Network Working Group                                      M. Richardson
Internet-Draft                                                       SSW
Intended status: Informational                         November 20, 2015
Expires: May 23, 2016

                     6tisch secure join using 6top


   This document details a security architecture that permits a new
   6tisch compliant node to join an 802.15.4e network.  The process
   bootstraps the new node authenticating the node to the network, and
   the network to the node, and configuring the new node with the
   required 6tisch schedule.  Any resemblance to WirelessHART/IEC62591
   is entirely intentional.

Requirements Language

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

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 May 23, 2016.

Copyright Notice

   Copyright (c) 2015 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
   ( 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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Assumptions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Roles . . . . . . . . . . . . . . . . . . . .   4
   3.  Architectural requirements of join protocol . . . . . . . . .   6
     3.1.  Entities involves in the join processions . . . . . . . .   6
     3.2.  Join Protocol deliverables  . . . . . . . . . . . . . . .   6
     3.3.  Join Protocol connection setup  . . . . . . . . . . . . .   7
     3.4.  End to End considerations for Join Protocol . . . . . . .   8
       3.4.1.  Security Considerations: alternatives to source
               routes  . . . . . . . . . . . . . . . . . . . . . . .   9
     3.5.  Join node discovery mechanism . . . . . . . . . . . . . .  10
       3.5.1.  prefixes to use for join traffic  . . . . . . . . . .  11
   4.  security requirements . . . . . . . . . . . . . . . . . . . .  12
     4.1.  threat model  . . . . . . . . . . . . . . . . . . . . . .  12
       4.1.1.  threats to the joining node . . . . . . . . . . . . .  12
       4.1.2.  threats to the resources of the network . . . . . . .  13
       4.1.3.  threats to other joining nodes  . . . . . . . . . . .  13
     4.2.  implementation cost . . . . . . . . . . . . . . . . . . .  14
     4.3.  denial of service . . . . . . . . . . . . . . . . . . . .  14
   5.  protocol requirements/constraints/assumptions . . . . . . . .  14
     5.1.  inline/offline  . . . . . . . . . . . . . . . . . . . . .  14
   6.  time sequence diagram . . . . . . . . . . . . . . . . . . . .  14
     6.1.  explanation of each step  . . . . . . . . . . . . . . . .  15
       6.1.1.  step (1): enhanced beacon . . . . . . . . . . . . . .  16
       6.1.2.  step (1B): send router solicitation . . . . . . . . .  16
       6.1.3.  step (1C): receive router advertisement . . . . . . .  16
       6.1.4.  step (2): certificate cache load  . . . . . . . . . .  16
       6.1.5.  step (3): receive certificate cache . . . . . . . . .  16
       6.1.6.  step (4): join request  . . . . . . . . . . . . . . .  17
       6.1.7.  step (5): NS duplicate address request (DAR)  . . . .  17
       6.1.8.  step (7): 6LBR informs JCE of new node  . . . . . . .  17
       6.1.9.  step (8): JCE informs/acks to 6LBR of new node  . . .  17
       6.1.10. step (9): NS duplicate address confirmation (DAC) . .  17
       6.1.11. step (10): JCE initiates connection to joining node .  17
       6.1.12. step (11): Join Assistant forwards packet to joining
               node  . . . . . . . . . . . . . . . . . . . . . . . .  17

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       6.1.13. step (12): Joining node replies . . . . . . . . . . .  17
       6.1.14. step (13): Join Assistant forwards reply to JCE . . .  17
     6.2.  size of each packet . . . . . . . . . . . . . . . . . . .  18
   7.  resulting security properties obtained from this process  . .  18
   8.  deployment scenarios underlying protocol requirements . . . .  18
   9.  device identification . . . . . . . . . . . . . . . . . . . .  18
     9.1.  PCE/Proxy vs Node identification  . . . . . . . . . . . .  18
     9.2.  Time source authentication / time validation  . . . . . .  18
     9.3.  description of certificate contents . . . . . . . . . . .  18
     9.4.  privacy aspects . . . . . . . . . . . . . . . . . . . . .  18
   10. slotframes to be used during join . . . . . . . . . . . . . .  19
   11. configuration aspects . . . . . . . . . . . . . . . . . . . .  19
   12. authorization aspects . . . . . . . . . . . . . . . . . . . .  19
     12.1.  how to determine a proxy/PCE from a end node . . . . . .  19
     12.2.  security considerations  . . . . . . . . . . . . . . . .  19
   13. security architecture . . . . . . . . . . . . . . . . . . . .  19
   14. Posture Maintenance . . . . . . . . . . . . . . . . . . . . .  19
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  19
   16. Other Related Protocols . . . . . . . . . . . . . . . . . . .  19
   17. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   18. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     19.1.  Normative references . . . . . . . . . . . . . . . . . .  19
     19.2.  Informative references . . . . . . . . . . . . . . . . .  21
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   A challenging part with constructing an LLN with nodes from multiple
   vendors is providing enough security context to each node such that
   the network communication can form and remain secure.  Most LLNs are
   small and have no operator interfaces at all, and even if they have
   debug interfaces (such as JTAG) with personnel trained to use that,
   doing any kind of interaction involving electrical connections in a
   dirty environment such as a factory or refinery is hopeless.

   It is necessary to have a way to introduce new nodes into a 6tisch
   network that does not involve any direct manipulation of the nodes
   themselves.  This act has been called "zero-touch" provisioning, and
   it does not occur by chance, but requires coordination between the
   manufacturer of the node, the service operator running the LLN, and
   the installers actually taking the devices out of the shipping boxes.

1.1.  Assumptions

   For the process described in this document to work, some assumptions
   about available infrastructure are made.  These are perhaps more than
   assumptions, but rather architectural requirements; the exact

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   operation of said infrastructure to be defined in a subsequent

   In the diagrams and text that follows entities are named (and defined
   in the terminology section).  Unless otherwise stated these are
   roles, not actual machines/systems.  The roles are seperated by
   network protocols in order that they roles can be performed by
   different systems, not because they have to be.  Different
   deployments will have different scaling requirements for those
   entities.  Smaller deployments might co-located many roles together
   into a single ruggedized platform, while other deployments might
   operate all of the roles on distinct, multiply-redundant server
   classes located in a fully equipped datacentre.

2.  Terminology and Roles

   Most terminology should be taken from [I-D.ietf-6tisch-architecture]
   and from [I-D.ietf-6tisch-6top-interface]  and
   [].  As well, many terms are taken from

   The following roles/things are defined:

   PCE                 the Path Computation Engine.  This entity reaches
                       out to each of the nodes in the LLN, and
                       configures an appropriate schedule using 6top.

   Authz Server/ACE    the Authorization Server.  This offloads
                       calculation of access control lists and other
                       access control decisions for constrainted nodes.
                       See [I-D.seitz-ace-problem-description]

   6top                the 6top protocol is defined abstractly in
                       [I-D.ietf-6tisch-6top-interface] and mapped to
                       run over CoAP in [I-D.ietf-6tisch-coap].  The
                       6top protocol is defined primarily to provision
                       the 6TiSCH schedule; this document proposes to
                       extend it for also provisioning of layer-2
                       security parameters.

   JCE                 the Join Coordination Entity.  This acronym is
                       chosen to parallel the PCE.

   joining node        The newly unboxed constrained node that needs to
                       join a network.

   join protocol       the protocol which secures initial communication
                       between the joining node and the JCE

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   join assistant      A constrained node near the joining node that
                       will act as it's first 6LR, and will relay
                       traffic to/from the joining node.

   unique join key     a key shared between a newly joining node, and
                       the JCE.  This key supports smaller installations
                       for which asymmetric methods are considered too

   production network  A 802.15.4e network whose encryption/
                       authentication keys are determined by some
                       algorithm/protocol.  There may have network-wide
                       group keys, or per-link keys.

   production network key  A L2-key known by all authorized nodes, used
                       for multicast messages

   per-peer L2 key     a key that results from an exchange (such as MLE)
                       that creates a pair-wise L2 key which is known
                       only to the two nodes involved,
                       [I-D.piro-6tisch-security-issues] calls this a

   The following terms are used in this document and come from other

   DevID               [IEEE.802.1AR] defines the secure DEVice
                       IDentifier as a device identifier that is
                       cryptographically bound to the device and is
                       composed of the Secure Device Identifier Secret
                       and the Secure Device Identifier Credential.

   IDevID              The Initial secure DEVice IDentifier (IDevID) is
                       the Device Identifier which was installed on the
                       device by the manufacturer.

   LDevID              A Locally significant secure DEVice IDentifiers
                       (LDevIDs) is a Secure Device Identifier
                       credential that is unique in the local
                       administrative domain in which the device is
                       used.  The LDevID is usually a new certificate
                       provisioned by some local means, such as the 6top
                       mechanism defined in this document.

   CoAP                The CoAP protocol, defined in [RFC7252] is an
                       HTTP-like resource access protocol.  CoAP runs
                       over UDP.

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   DTLS                The datagram version of TLS, defined in
                       [RFC6347], and which can be used to secure CoAP
                       in the same way that TLS secures HTTP.

   ARO                 [RFC6775]defines a number of new Neighbor
                       Discovery options including the Address
                       Registration Option

   DAR/DAC             [RFC6775]defines the Duplicate Address Request
                       and Duplicate Address Confirmation options to
                       turn the multicasted Duplicate Address Detection
                       protocol into a client/server process

   EARO                [I-D.thubert-6lo-rfc6775-update-reqs]extends the
                       ARO option to include some additional fields
                       necessary to distinguish duplicate addresses from
                       nodes that have moved networks when there are
                       mulitple LLNs linked over a backbone.

3.  Architectural requirements of join protocol

3.1.  Entities involves in the join processions

   The following actors are involved: there is a new joining node.  It
   is (radio) adjacent to the join assistant.  The join assistant is
   part of the production network, and participates in one or more
   DODAGs, such that it is reachable from the 6LBR, and the JCE.

3.2.  Join Protocol deliverables

   This section works from the ultimate goal, and goes backwards to
   prerequisite actions.  (Section 6 presents the protocol from
   beginning to end order)

   The ultimate goal of the join protocol is to provide a new node with
   a locally significant security credentials so that it is able to take
   part in the network directly.  The credentials may vary by
   deployment.  They can be one of:

   1)  a network-wide shared symmetric key (this is the production
       network key, or MasterKey)

   2)  a locally significant (one-level only) 802.11AR type LDevID
       certificate (which allows it to negotiate a pair-wise keys)

   One of these two items is delivered by JCE to the joining node using
   the 6top protocol.  That is, the JCE provisions using a secure

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   "northbound" interface.  The authentication of this interface the
   subject of the Join Protocol as explained below.

   The above credential are used for authentication to generate per-peer
   L2, using a key exchange protocol.  The choice of key exchange
   protocol, and what kind of link and multicast keying needs to be done
   is also provisioned by the JCE.  There are a number of options for
   doing this, such as:

   1)  Mesh Link Exchange [I-D.kelsey-intarea-mesh-link-establishment]
       (IMPORTANT, a good option.  Uses certificates from common CA)

   2)  work in 802.15.9 (uses certificates from common CA)

   3)  Security Framework and Key Management Protocol Requirements for
       6TiSCH [I-D.ohba-6tisch-security] (this document provides the
       phase 0 required, using the network-wide shared key)

   4)  Layer-2 security aspects for the IEEE 802.15.4e MAC
       [I-D.piro-6tisch-security-issues]: the MasterKey is used to
       derive per-peer L2 keys

   Per-peer L2 keying is critical when doing peer-2-peer schedule
   negotiation over 15.4 Information Elements.  Therefore a network-wide
   layer-2 key is inappropriate for the self-organizing networks, and a
   protocol (MLE, 802.15.9) SHOULD be used to derive per-peer L2 keys.

   For networks where there is a PCE present, it will do all schedule
   computation.  As a result the only trust relationship necessary is
   between the individual node and the PCE, and it MAY be acceptable to
   have a network-wide L2 key derived in ways such as
   [I-D.piro-6tisch-security-issues] describes in section ?.  The trust
   relationship between the PCE and the joining node flows from the
   LDevID certificate loaded by the JCE.  When the PCE and JCE are co-
   located, the existing 6top/DTLS security association could be reused.

3.3.  Join Protocol connection setup

   The intermediate level goal of the join protocol is to enable a Join
   Coordination Entity (JCE) to reach out to the new node, and install
   the credentials detailed above.  The JCE must authenticate itself to
   the joining node so that the joining node will know that it has
   joined the correct network, and the joining node must authenticate
   itself to the JCE so that the JCE will know that this node belongs in
   the network.  This two way authentication occurs in the 6top/CoAP/
   DTLS session that is established between the JCE and the joining

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   [I-D.ietf-6tisch-6top-interface] presents a way to interface to a
   6top information model (defined in YANG).  [I-D.ietf-6tisch-coap]
   explains how to access that information model using CoAP.  This
   information model will include security attributes for the network.
   The JCE would therefore reach out to the joining node and simply
   provision appropriate security properties into the joining node, much
   like the PCE will provision schedules.

   This 6top-based secure join protocol has defined a push model for
   security provisioning by the JCE.  This has been done for three

   1)  6tisch nodes already have to have a 6top CoAP server for schedule

   2)  this permits the JCE to manage how many nodes are trying to join
       at the same time, and limit how much bandwidth/energy is used for
       the join operation, and also for the JCE to prioritize the join
       order for nodes.

   3)  making the JCE initiate the DTLS connection significantly
       simplies the certificate chains that must be exchanged as the
       most constrained side (the joining node) provides it's
       credentials first, and lets the less constrained JCE figure out
       what kind of certificate chain will be required to authenticate
       the JCE to the joining node.  In EAP-TLS/802.1x situations, the
       TLS channel is created in the opposite direction, and it would
       have to complete in a tentative way, and then further
       authorization occur in-band.

3.4.  End to End considerations for Join Protocol

   In order for a 6top/DTLS/CoAP connection to occur between the JCE and
   the joining node, there needs to be end-to-end IPv6 connectivity
   between those two entities.  The joining node will not participate in
   the route-over RPL mesh, but rather will be seen by the network as
   being a 6lowpan only leaf-node.

   The joining node sends traffic to the join assistant, which forwards
   it using the normal RPL DODAG upwards routes, and which will reach
   the JCE using regular routing.

   The challenge is getting connectivity from the JCE to the joining
   node, as the DODAG and 6LBR root will have no information about this
   node.  Instead, the JCE will use loose-source routes (in the RH2) to
   address packets first to the Join Assistant, which will then forward
   to the joining node.  This has an interaction with the (strict)

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   source routes used by non-storing DODAGs which would be used by the
   6LBR to reach the Join Assistant.

   There are some alternatives to having full end to end connectivity
   which are discussed in the security considerations section.

3.4.1.  Security Considerations: alternatives to source routes

   This goes into security-considerations section

   A number of alternatives were considered for creating end to end
   connectivity between the joining node and the JCE, but were rejected.

   (1)  IPIP tunnel between Join Assistant and JCE

   (2)  using straight RPL routing: the Join Assistant sends a DAO

   (3)  using a separate RPL DODAG for join traffic

   (4)  establishing a specific multi-hop 6tisch track for join traffic
        for each Join Assistant  IPIP tunnel

   This mechanism requires 40 bytes overhead per packet, and may require
   specific state to be created on the Join Assistant, or may open the
   network up to a resource exhaustion by malicious join nodes.

   This mechanism was rejected on due to byte count, because it would
   require code only needed for join, and because doing it securely may
   require a per-tunnel state to be maintained on the join assistant.  join existing DODAG

   This mechanism is to just have the new node join the DODAG as a leaf
   node.  The join assistant would issue a DAO for the new node.  If a
   storing DODAG was used, this would directly cost state in all parent
   nodes of the Join Assistant, subjecting the lower-rank parts of the
   network to significant denial of service attacks.

   On a non-storing DODAG the situation is significantly better: no
   state is created by the presence of the leaf node except in the 6LBR,
   where available resources may be higher.

   This mechanism was rejected in favour of the loose source routed
   option as this the loose source routed option always works even for
   storing DODAGs, and is otherwise exactly equivalent in terms of
   network bandwidth cost.

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   One option to deal with the problem of resource consumption in the
   storing DODAG case is to use a second DODAG.

   This mechanism was rejected as it consumes resources in all nodes for
   the second DODAG, and many implementations support on a single DODAG.
   While storing DODAGs have a lighter network impact than non-storing
   ones (due to the lack of source routes), the PCE can control how much
   network bandwidth can be wasted by malicious join nodes using the
   regular 6tisch mechanisms, and this can be tuned.  A second DODAG
   would be a sunk cost with no tuning possible.  create 6tisch track to form mesh-under

   This mechanism would use 6tisch tracks so that traffic from the JCE
   would be switched from 6LBR to join node.  A track would be required
   to each join assistant.  This is an optimized form of source routing.

   This mechanism was not rejected, rather it was observed that it may
   be applied to any mechanism that uses source routing, and is an
   optimization; it has a certain cost in the form of intermediary node
   state, but that this state is not created by a malicious join node,
   rather it is created by the PCE.

3.5.  Join node discovery mechanism

   Continuing to work backwards, in order the JCE reach out to provision
   the Joining Node, it needs to know that the new node is present.
   This is done by taking advantage of the 6lowPAN Address Resolution
   Option (ARO) (section 4.1 [RFC6775]).  The ARO causes the new address
   to also be sent up to the 6LBR for duplicate detection using the DAR/
   DAC mechanism.  The 6LBR simply needs to tell the JCE about this.  A
   new protocol may be required for the situation where the JCE, PCE and
   6LBR are not co-located; it may be that this protocol could be simply
   a DAR in some encapsulation.  The details of this are currently out
   of scope for the architecture, as they affect interoperability
   between different vendors of JCE/6LBR/PCE rather than
   interoperability between the assistance/offload infrastructure, and
   the contrained nodes.  Future work may specify this part.

   In addition to needing to know the joining devices address from the
   DAR/NS, the JCE also needs to know the joining node's IDevID.  This
   is to determine if the node should even get any attention.  At this
   point, the IDevID can be forged, it will be authenticated during the
   setup of the 6top control protocol in the DTLS certificate exchange.
   If the serialNumber attribute of the IDevID is less than 64 bits,
   then it is possible that it could be placed into the EUI-64 option of

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   the ARO, or the OUI of the [I-D.thubert-6lo-rfc6775-update-reqs]
   EARO.  The JCE needs to know the joining node's serialNumber to know
   if this is device that it should even attempt to provision; and if
   so, it may need to retrieve an appropriate certificate chain (see
   [I-D.richardson-6tisch-idevid-cert]) from the Factory in order for
   the JCE to prove it is the legitimate owner of the joining node.

   Neither 802.1AR nor [RFC5280] provide any structure for the
   serialNumber, except that they are positive integers of up-to 20
   octets in size (numbers up to 2^160).  This specification would
   require that the serialNumber encoded in the IDevID be the same as
   the EUI-64 used by the device.  Some consideration needs to be given
   as to whether there are privacy considerations to doing this: any
   observer that can see the join traffic, can also see the source MAC
   address of the node as well.

   Prior to being able to announce itself in a NS, the joining node
   needs to find the Join Network.  This is done by listening to the
   extended beacon which are broadcast in designated slotframes by the
   network.  These are the same extended beacons which are used by the
   production network.  The extended beacons are transmitted in "MIC-
   only" (authentication only) mode.  Nodes with the production network
   key can authenticate the beacons.  The newly joining node can not
   authenticate the beacons, but it can read and process them, and can
   use this as a way to synchronize to the network.  During the Alpha
   period, the joining node can send a Router Soliticiation, and receive
   an appropriate Router Advertisement giving the Joining Node a prefix
   and default route to which to send the join traffic (the ND DAD
   mentioned above).

   It may be possible to eliminate a message exchange if space for a
   Router Advertisement can be found as part of the Join Network
   Extended Beacon.  This Enhanced Beacon would be distinct to the Join
   Network, and would be encrypted with the well-known Join Network key.

3.5.1.  prefixes to use for join traffic

   What prefix would the joining node for communication?  There are
   three options:

   (1)  just use link-local addresses (this may require that some
        traffic between 6LBR and JCE be IPIP tunneled)

   (2)  use a prefix specifically for join traffic (may be easier with a
        join-only DODAG)

   (3)  use the same prefix as the rest of the traffic (may require more
        complex ACLs, and leaks information to attackers)

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   It would be ideal to use link-local addresses, but they need to be
   scoped to the radio interface of the join assistant which can
   actually reach the joining node.  It may be that this can be made to
   work, but otherwise, the join assistant will have a ULA for each
   radio on which it expects join traffic.

4.  security requirements

4.1.  threat model

   There are three kinds of threats that a join process must deal with:
   threats to the joining node, threats to the resources of the network,
   and threats to other joining nodes.

4.1.1.  threats to the joining node

   A node may be taken out of it's box by a malicious entity and powered
   on.  This could happen during shipping, while being stored in a
   warehouse.  The device may be subject to physical theft, or the goal
   of the attacker may be to turn the device into a trojan horse of some
   kind.  Physical protection of the device is out of scope for this
   document; this document will henceforth assume that the device is
   sealed in some tamper-evident way and this document deals with
   attacks over the network.

   An attacker may attempt to convince the joining node that it is the
   legitimate Production Network; this is done by putting up a
   legitimate looking Join Network, and following the protocol as
   described in this document.  The Joining Node can not know if it has
   the corrrect Production Network until steps 11-13, when it attempts
   to validate the ClientCertificate provided by the JCE.

   When the joining node determines that this is the incorrect network,
   it must remember the PANID of the network that it has attempted to
   join, and then look for another network to try.  It SHOULD have some
   limit as the number of times it will try before going back to sleep,
   or shutting down, and it SHOULD take care not to consume more than
   some specified percentage of any battery it might have.

   Should a malicious production network be present at the same time/
   place as the legitimate production network, a the malicious agent
   could intercept and replay various packets from the proper join
   network, but ultimately this either results in a jamming-like denial
   of service, and/or the the ClientCertificate will not validate.

   It is a legitimate situation for there to be multiple possible join
   networks, and the joining node may have to try each one before it
   finds the network that it the right one for it.  The incorrect, but

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   non-malicious networks will not attempt the 6top provisioning step,
   and SHOULD return a negative result in steps 8/9, refusing the node's
   NS.  Those incorrect networks will be recognize that the node does
   not belong to them, because they will be able to see the Joining
   Node's IDevID in the ARO of step 4.

4.1.2.  threats to the resources of the network

   The production network has two important resources that may be
   attacked by malicious Joining nodes: 1) energy/bandwidth, 2) memory
   for routing entries.

   A malicious joining node could send many NS messages to the Join
   Assistant (from many made up addresses), which would send many NS/DAR
   messages to the 6LBR, and this would consume bandwidth, and therefore
   energy from the members of the mesh along the path to the 6LBR.  This
   can be mitigated by limited the total bandwidth available for

   A malicious joining node could send many NS messages, and if the 6LBR
   agreed to accept the new node (by IDevID), then the Join Assistant
   would MAY inject routing information into mesh for the Joining node.
   Non-storing DODAGs store are routing information in the DODAG Root
   (probably the 6LBR), which is generally not a constrained node.
   Storing DODAGs store routing entries at all nodes up to the DODAG,
   and those are constrained nodes.  Using a separate Join DODAG, and
   having that DODAG be non-storing will reduce any impact on
   intermediate nodes, but it does cause resources to be used for the
   second DODAG, and it may have a code impact if the nodes otherwise
   would not implement non-storing RPL.

4.1.3.  threats to other joining nodes

   A joining node (or the nodes of a malicious network, co-located near
   the legitimate production network) may mount attacks on legitimate
   nodes which have not yet joined.

   The malicious nodes may attempt to perform 6top operations against
   the joining node to keep it from being able to respond to the
   legitimate 6top session from the legitimate JCE.  During the Join
   phase, the Joining node MUST have all other resources and protocols
   turned off, even if they would normally be accessible as read-only
   unauthenticated CoAP resources.

   Malicious nodes could use the Join Network to mount various DTLS
   based attacks against the joining node, such as sending very long
   certificate chains to validate.  One might think to limit the length
   of such chains, but as shown in [I-D.richardson-6tisch-idevid-cert]

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   the chain may as a long as the supplier chain, plus may include
   additional certificates due to resales of plants/equipment/etc.
   Validating from a trusted certificate down to the specific
   certificate which proves ownership would eliminate random certificate
   chains, but the attacker could just feed the joining node legitimate
   chains that it observed (and replayed) from the legitimate JCE.  This
   does no good; the Joining node finds that the DTLS connection is
   invalid, but it may significantly run batteries down.

4.2.  implementation cost

   (storage of security material, computational cost)

4.3.  denial of service

   other communication impacts of security protocol mechanics

5.  protocol requirements/constraints/assumptions

5.1.  inline/offline

   dependencies on centralized or external functionality, inline and

6.  time sequence diagram

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   +-----+   +------+            +----------+              +-----------+
   |     |   |      |            |  JOIN    |              |  Joining  |
   | JCE |   | 6LBR |            | Assistant|              |   Node    |
   +-----+   +------+            |  (proxy) |              |           |
      |         |                +----------+              +-----------+
      |         |                     |                            |
      |         |                     |-------BEACON (1)---------->|
      |         |                     |                            |
      |         |                     |<----Router Solicitation----|
      |         |                     |---Router Advertisement---->|
      |         |                     |                            |
      |         |                     |<------CERT CACHE-----------|
      |         |                     |         LOAD    (2)        |
      |         |                     |                            |
      |         |                     |                            |
      |         |                     |-------CERT CACHE---------->|
      |         |                     |        RESPONSE (multiple) |
      |         |                     |                 (packets)  |
      |         |                     |                            |
      |         |                     |<-----JOIN REQUEST (4) -----|
      |         |                     |      (NS w/ARO )           |
      |         |                     |                            |
      |         |<---NS (DAR) (5)-----|                            |
      |<--??(6)-|                     |                            |
      |         |                     |                            |
      |--??(7)->|                     |                            |
      |         |                     |                            |
      |         |----NS (DAC)-(8)---->|                            |
      |         |     +------+        |                            |
      |         |<DAO-| mesh |<--DAO--|                            |
      |         |-DAO-| node |--DACK->|                            |
      |         | ACK +------+        |                            |
      |         |                     |-------JOIN ACK (9)-------->|
      |         |                     |                            |
      |         |                     |                            |
      |         |                     |          DTLS              |
      |         |                     |        (many packets)      |

                Figure 1: Message sequence for JOIN message

6.1.  explanation of each step

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6.1.1.  step (1): enhanced beacon

   A 6tisch join/synchronization beacon is broadcast periodically, and
   is authenticated with a symmetric "beacon key":

      well known JOIN key, such "JOIN6TISCH"

      another key, provisioned in advance (OOB)

      a shared symmetric key derived from public part of top level
      certificate (a closely held "secret")

   The purpose of this key is not to provide a high level of assurance,
   but rather to filter out 6tisch traffic from another random traffic
   that may be sharing the same radio frequencies.

   These beacons are used for JOIN purpose only, and are not related to
   the Enhanced Beacons used in the rest of 6tisch.

6.1.2.  step (1B): send router solicitation

   The joining node sends a router solicitation during the Aloha period
   of the beacon.

6.1.3.  step (1C): receive router advertisement

   The joining node receives a router advertisement from the Join
   Assistant.  It could include 6CO options to help compress packets,
   and should contain a prefix appropriate for join traffic.

6.1.4.  step (2): certificate cache load

   At step 10, the JCE will need to present a certificate chain anchored
   at a trusted CA built into the joining node.  It has been speculated
   that a significant amount of traffic could be avoided at step (10) if
   the common parts of the certificate chains could be cached in the
   join assistant.

   This optional step involves the joining node asking for certificates
   from the join assistant.

6.1.5.  step (3): receive certificate cache

   the proxy neighbour sends requested cached certificates to the
   joining node

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6.1.6.  step (4): join request

   A regular Neighbour Solicitation is sent.  This should contain an ARO
   (or EARO) option containing the Joining Nodes' IDevID.  The ARO/EARO
   will be proxied by the Join Assistant as part of normal 6LowPAN
   processing for leaf nodes (non-RPL nodes) upwards to the 6LBR

6.1.7.  step (5): NS duplicate address request (DAR)

6.1.8.  step (7): 6LBR informs JCE of new node

6.1.9.  step (8): JCE informs/acks to 6LBR of new node

   The JCE could reply in the negative, and this would cause a DAC
   failure, TBD

6.1.10.  step (9): NS duplicate address confirmation (DAC)

6.1.11.  step (10): JCE initiates connection to joining node

   The double lines indicate that an IPIP tunnel operation may be
   required.  If a straight DAO or seperate Join DODAG is used, then
   this is just a straight forwarding root to leaf node forwarding
   operation, and involves either using source routes (non-storing), or
   just forwarding for storing DODAGs.

   A specific bandwidth allocation would be used for this join traffic

   The production network encryption keys would be used for the join

6.1.12.  step (11): Join Assistant forwards packet to joining node

   The JOIN Assistant would forward traffic to the Joining Node.
   Recognizing that this traffic the JOIN Network, the JOIN Assistant
   would use the JOIN Network key.

6.1.13.  step (12): Joining node replies

   The joining node replies, using JOIN Network key.

6.1.14.  step (13): Join Assistant forwards reply to JCE

   The JOIN Assistant, recognizing that the traffic came from the JOIN
   Network, restricts the destination that can be reached to the the JCE
   only.  It can do this in a stateless way, and it does NOT need to
   track the traffic at (10) to open pinhole, etc.

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   Recognizing that the traffic came from the JOIN Network, the traffic
   would be placed into a bandwidth allocation (track?) that allows such

6.2.  size of each packet

   and number of frames needed to contain it.

7.  resulting security properties obtained from this process

   An end to end IPv6 CoAP/DTLS connection is created between the JCE
   and the Joining Node.  This connection carries 6top commands to
   update security parameters.  This results in either deployment of a
   single-level, locally relevant certificate (LDevID), or deployment of
   a network-wide symmetric "Master Key"

8.  deployment scenarios underlying protocol requirements

9.  device identification

   The JCE authenticates the joining node using a certificate chain
   provided inline during the DTLS negotiation.  The certificate chain
   is rooted in a vendor certificate that the JCE must have preloaded,
   and is a statement as to the node's 802.1AR IDevID.  The joining node
   authenticates the

9.1.  PCE/Proxy vs Node identification

9.2.  Time source authentication / time validation

   Note: RPL Root authentication is a chartered item

9.3.  description of certificate contents

9.4.  privacy aspects

   The EUI-64 of the Joining node is transmitted using a Well Known
   layer-2 encryption key.  Within the ARO/EARO of the Neighbour
   Solicitation is an OUI, which may be identical to the EUI-64 of the
   Joining node, or it might be an unrelated IDevID.

   An eavesdropper can therefore learn something about the manufacturer
   of every device as it joins.

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10.  slotframes to be used during join

   how is this communicated in the (extended) beacon.

11.  configuration aspects

   (allocation of slotframes after join, network statistics,

12.  authorization aspects

   lifecycle (key management, trust management)

12.1.  how to determine a proxy/PCE from a end node

12.2.  security considerations

   what prevents a node from transmitting when it is not their turn
   (part one: jamming)

   can a node successfully communicate with a peer at a time when not
   supposed to, may be tied to link layer security, or will it be
   policed by receiver?

13.  security architecture

   security architecture and fit of e.g. join protocol and provisioning
   into this

14.  Posture Maintenance

   (SACM related work)

15.  Security Considerations

16.  Other Related Protocols

17.  IANA Considerations

18.  Acknowledgements

19.  References

19.1.  Normative references

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

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   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., 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, DOI 10.17487/
              RFC6550, March 2012,

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC
              6775, DOI 10.17487/RFC6775, November 2012,

              Institute of Electrical and Electronics Engineers, "Secure
              Device Identity", IEEE 802.1AR, 2009,

              Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and
              Interaction using CoAP", draft-ietf-6tisch-coap-03 (work
              in progress), March 2015.

              Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
              (6top) Interface", draft-ietf-6tisch-6top-interface-04
              (work in progress), July 2015.

              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work
              in progress), May 2015.

              Behringer, M., Pritikin, M., Bjarnason, S., Clemm, A.,
              Carpenter, B., Jiang, S., and L. Ciavaglia, "Autonomic
              Networking - Definitions and Design Goals", draft-irtf-
              nmrg-autonomic-network-definitions-07 (work in progress),
              March 2015.

              Seitz, L. and G. Selander, "Problem Description for
              Authorization in Constrained Environments", draft-seitz-
              ace-problem-description-03 (work in progress), March 2015.

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              Richardson, M., "X509.v3 certificate extension for
              authorization of device ownership", draft-richardson-
              6tisch-idevid-cert-01 (work in progress), March 2015.

              Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
              (6top)", draft-wang-6tisch-6top-sublayer-04 (work in
              progress), November 2015.

              Thubert, P. and P. Stok, "Requirements for an update to
              6LoWPAN ND", draft-thubert-6lo-rfc6775-update-reqs-06
              (work in progress), January 2015.

19.2.  Informative references

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252, DOI 10.17487/
              RFC7252, June 2014,

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <>.

              Thubert, P., "LoWPAN Backbone Router", draft-thubert-
              6lowpan-backbone-router-00 (work in progress), March 2008.

              Watsen, K., Clarke, J., and M. Abrahamsson, "Zero Touch
              Provisioning for NETCONF Call Home", draft-ietf-netconf-
              zerotouch-04 (work in progress), October 2015.

              Kelsey, R., "Mesh Link Establishment", draft-kelsey-
              intarea-mesh-link-establishment-06 (work in progress), May

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              Chasko, S., Das, S., Lopez, R., Ohba, Y., Thubert, P., and
              A. Yegin, "Security Framework and Key Management Protocol
              Requirements for 6TiSCH", draft-ohba-6tisch-security-01
              (work in progress), March 2014.

              Piro, G., Boggia, G., and L. Grieco, "Layer-2 security
              aspects for the IEEE 802.15.4e MAC", draft-piro-6tisch-
              security-issues-03 (work in progress), December 2014.

Author's Address

   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7


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