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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 6786

Network Working Group                                           A. Yegin
Internet-Draft                                                   Samsung
Intended status: Standards Track                               R. Cragie
Expires: April 21, 2012                                   Gridmerge Ltd.
                                                        October 19, 2011


                          Encrypting PANA AVPs
                      draft-yegin-pana-encr-avp-00

Abstract

   This document specifies a mechanism for delivering PANA (Protocol for
   Carrying Authentication for Network Access) AVPs (Attribute-Value
   Pairs) in encrypted form.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 21, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Specification of Requirements . . . . . . . . . . . . . . . 3
   2.  Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Encryption Key  . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Encryption-Algorithm AVP  . . . . . . . . . . . . . . . . . . . 4
   5.  Encr-Encap AVP  . . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Encryption Policy . . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Encryption Policy Specification . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   10. Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8




































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1.  Introduction

   PANA [RFC5191] is a UDP-based protocol to perform EAP authentication
   between a PaC (PANA Client) and a PAA (PANA Authentication Agent).

   Various types of payloads are exchanged as part of the network access
   authentication and authorization.  These payloads are carried in
   AVPs.  AVPs can be integrity-protected using the AUTH AVP when EAP
   authentication generates cryptographic keying material.  PANA AVPs
   are transmitted in the clear (i.e., not encrypted).

   There are certain types of payloads that need to be delivered
   privately (e.g., network keys, private identifiers, etc.).  This
   document defines a mechanism for applying encryption to selected
   AVPs.

1.1.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  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 [RFC2119].


2.  Details

   Encr-Encap AVP is used for delivering AVPs in encrypted form.

   Each AVP that requires encryption SHALL be encapsulated inside an
   Encr-Encap AVP.  Encr-Encap AVP can encapsulate one or more AVPs.
   There SHALL be only one Encr-Encap AVP in a PANA message.

   Encr-Encap AVP uses the PANA_ENCR_KEY and the encryption algorithm
   negotiated by the Encr-Algorithm AVP.  These AVPs SHALL NOT be used
   if the EAP method does not generate cryptographic keys (more
   specifically, MSK).

   When encryption needs to be used, the required algorithm is
   negotiated as follows: the PAA SHALL send the initial PANA-Auth-
   Request carrying one or more Encryption-Algorithm AVPs supported by
   it.  The PaC SHALL select one of the algorithms from this AVP, and it
   SHALL respond with the initial PANA-Auth-Answer carrying one
   Encryption-Algorithm AVP for the selected algorithm.

   Encr-Encap AVP MAY be used in any PANA message once the encryption
   algorithm is successfully negotiated and the PANA_ENCR_KEY is
   generated.  The PRF used for computing the PANA_ENCR_KEY SHALL be



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   negotiated by the PRF-Algorithm-AVP according to RFC 5191.


3.  Encryption Key

   PANA_ENCR_KEY is used for encrypting the AVP payload of the Encr-
   Encap AVP.  PANA_ENCR_KEY SHALL be computed according to the
   following formula.

     PANA_ENCR_KEY = prf+(MSK, "IETF PANA Encryption Key" | I_PAR |
                          I_PAN | PaC_nonce | PAA_nonce | Key_ID)



   where:

      - The prf+ function is defined in IKEv2 [RFC4306].  The pseudo-
      random function to be used for the prf+ function is negotiated
      using PRF-Algorithm AVP in the initial PANA-Auth-Request and PANA-
      Auth-Answer exchange with 'S' (Start) bit set.

      - MSK is the master session key generated by the EAP method.

      - "IETF PANA Encryption Key" is the ASCII code representation of
      the non-NULL terminated string (excluding the double quotes around
      it).

      - I_PAR and I_PAN are the initial PANA-Auth-Request and PANA-Auth-
      Answer messages (the PANA header and the following PANA AVPs) with
      'S' (Start) bit set, respectively.

      - PaC_nonce and PAA_nonce are values of the Nonce AVP carried in
      the first non-initial PANA-Auth-Answer and PANA-Auth-Request
      messages in the authentication and authorization phase or the
      first PANA-Auth-Answer and PANA-Auth-Request messages in the re-
      authentication phase, respectively.

      - Key_ID is the value of the Key-Id AVP.

   The length of PANA_ENCR_KEY depends on the integrity algorithm in
   use.


4.  Encryption-Algorithm AVP

   The Encryption-Algorithm AVP (AVP Code 12 ** needs IANA allocation
   **) is used for conveying the encryption algorithm to be used with
   the Encr-Encap AVP.  The AVP data is of type Unsigned32.



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   Only AES_CTR (code 1) is identified by this document.  Algorithm
   codes other than 1 are reserved for future use.  Future
   specifications are allowed to extend this list.

      AES_CTR: 1

      AES-CTR (Counter) encryption algorithm as specified in
      [NIST_SP800_38A].  The formatting function and counter generation
      function as specified in Appendix A of [NIST_SP800_38C] are used,
      with the following parameters:


            n, octet length of nonce, is 12.
            q, octet length of message length field, is 3.


      The 12-octet nonce consists of a 4-octet Key-Id, a 4-octet Session
      ID and a 4-octet Sequence Number in that order where each 4-octet
      value is encoded in network byte order.  The Session ID and
      Sequence Number values SHALL be the same as those in the PANA
      message carrying the key Encr-Encap AVP.  The Key-Id value SHALL
      be the same as the one used for deriving the PANA_ENCR_KEY.  The
      output blocks of the encryption processing are encoded as
      OctetString data in the Value field of a Encr-Encap AVP.

   In the absence of an application profile specifying otherwise, all
   implementations SHALL support AES_CTR.


5.  Encr-Encap AVP

   The Encr-Encap AVP (AVP Code 13 ** needs IANA allocation **) is used
   to encrypt one or more PANA AVPs.  Format of the Encr-Encap AVP
   depends on the negotiated encryption algorithm.

   When the negotiated encryption algorithm is AES-CTR (code 1), AVP
   data payload is occupied by the encrypted AVPs.


6.  Encryption Policy

   The specification of any AVP SHOULD state that the AVP either shall
   or shall not be encrypted using Encr-Encap AVP.  The specification of
   an AVP MAY state that the AVP may (or may not) be encrypted using
   Encr-Encap AVP.  The specification SHOULD use a table in the format
   specified in Section 6.1.  If the specification of an AVP is silent
   about whether the AVP shall or shall not be encrypted using Encr-
   Encap AVP, this implies that the AVP MAY be encrypted using Encr-



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   Encap AVP.

6.1.  Encryption Policy Specification

   This section defines a table format for the specification of whether
   an AVP shall or shall not be encrypted using Encr-Encap AVP.

   The table uses the following symbols:

   Y: The AVP SHALL be encrypted using Encr-Encap AVP.  If the AVP is
      encountered not encrypted using Encr-Encap AVP, it SHALL be
      considered invalid and the message containing the AVP SHALL be
      discarded.

   N: The AVP SHALL NOT be encrypted using Encr-Encap AVP.  If the AVP
      is encountered encrypted using Encr-Encap AVP, it SHALL be
      considered invalid and the message containing the AVP SHALL be
      discarded.

   X: The AVP MAY be encrypted using Encr-Encap AVP.  If the AVP is
      encountered either encrypted or not encrypted using Encr-Encap
      AVP, it SHALL be considered valid.

   The following table shows the encryption requirements for the
   existing AVPs defined in [RFC5191]:

            Attribute Name        |Enc|
            ----------------------+---+
            AUTH                  | N |
            EAP-Payload           | X |
            Integrity-Algorithm   | N |
            Key-Id                | N |
            Nonce                 | X |
            PRF-Algorithm         | N |
            Result-Code           | N |
            Session-Lifetime      | X |
            Termination-Cause     | X |
            ----------------------+---+


   The following table shows the encryption requirements for the AVPs
   defined in this document:

            Attribute Name        |Enc|
            ----------------------+---+
            Encr-Algorithm        | N |
            Encr-Encap            | N |
            ----------------------+---+



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   The following table is an example of showing the encryption
   requirements for a newly-defined AVP, Example-AVP:

            Attribute Name        |Enc|
            ----------------------+---+
            Example-AVP           | Y |
            ----------------------+---+



7.  Security Considerations

   PANA_ENCR_KEY is a secret key shared between the PaC and the PAA.  It
   SHALL NOT be used for purposes other than the one specified in this
   document.  Compromise of this key would lead to compromise of the
   secret information protected by this key.


8.  IANA Considerations

   The following IANA actions are required by this specification:

      - Assignment of a standard AVP code TBD for Encr-Encap AVP

      - Assignment of a standard AVP code TBD for Encryption-Algorith
      AVP.

      - Creation of encryption algorithm identifier space for PANA.

      - Assignment of an encryption code 1 for AES_CTR.


9.  Acknowledgments

   The authors would like to thank Yoshihiro Ohba for his valuable
   comments.


10.  Normative References

   [NIST_SP800_38A]
              Dworkin, M., "Recommendation for Block Cipher Modes of
              Operation: Methods and Techniques", December 2001.

   [NIST_SP800_38C]
              Dworkin, M., "Recommendation for Block Cipher Modes of
              Operation:  The CCM Mode for Authentication and
              Confidentiality", May 2004.



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

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC5191]  Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
              Yegin, "Protocol for Carrying Authentication for Network
              Access (PANA)", RFC 5191, May 2008.


Authors' Addresses

   Alper Yegin
   Samsung
   Istanbul
   Turkey

   Email: alper.yegin@yegin.org


   Robert Cragie
   Gridmerge Ltd.
   89 Greenfield Crescent
   Wakefield, WF4 4WA
   UK

   Email: robert.cragie@gridmerge.com























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