Re: [openpgp] Message padding in OpenPGP

[Daniel Kahn Gillmor <[e-mail]>]

On Fri 2019-09-27 01:41:55 +0100, Stephen Farrell wrote:
> On 27/09/2019 00:12, Daniel Kahn Gillmor wrote:
>> The ideal place to apply padding is at the application layer
>
> That's not clear to me. It may be true or it may not.
> (Perhaps that's just me being suspicious of terms like
> "ideal" though:-)
>
> As a (possible) counter-example, application layer code
> is perhaps not (yet) well positioned to deal with padding
> of both DNS and application layer traffic, all at once.

i agree with your concerns, Stephen, though maybe not the specific
wording.  :) I mean, DNS *is* application layer traffic, right?

But you're right, as we move toward multiplexed application layer
protocols within a standard encryption layer (e.g. DNS over HTTPS on the
same endpoint that is serving "normal" HTTPS traffic as well), the
padding designs needed to mitigate size-based traffic analysis require
some sort of systemic reasoning about the combination of the application
layers involved.

So maybe the better way to say this is that padding policy should be
designed and set based on the encryption layer's properties (and padding
capabilities) and the union of all the traffic that is expected to be
encapsulated by that layer.

       --dkg