Subject: [TLS] TLS False Start

From: Hannes Tschofenig <[email-masked]>
Date: Fri, 28 Nov 2014 20:36:23 +0100

Hi Bodo,
Hi all,

I read through <draft-bmoeller-tls-falsestart-01>. The document is well
written but I have a few questions.

There are various conditions specified when the TLS False Start
mechanism is fit for use. I believe there is room for improvement
regarding the way how these conditions are formulated. At the moment,
they are more written as examples rather than a list of security
properties.

I am worried that many of the provided examples will be outdated fairly
soon as algorithms continuously evolve.

For example, you say that AES-GCM is OK. You cite the key length and I
guess you are also including the current state of security analysis of
the given cipher in that consideration. Would it be OK to use AES-CCM
with False Start? I think so.

Then, you list a couple of key exchange methods (DHE_RSA, ECDHE_RSA,
DHE_DSS, ECDHE_ECDSA), which you consider being fit for TLS False Start.
You indicate that an ephemeral DH exchange is need and I was wondering
why this is the case? Why isn't a "normal" DH not acceptable?

Would a ciphersuite like TLS_PSK_WITH_AES_128_CCM_8 be acceptable since
it does not use a public key based ciphersuite and it also does not use
an ephemeral Diffie-Hellman exchange.

Finally, you list "client certificate types". As someone who is
interested in the PSK case I am wondering whether you would consider PSK
ciphersuites as acceptable as well. With the indicated criteria it is a
bit hard to tell.

Ciao
Hannes