Subject: Re: [Trans] WGLC comments on draft-ietf-trans-6962-bis-24

From: Andrew Ayer <[email-masked]>
Date: Thu, 2 Feb 2017 14:29:44 -0800

On Mon, 16 Jan 2017 17:23:27 -0500
Richard Barnes <[email-masked]> wrote:

> Clearly in order to be efficient, multiple certs must chain back up
> to the same STH; this is also a privacy requirement because otherwise
> retrieving a given STH leaks which certificate you are verifying.
> For similar privacy reasons, clients need to proactively download and
> validate every STH they might encounter, to avoid making queries for
> STHs (which leak browsing history). 

Hi Richard,

As you point out, the privacy concern with fetching an STH's consistency
proof can be addressed by requiring that multiple certificates "chain
back" to any given STH.  Why then is it necessary for clients to
proactively download and validate every STH?  Could clients not fetch
consistency proofs on demand the first time they see an STH (and then
cache the STH so they don't have to fetch the proof again)?  If so,
that would eliminate your concern with clients having to download 4MB
a month.

Regards,
Andrew