eap Mailing List: draft-ietf-eap-keying-11: Some comments in section 2

[Rafa Marin Lopez (rafa]

Hi all

Following next four paragraphs in section 2....
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"On the EAP server, keying material requested by and passed down to
the AAA layer may be replicated to the AAA layer on the
authenticator.  On the authenticator, the AAA layer provides the
replicated keying material to the lower layer over which the EAP
authentication conversation took place.  This enables "mode
independence" to be maintained.

  The EMSK MUST NOT be provided to an entity outside the EAP server or
  peer,  nor is it permitted to pass any quantity to an entity outside
  the EAP server or peer from which the EMSK could be computed without
  breaking some cryptographic assumption, such as inverting a one-way
  function.  The EMSK MUST NOT be transported by the AAA layer.  As
  noted in [RFC3748] Section 7.10:

     The EMSK is reserved for future use and MUST remain on the EAP
     peer and EAP server where it is derived; it MUST NOT be
     transported to, or shared with, additional parties, or used to
     derive any other keys.

  The EAP layer as well as the peer and authenticator layers MUST NOT
  modify or cache keying material or parameters (including Channel
  Bindings) passing in either direction between the EAP method layer
  and the lower layer or AAA layer."

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My understanding is :

1) EMSK "arrives" to AAA layer when EAP server is co-located with AAA 
server but no replicated on the AAA layer in the EAP authenticator. 
Thus, AAA layer in EAP server can manage and use EMSK.

2) In EAP peer side, EMSK arrives to EAP lower layer and it could manage 
and use EMSK to derive new keys

3) EAP lower layer's implementation/behaviour in EAP authenticator side 
should be different depending on either a) Standalone Authenticator or 
b) Pass-Through Authenticator:

   a) Standalone Authenticator: EAP lower layer receives the EMSK and 
it should run some key derivation mechanism by using EMSK if it is needed.
   b) Pass-Through Authenticator: EAP lower layer does not receive EMSK 
but it might receive another keys derived from EMSK through AAA layer. 
EAP lower layer in Pass-Through authenticator does not need to 
implement/run any key derivation mechanism which uses EMSK.

Is this correct?

Thanks.
     


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Rafael Marin Lopez
Faculty of Computer Science-University of Murcia
30071 Murcia - Spain
Telf: +34968367645    e-mail: rafa [at] dif.um.es
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