6TiSCH                                                         S. Chasko
Internet-Draft                                                       L+G
Intended status: Informational                                    S. Das
Expires: April 24, 2014                                              ACS
                                                          R. Marin-Lopez
                                                    University of Murcia
                                                            Y. Ohba, Ed.
                                                              P. Thubert
                                                                A. Yegin
                                                        October 21, 2013

 Security Framework and Key Management Protocol Requirements for 6TiSCH


   Since 6TiSCH forms layer 3 meshes over IPv6, use of key management
   protocols defined at layer 3 or above matches the target architecture
   so they 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 6TiSCH 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
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   This Internet-Draft will expire on April 24, 2014.

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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Security Framework  . . . . . . . . . . . . . . . . . . . . .   4
   4.  KMP requirements  . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Phase-1 KMP requirements  . . . . . . . . . . . . . . . .   7
     4.2.  Phase-2 KMP requirements  . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
     8.3.  External Informative References . . . . . . . . . . . . .  10
   Appendix A.  KMP candidates . . . . . . . . . . . . . . . . . . .  11
     A.1.  Phase-1 KMP candidates  . . . . . . . . . . . . . . . . .  11
     A.2.  Phase-2 KMP candidates  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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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   6TiSCH aims at providing an open standard with new capabilities, both
   in terms of scalability (number of IPv6 devices in a single subnet)
   and in terms of guarantees (delivery and timeliness).  Both the
   ISA100.11a and Wireless HART protocols are gaining acceptance in the
   automation industry and demonstrate that a level of determinism can
   be achieved on a wireless medium with adequate guarantees for low
   speed control loops, used in mission critical Process Control
   applications.  For industrial applications, security is not an option
   and a power efficient authentication mechanism is strictly required.

   For other usages such as rust control, intrusion detection or seismic
   activity monitoring, the capability to correlate inputs from multiple
   sources can be critical, and the value of the network directly
   augments with the number of connected devices.  In order to scale to
   appropriate levels, the need for spatial reuse of the spectrum often
   implies routing capabilities over short range radios.  Proprietary
   variations demonstrate that RPL can scale to multiple thousands of
   devices, but at the same time expose a new challenge for security
   that must enable deployments of any scale with security requirements
   that may vary widely.  If the cost of the security in terms of
   network operations and system resources depends on that degree of
   security, then 6TiSCH should enable different profiles that can match
   different requirements and capabilities.

   Since 6TiSCH forms layer 3 meshes over IPv6, key management protocols
   defined at layer 3 or above 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 6TiSCH architecture.

   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 formed over unslotted CSMA-CA MAC of 802.15.4.  Each mesh node
   in the same ZigBee IP network derives the same link-layer key from
   the Network Key to protect IEEE 802.15.4 MAC frames exchanged between
   adjacent mesh nodes.  While sharing the same link-layer 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 link-layer key
   leakage in the entire ZigBee IP network.  Also, the cost of updating
   the link-layer key can be high as the key needs to be updated at all
   mesh nodes whenever the 4-octet frame counter at any single node
   wraps or the key is considered to be compromised or weak.

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   In the case of TSCH MAC which uses 5-octet global frame counter
   referred to as Absolute Slot Number (ASN), the frame counter is not
   likely to wrap in the expected lifetime of the device, but key update
   for a common link-layer key is still issue if the key needs to be
   changed for other reasons.

   This document introduces a more secure and scalable key management
   framework for 6TiSCH networks and identifies requirements for key
   management protocols to be used in the framework.

2.  Acronyms

   In addition to the acronyms defined in
   [I-D.palattella-6tisch-terminology], the following acronyms are used
   in this document.

   KMP: Key Management Protocol

   PANA: Protocol for carrying Authentication for Network Access

   SA: Security Association

   MAC: Media Access Control

3.  Security Framework

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

   o  Phase-0 (Implanting Phase): In this phase, a node installs
      credentials used for subsequent phases in a physically secure and
      managed location before the node is placed to where it is expected
      to operate.  Details on Phase-0 is outside the scope of this

   o  Phase-1 (Bootstrapping Phase): In this phase, a node (re)installs
      credentials used for subsequent phases from an authentication
      server after it is placed to where it is expected to operate.  The
      credentials installed during Phase-1 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 temporary 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

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      renewed using the Phase-1 credentials.  Both symmetric and
      asymmetric key credentials can be used as Phase-1 credentials.  In
      Phase-1 KMP, the Phase-2 and Phase-3 credentials are 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) co-located with the
      coordinator of the mesh network.  Phase-1 is optional if Phase-2
      credentials are installed during Phase-0 and do not need to be

   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, certificates are
      used as the Phase-2 credentials.  The SA of a link between node i
      and node j maintains link-layer keys, i.e., 128-bit keys used in
      AES-CCM* mode, a variant of the Counter with Cipher Block Chaining
      - Message Authentication Code (CBC-MAC) Mode, for encryption,
      authentication or authenticated encryption of 802.15.4 frames.
      K_i denotes a link-layer key for protecting broadcast MAC frames
      originated at node i.  K_ij denotes a link-layer key for
      protecting unicast MAC frames originated at node i and destined
      for node j.  There are several variations of forming link-layer

      1.  K_ij=K_i for all 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)

      In model 1, unicast and broadcast keys for protecting MAC frames
      originated at a given node are the same.  K_i and K_j may or may
      not be the same in model 1, and when K_i=K_j=K forall i and j,
      then such K is considered as a common network key.  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-directional in model 2 while they are uni-directional
      in model 3.  One model may be chosen among three depending on the
      required security level and the number of keys maintained by each

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   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-0 (Implanting)     |
              |      Phase-1 (Bootstrapping)    |
              |   Phase-2 (Link Establishment)  |
              |        Phase-3 (Operational)    |

                  Figure 1: 4-Phase Key Management Model

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              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

        .          .           ..         ...        ...         ...
        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 are in Phase-1.  (1) Nodes B and C run
   Phase-1 KMP with Node A (i.e., the authentication server) 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

                        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 section.

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.

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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.

   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 certificates for scalable operation.

   R2-5: Phase-2 KMP message exchanges MUST be integrity and replay
   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 support confidentiality to distribute the
   broadcast session keys securely.

5.  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
   [I-D.watteyne-6tsch-tsch-lln-context].  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 6TiSCH solution MUST
   provide a mechanism by which mesh nodes can use the available time
   slots to run Phase-1 and Phase-2 KMPs and provide integrity
   protection to EB frames.

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6.  IANA Considerations

   There is no IANA action required for this document.

7.  Acknowledgments

   We would like to thank Thomas Watteyne, Jonathan Simon, Maria Rita
   Palattella and Rene Struik for their valuable comments.

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.

   [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.

              Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
              "Terminology in IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-palattella-6tisch-terminology-00 (work
              in progress), October 2013.

              Watteyne, T., Palattella, M., and L. Grieco, "Using
              IEEE802.15.4e TSCH in an LLN context: Overview, Problem
              Statement and Goals", draft-watteyne-6tsch-tsch-lln-
              context-02 (work in progress), May 2013.

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

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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-14 (work in progress), October 2013.

              Palattella, MR., Ed., Thubert, P., Watteyne, T., and Q.
              Wang, "Terminology in IPv6 over Time Slotted Channel
              Hopping. draft-palattella-6tisch-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-6tisch-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

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              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.

Appendix A.  KMP candidates

A.1.  Phase-1 KMP candidates

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

A.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
   candidate 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
      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

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      CERT parameter for carrying this certificate.  Once the HIP DEX
      protocol has successfully 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.
      Furthermore, 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.

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   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
      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, a mechanism for exporting
      multicast key 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 multicast key management using
      DTLS for multicast IEEE 802.15.4 protection need further

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

   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

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   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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