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Versions: (draft-ietf-roll-security-framework) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7416

Routing Over Low-Power and Lossy Networks                        T. Tsao
Internet-Draft                                              R. Alexander
Intended status: Informational                      Cooper Power Systems
Expires: April 05, 2015                                        M. Dohler
                                                                    CTTC
                                                                 V. Daza
                                                               A. Lozano
                                                Universitat Pompeu Fabra
                                                      M. Richardson, Ed.
                                                Sandelman Software Works
                                                        October 02, 2014


A Security Threat Analysis for Routing Protocol for Low-power and lossy
                             networks (RPL)
                  draft-ietf-roll-security-threats-11

Abstract

   This document presents a security threat analysis for the Routing
   Protocol for Low-power and lossy networks (RPL, ROLL).  The
   development builds upon previous work on routing security and adapts
   the assessments to the issues and constraints specific to low-power
   and lossy networks.  A systematic approach is used in defining and
   evaluating the security threats.  Applicable countermeasures are
   application specific and are addressed in relevant applicability
   statements.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 05, 2015.

Copyright Notice





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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   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
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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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Relationship to other documents . . . . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Considerations on RPL Security  . . . . . . . . . . . . . . .   5
     4.1.  Routing Assets and Points of Access . . . . . . . . . . .   6
     4.2.  The ISO 7498-2 Security Reference Model . . . . . . . . .   8
     4.3.  Issues Specific to or Amplified in LLNs . . . . . . . . .  10
     4.4.  RPL Security Objectives . . . . . . . . . . . . . . . . .  12
   5.  Threat Sources  . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Threats and Attacks . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  Threats due to failures to Authenticate . . . . . . . . .  14
       6.1.1.  Node Impersonation  . . . . . . . . . . . . . . . . .  14
       6.1.2.  Dummy Node  . . . . . . . . . . . . . . . . . . . . .  14
       6.1.3.  Node Resource Spam  . . . . . . . . . . . . . . . . .  14
     6.2.  Threats due to failure to keep routing information
           confidential  . . . . . . . . . . . . . . . . . . . . . .  15
       6.2.1.  Routing Exchange Exposure . . . . . . . . . . . . . .  15
       6.2.2.  Routing Information (Routes and Network Topology)
               Exposure  . . . . . . . . . . . . . . . . . . . . . .  15
     6.3.  Threats and Attacks on Integrity  . . . . . . . . . . . .  16
       6.3.1.  Routing Information Manipulation  . . . . . . . . . .  16
       6.3.2.  Node Identity Misappropriation  . . . . . . . . . . .  17
     6.4.  Threats and Attacks on Availability . . . . . . . . . . .  17
       6.4.1.  Routing Exchange Interference or Disruption . . . . .  17
       6.4.2.  Network Traffic Forwarding Disruption . . . . . . . .  17
       6.4.3.  Communications Resource Disruption  . . . . . . . . .  19
       6.4.4.  Node Resource Exhaustion  . . . . . . . . . . . . . .  19
   7.  Countermeasures . . . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Confidentiality Attack Countermeasures  . . . . . . . . .  20
       7.1.1.  Countering Deliberate Exposure Attacks  . . . . . . .  20
       7.1.2.  Countering Passive Wiretapping Attacks  . . . . . . .  21
       7.1.3.  Countering Traffic Analysis . . . . . . . . . . . . .  22
       7.1.4.  Countering Remote Device Access Attacks . . . . . . .  23



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     7.2.  Integrity Attack Countermeasures  . . . . . . . . . . . .  23
       7.2.1.  Countering Unauthorized Modification Attacks  . . . .  23
       7.2.2.  Countering Overclaiming and Misclaiming Attacks . . .  24
       7.2.3.  Countering Identity (including Sybil) Attacks . . . .  24
       7.2.4.  Countering Routing Information Replay Attacks . . . .  25
       7.2.5.  Countering Byzantine Routing Information Attacks  . .  25
     7.3.  Availability Attack Countermeasures . . . . . . . . . . .  26
       7.3.1.  Countering HELLO Flood Attacks and ACK Spoofing
               Attacks . . . . . . . . . . . . . . . . . . . . . . .  26
       7.3.2.  Countering Overload Attacks . . . . . . . . . . . . .  27
       7.3.3.  Countering Selective Forwarding Attacks . . . . . . .  28
       7.3.4.  Countering Sinkhole Attacks . . . . . . . . . . . . .  29
       7.3.5.  Countering Wormhole Attacks . . . . . . . . . . . . .  30
   8.  RPL Security Features . . . . . . . . . . . . . . . . . . . .  31
     8.1.  Confidentiality Features  . . . . . . . . . . . . . . . .  31
     8.2.  Integrity Features  . . . . . . . . . . . . . . . . . . .  32
     8.3.  Availability Features . . . . . . . . . . . . . . . . . .  33
     8.4.  Key Management  . . . . . . . . . . . . . . . . . . . . .  33
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  34
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  34
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     12.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  38

1.  Introduction

   In recent times, networked electronic devices have found an
   increasing number of applications in various fields.  Yet, for
   reasons ranging from operational application to economics, these
   wired and wireless devices are often supplied with minimum physical
   resources; the constraints include those on computational resources
   (RAM, clock speed, storage), communication resources (duty cycle,
   packet size, etc.), but also form factors that may rule out user
   access interfaces (e.g., the housing of a small stick-on switch), or
   simply safety considerations (e.g., with gas meters).  As a
   consequence, the resulting networks are more prone to loss of traffic
   and other vulnerabilities.  The proliferation of these low-power and
   lossy networks (LLNs), however, are drawing efforts to examine and
   address their potential networking challenges.  Securing the
   establishment and maintenance of network connectivity among these
   deployed devices becomes one of these key challenges.

   This document presents a threat analysis for securing the Routing
   Protocol for LLNs (RPL).  The process requires two steps.  First, the
   analysis will be used to identify pertinent security issues.  The
   second step is to identify necessary countermeasures to secure RPL.



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   As there are multiple ways to solve the problem and the specific
   tradeoffs are deployment specific, the specific countermeasure to be
   used is detailed in applicability statements.

   This document uses [ISO.7498-2.1988]] model, which describes
   Authentication, Access Control, Data Confidentiality, Data Integrity,
   and Non-Repudiation security services and to which Availability is
   added.  As explained below, Non-Repudiation does not apply to routing
   protocols.

   Many of the issues in this document were also covered in The IAB
   Smart Object Workshop [RFC6574], and The IAB Smart Object Security
   Workshop [I-D.gilger-smart-object-security-workshop].

   All of this document concerns itself with securing the control plane
   traffic.  As such it does not address authorization or authentication
   of application traffic.  RPL uses multicast as part of its protocol,
   and therefore mechanisms which RPL uses to secure this traffic might
   also be applicable to MPL control traffic as well: the important part
   is that the threats are similar.

2.  Relationship to other documents

   ROLL has specified a set of routing protocols for Lossy and Low-
   resource Networks (LLN) [RFC6550].  A number of applicability texts
   describes a subset of these protocols and the conditions which make
   the subset the correct choice.  The text recommends and motivates the
   accompanying parameter value ranges.  Multiple applicability domains
   are recognized including: Building and Home, and Advanced Metering
   Infrastructure.  The applicability domains distinguish themselves in
   the way they are operated, their performance requirements, and the
   most probable network structures.  Each applicability statement
   identifies the distinguishing properties according to a common set of
   subjects described in as many sections.

   The common set of security threats herein are referred to by the
   applicability statements, and that series of documents describes the
   preferred security settings and solutions within the applicability
   statement conditions.  This applicability statements may recommend
   more light weight security solutions and specify the conditions under
   which these solutions are appropriate.

3.  Terminology

   This document adopts the terminology defined in [RFC6550], in
   [RFC4949], and in [RFC7102].





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   The terms control plane and forwarding plane are used consistently
   with section 1 of [RFC6192].

   The term DODAG is from [RFC6550].

   EAP-TLS is defined in [RFC5216].

   PANA is defined in [RFC5191].

   CCM mode is defined in [RFC3610].

   [RFC7102] introduces the term Sleepy Node, referring to a node which
   may somtimes go into a low-power state, suspending protocol
   communications

   The terms SSID, ESSID and PAN refer to network identifiers, defined
   in [IEEE.802.11] and [IEEE.802.15.4].

   Although this is not a protocol specification, the key words "MUST",
   "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] in order to
   clarify and emphasize the guidance and directions to implementers and
   deployers of LLN nodes that utilize RPL.

4.  Considerations on RPL Security

   Routing security, in essence, ensures that the routing protocol
   operates correctly.  It entails implementing measures to ensure
   controlled state changes on devices and network elements, both based
   on external inputs (received via communications) or internal inputs
   (physical security of device itself and parameters maintained by the
   device, including, e.g., clock).  State changes would thereby involve
   not only authorization of injector's actions, authentication of
   injectors, and potentially confidentiality of routing data, but also
   proper order of state changes through timeliness, since seriously
   delayed state changes, such as commands or updates of routing tables,
   may negatively impact system operation.  A security assessment can
   therefore begin with a focus on the assets [RFC4949] that may be the
   target of the state changes and the access points in terms of
   interfaces and protocol exchanges through which such changes may
   occur.  In the case of routing security, the focus is directed
   towards the elements associated with the establishment and
   maintenance of network connectivity.

   This section sets the stage for the development of the analysis by
   applying the systematic approach proposed in [Myagmar2005] to the
   routing security, while also drawing references from other reviews



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   and assessments found in the literature, particularly, [RFC4593] and
   [Karlof2003] (i.e. selective forwarding, wormhole and sinkhole
   attacks).  The subsequent subsections begin with a focus on the
   elements of a generic routing process that is used to establish
   routing assets and points of access to the routing functionality.
   Next, the [ISO.7498-2.1988] security model is briefly described.
   Then, consideration is given to issues specific to or amplified in
   LLNs.  This section concludes with the formulation of a set of
   security objectives for RPL.

4.1.  Routing Assets and Points of Access

   An asset is an important system resource (including information,
   process, or physical resource), the access to, corruption or loss of
   which adversely affects the system.  In the control plane context, an
   asset is information about the network, processes used to manage and
   manipulate this data, and the physical devices on which this data is
   stored and manipulated.  The corruption or loss of these assets may
   adversely impact the control plane of the network.  Within the same
   context, a point of access is an interface or protocol that
   facilitates interaction between control plane assets.  Identifying
   these assets and points of access will provide a basis for
   enumerating the attack surface of the control plane.

   A level-0 data flow diagram [Yourdon1979] is used here to identify
   the assets and points of access within a generic routing process.
   The use of a data flow diagram allows for a clear and concise model
   of the way in which routing nodes interact and process information,
   and hence provides a context for threats and attacks.  The goal of
   the model is to be as detailed as possible so that corresponding
   assets, points of access, and process in an individual routing
   protocol can be readily identified.

   Figure 1 shows that nodes participating in the routing process
   transmit messages to discover neighbors and to exchange routing
   information; routes are then generated and stored, which may be
   maintained in the form of the protocol forwarding table.  The nodes
   use the derived routes for making forwarding decisions.


                   ...................................................
                    :                                                 :
                    :                                                 :
        |Node_i|<------->(Routing Neighbor       _________________    :
                    :     Discovery)------------>Neighbor Topology    :
                    :                            -------+---------    :
                    :                                   |             :
        |Node_j|<------->(Route/Topology       +--------+             :



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                    :     Exchange)            |                      :
                    :           |              V            ______    :
                    :           +---->(Route Generation)--->Routes    :
                    :                                       ---+--    :
                    :                                          |      :
                    : Routing on a Node Node_k                 |      :
                    ...................................................
                                                               |
        |Forwarding                                            |
        |On Node_l|<-------------------------------------------+


   Notation:

   (Proc)     A process Proc

   ________
   topology   A structure storing neighbor adjacency (parent/child)
   --------
   ________
    routes    A structure storing the forwarding information base (FIB)
   --------

   |Node_n|   An external entity Node_n

   ------->   Data flow


         Figure 1: Data Flow Diagram of a Generic Routing Process

   It is seen from Figure 1 that

   o  Assets include

      *  routing and/or topology information;

      *  route generation process;

      *  communication channel resources (bandwidth);

      *  node resources (computing capacity, memory, and remaining
         energy);

      *  node identifiers (including node identity and ascribed
         attributes such as relative or absolute node location).

   o  Points of access include




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      *  neighbor discovery;

      *  route/topology exchange;

      *  node physical interfaces (including access to data storage).

   A focus on the above list of assets and points of access enables a
   more directed assessment of routing security; for example, it is
   readily understood that some routing attacks are in the form of
   attempts to misrepresent routing topology.  Indeed, the intention of
   the security threat analysis is to be comprehensive.  Hence, some of
   the discussion which follows is associated with assets and points of
   access that are not directly related to routing protocol design but
   nonetheless provided for reference since they do have direct
   consequences on the security of routing.

4.2.  The ISO 7498-2 Security Reference Model

   At the conceptual level, security within an information system in
   general and applied to RPL in particular is concerned with the
   primary issues of authentication, access control, data
   confidentiality, data integrity, and non-repudiation.  In the context
   of RPL:

   Authentication
         Authentication involves the mutual authentication of the
         routing peers prior to exchanging route information (i.e., peer
         authentication) as well as ensuring that the source of the
         route data is from the peer (i.e., data origin authentication).
         [RFC5548] points out that LLNs can be drained by
         unauthenticated peers before configuration.  [RFC5673] requires
         availability of open and untrusted side channels for new
         joiners, and it requires strong and automated authentication so
         that networks can automatically accept or reject new joiners.

   Access Control
         Access Control provides protection against unauthorized use of
         the asset, and deals with the authorization of a node.

   Confidentiality











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         Confidentiality involves the protection of routing information
         as well as routing neighbor maintenance exchanges so that only
         authorized and intended network entities may view or access it.
         Because LLNs are most commonly found on a publicly accessible
         shared medium, e.g., air or wiring in a building, and sometimes
         formed ad hoc, confidentiality also extends to the neighbor
         state and database information within the routing device since
         the deployment of the network creates the potential for
         unauthorized access to the physical devices themselves.

   Integrity
         Integrity entails the protection of routing information and
         routing neighbor maintenance exchanges, as well as derived
         information maintained in the database, from unauthorized
         modification, insertions, deletions or replays. to be addressed
         beyond the routing protocol.

   Non-repudiation
         Non-repudiation is the assurance that the transmission and/or
         reception of a message cannot later be denied.  The service of
         non-repudiation applies after-the-fact and thus relies on the
         logging or other capture of on-going message exchanges and
         signatures.  Routing protocols typically do not have a notion
         of repudiation, so non-repudiation services are not required.
         Further, with the LLN application domains as described in
         [RFC5867] and [RFC5548], proactive measures are much more
         critical than retrospective protections.  Finally, given the
         significant practical limits to on-going routing transaction
         logging and storage and individual device digital signature
         verification for each exchange, non-repudiation in the context
         of routing is an unsupportable burden that bears no further
         considered as an RPL security issue.

   It is recognized that, besides those security issues captured in the
   ISO 7498-2 model, availability, is a security requirement:

   Availability
         Availability ensures that routing information exchanges and
         forwarding services need to be available when they are required
         for the functioning of the serving network.  Availability will
         apply to maintaining efficient and correct operation of routing
         and neighbor discovery exchanges (including needed information)
         and forwarding services so as not to impair or limit the
         network's central traffic flow function







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   It should be emphasized here that for RPL security the above
   requirements must be complemented by the proper security policies and
   enforcement mechanisms to ensure that security objectives are met by
   a given RPL implementation.

4.3.  Issues Specific to or Amplified in LLNs

   The requirements work detailed in Urban Requirements ([RFC5548]),
   Industrial Requirements ([RFC5673]), Home Automation ([RFC5826], and
   Building Automation ([RFC5867]) have identified specific issues and
   constraints of routing in LLNs.  The following is a list of
   observations from those requirements and evaluation of their impact
   on routing security considerations.

   Limited energy, memory, and processing node resources
         As a consequence of these constraints, there is an even more
         critical need than usual for a careful study of trade-offs on
         which and what level of security services are to be afforded
         during the system design process.  The chosen security
         mechanisms also needs to work within these constraints.
         Synchronization of security states with sleepy nodes [RFC7102]
         is yet another issue.  A non-rechargeable battery powered node
         may well be limited in energy for it's lifetime: once
         exchausted, it may well never function again.

   Large scale of rolled out network
         The possibly numerous nodes to be deployed make manual on-site
         configuration unlikely.  For example, an urban deployment can
         see several hundreds of thousands of nodes being installed by
         many installers with a low level of expertise.  Nodes may be
         installed and not activated for many years, and additional
         nodes may be added later on, which may be from old inventory.
         The lifetime of the network is measured in decades, and this
         complicates the operation of key management.

   Autonomous operations
         Self-forming and self-organizing are commonly prescribed
         requirements of LLNs.  In other words, a routing protocol
         designed for LLNs needs to contain elements of ad hoc
         networking and in most cases cannot rely on manual
         configuration for initialization or local filtering rules.
         Network topology/ownership changes, partitioning or merging, as
         well as node replacement, can all contribute to complicating
         the operations of key management.

   Highly directional traffic
         Some types of LLNs see a high percentage of their total traffic
         traverse between the nodes and the LLN Border Routers (LBRs)



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         where the LLNs connect to non-LLNs.  The special routing status
         of and the greater volume of traffic near the LBRs have routing
         security consequences as a higher valued attack target.  In
         fact, when Point-to-MultiPoint (P2MP) and MultiPoint-to-Point
         (MP2P) traffic represents a majority of the traffic, routing
         attacks consisting of advertising incorrect preferred routes
         can cause serious damage.

         While it might seem that nodes higher up in the acyclic graph
         (i.e. those with lower rank) should be secured in a stronger
         fashion, it is not in general easy to predict which nodes will
         occupy those positions until after deployment.  Issues of
         redundancy and inventory control suggests that any node might
         wind up in such a sensitive attack position, so all nodes to be
         capable of being fully secured.

         In addition, even if it were possible to predict which nodes
         will occupy positions of lower rank and provision them with
         stronger security mechanisms, in the absense of a strong
         authorization model, any node could advertise an incorrect
         preferred route.

   Unattended locations and limited physical security
         Many applications have the nodes deployed in unattended or
         remote locations; furthermore, the nodes themselves are often
         built with minimal physical protection.  These constraints
         lower the barrier of accessing the data or security material
         stored on the nodes through physical means.

   Support for mobility
         On the one hand, only a limited number of applications require
         the support of mobile nodes, e.g., a home LLN that includes
         nodes on wearable health care devices or an industry LLN that
         includes nodes on cranes and vehicles.  On the other hand, if a
         routing protocol is indeed used in such applications, it will
         clearly need to have corresponding security mechanisms.

         Additionally nodes may appear to move from one side of a wall
         to another without any actual motion involved, the result of
         changes to electromagnetic properties, such as opening and
         closing of a metal door.

   Support for multicast and anycast
         Support for multicast and anycast is called out chiefly for
         large-scale networks.  Since application of these routing
         mechanisms in autonomous operations of many nodes is new, the
         consequence on security requires careful consideration.




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   The above list considers how an LLN's physical constraints, size,
   operations, and variety of application areas may impact security.
   However, it is the combinations of these factors that particularly
   stress the security concerns.  For instance, securing routing for a
   large number of autonomous devices that are left in unattended
   locations with limited physical security presents challenges that are
   not found in the common circumstance of administered networked
   routers.  The following subsection sets up the security objectives
   for the routing protocol designed by the ROLL WG.

4.4.  RPL Security Objectives

   This subsection applies the ISO 7498-2 model to routing assets and
   access points, taking into account the LLN issues, to develop a set
   of RPL security objectives.

   Since the fundamental function of a routing protocol is to build
   routes for forwarding packets, it is essential to ensure that:

   o  routing/topology information integrity remains intact during
      transfer and in storage;

   o  routing/topology information is used by authorized entities;

   o  routing/topology information is available when needed.

   In conjunction, it is necessary to be assured that

   o  authorized peers authenticate themselves during the routing
      neighbor discovery process;

   o  the routing/topology information received is generated according
      to the protocol design.

   However, when trust cannot be fully vested through authentication of
   the principals alone, i.e., concerns of insider attack, assurance of
   the truthfulness and timeliness of the received routing/topology
   information is necessary.  With regard to confidentiality, protecting
   the routing/topology information from unauthorized exposure may be
   desirable in certain cases but is in itself less pertinent in general
   to the routing function.

   One of the main problems of synchronizing security states of sleepy
   nodes, as listed in the last subsection, lies in difficulties in
   authentication; these nodes may not have received in time the most
   recent update of security material.  Similarly, the issues of minimal
   manual configuration, prolonged rollout and delayed addition of
   nodes, and network topology changes also complicate key management.



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   Hence, routing in LLNs needs to bootstrap the authentication process
   and allow for flexible expiration scheme of authentication
   credentials.

   The vulnerability brought forth by some special-function nodes, e.g.,
   LBRs, requires the assurance, particularly in a security context,

   o  of the availability of communication channels and node resources;

   o  that the neighbor discovery process operates without undermining
      routing availability.

   There are other factors which are not part of RPL but directly
   affecting its function.  These factors include weaker barrier of
   accessing the data or security material stored on the nodes through
   physical means; therefore, the internal and external interfaces of a
   node need to be adequate for guarding the integrity, and possibly the
   confidentiality, of stored information, as well as the integrity of
   routing and route generation processes.

   Each individual system's use and environment will dictate how the
   above objectives are applied, including the choices of security
   services as well as the strengths of the mechanisms that must be
   implemented.  The next two sections take a closer look at how the RPL
   security objectives may be compromised and how those potential
   compromises can be countered.

5.  Threat Sources

   [RFC4593] provides a detailed review of the threat sources: outsiders
   and byzantine.  RPL has the same threat sources.

6.  Threats and Attacks

   This section outlines general categories of threats under the ISO
   7498-2 model and highlights the specific attacks in each of these
   categories for RPL.  As defined in [RFC4949], a threat is "a
   potential for violation of security, which exists when there is a
   circumstance, capability, action, or event that could breach security
   and cause harm."

   An attack is "an assault on system security that derives from an
   intelligent threat, i.e., an intelligent act that is a deliberate
   attempt (especially in the sense of a method or technique) to evade
   security services and violate the security policy of a system."

   The subsequent subsections consider the threats and the attacks that
   can cause security breaches under the ISO 7498-2 model to the routing



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   assets and via the routing points of access identified in
   Section 4.1.  The assessment steps through the security concerns of
   each routing asset and looks at the attacks that can exploit routing
   points of access.  The threats and attacks identified are based on
   the routing model analysis and associated review of the existing
   literature.  The source of the attacks is assumed to be from either
   inside or outside attackers.  While some attackers inside the network
   will be using compromised nodes, and therefore are only able to do
   what an ordinary node can ("node-equivalent"), other attacks may not
   limited in memory, CPU, power consumption or long term storage.
   Moore's law favours the attacker with access to the latest
   capabilities, while the defenders will remain in place for years to
   decades.

6.1.  Threats due to failures to Authenticate

6.1.1.  Node Impersonation

   If an attacker can join a network using any identity, then it may be
   able to assume the role of a legitimate (and existing node).  It may
   be able to report false readings (in metering applications), or
   provide inappropriate control messages (in control systems involving
   actuators) if the security of the application is implied by the
   security of the routing system.

   Even in systems where there application layer security, the ability
   to impersonate a node would permit an attacker to direct traffic to
   itself.  This may permit various on-path attacks which would
   otherwise be difficult, such replaying, delaying, or duplicating
   (application) control messages.

6.1.2.  Dummy Node

   If an attacker can join a network using any identify, then it can
   pretend to be a legitimate node, receiving any service legitimate
   nodes receive.  It may also be able to report false readings (in
   metering applications), or provide inappropriate authorizations (in
   control systems involving actuators), or perform any other attacks
   that are facilitated by being able to direct traffic towards itself.

6.1.3.  Node Resource Spam

   If an attacker can join a network with any identify, then it can
   continously do so with new (random) identities.  This act may drain
   down the resources of the network (battery, RAM, bandwidth).  This
   may cause legitimate nodes of the network to be unable to
   communicate.




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6.2.  Threats due to failure to keep routing information confidential

   The assessment in Section 4.2 indicates that there are attacks
   against the confidentiality of routing information at all points of
   access.  This threat may result in disclosure, as described in
   Section 3.1.2 of [RFC4593], and may involve a disclosure of routing
   information.

6.2.1.  Routing Exchange Exposure

   Routing exchanges include both routing information as well as
   information associated with the establishment and maintenance of
   neighbor state information.  As indicated in Section 4.1, the
   associated routing information assets may also include device
   specific resource information, such as available memory, remaining
   power, etc., that may be metrics of the routing protocol.

   The routing exchanges will contain reachability information, which
   would identify the relative importance of different nodes in the
   network.  Nodes higher up in the DODAG, to which more streams of
   information flow, would be more interesting targets for other
   attacks, and routing exchange exposures can identify them.

6.2.2.  Routing Information (Routes and Network Topology) Exposure

   Routes (which may be maintained in the form of the protocol
   forwarding table) and neighbor topology information are the products
   of the routing process that are stored within the node device
   databases.

   The exposure of this information will allow attackers to gain direct
   access to the configuration and connectivity of the network thereby
   exposing routing to targeted attacks on key nodes or links.  Since
   routes and neighbor topology information is stored within the node
   device, attacks on the confidentiality of the information will apply
   to the physical device including specified and unspecified internal
   and external interfaces.

   The forms of attack that allow unauthorized access or disclosure of
   the routing information will include:

   o  Physical device compromise;

   o  Remote device access attacks (including those occurring through
      remote network management or software/field upgrade interfaces).

   Both of these attack vectors are considered a device specific issue,
   and are out of scope for RPL to defend against.  In some



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   applications, physical device compromise may be a real threat and it
   may be necessary to provide for other devices to securely detect a
   compromised device and react quickly to exclude it.

6.3.  Threats and Attacks on Integrity

   The assessment in Section 4.2 indicates that information and identity
   assets are exposed to integrity threats from all points of access.
   In other words, the integrity threat space is defined by the
   potential for exploitation introduced by access to assets available
   through routing exchanges and the on-device storage.

6.3.1.  Routing Information Manipulation

   Manipulation of routing information that range from neighbor states
   to derived routes will allow unauthorized sources to influence the
   operation and convergence of the routing protocols and ultimately
   impact the forwarding decisions made in the network.

   Manipulation of topology and reachability information will allow
   unauthorized sources to influence the nodes with which routing
   information is exchanged and updated.  The consequence of
   manipulating routing exchanges can thus lead to sub-optimality and
   fragmentation or partitioning of the network by restricting the
   universe of routers with which associations can be established and
   maintained.

   A sub-optimal network may use too much power and/or may congest some
   routes leading to premature failure of a node, and a denial of
   service on the entire network.

   In addition, being able to attract network traffic can make a
   blackhole attack more damaging.

   The forms of attack that allow manipulation to compromise the content
   and validity of routing information include

   o  Falsification, including overclaiming and misclaiming (claiming
      routes to devices which the device can not in fact reach);

   o  Routing information replay;

   o  Byzantine (internal) attacks that permit corruption of routing
      information in the node even where the node continues to be a
      validated entity within the network (see, for example, [RFC4593]
      for further discussions on Byzantine attacks);

   o  Physical device compromise or remote device access attacks.



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6.3.2.  Node Identity Misappropriation

   Falsification or misappropriation of node identity between routing
   participants opens the door for other attacks; it can also cause
   incorrect routing relationships to form and/or topologies to emerge.
   Routing attacks may also be mounted through less sophisticated node
   identity misappropriation in which the valid information broadcast or
   exchanged by a node is replayed without modification.  The receipt of
   seemingly valid information that is however no longer current can
   result in routing disruption, and instability (including failure to
   converge).  Without measures to authenticate the routing participants
   and to ensure the freshness and validity of the received information
   the protocol operation can be compromised.  The forms of attack that
   misuse node identity include

   o  Identity attacks, including Sybil attacks (see [Sybil2002]) in
      which a malicious node illegitimately assumes multiple identities;

   o  Routing information replay.

6.4.  Threats and Attacks on Availability

   The assessment in Section 4.2 indicates that the process and
   resources assets are exposed to threats against availability; attacks
   in this category may exploit directly or indirectly information
   exchange or forwarding (see [RFC4732] for a general discussion).

6.4.1.  Routing Exchange Interference or Disruption

   Interference is the threat action and disruption is threat
   consequence that allows attackers to influence the operation and
   convergence of the routing protocols by impeding the routing
   information exchange.

   The forms of attack that allow interference or disruption of routing
   exchange include:

   o  Routing information replay;

   o  ACK spoofing;

   o  Overload attacks.  (Section 7.3.2)

   In addition, attacks may also be directly conducted at the physical
   layer in the form of jamming or interfering.

6.4.2.  Network Traffic Forwarding Disruption




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   The disruption of the network traffic forwarding capability will
   undermine the central function of network routers and the ability to
   handle user traffic.  This affects the availability of the network
   because of the potential to impair the primary capability of the
   network.

   In addition to physical layer obstructions, the forms of attack that
   allows disruption of network traffic forwarding include [Karlof2003]

   o  Selective forwarding attacks;


         |Node_1|--(msg1|msg2|msg3)-->|Attacker|--(msg1|msg3)-->|Node_2|


                  Figure 2: Selective forwarding example

   o  Wormhole attacks;


                  |Node_1|-------------Unreachable---------x|Node_2|
                     |                                         ^
                     |               Private Link              |
                     '-->|Attacker_1|===========>|Attacker_2|--'


                        Figure 3: Wormhole Attacks

   o  Sinkhole attacks.






















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                    |Node_1|     |Node_4|
                        |            |
                        `--------.   |
                    Falsify as    \  |
                    Good Link \   |  |
                    To Node_5  \  |  |
                                \ V  V
                    |Node_2|-->|Attacker|--Not Forwarded---x|Node_5|
                                  ^  ^ \
                                  |  |  \ Falsify as
                                  |  |   \Good Link
                                  /  |    To Node_5
                         ,-------'   |
                         |           |
                    |Node_3|     |Node_i|


                     Figure 4: sinkhole attack example

   These attacks are generally done to both control plane and forwarding
   plane traffic.  A system that prevents control plane traffic (RPL
   messages) from being diverted in these ways will also prevent actual
   data from being diverted.

6.4.3.  Communications Resource Disruption

   Attacks mounted against the communication channel resource assets
   needed by the routing protocol can be used as a means of disrupting
   its operation.  However, while various forms of Denial of Service
   (DoS) attacks on the underlying transport subsystem will affect
   routing protocol exchanges and operation (for example physical layer
   RF jamming in a wireless network or link layer attacks), these
   attacks cannot be countered by the routing protocol.  As such, the
   threats to the underlying transport network that supports routing is
   considered beyond the scope of the current document.  Nonetheless,
   attacks on the subsystem will affect routing operation and so must be
   directly addressed within the underlying subsystem and its
   implemented protocol layers.

6.4.4.  Node Resource Exhaustion

   A potential threat consequence can arise from attempts to overload
   the node resource asset by initiating exchanges that can lead to the
   exhaustion of processing, memory, or energy resources.  The
   establishment and maintenance of routing neighbors opens the routing
   process to engagement and potential acceptance of multiple
   neighboring peers.  Association information must be stored for each
   peer entity and for the wireless network operation provisions made to



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   periodically update and reassess the associations.  An introduced
   proliferation of apparent routing peers can therefore have a negative
   impact on node resources.

   Node resources may also be unduly consumed by attackers attempting
   uncontrolled topology peering or routing exchanges, routing replays,
   or the generating of other data traffic floods.  Beyond the
   disruption of communications channel resources, these consequences
   may be able to exhaust node resources only where the engagements are
   able to proceed with the peer routing entities.  Routing operation
   and network forwarding functions can thus be adversely impacted by
   node resources exhaustion that stems from attacks that include:

   o  Identity (including Sybil) attacks (see [Sybil2002]);

   o  Routing information replay attacks;

   o  HELLO-type flood attacks;

   o  Overload attacks.  (Section 7.3.2)

7.  Countermeasures

   By recognizing the characteristics of LLNs that may impact routing,
   this analysis provides the basis for understanding the capabilities
   within RPL used to deter the identified attacks and mitigate the
   threats.  The following subsections consider such countermeasures by
   grouping the attacks according to the classification of the ISO
   7498-2 model so that associations with the necessary security
   services are more readily visible.

7.1.  Confidentiality Attack Countermeasures

   Attacks to disclosure routing information may be mounted at the level
   of the routing information assets, at the points of access associated
   with routing exchanges between nodes, or through device interface
   access.  To gain access to routing/topology information, the attacker
   may rely on a compromised node that deliberately exposes the
   information during the routing exchange process, may rely on passive
   wiretapping or traffic analysis, or may attempt access through a
   component or device interface of a tampered routing node.

7.1.1.  Countering Deliberate Exposure Attacks

   A deliberate exposure attack is one in which an entity that is party
   to the routing process or topology exchange allows the routing/
   topology information or generated route information to be exposed to
   an unauthorized entity.



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   For instance, due to mis-configuration or inappropriate enabling of a
   diagnostic interface, an entity might be copying ("bridging") traffic
   from a secured ESSID/PAN to an unsecured interface.

   A prerequisite to countering this attack is to ensure that the
   communicating nodes are authenticated prior to data encryption
   applied in the routing exchange.  The authentication ensures the LLN
   starts with trusted nodes, but it does not provide an indication of
   whether the node has been compromised.

   Reputation systems could be be used to help when some nodes may sleep
   for extended periods of times.  It is also unclear if resulting
   dataset would even fit into constrained devices.

   To mitigate the risk of deliberate exposure, the process that
   communicating nodes use to establish session keys must be peer-to-
   peer (i.e., between the routing initiating and responding nodes).  As
   is pointed out in [RFC4107], automatic key management is critical for
   good security.  This helps ensure that neither node is exchanging
   routing information with another peer without the knowledge of both
   communicating peers.  For a deliberate exposure attack to succeed,
   the comprised node will need to be more overt and take independent
   actions in order to disclose the routing information to 3rd party.

   Note that the same measures which apply to securing routing/topology
   exchanges between operational nodes must also extend to field tools
   and other devices used in a deployed network where such devices can
   be configured to participate in routing exchanges.

7.1.2.  Countering Passive Wiretapping Attacks

   A passive wiretap attack seeks to breach routing confidentiality
   through passive, direct analysis and processing of the information
   exchanges between nodes.

   Passive wiretap attacks can be directly countered through the use of
   data encryption for all routing exchanges.  Only when a validated and
   authenticated node association is completed will routing exchange be
   allowed to proceed using established session keys and an agreed
   encryption algorithm.  The mandatory to implement CCM mode AES-128
   method, is described in [RFC3610], and is believed to be secure
   against a brute force attack by even the most well-equipped
   adversary.








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   The significant challenge for RPL is in the provisioning of the key,
   which in some modes of RFC6550 is used network-wide.  RFC6550 does
   not solve this problem, and it is the subject of significant future
   work: see, for instance: [AceCharterProposal], [SolaceProposal],
   [SmartObjectSecurityWorkshop].

   A number of deployments, such as [ZigBeeIP] specify no layer-3/RPL
   encryption or authentication and rely upon similiar security at
   layer-2.  These networks are immune to outside wiretapping attacks,
   but are vulnerable to passive (and active) routing attacks through
   compromises of nodes.  (see Section 8.2).

   Section 10.9 of [RFC6550] specifies AES-128 in CCM mode with a 32-bit
   MAC.

   Section 5.6 Zigbee IP [ZigBeeIP] specifies use of CCM, with PANA and
   EAP-TLS for key management.

7.1.3.  Countering Traffic Analysis

   Traffic analysis provides an indirect means of subverting
   confidentiality and gaining access to routing information by allowing
   an attacker to indirectly map the connectivity or flow patterns
   (including link-load) of the network from which other attacks can be
   mounted.  The traffic analysis attack on an LLN, especially one
   founded on shared medium, is passive and relies on the ability to
   read the immutable source/destination layer-2 and/or layer-3 routing
   information that must remain unencrypted to permit network routing.

   One way in which passive traffic analysis attacks can be muted is
   through the support of load balancing that allows traffic to a given
   destination to be sent along diverse routing paths.  RPL does not
   generally support multi-path routing within a single DODAG.  Multiple
   DODAGs are supported in the protocol, and an implementation could
   make use of that.  RPL does not have any inherent or standard way to
   guarantee that the different DODAGs would have significantly diverse
   paths.  Having the diverse DODAGs routed at different border routers
   might work in some instances, and this could be combined with a
   multipath technology like MPTCP ([RFC6824].  It is unlikely that it
   will be affordable in many LLNs, as few deployments will have memory
   space for more than a few sets of DODAG tables.

   Another approach to countering passive traffic analysis could be for
   nodes to maintain constant amount of traffic to different
   destinations through the generation of arbitrary traffic flows; the
   drawback of course would be the consequent overhead and energy
   expenditure.




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   The only means of fully countering a traffic analysis attack is
   through the use of tunneling (encapsulation) where encryption is
   applied across the entirety of the original packet source/destination
   addresses.  Deployments which use layer-2 security that includes
   encryption already do this for all traffic.

7.1.4.  Countering Remote Device Access Attacks

   Where LLN nodes are deployed in the field, measures are introduced to
   allow for remote retrieval of routing data and for software or field
   upgrades.  These paths create the potential for a device to be
   remotely accessed across the network or through a provided field
   tool.  In the case of network management a node can be directly
   requested to provide routing tables and neighbor information.

   To ensure confidentiality of the node routing information against
   attacks through remote access, any local or remote device requesting
   routing information must be authenticated, and must be authorized for
   that access.  Since remote access is not invoked as part of a routing
   protocol, security of routing information stored on the node against
   remote access will not be addressable as part of the routing
   protocol.

7.2.  Integrity Attack Countermeasures

   Integrity attack countermeasures address routing information
   manipulation, as well as node identity and routing information
   misuse.  Manipulation can occur in the form of falsification attack
   and physical compromise.  To be effective, the following development
   considers the two aspects of falsification, namely, the unauthorized
   modifications and the overclaiming and misclaiming content.  The
   countering of physical compromise was considered in the previous
   section and is not repeated here.  With regard to misuse, there are
   two types of attacks to be deterred, identity attacks and replay
   attacks.

7.2.1.  Countering Unauthorized Modification Attacks

   Unauthorized modifications may occur in the form of altering the
   message being transferred or the data stored.  Therefore, it is
   necessary to ensure that only authorized nodes can change the portion
   of the information that is allowed to be mutable, while the integrity
   of the rest of the information is protected, e.g., through well-
   studied cryptographic mechanisms.







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   Unauthorized modifications may also occur in the form of insertion or
   deletion of messages during protocol changes.  Therefore, the
   protocol needs to ensure the integrity of the sequence of the
   exchange sequence.

   The countermeasure to unauthorized modifications needs to:

   o  implement access control on storage;

   o  provide data integrity service to transferred messages and stored
      data;

   o  include sequence number under integrity protection.

7.2.2.  Countering Overclaiming and Misclaiming Attacks

   Both overclaiming and misclaiming aim to introduce false routes or a
   false topology that would not occur otherwise, while there are not
   necessarily unauthorized modifications to the routing messages or
   information.  In order to counter overclaiming, the capability to
   determine unreasonable routes or topology is required.

   The counter to overclaiming and misclaiming may employ:

   o  comparison with historical routing/topology data;

   o  designs which restrict realizable network topologies.

   RPL includes no specific mechanisms in the protocol to counter
   overclaims or misclaims.  An implementation could have specific
   heuristics implemented locally.

7.2.3.  Countering Identity (including Sybil) Attacks

   Identity attacks, sometimes simply called spoofing, seek to gain or
   damage assets whose access is controlled through identity.  In
   routing, an identity attacker can illegitimately participate in
   routing exchanges, distribute false routing information, or cause an
   invalid outcome of a routing process.

   A perpetrator of Sybil attacks assumes multiple identities.  The
   result is not only an amplification of the damage to routing, but
   extension to new areas, e.g., where geographic distribution is
   explicitly or implicitly an asset to an application running on the
   LLN, for example, the LBR in a P2MP or MP2P LLN.

   RPL includes specific public key based authentication at layer-3 that
   provide for authorization.  Many deployments use layer-2 security



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   that includes admission controls at layer-2 using mechanisms such as
   PANA.

7.2.4.  Countering Routing Information Replay Attacks

   In many routing protocols, message replay can result in false
   topology and/or routes.  This is often counted with some kind of
   counter to ensure the freshness of the message.  Replay of a current,
   literal RPL message are in general idempotent to the topology.  An
   older (lower DODAGVersionNumber) message, if replayed would be
   rejected as being stale.  The trickle algorithm further dampens the
   effect of any such replay, as if the message was current, then it
   would contain the same information as before, and it would cause no
   network changes.

   Replays may well occur in some radio technologies (not very likely,
   802.15.4) as a result of echos or reflections, and so some replays
   must be assumed to occur naturally.

   Note that for there to be no affect at all, the replay must be done
   with the same apparent power for all nodes receiving the replay.  A
   change in apparent power might change the metrics through changes to
   the ETX and therefore might affect the routing even though the
   contents of the packet were never changed.  Any replay which appears
   to be different should be analyzed as a Selective Forwarding Attack,
   Sinkhole Attack or Wormhole Attack.

7.2.5.  Countering Byzantine Routing Information Attacks

   Where a node is captured or compromised but continues to operate for
   a period with valid network security credentials, the potential
   exists for routing information to be manipulated.  This compromise of
   the routing information could thus exist in spite of security
   countermeasures that operate between the peer routing devices.

   Consistent with the end-to-end principle of communications, such an
   attack can only be fully addressed through measures operating
   directly between the routing entities themselves or by means of
   external entities able to access and independently analyze the
   routing information.  Verification of the authenticity and liveliness
   of the routing entities can therefore only provide a limited counter
   against internal (Byzantine) node attacks.

   For link state routing protocols where information is flooded with,
   for example, areas (OSPF [RFC2328]) or levels (ISIS [RFC7142]),
   countermeasures can be directly applied by the routing entities
   through the processing and comparison of link state information
   received from different peers.  By comparing the link information



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   from multiple sources decisions can be made by a routing node or
   external entity with regard to routing information validity; see
   Chapter 2 of [Perlman1988] for a discussion on flooding attacks.

   For distance vector protocols, such as RPL, where information is
   aggregated at each routing node it is not possible for nodes to
   directly detect Byzantine information manipulation attacks from the
   routing information exchange.  In such cases, the routing protocol
   must include and support indirect communications exchanges between
   non-adjacent routing peers to provide a secondary channel for
   performing routing information validation.  S-RIP [Wan2004] is an
   example of the implementation of this type of dedicated routing
   protocol security where the correctness of aggregate distance vector
   information can only be validated by initiating confirmation
   exchanges directly between nodes that are not routing neighbors.

   RPL does not provide any direct mechanisms like S-RIP.  It does
   listen to multiple parents, and may switch parents if it begins to
   suspect that it is being lied to.

7.3.  Availability Attack Countermeasures

   As alluded to before, availability requires that routing information
   exchanges and forwarding mechanisms be available when needed so as to
   guarantee proper functioning of the network.  This may, e.g., include
   the correct operation of routing information and neighbor state
   information exchanges, among others.  We will highlight the key
   features of the security threats along with typical countermeasures
   to prevent or at least mitigate them.  We will also note that an
   availability attack may be facilitated by an identity attack as well
   as a replay attack, as was addressed in Section 7.2.3 and
   Section 7.2.4, respectively.

7.3.1.  Countering HELLO Flood Attacks and ACK Spoofing Attacks

   HELLO Flood [Karlof2003],[I-D.suhopark-hello-wsn] and ACK Spoofing
   attacks are different but highly related forms of attacking an LLN.
   They essentially lead nodes to believe that suitable routes are
   available even though they are not and hence constitute a serious
   availability attack.

   A HELLO attack mounted against RPL would involve sending out (or
   replaying) DIO messages by the attacker.  Lower power LLN nodes might
   then attempt to join the DODAG at a lower rank than they would
   otherwise.

   The most effective method from [I-D.suhopark-hello-wsn] is the verify
   bidirectionality.  A number of layer-2 links are arranged in



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   controller/spoke arrangements, and continuously are validating
   connectivity at layer 2.

   In addition, in order to calculate metrics, the ETX must be computed,
   and this involves, in general, sending a number of messages between
   nodes which are believed to be adjacent.
   [I-D.kelsey-intarea-mesh-link-establishment] is one such protocol.

   In order to join the DODAG, a DAO message is sent upwards.  In RPL
   the DAO is acknowledged by the DAO-ACK message.  This clearly checks
   bidirectionality at the control plane.

   As discussed in section 5.1, [I-D.suhopark-hello-wsn] a receiver with
   a sensitive receiver could well hear the DAOs, and even send DAO-ACKs
   as well.  Such a node is a form of wormhole attack.

   These attacks are also all easily defended against using either
   layer-2 or layer-3 authentication.  Such an attack could only be made
   against a completely open network (such as might be used for
   provisioning new nodes), or by a compromised node.

7.3.2.  Countering Overload Attacks

   Overload attacks are a form of DoS attack in that a malicious node
   overloads the network with irrelevant traffic, thereby draining the
   nodes' energy store more quickly, when the nodes rely on batteries or
   energy scavenging.  It thus significantly shortens the lifetime of
   networks of energy-constrained nodes and constitutes another serious
   availability attack.

   With energy being one of the most precious assets of LLNs, targeting
   its availability is a fairly obvious attack.  Another way of
   depleting the energy of an LLN node is to have the malicious node
   overload the network with irrelevant traffic.  This impacts
   availability since certain routes get congested which:

   o  renders them useless for affected nodes and data can hence not be
      delivered;

   o  makes routes longer as shortest path algorithms work with the
      congested network;

   o  depletes battery and energy scavenging nodes more quickly and thus
      shortens the network's availability at large.

   Overload attacks can be countered by deploying a series of mutually
   non-exclusive security measures:




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   o  introduce quotas on the traffic rate each node is allowed to send;

   o  isolate nodes which send traffic above a certain threshold based
      on system operation characteristics;

   o  allow only trusted data to be received and forwarded.

   As for the first one, a simple approach to minimize the harmful
   impact of an overload attack is to introduce traffic quotas.  This
   prevents a malicious node from injecting a large amount of traffic
   into the network, even though it does not prevent said node from
   injecting irrelevant traffic at all.  Another method is to isolate
   nodes from the network at the network layer once it has been detected
   that more traffic is injected into the network than allowed by a
   prior set or dynamically adjusted threshold.  Finally, if
   communication is sufficiently secured, only trusted nodes can receive
   and forward traffic which also lowers the risk of an overload attack.

   Receiving nodes that validate signatures and sending nodes that
   encrypt messages need to be cautious of cryptographic processing
   usage when validating signatures and encrypting messages.  Where
   feasible, certificates should be validated prior to use of the
   associated keys to counter potential resource overloading attacks.
   The associated design decision needs to also consider that the
   validation process requires resources and thus itself could be
   exploited for attacks.  Alternatively, resource management limits can
   be placed on routing security processing events (see the comment in
   Section 6, paragraph 4, of [RFC5751]).

7.3.3.  Countering Selective Forwarding Attacks

   Selective forwarding attacks are a form of DoS attack which impacts
   the availability of the generated routing paths.

   A selective forwarding attack may be done by a node involved with the
   routing process, or it may be done by what otherwise appears to be a
   passive antenna or other RF feature or device, but is in fact an
   active (and selective) device.  An RF antenna/repeater which is not
   selective, is not a threat.












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   An insider malicious node basically blends neatly in with the network
   but then may decide to forward and/or manipulate certain packets.  If
   all packets are dropped, then this attacker is also often referred to
   as a "black hole".  Such a form of attack is particularly dangerous
   if coupled with sinkhole attacks since inherently a large amount of
   traffic is attracted to the malicious node and thereby causing
   significant damage.  In a shared medium, an outside malicious node
   would selectively jam overheard data flows, where the thus caused
   collisions incur selective forwarding.

   Selective Forwarding attacks can be countered by deploying a series
   of mutually non-exclusive security measures:

   o  multipath routing of the same message over disjoint paths;

   o  dynamically selecting the next hop from a set of candidates.

   The first measure basically guarantees that if a message gets lost on
   a particular routing path due to a malicious selective forwarding
   attack, there will be another route which successfully delivers the
   data.  Such a method is inherently suboptimal from an energy
   consumption point of view; it is also suboptimal from a network
   utilization perspective.  The second method basically involves a
   constantly changing routing topology in that next-hop routers are
   chosen from a dynamic set in the hope that the number of malicious
   nodes in this set is negligible.  A routing protocol that allows for
   disjoint routing paths may also be useful.

7.3.4.  Countering Sinkhole Attacks

   In sinkhole attacks, the malicious node manages to attract a lot of
   traffic mainly by advertising the availability of high-quality links
   even though there are none [Karlof2003].  It hence constitutes a
   serious attack on availability.

   The malicious node creates a sinkhole by attracting a large amount
   of, if not all, traffic from surrounding neighbors by advertising in
   and outwards links of superior quality.  Affected nodes hence eagerly
   route their traffic via the malicious node which, if coupled with
   other attacks such as selective forwarding, may lead to serious
   availability and security breaches.  Such an attack can only be
   executed by an inside malicious node and is generally very difficult
   to detect.  An ongoing attack has a profound impact on the network
   topology and essentially becomes a problem of flow control.

   Sinkhole attacks can be countered by deploying a series of mutually
   non-exclusive security measures:




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   o  use geographical insights for flow control;

   o  isolate nodes which receive traffic above a certain threshold;

   o  dynamically pick up next hop from set of candidates;

   o  allow only trusted data to be received and forwarded.

   A canary node could periodically call home (using a cryptographic
   process), with the home system noting if it fails to call in.  This
   provides detection of a problem, but does not mitigate it, and it may
   have significant energy consequences for the LLN.

   Some LLNs may provide for geolocation services, often derived from
   solving triangulation equations from radio delay calculations, such
   calculations could in theory be subverted by a sinkhole that
   transmitted at precisely the right power in a node to node fashion.

   While geographic knowledge could help assure that traffic always went
   in the physical direction desired, it would not assure that the
   traffic was taking the most efficient route, as the lowest cost real
   route might be match the physical topology; such as when different
   parts of an LLN are connected by high-speed wired networks.

7.3.5.  Countering Wormhole Attacks

   In wormhole attacks at least two malicious nodes claim to have a
   short path between themselves [Karlof2003].  This changes the
   availability of certain routing paths and hence constitutes a serious
   security breach.

   Essentially, two malicious insider nodes use another, more powerful,
   transmitter to communicate with each other and thereby distort the
   would-be-agreed routing path.  This distortion could involve
   shortcutting and hence paralyzing a large part of the network; it
   could also involve tunneling the information to another region of the
   network where there are, e.g., more malicious nodes available to aid
   the intrusion or where messages are replayed, etc.

   In conjunction with selective forwarding, wormhole attacks can create
   race conditions which impact topology maintenance, routing protocols
   as well as any security suits built on "time of check" and "time of
   use".

   A pure wormhole attack is nearly impossible to detect.  A wormhole
   which is used in order to subsequently mount another kind of attack
   would be defeated by defeating the other attack.  A perfect wormhole,
   in which there is nothing adverse that occurs to the traffic, would



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   be difficult to call an attack.  The worst thing that a benign
   wormhole can do in such a situation is to cease to operate (become
   unstable), causing the network to have to recalculate routes.

   A highly unstable wormhole is no different than a radio opaque (i.e.
   metal) door that opens and closes a lot.  RPL includes hysteresis in
   its objective functions [RFC6719] in an attempt to deal with frequent
   changes to the ETX between nodes.

8.  RPL Security Features

   The assessments and analysis in Section 6 examined all areas of
   threats and attacks that could impact routing, and the
   countermeasures presented in Section 7 were reached without confining
   the consideration to means only available to routing.  This section
   puts the results into perspective; dealing with those threats which
   are endemic to this field, those which have been mitigated through
   RPL protocol design, and those which require specific decisions to be
   made as part of provisioning a network.

   The first part of this section, Section 8.1 to Section 8.3, is a
   description of RPL security features that address specific threats.
   The second part of this section, Section 8.4, discusses issues of
   provisioning of security aspects that may impact routing but that
   also require considerations beyond the routing protocol, as well as
   potential approaches.

   RPL employs multicast and so these alternative communications modes
   MUST be secured with the same routing security services specified in
   this section.  Furthermore, irrespective of the modes of
   communication, nodes MUST provide adequate physical tamper resistance
   commensurate with the particular application domain environment to
   ensure the confidentiality, integrity, and availability of stored
   routing information.

8.1.  Confidentiality Features

   With regard to confidentiality, protecting the routing/topology
   information from unauthorized disclosure is not directly essential to
   maintaining the routing function.  Breaches of confidentiality may
   lead to other attacks or the focusing of an attacker's resources (see
   Section 6.2) but does not of itself directly undermine the operation
   of the routing function.  However, to protect against, and reduce
   consequences from other more direct attacks, routing information
   should be protected.  Thus, to secure RPL:

   o  implement payload encryption using layer-3 mechanisms described in
      [RFC6550];



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   o  or: implement layer-2 confidentiality;

   Where confidentiality is incorporated into the routing exchanges,
   encryption algorithms and key lengths need to be specified in
   accordance with the level of protection dictated by the routing
   protocol and the associated application domain transport network.
   For most networks, this means use of AES128 in CCM mode, but this
   needs to be specified clearly in the applicability statement.

   In terms of the life time of the keys, the opportunity to
   periodically change the encryption key increases the offered level of
   security for any given implementation.  However, where strong
   cryptography is employed, physical, procedural, and logical data
   access protection considerations may have more significant impact on
   cryptoperiod selection than algorithm and key size factors.
   Nevertheless, in general, shorter cryptoperiods, during which a
   single key is applied, will enhance security.

   Given the mandatory protocol requirement to implement routing node
   authentication as part of routing integrity (see Section 8.2), key
   exchanges may be coordinated as part of the integrity verification
   process.  This provides an opportunity to increase the frequency of
   key exchange and shorten the cryptoperiod as a complement to the key
   length and encryption algorithm required for a given application
   domain.

8.2.  Integrity Features

   The integrity of routing information provides the basis for ensuring
   that the function of the routing protocol is achieved and maintained.
   To protect integrity, RPL must either run using only the Secure
   versions of the messages, or must run over a layer-2 that uses
   channel binding between node identity and transmissions.

   Some layer-2 security mechanisms use a single key for the entire
   network, and these networks can not provide significant amount of
   integrity protection, as any node that has that key may impersonate
   any other node.  This mode of operation is likely acceptable when an
   entire deployment is under the control of a single administrative
   entity.

   Other layer-2 security mechanisms form a unique session key for every
   pair of nodes that needs to communicate; this is often called a per-
   link key.  Such networks can provide a strong degree of origin
   authentication and integrity on unicast messages.

   However, some RPL messages are broadcast, and even when per-node
   layer-2 security mechanisms are used, the integrity and origin



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   authentication of broadcast messages can not be as trusted due to the
   proliferation of the key used to secure them.

   RPL has two specific options which are broadcast in RPL Control
   Messages: the DODAG Information Object (DIO), and the DODAG
   Information Solicitation (DIS).  The purpose of the DIS is to cause
   potential parents to reply with a DIO, so the integrity of the DIS is
   not of great concern.  The DIS may also be unicast.

   The DIO is a critical piece of routing and carries many critical
   parameters.  RPL provides for asymmetric authentication at layer 3 of
   the RPL Control Message carrying the DIO and this may be warranted in
   some deployments.  A node could, if it felt that the DIO that it had
   received was suspicious, send a unicast DIS message to the node in
   question, and that node would reply with a unicast DIS.  Those
   messages could be protected with the per-link key.

8.3.  Availability Features

   Availability of routing information is linked to system and network
   availability which in the case of LLNs require a broader security
   view beyond the requirements of the routing entities.  Where
   availability of the network is compromised, routing information
   availability will be accordingly affected.  However, to specifically
   assist in protecting routing availability, nodes:

   o  MAY restrict neighborhood cardinality;

   o  MAY use multiple paths;

   o  MAY use multiple destinations;

   o  MAY choose randomly if multiple paths are available;

   o  MAY set quotas to limit transmit or receive volume;

   o  MAY use geographic information for flow control.

8.4.  Key Management

   The functioning of the routing security services requires keys and
   credentials.  Therefore, even though not directly a RPL security
   requirement, an LLN MUST have a process for initial key and
   credential configuration, as well as secure storage within the
   associated devices.  Anti-tampering SHOULD be a consideration in
   physical design.  Beyond initial credential configuration, an LLN is
   also encouraged to have automatic procedures for the revocation and
   replacement of the maintained security credentials.



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   While RPL has secure modes, but some modes are impractical without
   use of public key cryptography believed to be too expensive by many.
   RPL layer-3 security will often depend upon existing LLN layer-2
   security mechanisms, which provides for node authentication, but
   little in the way of node authorization.

9.  IANA Considerations

   This memo includes no request to IANA.

10.  Security Considerations

   The analysis presented in this document provides security analysis
   and design guidelines with a scope limited to RPL.  Security services
   are identified as requirements for securing RPL.  The specific
   mechanisms to be used to deal with each threat is specified in link-
   layer and deployment specific applicability statements.

11.  Acknowledgments

   The authors would like to acknowledge the review and comments from
   Rene Struik and JP Vasseur.  The authors would also like to
   acknowledge the guidance and input provided by the RPL Chairs, David
   Culler, and JP Vasseur, and the Area Director Adrian Farrel.

   This document started out as a combined threat and solutions
   document.  As a result of a series of security reviews performed by
   Steve Kent, the document was split up by RPL co-Chair Michael
   Richardson and security Area Director Sean Turner as it went through
   the IETF publication process.  The solutions to the threats are
   application and layer-2 specific, and have therefore been moved to
   the relevant applicability statements.

   Ines Robles and Robert Cragie kept track of the many issues that were
   raised during the development of this document

12.  References

12.1.  Normative References

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

   [RFC4107]  Bellovin, S. and R. Housley, "Guidelines for Cryptographic
              Key Management", BCP 107, RFC 4107, June 2005.

   [RFC6550]  Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
              Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.



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              Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
              Lossy Networks", RFC 6550, March 2012.

   [RFC6719]  Gnawali, O. and P. Levis, "The Minimum Rank with
              Hysteresis Objective Function", RFC 6719, September 2012.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, January 2014.

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

12.2.  Informative References

   [AceCharterProposal]
              Li, Kepeng., Ed., "Authentication and Authorization for
              Constrained Environment Charter (work-in-progress)",
              December 2013, <http://trac.tools.ietf.org/wg/core/trac/
              wiki/ACE_charter>.

   [I-D.gilger-smart-object-security-workshop]
              Gilger, J. and H. Tschofenig, "Report from the 'Smart
              Object Security Workshop', March 23, 2012, Paris, France",
              draft-gilger-smart-object-security-workshop-02 (work in
              progress), October 2013.

   [I-D.kelsey-intarea-mesh-link-establishment]
              Kelsey, R., "Mesh Link Establishment", draft-kelsey-
              intarea-mesh-link-establishment-05 (work in progress),
              February 2013.

   [I-D.suhopark-hello-wsn]
              Park, S., "Routing Security in Sensor Network: HELLO Flood
              Attack and Defense", draft-suhopark-hello-wsn-00 (work in
              progress), December 2005.

   [IEEE.802.11]
              , "Draft Standard for Information Technology -
              Telecommunications and information exchange between
              systems - Local and metropolitan area networks Specific
              requirements - Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) specifications ", IEEE
              802.11-REVma, 2006.

   [IEEE.802.15.4]
              , "Information technology - Telecommunications and
              information exchange between systems - Local and



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              metropolitan area networks - Specific requirements - Part
              15.4: Wireless Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications for Low Rate Wireless Personal
              Area Networks (LR-WPANs) ", IEEE Std 802.15.4-2006, June
              2006, <http://standards.ieee.org/getieee802/802.15.html>.

   [ISO.7498-2.1988]
              International Organization for Standardization,
              "Information Processing Systems - Open Systems
              Interconnection Reference Model - Security Architecture",
              ISO Standard 7498-2, 1988.

   [Karlof2003]
              Karlof, C. and D. Wagner, "Secure routing in wireless
              sensor networks: attacks and countermeasures", Elsevier
              AdHoc Networks Journal, Special Issue on Sensor Network
              Applications and Protocols, 1(2):293-315, September 2003,
              <http://nest.cs.berkeley.edu/papers/sensor-route-
              security.pdf>.

   [Myagmar2005]
              Myagmar, S., Lee, AJ., and W. Yurcik, "Threat Modeling as
              a Basis for Security Requirements", in Proceedings of the
              Symposium on Requirements Engineering for Information
              Security (SREIS'05), Paris, France, pp. 94-102, Aug 29,
              2005.

   [Perlman1988]
              Perlman, N., "Network Layer Protocols with Byzantine
              Robustness", MIT LCS Tech Report, 429, 1988.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, September 2003.

   [RFC4593]  Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
              Routing Protocols", RFC 4593, October 2006.

   [RFC4732]  Handley, M., Rescorla, E., IAB, "Internet Denial-of-
              Service Considerations", RFC 4732, December 2006.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2", RFC
              4949, August 2007.

   [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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   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, March 2008.

   [RFC5548]  Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
              "Routing Requirements for Urban Low-Power and Lossy
              Networks", RFC 5548, May 2009.

   [RFC5673]  Pister, K., Thubert, P., Dwars, S., and T. Phinney,
              "Industrial Routing Requirements in Low-Power and Lossy
              Networks", RFC 5673, October 2009.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks", RFC
              5826, April 2010.

   [RFC5867]  Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
              "Building Automation Routing Requirements in Low-Power and
              Lossy Networks", RFC 5867, June 2010.

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, March 2011.

   [RFC6574]  Tschofenig, H. and J. Arkko, "Report from the Smart Object
              Workshop", RFC 6574, April 2012.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, January 2013.

   [RFC7142]  Shand, M. and L. Ginsberg, "Reclassification of RFC 1142
              to Historic", RFC 7142, February 2014.

   [SmartObjectSecurityWorkshop]
              Klausen, T., Ed., "Workshop on Smart Object Security",
              March 2012, <http://www.lix.polytechnique.fr/hipercom/
              SmartObjectSecurity>.

   [SolaceProposal]
              Bormann, C., Ed., "Notes from the SOLACE ad-hoc at IETF85
              (work-in-progress)", November 2012, <http://www.ietf.org/
              mail-archive/web/solace/current/msg00015.html>.

   [Sybil2002]




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              Douceur, J., "The Sybil Attack", First International
              Workshop on Peer-to-Peer Systems , March 2002.

   [Wan2004]  Wan, T., Kranakis, E., and PC. van Oorschot, "S-RIP: A
              Secure Distance Vector Routing Protocol", in Proceedings
              of the 2nd International Conference on Applied
              Cryptography and Network Security, Yellow Mountain, China,
              pp. 103-119, Jun. 8-11 2004.

   [Yourdon1979]
              Yourdon, E. and L. Constantine, "Structured Design",
              Yourdon Press, New York, Chapter 10, pp. 187-222, 1979.

Authors' Addresses

   Tzeta Tsao
   Cooper Power Systems
   910 Clopper Rd. Suite 201S
   Gaithersburg, Maryland  20878
   USA

   Email: tzeta.tsao@cooperindustries.com


   Roger K. Alexander
   Cooper Power Systems
   910 Clopper Rd. Suite 201S
   Gaithersburg, Maryland  20878
   USA

   Email: roger.alexander@cooperindustries.com


   Mischa Dohler
   CTTC
   Parc Mediterrani de la Tecnologia, Av. Canal Olimpic S/N
   Castelldefels, Barcelona  08860
   Spain

   Email: mischa.dohler@cttc.es











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   Vanesa Daza
   Universitat Pompeu Fabra
   P/ Circumval.lacio 8, Oficina 308
   Barcelona  08003
   Spain

   Email: vanesa.daza@upf.edu


   Angel Lozano
   Universitat Pompeu Fabra
   P/ Circumval.lacio 8, Oficina 309
   Barcelona  08003
   Spain

   Email: angel.lozano@upf.edu


   Michael Richardson (ed) (editor)
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z5V7
   Canada

   Email: mcr+ietf@sandelman.ca


























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