Network Working Group                                        B. Sarikaya
Internet-Draft                                                    Huawei
Intended status: Informational                                  M. Sethi
Expires: August 5, 2017                                         Ericsson
                                                               AR. Sangi
                                                     Huawei Technologies
                                                        February 1, 2017

                   Secure IoT Bootstrapping: A Survey


   This document presents a survey of secure bootstrapping mechanisms
   available for smart objects that are part of an Internet of Things
   (IoT) network.  It aims to provide a structured classification of the
   available mechanisms.  The document does not prescribe any one secure
   bootstrapping mechanism and rather presents IoT developers with
   different options to choose from, depending on their use-case,
   security requirements and the user interface available on their smart

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on August 5, 2017.

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
   ( in effect on the date of

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Classification of available mechanisms  . . . . . . . . . . .   5
   4.  IoT Device Bootstrapping Methods  . . . . . . . . . . . . . .   6
     4.1.  Managed Methods . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Peer to Peer or Adhoc Methods . . . . . . . . . . . . . .  10
     4.3.  Leap-of-faith/Opportunistic Methods . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   An Internet of Things (IoT) network consists of connected things that
   cooperate together to accomplish tasks such as smart buildings, smart
   environment monitoring system, and intelligent transport systems.
   The size of an IoT network varies from a couple of devices to tens of
   thousands depending on the application.  A smart object, or a thing,
   or a device in an IoT network is typically produced by a variety of
   vendors and are typically heterogeneous in terms of the constraints
   on their power supply, communication capability, computation capacity
   and memory available.  Due to this heterogeneity, a wide variety of
   bootstrapping mechanisms are proposed and used for these smart

   Before classifying and describing the various methods of
   bootstrapping, it is important to discuss what is meant by the term
   bootstrapping.  In order to understand the term bootstrapping, we
   need to discuss some important preliminaries first.  We start by
   discussing the meaning of identity and identifiers.  The dictionary
   defines identity as "something that distinguishes an entity from
   other entities".  Dick Hardt (an advocate of identity 2.0 concept) in
   his keynote talk on identity describes human identity as "who you
   are, what you like, what you say about yourself and what others say
   about you" [identity2.0].  In addition to human beings, other
   entities in our physical environment such as the electronic devices
   we use, our pets and wildlife also have identities.

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   Just as in the real world, humans also have identities in the digital
   world.  For example, a digital identity may be used by online service
   to verify the identity of a registered user and provide it with
   secure personalized service.  This process of identity verification
   is also known as authentication.  An attribute that can be used to
   identify and distinguish one entity from another is referred to as an
   identifier.  The passport number of a citizen is an example of an
   real-world identifier.  Similarly, an email address is an example of
   a digital identifier.  Often the digital identifier of a human user
   and the digital identifier of its electronic devices are used
   interchangeably and one may subsume the other for authentication
   purposes.  For instance, when performing network access
   authentication, the user may enter its identity credentials on the
   device that should connect to the network.  In this case, the device
   assumes the user identity on its behalf and authenticates to obtain
   network access.  Ubiquitous computing devices increasingly interact
   with each other without human intervention.  This essentially
   requires the devices to have their own identifiers for authentication
   and secure communication.

   With these preliminaries in mind, we try to decipher the meaning of
   bootstrapping.  The term itself has often been used in many different
   contexts.  For instance, [RFC4640] describes bootstrapping as the
   process by which a mobile IPv6 node obtains information about the
   home address, the home agent address, and a security association.
   The IoT@Work project defines bootstrapping in the context of Internet
   of Things (IoT) as the process by which the state of a device, a
   subsystem, a network, or an application changes from not operational
   to operational [iotwork].  [I-D.oflynn-core-bootstrapping] also
   discusses the problem of secure bootstrapping for resource-
   constrained devices and highlights the role of IETF in defining
   suitable solutions.

   We define bootstrapping as any process that is required before the
   resource-constrained device network can operate.  Similarly,
   Vermillard [vermillard] describes bootstrapping as the procedure by
   which an IoT device gets the secret keys and URL for reaching the
   necessary servers.  Vermillard notes that this procedure is also
   useful for re-keying, upgrading the security schemes and for
   redirecting the devices to other servers.  The term device onboarding
   refers to similar ideas and is often used interchangeably with the
   term bootstrapping.  As an example, the AllSeen Alliance [allseen]
   defines onboarding as a service that provides a common and simple way
   for new devices to be brought onto an existing WiFi network.  Some
   solutions and standards organizations distinguish the processes
   involved in bootstrapping into the following sub-processes:

   a.  initial establishment of keys and configuration information

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   b.  subsequent provisioning of keys and configuration information

   The Open Connectivity Foundation (OCF), for example, uses the term
   onboarding for (a) and bootstrapping for (b).  Some specifications
   consider (a) out of scope and assume that this information is
   manufacturer provisioned.  However, in many cases the two processes
   are interdependent and may require business agreements and/or
   protocols to ensure security for both the sub-processes.  Instead of
   providing yet another definition of bootstrapping, here we list the
   different goals that bootstrapping may be used to fulfill:

   o  Authentication of a pre-established identity or creation of a new
      identity: To illustrate this with an example, consider the case
      where a user wishes to use one of the many free online mail
      services.  The user in this case needs to first register and
      create a unique identifier (email address) for its identity.
      Thereafter, the user will use this email address along with the
      password to authenticate and access the mails.  Both these
      processes can be considered as a part of bootstrapping.

   o  Authorization for network access that may include configuration of
      communication parameters: Bootstrapping also includes the process
      by which a device authenticates to the network and receives
      authorization and credentials for subsequent secure communication.

   o  Registration or joining a domain or group: The process by which a
      windows device joins a windows domain can also be seen as

   o  Pairing with a specific node, or connecting to a cloud service:
      Securely pairing two personal computing devices that have no
      a-priori information about each other, and securely connecting a
      device to an online cloud service are both different forms of

   It is evident that bootstrapping maybe used in many diverse scenarios
   to fulfill different goals.  Thus, it is not surprising that there
   are many different bootstrapping protocols and methods available.
   Rather than trying to achieve the impossible target of enlisting all
   the different bootstrapping solutions, we instead classify them into
   the following categories in section 3.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

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3.  Classification of available mechanisms

   While some bootstrapping approaches are more user-intensive and
   require extensive user-involvement by scanning QR codes or entering
   passwords; others maybe more automated, such as those that rely on
   mobile networks [I-D.sethi-gba-constrained].  We classify available
   bootstrapping solutions into the following major categories:

   o  Managed methods: These bootstrapping methods rely on pre-
      established trust relations and authentication credentials.  They
      typically utilize centralized servers for authentication, although
      several such servers may join to form a distributed federation.
      Example methods include Extensible Authentication Protocol (EAP)
      [RFC3748], Generic Bootstrapping Architecture (GBA) [TS33220],
      Kerberos [RFC4120], and vendor certificates [vendorcert].  EAP
      Transport Layer Security EAP-TLS [RFC5216] for instance assumes
      that both the client and the server have certificates to
      authenticate each other.  Based on this authentication, the server
      would then authorize the client for network access.  The Eduroam
      federation [RFC7593] uses a network of such servers to support
      roaming clients.

   o  Peer-to-Peer (P2P) and Ad-hoc methods: These bootstrapping methods
      do not rely on any pre-established credentials.  Instead, the
      bootstrapping protocol results in credentials being established
      for subsequent secure communication.  Such bootstrapping methods
      typically perform an unauthenticated Diffie-Hellman exchange [dh]
      and then use an out-of-band (OOB) communication channel to prevent
      a man-in-the-middle attack (MitM).  Various secure device pairing
      protocols fall in this category.  Another example P2P or Ad-hoc
      method is EAP-NOOB [I-D.aura-eap-noob] that specifies nimble out-
      of-band authentication for EAP.  Based on how the OOB channel is
      used, the P2P methods can be further classified into two sub

      *  Key derivation: Contextual information received over the OOB
         channel is used for shared key derivation.  For example,
         [proximate] relies on the common radio environment of the
         devices being paired to derive the shared secret which would
         then be used for secure communication.

      *  Key confirmation: A Diffie-Hellman key exchange occurs over the
         insecure network and the established key is used to
         authenticate with the help of the OOB channel.  For example,
         Bluetooth simple pairing [SimplePairing] use the OOB channel to
         ask the user to compare pins and approve the completed

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   o  Opportunistic and leap-of-faith methods: In these bootstrapping
      methods, rather than verifying the initial authentication, the
      continuity of the initial identity or connection is verified.
      Some of these methods assume that the attacker is not present
      during the initial setup.  Example methods include Secure Neighbor
      Discovery (SEND) [RFC3971] and Cryptographically Generated
      Addresses (CGA) [RFC3972], Wifi Protected Setup (WPS) push button
      [wps], and Secure Shell (SSH) [RFC4253].  Additionally, various
      online services such as Gmail and Facebook allow anyone to create
      a new identity during the initial setup and later only verify the
      continuity of the same identity.

   o  Hybrid methods: Most deployed methods are hybrid and use
      components from both managed and ad-hoc methods.  For instance,
      central management may be used for devices after they have been
      registered with the server using ad-hoc registration methods.

   It is important to note here that categorization of different
   bootstrapping methods is not always easy or clear.  For example, all
   the opportunistic and leap-of-faith methods become managed methods
   after the initial vulnerability window.  The choice of bootstrapping
   method used for devices depends heavily on the business case.
   Questions that may govern the choice include: What third parties are
   available?  Who wants to retain control or avoid work?  In each
   category, there are many different methods of secure bootstrapping
   available.  The choice of the method may also be governed by the type
   of device being bootstrapped.  Depending on the link-layer technology
   used, and the User Interface (UI) available, one or more of the above
   mentioned methods might be suitable.

4.  IoT Device Bootstrapping Methods

   In this section we look at some of the recent bootstrapping proposals
   for IoT devices both at the IETF and elsewhere.  Needless to say, if
   the devices are capable in terms of their computation power and UI
   available, they can always rely on many existing methods such as
   username and password combinations and various EAP methods.

4.1.  Managed Methods

   We first discuss some examples of managed bootstrapping methods.

   EAP-TLS is a widely used EAP method for network access authentication
   [RFC7250].  It allows mutual authentication and distributes the
   keying material for secure subsequent communications.  However it
   only supports certificate-based mutual authentication, and therefore
   a public key infrastructure is required.  The ZigBee Alliance has
   specified an IPv6 stack aimed at IEEE 802.15.4 [IEEE802.15.4] devices

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   mainly used in smart meters developed primarily for SEP 2.0 (Smart
   Energy Profile) application layer traffic [SEP2.0].  The ZigBee IP
   stack uses EAP-TLS for secure bootstrapping of devices.

   EAP-PSK [RFC4764] is another EAP method.  It realizes mutual
   authentication and session key derivation using a Pre-Shared Key
   (PSK).  Normally four messages are exchanged in the authentication
   process.  Once the authentication is successful, EAP-PSK provides a
   protected communication channel.  Given the light-weight nature of
   EAP-PSK, it can often be a good choice on constrained devices.

   EAP-COAP [I-D.marin-ace-wg-coap-eap] uses EAP transported over CoAP
   [RFC7252] messages for authenticating two CoAP endpoints and
   configuring key material to protect CoAP messages exchanged between
   them.  They discuss the use of EAP-PSK in the draft, but state that
   any EAP method that results in generation of cryptographic material
   is suitable.

   Protocol for Carrying Authentication for Network Access (PANA)
   [RFC5191] is a network layer protocol with which a node can
   authenticate itself to gain access to the network.  PANA does not
   define a new authentication protocol and rather uses EAP over User
   Datagram Protocol (UDP) for authentication.  Colin O'Flynn
   [I-D.oflynn-core-bootstrapping]proposes the use of PANA for secure
   bootstrapping of resource constrained devices.  He demonstrates how a
   6LowPAN Border Router (PANA Authentication Agent (PAA)) can
   authenticate the identity of a joining constrained device (PANA
   Client).  Once the constrained device has been successfully
   authenticated, the border router can also provide network and
   security parameters to the joining device.  Hernandez-Ramos et al.
   [panaiot] also use EAP-TLS over PANA for secure bootstrapping of
   smart objects.  They also extend their bootstrapping scheme for
   configuring additional keys that are used for secure group

   When a device is not a direct neighbor of the authenticator, its
   parent node MUST act as relay.  Different EAP encapsulation protocols
   have different mechanisms for the relay function, such as the PANA
   Relay Element (PRE).

   After a successful bootstrapping, the device runs neighbor discovery
   protocol to get an IPv6 address assigned [RFC6775].  Data transfer
   can be secured using DTLS or IPSec.  Keys derived from EAP TLS are
   used in either generating DTLS ciphering keys after a successful DTLS
   handshake or IPSec ESP ciphering keys after a successful IKEv2

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   Generic Bootstrapping Architecture (GBA) is another bootstrapping
   method that falls in centralized category.  GBA is part of the 3GPP
   standard [TS33220] and is based on 3GPP Authentication and Key
   Agreement (3GPP AKA).  GBA is an application independent mechanism to
   provide a client application (running on the User equipment (UE)) and
   any application server with a shared session secret.  This shared
   session secret can subsequently be used to authenticate and protect
   the communication between the client application and the application
   server.  GBA authentication is based on the permanent secret shared
   between the UE's Universal Integrated Circuit Card (UICC), for
   example SIM card, and the corresponding profile information stored
   within the cellular network operator's Home Subscriber System (HSS)
   database.  [I-D.sethi-gba-constrained] describes a resource-
   constrained adaptation of GBA to IoT applications.

   Open Mobile Alliance (OMA) Light-weight M2M standard also defines
   secure bootstrapping for resource-constrained IoT devices with a
   centralized Bootstrapping Server (BS).  The current standard defines
   the following four bootstrapping modes:

   o  Factory Bootstrap: An IoT device in this case is configured with
      all the necessary bootstrap information during manufacturing and
      prior to its deployment.

   o  Bootstrap from Smartcard: An IoT device retrieves and processes
      all the necessary bootstrap data from a Smartcard.

   o  Client Initiated Bootstrap: This mode provides a mechanism for an
      IoT client device to retrieve the bootstrap information from a
      Bootstrap Server.  This requires the client device to have an
      account at the Bootstrap Server and credentials to obtain the
      necessary information securely.

   o  Server Initiated Bootstrap: In this bootstrapping mode, the
      bootstrapping server configures all the bootstrap information on
      the IoT device without receiving a request from the client.  This
      means that the bootstrap server needs to know if a client IoT
      Device is ready for bootstrapping before it can be configured.
      For example, a network may inform the bootstrap server of a new
      connecting IoT client device.

   The Kerberos protocol [RFC4120] is a network authentication protocol
   that allows several endpoints to communicate over an insecure
   network.  Kerberos relies on a symmetric cryptography scheme and
   requires a trusted third party, that guarantees the identities of the
   various actors.  It relies on the use of "tickets" for nodes to prove
   identity to one another in a secure manner.  There has been research
   work on using Kereberos for IoT devices[kerberosiot].

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   The ANIMA working group is also working on a bootstrapping solution
   for resource-constrained devices that relies on 802.1AR vendor
   certificates [I-D.ietf-anima-bootstrapping-keyinfra] called
   Bootstrapping Remote Secure Key Infrastructures (BRSKI).  In addition
   to vendor installed IEEE 802.1AR certificates, a vendor based service
   on the Internet is required.  Before being authenticated, a new
   device only needs link-local connectivity, and does not require a
   routable address.  When a vendor provides an Internet based service,
   devices can be forced to join only specific domains.  The draft
   highlights that the described solution is aimed in general at non-
   constrained (i.e. class 2+ defined in [RFC7228]) devices operating in
   a non-Challenged network.  It claims to scale to thousands of devices
   located in hostile environments, such as ISP provided CPE devices
   which are drop-shipped to the end user.

   [I-D.kumar-6lo-selective-bootstrap] presents a selective
   bootstrapping/commissioning method by introducing the concept of
   Commissioning Tool (CT).  In this method the devices are left to
   connect to the network and execute 6LowPAN neighbor discovery
   protocol and have an IPv6 address before they are authenticated.
   Then the devices are selected one by one in some order to communicate
   with the CT via untrusted constructed route.  Once the ID of joining
   device is authenticated, the CT sends the layer-2 key material to the
   device via secured channel.  This secure channel is established with
   DTLS with credential material that has to be installed onto the
   device during its manufacture.

   [I-D.ietf-netconf-zerotouch] defines a bootstrapping strategy for
   enabling devices to securely obtain all the configuration information
   with no installer input, beyond the actual physical placement and
   connection of cables.  Their goal is to enable a secure NETCONF
   [RFC6241] or RESTCONF [RFC8040] connection to the deployment specific
   network management system (NMS).  This bootstrapping method requires
   the devices to be configured with trust anchors in the form of X.509

   Before closing the discussion on managed methods, it is also
   important to mention some of the work done on implicit certificates
   and identity-based cryptographic schemes [himmo], [implicit].  While
   these are interesting and novel schemes that can be a part of
   securely bootstrapping devices, at this point, it is hard to
   speculate on whether such schemes would see large-scale deployment in
   the future.

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4.2.  Peer to Peer or Adhoc Methods

   While managed methods are viable for many IoT devices, they may not
   be suitable or desirable in all scenarios.  All the managed methods
   assume that some credentials are provisioned into the device.  These
   credentials may be in the device micro-controller or in a replaceable
   smart card such as a SIM card.  The methods also sometimes assume
   that the manufacturer embeds these credentials during the device
   manufacture on the factory floor.  However, in many cases the
   manufacturer may not have sufficient incentive to do this.  In other
   scenarios, it may be hard to completely trust and rely on the device
   manufacturer to securely perform this task.  Therefore, many times,
   P2P or Adhoc methods of bootstrapping are used.  We discuss a few
   example next.

   P2P or ad-hoc bootstrapping methods are used for establishing keys
   and credential information for secure communication without any pre-
   provisioned information.  These bootstrapping mechanisms typically
   rely on an out-of-band (OOB) channel in order to prevent man-in-the-
   middle (MitM) attacks.  P2P and ad-hoc methods have typically been
   used for securely pairing personal computing devices such as smart
   phones. [devicepairing] provides a survey of such secure device
   pairing methods.  Many original pairing schemes required the user to
   enter the same key string or authentication code to both devices or
   to compare and approve codes displayed by the devices.  While these
   methods can provide reasonable security, they require user
   interaction that is relatively unnatural and often considered a
   nuisance.  Thus, there is ongoing research for more natural ways of
   pairing devices.  To reduce the amount of user-interaction required
   in the pairing process, several proposals use contextual or location-
   dependent information, or natural user input such as sound or
   movement, for device pairing [proximate].

   The local association created between two devices may later be used
   for connecting/introducing one of the devices to a centralized
   server.  Such methods would however be classified as hybrids.

   EAP-NOOB [I-D.aura-eap-noob] is an example of P2P and ad-hoc
   bootstrapping method that establishes a security association between
   an IoT device (node) and an online server (unlike pairing two devices
   for local connections over WiFi or Bluetooth).

   EAP-NOOB defines an EAP method where the authentication is based on a
   user-assisted out-of-band (OOB) channel between the server and peer.
   It is intended as a generic bootstrapping solution for Internet-of-
   Things devices which have no pre-configured authentication
   credentials and which are not yet registered on the authentication
   server.  This method claims to be more generic than most ad-hoc

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   bootstrapping solutions in that it supports many types of OOB
   channels.  The exact in-band messages and OOB message contents are
   specified and not the OOB channel details.  Also, EAP-NOOB supports
   IoT devices with only output (e.g. display) or only input (e.g.
   camera).  It makes combined use of both secrecy and integrity of the
   OOB channel for more robust security than the ad-hoc solutions.

   Thread Group commissioning [threadcommissioning] introduces a two
   phased process i.e. Petitioning and Joining.  Entities involved are
   Leader, Joiner, Commissioner, Joiner Router and Border Router.
   Leader is the first device in Thread Network that must be
   commissioned using out-of-band process and is used to inject correct
   user generated Commissioning Credentials (can be changed later) into
   Thread Network.  Joiner is the node that intends to get authenticated
   and authorized on Thread Network.  Commissioner is either within the
   Thread Network (Native) or connected with Thread Network via a WLAN

   Under some topologies, Joiner Router and Border Router facilitate the
   Joiner node to reach Native and External Commissioner, respectively.
   Petitioning begins before Joining process and is used to grant sole
   commissioning authority to a Commissioner.  After an authorized
   Commissioner is designated, eligible thread devices can join network.
   Pair-wise key is shared between Commissioner and Joiner, network
   parameters (Network Name, Security Policy, Steering Data,
   Commissioning Data Timestamp, Commissioning Credential, Network
   Master Key, Network Key Sequence, Network Mesh-Local ULA, Border
   Router Locator, Commissioner Session ID, XPANID, PANID and Channel)
   are sent out securely (using pair-wise key) by Joiner Router to
   Joiner for letting Joiner to join the Thread Network.  Entities
   involved in Joining process depends on system topology i.e. location
   of Commissioner and Joiner.

   Thread networks only operates using IPv6.  Thread devices can devise
   GUAs (Global Unicast Addresses) [RFC4291].  Provision also exist via
   Border Router, for Thread device to acquire individual global address
   by means of DHCPv6 or using SLAAC (Stateless Address
   Autoconfiguration) address derived with advertised network prefix.

   DPP (Device Provisioning Protocol) [dpp] is a 3 message
   authentication protocol currently being standardized by the WiFi
   Alliance for devices that rely on IEEE 802.11 link-layer for
   communication.  The current DPP specification is only aimed at
   networks that use WPA2-PSK (also known as WPA2-Home) for network
   access authentication.  Authentication Request, Response and Confirm
   are 3 messages types based on [IEEE802.11] format.  It provides
   authentication and key establishment between an initiator and a
   responder.  Out of band mechanisms i.e. QR code, USB, NFC, Bluetooth

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   or proof of shared code/phrase/word is used to acquire bootstrapping
   key [dpptech].  Afterwards, authentication and configuration exchange
   takes place.  Bootstrap trust in public key can be only for
   responder's public key or for both parties in mutual authentication
   manner.  The role of initiator and responder as either enrollee or
   configurator is decided during initial exchange of DPP Authentication
   frames.  Configurator's protocol key is always a one-time-used
   (ephemeral) key but enrollee's protocol key always becomes its
   network access provisioning key.

4.3.  Leap-of-faith/Opportunistic Methods

   Next, we look at a leap-of-faith/opportunistic bootstrapping method
   for IoT devices.

   Bergmann et al. [simplekey] develop a secure bootstrapping mechanism
   that does not rely on pre-provisioned credentials using resurrecting-
   duckling imprinting scheme.  Their bootstrapping protocol involves
   three distinct phases: discover (the duckling node searches for
   network nodes that can act as mother node), imprint (the mother node
   imprints a shared secret establishing a secure channel once a
   positive response is received for the imprinting request) and
   configure (additional configuration information such as network
   prefix and default gateway are configured).  In this model for
   bootstrapping, a small initial vulnerability window is acceptable and
   can be mitigated using techniques such as a Faraday Cage (securing
   the communication physically) to protect the environment of the
   mother and duck nodes, though this may be inconvenient for the user.

   [RFC7250] defines how raw public keys can be used to authenticate
   constrained devices for mutual authentication using EAP-TLS or DTLS.
   Raw public key TLS/DTLS extension simplifies client_certificate_type
   and server_certificate_type to carry only SubjectPublicKeyInfo
   structure with the raw public key instead of many other parameters
   found in the certificates.  The device and the authentication server
   (AS) exchange client_hello and server_hello messages and send their
   raw public keys.  The device and AS validate the keys by comparing
   the pre-configured values [I-D.sarikaya-6lo-bootstrapping-solution].
   This bootstrapping method can be seen as a hybrid.  This is because
   it generally requires an out-of-band (OOB) step (P2P/Ad-hoc) where
   the raw public keys [RFC7250] are provided to the authenticating
   entities, after which the actual authentication occurs online
   (managed).  Raw public key approach when used with DTLS offers a
   simple secure bootstrapping solution especially for smart energy and
   building automation applications.  It can be easily integrated with
   the Constrained Application Protocol (CoAP).

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5.  Security Considerations

   Bootstrapping protocols that do not rely on a pre-shared key for peer
   authentication generally rely on an online or offline third-party
   (e.g., an authentication server, a key distribution center in
   Kerberos, a certification authority in PKI, a private key generator
   in ID-based cryptography and so on) to prevent man-in-the-middle
   attacks during bootstrapping.  Depending on use cases, a resource-
   constrained device may not always have access to an online third-
   party for bootstrapping.  Some bootstrapping methods therefore rely
   on a configuration tool (such as a smartphone) that assists the
   bootstrapping process by providing temporary reachability to the
   online server.

   Depending on use cases, a bootstrapping protocol may deal with
   authorization separately from authentication in terms of timing and
   signaling path.  For example, two resource-constrained devices A and
   B may perform mutual authentication using authentication credentials
   provided by an offline third-party X whereas resource-constrained
   device A obtains authorization for running a particular application
   with resource-constrained device B from an online third-party Y
   before or after the authentication.  In some use cases,
   authentication and authorization are tightly coupled, e.g.,
   successful authentication also means successful authorization.

   If authorization information communicated includes cryptographic
   keys, care must be taken for provisioning the keys, e.g., guidelines
   for AAA-based key management are described in [RFC4962].  Re-
   bootstrapping of IoT devices may required and therefore there must be
   adequate provisions for revocation and re-bootstrapping of
   authentication/authorization credentials.  Re-bootstrapping must be
   as secure as the initial bootstrapping regardless of whether this re-
   bootstrapping is done manually or automatically over the network.

   If resource-constrained devices use a multicast group key for
   authentications of peers that belong to the group, or for message
   authentication/encryption, the group key must be securely distributed
   to the current members of the group.  Protocols designed for group
   key management [RFC4046] may be used for group key distribution after
   the initial bootstrapping.  Alternatively, key wrap attributes for
   securely encapsulating group key may be defined in network access
   authentication protocols such as PANA.  Those protocols use an end-
   to-end, point-to-point communication channel with a pair-wise
   security association between a key distribution center and each key
   recipient.  Further considerations may be needed for more efficient
   group key management to support a large number of resource-
   constrained devices.

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6.  IANA Considerations

   There are no IANA considerations for this document.

7.  Acknowledgements

   We would like to thank Tuomas Aura and Hannes Tschofenig for
   providing extensive feedback.

8.  Informative References

   [allseen]  AllSeen Alliance, "Onboarding service",

              Mirzadeh, S., Cruickshank, H., and R. Tafazolli, "Secure
              Device Pairing: A Survey", IEEE Communications Surveys and
              Tutorials , pp. 17-40, 2014.

   [dh]       Diffie, W. and M. Hellman, "New directions in
              cryptography", IEEE Transactions on Information Theory ,
              vol. 22, no. 6, pp. 644-654, 1976.

   [dpp]      Overview Document, , "Wi-Fi Device Provisioning Protocol
              (DPP)", Wi-Fi Alliance , 2016.

   [dpptech]  Technical Specification, , "Technical Specification Draft
              for DPP", Wi-Fi Alliance , 2016.

   [himmo]    Garcia-Morchon, O., Rietman, R., Sharma, S., Tolhuizen,
              L., and J. Torre-Arce, "DTLS-HIMMO: Efficiently Securing a
              Post-Quantum World with a Fully-Collusion Resistant KPS",
              Submitted to NIST Workshop on Cybersecurity in a Post-
              Quantum World , version 20141225:065757, December 2014,

              Aura, T. and M. Sethi, "Nimble out-of-band authentication
              for EAP (EAP-NOOB)", draft-aura-eap-noob-01 (work in
              progress), July 2016.

              Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
              S., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-04 (work in progress), October 2016.

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              Watsen, K. and M. Abrahamsson, "Zero Touch Provisioning
              for NETCONF or RESTCONF based Management", draft-ietf-
              netconf-zerotouch-12 (work in progress), January 2017.

              Kumar, S. and P. Stok, "Security Bootstrapping over IEEE
              802.15.4 in selective order", draft-kumar-6lo-selective-
              bootstrap-00 (work in progress), March 2015.

              Lopez, R. and D. Garcia, "EAP-based Authentication Service
              for CoAP", draft-marin-ace-wg-coap-eap-04 (work in
              progress), October 2016.

              Sarikaya, B., Ohba, Y., Cao, Z., and R. Cragie, "Security
              Bootstrapping of Resource-Constrained Devices", draft-
              oflynn-core-bootstrapping-03 (work in progress), November

              Sarikaya, B., "Secure Bootstrapping Solution for Resource-
              Constrained Devices", draft-sarikaya-6lo-bootstrapping-
              solution-00 (work in progress), June 2013.

              Sethi, M., Lehtovirta, V., and P. Salmela, "Using Generic
              Bootstrapping Architecture with Constrained Devices",
              draft-sethi-gba-constrained-01 (work in progress),
              February 2014.

              Hardt, D., "Identity 2.0", O'Reilly Open Source Convention
              (OSCON) , 2005.

              IEEE Standard, , "IEEE Std. 802.11-2016", December 2016,

              IEEE Standard, , "IEEE Std. 802.15.4-2015", April 2016,

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              Porambage, P., Schmitt, C., Kumar, P., Gurtov, A., and M.
              Ylianttila, "Pauthkey: A pervasive authentication protocol
              and key establishment scheme for wireless sensor networks
              in distributed iot applications", International Journal of
              Distributed Sensor Networks , Hindawi Publishing
              Corporation , 2014.

   [iotwork]  European Commission FP7, "IoT@Work bootstrapping
              architecture Deliverable D2.2", June 2011.

              Hardjono, , "Kerberos for Internet-of-Things", February
              2014, <

   [panaiot]  Hernandez-Ramos, J., Carrillo, D., Marin-Lopez, R., and A.
              Skarmeta, "Dynamic Security Credentials PANA-based
              Provisioning for IoT Smart Objects", 2nd World Forum on
              Internet of Things (WF-IoT) , IEEE , 2015.

              Mathur, , Miller, , Varshavsky, , Trappe, , and Mandayam,
              "Proximate: proximity-based secure pairing using ambient
              wireless signals.", Proceedings of MobiSys International
              Conference , pp. 211-224, June 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,

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   [RFC4046]  Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
              "Multicast Security (MSEC) Group Key Management
              Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005,

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              DOI 10.17487/RFC4120, July 2005,

   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <>.

   [RFC4640]  Patel, A., Ed. and G. Giaretta, Ed., "Problem Statement
              for bootstrapping Mobile IPv6 (MIPv6)", RFC 4640,
              DOI 10.17487/RFC4640, September 2006,

   [RFC4764]  Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: A
              Pre-Shared Key Extensible Authentication Protocol (EAP)
              Method", RFC 4764, DOI 10.17487/RFC4764, January 2007,

   [RFC4962]  Housley, R. and B. Aboba, "Guidance for Authentication,
              Authorization, and Accounting (AAA) Key Management",
              BCP 132, RFC 4962, DOI 10.17487/RFC4962, July 2007,

   [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, <>.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
              March 2008, <>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,

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

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <>.

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

   [RFC7593]  Wierenga, K., Winter, S., and T. Wolniewicz, "The eduroam
              Architecture for Network Roaming", RFC 7593,
              DOI 10.17487/RFC7593, September 2015,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

   [SEP2.0]   ZigBee Alliance, "ZigBee IP Specification", March 2014,

              Bergmann, O., Gerdes, S., and C. Bormann, "Simple Keys for
              Simple Smart Objects", Smart Object Security Workshop,
              IETF 83 , March 2012.

              Bluetooth, SIG, "Simple pairing whitepaper", Technical
              report , 2007.

              White Paper, , "Thread Commissioning", Thread Group,
              Inc. , 2015.

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   [TS33220]  3GPP, "3rd Generation Partnership Project; Technical
              Specification Group Services and System Aspects; Generic
              Authentication Architecture (GAA); Generic Bootstrapping
              Architecture (GBA) (Release 14)", December 2016,

              IEEE std. 802.1ar-2009, "Standard for local and
              metropolitan area networks - secure device identity",
              December 2009.

              Vermillard, J., "Bootstrapping device security with
              lightweight M2M", Appeared on blog at ,
              February 2015.

   [wps]      IEEE Standard, , "Wi-fi protected setup", Wi-Fi Alliance ,

Authors' Addresses

   Behcet Sarikaya
   5340 Legacy Dr. Building 3
   Plano, TX  75024


   Mohit Sethi
   Hirsalantie 11
   Jorvas  02420


   Abdur Rashid Sangi
   Huawei Technologies
   No.156 Beiqing Rd. Haidian District
   Beijing  100095
   P.R. China


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