Re: [TLS] Encrypting record headers: practical for TLS 1.3 after all?

[Eric Mill <[e-mail]>]

On Wed, Dec 2, 2015 at 7:52 PM, Jacob Appelbaum <[e-mail]> wrote:

> On 12/2/15, Salz, Rich <[e-mail]> wrote:
> >> it seems blindingly obvious to me that we want it
> >
> > Few things, particularly in the security arena, are blindingly obvious.
> If
> > it actually provides no true protection, then it's just as bad as the
> > security theater in US airports.
>
> It provides protection. Specifically it provides confidentially.
>
> It doesn't solve the fact that the DNS is a privacy violating
> nightmare. It doesn't change the fact that the NSA breaks the rules.
>

And what Don and Rich's analysis is trying to isolate is how much real
protection you get from that level of confidentiality, so that a decision
that weighs all available factors can be made, including the complexity
cost.

It's not just a collective action problem because DNS isn't encrypted too.
Their analysis also looks at what you get when both are encrypted. And
regardless of DNS being encrypted, rainbow-table style reverse lookups of
IP to DNS name are always possible. That doesn't mean encrypted SNI isn't
worth it -- it clearly provides a security attribute (confidentiality) to
an important piece of information.

But it's not enough to drive ahead and say that some attribute outweighs
every other consideration. For example, HSTS' persistence of memory can be
abused as a tracking device:

http://zyan.scripts.mit.edu/sniffly/

And this was known at the time the spec was finalized:

https://tools.ietf.org/html/rfc6797#section-14.9

But HSTS creates security benefits that are well worth the cost of that
tracking potential (which can also be mitigated through preloading). There
are a lot of browsers and communities which use and advocate for HSTS that
might generally balk at creating tracking devices.

I'm not advocating a strong stance on whether encrypted SNI is worth
pursuing, or whether TLS record headers should be encrypted in TLS 1.3. But
it's useful to keep the debate framed in its full context, rather than
narrowing it to a black-and-white discussion over whether a generally good
attribute is good or not.

-- Eric