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Versions: (draft-wang-hokey-erp-aak) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 6630

Network Working Group                                             Z. Cao
Internet-Draft                                                   H. Deng
Intended status: Standards Track                            China Mobile
Expires: November 3, 2012                                          Q. Wu
                                                                  Huawei
                                                            G. Zorn, Ed.
                                                             Network Zen
                                                             May 2, 2012


EAP Re-authentication Protocol Extensions for Authenticated Anticipatory
                            Keying (ERP/AAK)
                      draft-ietf-hokey-erp-aak-11

Abstract

   The Extensible Authentication Protocol (EAP) is a generic framework
   supporting multiple types of authentication methods.

   The EAP Re-authentication Protocol (ERP) specifies extensions to EAP
   and the EAP keying hierarchy to support an EAP method-independent
   protocol for efficient re-authentication between the peer and an EAP
   re-authentication server through any authenticator.

   Authenticated Anticipatory Keying (AAK) is a method by which
   cryptographic keying material may be established upon one or more
   candidate attachment points (CAPs) prior to handover.  AAK uses the
   AAA infrastructure for key transport.

   This document specifies the extensions necessary to enable AAK
   support in ERP.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 3, 2012.



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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Standards Language . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  ERP/AAK Description  . . . . . . . . . . . . . . . . . . . . .  4
   4.  ERP/AAK Key Hierarchy  . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Derivation of the pRK and pMSK . . . . . . . . . . . . . .  8
   5.  Packet and TLV Extension . . . . . . . . . . . . . . . . . . .  9
     5.1.  EAP-Initiate/Re-auth-Start Packet and TLV Extension  . . .  9
     5.2.  EAP-Initiate/Re-auth Packet and TLV Extension  . . . . . . 10
     5.3.  EAP-Finish/Re-auth packet and TLV extension  . . . . . . . 12
     5.4.  TV and TLV Attributes  . . . . . . . . . . . . . . . . . . 14
   6.  Lower Layer Considerations . . . . . . . . . . . . . . . . . . 15
   7.  AAA Transport Considerations . . . . . . . . . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   10. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 18
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     11.2. Informative References . . . . . . . . . . . . . . . . . . 18














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1.  Introduction

   The Extensible Authentication Protocol (EAP) [RFC3748] is a generic
   framework supporting multiple types of authentication methods.  In
   systems where EAP is used for authentication, it is desirable to not
   repeat the entire EAP exchange with another authenticator.  The EAP
   Re-authentication Protocol (ERP) [RFC5296] specifies extensions to
   EAP and the EAP keying hierarchy to support an EAP method-independent
   protocol for efficient re-authentication between the EAP re-
   authentication peer and an EAP re-authentication server through any
   authenticator.  The re-authentication server may be in the home
   network or in the local network to which the mobile host (i.e., the
   EAP re-authentication peer) is connecting.

   Authenticated Anticipatory Keying (AAK) [RFC5836] is a method by
   which cryptographic keying materials may be established prior to
   handover upon one or more candidate attachment points (CAPs).  AAK
   utilizes the AAA infrastructure for key transport.

   This document specifies the extensions necessary to enable AAK
   support in ERP.

2.  Terminology

2.1.  Standards Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.2.  Acronyms

   The following acronyms are used in this document; see the references
   for more details.

   AAA
       Authentication, Authorization and Accounting [RFC3588]

   CAP
       Candidate Attachment Point [RFC5836]

   EA
       Abbreviation for "ERP/AAK"

   EA Peer
       An EAP peer that supports the ERP/AAK.  Note that all references
       to "peer" in this document imply an EA peer, unless specifically
       noted otherwise.



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   SAP
       Serving Attachment Point [RFC5836]

3.  ERP/AAK Description

   ERP/AAK is intended to allow the establishment of cryptographic
   keying materials on a single Candidate Attachment Point prior to the
   arrival of the peer at the Candidate Access Network (CAN) upon
   request by the peer.

   In this document, ERP/AAK support by the peer is assumed.  Also it is
   assumed that the peer has previously completed full EAP
   authentication and that either the peer or SAP knows the identities
   of neighboring attachment points.  Note that the behavior of a peer
   that does not support the ERP-AAK scheme defined in this
   specification is out of the scope of this document.  Figure 1 shows
   the general protocol exchange by which the keying material is
   established on the CAP.

































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     +------+         +-----+        +-----+          +-----------+
     | Peer |         | SAP |        | CAP |          | EA Server |
     +--+---+         +--+--+        +--+--+          +-----+-----+
        |                |              |                   |
     a. | [EAP-Initiate/ |              |                   |
        | Re-auth-start  |              |                   |
        | (E-flag)]      |              |                   |
        |<---------------|              |                   |
        |                |              |                   |
     b. | EAP-Initiate/  |              |                   |
        | Re-auth        |              |                   |
        | (E-flag)       |              |                   |
        |--------------->|              |                   |
     c. |                | AAA(EAP-Initiate/Re-auth(E-flag))|
        |                |--------------------------------->|
        |                |              |         +---------+---------+
        |                |              |         | CA authorized &   |
     d. |                |              |         |  and EA Keying    |
        |                |              |         |   Distribution    |
        |                |              |         +---------+---------+
        |                |              |                   |
        |                |              |                   |
     f. |                | AAA (EAP-Finish/Re-auth(E-flag)) |
        |                |<---------------------------------|
     g. | EAP-Finish/    |              |                   |
        | Re-auth(E-flag)|              |                   |
        |<---------------|              |                   |
        |                |              |                   |

                        Figure 1: ERP/AAK Exchange





















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                  +-----------+               +---------+
                  |           |               |         |
                  | EA Server |               |   CAP   |
                  |           |               |         |
                  +-----|-----+               +----|----+
                        |                          |
                        |                          |
                        |    AAA Request(pMSK)     |
                     e.1|------------------------->|
                        |                          |
                        |                          |
                        |                          |
                        |  AAA Response (Success)  |
                     e.2|<-------------------------|
                        |                          |
                        |                          |
                        |                          |

                  Figure 2: Key Distribution for ERP/AAK

   ERP/AAK re-uses the packet format defined by ERP, but specifies a new
   flag to differentiate EAP early-authentication from EAP re-
   authentication.  The peer initiates ERP/AAK itself, or does so in
   response to an EAP-Initiate/Re-Auth-Start message from the SAP.

   In the latter case, the SAP MAY send the identity of one or more
   Candidate Attachment Points to which the SAP is adjacent to the peer
   in the EAP-Initiate/Re-auth-Start message (see a. in Figure 1).  The
   Peer SHOULD override the identity of CAP(s) carried in EAP-Initiate/
   Re-auth-Start message by sending EAP-Initiate/Re-auth with the 'E'
   flag set if it knows to which CAP it will move.  If the EAP-Initiate/
   Re-auth-Start packet is not supported by the peer, it MUST be
   silently discarded.

   If the peer initiates ERP/AAK, the peer MAY send an early-
   authentication request message (EAP-Initiate/Re-auth with the 'E'
   flag set) containing the keyName-NAI, the CAP-Identifier, rIK and
   sequence number (see b. in Figure 1).  The realm in the keyName-NAI
   field is used to locate the peer's ERP/AAK server.  The CAP-
   Identifier is used to identify the CAP.  The rIK is defined in
   Narayanan & Dondeti [RFC5296] and used to protect the integrity of
   the message.  The sequence number is used for replay protection.

   The SAP SHOULD verify the integrity of thus message at step b.  If
   this verification fails, the SAP MUST send an EAP-Finish/Re-auth
   message with the Result flag set to '1' (Failure).  If the
   verification succeeds, the SAP SHOULD encapsulate the early-
   authentication message into a AAA message and send it to the peer's



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   ERP/AAK server in the realm indicated in the keyName-NAI field (see
   c. in Figure 1).

   Upon receiving the message, the ERP/AAK server MUST first use the
   keyName indicated in the keyName-NAI to look up the rIK and check the
   integrity and freshness of the message.  Then the ERP/AAK server MUST
   verify the identity of the peer by checking the username portion of
   the KeyName-NAI.  If any of the checks fail, the server MUST send an
   early- authentication finish message (EAP-Finish/Re-auth with E-flag
   set) with the Result flag set to '1'.  Next, the server MUST
   authorize the CAP specified in the CAP-Identifier TLV.  In the
   success case, the server MUST derive a pMSK from the pRK for the CAP
   carried in the the CAP-Identifier field using the sequence number
   associated with CAP-Identifier as an input to the key derivation.
   (see d. in Figure 1).

   Then the ERP/AAK server MUST transport the pMSK to the authorized CAP
   via AAA Section 7 as illustrated above (see e.1 and e.2 in Figure 2).
   Note that key distribution in Figure 2 is one part of step d. in
   Figure 1.

   Finally, in response to the EAP-Initiate/Re-auth message, the ERP/AAK
   server SHOULD send the early-authentication finish message (EAP-
   Finish/ Re-auth with E-flag set) containing the identity of the
   authorized CAP to the peer via the SAP along with the lifetime of the
   pMSK.  If the peer also requests the rRK lifetime, the ERP/AAK server
   SHOULD send the rRK lifetime in the EAP-Finish/Re-auth message. (see
   f. and g. in Figure 1).

4.  ERP/AAK Key Hierarchy

   ERP/AAK uses a key hierarchy similar to that of ERP.  The ERP/AAK
   pre-established Root Key (pRK) is derived from either the EMSK or the
   DSRK as specified below (see Section 4.1).  In general, the pRK is
   derived from the EMSK if the peer is located in the home AAA realm
   and derived from the DRSK if the peer is in a visited realm.  The
   DSRK is delivered from the EAP server to the ERP/AAK server as
   specified in [I-D.ietf-dime-local-keytran].  If the peer has
   previously been authenticated by means of ERP or ERP/AAK, the DSRK
   SHOULD be directly re-used.

                                 DSRK    EMSK
                                  |       |
                              +---+---+---+---+
                              |
                             pRK            ...

                   Figure 3: ERP/AAK Root Key Derivation



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   Similarly, the pre-established Master Session Key (pMSK) is derived
   from the pRK.  The pMSK is established for the CAP when the peer
   early authenticates to the network.  The hierarchy relationship is
   illustrated Figure 4,

                                    pRK
                                     |
                            +--------+--------+
                            |
                            pMSK             ...

                      Figure 4: ERP/AAK Key Hierarchy

   below.

4.1.  Derivation of the pRK and pMSK

   The rRK is derived as specified in [RFC5295].

   pRK = KDF (K, S), where

      K = EMSK or K = DSRK and

      S = pRK Label | "\0" | length

   The pRK Label is an IANA-assigned 8-bit ASCII string:

      EAP Early-Authentication Root Key@ietf.org

   assigned from the "USRK key labels" name space in accordance with
   Salowey, et al.  [RFC5295].  The KDF and algorithm agility for the
   KDF are also defined in RFC 5295.  The KDF algorithm is indicated in
   the cryptosuit field or list of cryptosuits TLV payload as specified
   in the section 5.2 and section 5.3.

   The pMSK uses the same PDF as pRK and is derived as follows:

   pMSK = KDF (K, S), where

      K = pRK and

      S = pMSK label | "\0" | SEQ | length

   The pMSK label is the 8-bit ASCII string:

      EAP Early-Authentication Master Session Key@ietf.org

   The length field refers to the length of the pMSK in octets encoded



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   as specified in RFC 5295.  SEQ is sent by either the peer or the
   server in the ERP/AAK message using the SEQ field or the Sequence
   number TLV and encoded as an 16-bit number as specified in
   Section 5.2 and Section 5.3.

5.  Packet and TLV Extension

   This section describes the packet and TLV extensions for the ERP/AAK
   exchange.

5.1.  EAP-Initiate/Re-auth-Start Packet and TLV Extension

   Figure 5 shows the new parameters contained in the EAP-Initiate/
   Re-auth-Start packet defined in RFC 5296 [RFC5296].

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Code      |  Identifier   |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |E| Reserved    |     1 or more TVs or TLVs     ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 5

   Flags

   'E' - The E flag is used to indicate early-authentication.  This
   field MUST be set to '1' if early authentication is in use and MUST
   be set to '0' otherwise.

   The rest of the 7 bits (Reserved ) MUST be set to 0 and ignored on
   reception.

   TVs and TLVs

   CAP-Identifier: Carried in a TLV payload.  The format is identical to
   that of a DiameterIdentity [RFC3588].  It is used by the SAP to
   advertise the identity of the CAP to the peer.  Exactly one CAP-
   Identifier TLV MAY be included in the EAP-Initiate/Re-auth-Start
   packet if the SAP has performed CAP discovery.

   If the EAP-Initiate/Re-auth-Start packet is not supported by the
   peer, it SHOULD be discarded silently.







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5.2.  EAP-Initiate/Re-auth Packet and TLV Extension

   Figure 6 illustrates the new parameters contained in the EAP-
   Initiate/Re-auth packet defined in RFC 5296 [RFC5296].

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Code      |  Identifier   |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |R|x|L|E|Resved |             SEQ               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 1 or more TVs or TLVs                         ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Cryptosuite  |         Authentication Tag                     ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 6

   Flags

   'x' - The x flag is reserved.  It MUST be ignored on receipt.

   'L' - As defined in section 5.3.2 of [RFC5296], this bit is used to
   request the key lifetimes from the server.

   'E' - The E flag is used to indicate early-authentication.

   The first bit(R) and final 4 bits (Resved) MUST be set to 0 and
   ignored on reception.

   SEQ

   As defined in Section 5.3.2 of [RFC5296],this field is 16-bit
   sequence number and used for replay protection.

   TVs and TLVs

   keyName-NAI: As defined in RFC 5296 [RFC5296], this is carried in a
   TLV payload.  The Type is 1.  The NAI is variable in length, not
   exceeding 253 octets.  The username part of the NAI is the EMSKname
   used to identify the peer.  The realm part of the NAI is the peer's
   home domain name if the peer communicates with the home EA server or
   the domain to which the peer is currently attached (i.e., local
   domain name) if the peer communicates with a local EA server.  The
   SAP knows whether the KeyName-NAI carries the local domain name by
   comparing the domain name carried in KeyName-NAI with the local
   domain name which is associated with the SAP.  Exactly one keyName-



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   NAI attribute SHALL be present in an EAP-Initiate/Re-auth packet and
   the realm part of it SHOULD follow the use of internationalized
   domain names defined in RFC5890 [RFC5890].

   CAP-Identifier: Carried in a TLV payload.The Type is TBD (less than
   128).  This field is used to indicate the FQDN of a CAP.  The value
   field MUST be encoded as specified in Section 8 of RFC 3315
   [RFC3315].  Exactly one instance of the CAP-Identifier TLV MUST be
   present in the ERP/AAK-Key TLV.

   Sequence number: The Type is TBD (less than 128).  The value field is
   a 16-bit field and used in the derivation of the pMSK for a CAP.

   Cryptosuite

   This field indicates the integrity algorithm used for ERP/AAK.  Key
   lengths and output lengths are either indicated or obvious from the
   cryptosuite name, e.g., HMAC-SHA256-128 denotes HMAC computed using
   the SHA-256 function [RFC4868] with 256-bit key length and the output
   truncated to 128 bits [RFC2104].  We specify some cryptosuites below:

   0-1  RESERVED

   2  HMAC-SHA256-128

   3  HMAC-SHA256-256

   HMAC-SHA256-128 is REQUIRED to implement and SHOULD be enabled in the
   default configuration.

   Authentication Tag

   This field contains an integrity checksum over the ERP/AAK packet
   from the first bit of the Code field to the last bit of the
   Cryptosuite field, excluding the Authentication Tag field itself.
   The value field is calculated using the integrity algorithm indicated
   in the Cryptosuite field and rIK specified in [RFC5296] as the secret
   key.  The length of the field is indicated by the Cryptosuite.

   The peer uses the Authentication Tag to determine the validity of the
   EAP-Finish/Re-auth message from the server.

   If the message doesn't pass verification or the Authentication Tag is
   not included in the message, the message SHOULD be discarded
   silently.

   If the EAP-Initiate/Re-auth packet is not supported by the SAP, it
   SHOULD be discarded silently.  The peer MUST maintain retransmission



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   timers for reliable transport of the EAP-Initiate/Re-auth message.
   If there is no response to the EAP-Initiate/Re-auth message from the
   server after the necessary number of retransmissions (see Section 6),
   the peer MUST assume that ERP/AAK is not supported by the SAP.

5.3.  EAP-Finish/Re-auth packet and TLV extension

   Figure 7 shows the new parameters contained in the EAP-Finish/Re-auth
   packet defined in [RFC5296].

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Code      |  Identifier   |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |R|x|L|E|Resved |             SEQ               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 1 or more TVs or TLVs                         ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Cryptosuite  |         Authentication Tag                     ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 7

   Flags

   'R' - As defined in Section 5.3.3 of [RFC5296], this bit is used to
   used as the Result flag.  This field MUST be set to '1' if indicates
   success and MUST be set to '0' otherwise.

   'x' - The x flag is reserved.  It MUST be ignored on receipt.

   'L' - As defined in section 5.3.3 of [RFC5296], this bit is used to
   request the key lifetimes from the server.

   'E' - The E flag is used to indicate early-authentication.

   The final 4 bits (Resved) MUST be set to 0 and ignored on reception.

   SEQ

   As defined in Section 5.3.3 of [RFC5296], this field is a 16-bit
   sequence number and used for replay protection.

   TVs and TLVs

   keyName-NAI: As defined in RFC 5296 [RFC5296], this is carried in a
   TLV payload.  The Type is 1.  The NAI is variable in length, not



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   exceeding 253 octets.  Exactly one keyName-NAI attribute SHALL be
   present in an EAP-Finish/Re-auth packet.

   ERP/AAK-Key: Carried in a TLV payload for the key container.  The
   type is TBD.  Exactly one ERP/AAK-key SHALL only be present in an
   EAP-Finish/Re-auth packet.

   ERP/AAK-Key ::=
        { sub-TLV: CAP-Identifier }
        { sub-TLV: pMSK-lifetime }
        { sub-TLV: pRK-lifetime }
        { sub-TLV: Cryptosuites }

   CAP-Identifier
      Carried in a sub-TLV payload.  The Type is TBD (less than 128).
      This field is used to indicate the identifier of the candidate
      authenticator.  The value field MUST be encoded as specified in
      Section 8 of RFC 3315 [RFC3315].  There at least one instance of
      the CAP-Identifier TLV MUST be present in the ERP/AAK-Key TLV.

   pMSK-lifetime
      Carried in a sub-TLV payload of the EAP-Finish/Re-auth message.
      The Type is TBD.  The value field is an unsigned 32-bit field and
      contains the lifetime of the pMSK in seconds.  This value is
      calculated by the server after pRK-lifetime computation upon
      receiving the EAP-Initiate/Re-auth message.  The rIK SHOULD share
      the same lifetime as the pMSK.  If the 'L' flag is set, the pMSK-
      Lifetime attribute MUST be present.

   pRK-lifetime
      Carried in a sub-TLV payload of EAP-Finish/Re-auth message.  The
      Type is TBD.  The value field is an unsigned 32-bit field and
      contains the lifetime of the pRK in seconds.  This value is
      calculated by the server before pMSK-lifetime computation upon
      receiving a EAP-Initiate/Re-auth message.  If the 'L' flag is set,
      the pRK-Lifetime attribute MUST be present.

   List of Cryptosuites
      Carried in a sub-TLV payload.  The Type is 5 [RFC5296].  The value
      field contains a list of cryptosuites (at least one cryptosuite
      SHOULD be included), each 1 octet in length.  The allowed
      cryptosuite values are as specified in Section 5.2, above.  The
      server SHOULD include this attribute if the cryptosuite used in
      the EAP-Initiate/Re-auth message was not acceptable and the
      message is being rejected.  The server MAY include this attribute
      in other cases.  The server MAY use this attribute to signal to
      the peer about its cryptographic algorithm capabilities.




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   Cryptosuite

   This field indicates the integrity algorithm and PRF used for ERP/
   AAK.  HMAC-SHA256-128 is REQUIRED to implement and SHOULD be enabled
   in the default configuration.  Key lengths and output lengths are
   either indicated or obvious from the cryptosuite name.

   Authentication Tag

   This field contains the integrity checksum over the ERP/AAK packet
   from the first bit of the Code field to the last bit of the
   Cryptosuite field excluding the Authentication Tag field itself.  The
   value field is calculated using the integrity algorithm indicated in
   the Cryptosuite field and the rIK [RFC5296] as the integrity key.
   The length of the field is indicated by the corresponding
   Cryptosuite.

   The peer uses the authentication tag to determine the validity of the
   EAP-Finish/Re-auth message from a server.

   If the message doesn't pass verification or the authentication tag is
   not included in the message, the message SHOULD be discarded
   silently.

   If the EAP-Initiate/Re-auth packet is not supported by the SAP, it is
   discarded silently.  The peer MUST maintain retransmission timers for
   reliable transport of EAP-Initiate/Re-auth message.  If there is no
   response to the EAP-Initiate/Re-auth message from the server after
   the necessary number of retransmissions (See Section 6), the peer
   MUST assume that ERP/AAK is not supported by the SAP.

5.4.  TV and TLV Attributes

   With the exception of the rRK-Lifetime and rMSK-Lifetime TV payloads,
   the attributes specified in Section 5.3.4 of [RFC5296] also apply to
   this document.  In this document, new attributes which may be present
   in the EAP-Initiate and EAP-Finish messages are defined as below:

   o  Sequence number: This is a TV payload.  The type is 7.

   o  ERP/AAK-Key: This is a TLV payload.  The type is 8.

   o  pRK-Lifetime: This is a TV payload.  The type is 9.

   o  pMSK-Lifetime: This is a TV payload.  The type is 10.

   o  CAP-Identifier: This is a TLV payload.  The type is 11.




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6.  Lower Layer Considerations

   Similar to ERP, some lower layer specifications may need to be
   revised to support ERP/AAK; refer to Section 6 of [RFC5296] for
   additional guidance.

7.  AAA Transport Considerations

   The AAA transport of ERP/AAK messages is the same as that of the ERP
   message [RFC5296].  In addition, this document requires AAA transport
   of the ERP/AAK keying materials delivered by the ERP/AAK server to
   the CAP.  Hence, a new AAA message for the ERP/AAK application should
   be specified to transport the keying materials.

8.  Security Considerations

   This section provides an analysis of the protocol in accordance with
   the AAA key management requirements specified in RFC 4962 [RFC4962].

   o  Cryptographic algorithm independence: ERP-AAK satisfies this
      requirement.  The algorithm chosen by the peer for calculating the
      authentication tag is indicated in the EAP-Initiate/Re-auth
      message.  If the chosen algorithm is unacceptable, the EAP server
      returns an EAP-Finish/Re-auth message with a Failure indication.

   o  Strong, fresh session keys: ERP-AAK results in the derivation of
      strong, fresh keys that are unique for the given CAP.  An pMSK is
      always derived on-demand when the peer requires a key with a new
      CAP.  The derivation ensures that the compromise of one pMSK does
      not result in the compromise of a different pMSK at any time.

   o  Limit key scope: The scope of all the keys derived by ERP-AAK is
      well defined.  The pRK is used to derive the pMSK for the CAP.
      Different sequence numbers for each CAP MUST be used to derive a
      unique pMSK.

   o  Replay detection mechanism: For replay protection a sequence
      number associated with the pMSK is used.The peer increments the
      sequence number by one after it sends an ERP/AAK message.  The
      server sets the expected sequence number to the received sequence
      number plus one after verifying the validity of the received
      message and responds to the message.

   o  Authenticate all parties: The EAP Re-auth Protocol provides mutual
      authentication of the peer and the server.  The peer and SAP are
      authenticated via ERP.  The CAP is authenticated and trusted by
      the SAP.




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   o  Peer and authenticator authorization: The peer and authenticator
      demonstrate possession of the same keying material without
      disclosing it, as part of the lower layer secure authentication
      protocol.

   o  Keying material confidentiality: The peer and the server derive
      the keys independently using parameters known to each entity.

   o  Uniquely named keys: All keys produced within the ERP context can
      be referred to uniquely as specified in this document.

   o  Prevent the domino effect: Different sequence numbers for each CAP
      MUST be used to derive the unique pMSK.  So the compromise of one
      pMSK does not hurt any other CAP.

   o  Bind key to its context: the pMSK are bound to the context in
      which the sequence numbers are transmitted.

   o  Confidentiality of identity: this is the same as with the ERP
      protocol [RFC5296].

   o  Authorization restriction: All the keys derived are limited in
      lifetime by that of the parent key or by server policy.  Any
      domain-specific keys are further restricted to be used only in the
      domain for which the keys are derived.  Any other restrictions of
      session keys may be imposed by the specific lower layer and are
      out of scope for this specification.

9.  IANA Considerations

   IANA is requested to assign five TLV type values from the registry of
   EAP Initiate and Finish Attributes maintained at
   http://www.iana.org/assignments/eap-numbers/eap-numbers.xml.
   with the following numbers:

   o  Sequence number: This is a TV payload.  The type is 7.

   o  ERP/AAK-Key: This is a TLV payload.  The type is 8.

   o  pRK Lifetime: This is a TLV payload.  The type is 9.

   o  pMSK Lifetime: This is a TLV payload.  The type is 10.

   o  CAP-Identifier: This is a TLV payload.  The type is 11.

   This document reuses the crytosuites have already created for 'Re-
   authentication Cryptosuites' in [RFC5296].




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   Further, this document instructs IANA to add a new label in the User
   Specific Root Keys (USRK) Key Labels of the Extended Master Session
   Key (EMSK) Parameters registry, as follows:

      EAP Early-Authentication Root Key@ietf.org

   This document creates a new registry for the flags in the EAP
   Initiate/Re-auth-Start message called the "EAP Initiate/Re-auth-Start
   Flags" and assigns a new flag (E) as follows:

      (E) 0x80

   The rest of the values in the 8-bit field are reserved.  New values
   can be assigned by Standards Action or IESG approval.

   This document also creates a new registry for the flags in the EAP
   Initiate/Re-auth message called the "EAP Initiate/Re-auth Flags".
   The following flag are reserved:

      (R) 0x80 [RFC5296]

      (B) 0x40 [RFC5296]

      (L) 0x20 [RFC5296]

   This document assigns a new flag (E) as follows:

      (E) 0x10

   The rest of the values in the 8-bit field are reserved.  New values
   can be assigned by Standards Action or IESG approval.

   Further,this document creates a new registry for the flags in the EAP
   Finish/Re-auth message called the "EAP Finish/Re-auth Flags".  The
   following values are reserved.

      (R) 0x80 [RFC5296]

      (B) 0x40 [RFC5296]

      (L) 0x20 [RFC5296]

   This document assigns a new flag (E) as follows:

      (E) 0x10

   The rest of the values in the 8-bit field are reserved.  New values
   can be assigned by Standards Action or IESG approval.



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10.  Acknowledgement

   In writing this document, Yungui Wang contributed to early versions
   of this document and we have received reviews from many experts in
   the IETF, including Tom Taylor, Tena Zou, Tim Polk, Tan Zhang, Semyon
   Mizikovsky, Stephen Farrell, Radia Perlman, Miguel A. Garcia and
   Sujing Zhou.  We apologize if we miss some of those who have helped
   us.

11.  References

11.1.  Normative References

   [RFC2119]                      Bradner, S., "Key words for use in
                                  RFCs to Indicate Requirement Levels",
                                  BCP 14, RFC 2119, March 1997.

   [RFC3315]                      Droms, R., Ed., Bound, J., Volz, B.,
                                  Lemon, T., Perkins, C., and M. Carney,
                                  "Dynamic Host Configuration Protocol
                                  for IPv6 (DHCPv6)", RFC 3315,
                                  July 2003.

   [RFC5295]                      Salowey, J., Dondeti, L., Narayanan,
                                  V., and M. Nakhjiri, "Specification
                                  for the Derivation of Root Keys from
                                  an Extended Master Session Key
                                  (EMSK)", August 2008.

   [RFC5296]                      Narayanan, V. and L. Dondeti, "EAP
                                  Extensions for EAP Re-authentication
                                  Protocol (ERP)", RFC 5296,
                                  August 2008.

11.2.  Informative References

   [I-D.ietf-dime-local-keytran]  Zorn, G., Wu, W., and V. Cakulev,
                                  "Diameter Attribute-Value Pairs for
                                  Cryptographic Key Transport",
                                  draft-ietf-dime-local-keytran-14 (work
                                  in progress), August 2011.

   [RFC2104]                      Krawczyk, H., Bellare, M., and R.
                                  Canetti, "HMAC: Keyed-Hashing for
                                  Message Authentication", RFC 2104,
                                  February 1997.

   [RFC3588]                      Calhoun, P., Loughney, J., Guttman,



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                                  E., Zorn, G., and J. Arkko, "Diameter
                                  Base Protocol", RFC 3588,
                                  September 2003.

   [RFC3748]                      Aboba, B., Blunk, L., Vollbrecht, J.,
                                  Carlson, J., and H. Levkowetz,
                                  "Extensible Authentication Protocol
                                  (EAP)", RFC 3748, June 2004.

   [RFC4868]                      Kelly, S. and S. Frankel, "Using HMAC-
                                  SHA-256, HMAC-SHA-384, and HMAC-SHA-
                                  512 with IPsec", RFC 4868, May 2007.

   [RFC4962]                      Housley, R. and B. Aboba, "Guidance
                                  for Authentication, Authorization, and
                                  Accounting (AAA) Key Management",
                                  BCP 132, RFC 4962, July 2007.

   [RFC5836]                      Ohba, Y., Wu, Q., and G. Zorn,
                                  "Extensible Authentication Protocol
                                  (EAP) Early Authentication Problem
                                  Statement", RFC 5836, April 2010.

   [RFC5890]                      Klensin, J., "Internationalized Domain
                                  Names for Applications (IDNA):
                                  Definitions and Document Framework",
                                  RFC 5890, August 2010.

Authors' Addresses

   Zhen Cao
   China Mobile
   53A Xibianmennei Ave., Xuanwu District
   Beijing, Beijing  100053
   P.R. China

   EMail: zehn.cao@gmail.com


   Hui Deng
   China Mobile
   53A Xibianmennei Ave., Xuanwu District
   Beijing, Beijing  100053
   P.R. China

   EMail: denghui02@gmail.com





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   Qin Wu
   Huawei
   Floor 12, HuiHong Mansion, No.91 BaiXia Rd.
   Nanjing, Jiangsu  210001
   P.R. China

   Phone: +86 25 56623633
   EMail: sunseawq@huawei.com


   Glen Zorn (editor)
   Network Zen
   227/358 Thanon Sanphawut
   Bang Na, Bangkok  10260
   Thailand

   Phone: +66 (0) 87-040-4617
   EMail: glenzorn@gmail.com

































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