Re: [Trans] AD Review: draft-ietf-trans-gossip-04

[Tom Ritter <[e-mail]>]

I'm going to cherry pick a single thing to ask about before we try to
address everything.

On 16 October 2017 at 16:41, Richard Barnes <[e-mail]> wrote:
> As far as SCT feedback, note that the
> privacy issues here (around server tracking) are unnecessary to meet the
> need here -- only the auditor needs to see the SCTs, not the server.  If you
> had a way for clients to encrypt SCTs to specific auditors, you would no
> longer have an issue with server tracking.
>
> ...
>
> 2. Add a through-encryption modality for SCT feedback

This is an interesting idea. However, I'm worried it's infeasible
because of abuse concerns.

A client needs to pass the (encrypted) SCT through a third party to
prevent the auditor from knowing who visited a particular site. But
the third party has no assurance that the payload is a valid SCT and
not garbage, so there's DOS concerns. Even if we waved the crypto
magic wand (I would be surprised if there wasn't a crypto primitive
for this problem, I didn't search), the third party is essentially
opening itself to being given every SCT in the log.

Attempts at putting a cap on the data received open the doors to
flooding attacks that would fill up any cap before the client can
provide its data.

Am I thinking about the design the same way you were? Do you think
this is a problem, and if so, know how you'd work around it?

-tom