Subject: Re: [TLS] Comments on draft-celi-wiggers-tls-authkem-00.txt

From: Thom Wiggers <[email-masked]>
Date: Tue, 26 Oct 2021 17:03:32 +0200

Dear list,

This email is in regards to draft-celi-wiggers-tls-authkem.

We’ve only made some minor fixes to the authentication-via-KEM proposal
that we submitted and presented at the last IETF meeting (IETF111) at the
working group. We did receive a few questions and comments on the draft
during that presentation and prior to it that we would like to address. We
had the impression that those questions were mainly focused on the
motivation: the reason for the draft's existence.

Because we found there is not really a lot of space for the motivation of
certain choices in the text of the draft itself, we instead wrote a
document that we call “AuthKEM abridged”. In it, we try to clearly point
out our motivations, design choices and provide an intuition of the
security model. You can find it at
https://claucece.github.io/draft-celi-wiggers-tls-authkem/docs/authkem-abridged.html.
We hope that you will find it useful and if there is anything we should add
or explain better, please let us know. We touch over questions such as:

   -

   Why consider KEMs for authentication?
   -

   Why now if post-quantum KEMs or post-quantum signatures aren’t
   standardized yet?
   -

   Discussion about the extra half-round trip that is added

Meanwhile, we’ve been putting some cycles towards the formal analysis of
the KEMTLS protocol (which should extend to the AuthKEM one) in Tamarin,
building on the existing TLS 1.3 model. There’s still a lot to be done, but
we hope to be able to back this draft proposal with some machine-checked
analysis in the future.

Noting here as there seemed to be some confusion around it: KEMs are not
compatible with non-interactive key exchange schemes such as
draft-ietf-tls-semistatic-dh. At the moment, CSIDH is the only post-quantum
scheme compatible with semistatic-DH-like protocols. CSIDH is probably not
practical for use in TLS due to it being very slow, and its security level
is still the subject of intense debate.

Cheers and have a nice IETF 112,

Thom Wiggers and Sofía Celi