Re: [Emu] review of draft-ietf-emu-eaptunnel-req-04

["Dan Harkins" <[e-mail]>]

  Hi Katrin,

  Section 4.6.3 will address a man-in-the-middle attack against an
anonymous TLS tunnel followed by a mutually-authenticating and key
generating EAP method, like EAP-pwd. The keying material from both
the anonymous tunnel and the tunneled EAP method will be mixed
together (according to 4.6.3) to derive an MSK and EMSK.

  The value is that such a technique can be used for initial credential
provisioning. And it is secure. Please reconsider your opposition to
allowing this technique.

  regards,

  Dan.

On Tue, March 2, 2010 7:03 am, Hoeper Katrin-QWKN37 wrote:
> Dan,
>
> The current text allows server-side only authentication for the tunnel,
> i.e. the peer can remain anonymous during that phase and only transmit
> its credential inside the tunnel. This enables peer privacy.
>
> I think what you are talking about is mutually anonymous tunnels, i.e.
> both peer and server remain anonymous during the tunnel establishment.
> These types of tunnels are prone to man-in-the-middle attacks in which
> the privacy of both tunnel endpoints is compromised. I don't see any
> value of those anonymous tunnels. In fact they are not secure.
>
> I strongly oppose to allowing these tunnels and believe that the current
> text about this topic should be kept as is.
>
> Best regards,
> Katrin
>
> PS: Details on the mentioned MitM attacks are in
> http://portal.acm.org/citation.cfm?id=1577285
>
>
>
>> -----Original Message-----
>> From: [e-mail] [mailto:[e-mail]] On Behalf Of
>> Joseph Salowey (jsalowey)
>> Sent: Monday, March 01, 2010 11:53 PM
>> To: Dan Harkins; [e-mail]
>> Subject: Re: [Emu] review of draft-ietf-emu-eaptunnel-req-04
>>
>> Thanks Dan,
>>
>> I haven't seen any responses on the list yet so I provided some inline
>> below.
>>
>> > -----Original Message-----
>> > From: [e-mail] [mailto:[e-mail]] On Behalf
> Of
>> Dan
>> > Harkins
>> > Sent: Monday, November 30, 2009 12:57 PM
>> > To: [e-mail]
>> > Subject: [Emu] review of draft-ietf-emu-eaptunnel-req-04
>> >
>> >
>> >   Hello,
>> >
>> >   I made some of these comments at the mic in Hiroshima but was
>> > asked to submit them to the list.
>> >
>> >   - I get the feeling that this document is being written to
>> >     ensure some end-game and not simply as a protocol requirements
>> >     document.
>> >
>> >     I mentioned that it would be nice if the tunneled method
>> >     described a way to establish an EAP-TLS -style connection,
>> >     either anonymous or server-side-auth-only, and then allow
>> >     for subsequent authentication using another EAP method (or
>> >     using specific TLVs for some password authentication) or
>> >     EAP methods chained together by the tunnel. Pasi said that
>> >     is the intention but it sure doesn't seem that way.
>> >
>> [Joe] Currently the scope of the work does not include anonymous
>> authentication.  I think this could be follow-on work to the tunnel
>> method.  I don't think the current document should prohibit anonymous
>> cipher suites from being used in follow-on specifications.   See the
>> response to 4.2.1.1.3 for some suggested text.
>>
>> >   - section 3.4 states that the tunnel method MUST ensure "that
>> >     peer identity is not disclosed to the authenticator and any
>> >     other intermediaries before the server that terminates the
>> >     tunnel method."
>> >
>> >     EAP is supposed to be a 2 party protocol that, for optimization,
>> >     can have functionality split between a pass-thru authenticator
>> >     and a EAP method-terminating server. But it seems wrong to
>> >     put forth the optimization as if it's a requirement for the
>> >     tunnel method.
>> >
>> >     Please change this to something like "the identity of the peer
>> >     used for authentication purposes MUST NOT be obtainable by any
>> >     entity other than the EAP server terminating the tunnel method."
>> >
>> [Joe] OK
>>
>> >   - 3.6 seems somewhat pointless. "The tunnel method SHOULD support
>> >     carrying of NEA protocols" and "these protocols may be required
>> >     to be carried in an EAP method."
>> >
>> >     Since the tunneled EAP method can tunnel EAP methods then this
>> >     "requirement" should just naturally flow out of another
>> requirement.
>> >     Please remove section 3.6.
>> >
>> [Joe] While, it is true that carrying NEA protocols should be met by
>> either the extensibility or carrying EAP method requirements,  I
> believe
>> that NEA use case is pertinent to the tunnel method work and should be
>> mentioned somewhere in the document.  What is the harm in mentioning
> it
>> here?
>>
>> >   - 3.7 describes "credentials [that] may only partially
> authenticate
>> >     the identity of the peer".
>> >
>> >     Huh? What kind of credentials are these? Please describe these
>> >     credentials.
>> >
>> [Joe] OK
>>
>> >     Additionally, "the tunnel may be used to communicate additional
>> >     data".
>> >
>> >     This is so vague as to be meaningless. A nonce could satisfy
>> >     this "requirement", and so could 8 bits of RESERVED-- set to
> zero
>> >     before transmitting and ignored upon receipt-- for that matter.
>> >     Please remove this.
>> >
>> [Joe] Removed
>>
>> >   - 3.8 mentions a use of "extensibility is support for
> authentication
>> >     frameworks other than EAP."
>> >
>> >     That seems like a huge stretch of the work we are chartered to
> do.
>> >     I suggest that line be removed.
>> >
>> [Joe] Alan had a similar comment that this text is confusing. The
>> suggest text is:
>> " Another use for extensibility is support for alternate
> authentication
>> frameworks within the tunnel."
>>
>>
>>
>> >   - 4.1.2 is inappropriate. It is not the purpose of a document
>> describing
>> >     the requirements for a protocol to direct the working group how
> to
>> >     evaluate potential protocols against those requirements.
>> >
>> >     When I brought this up in Hiroshima a response was (I
> paraphrase),
>> >     "that the working group had consensus to use existing work and
> so
>> >     this is just a restatement of that consensus." Which raises
>> another
>> >     interesting point without addressing my comment. That other
> point
>> is
>> >     that if there is working group consensus then it is not
> necessary
>> to
>> >     have section 4.1.2 then. The fact that 4.1.2 is in the document
>> leads
>> >     one to believe that perhaps there is a fear that such support
>> might
>> >     have evaporated.
>> >
>> >     The working group does not need to be constrained in its
> decision-
>> >     making process. The process is defined and understood and it is
>> >     inappropriate for a _protocol requirements document_ to say,
> "hey
>> >     remember way back when a sample of active participants seemed to
>> >     agree on a vague concept, well now you SHOULD select one of the
>> two
>> >     candidates here."
>> >
>> >     Please remove 4.1.2.
>> >
>> [Joe]  Needs more discussion.
>>
>> >   - 4.2.1.1.1 if TLS is required and "[a]ll versions of TLS meet
>> >     [cipher suite negotiation] requirements" then what's the point
> of
>> >     this section?
>> >
>> >     Please remove section 4.2.1.1.1.
>> >
>> [Joe]  I think the comment is still relevant, suggested text:
>> " TLS provides protected cipher suite negotiation as long as all the
>> cipher suites supported provide strong authentication, key
> establishment
>> and data integrity protection."
>>
>> >   - 4.2.1.1.3 begins saying "A tunnel method MUST provide
>> unidirectional
>> >     authentication from authentication server to EAP peer and mutual
>> >     authentication between authentication server and EAP peer."
>> >
>> >     This is a nonsense statement. Either it's unidirectional or it's
>> >     mutual, it can't be both.
>> >
>> >     Additionally, it says "mandatory to implement cipher suites MUST
>> NOT
>> >     include...mutually anonymous authentication...."
>> >
>> >     Seeing as how this subsection is under 4.2.1 and 4.2.1.1.1
>> describes
>> >     these as TLS cipher suites then I really think this should be
>> changed.
>> >     An anonymous TLS cipher suite negotiated by the EAP tunnel
> method
>> >     will be extremely valuable when combined with something like
>> EAP-pwd
>> >     as the inner method. That would provide a way to securely
> satisfy
>> the
>> >     credential provisioning requirement (which is a MUST by the
> way).
>> >
>> >     Please restate the requirement to say something along the lines
> of
>> >     "if an anonymous TLS ciphersuite is used by the outer tunnel
> then
>> an
>> >     inner method providing mutual authentication MUST be used."
>> >
>> [Joe]  I agree that anonymous cipher suites might be useful in the
>> context you describe.  I do not that this is the main purpose of the
>> tunnel method work.   I think this would be done in a separate
> document
>> building on top of the tunnel method.   I can see how the existing
> text
>> might be a bit problematic, but your suggested text makes me a bit
>> nervous because it may require more consideration.  How about
> something
>> along the lines of:
>>
>> "Other specifications may define uses of the tunnel method the build
> on
>> anonymous cipher suites.  These specifications must take care to
> address
>> the security issues inherent in anonymous cipher suites. "
>>
>> >   - 4.2.1.2 requires replay protection and then goes on to say that
>> TLS
>> >     (which is required by 4.2.1) satisfies this requirement.
>> >
>> >     Please remove 4.2.1.2 since it does not add a new requirement.
>> >
>> [Joe] Suggested Text:
>> " TLS provides sufficient replay protection to meet this requirements
> as
>> long as strong cipher suites are used."
>>
>> >   regards,
>> >
>> >   Dan.
>> >
>> >
>> >
>> >
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