Re: [Emu] POST WGLC Comments draft-ietf-emu-eap-tls13

["Owen Friel (ofriel)" <[e-mail]>]

> -----Original Message-----
> From: Emu <[e-mail]> On Behalf Of Alan DeKok
> Sent: 12 September 2019 16:28
> To: John Mattsson <[e-mail]>
> Cc: [e-mail]; EMU WG <[e-mail]>
> Subject: Re: [Emu] POST WGLC Comments draft-ietf-emu-eap-tls13
> 
> On Sep 12, 2019, at 10:55 AM, John Mattsson
> <[e-mail]> wrote:
> >
> >>     See Section 2.1.2.  TLS 1.3 uses PSK for resumption.  As a result, we
> *cannot* use PSK for >authentication in EAP-TLS.
> >
> > I don't understand why this could not be done. My view is that allowing PSK
> authentication would be quite easy.
> 
>   How would systems tell the difference between "raw" PSK and
> "resumption" PSK?
> 
>   When allowing resumption, the server has sent a PSK identity in a
> NewSessionTicket message.  The client caches this and re-uses this.  But the
> client signals that it is performing resumption via the act of using PSK.  There's
> nothing else.
> 
>   Which means that if PSK was allowed, the server can't look at the packets to
> distinguish resumption from "raw" PSK.  Instead, the server has to look at it's
> resumption cache which may be in a DB.

The server can use the PskIdentity in the PreSharedKeyExtension to differentiate between an offline PSK used for authentication vs. a PSK established via NewSessionTicket.

There should be no problem here, and the statement

" Pre-Shared Key (PSK) authentication SHALL NOT be used except
   for resumption. "

should be updated to clarify.

> 
> >>> While there is the EAP-PSK method, I would much rather use EAP-TLS
> with PSK because it >provides identity protection and perfect forward
> secrecy, unlike EAP-PSK.
> >>
> >>     Use EAP-PWD for that.
> >
> > Standardizing EAP-TLS should only be done if it has some significant
> advantages over EAP-PWD, and there are people wanting to implement and
> use it. 3GPP is e.g. adding  identity protection and perfect forward secrecy to
> EAP-AKA instead.
> 
>   I would prefer to forbid PSK in EAP-TLS.
> 
>   Alan DeKok.
> 
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