Hi Jorge,
For Microsoft supported protocol suite PEAP/TTLS/TEAP - are you planning to
find the common method of TLS 1.3 support for all three or you just want to
release TLS 1.3 support at the same time for all three?
For TEAP errata 5770:
Technically TEAP RFC suggests the implicit method of taking the correct
IMSK[j] and all the subsequent keys after each inner method via negotiation
taking place in Crypto-Binding TLV exchange.
Let's say we are on the inner method number j that supports both MSK and
EMSK and we are server which implementation generates both MSK and EMSK for
this inner method. We generated keys according to the rules below - two
sets, for IMSK[j] derived from inner method EMSK and for IMSK[j] equal to
inner method MSK. Because we don't know whether client implementation
supports both MSK and EMSK.
S-IMCK[0] = session_key_seed
For j = 1 to n-1 do
IMCK[j] = TLS-PRF(S-IMCK[j-1], "Inner Methods Compound Keys",
IMSK[j], 60)
S-IMCK[j] = first 40 octets of IMCK[j]
CMK[j] = last 20 octets of IMCK[j]
So we have two CMK[j] and we create Crypto-Binding TLV with both Compound
MAC for MSK and EMSK. The client sends Crypto-Binding TLV in response and
we can understand from it whether it supports EMSK for this inner method or
not. And here we can decide which version of IMCK[j] to take for this inner
method - derived from EMSK or MSK. This is just not explicitly specified in
the RFC.
Could this method work? Should we make it more clearly specified? Or should
we change the protocol to arrive explicitly to the understanding which type
(MSK/EMSK) of IMSK[j] to use?
Thanks
Oleg
On Wed, Apr 8, 2020 at 12:09 AM Jorge Vergara <jovergar=
40microsoft....@dmarc.ietf.org> wrote:
> >Microsoft has already said that they won't rev their EAP-TLS
> implementation until they can also rev PEAP.
>
> PEAP/TTLS/TEAP - we (Microsoft) believe all should be addressed at the
> same time and will postpone TLS 1.3 support until such a time as we are
> able to make the updates together.
>
> >* should the document drop references to TEAP?
> > Given Jouni Malinen's comments on implementing TEAP, it may be worth
> simply noting that we're waiting for a TEAP update document
>
> I've reviewed the current errata, and acknowledge their validity, but am
> not sure that any of them would impact this document.
>
> The most relevant errata to this document seems to be
> https://www.rfc-editor.org/errata/eid5770. As noted in the errata, the
> calculation of keys becomes confusing when methods export both MSK and EMSK
> because it is not clearly specified which value IMCK[j] should take on
> during the calculation of S-IMCK[j]. The addition of clarifying information
> is welcome, but I don't believe this ambiguity currently prevents a
> compliant implementation - for example, an implementation could avoid this
> ambiguity by choosing to use either the MSK/EMSK exclusively, and
> communicating that to the server via the Compound MAC TLV. The server can
> then make a policy decision on whether it is accepting of this decision by
> the client and follow suit, or reject the client.
>
> The specifics of resolving this particular errata is a digression from my
> main point - I believe a clarification can be added to the main TEAP
> document at a future time without impacting the contents of this document..
> Ambiguity about which IMCK to use in S-IMCK calculation should not impact
> the definition of the cryptographic calculations.
>
> On the document contents themselves, I have this review: The key
> derivation proposed for TEAP/FAST uses the definition from FAST, which is
> not identical to the TEAP derivation. Namely, FAST used MSK[j] in the
> derivation, but TEAP uses IMSK[j], which may be equivalent in some cases,
> but may not in others where the inner method exports an EMSK.
>
> Specifically, I believe this line of section 2.2 should change from
> IMCK[j] = TLS-Exporter("EXPORTER: Inner Methods Compound Keys",
> S-IMCK[j-1] | MSK[j], 60)
> To
> IMCK[j] = TLS-Exporter("EXPORTER: Inner Methods Compound Keys",
> S-IMCK[j-1] | IMSK[j], 60)
> For TEAP.
>
> Jorge
>
> -----Original Message-----
> From: Emu <emu-boun...@ietf.org> On Behalf Of Alan DeKok
> Sent: Friday, April 3, 2020 1:48 PM
> To: EMU WG <emu@ietf.org>
> Subject: [Emu] draft-dekok-emu-tls-eap-types discussion
>
>
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools..ietf.org%2Fhtml%2Fdraft-dekok-emu-tls-eap-types-01&data=02%7C01%7Cjovergar%40microsoft.com%7C2c42095edc4e4cd61ce408d7d8106200%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637215437188744711&sdata=ndLp%2FSzsDlX%2FKYx0UR0uf77rHgCjGej4kdZPpywuD9Q%3D&reserved=0
>
> I haven't seen much discussion on the document. There are still some
> open questions:
>
> * should it be published simultaneously with draft-ietf-emu-eap-tls13?
> If so, we need some consensus on this document, and quick.
>
> If not, when do we publish this draft? Microsoft has already said that
> they won't rev their EAP-TLS implementation until they can also rev PEAP.
>
> * Should the document simply drop references to FAST?
> It looks like the effort has moved to TEAP.
> Perhaps we should note that FAST cannot be used with TLS 1.3, and that
> TEAP should be used instead
>
> * should the document drop references to TEAP?
> Given Jouni Malinen's comments on implementing TEAP, it may be worth
> simply noting that we're waiting for a TEAP update document
>
> * Without FAST / TEAP, the document is about 4 pages of text. Is there
> anything controversial, missing, etc?
>
> * What are the barriers to adoption and publication?
>
> Alan DeKok.
>
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