Re: [Unbearable] Comments on draft-campbell-tokbind-tls-term

[Piotr Sikora <[e-mail]>]

Hey Brian,

> I hope to discuss much of this stuff in more detail tomorrow from 9am-10am
> in Lugano during the ad hoc meeting I requested/announced on the list at
> https://www.ietf.org/mail-archive/web/unbearable/current/msg01338.html. Feel
> free to join the discussion, if you are still in Chicago and available.

I'll do my best to be there.

> The intended value of this approach is to keep the reverse proxy as light as
> possible.

But why? What's the gain of removing that from a proxy that already
terminates TLS?

Also, keep in mind that it's the proxy that negotiates Token Binding
key parameters using crypto algorithms at its disposal. It's not
unlikely that it would negotiate key parameters that backend server
doesn't support, leading to a scenario where Token Binding was
negotiated at the TLS layer, but backend server was unable to verify
Token Binding Message.

> The server as a logical entity must validate the Token Binding Message. But
> that doesn't mean the front end necessarily has to do it. The approach in
> this -00 document enables a back end component of the server as a whole to
> do the Token Binding Message validation. But the server as a logical entity
> is still validating the TB message.

I think it would be irresponsible for a proxy to pass not validated
Token Binding Message to the backend.

> That's true. But I think it is okay because establishing Token Binding
> between infrastructure components under the same operational control doesn't
> really add much value. Token Binding is good for the logical endpoints of
> the client and server in a connection.

Why do you assume that reverse proxy and backend servers are part of
the same organization? What about CDNs and Cloud Load Balancers? While
I cannot think of an obvious use case for Token Binding with those, I
don't think we should exclude it.

> Treating the different components of the server as a single logical entity
> with respect to Token Binding does allow LS between reverse proxy and
> backend server.

But it gets quite ugly, since backend server receives
"Sec-Token-Binding" HTTP header over a TLS connection that _didn't_
negotiate Token Binding extension. AFAIK, the core spec requires
bindings to be dropped in such case.

Best regards,
Piotr Sikora