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6TSCH                                                          S. Chasko
Internet-Draft                                                       L+G
Intended status: Informational                                    S. Das
Expires: December 26, 2013                                           ACS
                                                          R. Marin-Lopez
                                                    University of Murcia
                                                            Y. Ohba, Ed.
                                                              P. Thubert
                                                                A. Yegin
                                                           June 24, 2013

 Security Framework and Key Management Protocol Requirements for 6TSCH


   Since 6TSCH forms layer 3 meshes over IPv6, PANA model matches the
   target architecture so PANA can apply for the process by a new device
   of joining the mesh to extend it.  This document details that
   particular operation within the whole 6TSCH architecture.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 December 26, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Framework  . . . . . . . . . . . . . . . . . . . . .   3
   4.  KMP requirements  . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Phase-1 KMP requirements  . . . . . . . . . . . . . . . .   6
     4.2.  Phase-2 KMP requirements  . . . . . . . . . . . . . . . .   6
   5.  KMP candidates  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Phase-1 KMP candidates  . . . . . . . . . . . . . . . . .   7
     5.2.  Phase-2 KMP candidates  . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
     8.3.  External Informative References . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The emergence of radio technology enabled a large variety of new
   types of devices to be interconnected, at a very low marginal cost
   compared to wire, at any range from Near Field to interplanetary
   distances, and in circumstances where wiring could be less than
   practical, for instance rotating devices.

   At the same time, a new breed of Time Sensitive Networks is being
   developed to enable traffic that is highly sensitive to jitter and
   quite sensitive to latency.  Such traffic is not limited to voice and
   video, but also includes command and control operations such as found
   in industrial automation or in-vehicular sensors and actuators.

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   6TSCH builds on a series of semi-proprietary wireless protocols that
   provide adequate Time Sensitive behaviors for low speed control
   loops, protocols that are rapidly gaining acceptance in the
   automation industry for mission critical Process Control
   applications.  For such applications, security is not an option and a
   power efficient authentication mechanism is strictly required.

   Following Metcalf's law, value of using radios augments with the
   square of the number of devices connected, and this implies the
   capability to form autonomic mesh networks be it only for reasons of
   spatial reuse of the spectrum.  Since 6TSCH forms layer 3 meshes over
   IPv6, the PANA model matches the target architecture so PANA can
   apply for the process by a new device of joining the mesh to extend

   ZigBee IP [ZigBeeIP] ("ZigBee" is a registered trademark of the
   ZigBee Alliance) is a standard for IPv6-based wireless mesh networks
   using PANA for network access authentication and secure distribution
   of a link-layer group key called Network Key to authenticated mesh
   nodes.  Each mesh node in the same ZigBee IP network derives the same
   MAC key from the Network Key to protect IEEE 802.15.4 MAC frames
   exchanged between adjacent mesh nodes.  While sharing the same MAC
   key among all mesh nodes can make the required key state maintained
   by each mesh node compact, a compromise of a mesh node can lead to
   MAC key leakage in the entire ZigBee IP network.  Also, the cost of
   updating the MAC key can be high as the key needs to be updated at
   all mesh nodes whenever the frame counter at any single node wraps up
   or the key is considered to be weak.

   This document introduces a more secure and scalable key management
   framework for 6TSCH networks using PANA as the boostrapping mechansim
   and identifies requirements for key management protocols to be used
   in the framework.

2.  Acronyms

   6TSCH: TBD (Editor's note: what is the expansion of 6TSCH?)

   KMP: Key Managment Protocol

   PANA: Protocol for carrying Authentication for Network Access

   SA: Security Association

   MAC: Media Access Control

3.  Security Framework

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   This section describes a security framework consisting of three
   phases as shown in Figure 1.  The architecture is applicable to not
   only 6TSCH networks but also non-time synchronized mesh networks.
   Each node in a mesh network runs through the following phases:

   o  Phase-1 (Bootstrapping Phase): In this phase, a node (re)installs
      credentials used for subsequent phases from an authentication
      server.  The credentials include Phase-2 credentials and Phase-3
      credentials, and may also include long-term Phase-1 credentials if
      the initial Phase-1 credentials are intended for one-time use such
      as a temporal PIN.  An authentication and key establishment
      protocol called a Phase-1 KMP is conducted between the node and
      the authentication server using Phase-1 credentials.  The Phase-1
      credentials have longer lifetime than Phase-2 and Phase-3
      credentials so that Phase-2 and Phase-3 credentials can be renewed
      using the Phase-1 credentials.  Both symmetric and asymmetric key
      credentials can be used as Phase-1 credentials.  A symmetric key
      that is established as a result of successful Phase-1 KMP is used
      for encrypting the Phase-2 and Phase-3 credentials distributed
      from the authentication server to the node.  When the
      authentication server is multiple hops away from the node, mutual
      authentication between the node and the authentication server is
      conducted via a neighboring node acting as an authentication
      relay.  There may be no link-layer security available between the
      node and its neighboring node in this phase.  An authentication
      server is typically (but is not necessarily) located in the
      coordinator of the mesh network.

   o  Phase-2 (Link Establishment Phase): In this phase, the node
      performs mutual authentication with its neighboring node using the
      Phase-2 credentials to establish SAs between adjacent nodes for
      protecting 802.15.4 MAC frames.  The authentication and key
      establishment protocol used in this phase is referred as a Phase-2
      KMP or a link establishment KMP.  For highly scalable mesh
      networks consisting of thousands of mesh nodes, asymmetric key
      credentials are used as the Phase-2 credentials.  The SA of a link
      between node i and node j maintains MAC keys.  K_i denotes a MAC
      key for protecting broadcast MAC frames originated at node i.
      K_ij denotes a MAC key for protecting unicast MAC frames
      originated at node i and destined for node j.  There are several
      variations of forming MAC keys.

      1.  K_ij=K_i for all j, K_i!=K_j for all i, j (i!=j)

      2.  K_ij=K_ji, K_i!=K_j for all i,j (i!=j)

      3.  K_ij!=K_ji, K_i!=K_j for all i,j (i!=j)

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      In model 1, unicast and broadcast keys for protecting MAC frames
      originated at a given node are the same.  In models 2 and 3,
      unicast and broadcast keys originated at a given node are
      distinct.  The difference between models 2 and 3 is that unicast
      keys are bi-directinal in model 2 while they are uni-directinal in
      model 3.  One model may be chosen among three depending on
      required security level and the number of keys maintained by each

   o  Phase-3 (Operational Phase): In this phase, the node is able to
      run various higher-layer protocols over IP over an established
      secure link.  Additional authentication and key establishment may
      take place for the higher-layer protocols using Phase-3
      credentials.  A node in Phase-3 is able to process Phase-1 and
      Phase-2 KMPs.  Example use cases are:

      *  A Phase-3 node can initiate a Phase-1 KMP to update its Phase-2
         or Phase-3 credentials.

      *  A Phase-3 node can forward Phase-1 KMP messages originated from
         or destined for a Phase-1 node that is joining the mesh network
         through the Phase-3 node.

      *  A Phase-3 node can initiate a Phase 2 KMP to establish a new
         link with a newly discovered neighbor node.

              |        Phase-1 (Bootstrap)      |
              |   Phase-2 (Link Establishment)  |
              |        Phase-3 (Operational)    |

                  Figure 1: 3-Phase Key Management Model

              N)s - Node N is running Phase-1 KMP as a server
              N)c - Node N is running Phase-1 KMP as a client
              N)r - Node N is running Phase-1 KMP as a relay
              N)) - Node N is running Phase-2 KMP
              .  .. ...
              N, N,  N  - Node N is in Phase-1, -2 and -3, respectively

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        .          .           ..         ...        ...         ...
        A          A)s         A))         A)s        A           A
                  / \         / \         / \        / \         / \
      .   .      .   .       ..  ..     ... ...    ... ...     ... ...
      B   C      B)c C)c     B)) C))     B)r C      B)) C))     B   C
                                        / \ /      / \ /       / \ /
    .   .      .   .        .   .       .   .      ..  ..     ... ...
    D   E      D   E       D   E       D)c E)c    D)) E))     D   E

       (0)  ->    (1)   ->    (2)   ->    (3)  ->    (4)   ->    (5)

   (0) Initially all nodes but Node A (i.e., the authentication server)
   are in Phase-1.  (1) Nodes B and C run Phase-1 KMP with Node A to
   obtain Phase-2 and Phase-3 credentials.  (2) Nodes B and C run
   Phase-2 KMP with Node A.  (3) Nodes D and E run Phase-1 KMP using
   Node B as an authentication relay.  (Alternatively, Node E may use
   Node C as an authentication relay.) (4) Node D runs Phase-2 KMP with
   Node B.  Node E runs Phase-2 KMP with Nodes B and C.  (5) All nodes
   are operational.

                        Figure 2: Example Sequence

   Since we already identified PANA as the Phase-1 KMP due to its
   authentication relay and secure credential distribution capabilities,
   and Phase-3 KMP requirements would depend on application protocols,
   we focus on Phase-2 KMP requirements in the next seciton.

4.  KMP requirements

4.1.  Phase-1 KMP requirements

   Requirements on Phase-1 KMP are listed below.

   R1-1: Phase-1 KMP MUST support mutual authentication.

   R1-2: Phase-1 KMP MUST support stateless authentication relay

   R1-3:s Phase-1 KMP MUST support secure credential distribution.

4.2.  Phase-2 KMP requirements

   Requirements on Phase-2 KMP are listed below.

   R2-1: Phase-2 KMP Nodes MUST mutually authenticate each other before
   establishing a link and forming a mesh network.  No authentication
   server is involved in the Phase-2 authentication.

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   R2-2: Phase-2 KMP authentication credentials MAY be pre-provisioned
   or MAY be obtained via Phase-1 KMP.

   R2-3: Phase-2 KMP authentication credentials MUST have a lifetime.

   R2-4: Phase-2 KMP MUST support asymmetric key-based credentials for
   scalable operation.

   R2-5: Phase-2 KMP message exchanges MUST be integrity and reply
   protected after successful authentication.

   R2-6: Phase-2 KMP MUST have the capability to establish security
   association and unicast session keys after successful authentication
   to protect unicast MAC frames between nodes.

   R2-7: Phase-2 KMP MUST have the capability to establish security
   association and broadcast session keys after successful
   authentication to protect broadcast MAC frames between nodes.

   R2-8: Phase-2 KMP MUST have the capability to distribute the
   broadcast session keys securely.

5.  KMP candidates

5.1.  Phase-1 KMP candidates

   PANA [RFC5191] is the Phase-1 KMP candidate since it supports mutual
   authenticatio, stateless authentication relay function [RFC6345] and
   encrypted distribution of attributes [RFC6786].  The PANA
   Authentication Agent (PAA) is located in the coordinator of the mesh

5.2.  Phase-2 KMP candidates

   Once Phase-1 is complete by using PANA, it is assumed that node will
   have a certified public key (and associated private key).  A candiate
   Phase 2 KMP must use this certified public key to perform an
   authentication process.  As a consequence of a successful
   authentication some cryptographic material for unicast and multicast
   link protection between nodes must be generated.

   A list of candidate protocols may provide the requirements defined in
   Section 4.2 (this is a preliminary list that may be extended in the

   o  HIP DEX [I-D.moskowitz-hip-rg-dex].  The Host Identity Protocol
      Diet EXchange (HIP DEX) is a lighter version of the HIP Base
      Exchange (HIP BEX) [I-D.ietf-hip-rfc5201-bis] specifically

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      designed to be used in constrained devices (e.g sensor networks).
      In particular, HIP DEX may be used to authenticate two IEEE
      802.15.4 nodes and provide key material for a MAC layer security
      protocol as supported in IEEE 802.15.4.  However, by just using
      the value of the public key and the private key is not enough to
      carry out the authentication between nodes.  In particular, a node
      A and node B should not be able to successfully finish HIP DEX
      execution if they both have not been authenticated in Phase-1.
      Thus, HIP DEX will require the inclusion of the certificate of
      each node to achieve full mutual authentication.  The information
      in the certificate must ensure that the node was authenticated in
      Phase-1.  In consequence, HIP DEX must include a CERT parameter
      for carrying this certificate.  Once the HIP DEX protocol has
      succesfully finished a Pair-Wise Key SA is derived.  This SA is
      used to secure and authenticate user data, thus it can be used to
      provide the required keys for protecting IEEE 802.15.4 unicast MAC
      frames.  The same message is used to refresh the Pair-Wise Key SA.
      So far HIP DEX only specifies how this key material is used for
      protecting data traffic with ESP.  To distribute multicast keys
      HIP DEX may also use UPDATE message.  For less resource-
      constrained devices, HIP-BEX (Basic Exchange) is more suitable
      than HIP-DEX since HIP-BEX has better security properties (such as
      use of ephemeral Diffie-Hellman) than HIP-DEX at the cost of
      increased complexity.

   o  PANA [RFC5191] and some certificate-based EAP method.  Another
      candidate is to use PANA between node A and node B.  In this case,
      one of the nodes (e.g. node A) acts as PaC while the other (e.g.
      node B) is acting as PAA.  Moreover the PAA will operate in
      standalone mode [RFC4137].  That is, the EAP server is placed on
      the PAA and not in a backend authentication server.  Finally, the
      selected EAP method must work with public key/private key
      cryptography.  Once the PAA authentication is complete, the PaC
      and PAA can derive cryptographic material (for instance, from the
      MSK) which can be used to protect unicast MAC frames.  Futhermore,
      by using the extension defined in [RFC6345] is possible to
      distribute a multicast key encrypted with the PANA SA.  It is
      worth noting that, though this candidate solution leverages the
      PaC implementation from Phase-1, each node needs to deploy a PAA
      implementation, an EAP server and a specific EAP method, which may
      be different from the one used for Phase-1.

   o  DTLS[RFC6347].  Datagram Transport Layer Security (DTLS) is being
      considered in constrained devices for protecting application data
      traffic (e.g. CoAP).  It is not only being considered for unicast
      application data traffic but also for multicast data traffic
      [I-D.keoh-tls-multicast-security].  In particular, a multicast key
      is distributed over an unicast DTLS channel established between

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      two nodes (node A and node B).  This multicast key is used to
      protect multicast traffic by using TLS records.  The Phase2-KMP
      should be able to export this key material to the IEEE 802.15.4
      MAC layer so that the protection is carried out at link layer.  In
      [RFC5705], a mechanism for exporting key material after a TLS/DTLS
      execution is defined.  Nevertheless, the exported key material is
      intended to be used in unicast communications for upper layers or
      protocols at upper layers.  However, multicast key exportation is
      not specified.  In principle, this exported key material may be
      used for protecting unicast IEEE 802.15.4 MAC frames.  However,
      this usage and the multicast key exportation for multicast IEEE
      802.15.4 protection need further investigation.

6.  Security Considerations

   In this section, security issues that can potentially impact the
   operation of IEEE 802.15.4e TSCH MAC are described.

   In TSCH MAC, time synchronization and channel hopping information are
   advertised in Enhanced Beacon (EB) frames.  The advertised
   information is used by mesh nodes to determine the timeslots
   available for transmission and reception of MAC frames.  A rogue node
   can inject forged EB frames and can cause replay and DoS attacks to
   TSCH MAC operation.  To mitigate such attacks, all EB frames MUST be
   integrity protected.  While it is possible to use a pre-installed
   static key for protecting EB frames to every node, the static key
   becomes vulnerable when the associated MAC frame counter continues to
   be used after the frame counter wraps.  Therefore, the 6TSCH solution
   MUST provide a mechanism by which mesh nodes can use the available
   time slots to run an authentication and key exchange protocol and
   provide intergrity protection to EB frames.

7.  IANA Considerations

   There is no IANA action required for this document.

8.  References

8.1.  Normative References

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

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

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   [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.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6786]  Yegin, A. and R. Cragie, "Encrypting the Protocol for
              Carrying Authentication for Network Access (PANA)
              Attribute-Value Pairs", RFC 6786, November 2012.

              Moskowitz, R., "HIP Diet EXchange (DEX)", draft-moskowitz-
              hip-rg-dex-06 (work in progress), May 2012.

8.2.  Informative References

   [RFC4137]  Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba,
              "State Machines for Extensible Authentication Protocol
              (EAP) Peer and Authenticator", RFC 4137, August 2005.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC5705]  Rescorla, E., "Keying Material Exporters for Transport
              Layer Security (TLS)", RFC 5705, March 2010.

   [RFC6550]  Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
              Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
              Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
              Lossy Networks", RFC 6550, March 2012.

              Keoh, S., Kumar, S., and E. Dijk, "DTLS-based Multicast
              Security for Low-Power and Lossy Networks (LLNs)", draft-
              keoh-tls-multicast-security-00 (work in progress), October

              Moskowitz, R., Heer, T., Jokela, P., and T. Henderson,
              "Host Identity Protocol Version 2 (HIPv2)", draft-ietf-
              hip-rfc5201-bis-11 (work in progress), February 2013.


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              Palattella, MR., Ed., Thubert, P., Watteyne, T., and Q.
              Wang, "Terminology in IPv6 over Time Slotted Channel
              Hopping. draft-palattella-6tsch-terminology-00 (work in
              progress) ", March 2013.

              Thubert, P., Ed., Assimiti, R., and T. Watteyne, "An
              Architecture for IPv6 over Time Synchronized Channel
              Hopping. draft-thubert-6tsch-architecture-00 (work in
              progress) ", March 2013.

8.3.  External Informative References

              IEEE standard for Information Technology, "IEEE std.
              802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
              Networks (LR-WPANs) Amendament 1: MAC sublayer", April

              IEEE standard for Information Technology, "IEEE std.
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks", June 2011.

              ZigBee Public Document 15-002r00, "ZigBee IP
              Specification", 2013.

Authors' Addresses

   Stephen Chasko
   3000 Mill Creek Ave.
   Alpharetta, GA  30022

   Email: Stephen.Chasko@landisgyr.com

   Subir Das
   Applied Communication Sciences
   1 Telcordia Drive
   Piscataway, NJ  08854

   Email: sdas@appcomsci.com

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   Rafa Marin-Lopez
   University of Murcia
   Campus de Espinardo S/N, Faculty of Computer Science
   Murcia  30100

   Phone: +34 868 88 85 01
   Email: rafa@um.es

   Yoshihiro Ohba (editor)
   Toshiba Corporate Research and Development Center
   1 Komukai-Toshiba-cho
   Saiwai-ku, Kawasaki, Kanagawa  212-8582

   Phone: +81 44 549 2127
   Email: yoshihiro.ohba@toshiba.co.jp

   Pascal Thubert
   Cisco Systems, Inc
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

   Alper Yegin

   Email: alper.yegin@yegin.org

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