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Network Working Group                                  O. Garcia-Morchon
Internet-Draft                                              Philips IP&S
Intended status: Informational                                  S. Kumar
Expires: November 25, 2017                              Philips Research
                                                                M. Sethi
                                                                Ericsson
                                                            May 24, 2017


       State of the Art and Challenges for the Internet of Things
                      draft-irtf-t2trg-iot-seccons-03

Abstract

   The Internet of Things (IoT) concept refers to the usage of standard
   Internet protocols to allow for human-to-thing and thing-to-thing
   communication.  The security needs are well-recognized and and many
   standardization steps for providing security have been taken, for
   example, the specification of Constrained Application Protocol (CoAP)
   over Datagram Transport Layer Security (DTLS).  However, security
   challenges still exist and there are some use cases that lack a
   suitable solution.  In this document, we first discuss the various
   stages in the lifecycle of a thing.  We then look at the security
   building blocks available for securing the different layers of the
   Internet protocol suite.  Next, we document the various security
   threats to a thing and the challenges that one might face in order to
   protect against these threats.  Lastly, we discuss the next steps
   needed to ensure roll out of secure Internet of Things services.

   This document is a product of the IRTF Thing-to-Thing Research Group
   (T2TRG).

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 November 25, 2017.



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Copyright Notice

   Copyright (c) 2017 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.  Conventions and Terminology Used in this Document . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation and background . . . . . . . . . . . . . . . . . .   4
     3.1.  The Thing Lifecycle . . . . . . . . . . . . . . . . . . .   4
     3.2.  Security building blocks  . . . . . . . . . . . . . . . .   6
   4.  Managing Threats and Risks  . . . . . . . . . . . . . . . . .  10
   5.  State of the Art  . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  IP-based IoT Protocols and Standards  . . . . . . . . . .  15
     5.2.  Existing IP-based Security Protocols and Solutions  . . .  17
     5.3.  IoT Security Guidelines . . . . . . . . . . . . . . . . .  20
     5.4.  Guidelines and IoT Security Regulations . . . . . . . . .  22
   6.  Challenges for a Secure IoT . . . . . . . . . . . . . . . . .  23
     6.1.  Constraints and Heterogeneous Communication . . . . . . .  23
       6.1.1.  Tight Resource Constraints  . . . . . . . . . . . . .  23
       6.1.2.  Denial-of-Service Resistance  . . . . . . . . . . . .  24
       6.1.3.  End-to-End Security, protocol translation, and the
               role of middleboxes . . . . . . . . . . . . . . . . .  25
       6.1.4.  New network architectures and paradigm  . . . . . . .  27
     6.2.  Bootstrapping of a Security Domain  . . . . . . . . . . .  27
     6.3.  Operation . . . . . . . . . . . . . . . . . . . . . . . .  27
       6.3.1.  End-to-End Security . . . . . . . . . . . . . . . . .  27
       6.3.2.  Group Membership and Security . . . . . . . . . . . .  28
       6.3.3.  Mobility and IP Network Dynamics  . . . . . . . . . .  29
     6.4.  Software update . . . . . . . . . . . . . . . . . . . . .  29
     6.5.  Verifying device behavior . . . . . . . . . . . . . . . .  30
     6.6.  End-of-life . . . . . . . . . . . . . . . . . . . . . . .  31
     6.7.  Testing: bug hunting and vulnerabilities  . . . . . . . .  31
     6.8.  Quantum-resistance  . . . . . . . . . . . . . . . . . . .  32
     6.9.  Privacy protection  . . . . . . . . . . . . . . . . . . .  32
     6.10. Data leakage  . . . . . . . . . . . . . . . . . . . . . .  33
     6.11. Trustworthy IoT Operation . . . . . . . . . . . . . . . .  34



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   7.  Conclusions and Next Steps  . . . . . . . . . . . . . . . . .  34
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  35
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  35
   11. Informative References  . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46

1.  Conventions and Terminology Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in "Key words for use in
   RFCs to Indicate Requirement Levels" [RFC2119].

2.  Introduction

   The Internet of Things (IoT) denotes the interconnection of highly
   heterogeneous networked entities and networks following a number of
   communication patterns such as: human-to-human (H2H), human-to-thing
   (H2T), thing-to-thing (T2T), or thing-to-things (T2Ts).  The term IoT
   was first coined by the Auto-ID center [AUTO-ID] in 1999.  Since
   then, the development of the underlying concepts and technologies has
   ever increased the pace of its adoption.  It is not surprising that
   IoT has received significant attention from the research community to
   (re)design, apply, and use of standard Internet technology and
   protocols for IoT.

   The introduction of IPv6 and web services as fundamental building
   blocks for IoT applications [RFC6568] promises to bring a number of
   basic advantages including: (i) a homogeneous protocol ecosystem that
   allows simple integration with Internet hosts; (ii) simplified
   development for devices that significantly vary in their
   capabilities; (iii) an unified interface for applications, removing
   the need for application-level proxies.  These building blocks
   greatly simplify the deployment of the envisioned scenarios ranging
   from building automation to production environments to personal area
   networks, in which very different things such as a temperature
   sensor, a luminaire, or an RFID tag might interact with each other,
   with a human carrying a smart phone, or with backend services.

   This Internet Draft presents an overview of the security aspects of
   the envisioned all-IP architecture as well as of the lifecycle of an
   IoT device, a "thing", within this architecture.  In particular, we
   review the most crucial aspects and functionalities that are required
   for a secure all-IP solution.

   With this, this Internet-Draft pursues several goals.  First, we aim
   at presenting a comprehensive view of the interactions and



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   relationships between an IoT application and security.  Second, we
   aim at describing challenges for a secure IoT in the specific context
   of the lifecycle of a resource-constrained device.  The final goal of
   this draft is to discuss the security considerations that are
   necessary for deploying secure IoT services.

   The first draft version of this document was submitted in March 2011.
   Initial draft versions of this document were presented and discussed
   during the CORE meetings at IETF 80 and later.  Discussions on
   security lifecycle at IETF 92 (March 2015) evolved into more general
   security considerations.  Thus, the draft was selected to address the
   T2TRG work item on the security considerations and challenges for the
   Internet of Things.  Further updates of the draft were presented and
   discussed during the T2TRG meetings at IETF 96 (July 2016) and IETF
   97 (November 2016) and at the joint interim in Amsterdam (March
   2017).  This document has been reviewed, commented, and discussed
   extensively for a period of nearly six years by the vast majority of
   T2TRG members and related groups such as CORE, which certainly
   exceeds 100 individuals.  It is the consensus of T2TRG that the
   baseline scenarios described in this document should be published in
   the IRTF Stream of the RFC series.  This document does not constitute
   a standard.

   The rest of the Internet-Draft is organized as follows.  Section 3
   depicts the lifecycle of a thing and gives general definitions for
   the main security building blocks within the IoT domain.  In
   Section 4, we discuss threats and methodologies for managing risks
   when designing a secure IoT system.  Section 5 reviews existing IP-
   based (security) protocols for the IoT and briefly summarizes
   existing guidelines and regulations in IoT security.  Section 6
   identifies remaining challenges for a secure IoT and discusses
   potential solutions.  Section 7 includes final remarks and
   conclusions.

3.  Motivation and background

3.1.  The Thing Lifecycle

   The lifecycle of a thing refers to the operational phases of a thing
   in the context of a given application or use case.  Figure 1 shows
   the generic phases of the lifecycle of a thing.  This generic
   lifecycle is applicable to very different IoT applications and
   scenarios.

   We consider for example, a Building Automation and Control (BAC)
   system, to illustrate the lifecycle and the meaning of these
   different phases.  A BAC system consists of a network of
   interconnected nodes that performs various functions in the domains



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   of HVAC (Heating, Ventilating, and Air Conditioning), lighting,
   safety etc.  The nodes vary in functionality and a majority of them
   represent resource-constrained devices such as sensors and
   luminaries.  Some devices may be battery operated or may rely energy
   harvesting.  This requires us to also consider devices that that
   sleep during their operation to save energy.  In our example, the
   life of a thing starts when it is manufactured.  Due to the different
   application areas (i.e., HVAC, lighting, safety) nodes are tailored
   to a specific task.  It is therefore unlikely that one single
   manufacturer will create all nodes in a building.  Hence,
   interoperability as well as trust bootstrapping between nodes of
   different vendors is important.  The thing is later installed and
   commissioned within a network by an installer during the
   bootstrapping phase.  Specifically, the device identity and the
   secret keys used during normal operation are provided to the device
   during this phase.  Different subcontractors may install different
   IoT devices for different purposes.  Furthermore, the installation
   and bootstrapping procedures may not be a defined event but may
   stretch over an extended period of time.  After being bootstrapped,
   the device and the system of things are in operational mode and
   execute the functions of the BAC system.  During this operational
   phase, the device is under the control of the system owner.  For
   devices with lifetimes spanning several years, occasional maintenance
   cycles may be required.  During each maintenance phase, the software
   on the device can be upgraded or applications running on the device
   can be reconfigured.  The maintenance tasks can thereby be performed
   either locally or from a backend system by means of an end-to-end
   connection.  Depending on the operational changes of the device, it
   may be required to re-bootstrap at the end of a maintenance cycle.
   The device continues to loop through the operational phase and the
   eventual maintenance phase until the device is decommissioned at the
   end of its lifecycle.  However, the end-of-life of a device does not
   necessarily mean that it is defective but rather denotes a need to
   replace and upgrade the network to next-generation devices in order
   to provide additional functionality.  Therefore the device can be
   removed and re-commissioned to be used in a different system under a
   different owner by starting the lifecycle all over again.














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    _Manufactured           _SW update          _Decommissioned
   /                       /                   /
   |   _Installed          |   _ Application   |   _Removed &
   |  /                    |  / reconfigured   |  /  replaced
   |  |   _Commissioned    |  |                |  |
   |  |  /                 |  |                |  |   _Reownership &
   |  |  |    _Application |  |   _Application |  |  / recommissioned
   |  |  |   /   running   |  |  / running     |  |  |
   |  |  |   |             |  |  |             |  |  |             \\
   +##+##+###+#############+##+##+#############+##+##+##############>>>
       \/  \______________/ \/  \_____________/ \___/         time //
       /           /         \          \          \
   Bootstrapping  /      Maintenance &   \     Maintenance &
                 /      re-bootstrapping  \   re-bootstrapping
           Operational                Operational

       Figure 1: The lifecycle of a thing in the Internet of Things.

3.2.  Security building blocks

   Security is a key requirement in the IoT due to several reasons.
   First, an IoT systems enable very specific applications in which
   users are involved.  A broken IoT system means that the privacy and
   safety of the users is endangered, this is key requirement in
   application areas such as critical infrastructure or health care.
   Second, a compromised IoT system means that an attacker altered the
   functionality of the devices of a given manufacturer, this not only
   affects the manufacturer's brand image in a negative way but can also
   leak information that is very valuable for the manufacturer, such as
   proprietary algorithms.  Third, the impact of attacking the IoT goes
   beyond a specific device or isolated systems since compromised IoT
   systems can be misused at scale, e.g., performing a Distribute Denial
   of Service (DDoS) attack that limits the availability of the
   compromised system or even other IT networks.  The fact that many IoT
   systems rely on standard IP protocols allows for easier system
   integration increasing the value of the realized use cases, but this
   also makes standard attacks applicable to a wide number of devices
   deployed in multiple systems.  This results in new requirements
   regarding the implementation of security.

   The term security subsumes a wide range of primitives, protocols, and
   procedures.  In the first place, it includes the basic provision of
   security services including confidentiality, authentication,
   integrity, authorization, non-repudiation, and availability, and some
   augmented services, such as duplicate detection and detection of
   stale packets (timeliness).  These security services can be
   implemented by a combination of cryptographic mechanisms, such as
   block ciphers, hash functions, or signature algorithms, and non-



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   cryptographic mechanisms, which implement authorization and other
   security policy enforcement aspects.  For each of the cryptographic
   mechanisms, a secure key management infrastructure is fundamental to
   handling the required cryptographic keys, whereas for security policy
   enforcement, one needs to properly codify authorizations as a
   function of device roles and a security policy engine that implements
   these authorization checks and that can implement changes hereto
   throughout the system's lifecycle.

   In the particular context of the IoT, security must not only focus on
   the required security services, but also pay special attention to how
   these are realized in the overall system and how the security
   functionalities are executed.  To this end, we consider five major
   "building blocks" to analyze and classify security aspects in the
   IoT:

   1.  The IoT security architecture: refers to the system elements
       involved in the management of the security relationships between
       things and the way these security interactions are handled (e.g.,
       centralized or distributed) during the lifecycle of a thing.  For
       instance, a smart home could rely on a centralized key
       distribution center in charge of managing cryptographic keys,
       devices & users, access control and privacy policies.

   2.  The security model within a smart object: describes the way
       security parameters, key, processes, and applications are managed
       within a smart object.  This includes aspects such as application
       process separation, secure storage of key materials, protection
       of algorithms, etc.  For instance, some smart objects might have
       extremely limited resources and have limited capabilities to
       protect secret keys; in contrast, other devices used in critical
       applications, e.g., a pacemaker, would rely on methods to
       securely protect cryptographic keys and functionality making sure
       that an attacker having physical access to the device cannot
       modify its operation.

   3.  Security bootstrapping: denotes the process by which a thing
       securely joins an IoT system at a given location and point in
       time.  For instance, bootstrapping of a connected camera can
       include the authentication and authorization of a device as well
       as the transfer of security parameters allowing for its trusted
       operation in a given network.

   4.  Network security: describes the mechanisms applied within a
       network to ensure trusted operation of the IoT.  Specifically, it
       prevents attackers from endangering or modifying the expected
       operation of an smart object, it also protects the network itself
       from malicious things.  For instance, network security can



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       include a number of mechanisms ranging from data link layer
       security, secure routing, and network layer security.

   5.  Application security: describes mechanisms to allow transfer of
       application data at the transport or upper layers (object
       security).  For instance, assuming an smart object such as an
       environmental sensor connected to a backend system, it can mean
       the exchange of secure blocks of data such as measurements by the
       sensor or a software update.  This data is exchanged end-to-end
       independently of communication pattern, for e.g through proxies
       or other store-and-forward mechanisms.








































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               ..........................
               :           +-----------+:
               :       *+*>|Application|*****
               :       *|  +-----------+:   *
               :       *|  +-----------+:   *
               :       *|->| Transport |:   *
               :    * _*|  +-----------+:   *
               :    *|  |  +-----------+:   *
               :    *|  |->|  Network  |:   *
               :    *|  |  +-----------+:   *
               :    *|  |  +-----------+:   *    *** Bootstrapping
               :    *|  +->|     L2    |:   *    ~~~ Transport Security
               :    *|     +-----------+:   *    ''' Object Security
               :+--------+              :   *
               :|Security| Configuration:   *
               :|Service |   Entity     :   *
               :+--------+              :   *
               :........................:   *
                                            *
   .........................                *  .........................
   :+--------+             :                *  :             +--------+:
   :|Security|   Node B    :                *  :   Node A    |Security|:
   :|Service |             :                *  :             |Service |:
   :+--------+             :                *  :             +--------+:
   :    |     +-----------+:                *  :+-----------+     |*   :
   :    |  +->|Application|:                ****|Application|<*+* |*   :
   :    |  |  +-----------+:''''''''''''''''''''+-----------+  |* |*   :
   :    |  |  +-----------+:                   :+-----------+  |* |*   :
   :    |  |->| Transport |~~~~~~~~~~~~~~~~~~~~~| Transport |<-|* |*   :
   :    |__|  +-----------+: ................. :+-----------+  |*_|*   :
   :       |  +-----------+: : +-----------+ : :+-----------+  | *     :
   :       |->|  Network  |: : |  Network  | : :|  Network  |<-|       :
   :       |  +-----------+: : +-----------+ : :+-----------+  |       :
   :       |  +-----------+: : +-----------+ : :+-----------+  |       :
   :       +->|     L2    |: : |     L2    | : :|     L2    |<-+       :
   :          +-----------+: : +-----------+ : :+-----------+          :
   :.......................: :...............: :.......................:
                      Overview of Security Mechanisms.

                                 Figure 2

   We now discuss an exemplary security architecture relying on a
   configuration entity for the management of the system with regard to
   the introduced security aspects (see Figure 2).  Inspired by the
   security framework for routing over low power and lossy network
   [ID-Tsao], we show an example of the security model of a smart object
   and illustrates how different security concepts and the lifecycle
   phases map to the Internet communication stack.



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   In our example, we consider a centralized architecture in which a
   configuration entity stores and manages the identities of the things
   associated with BAC system along with their cryptographic keys.
   During the bootstrapping phase, each thing executes the bootstrapping
   protocol with the configuration entity, thus obtaining the required
   device identities and some operational keying material.  The security
   service on a thing in turn stores the received keying material for
   the network layer and application security mechanisms for secure
   communication.  The criticality of the application requires an
   implementation of cryptographic algorithms that is resistant to side-
   channel attacks and the protection of the proprietary application-
   related algorithms executed in the device.  Things can then securely
   communicate with each other during their operational phase by means
   of the employed network and application security mechanisms.  Within
   the network, communication is protected by the network provider at
   MAC and network layer.  At application layer, the communication
   between any smart object and the application server is protected end-
   to-end, ensuring the forward secrecy of the communication.

4.  Managing Threats and Risks

   This section explores security threats and vulnerabilities in the IoT
   and discusses how to manage risks.

   Security threats have been analyzed in related IP protocols including
   HTTPS [RFC2818], COAP[RFC7252] 6LoWPAN [RFC4919], ANCP [RFC5713], DNS
   security threats [RFC3833], SIP [RFC3261], IPv6 ND [RFC3756], and
   PANA [RFC4016].  Nonetheless, the challenge is about their impacts on
   scenarios of the IoTs.  In this section, we specifically discuss the
   threats that could compromise an individual thing, or network as a
   whole.  Note that these set of threats might go beyond the scope of
   Internet protocols but we gather them here for the sake of
   completeness.  We also note that these threats can be classified
   according to either (i) the thing's lifecycle phases (when does the
   threat occur?) or (ii) the security building blocks (which
   functionality is affected by the threat?).  All these threats are
   summarized in Table 2.

   1.  Cloning of things: During the manufacturing process of a thing,
       an untrusted factory can easily clone the physical
       characteristics, firmware/software, or security configuration of
       the thing.  Deployed things might also be compromised and their
       software reserve engineered allowing for cloning or software
       modifications.  Such a cloned thing may be sold at a cheaper
       price in the market, and yet be able to function normally, as a
       genuine thing.  For example, two cloned devices can still be
       associated and work with each other.  In the worst case scenario,
       a cloned device can be used to control a genuine device or



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       perform an attack.  One should note here, that an untrusted
       factory may also change functionality of the cloned thing,
       resulting in degraded functionality with respect to the genuine
       thing (thereby, inflicting potential damage to the reputation of
       the original thing manufacturer).  Moreover, additional
       functionality can be implemented within the cloned thing, such as
       a backdoor.

   2.  Malicious substitution of things: During the installation of a
       thing, a genuine thing may be substituted with a similar variant
       of lower quality without being detected.  The main motivation may
       be cost savings, where the installation of lower-quality things
       (e.g., non-certified products) may significantly reduce the
       installation and operational costs.  The installers can
       subsequently resell the genuine things in order to gain further
       financial benefits.  Another motivation may be to inflict damage
       to the reputation of a competitor's offerings.

   3.  Eavesdropping attack: During the commissioning of a thing into a
       network, it may be susceptible to eavesdropping, especially if
       operational keying materials, security parameters, or
       configuration settings, are exchanged in clear using a wireless
       medium or if used cryptographic algorithms are not suitable for
       the envisioned lifetime of the device and the system.  After
       obtaining the keying material, the attacker might be able to
       recover the secret keys established between the communicating
       entities (e.g., H2T, T2Ts, or Thing to the backend management
       system), thereby compromising the authenticity and
       confidentiality of the communication channel, as well as the
       authenticity of commands and other traffic exchanged over this
       communication channel.  When the network is in operation, T2T
       communication may be eavesdropped upon if the communication
       channel is not sufficiently protected or in the event of session
       key compromise due to a long period of usage without key renewal
       or updates.

   4.  Man-in-the-middle attack: Both the commissioning phase and
       operational phases may also be vulnerable to man-in-the-middle
       attacks, e.g., when keying material between communicating
       entities are exchanged in the clear and the security of the key
       establishment protocol depends on the tacit assumption that no
       third party is able to eavesdrop during the execution of this
       protocol.  Additionally, device authentication or device
       authorization may be non-trivial, or may need support of a human
       decision process, since things usually do not have a-priori
       knowledge about each other and cannot always be able to
       differentiate friends and foes via completely automated
       mechanisms.  Thus, even if the key establishment protocol



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       provides cryptographic device authentication, this knowledge on
       device identities may still need complementing with a human-
       assisted authorization step (thereby, presenting a weak link and
       offering the potential of man-in-the-middle attacks this way).

   5.  Firmware Replacement attack: When a thing is in operation or
       maintenance phase, its firmware or software may be updated to
       allow for new functionality or new features.  An attacker may be
       able to exploit such a firmware upgrade by replacing the thing's
       software with malicious software, thereby influencing the
       operational behavior of the thing.  For example, an attacker
       could add a piece of malicious code to the firmware that will
       cause it to periodically report the energy usage of the lamp to a
       data repository for analysis.  Similarly, devices whose software
       has not been properly maintained and updated might contain
       vulnerabilities that might be exploited by attackers.

   6.  Extraction of private information: in the ambient environment the
       things (such as sensors, actuators, etc.) are usually physically
       unprotected and could easily be captured by an attacker.  Such an
       attacker may then attempt to extract private information such as
       keys (e.g., device's key, private-key, group key), sensed data
       (e.g., healthcare status of a user), configuration parameters
       (e.g., the WiFi key), or proprietary algorithms (e.g., algorithm
       performing some data analytic task) from this thing.  Compromise
       of a thing's unique key compromises communication channels of
       this particular thing and also compromise all data communicated
       over this channel.

   7.  Routing attack: As highlighted in [ID-Daniel], routing
       information in IoT can be spoofed, altered, or replayed, in order
       to create routing loops, attract/repel network traffic, extend/
       shorten source routes, etc.  Other relevant routing attacks
       include 1) Sinkhole attack (or blackhole attack), where an
       attacker declares himself to have a high-quality route/path to
       the base station, thus allowing him to do manipulate all packets
       passing through it. 2) Selective forwarding, where an attacker
       may selectively forward packets or simply drop a packet. 3)
       Wormhole attack, where an attacker may record packets at one
       location in the network and tunnel them to another location,
       thereby influencing perceived network behavior and potentially
       distorting statistics, thus greatly impacting the functionality
       of routing. 4) Sybil attack, whereby an attacker presents
       multiple identities to other things in the network.

   8.  Privacy threat: The tracking of a thing's location and usage may
       pose a privacy risk to its users.  An attacker can infer
       information based on the information gathered about individual



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       things, thus deducing behavioral patterns of the user of interest
       to him.  Such information can subsequently be sold to interested
       parties for marketing purposes and targeted advertising.

   9.  Denial-of-Service attack: Typically, things have tight memory and
       limited computation, they are thus vulnerable to resource
       exhaustion attack.  Attackers can continuously send requests to
       be processed by specific things so as to deplete their resources.
       This is especially dangerous in the IoTs since an attacker might
       be located in the backend and target resource-constrained devices
       in an Low-Latency Network (LLN).  Additionally, DoS attack can be
       launched by physically jamming the communication channel, thus
       breaking down the T2T communication channel.  Network
       availability can also be disrupted by flooding the network with a
       large number of packets.  On the other hand, things compromised
       by attackers can be used to disrupt the operation of other
       networks or systems by means of a Distributed DoS attack.

   The following table summarizes the above generic security threats and
   the potential point of vulnerabilities at different layers of the
   communication stack.  We also include related RFCs and ongoing
   standardization efforts that include a threat model that might apply
   to the IoTs.

              +------------------+------------------+------------------+
              | Manufacturing    | Installation/    | Operation        |
              |                  | Commissioning    |                  |
 +------------+------------------+------------------+------------------+
 |Thing's     | Device Cloning   |Substitution      |Privacy threat    |
 |Model       |                  |ACE-OAuth(draft)  |Extraction of     |
 |            |                  |                  |private inform.   |
 +------------+------------------+------------------+------------------+
 |Application |                  |RFC2818, RFC7252  |RFC2818, Firmware |
 |Layer       |                  |OSCOAP(draft)     |replacement       |
 +------------+------------------+------------------+------------------+
 |Transport   |                  | Eavesdropping &  |Eavesdropping     |
 |Layer       |                  | Man-in-the-middle|Man-in-the-middle |
 +------------+------------------| attack, RFC7925  |------------------+
 |Network     |                  | RFC4919, RFC5713 |RFC4919,DoS attack|
 |Layer       |                  | RFC3833, RFC3756 |Routing attack    |
 |            |                  |                  |RFC3833           |
 +------------+------------------+------------------+------------------+
 |Physical    |                  |                  |DoS attack        |
 |Layer       |                  |                  |                  |
 +-------------------------------+------------------+------------------+

   Figure 3: Classification of threats according to the lifecycle phases
                       and security building blocks.



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   Dealing with above threats and finding suitable security mitigations
   is challenging: there are very sophisticated threats that a very
   powerful attacker could use; also, new threats and exploits appear in
   a daily basis.  Therefore, the existence of proper secure product
   creation processes that allow managing and minimizing risks during
   the lifecycle of the IoT devices is at least as important as being
   aware of the threats.  A non-exhaustive list of relevant processes
   include:

   1.  A Business Impact Analysis (BIA) assesses the consequences of
       loss of basic security attributes, namely, confidentiality,
       integrity and availability in an IoT system.  These consequences
       might include impact on data lost, sales lost, increased
       expenses, regulatory fines, customer dissatisfaction, etc.
       Performing a business impact analysis allow determining the
       business relevance of having a proper security design placing
       security in the focus.

   2.  A Risk Assessment (RA) analyzes security threats to the IoT
       system, considering their likelihood and impact, and deriving for
       each of them a risk level.  Risks classified as moderate or high
       must be mitigated, i.e., security architecture should be able to
       deal with that threat bringing the risk to a low level.  Note
       that threats are usually classified according to their goal:
       confidentiality, integrity, and availability.  For instance, a
       specific threat to recover a symmetric-key used in the system
       relates to confidentiality.

   3.  A privacy impact assessment (PIA) aims at assessing Personal
       Identifiable Information (PII) that is collected, processed, or
       used in the IoT system.  By doing so, the goals is to fulfill
       applicable legal requirements, determine risks and effects of the
       manipulation of PII, and evaluate proposed protections.

   4.  Procedures for incident reporting and mitigation refer to the
       methodologies that allow becoming aware of any security issues
       that affect an IoT system.  Furthermore, this includes steps
       towards the actual deployment of patches that mitigate the
       identified vulnerabilities.

   BIA, RA, and PIA are usually to be realized during the creation of a
   new IoT system, introduction of new technologies in the IoT system,
   or deployment of significant system upgrades.  In general, it is
   recommended to re-assess them on a regular basis taking into account
   new use cases or threats.






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5.  State of the Art

   This section is organized as follows.  Section 5.1 summarizes state
   of the art on IP-based systems, within IETF and in other
   standardization bodies.  Section 5.2 summarizes state of the art on
   IP-based security protocols and their usage.  Section 5.3 discusses
   guidelines for securing the IoT as proposed by other bodies.
   Section 5.4 analyzes status of other relevant standards, in
   particular, those by NIST regarding IoT and IoT security.

5.1.  IP-based IoT Protocols and Standards

   Nowadays, there exists a multitude of control protocols for the IoT.
   For BAC systems, the ZigBee standard [ZB], BACNet [BACNET], or DALI
   [DALI] play key roles.  Recent trends, however, focus on an all-IP
   approach for system control.

   In this setting, a number of IETF working groups are designing new
   protocols for resource constrained networks of smart things.  The
   6LoWPAN working group [WG-6LoWPAN] concentrates on the definition of
   methods and protocols for the efficient transmission and adaptation
   of IPv6 packets over IEEE 802.15.4 networks [RFC4944].

   The CoRE working group [WG-CoRE] provides a framework for resource-
   oriented applications intended to run on constrained IP network
   (6LoWPAN).  One of its main tasks is the definition of a lightweight
   version of the HTTP protocol, the Constrained Application Protocol
   (CoAP) [RFC7252], that runs over UDP and enables efficient
   application-level communication for things.

   In many smart object networks, the smart objects are dispersed and
   have intermittent reachability either because of network outages or
   because they sleep during their operational phase to save energy.  In
   such scenarios, direct discovery of resources hosted on the
   constrained server might not be possible.  To overcome this barrier,
   the CoRE working group is specifying the concept of a Resource
   Directory (RD) [ID-rd].  The Resource Directory hosts descriptions of
   resources which are located on other nodes.  These resource
   descriptions are specified as CoRE link format [RFC6690] URIs.

   While CoAP defines a standard communication protocol, a format for
   representing sensor measurements and parameters over CoAP is
   required.  The Sensor Measurement Lists (SenML) [ID-senml] is a
   specification that is currently being written to define media types
   for simple sensor measurements and parameters.  It has a minimalistic
   design so that constrained devices with limited computational
   capabilities can easily encode their measurements and, at the same
   time, servers can efficiently collect large number of measurements.



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   In many IoT deployments, the resource-constrained smart objects are
   connected to the Internet via a gateway that is directly reachable.
   For example, an IEEE 802.11 Access Point (AP) typically connects the
   client devices to the Internet over just one wireless hop.  However,
   some deployments of smart object networks require routing between the
   smart objects themselves.  The IETF has therefore defined the IPv6
   Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550].
   RPL provides support for multipoint-to-point traffic from resource-
   constrained smart objects towards a more resourceful central control
   point, as well as point-to-multipoint traffic in the reverse
   direction.  It also supports point-to-point traffic between the
   resource-constrained devices.  A set of routing metrics and
   constraints for path calculation in RPL are also specified [RFC6551].

   In addition to defining a routing protocol, the IETF has also
   specified how IPv6 packets can be transmitted over various link layer
   protocols that are commonly employed for resource-constrained smart
   object networks.  There is also ongoing work to specify IPv6
   connectivity for a Non-Broadcast Multi-Access (NBMA) mesh network
   that is formed by IEEE 802.15.4 TimeSlotted Channel Hopping (TSCH}
   links [ID-6tisch].  Other link layer protocols for which IETF has
   specified or is currently specifying IPv6 support include Bluetooth
   [RFC7668], Digital Enhanced Cordless Telecommunications (DECT) Ultra
   Low Energy (ULE) air interface [ID-6lodect], and Near Field
   Communication (NFC) [ID-6lonfc].

   JavaScript Object Notation (JSON) is a lightweight text
   representation format for structured data [RFC7158].  It is often
   used for transmitting serialized structured data over the network.
   IETF has defined specifications for encoding public keys, signed
   content, and claims to be transferred between two parties as JSON
   objects.  They are referred to as JSON Web Keys (JWK) [RFC7517], JSON
   Web Signatures (JWS) [RFC7515] and JSON Web Token (JWT) [RFC7519].

   An alternative to JSON, Concise Binary Object Representation (CBOR)
   [RFC7049] is a concise binary data format that is used for
   serialization of structured data.  It is designed for extremely
   resource-constrained nodes and therefore it aims to provide a fairly
   small message size with minimal implementation code, and
   extensibility without the need for version negotiation.  There is
   ongoing work to specify CBOR Object Signing and Encryption (COSE)
   [ID-cose], which would provide services similar to JWS and JWT.

   The Light-Weight Implementation Guidance (LWIG) working group
   [WG-LWIG] is collecting experiences from implementers of IP stacks in
   constrained devices.  The working group has already produced
   documents such as RFC7815 [RFC7815] which defines how a minimal
   Internet Key Exchange Version 2 (IKEv2) initiator can be implemented.



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   The Thing-2-Thing Research Group (T2TRG) [RG-T2TRG] is investigating
   the remaining research issues that need to be addressed in order to
   quickly turn the vision of IoT into a reality where resource-
   constrained nodes can communicate with each other and with other more
   capable nodes on the Internet.

   Additionally industry alliances and other standardization bodies are
   creating constrained IP protocol stacks based on the IETF work.  Some
   important examples of this include:

   1.  Thread [Thread]: Specifies the Thread protocol that is intended
       for a variety of IoT devices.  It is an IPv6-based network
       protocol that runs over IEEE 802.15.4.

   2.  Industrial Internet Consortium [IIoT]: The consortium defines
       reference architectures and security frameworks for development,
       adoption and widespread use of Industrial Internet technologies
       based on existing IETF standards.

   3.  Internet Protocol for Smart Objects IPSO [IPSO]: The alliance
       specifies a common object model that would enable application
       software any device to interoperate with other conforming
       devices.

   4.  OneM2M [OneM2M]: The standards body defines technical and API
       specifications for IoT devices.  It aims to create a service
       layer that can run on any IoT device hardware and software.

   5.  Open Connectivity Foundation (OCF) [OCF]: The foundation develops
       standards and certifications primarily for IoT devices that use
       Constrained Application Protocol (CoAP) as the application layer
       protocol.

   6.  Fairhair Alliance [Fairhair]: Specifies a middle-ware for IoT
       based Building Automation and Lighting System that can
       interoperate with different application standards for the
       professional domain.

5.2.  Existing IP-based Security Protocols and Solutions

   In the context of the IP-based IoT solutions, consideration of TCP/IP
   security protocols is important.  There are a wide range of
   specialized as well as general-purpose key exchange and security
   solutions for the Internet domain such as IKEv2/IPsec [RFC7296], TLS
   [RFC5246], DTLS [RFC6347], HIP [RFC7401], PANA [RFC5191], and EAP
   [RFC3748].





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   There is ongoing work to define an authorization and access-control
   framework for resource-constrained nodes.  The Authentication and
   Authorization for Constrained Environments (ACE) [WG-ACE] working
   group is defining a solution to allow only authorized access to
   resources that are hosted on a smart object server and are identified
   by a URI.  The current proposal [ID-aceoauth] is based on the OAuth
   2.0 framework [RFC6749].

   The CoAP base specification [RFC7252] provides a description of how
   DTLS can be used for securing CoAP.  It proposes three different
   modes for using DTLS: the PreSharedKey mode, where nodes have pre-
   provisioned keys for initiating a DTLS session with another node,
   RawPublicKey mode, where nodes have asymmetric-key pairs but no
   certificates to verify the ownership, and Certificate mode, where
   public keys are certified by a certification authority.  An IoT
   implementation profile [RFC7925] is defined for TLS version 1.2 and
   DTLS version 1.2 that offers communications security for resource-
   constrained nodes.

   There is also work on Object Security based CoAP protection mechanism
   being defined in OSCOAP [ID-OSCOAP].

   Migault et al.{ID-dietesp} are working on a compressed version of
   IPsec so that it can easily be used by resource-constrained IoT
   devices.  They rely on the Internet Key Exchange Protocol version 2
   (IKEv2) for negotiating the compression format.

   Figure 3 depicts the relationships between the discussed protocols in
   the context of the security terminology introduced in Section 3.






















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             ..........................
             :           +-----------+:
             :       *+*>|Application|*****     *** Bootstrapping
             :       *|  +-----------+:   *     ### Transport Security
             :       *|  +-----------+:   *     === Network security
             :       *|->| Transport |:   *     ... Object security
             :    * _*|  +-----------+:   *
             :    *|  |  +-----------+:   *
             :    *|  |->|  Network  |:   *--> -PANA/EAP
             :    *|  |  +-----------+:   *    -HIP
             :    *|  |  +-----------+:   *
             :    *|  +->|     L2    |:   *     ## DTLS
             :    *|     +-----------+:   *     .. OSCOAP
             :+--------+              :   *
             :|Security| Configuration:   *     [] HIP,IKEv2
             :|Service |   Entity     :   *     [] ESP/AH
             :+--------+              :   *
             :........................:   *
                                          *
 .........................                *    .........................
 :+--------+             :                *    :             +--------+:
 :|Security|   Node B    :    Secure      *    :   Node A    |Security|:
 :|Service |             :    routing     *    :             |Service |:
 :+--------+             :   framework    *    :             +--------+:
 :    |     +-----------+:        |       **** :+-----------+     |*   :
 :    |  +->|Application|:........|............:|Application|<*+* |*   :
 :    |  |  +----##-----+:        |            :+----##-----+  |* |*   :
 :    |  |  +----##-----+:        |            :+----##-----+  |* |*   :
 :    |  |->| Transport |#########|#############| Transport |<-|* |*   :
 :    |__|  +----[]-----+:  ......|..........  :+----[]-----+  |*_|*   :
 :       |  +====[]=====+=====+===========+=====+====[]=====+  | *     :
 :       |->|| Network  |:  : |  Network  | :  :|  Network ||<-|       :
 :       |  +|----------+:  : +-----------+ :  :+----------|+  |       :
 :       |  +|----------+:  : +-----------+ :  :+----------|+  |       :
 :       +->||    L2    |:  : |     L2    | :  :|     L2   ||<-+       :
 :          +===========+=====+===========+=====+===========+          :
 :.......................:  :...............:  :.......................:
            Relationships between IP-based security protocols.

                                 Figure 4

   The Internet Key Exchange (IKEv2)/IPsec and the Host Identity
   protocol (HIP) reside at or above the network layer in the OSI model.
   Both protocols are able to perform an authenticated key exchange and
   set up the IPsec transforms for secure payload delivery.  Currently,
   there are also ongoing efforts to create a HIP variant coined Diet
   HIP [ID-HIP] that takes lossy low-power networks into account at the
   authentication and key exchange level.



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   Transport Layer Security (TLS) and its datagram-oriented variant DTLS
   secure transport-layer connections.  TLS provides security for TCP
   and requires a reliable transport, while DTLS secures and uses
   datagram-oriented protocols such as UDP.  Both protocols are
   intentionally kept similar and share the same ideology and cipher
   suites.

   The Extensible Authentication Protocol (EAP) is an authentication
   framework supporting multiple authentication methods.  EAP runs
   directly over the data link layer and, thus, does not require the
   deployment of IP.  It supports duplicate detection and
   retransmission, but does not allow for packet fragmentation.  The
   Protocol for Carrying Authentication for Network Access (PANA) is a
   network-layer transport for EAP that enables network access
   authentication between clients and the network infrastructure.  In
   EAP terms, PANA is a UDP-based EAP lower layer that runs between the
   EAP peer and the EAP authenticator.

   In addition, there is also new activities in IETF and W3C to define
   security protocols better tailored to IoT or for specific deployment
   situations.

5.3.  IoT Security Guidelines

   Recent large scale Denial of Service (DoS) Attacks on the Internet
   Infrastructure from compromised IoT devices has prompted many
   different standards bodies and consortia to provide guidelines for
   developers and the Internet community at large to build secure IoT
   devices and services.  A subset of the different guidelines and
   ongoing projects are as follows:

   1.   GSMA IoT security guidelines [GSMAsecurity]: GSMA has published
        a set of security guidelines for the benefit of new IoT product
        and service providers.  The guideline are aimed at device
        manufacturers, service providers, developers and network
        operators.  An enterprise can complete an IoT Security Self-
        Assessment to demonstrate that its products and services are
        aligned with the security guidelines of the GSMA.

   2.   BITAG Internet of Things (IoT) Security and Privacy
        Recommendations [BITAG]: Broadband Internet Technical Advisory
        Group (BITAG) has also published recommendations for ensuring
        security and privacy of IoT device users.  BITAG observes that
        many IoT devices are shipped from the factory with software that
        is already outdated and vulnerable.  The report also states that
        many devices with vulnerabilities will not be fixed either
        because the manufacturer does not provide updates or because the
        user does not apply them.  The recommendations include that IoT



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        devices should function without cloud and Internet connectivity,
        and that all IoT devices should have methods for automatic
        secure software updates.

   3.   CSA New Security Guidance for Early Adopters of the IoT [CSA]:
        The Cloud Security Alliance (CSA) recommendations for early
        adopters of IoT encourages enterprises to implement security at
        different layers of the protocol stack.  It also recommends
        implementation of an authentication/authorization framework for
        IoT deployments.  A complete list of recommendations is
        available in the report [CSA].

   4.   U.S.  Department of Homeland Security [DHS]: DHS has put forth
        six strategic principles that would enable IoT developers,
        manufacturers, service providers and consumers to maintain
        security as they develop, manufacture, implement or use network-
        connected IoT devices.

   5.   NIST [NIST-Guide]: The NIST special publication urges enterprise
        and US federal agencies to address security throughout the
        systems engineering process.  The publication builds upon the
        ISO/IEC/IEEE 15288 standard and augments each process in the
        system lifecyle with security enhancements.

   6.   NIST [nist_lightweight_project]: NIST is running a project on
        lightweight cryptography with the purpose of: (i) identifying
        application areas for which standard cryptographic algorithms
        are too heavy, classifying them according to some application
        profiles to be determined; (ii) determining limitations in those
        existing cryptographic standards; and (iii) standardizing
        lightweight algorithms that can be used in specific application
        profiles.

   7.   OWASP [OWASP]: Open Web Application Security Project (OWASP)
        provides security guidance for IoT manufactures, developers and
        consumers.  OWASP also includes guidelines for those who intend
        to test and analyze IoT devices and applications.

   8.   IoT Security foundation [IoTSecFoundation]: IoT security
        foundation has published a document that enlists various
        considerations that need to be taken into account when
        developing IoT applications.  For example, the document states
        that IoT device could use hardware-root of trust to ensure that
        only authorized software runs on the device.

   9.   NHTSA [NHTSA]: The US National Highway Traffic Safety
        Administration provides a set of non-binding guidance to the
        automotive industry for improving the cyber security of



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        vehicles.  While some of the guidelines are general, the
        document provides specific recommendations for the automotive
        industry such as how various automotive manufacturer can share
        cyber security vulnerabilities discovered.

   10.  BCP for IoT devices [ID-Moore]: This Internet draft provides a
        list of minimum requirements that vendors of Internet of Things
        (IoT) devices should to take into account while developing
        applications, services and firmware updates in order to reduce
        the frequency and severity of security incidents that arise from
        compromised IoT devices.

   11.  ENISA [ENISA_ICS]: The European Union Agency for Network and
        Information Security published a document on communication
        network dependencies for ICS/SCADA systems in which security
        vulnerabilities, guidelines and general recommendations are
        summarized.

   Other guideline and recommendation documents may exist or may later
   be published.  This list should be considered non-exhaustive.

5.4.  Guidelines and IoT Security Regulations

   Despite the acknowledgement that security in the Internet is needed
   and multiple guidelines exist, the fact is that many IoT devices and
   systems are not fully secure.  There are multiple reasons for this.
   For instance, some manufactures focus on delivering a product without
   paying enough attention to the delivered security level, lack of
   expertise or budget.  This, however, poses a severe threat when such
   devices are deployed.  The vast amount of devices and their inherent
   mobile nature also implies that an initially secure system can become
   insecure if a compromised device gains access to the system at some
   point in time.  Even if all other devices in a given environment are
   secure, it does not prevent external (passive) attacks originating
   due to insecure devices.

   Recently [FCC] the FCC has stated the need for higher regulation for
   IoT systems.  In fact this might be a missing component, at least in
   Federal Information Systems (FIS).  Today, security in US FIS is
   regulated according to Federal Information Security Management Act
   (FISMA).  From this law, NIST derived a number of documents to
   establish how to categorize FIS and determine minimum security
   requirements (FIPS-PUB-199 and FIPS-PUB-200).  Minimum security
   requirements for FIS are specified in NIST SP 800-53r4 [NIST-FIS].
   However, it is very likely that existing regulations do not take into
   account the specific challenges of IoT devices and networks.





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   Even if such a regulation is put in place, the question is how such a
   regulation can be applied in practice to non-federal deployments,
   such as industrial, homes, offices, or smart cites.  Each of them
   exhibits unique features, involves very diverse types of users, has
   different operational requirements, and combines IoT devices from
   multiple manufacturers.  Therefore future regulations should consider
   such diverse deployment scenarios.

6.  Challenges for a Secure IoT

   In this section, we take a closer look at the various security
   challenges in the operational and technical features of the IoT and
   then discuss how existing Internet security protocols cope with these
   technical and conceptual challenges through the lifecycle of a thing.
   Figure 2 summarizes which requirements need to be met in the
   lifecycle phases as well as some of the considered protocols.  This
   discussion should neither be understood as a comprehensive evaluation
   of all protocols, nor can it cover all possible aspects of IoT
   security.  Yet, it aims at showing concrete limitations of existing
   Internet security protocols in some areas rather than giving an
   abstract discussion about general properties of the protocols.  In
   this regard, the discussion handles issues that are most important
   from the authors' perspectives.

6.1.  Constraints and Heterogeneous Communication

   Coupling resource constrained networks and the powerful Internet is a
   challenge because the resulting heterogeneity of both networks
   complicates protocol design and system operation.  In the following
   we briefly discuss the resource constraints of IoT devices and the
   consequences for the use of Internet Protocols in the IoT domain.

6.1.1.  Tight Resource Constraints

   The IoT is a resource-constrained network that relies on lossy and
   low-bandwidth channels for communication between small nodes,
   regarding CPU, memory, and energy budget.  These characteristics
   directly impact the threats to and the design of security protocols
   for the IoT domain.  First, the use of small packets, e.g., IEEE
   802.15.4 supports 127-byte sized packets at the physical layer, may
   result in fragmentation of larger packets of security protocols.
   This may open new attack vectors for state exhaustion DoS attacks,
   which is especially tragic, e.g., if the fragmentation is caused by
   large key exchange messages of security protocols.  Moreover, packet
   fragmentation commonly downgrades the overall system performance due
   to fragment losses and the need for retransmissions.  For instance,
   fate-sharing packet flight as implemented by DTLS might aggravate the
   resulting performance loss.



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   The size and number of messages should be minimized to reduce memory
   requirements and optimize bandwidth usage.  In this context, layered
   approaches involving a number of protocols might lead to worse
   performance in resource-constrained devices since they combine the
   headers of the different protocols.  In some settings, protocol
   negotiation can increase the number of exchanged messages.  To
   improve performance during basic procedures such as, e.g.,
   bootstrapping, it might be a good strategy to perform those
   procedures at a lower layer.

   Small CPUs and scarce memory limit the usage of resource-expensive
   crypto primitives such as public-key cryptography as used in most
   Internet security standards.  This is especially true, if the basic
   crypto blocks need to be frequently used or the underlying
   application demands a low delay.

   Independently from the development in the IoT domain, all discussed
   security protocols show efforts to reduce the cryptographic cost of
   the required public-key-based key exchanges and signatures with ECC
   [RFC5246][RFC5903][RFC7401][ID-HIP].  Moreover, all protocols have
   been revised in the last years to enable crypto agility, making
   cryptographic primitives interchangeable.  However, these
   improvements are only a first step in reducing the computation and
   communication overhead of Internet protocols.  The question remains
   if other approaches can be applied to leverage key agreement in these
   heavily resource-constrained environments.

   A further fundamental need refers to the limited energy budget
   available to IoT nodes.  Careful protocol (re)design and usage is
   required to reduce not only the energy consumption during normal
   operation, but also under DoS attacks.  Since the energy consumption
   of IoT devices differs from other device classes, judgements on the
   energy consumption of a particular protocol cannot be made without
   tailor-made IoT implementations.

6.1.2.  Denial-of-Service Resistance

   The tight memory and processing constraints of things naturally
   alleviate resource exhaustion attacks.  Especially in unattended T2T
   communication, such attacks are difficult to notice before the
   service becomes unavailable (e.g., because of battery or memory
   exhaustion).  As a DoS countermeasure, DTLS, IKEv2, HIP, and Diet HIP
   implement return routability checks based on a cookie mechanism to
   delay the establishment of state at the responding host until the
   address of the initiating host is verified.  The effectiveness of
   these defenses strongly depends on the routing topology of the
   network.  Return routability checks are particularly effective if
   hosts cannot receive packets addressed to other hosts and if IP



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   addresses present meaningful information as is the case in today's
   Internet.  However, they are less effective in broadcast media or
   when attackers can influence the routing and addressing of hosts
   (e.g., if hosts contribute to the routing infrastructure in ad-hoc
   networks and meshes).

   In addition, HIP implements a puzzle mechanism that can force the
   initiator of a connection (and potential attacker) to solve
   cryptographic puzzles with variable difficulties.  Puzzle-based
   defense mechanisms are less dependent on the network topology but
   perform poorly if CPU resources in the network are heterogeneous
   (e.g., if a powerful Internet host attacks a thing).  Increasing the
   puzzle difficulty under attack conditions can easily lead to
   situations, where a powerful attacker can still solve the puzzle
   while weak IoT clients cannot and are excluded from communicating
   with the victim.  Still, puzzle-based approaches are a viable option
   for sheltering IoT devices against unintended overload caused by
   misconfiguration or malfunctioning things.

6.1.3.  End-to-End Security, protocol translation, and the role of
        middleboxes

   The term end-to-end security often has multiple interpretations.
   Here, we consider end-to-end security in the context end-to-end IP
   connectivity.  Note that this does not necessarily mean from sensor
   to actuator.

   Even though 6LoWPAN and CoAP progress towards reducing the gap
   between Internet protocols and the IoT, they do not target protocol
   specifications that are identical to their Internet counterparts due
   to performance reasons.  Hence, more or less subtle differences
   between IoT protocols and Internet protocols will remain.  While
   these differences can easily be bridged with protocol translators at
   middleboxes, they become major obstacles if end-to-end security
   measures between IoT devices and Internet hosts are used.

   Regarding end-to-end security in the context of confidentiality and
   integrity protection, the packets are processed by applying message
   authentication codes or encryption.  These protection methods render
   the protected parts of the packets immutable as rewriting is either
   not possible because a) the relevant information is encrypted and
   inaccessible to the gateway or b) rewriting integrity-protected parts
   of the packet would invalidate the end-to-end integrity protection.
   There are essentially five approaches to handle such end-to-end
   confidentiality and integrity protection while letting middleboxes
   access/modify data for different purposes:





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   1.  Sharing credentials with middleboxes enables middleboxes to
       transform (e.g., decompress, convert, etc.) packets and re-apply
       the security measures after transformation.  This method abandons
       end-to-end security and is only applicable to simple scenarios
       with a rudimentary security model.

   2.  Reusing the Internet wire format in the IoT makes conversion
       between IoT and Internet protocols unnecessary.  However, it can
       lead to poor performance in some use cases because IoT specific
       optimizations (e.g., stateful or stateless compression) are not
       possible.

   3.  Selectively protecting vital and immutable packet parts with a
       MAC or with encryption requires a careful balance between
       performance and security.  Otherwise, this approach will either
       result in poor performance (protect as much as possible) or poor
       security (compress and transform as much as possible).

   4.  Message authentication codes that sustain transformation can be
       realized by considering the order of transformation and
       protection (e.g., by creating a signature before compression so
       that the gateway can decompress the packet without recalculating
       the signature).  [ID-OSCOAP] proposes a solution in this
       direction, also preventing proxies from changing relevant CoAP
       fields.  Such an approach enables IoT specific optimizations but
       is more complex and may require application-specific
       transformations before security is applied.  Moreover, it cannot
       be used with encrypted data because the lack of cleartext
       prevents gateways from transforming packets.

   5.  Object security based mechanisms can bridge the protocol worlds,
       but still requires that the two worlds use the same object
       security formats.  Currently the IoT based object security format
       based on COSE [ID-cose] is different from the Internet based JOSE
       or CMS.  Legacy devices on the Internet side will need to update
       to the newer IoT protocols to enable real end-to-end security.
       Furthermore, middleboxes do not have any access to the data and
       this approach does not prevent an attacker from modifying
       relevant fields in CoAP.

   To the best of our knowledge, none of the mentioned security
   approaches that focus on the confidentiality and integrity of the
   communication exchange between two IP end-points provides a fully
   customizable solution in this problem space.

   We note that end-to-end security could also be considered in the
   context of availability: making sure that the messages are delivered.
   In this case, the end-points cannot control this, but the middleboxes



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   play a fundamental role to make sure that exchanged messages are not
   dropped, e.g., due to a DDoS attack.

6.1.4.  New network architectures and paradigm

   There is a multitude of new link layer protocols that aim to address
   the resource-constrained nature of IoT devices.  For example, the
   IEEE 802.11 ah [IEEE802ah] has been specified for extended range and
   lower energy consumption to support Internet of Things (IoT) devices.
   Similarly, Low-Power Wide-Area Network (LPWAN) protocols such as LoRa
   [lora], Sigfox [sigfox], NarrowBand IoT (NB-IoT) [nbiot] are all
   designed for resource-constrained devices that require long range and
   low bit rates.  While these protocols allow the IoT devices to
   conserve energy and operate efficiently, they also add additional
   security challenges.  For example, the relatively small MTU can make
   security handshakes with large X509 certificates a significant
   overhead.  At the same time, new communication paradigms also allow
   IoT devices to communicate directly amongst themselves with or
   without support from the network.  This communication paradigm is
   also referred to as Device-to-Device (D2D) or Machine-to-Machine
   (M2M) or Thing-to-Thing (T2T) communication.  D2D is primarily driven
   by network operators that want to utilize short range communication
   to improve the network performance and for supporting proximity based
   service

6.2.  Bootstrapping of a Security Domain

   Creating a security domain from a set of previously unassociated IoT
   devices is a key operation in the lifecycle of a thing and in the IoT
   network.  This aspect is further elaborated and discussed in the
   T2TRG draft on bootstrapping [ID-bootstrap].

6.3.  Operation

   After the bootstrapping phase, the system enters the operational
   phase.  During the operational phase, things can relate to the state
   information created during the bootstrapping phase in order to
   exchange information securely and in an authenticated fashion.  In
   this section, we discuss aspects of communication patterns and
   network dynamics during this phase.

6.3.1.  End-to-End Security

   Providing end-to-end IP security is of great importance to address
   and secure individual T2T or H2T communication within one IoT domain.
   Moreover, end-to-end security associations are an important measure
   to bridge the gap between the IoT and the Internet.  IKEv2, TLS and
   DTLS provide end-to-end security services including peer entity



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   authentication, end-to-end encryption and integrity protection above
   the network layer and the transport layer respectively.  Once
   bootstrapped, these functions can be carried out without online
   connections to third parties, making the protocols applicable for
   decentralized use in the IoT.  However, protocol translation by
   intermediary nodes may invalidate end-to-end protection measures (see
   Section 6.1.3).  Also these protocols require end-to-end connectivity
   between the devices and do not support store-and-forward scenarios.
   Object security is an option for such scenarios and the work on
   OSCOAP [ID-OSCOAP] is a potential solution in this space, in
   particular, in the context of forwarding proxies.

6.3.2.  Group Membership and Security

   In addition to end-to-end security, group key negotiation is an
   important security service for the T2Ts and Ts2T communication
   patterns in the IoT as efficient local broadcast and multicast relies
   on symmetric group keys.

   All discussed protocols only cover unicast communication and
   therefore do not focus on group-key establishment.  However, the
   Diffie-Hellman keys that are used in IKEv2 and HIP could be used for
   group Diffie-Hellman key-negotiations.  Conceptually, solutions that
   provide secure group communication at the network layer (IPsec/IKEv2,
   HIP/Diet HIP) may have an advantage regarding the cryptographic
   overhead compared to application-focused security solutions (TLS/
   DTLS or OSCOAP).  This is due to the fact that application-focused
   solutions require cryptographic operations per group application,
   whereas network layer approaches may allow to share secure group
   associations between multiple applications (e.g., for neighbor
   discovery and routing or service discovery).  Hence, implementing
   shared features lower in the communication stack can avoid redundant
   security measures.

   A number of group key solutions have been developed in the context of
   the IETF working group MSEC in the context of the MIKEY architecture
   [WG-MSEC][RFC4738].  These are specifically tailored for multicast
   and group broadcast applications in the Internet and should also be
   considered as candidate solutions for group key agreement in the IoT.
   The MIKEY architecture describes a coordinator entity that
   disseminates symmetric keys over pair-wise end-to-end secured
   channels.  However, such a centralized approach may not be applicable
   in a distributed environment, where the choice of one or several
   coordinators and the management of the group key is not trivial.







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6.3.3.  Mobility and IP Network Dynamics

   It is expected that many things (e.g., wearable sensors, and user
   devices) will be mobile in the sense that they are attached to
   different networks during the lifetime of a security association.
   Built-in mobility signaling can greatly reduce the overhead of the
   cryptographic protocols because unnecessary and costly re-
   establishments of the session (possibly including handshake and key
   agreement) can be avoided.  IKEv2 supports host mobility with the
   MOBIKE [RFC4555][RFC4621] extension.  MOBIKE refrains from applying
   heavyweight cryptographic extensions for mobility.  However, MOBIKE
   mandates the use of IPsec tunnel mode which requires to transmit an
   additional IP header in each packet.  This additional overhead could
   be alleviated by using header compression methods or the Bound End-
   to-End Tunnel (BEET) mode [ID-Nikander], a hybrid of tunnel and
   transport mode with smaller packet headers.

   HIP offers a simple yet effective mobility management by allowing
   hosts to signal changes to their associations [RFC5206].  However,
   slight adjustments might be necessary to reduce the cryptographic
   costs, for example, by making the public-key signatures in the
   mobility messages optional.  Diet HIP does not define mobility yet
   but it is sufficiently similar to HIP to employ the same mechanisms.
   TLS and DTLS do not have standards for mobility support, however,
   work on DTLS mobility exists in the form of an Internet draft
   [ID-Williams].  The specific need for IP-layer mobility mainly
   depends on the scenario in which nodes operate.  In many cases,
   mobility support by means of a mobile gateway may suffice to enable
   mobile IoT networks, such as body sensor networks.  However, if
   individual things change their point of network attachment while
   communicating, mobility support may gain importance.

6.4.  Software update

   IoT devices have a reputation for being insecure at the time of
   manufacture.  Yet they are often expected to stay functional in live
   deployments for years and even decades.  Additionally, these devices
   typically operate unattended with direct Internet connectivity.
   Therefore, a remote software update mechanism to fix vulnerabilities,
   to update configuration settings, and for adding new functionality is
   needed.

   Schneier [SchneierSecurity] in his essay expresses concerns about the
   status of software and firmware update mechanisms for Internet of
   Things (IoT) devices.  He highlights several challenges that hinder
   mechanisms for secure software update of IoT devices.  First, there
   is a lack of incentives for manufactures, vendors and others on the
   supply chain to issue updates for their devices.  Second, parts of



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   the software running on the IoT devices is simply a binary blob
   without any source code available.  Since the complete source code is
   not available, no patches can be written for that piece of code.
   Third, even when updates are available, users generally have to
   manually download and install those updates.  However, users are
   never alerted about security updates and many times do not have the
   necessary expertise to manually administer the required updates.

   The FTC staff report on Internet of Things - Privacy & Security in a
   Connected World [FTCreport] and the Article 29 Working Party Opinion
   8/2014 on the on Recent Developments on the Internet of Things
   [Article29] also document the challenges for secure remote software
   update of IoT devices.  They note that even providing such a software
   update capability may add new vulnerabilities for constrained
   devices.  For example, a buffer overflow vulnerability in the
   implementation of a software update protocol (TR69) [TR69] and an
   expired certificate in a hub device [wink] demonstrate how the
   software update process itself can introduce vulnerabilities.

   While powerful IoT devices that run general purpose operating systems
   can make use of sophisticated software update mechanisms known from
   the desktop world, a more considerate effort is needed for resource-
   constrained devices that don't have any operating system and are
   typically not equipped with a memory management unit or similar
   tools.  The IAB also organized a workshop to understand the
   challenges for secure software update of IoT devices.  A summary of
   the workshop and the proposed next steps have been documented
   [iotsu].

6.5.  Verifying device behavior

   Users often have a false sense of privacy when using new Internet of
   Things (IoT) appliances such as Internet-connected smart televisions,
   speakers and cameras.  Recent revelations have shown that this user
   belief is often unfounded.  Many IoT device vendors have been caught
   collecting sensitive private data through these connected appliances
   with or without appropriate user warnings [cctv].

   An IoT device user/owner would like to monitor and know if the device
   is calling home (i.e. verify its operational behavior).  The calling
   home feature may be necessary in some scenarios, such as during the
   initial configuration of the device.  However, the user should be
   kept aware of the data that the device is sending back to the vendor.
   For example, the user should be ensured that his/her TV is not
   sending data when he/she inserts a new USB stick.

   Providing such information to the users in an understandable fashion
   is challenging.  This is because the IoT devices are not only



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   resource-constrained in terms of their computational capability, but
   also in terms of the user interface available.  Also, the network
   infrastructure where these devices are deployed will vary
   significantly from one user environment to another.  Therefore, where
   and how this monitoring feature is implemented still remains an open
   question.

6.6.  End-of-life

   Like all commercial devices, most IoT devices will be end-of-lifed by
   vendors or even network operators.  This may be planned or unplanned
   (for example when the vendor or manufacturer goes bankrupt or when a
   network operator moves to a different type of networking technology).
   A user should still be able to use and perhaps even update the
   device.  This requires for some form of authorization handover.

   Although this may seem far fetched given the commercial interests and
   market dynamics, we have examples from the mobile world where the
   devices have been functional and up-to-date long after the original
   vendor stopped supporting the device.  CyanogenMod for Android
   devices and OpenWrt for home routers are two such instances where
   users have been able to use and update their devices even after they
   were end-of-lifed.  Admittedly these are not easy for an average
   users to install and configure on their devices.  With the deployment
   of millions of IoT devices, simpler mechanisms are needed to allow
   users to add new root-of-trusts and install software and firmware
   from other sources once the device has been end-of-lifed.

6.7.  Testing: bug hunting and vulnerabilities

   Given that the IoT devices often have inadvertent vulnerabilities,
   both users and developers would want to perform extensive testing on
   their IoT devices, networks, and systems.  Nonetheless, since the
   devices are resource-constrained and manufactured by multiple
   vendors, some of them very small, devices might be shipped with very
   limited testing, so that bugs can remain and can be exploited at a
   later stage.  This leads to two main types of challenges:

   1.  It remains to be seen how the software testing and quality
       assurance mechanisms used from the desktop and mobile world will
       be applied to IoT devices to give end users the confidence that
       the purchased devices are robust.

   2.  It is also an open question how combination of devices of
       multiple vendors might actually lead to dangerous network
       configurations, e.g., if combination of specific devices can
       trigger unexpected behavior.




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6.8.  Quantum-resistance

   Many IoT systems that are being deployed today will remain
   operational for many years.  With the advancements made in the field
   of quantum computers, it is possible that large-scale quantum
   computers are available in the future for performing cryptanalysis on
   existing cryptographic algorithms and cipher suites.  If and when
   this happens, it would have two consequences.  First, functionalities
   enabled by means of RSA/ECC - namely key exchange, public-key
   encryption and signature - would not be secure anymore due to Shor's
   algorithm.  Second, the security level of symmetric algorithms will
   decrease, e.g., the security of a block cipher with a key size of b
   bits will only offer b/2 bits of security due to Grover's algorithm.

   This would require us to move to quantum-resistant alternatives, in
   particular, for those functionalities involving key exchange, public-
   key encryption and signatures.  While such future planning is hard,
   it may be a necessity in certain critical IoT deployments which are
   expected to last decades or more.  Although increasing the key-size
   of the different algorithms is definitely an option, it would also
   incur additional computational overhead and network traffic.  This
   would be undesirable in most scenarios.  There have been recent
   advancements in quantum-resistant cryptography.

   We refer to [ETSI_GR_QSC_001] for an extensive overview of existing
   quantum-resistant cryptography.  [RFC7696] provides guidelines for
   cryptographic algorithm agility.

6.9.  Privacy protection

   Users will be surrounded by hundreds of connected devices.  Even if
   the communication links are encrypted and protected, information
   about the users might be collected for different purposes affecting
   their privacy.  In [Ziegeldorf], privacy in the IoT is defined as the
   threefold guarantee to the user for: 1. awareness of privacy risks
   imposed by smart things and services surrounding the data subject, 2.
   individual control over the collection and processing of personal
   information by the surrounding smart things, 3. awareness and control
   of subsequent use and dissemination of personal information by those
   entities to any entity outside the subject's personal control sphere.

   Based on this definition, several privacy threats and challenges are
   identified in the work of Ziegeldorf:

   1.  Identification - refers to the identification of the users and
       their objects.





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   2.  Localization - relates to the capability of locating a user and
       even tracking him.

   3.  Profiling - is about creating a profile of the user and her
       preferences.

   4.  Interaction - occurs when a user has been profiled and a given
       interaction is preferred, presenting (e.g., visually) some
       information that discloses private information.

   5.  Lifecycle transitions - take place when devices are, e.g., sold
       without properly removing private data.

   6.  Inventory attacks - happen if specific information about (smart)
       objects in possession of a user is disclosed.

   7.  Linkage - is about when information of two of more IoT systems is
       combined so that a broader view on the personal data is created.

   When IoT systems are deployed, the above issues should be considered
   to ensure that private data remains private.  How to achieve this in
   practice is still an area of ongoing research.

6.10.  Data leakage

   IoT devices are resource-constrained and often deployed in unattended
   environments.  Some of these devices can also be purchased off-the-
   shelf or online without any credential-provisioning process.
   Therefore, an attacker can have direct access to the device and apply
   more advance techniques that a traditional black box model does not
   consider such as side-channel attacks or code disassembly.  By doing
   this, the attacker can try to retrieve data such as:

   1.  long term keys that might be used perform attacks on devices
       deployed in other locations.

   2.  source code that might let the user determine bugs or find
       exploits to perform other types of attacks, or just sell it,

   3.  proprietary algorithms that could be counterfeited or modified to
       perform advanced attacks.

   Protection against such data leakage patterns is not trivial since
   devices are inherently resource-constrained.  An open question is
   which techniques can be used to protect IoT devices in such an
   adversarial model.





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6.11.  Trustworthy IoT Operation

   Flaws in the design and implementation of a secure IoT device and
   network can lead to secure vulnerabilities.  An example is a flaw is
   the distribution of an Internet-connected IoT device in which a
   default password is used in all devices.  Many IoT devices can be
   found in the Internet by means of tools such as Shodan, and if they
   have any vulnerability, it can then be exploited at scale, e.g., to
   launch DDoS attacks.  This is not fiction but reality as Dyn, a mayor
   DNS was attacked by means of a DDoS attack originated from a large
   IoT botnet composed of thousands of compromised IP-cameras.  Open
   questions in this area are:

   1.  How to prevent large scale vulnerabilities in IoT devices?

   2.  How to prevent attackers from exploiting vulnerabilities in IoT
       devices at large scale?

   3.  If the vulnerability has been exploited, how do we stop a large
       scale attack before any damage is caused?

   Some ideas are being explored to address this issue.  One of this
   approaches refers to the specification of Manufacturer Usage
   Description (MUD) files [ID-MUD].  The idea behind MUD files is
   simple: devices would disclose the location of its MUD file to the
   network during installation.  The network can then (i) retrieve those
   files, (ii) learn from the manufacturers the intended usage of the
   devices, e.g., which services they require to access, and then (iii)
   create suitable filters.

7.  Conclusions and Next Steps

   This Internet Draft provides IoT security researchers, system
   designers and implements with an overview of both operational and
   security requirements in the IP-based Internet of Things.  We discuss
   a general threat model, security issues, and state of the art to
   mitigate security threats.  We further analyze key security
   challenges.

   Although plenty of steps have been realized during the last few years
   ( summarized in Section 5.1) and many organizations are publishing
   general recommendations (Section 5.3) describing how the IoT should
   be secured, there are many challenges ahead that require further
   attention.  Challenges of particular importance are bootstrapping of
   security, group security, secure software updates, long-term security
   and quantum-resistance, privacy protection, data leakage prevention -
   where data could be cryptographic keys, personal data, or even
   algorithms - and ensuring trustworthy IoT operation.  All these



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   problems are important; however, different deployment environments
   have different operational and security demands.  Thus, a potential
   approach is the definition and standardization of security profiles,
   each with specific mitigation strategies according to the risk
   assessment associated with the security profile.  Such an approach
   would ensure minimum security capabilities in different environments
   while ensuring interoperability.

8.  Security Considerations

   This document reflects upon the requirements and challenges of the
   security architectural framework for the Internet of Things.

9.  IANA Considerations

   This document contains no request to IANA.

10.  Acknowledgments

   We gratefully acknowledge feedback and fruitful discussion with
   Tobias Heer, Robert Moskowitz, Thorsten Dahm, Hannes Tschofenig,
   Barry Raveendran and Eliot Lear.  We acknowledge the additional
   authors of the previous version of this document Sye Loong Keoh, Rene
   Hummen and Rene Struik.

11.  Informative References

   [Article29]
              "Opinion 8/2014 on the on Recent Developments on the
              Internet of Things", Web http://ec.europa.eu/justice/data-
              protection/article-29/documentation/opinion-
              recommendation/files/2014/wp223_en.pdf, n.d..

   [AUTO-ID]  "AUTO-ID LABS", Web http://www.autoidlabs.org/, September
              2010.

   [BACNET]   "BACnet", Web http://www.bacnet.org/, February 2011.

   [BITAG]    "Internet of Things (IoT) Security and Privacy
              Recommendations", Web http://www.bitag.org/report-
              internet-of-things-security-privacy-recommendations.php,
              n.d..

   [cctv]     "Backdoor In MVPower DVR Firmware Sends CCTV Stills To an
              Email Address In China", Web
              https://hardware.slashdot.org/story/16/02/17/0422259/
              backdoor-in-mvpower-dvr-firmware-sends-cctv-stills-to-an-
              email-address-in-china, n.d..



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   [CSA]      "Security Guidance for Early Adopters of the Internet of
              Things (IoT)", Web
              https://downloads.cloudsecurityalliance.org/whitepapers/Se
              curity_Guidance_for_Early_Adopters_of_the_Internet_of_Thin
              gs.pdf, n.d..

   [d2dsecurity]
              Haus, M., Waqas, M., Ding, A., Li, Y., Tarkoma, S., and J.
              Ott, "Security and Privacy in Device-to-Device (D2D)
              Communication: A Review", Paper IEEE Communications
              Surveys and Tutorials, 2016.

   [DALI]     "DALI", Web http://www.dalibydesign.us/dali.html, February
              2011.

   [DHS]      "Strategic Principles For Securing the Internet of Things
              (IoT)", Web
              https://www.dhs.gov/sites/default/files/publications/
              Strategic_Principles_for_Securing_the_Internet_of_Things-
              2016-1115-FINAL....pdf, n.d..

   [ENISA_ICS]
              "Communication network dependencies for ICS/SCADA
              Systems", European Union Agency For Network And
              Information Security , February 2017.

   [ETSI_GR_QSC_001]
              "Quantum-Safe Cryptography (QSC);Quantum-safe algorithmic
              framework", European Telecommunications Standards
              Institute (ETSI) , June 2016.

   [Fairhair]
              "Fairhair Alliance", Web https://www.fairhair-
              alliance.org/, n.d..

   [FCC]      "Federal Communications Comssion Response 12-05-2016",
              FCC , February 2016.

   [FTCreport]
              "FTC Report on Internet of Things Urges Companies to Adopt
              Best Practices to Address Consumer Privacy and Security
              Risks", Web https://www.ftc.gov/news-events/press-
              releases/2015/01/ftc-report-internet-things-urges-
              companies-adopt-best-practices, n.d..







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   [GSMAsecurity]
              "GSMA IoT Security Guidelines", Web
              http://www.gsma.com/connectedliving/future-iot-networks/
              iot-security-guidelines/, n.d..

   [ID-6lodect]
              Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D.
              Barthel, "Transmission of IPv6 Packets over DECT Ultra Low
              Energy", draft-ietf-6lo-dect-ule-09 , December 2016.

   [ID-6lonfc]
              Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
              "Transmission of IPv6 Packets over Near Field
              Communication", draft-ietf-6lo-nfc-05 , October 2016.

   [ID-6tisch]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 ,
              January 2017.

   [ID-aceoauth]
              Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE)", draft-ietf-ace-oauth-
              authz-05 , March 2011.

   [ID-bootstrap]
              Sarikaya, B. and M. Sethi, "Secure IoT Bootstrapping : A
              Survey", draft-sarikaya-t2trg-sbootstrapping-01 , July
              2016.

   [ID-cose]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              draft-ietf-cose-msg-24 , November 2016.

   [ID-Daniel]
              Park, S., Kim, K., Haddad, W., Chakrabarti, S., and J.
              Laganier, "IPv6 over Low Power WPAN Security Analysis",
              draft-daniel-6lowpan-security-analysis-05 , March 2011.

   [ID-dietesp]
              Migault, D., Guggemos, T., and C. Bormann, "Diet-ESP: a
              flexible and compressed format for IPsec/ESP", draft-mglt-
              6lo-diet-esp-02 , August 2016.

   [ID-Hartke]
              Hartke, K. and O. Bergmann, "Datagram Transport Layer
              Security in Constrained Environments", draft-hartke-core-
              codtls-02 , July 2012.



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   [ID-HIP]   Moskowitz, R., "HIP Diet EXchange (DEX)", draft-moskowitz-
              hip-rg-dex-06 , May 2012.

   [ID-Moore]
              Moore, K., Barnes, R., and H. Tschofenig, "Best Current
              Practices for Securing Internet of Things (IoT) Devices",
              draft-moore-iot-security-bcp-00 , October 2016.

   [ID-MUD]   Lear, E., Droms, R., and D. Domascanu, "Manufacturer Usage
              Description Specification", March 2017.

   [ID-Nikander]
              Nikander, P. and J. Melen, "A Bound End-to-End
              Tunnel(BEET) mode for ESP", draft-nikander-esp-beet-
              mode-09 , August 2008.

   [ID-OFlynn]
              O'Flynn, C., Sarikaya, B., Ohba, Y., Cao, Z., and R.
              Cragie, "Security Bootstrapping of Resource-Constrained
              Devices", draft-oflynn-core-bootstrapping-03 , November
              2010.

   [ID-OSCOAP]
              Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security of CoAP (OSCOAP)", draft-selander-ace-
              object-security-05 , July 2016.

   [ID-proHTTPCoAP]
              Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
              E. Dijk, "Best practices for HTTP-CoAP mapping
              implementation", draft-castellani-core-http-mapping-07 ,
              February 2013.

   [ID-rd]    Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE
              Resource Directory", draft-ietf-core-resource-
              directory-09 , October 2016.

   [ID-senml]
              Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Media Types for Sensor Measurement Lists
              (SenML)", draft-ietf-core-resource-directory-09 , October
              2016.

   [ID-Tsao]  Tsao, T., Alexander, R., Dohler, M., Daza, V., and A.
              Lozano, "A Security Framework for Routing over Low Power
              and Lossy Networks", draft-ietf-roll-security-
              framework-07 , January 2012.




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   [ID-Williams]
              Williams, M. and J. Barrett, "Mobile DTLS", draft-barrett-
              mobile-dtls-00 , March 2009.

   [IEEE802ah]
              "Status of Project IEEE 802.11ah, IEEE P802.11- Task Group
              AH-Meeting Update.",
              Web http://www.ieee802.org/11/Reports/tgah_update.htm,
              n.d..

   [IIoT]     "Industrial Internet Consortium",
              Web http://www.iiconsortium.org/, n.d..

   [IoTSecFoundation]
              "Establishing Principles for Internet of Things Security",
              Web https://iotsecurityfoundation.org/establishing-
              principles-for-internet-of-things-security/, n.d..

   [iotsu]    "Patching the Internet of Things: IoT Software Update
              Workshop 2016", Web
              https://www.ietf.org/blog/2016/07/patching-the-internet-
              of-things-iot-software-update-workshop-2016/, n.d..

   [IPSO]     "IPSO Alliance", Web http://www.ipso-alliance.org, n.d..

   [JOURNAL-Perrig]
              Perrig, A., Szewczyk, R., Wen, V., Culler, D., and J.
              Tygar, "SPINS: Security protocols for Sensor Networks",
              Journal Wireless Networks, September 2002.

   [lora]     "LoRa - Wide Area Networks for IoT", Web https://www.lora-
              alliance.org/, n.d..

   [nbiot]    "NarrowBand IoT", Web
              http://www.3gpp.org/ftp/tsg_ran/TSG_RAN/TSGR_69/Docs/
              RP-151621.zip, n.d..

   [NHTSA]    "Cybersecurity Best Practices for Modern Vehicles", Web
              https://www.nhtsa.gov/staticfiles/nvs/
              pdf/812333_CybersecurityForModernVehicles.pdf, n.d..

   [NIST]     Dworkin, M., "NIST Specification Publication 800-38B",
              2005.

   [NIST-FIS]
              "Security and Privacy Controls for Federal Information
              Systems and Organizations",
              Web http://dx.doi.org/10.6028/NIST.SP.800-53r4, n.d..



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   [NIST-Guide]
              Ross, R., McEvilley, M., and J. Oren, "Systems Security
              Engineering", Web
              http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
              NIST.SP.800-160.pdf, n.d..

   [nist_lightweight_project]
              "NIST lightweight Project", Web www.nist.gov/programs-
              projects/lightweight-cryptography,
              www.nist.gov/sites/default/files/documents/2016/10/17/
              sonmez-turan-presentation-lwc2016.pdf, n.d..

   [OCF]      "Open Connectivity Foundation",
              Web https://openconnectivity.org/, n.d..

   [OneM2M]   "OneM2M", Web http://www.onem2m.org/, n.d..

   [OWASP]    "IoT Security Guidance",
              Web https://www.owasp.org/index.php/IoT_Security_Guidance,
              n.d..

   [PROC-Chan]
              Chan, H., Perrig, A., and D. Song, "Random Key
              Predistribution Schemes for Sensor Networks",
              Proceedings IEEE Symposium on Security and Privacy, 2003.

   [PROC-Gupta]
              Gupta, V., Wurm, M., Zhu, Y., Millard, M., Fung, S., Gura,
              N., Eberle, H., and S. Shantz, "Sizzle: A Standards-based
              End-to-End Security Architecture for the Embedded
              Internet", Proceedings Pervasive Computing and
              Communications (PerCom), 2005.

   [PROC-Smetters-02]
              Balfanz, D., Smetters, D., Steward, P., and H. Chi Wong,,
              "Talking To Strangers: Authentication in Ad-Hoc Wireless
              Networks", Paper NDSS, 2002.

   [PROC-Smetters-04]
              Balfanz, D., Durfee, G., Grinter, R., Smetters, D., and P.
              Steward, "Network-in-a-Box: How to Set Up a Secure
              Wireless Network in Under a Minute", Paper USENIX, 2004.

   [PROC-Stajano-99]
              Stajano, F. and R. Anderson, "Resurrecting Duckling -
              Security Issues for Adhoc Wireless Networks",
              7th International Workshop Proceedings, November 1999.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <http://www.rfc-editor.org/info/rfc3748>.

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, DOI 10.17487/RFC3756, May 2004,
              <http://www.rfc-editor.org/info/rfc3756>.

   [RFC3833]  Atkins, D. and R. Austein, "Threat Analysis of the Domain
              Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August
              2004, <http://www.rfc-editor.org/info/rfc3833>.

   [RFC4016]  Parthasarathy, M., "Protocol for Carrying Authentication
              and Network Access (PANA) Threat Analysis and Security
              Requirements", RFC 4016, DOI 10.17487/RFC4016, March 2005,
              <http://www.rfc-editor.org/info/rfc4016>.

   [RFC4251]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
              January 2006, <http://www.rfc-editor.org/info/rfc4251>.

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
              <http://www.rfc-editor.org/info/rfc4555>.

   [RFC4621]  Kivinen, T. and H. Tschofenig, "Design of the IKEv2
              Mobility and Multihoming (MOBIKE) Protocol", RFC 4621,
              DOI 10.17487/RFC4621, August 2006,
              <http://www.rfc-editor.org/info/rfc4621>.





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   [RFC4738]  Ignjatic, D., Dondeti, L., Audet, F., and P. Lin, "MIKEY-
              RSA-R: An Additional Mode of Key Distribution in
              Multimedia Internet KEYing (MIKEY)", RFC 4738,
              DOI 10.17487/RFC4738, November 2006,
              <http://www.rfc-editor.org/info/rfc4738>.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, DOI 10.17487/RFC4919, August 2007,
              <http://www.rfc-editor.org/info/rfc4919>.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
              <http://www.rfc-editor.org/info/rfc4944>.

   [RFC5191]  Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H.,
              and A. Yegin, "Protocol for Carrying Authentication for
              Network Access (PANA)", RFC 5191, DOI 10.17487/RFC5191,
              May 2008, <http://www.rfc-editor.org/info/rfc5191>.

   [RFC5206]  Nikander, P., Henderson, T., Ed., Vogt, C., and J. Arkko,
              "End-Host Mobility and Multihoming with the Host Identity
              Protocol", RFC 5206, DOI 10.17487/RFC5206, April 2008,
              <http://www.rfc-editor.org/info/rfc5206>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5713]  Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security
              Threats and Security Requirements for the Access Node
              Control Protocol (ANCP)", RFC 5713, DOI 10.17487/RFC5713,
              January 2010, <http://www.rfc-editor.org/info/rfc5713>.

   [RFC5903]  Fu, D. and J. Solinas, "Elliptic Curve Groups modulo a
              Prime (ECP Groups) for IKE and IKEv2", RFC 5903,
              DOI 10.17487/RFC5903, June 2010,
              <http://www.rfc-editor.org/info/rfc5903>.

   [RFC6345]  Duffy, P., Chakrabarti, S., Cragie, R., Ohba, Y., Ed., and
              A. Yegin, "Protocol for Carrying Authentication for
              Network Access (PANA) Relay Element", RFC 6345,
              DOI 10.17487/RFC6345, August 2011,
              <http://www.rfc-editor.org/info/rfc6345>.




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   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.

   [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,
              <http://www.rfc-editor.org/info/rfc6550>.

   [RFC6551]  Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
              and D. Barthel, "Routing Metrics Used for Path Calculation
              in Low-Power and Lossy Networks", RFC 6551,
              DOI 10.17487/RFC6551, March 2012,
              <http://www.rfc-editor.org/info/rfc6551>.

   [RFC6568]  Kim, E., Kaspar, D., and JP. Vasseur, "Design and
              Application Spaces for IPv6 over Low-Power Wireless
              Personal Area Networks (6LoWPANs)", RFC 6568,
              DOI 10.17487/RFC6568, April 2012,
              <http://www.rfc-editor.org/info/rfc6568>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <http://www.rfc-editor.org/info/rfc6690>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <http://www.rfc-editor.org/info/rfc6749>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <http://www.rfc-editor.org/info/rfc7049>.

   [RFC7158]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7158, DOI 10.17487/RFC7158, March
              2014, <http://www.rfc-editor.org/info/rfc7158>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <http://www.rfc-editor.org/info/rfc7296>.



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   [RFC7390]  Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
              the Constrained Application Protocol (CoAP)", RFC 7390,
              DOI 10.17487/RFC7390, October 2014,
              <http://www.rfc-editor.org/info/rfc7390>.

   [RFC7401]  Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
              Henderson, "Host Identity Protocol Version 2 (HIPv2)",
              RFC 7401, DOI 10.17487/RFC7401, April 2015,
              <http://www.rfc-editor.org/info/rfc7401>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC7668]  Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
              Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
              <http://www.rfc-editor.org/info/rfc7668>.

   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
              <http://www.rfc-editor.org/info/rfc7696>.

   [RFC7815]  Kivinen, T., "Minimal Internet Key Exchange Version 2
              (IKEv2) Initiator Implementation", RFC 7815,
              DOI 10.17487/RFC7815, March 2016,
              <http://www.rfc-editor.org/info/rfc7815>.

   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,
              <http://www.rfc-editor.org/info/rfc7925>.

   [RG-T2TRG]
              "IRTF Thing-to-Thing (T2TRG) Research Group",
              Web https://datatracker.ietf.org/rg/t2trg/charter/,
              December 2015.




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   [SchneierSecurity]
              "The Internet of Things Is Wildly Insecure--And Often
              Unpatchable", Web
              https://www.schneier.com/essays/archives/2014/01/
              the_internet_of_thin.html, n.d..

   [sigfox]   "Sigfox - The Global Communications Service Provider for
              the Internet of Things (IoT)",
              Web https://www.sigfox.com/, n.d..

   [SPEKE]    "IEEE P1363.2: Password-based Cryptography", 2008.

   [THESIS-Langheinrich]
              Langheinrich, M., "Personal Privacy in Ubiquitous
              Computing", PhD Thesis ETH Zurich, 2005.

   [Thread]   "Thread Group", Web http://threadgroup.org/, n.d..

   [TinyDTLS]
              "TinyDTLS", Web http://tinydtls.sourceforge.net/, February
              2012.

   [TR69]     "Too Many Cooks - Exploiting the Internet-of-TR-
              069-Things", Web https://media.ccc.de/v/31c3_-_6166_-_en_-
              _saal_6_-_201412282145_-_too_many_cooks_-
              _exploiting_the_internet-of-tr-069-things_-
              _lior_oppenheim_-_shahar_tal, n.d..

   [WG-6LoWPAN]
              "IETF 6LoWPAN Working Group",
              Web http://tools.ietf.org/wg/6lowpan/, February 2011.

   [WG-ACE]   "IETF Authentication and Authorization for Constrained
              Environments (ACE) Working Group",
              Web https://datatracker.ietf.org/wg/ace/charter/, June
              2014.

   [WG-CoRE]  "IETF Constrained RESTful Environment (CoRE) Working
              Group", Web https://datatracker.ietf.org/wg/core/charter/,
              February 2011.

   [WG-LWIG]  "IETF Light-Weight Implementation Guidance (LWIG) Working
              Group", Web https://datatracker.ietf.org/wg/lwig/charter/,
              March 2011.

   [WG-MSEC]  "MSEC Working Group",
              Web http://datatracker.ietf.org/wg/msec/, n.d..




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   [wink]     "Wink's Outage Shows Us How Frustrating Smart Homes Could
              Be",
              Web http://www.wired.com/2015/04/smart-home-headaches/,
              n.d..

   [ZB]       "ZigBee Alliance", Web http://www.zigbee.org/, February
              2011.

   [Ziegeldorf]
              Ziegeldorf, J., Garcia-Morchon, O., and K. Wehrle,,
              "Privacy in the Internet of Things: Threats and
              Challenges", Paper Security and Communication Networks -
              Special Issue on Security in a Completely Interconnected
              World, 2013.

Authors' Addresses

   Oscar Garcia-Morchon
   Philips IP&S
   High Tech Campus 5
   Eindhoven,   5656 AA
   The Netherlands

   Email: oscar.garcia-morchon@philips.com


   Sandeep S. Kumar
   Philips Research
   High Tech Campus
   Eindhoven,   5656 AA
   The Netherlands

   Email: sandeep.kumar@philips.com


   Mohit Sethi
   Ericsson
   Hirsalantie 11
   Jorvas
   Finland

   Email: mohit@piuha.net









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