.org>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
Cc: "openpgp@ietf.org" <openpgp@ietf.org>, Justus Winter <justuswinter@gmail.com>, Jon Callas <joncallas@icloud.com>, Jon Callas <joncallas=40icloud.com@dmarc.ietf.org>
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Subject: Re: [openpgp] AEAD Chunk Size
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On Fri, 29 Mar 2019 13:53:42 +0100,
Peter Gutmann wrote:
> 
> Neal H. Walfield <neal@walfield.org> writes:
> 
> >I'm having trouble imagining why a larger chunk size would ever be better in
> >either of these cases.
> >
> >  - File encryption: smaller chunk size means finding errors faster
> 
> See my followup messages, for data at rest you probably don't care about
> errors at all, and if you really do then having the report at the whole-file
> level is fine.  What's the benefit gained from knowing that the 64kB block at
> offset xyz is corrupt?

But what is the cost?  I would say there is basically none.  So it
makes no sense to me to optimize for this case.  It's irrelevant.

So, why make the important case (when you actually do want to stream)
more complicated?

> As I mentioned earlier, we really need some data on real-world use cases
> rather than hypothesising problematic corner cases that will rarely, if ever,
> occur.

Efail occured.  Why is that not enough?