> -----Original Message-----
> From: Emu <[email protected]> On Behalf Of Alan DeKok
> Sent: 12 September 2019 16:28
> To: John Mattsson <[email protected]>
> Cc: [email protected]; EMU WG <[email protected]>
> Subject: Re: [Emu] POST WGLC Comments draft-ietf-emu-eap-tls13
>
> On Sep 12, 2019, at 10:55 AM, John Mattsson
> <[email protected]> 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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