Re: [Emu] Potential Notes in EAP-FAST Documents

[David Mitton <[e-mail]>]

I'm sorry,  I haven't responded earlier either, but I would like to pile on with some of my comments.

When I read the Cisco EAP-FAST GTC description and was similarly shocked by the nature of the changes, and how poorly they technically met their own rationale.

Encoding the "REQ=" and "RESP=" into Request and Response text, is absolutely useless, since the data flow is unidirectional and known to the requester/responder peers.

And then claiming that is more efficent because the username and OTP are combined in one response, really ignores the issue that GTC doesn't define what the appropriate response is.  And they did nothing to clue the client as to what is being requested, or the format of the response.

Given that, a Client can only strip the useless cybercrud, and continue with the normal GTC state machine which is let the user type something in and send it.

A more robust OTP implementation may have several different inputs that it wants from the user besides for username and OTP.  (BTW; username could be derived from the EAP Identity)   There are possible next token challenges,  new PIN assignment (user or system generated)  and followup re-authentications.   Their protocol did nothing to codify a standard for interoperation where a sequence of requests were enumerated or named, and response items were described. 

I'm all for documenting practice, but this design/implementation doesn't really seem to solve anything and just creates more confusion.

Dave Mitton

Feb 3, 2009 11:13:36 AM, [e-mail] wrote:

The interoperability concern with existing EAP-MSCHAPv2 and EAP-GTC
implementations and incorrect re-use of EAP Types must be addressed/corrected prior to publication.

One solution is to

(a) Get a new, correct type number for use by the method in the published document, and change the name of the method
(could use "name-CR" for "corrected/revision", or similar). This eliminates the interoperability concern with existing methods,
and uniquely identifies the IETF published method.

and

(b) Add descriptive text in the document to explain the difference between this IETF published method and similar  deployed
methods - to meet the desire to document deployed methods.

Dorothy Stanley

On Mon, Feb 2, 2009 at 6:56 PM, Glen Zorn <[e-mail]> wrote:

> Dear EMU WG:
>
> These two documents are in the RFC Editor queue:
>
>    draft-cam-winget-eap-fast-provisioning-10.txt
>    draft-zhou-emu-fast-gtc-05.txt
>
> The IESG has received a very late comment about these documents, and
> we seek your input on the proposed resolution.
>
> The late comment raises a potential interoperability concern with
> existing implementations of EAP-MSCHAPv2 and EAP-GTC.
>
> The draft-cam-winget-eap-fast-provisioning-10.txt document specifies
> a very specific way to generate the challenges used in EAP-MSCHAPv2
> that provides binding between the EAP-FAST tunnel and the EAP-MSCHAPv2
> exchanges.
>
> The draft-zhou-emu-fast-gtc-05.txt describes EAP-FAST-GTC, which is
> uses EAP Type 6, originally allocated to EAP-GTC [RFC3748]. EAP-FAST-
> GTC
> employs a subset of the EAP-GTC formatting.
>
> The IESG recognizes the difficulties caused by re-use of an EAP Type.
> Further, the IESG recognizes the concern about implementations that
> might not easily adapt to additional requirements.  However, the IESG
> also recognizes the significant value in documenting EAP methods that
> are implemented and deployed in the Internet today.
>
> The IESG believes that the right thing to do in this situation is to
> proceed with the publication of these documents.  However, the IESG
> also
> sees value in warning future EAP method designers about this experience
> so that this pain might be avoided in the future.
>
> The IESG is considering the additional informative paragraph in the
> IANA
> considerations section of both documents that says:
>
>     IESG Note: EAP-FAST has been implemented by many vendors and it is
>     used in the Internet.  Publication of this is intended to promote
>     interoperability, even though the use of the EAP-MSCHAPv2 and
>     EAP-FAST-GTC EAP methods might be difficult in some software
>     environments.  If EAP-FAST were to be designed today, these
>     difficulties could be avoided by the assignment of new EAP Type
>     codes.
>
> Please provide comments on the proposed way forward.

I am strongly opposed to the publication of these documents as RFCs in their
current form.  Not only is the "fast provisioning" for EAP-FAST what can
only be characterized as a security disaster, but EAP-FAST-GTC has nothing
whatsoever to do with the EAP-GTC type.  EAP-GTC was "defined for use with
various Token Card implementations which require user input" but
EAP-FAST-GTC is used solely to transfer a username/password combination, the
password in plaintext.  It's hard to see what this has to do with actual
token cards & appears to be a lazy misuse of an existing type.  Furthermore,
it's even harder to see how rewarding this kind of nonsense with publication
will serve as a warning of any kind; I would expect that the action of
publication (with or without IESG note) would be more likely taken as notice
that one can do whatever one please without fear.

> On behalf of the IESG,
>   Russ
>
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