[OAUTH-WG] Questions about OAuth and DTLS

[Ludwig Seitz <[e-mail]>]

Hello list(s),

in the process of updating our draft [1] (mainly in reaction to the 
reviewer's comments) I've come up with a question I'd like to put to the 
list (crossposting to OAuth as well, they might have considered that 
already):

Assuming we are using (D)TLS to secure the connection between C and RS, 
assuming further that we are using proof-of-possession tokens [2], i.e. 
tokens linked to a key, of which the client needs to prove possession in 
order for the RS to accept the token.

Do we need to support cases, where the type of key used with DTLS does 
not match the type of key in the PoP-token?

Example:

The client uses its raw public key as proof of possession, but the DTLS 
connection C - RS is secured with a pre-shared symmetric key.

Is that a realistic use case?

It would simplify the DTLS cases a lot, if I could just require the 
token and the DTLS session to use the same type of key. For starters we 
could use DTLS handshake to perform the proof-of-possession.

Would there be any security issues with using the PoP key in the DTLS 
handshake?

I'm thinking of using pre-shared symmetric PoP keys as PSK as in RFC4279 
and raw public PoP keys as client-authentication key as in
RFC7250.


Regards,

Ludwig

[1] https://datatracker.ietf.org/doc/draft-ietf-ace-oauth-authz/
[2] https://tools.ietf.org/html/draft-ietf-oauth-pop-key-distribution-02


-- 
Ludwig Seitz, PhD
SICS Swedish ICT AB
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