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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: March 11, 2013                                   Gridmerge Ltd.
                                                       September 7, 2012


                          Encrypting PANA AVPs
                      draft-yegin-pana-encr-avp-10

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
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 11, 2013.

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
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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 Keys  . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Encryption-Algorithm AVP . . . . . . . . . . . . . . . . . . .  5
     4.1.  AES128_CTR Encryption Algorithm  . . . . . . . . . . . . .  5
   5.  Encr-Encap AVP . . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Encryption Policy  . . . . . . . . . . . . . . . . . . . . . .  7
     6.1.  Encryption Policy Specification  . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     7.1.  AES-CTR Security Considerations  . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  PANA AVP codes . . . . . . . . . . . . . . . . . . . . . .  9
     8.2.  PANA Encryption-Algorithm AVP values . . . . . . . . . . . 10
     8.3.  PANA AVP codes encryption policy . . . . . . . . . . . . . 10
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11































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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 PANA
   Attribute-Value Pairs (AVPs).  AVPs can be integrity-protected using
   the AUTH AVP when EAP authentication generates cryptographic keying
   material.  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

   This document extends the AVP set defined in Section 8 of [RFC5191]
   by defining two new AVPs: the Encryption-Algorithm AVP (see
   Section 4) and the Encr-Encap AVP (see Section 5).  Two new
   encryption keys, PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY, are defined
   to encrypt AVPs from the PaC to the PAA and AVPs from the PAA to the
   PaC respectively (see Section 3).

   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.  Once
   PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY have been generated, a PANA
   message MAY contain an Encr-Encap AVP.


3.  Encryption Keys

   PANA_PAC_ENCR_KEY is used for encrypting the AVP payload of the Encr-
   Encap AVP sent in a PANA message from the PaC to the PAA.



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   PANA_PAC_ENCR_KEY SHALL be computed according to the following
   formula:

   PANA_PAC_ENCR_KEY = prf+(MSK, "IETF PANA PaC Encr" | I_PAR |
                            I_PAN | PaC_nonce | PAA_nonce | Key_ID)



   PANA_PAA_ENCR_KEY is used for encrypting the AVP payload of the Encr-
   Encap AVP sent in a PANA message from the PAA to the PaC.
   PANA_PAA_ENCR_KEY SHALL be computed according to the following
   formula:

   PANA_PAA_ENCR_KEY = prf+(MSK, "IETF PANA PAA Encr" | I_PAR |
                            I_PAN | PaC_nonce | PAA_nonce | Key_ID)



   In both cases:

      - The prf+ function is defined in IKEv2 [RFC5996].

      - The pseudo-random function (PRF) to be used for the prf+
      function SHALL be negotiated using PRF-Algorithm AVP in the
      initial PANA-Auth-Request and PANA-Auth-Answer exchange with 'S'
      (Start) bit set as described in Section 4.1 of [RFC5191]

      - MSK is the master session key generated by the EAP method
      [RFC3748].  PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY MUST be
      recalculated whenever a new MSK is generated by the EAP method.

      - "IETF PANA PaC Encr" and "IETF PANA PAA Encr" are the ASCII code
      representations of the respective non-NULL terminated strings
      (excluding the double quotes around them).

      - 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_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY depends on the



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   encryption algorithm in use.


4.  Encryption-Algorithm AVP

   The Encryption-Algorithm AVP (AVP code TBD1) is used for conveying
   the encryption algorithm to be used with the Encr-Encap AVP.  The AVP
   value data is of type Unsigned32.

   Only one encryption algorithm identifier AES128_CTR (code 1) is
   identified by this document.  Encryption algorithm identifier values
   other than 1 are reserved for future use.  Future specifications are
   allowed to extend this list.

      AES128_CTR: 1

   In the absence of an application profile specifying otherwise, all
   implementations SHALL support AES128_CTR.

4.1.  AES128_CTR Encryption Algorithm

      The AES128_CTR encryption algorithm uses the AES-CTR (Counter)
      mode of operation as specified in [NIST_SP800_38A] using the AES-
      128 block cipher.  The formatting function and counter generation
      function as specified in Appendix A of [NIST_SP800_38C] are used,
      with the following parameters:


            n = 12,
            q = 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 PANA_PAC_ENCR_KEY and
      PANA_PAA_ENCR_KEY.  The output blocks of the encryption processing
      are encoded as OctetString data in the Value field of a Encr-Encap
      AVP.

      Note the first counter block used for encryption is Ctr_1, where
      "_1" denotes "subscript 1" as described in section A.3 of
      [NIST_SP800_38C].  For example, given the following:






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            Key-Id = 0x55667788,
            Session ID = 0xaabbccdd,
            Sequence Number = 0x11223344


      The first counter block used for encryption will be:


            0x0255667788aabbccdd11223344000001


      where the initial 0x02 represents the Flags Field of the counter
      block.

   The nonce meets the requirement of uniqueness per key usage providing
   the sequence number does not wrap.  Therefore, for the purpose of
   generating new keys:

      - If Encr-Encap AVPs are being sent from the PaC to the PAA and
      the sequence number is about to wrap, the PaC SHALL initiate PANA
      re-authentication as described in Section 4.3 of [RFC5191].

      - If Encr-Encap AVPs are being sent from the PAA to the PaC and
      the sequence number is about to wrap, the PAA SHALL initiate PANA
      re-authentication as described in Section 4.3 of [RFC5191].

   Re-authentication ensures the generation of a new MSK [RFC3748] and
   thus a new PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY.


5.  Encr-Encap AVP

   The Encr-Encap AVP (AVP code TBD2) 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 identifier is AES128_CTR
   (code 1), AVP data payload is occupied by the encrypted AVPs.

   There SHALL be only one Encr-Encap AVP in a PANA message.  All AVPs
   that require encryption SHALL be encapsulated within the Encr-Encap
   AVP.

   The Encr-Encap AVP uses either PANA_PAC_ENCR_KEY or PANA_PAA_ENCR_KEY
   and the encryption algorithm negotiated by the Encryption-Algorithm
   AVP.  The Encr-Encap AVP SHALL only be used if the EAP method
   generates cryptographic keys (specifically the MSK [RFC3748]).




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   The Encr-Encap AVP MAY be used in a PANA message from the PaC to the
   PAA when the encryption algorithm has been successfully negotiated
   and once PANA_PAC_ENCR_KEY has been generated.

   The Encr-Encap AVP MAY be used in a PANA message from the PAA to the
   PaC when the encryption algorithm has been successfully negotiated
   and once PANA_PAA_ENCR_KEY has been generated.

   The Encr-Encap AVP MAY be used in the very first PANA message
   carrying the Result-Code AVP set to PANA_Success value, and any
   subsequent message within the same PANA session.


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-
   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 legitimate occurrence of unencrypted AVPs and AVPs after
   decryption and unencapsulation SHALL be subject to the AVP Occurrence
   Table (Figure 4 in [RFC5191]).



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   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                 | N |
            PRF-Algorithm         | N |
            Result-Code           | N |
            Session-Lifetime      | X |
            Termination-Cause     | X |
            ----------------------+---+


   The following table shows the encryption requirements for the AVPs
   defined in [RFC6345]:

            Attribute Name        |Enc|
            ----------------------+---+
            PaC-Information       | N |
            Relayed-Message       | N |
            ----------------------+---+


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

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


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

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


   The guidance for specifying the encryption requirements for a newly-
   defined AVP is as follows:



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   Y: If the payload needs privacy against eavesdroppers (e.g., carrying
      a secret key).

   N: If the payload may need to be observed by on-path network elements
      (i.e., subject to deep packet inspection).

   X: If neither concern applies.


7.  Security Considerations

   PANA_PAC_ENCR_KEY and PANA_PAA_ENCR_KEY are secret keys shared
   between the PaC and the PAA.  They SHALL NOT be used for purposes
   other than those specified in this document.  Compromise of these
   keys would lead to compromise of the secret information protected by
   these keys.

7.1.  AES-CTR Security Considerations

   The use of AES-CTR encryption has its own security considerations,
   which are detailed in the Security Considerations section of
   [RFC3686].  Specifically:

      - The nonce specified in Section 4.1 meets the requirement of
      uniqueness per key usage.

      - Section 4.1 of [RFC5191] states that if the EAP method generates
      cryptographic keys, an AUTH AVP will always be present in every
      PANA message after key generation.  Therefore, an Encr-Encap AVP
      will always be sent in conjunction with an AUTH AVP.  This meets
      the requirement of a companion authentication function.


8.  IANA Considerations

   As described in Section 4 and Section 5, and following the new IANA
   allocation policy on PANA messages [RFC5872], two PANA AVP codes and
   one set of AVP values are requested.  An additional encryption policy
   for AVP codes is also requested.

8.1.  PANA AVP codes

   The following AVP codes are requested in the PANA Parameters - AVP
   Codes registry:

   o  A standard AVP code of TBD1 (suggested value 12) for Encr-Encap
      AVP.




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   o  A standard AVP code of TBD2 (suggested value 13) for Encryption-
      Algorithm AVP.

8.2.  PANA Encryption-Algorithm AVP values

   The following AVP values representing the encryption algorithm
   identifier for the Encryption-Algorithm AVP code are requested as a
   sub-registry under the PANA Parameters - AVP Codes registry:

   o  An AVP value of 1 for AES128_CTR.

   o  All other AVP values (0, 2-4294967295) are unassigned

   The registration procedures are IETF Review or IESG Approval in
   accordance with [RFC5872].

8.3.  PANA AVP codes encryption policy

   The additional encryption policy defined in Section 6.1 is requested
   to be assigned as an additional column labeled "Enc" to the PANA AVP
   Codes parameter, applied to all existing AVP codes and those defined
   in this specification.


9.  Acknowledgments

   The authors would like to thank Yoshihiro Ohba, Yasuyuki Tanaka,
   Adrian Farrel, Brian Carpenter, Yaron Sheffer, Ralph Droms, Stephen
   Farrell, Barry Leiba and Sean Turner for their 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.

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

   [RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
              Counter Mode With IPsec Encapsulating Security Payload
              (ESP)", RFC 3686, January 2004.



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

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

   [RFC5872]  Arkko, J. and A. Yegin, "IANA Rules for the Protocol for
              Carrying Authentication for Network Access (PANA)",
              RFC 5872, May 2010.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

   [RFC6345]  Duffy, P., Chakrabarti, S., Cragie, R., Ohba, Y., and A.
              Yegin, "Protocol for Carrying Authentication for Network
              Access (PANA) Relay Element", RFC 6345, August 2011.


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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