Internet DRAFT - draft-irtf-t2trg-security-setup-iot-devices
draft-irtf-t2trg-security-setup-iot-devices
Network Working Group M. Sethi
Internet-Draft Aalto University
Intended status: Informational B. Sarikaya
Expires: 28 March 2024
D. Garcia-Carrillo
University of Oviedo
25 September 2023
Terminology and processes for initial security setup of IoT devices
draft-irtf-t2trg-security-setup-iot-devices-01
Abstract
This document provides an overview of terms that are commonly used
when discussing the initial security setup of Internet of Things
(IoT) devices. This document also presents a brief but illustrative
survey of protocols and standards available for initial security
setup of IoT devices. For each protocol, we identify the terminology
used, the entities involved, the initial assumptions, the processes
necessary for completion, and the knowledge imparted to the IoT
devices after the setup is complete.
Status of This Memo
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This Internet-Draft will expire on 28 March 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Standards and Protocols . . . . . . . . . . . . . . . . . . . 4
2.1. Bluetooth . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Device Provisioning Protocol (DPP) . . . . . . . . . . . 6
2.3. Enrollment over Secure Transport (EST) . . . . . . . . . 7
2.4. Open Mobile Alliance (OMA) Lightweight Machine to Machine
specification (LwM2M) . . . . . . . . . . . . . . . . . 8
2.5. Nimble out-of-band authentication for EAP (EAP-NOOB) . . 10
2.6. Open Connectivity Foundation (OCF) . . . . . . . . . . . 12
2.7. Fast IDentity Online (FIDO) alliance . . . . . . . . . . 13
2.8. Bootstrapping Remote Secure Key Infrastructures
(BRSKI) . . . . . . . . . . . . . . . . . . . . . . . . 14
2.9. Secure Zero Touch Provisioning (SZTP) . . . . . . . . . . 15
2.10. LPWAN . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.11. Thread . . . . . . . . . . . . . . . . . . . . . . . . . 17
3. Comparison . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1. Comparison of terminology . . . . . . . . . . . . . . . . 19
3.2. Comparison of players . . . . . . . . . . . . . . . . . . 22
3.3. Comparison of initial beliefs . . . . . . . . . . . . . . 22
3.3.1. No initial trust established . . . . . . . . . . . . 22
3.3.2. Initial trust based on the credentials installed . . 23
3.4. Comparison of processes . . . . . . . . . . . . . . . . . 24
3.5. Comparison of knowledge imparted to the device . . . . . 24
4. Security Considerations . . . . . . . . . . . . . . . . . . . 25
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
7. Informative References . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
Initial security setup for a device refers to any process that takes
place before a device can become fully operational. The phrase
*initial security setup* intentionally includes the term _security_
as setup of devices without adequate security or with insecure
processes is no longer acceptable. The initial security setup
process, among other things, involves network discovery and
selection, access authentication, configuration of necessary
credentials and parameters.
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Initial security setup for IoT devices is challenging because the
size of an IoT network varies from a couple of devices to tens of
thousands, depending on the application. Moreover, devices in IoT
networks are produced by a variety of vendors and are typically
heterogeneous in terms of the constraints on their power supply,
communication capability, computation capacity, and user interfaces
available. This challenge of initial security setup in IoT was
identified by Sethi et al. [Sethi14] while developing a solution for
smart displays.
Initial security setup of devices typically also involves providing
them with some sort of network connectivity. The functionality of a
disconnected device is rather limited. Initial security setup of
devices often assumes that some network has been setup a-priori.
Setting up and maintaining a network itself is challenging. For
example, users may need to configure the network name (called as
Service Set Identifier (SSID) in Wi-Fi networks) and passphrase
before new devices can be setup. Specifications such as the Wi-Fi
Alliance Simple Configuration [simpleconn] help users setup networks.
However, this document is only focused on terminology and processes
associated with initial security setup of devices and excludes any
discussion on setting up networks.
There are several terms that are used in the context of initial
security setup of devices:
* Bootstrapping
* Provisioning
* Onboarding
* Enrollment
* Commissioning
* Initialization
* Configuration
* Registration
* Discovery
In addition to using a variety of different terms, initial security
setup mechanisms can rely on a number of entities. For example, a
companion smartphone device maybe necessary for some initial security
setup mechanisms. Moreover, security setup procedures have diverse
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initial assumptions about the device being setup. As an example, an
initial security setup mechanism may assume that the device is
provisioned with a pre-shared key and a list of trusted network
identifiers. Finally, initial security setup mechanisms impart
different information to the device after completion. For example,
some mechanisms may only provide a key for use with an authorization
server, while others may configure elaborate access control lists
directly.
The next section provides an overview of some standards and protocols
for initial security setup of IoT devices. For each mechanism, the
following are explicitly identified:
* Terminology used
* Entities or "players" involved
* Initial assumptions about the device
* Processes necessary for completion
* Knowledge imparted to the device after completion
2. Standards and Protocols
2.1. Bluetooth
Bluetooth mesh specifies a provisioning protocol. The goal of the
provisioning phase is to securely incorporate a new Bluetooth mesh
node, by completing two critical tasks. First, to authenticate the
unprovisioned device and second, to create a secure link with said
device to share information.
The provisioning process is divided into five distinct stages
summarize next:
* Beaconing for discover: The new unprovisioned device is discovered
by the provisioner
* Negotiation: The unprovisioned device indicates to the provisioner
a set of capabilities such as the security algorithms supported,
the availability of its public key using an Out-of-Band (OOB)
channel and the input/output interfaces supported
* Public-key exchange: The authentication method is selected by the
provisioner and both devices exchange Elliptic-curve
Diffie–Hellman (ECDH) public keys. These keys may be static or
ephemeral. Their exchange can be done in two ways, either via
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Out-of-Band or directly through a Bluetooth link. Each device
then generates a symmetric key, named ECDHSecret, by combining its
own private key and the public key of the peer device. The
EDCHSecret is used to protect communication between the two
devices.
* Authentication: During this phase, the ECDH key exchange is
authenticated. The authentication method can be Output OOB, Input
OOB, static OOB, or No OOB. With Output OOB, the unprovisioned
device chooses a random number and outputs that number in manner
consistent with its capabilities. The provisioner then inputs
this number. Then, a check confirmation value operation is
performed. This involves a cryptographic exchange regarding (in
this case) the random number to complete the authentication. With
Input OOB, the roles are reversed, being the provisioner the
entity that generates the random number. When neither of the
previous authentication procedures are feasible, both the
provisioner and unprovisioned device generate a random number and
require the user supervising the setup to verify that values on
the device and provisioner are the same.
* Distribution of provisioning data: At this point, the provisioning
process can be protected. This involves the distribution of data
such as a Network key, to secure the communications at network
layer and a unicast address among other information.
Bluetooth mesh has the following characteristics:
* Terms: Configuration, discovery, provisioning.
* Players: Client, Device, Manager, Manufacturer, Peer, Server, User
* Initial beliefs assumed in the device: Previously to the
provisioning phase, there is no pre-shared credentials for a trust
relation.
* Processes: Provisioning
* Beliefs imparted to the device after protocol execution: After the
provisiong, the device trusts the provisioner entity and any other
device in the network sharing its network key.
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2.2. Device Provisioning Protocol (DPP)
The Wi-Fi Alliance Device provisioning protocol (DPP) [dpp] describes
itself as a standardized protocol for providing user friendly Wi-Fi
setup while maintaining or increasing the security. DPP relies on a
configurator, e.g. a smartphone application, for setting up all other
devices, called enrollees, in the network. DPP has the following
three phases/sub-protocols:
* Bootstrapping: The configurator obtains bootstrapping information
from the enrollee using an out-of-band channel such as scanning a
QR code or tapping NFC. The bootstrapping information includes
the public-key of the device and metadata such as the radio
channel on which the device is listening.
* Authentication: In DPP, either the configurator or the enrollee
can initiate the authentication protocol. The side initiating the
authentication protocol is called as the initiator while the other
side is called the responder. The authentication sub-protocol
provides authentication of the responder to an initiator. It can
optionally authenticate the initiator to the responder (only if
the bootstrapping information was exchange out-of-band in both
directions).
* Configuration: Using the key established from the authentication
protocol, the enrollee asks the configurator for network
information such as the SSID and passphrase of the access point.
DPP has the following characteristics:
* Terms: Bootstrapping, configuration, discovery, enrollment,
provisioning.
* Players: Authenticator, Client, Configurator, Device, Initiator,
Manufacturer, Owner, Peer, Persona, Responder, User, Enrollee
* Initial beliefs assumed in the device: There are two entities
involved in the DPP protocol, the Initiator and Responder. These
entities as a starting point do not have a trust relation, nor do
they share credentials or key material. DPP uses a decentralized
architecture with no central authority to coordinate or control
authentication and rely on a direct trust model. In DPP,
authentication does not rely on a pre-existing trust relation with
a third-party or centralized entity, hence all entities involved
in DPP need to perform the required validation.
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* Processes: Bootstrapping, authentication, provisioning, and
network access. Bootstrapping: To establish a secure provisioning
connection, the devices exchange public bootstrapping keys.
Authentication: To establish trust and build a secure channel, the
devices employ the DPP Authentication protocol's bootstrapping
keys. Configuration: The Configurator uses the DPP Configuration
protocol to provision the Enrollee through the secure channel
created during DPP Authentication. Network access: The Enrollee
establishes network access using the newly provisioned
credentials.
* Beliefs imparted to the device after protocol execution: DPP
bootstrapping relies on the transfer of the public-key that is
expected to be trusted. The beliefs when mutual authentication is
run, relies on the trust of a succesful DPP bootstrapping. When
mutual authentication is not supported, a device that can control
when and how its own public key is bootstrapped, can perform a
weak authentication to any entity that knows its public key.
2.3. Enrollment over Secure Transport (EST)
Enrollment over Secure Transport (EST) [RFC7030] defines a profile of
Certificate Management over CMS (CMC) [RFC5272]. EST relies on
Hypertext Transfer Protocol (HTTP) and Transport Layer Security (TLS)
for exchanging CMC messages and allows client devices to obtain
client certificates and associated Certification Authority (CA)
certificates. A companion specification for using EST over secure
CoAP has also been standardized [RFC9148]. EST assumes that some
initial information is already distributed so that EST client and
servers can perform mutual authentication before continuing with
protocol. [RFC7030] further defines "Bootstrap Distribution of CA
Certificates" which allows minimally configured EST clients to obtain
initial trust anchors. It relies on human users to verify
information such as the CA certificate "fingerprint" received over
the unauthenticated TLS connection setup. After successful
completion of this bootstrapping step, clients can proceed to the
enrollment step during which they obtain client certificates and
associated CA certificates.
EST has the following characteristics:
* Terms: Bootstrapping, enrollment, initialization, configuration.
* Players: Administrator, Client, Device, Manufacturer, Owner, Peer,
Server, User
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* Initial beliefs assumed in the device: There is a process of
distribution of initial information which provides both the EST
client and server with the information for the EST client and
server to perform mutual authentication as well as for
authorization.
* Processes: Distribution of Certificates, Bootstrap, Enrollment
* Beliefs imparted to the device after protocol execution: The EST
enrollment process is designed to make establishing automated
certificate issuing from a trustworthy CA as simple as possible.
After the processe have finished, the device is able to
automatically renew its certificates through re-enrollment as it
has a trust relation with the ESP server.
2.4. Open Mobile Alliance (OMA) Lightweight Machine to Machine
specification (LwM2M)
LwM2M specification developed by OMA [oma] defines a RESTful
architecture where a new IoT device (LwM2M client) first contacts an
LwM2M Bootstrap-Server for obtaining essential information such
credentials for subsequently registering with one or more LwM2M
Servers. These one or more LwM2M servers are used for performing
device management actions during the device lifecycle (reading sensor
data, controlling an actuator, modifying access controls etc.).
LwM2M specification does not deal with the initial network
configuration of IoT devices and assumes that the IoT client device
has network reachability to the LwM2M Bootstrap-Server and LwM2M
Server.
The current standard defines the following four bootstrapping modes:
* Factory Bootstrap: An IoT device is configured with all the
information necessary for securely communicating with an LwM2M
Bootstrap-Server and/or LwM2M Serverwhile it is manufactured and
prior to its deployment.
* Bootstrap from Smartcard: An IoT device retrieves all the
information necessary for securely communicating with an LwM2M
Bootstrap-Server and/or LwM2M Server from a Smartcard.
* Client Initiated Bootstrap: If the IoT device in one of the above
bootstrapping modes is only configured with information about an
LwM2M Bootstrap-Server, then the client device must first
communicate securely with the configured LwM2M Bootstrap-Server
and obtain necessary information and credentials to subsequently
register with one or more LwM2M Servers.
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* Server Initiated Bootstrap: In this bootstrapping mode, the LwM2M
server triggers the client device to begin the client initiated
bootstrap sequence described above.
The LwM2M specification is also quite flexible in terms of the
credentials and the transport security mechanism used between the
client device and the LwM2M Server or the LwM2M Bootstrap-Server.
Credentials such as a pre-shared symmetric key, a raw public key
(RPK), or x.509 certificates can be used with various transport
protocols such as Transport Layer Security (TLS) or Datagram
Transport Layer Security (DTLS) as specified in LwM2M transport
bindings specification [oma-transport].
As explained earlier, an LwM2M Bootstrap-Server is responsible for
provisioning credentials into an LwM2M Client. When x509
certificates are being provisioned, the asymmetric key pair is
generated on the Bootstrap-Server and then sent to the LwM2M client
device. This approach is not acceptable in all scenarios and
therefore, LwM2M specification also supports a mode where the client
device uses the Enrollment over Secure Transport (EST) certificate
management protocol for provisioning certificates from the LwM2M
Bootstrap-Server to the LwM2M Client.
OMA has the following characteristics:
* *Terms*:
- _Bootstrapping_ and _Unbootstrapping_: Bootstrapping is used
for describing the process of providing an IoT device with
credentials and information of one or more LwM2M server.
Interestingly, the transport bindings specification
[oma-transport] also uses the term unbootstrapping for the
process where objects corresponding to an LwM2M Server are
deleted on the client.
- _Provisioning_ and _configuration_: terms used to refer to the
process of providing some infomration to a LwM2M client.
- _Discovery_: term for the process by which a LwM2M Bootstrap-
Server or LwM2M Server discovers objects, object instances,
resources, and attributes supported by RESTful interfaces of a
LwM2M Client.
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- _Register_ and _De-register_: Register is the process by which
a client device sets up a secure association with an LwM2M
Server and provides the server with information about objects
and existing object instances of the client. De-register is
the process by which the client deletes information about
itself provided to the LwM2M server during the registration
process.
- _Intialization_: term for the process by which an LwM2M
Bootstrap-Server or LwM2M Server deletes objects on the client
before performing any write operations.
* *Players*: Device manufacturers or Smartcard manufacturers are
responsible for providing client IoT devices with initial
information and credentials of LwM2M Bootstrap-Server and/or LwM2M
server.
* *Initial beliefs assumed in the device*: The client at the very
least has necessary information to trust the LwM2M bootstrap
server in the .
* *Processes*: LwM2M does not require any actions from the device
owner/user. Once the device is registered with the LwM2M server,
various actions related to device management can be performed by
device owner/user via the LwM2M server.
* *Beliefs imparted to the device after protocol execution*: After
the bootstrapping is performed, the LwM2M client can register
(Security object and Server object) with the LwM2M servers.
2.5. Nimble out-of-band authentication for EAP (EAP-NOOB)
Extensible Authentication Protocol (EAP) framework provides support
for multiple authentication methods. EAP-NOOB [RFC9140] defines an
EAP method where the authentication is based on a user-assisted out-
of-band (OOB) channel between the IoT device (peer in EAP
terminology) and the server. It is intended as a generic
bootstrapping solution for IoT devices which have no pre-configured
authentication credentials and which are not yet registered on the
authentication server.
The application server where the IoT device is registered once EAP-
NOOB is completed may belong to the manufacturer or the local network
where the device is being deployed. EAP-NOOB uses the flexibility of
the Authentication, Authorization, and Accounting (AAA) [RFC2904]
architecture to allow routing of EAP-NOOB sessions to a specific
application server.
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EAP-NOOB claims to be more generic than most ad-hoc bootstrapping
solutions in that it supports many types of OOB channels and supports
IoT devices with only output (e.g. display) or only input (e.g.
camera).
EAP-NOOB has the following characteristics:
* *Terms*:
- _Bootstrapping_: term used to describe the entire process
involved during the initial security setup of an IoT device.
The specification does not use separate terms or distinguish
the process of obtaining identifier and credentials for
communicating with an application server where the user has an
account or for network connectivity.
- _Registration_: term used for describing the process of
associating the device with a user account on an application
server.
* *Players*: The device owner/user is responsible for transferring
an OOB message necessary for protocol completion. The application
server where the device is registered may be provided by different
service providers including the device manufacturer or device
owner. The local network needs standard AAA configuration for
routing EAP-NOOB sessions to the application server chosen by the
device owner/user.
* *Initial beliefs assumed in the device*: EAP-NOOB does not require
devices to have any pre-installed credentials but expects all
devices to use a standard identifier (noob@eap-noob.arpa) during
initial network discovery.
* *Processes*: The IoT device performs network discovery and one or
more OOB outputs maybe generated. The user is expected EAP
exchange is encompassed by Initial Exchange, OOB step, Completion
Exchange and Waiting Exchange.
* *Beliefs imparted to the device after protocol execution*: After
EAP-NOOB botstrapping process is complete, the device and server
establish a long-term secret which can renewed without further
user involvement. As a side-effect, the device also obtains
identifier and credentials for network and Internet connectivity
(via the EAP authenticator).
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2.6. Open Connectivity Foundation (OCF)
The Open Connectivity Foundation (OCF) [ocf] defines the process
before a device is operational as onboarding. The first step of this
onboarding process is configuring the ownership, i.e., establishing a
legitimate user that owns the device. For this, the user is supposed
to use an Onboarding tool (OBT) and an Owner Transfer Method (OTM).
The OBT is described as a logical entity that may be implemented on a
single or multiple entities such as a home gateway, a device
management tool, etc. OCF lists several optional OTMs. At the end
of the execution of an OTM, the onboarding tool must have provisioned
an Owner Credential onto the device. The following owner transfer
methods are specified:
* Just works: Performs an un-authenticated Diffie-Hellman key
exchange over Datagram Transport Layer Security (DTLS). The key
exchange results in a symmetric session key which is later used
for provisioning. Naturally, this mode is vulnerable to on-path
attackers.
* Random PIN: The device generates a PIN code that is entered into
the onboarding tool by the user. This pin code is used together
with TLS-PSK ciphersuites for establishing a symmetric session
key. OCF recommends PIN codes to have an entropy of 40 bits.
* Manufacturer certificate: An onboarding tool authenticates the
device by verifying a manufacturer installed certificate.
Similarly, the device may authenticate the onboarding tool by
verifying its signature.
* Vendor specific: Vendors implement their own transfer method that
accommodates any specific device constraints.
Once the onboarding tool and the new device have authenticated and
established secure communication, the onboarding tool provisions/
configures the device with Owner credentials. Owner credentials may
consist of certificates, shared keys, or Kerberos tickets for
example.
The OBT additionally configures/provisions information about the
Access Management Service (AMS), the Credential Management Service
(CMS), and the credentials for interacting with them. The AMS is
responsible for provisioning access control entries, while the CMS
provisions security credentials necessary for device operation.
OCF has the following characteristics:
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* Terms: Configuration, discovery, enrollment, onboarding,
provisioning, registration,
* Players: Client, Device, Manager, Manufacturer, Owner, Peer,
Server, User
* Initial beliefs assumed in the device: The device needs to be
associated with an owner in the onboarding process and then go
through the provisioning process before being considered as
trustworty.
* Processes: Onboarding, provisioning.
* Beliefs imparted to the device after protocol execution: In the
provisioning phase the device receives the necessary credentials
to interact with provisioning services and any other services or
devices that are part of the normal operation of the device.
2.7. Fast IDentity Online (FIDO) alliance
The Fast IDentity Online Alliance (FIDO) is currently specifying an
automatic onboarding protocol for IoT devices [fidospec]. The goal
of this protocol is to provide a new IoT device with information for
interacting securely with an online IoT platform. This protocol
allows owners to choose the IoT platform for their devices at a late
stage in the device lifecycle. The draft specification refers to
this feature as "late binding".
The FIDO IoT protocol itself is composed of one Device Initialization
(DI) protocol and 3 Transfer of Ownership (TO) protocols TO0, TO1,
TO2. Protocol messages are encoded in Concise Binary Object
Representation (CBOR) [RFC8949] and can be transported over
application layer protocols such as Constrained Application Protocol
(CoAP) [RFC7252] or directly over TCP, Bluetooth etc. FIDO IoT
however assumes that the device already has IP connectivity to a
rendezvous server. Establishing this initial IP connectivity is
explicitly stated as "out-of-scope" but the draft specification hints
at the usage of Hypertext Transfer Protocol (HTTP) [RFC7230] proxies
for IP networks and other forms of tunnelling for non-IP networks.
The specification only provides a non-normative example of the DI
protocol which must be executed in the factory during device
manufacture. This protocol embeds initial ownership and
manufacturing credentials into Restricted Operation Environment (ROE)
on the device. The initial information embedded also includes a
unique device identifier (called as GUID in the specification).
After DI is executed, the manufacturer has an ownership voucher which
is passed along the supply chain to the device owner.
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When a device is unboxed and powered on by the new owner, the device
discovers a network-local or an Internet-based rendezvous server.
Protocols (TO0, TO1, and TO2) between the device, the rendezvous
server, and the new owner (as the owner onboarding service) ensure
that the device and the new owner are able to authenticate each
other. Thereafter, the new owner establishes cryptographic control
of the device and provides it with credentials of the IoT platform
which the device should used.
FIDO has the following characteristics:
* Terms: Provisioning, onboarding, commissioning, initialisation.
* Players: Device, Manager, Manufacturer, Owner, Rendezvous Server,
User
* Initial beliefs assumed in the device: In the initial state the
device is not yet associated with a specific owner. The DI
process has to take place to embed owndership and manufacturing
credentials in the device, the first in a chaim to create an
ownership voucher that will be used to perform the transfer of
ownership of the device.
* Processes: Device Initialize Protocol (DI), Transfer Ownership
Protocol 0 (TO0), Transfer Ownership Protocol 1 (TO1), Transfer
Ownership Protocol 2 (TO2)
* Beliefs imparted to the device after protocol execution: When the
device is powered on, and all TO protocols run, the device figures
out by contacting with the rendezvous server, who the owner is,
authenticate with the owner. At this point the rendezvous server,
and owner are able to authenticate the device.
2.8. Bootstrapping Remote Secure Key Infrastructures (BRSKI)
The ANIMA working group is working on a bootstrapping solution for
devices that relies on 802.1AR [ieee8021ar] vendor certificates
called Bootstrapping Remote Secure Key Infrastructures (BRSKI)
[RFC8995]. 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 document 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
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to the end user.
BRSKI has the following characteristics:
* Terms: Bootstrapping, provisioning, enrollment, onboarding.
* Players: Administrator, Client, Cloud Registrar, Configurator,
Device, Domain Registrar, Initiator, Join Proxy, JRC,
Manufacturer, Owner, Peer, Pledge, Server, User
* Initial beliefs assumed in the device: Every device has an IDevID,
installed and signed by the manufacturer, which is used as a basis
for establishing further trust relations. In the initial stage,
when the device is deployed in a specific location it cannot
securely communicate with the registrar or JRC, to be integrated
into the network, so the device and the registrar need to
establish mutual trust.
* Processes: Discover, self-Identify, joint registrar, imprint
registrar, enroll.
* Beliefs imparted to the device after protocol execution: After the
process has finished and the device is imprinted, and trusts the
registrar/JRC, through a voucher issued by the manufacturer and
verified by the device.
2.9. Secure Zero Touch Provisioning (SZTP)
[RFC8572] 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). SZTP requires the devices to be configured with trust
anchors in the form of X.509 certificates. [RFC8572] is similar to
BRSKI based on [RFC8366].
SZTP has the following characteristics:
* Terms: Bootstrapping, provisioning, onboarding, enrollment,
configuration, discovery.
* Players: Administrator, Bootstrap Server, Client, Device,
Manufacturer, Onboarding Server, Owner, Redirect Server, Bootstrap
Server, User, Owner
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* Initial beliefs assumed in the device: Initially, the device needs
have pre-configured a state that allows allows the bootstrap
processs. Among other information, the trust anchor for ownership
voucher, client & intermediaries certificates, and list of trusted
bootstrap servers and their trust anchors.
* Processes: Initial state, Boot sequence, Processing bootstrapping
data, validating signed data, processing redirect information,
processing onboarding information.
* Beliefs imparted to the device after protocol execution: The
bootstrapping process provides the device with all the necessary
information (onboarding information) to create a trust relation
between the device and the bootstrap server. This allows the
device to download its boot image and the necessary initial
configuration. The enrollment information will allow a device to
be bootstrapped and operate establishing secure connections with
other systems.
2.10. LPWAN
Low Power Wide Area Network (LPWAN) encompasses a wide variety of
technologies whose link-layer characteristics are severely
constrained in comparison to other typical IoT link-layer
technologies such as Bluetooth or IEEE 802.15.4. While some LPWAN
technologies rely on proprietary bootstrapping solutions which are
not publicly accessible, others simply ignore the challenge of
bootstrapping and key distribution. In this section, we discuss the
bootstrapping methods used by LPWAN technologies covered in
[RFC8376].
* LoRaWAN [LoRaWAN] describes its own protocol to authenticate nodes
before allowing them join a LoRaWAN network. This process is
called as joining and it is based on pre-shared keys (called
AppKeys in the standard). The joining procedure comprises only
one exchange (join-request and join-accept) between the joining
node and the network server. There are several adaptations to
this joining procedure that allow network servers to delegate
authentication and authorization to a backend AAA infrastructure
[RFC2904].
* Wi-SUN Alliance Field Area Network (FAN) uses IEEE 802.1X
[ieee8021x] and EAP-TLS for network access authentication. It
performs a 4-way handshake to establish a session keys after EAP-
TLS authentication.
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* NB-IoT relies on the traditional 3GPP mutual authentication scheme
based on a shared-secret in the Subscriber Identity Module (SIM)
of the device and the mobile operator.
* Sigfox security is based on unique device identifiers and
cryptographic keys. As stated in [RFC8376], although the
algorithms and keying details are not publicly available, there is
sufficient information to indicate that bootstrapping in Sigfox is
based on pre-established credentials between the device and the
Sigfox network.
From the above, it is clear that all LPWAN technologies rely on pre-
provisioned credentials for authentication between a new device and
the network.
LPWAN has the following characteristics:
* Terms: Provisioning, configuration, discovery.
* Players: Administrator, Authenticator, Border Router, Client,
Device, Manager, Network Server, User
* Initial beliefs assumed in the device: The device normally has
credentials that are used to directly secure the communications or
to device key material to do so. There is a basic trust in the
network server.
* Processes: Provisioning
* Beliefs imparted to the device after protocol execution: Either
because of an authentication process that results in newly derived
key material or the pre-provisioned key material is used, the
device is able to exchange information securely through the
network server.
2.11. Thread
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
(External).
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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 (such as network name, security policy, etc.,) 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 operate 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.
Thread has the following characteristics:
* Terms: Commissioning, discovery, provisioning.
* Players: Administrator, Border Agent, Border Router, Commissioner,
Commissioner Candidate, Configurator, Device, End Device, End
Device, Endpoint Identifier, Initiator, Joiner, Joiner Router,
Owner, Peer, Responder, Server, User
* Initial beliefs assumed in the device: The joiner needs to share
credentials with an entity that belongs to the Thread network,
prior to the authentication process.
* Processes: Petitioning, Joining
* Beliefs imparted to the device after protocol execution: Once the
authentication takes place, a trust relation is established
between the Joiner and the Commissioner it receives the network
parameters needed to be attached to the Thread network.
3. Comparison
There are several stages before a device becomes fully operational.
There is typically a stage where some sort of credential is
installed. The nature or purpose of this credential can be varied,
form being part of the IoT device authentication, to a credential
from a 3rd trusted party, be it the manufacturer or the owner.
Solution differ on this initial process, and in some cases this can
even be done in an out-of-band fashion.
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After some initial credential is installed, there is a process that
typically involves authentication establishing initial trust, after
which credentials and/or parameters are configured or installed into
the device.
Finally, when the entities involved in the process are authenticated
and the configuration and key material established, the normal
operation of the IoT device can take place.
3.1. Comparison of terminology
The specifics of every term varies depending on the technology, but
we enumerate here the basic terminology and what it means for the
different solutions.
* Bootstrapping:
- DPP: Client obtains the Controller’s public bootstrapping key
and IP address
- OMA: An IoT device retrieves and processes all the bootstrap
data
- EST: installation of the Explicit TA database
- BRSKI: A protocol to obtain a local trust anchor.
- SZTP: The process by which obtains "bootstrapping data" such as
conveyed information, owner certificate and owner voucher.
- EAP-NOOB: For an IoT device to be registered, authenticated,
authorized and for it to derive key material to act as a
trustworty entity in the security domain where it is deployed.
* configuration:
- DPP: The process performed by a Configurator by which the
Enrollee is provisioned.
- OMA: Adding or removing an LwM2M Server Account to or from the
LwM2M Client configuration.
- OCF: The necessary information the Device must hold to be
considered as ready for normal operation.
- EST: The basic information (e.g., TA database) needed to
initiate protocol operation.
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- SZTP: The system configuration to be installed into the device
by the bootstrapping process.
- EAP-NOOB: Establishing necessary information for the device to
operate.
- LPWAN: In LoRaWAN, the information related to the working of
the device and protocol.
* discovery:
- DPP: Exchange that allows obtaining specific information such
as SSID, operating channel and band.
- OCF: Making the different resources available through URIs.
- BRSKI: Locating an entity that needs to take part of the
bootstrapping process (e.g., Join proxy)
* enrollment:
- EST: The process of obtaining the credentials needed to perform
the device normal operation.
- BRSKI: Same process describe as EST.
- SZTP: The process of an owner joining a manufacturer's SZTP
program.
* provisioning:
- DPP: Securely enabling a device to establish secure
associations with other devices in a network.
- OMA: Establishing security credentials and access control lists
by a dedicated LwM2M bootstrap server.
- OCF: A set of processes that take place both during and after
the ownership transfer. These entail configuration of
credentials, and security-related resources for any services or
devices that the provisioned device needs to interact with in
the future.
- Bluetooth: The procedure by which a device is authenticated,
and a secure link is established, becoming a trustworthy node
in the network.
- FIDO: Same as FIDO onboarding.
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- SZTP: The set of steps that take place to enable a device to
establish secure connections with other systems.
- LPWAN: In LoRaWAN, the establishment of configuration data and
credentials.
* intialization:
- OMA: When Bootstrap-Delete operation is used, to restore a
device.
- FIDO: Protocol (DI), establishing basic information at
manufacture.
* registration:
- OMA: Establishing a registration session, which is an
association between the client and the server.
- EAP-NOOB: Add information about an IoT device in a server
database.
* onboarding:
- OCF: The device is considered to complete the onboarding after
the ownership of the Device has been transferred and the Device
provisioned.
- FIDO: The procedure of installing configuration information and
secret to a device so that it may safely connect to and
communicate with an IoT platform.
- SZTP: information related to the boot image a device must be
running, an initial configuration the device must commit, and
scripts that the device must successfully execute.
* commissioning:
- Thread: The process of a Thread device joining a Thread
network.
* imprint:
- BRSKI: The process by which a device obtains the needed
information to act as trustworthy entity within the network or
domain
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3.2. Comparison of players
In this section we classify the different players.
Human User: user
Device that intends to securely join a network: pledge, device,
client, peer, persona, enrollee, candidate
Entity that makes the device: Manufacturer
Entity that owns the device: owner, manager
Entity with which the device establishes a connection: IoT platform,
Rendezvous Server, Server,
Entity that aids in the process: Join Proxy, Bootstrap Server,
Onboarding Server, Border Router
Person that manages a deployment or system: Administrator
Entity that steers the process for the IoT device to securely join
the network: Configurator, Bootstrap Server, Rendezvous Server, JRC,
Onboarding/Redirect Server, Commissioner.
External or third-party entity that intervenes in the process:
Registrar, MASA
3.3. Comparison of initial beliefs
The IoT devices may have different initial beliefs depending on the
credentials pre-installed, during the manufacturing process or prior
to being turned on. There are cases where the initial credentials
that need to be shared to establish basic trust, or they are
exchanged during one of the procedures after the device is turned on,
not installed during manufacturing.
3.3.1. No initial trust established
EAP-NOOB does not require initial configuration of credentials to
establish trust, since its done using the out-of-band process.
The OCF device starts as unowned. It has to perform an ownership
transfer, to establish basic trust to perform onboarding and
provisioning. Depending on the Owener Transfer Mode (OTM) it can be
considered to have not initial trust based on the credentials
installed.
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Bluetooth devices start as unprovisioned. Initial trust is
established as a consequence of exchanging public keys and performing
the authentication. If the public keys are ephemeral, there is no
initial credential establishment.
3.3.2. Initial trust based on the credentials installed
These credentials may very from the time of installing, and the
entity to which it related. In this sense, they could be from the
manufacturer, owner or other entity.
FIDO devices have installed during the manufacturing process a set of
ownership credentials (i.e., ownership voucher) and additional
information to determine the current owner of the device. Hence,
there is an initial trust from the IoT device and the owner. With
this basic setup, and and the cooperation among device, owner and
rendezvous server, the onboarding process can take place.
EST devices are configured with the needed information to perform
mutual authentication and for authorization between the EST client
and server.
BRSKI have manufacturer-installed certificates as starting point to
establish trust.
SZTP have pre-configured initial state which provides the basis for
trust.
LPWAN specifics depends on the technology, but they all have in
common some pre-installed credentials that allows the establishment
of trust and to secure the communications.
Thread devices, share credentials as well to establish trust.
OMA devices can have all the necessary information to start working
on the network where they are deployed, if they have the factory
bootstrap, hence all needed credentials to establish trust. There
need to be installed some basic credentials to establish trust with
the bootstrap server and perform the bootstrapping.
DPP initial trust is established during the bootstrapping where the
public key is transmitted.
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3.4. Comparison of processes
Analyzing the different terms used over the different solutions
reviewed in this document, we can identify several processes. These
are named differently in some cases, and not every technologies
considers them all as part of their the following common concepts:
* To refer to the process previous to the device being turned on, in
which some information, or credentials are installed into the
device. This process is commonly referred to as manufacture. Is
in this phase where the IoT devices have installed the needed
information (specifics depend on the technology) to provide the
basis for trust and to authenticate other entities.
* To refer to the process after the device is turned on and intends
to locate the entity with which it has to communicate to start the
authentication process to be integrated into the security domain.
Here is where the device start the process to get to perform its
normal operation.
* To the process by which the device obtains additional credentials,
in addition to what it already had installed before being turned
on.
* To the process by which the device is authenticated and
established a trust relation.
3.5. Comparison of knowledge imparted to the device
Even though the devices might start from a different place, in terms
of initial credentials as basis for trust, when they finish their
processes, they become trusted parties within the domain they are
deployed or at least have a trust relation with a specific entity.
The difference may strive in the number of trust relations are
stablished during the process, as they may have not only established
a trust relation with local entities where they perform their
operation, but other external entities as well.
In FIDO, once the onboarding process has taken place, the IoT device
is mutually authenticated with the current owner, and the needed
secrets and configuration data is installed into the device, which as
a result is able to connect and interact securely with the target IoT
platform.
In EAP-NOOB, once the bootstrapping is completed, the IoT device not
only has a trust relation with the EAP server, but the EAP
authenticator can be established as well, based on the shared
credentials that are derived during the authentication process.
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In Bluetooth the trust is expanded to the local network as there is
key material shared among the different entities of the network.
In Thread once the joiner has successfully completed the process, it
can communicate directly with all Thread devices in the network.
LPWAN has a more limited scope and they usually have specific keys
for applications and network communications.
EST provides the devices with the enrollment information such as
certificates and symmetric keys that can be used to establish trust
with different peers.
BRSKI after running it is able to verify that the communicating
entities are who they claim to be, and obtain domain specific
certificates to act as trustworhty entities within the domain.
SZTP after running, the device has obtained onboarding information
and is equipped to establish secure connections with other systems.
4. Security Considerations
This draft does not take any posture on the security properties of
the different bootstrapping protocols discussed. Specific security
considerations of bootstrapping protocols are present in the
respective specifications.
Nonetheless, we briefly discuss some important security aspects which
are not fully explored in various specifications.
Firstly, an IoT system may deal with authorization for resources and
services separately from initial security setup in terms of timing as
well as protocols. As an example, two resource-constrained devices A
and B may perform mutual authentication using credentials provided by
an offline third-party X before device A obtains authorization for
running a particular application on device B from an online third-
party Y. In some cases, authentication and authorization maybe
tightly coupled, e.g., successful authentication also means
successful authorization.
Secondly, initial security setup of IoT devices may be necessary
several times during the device lifecycle since keys have limited
lifetimes and devices may be lost or resold. Protocols and systems
must have adequate provisions for revocation and fresh security
setup. A rerun of the security setup mechanism must be as secure as
the initial security setup regardless of whether it is done manually
or automatically over the network.
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Lastly, some IoT networks use a common group key for multicast and
broadcast traffic. As the number of devices in a network increase
over time, a common group key may not be scalable and the same
network may need to be split into separate groups with different
keys. Bootstrapping and provisioning protocols may need appropriate
mechanisms for identifying and distributing keys to the current
member devices of each group.
5. IANA Considerations
There are no IANA considerations for this document.
6. Acknowledgements
We would like to thank Tuomas Aura, Hannes Tschofenig, and Michael
Richardson for providing extensive feedback as well as Rafa Marin-
Lopez for his support.
7. Informative References
[dpp] Wi-Fi Alliance, "Wi-Fi Easy Connect Specification", Wi-Fi
Alliance Version 3.0, 2018,
<https://www.wi-fi.org/wi-fi-download/35330>.
[fidospec] Fast Identity Online Alliance, "FIDO Device Onboard
Specification", Fido Alliance Version: 1.1, April 2022,
<https://fidoalliance.org/specifications/download-iot-
specifications/>.
[ieee8021ar]
IEEE, "IEEE Standard for Local and metropolitan area
networks–Secure Device Identity", 2018,
<https://1.ieee802.org/security/802-1ar/>.
[ieee8021x]
IEEE, "IEEE Standard for Local and metropolitan area
networks–Port-Based Network Access Control", 2020,
<https://1.ieee802.org/security/802-1x/>.
[LoRaWAN] LoRa Alliance, "LoRa Specification", LoRa
Alliance Version: 1.1, October 2017, <https://lora-
alliance.org/resource_hub/lorawan-specification-v1-1/>.
[ocf] Open Connectivity Foundation, "OCF Security
Specification", Version 2.2.6, October 2022,
<https://openconnectivity.org/specs/
OCF_Security_Specification.pdf>.
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[oma] Open Mobile Alliance, "Lightweight Machine to Machine
Technical Specification: Core", Approved Version 1.2.1,
December 2022,
<https://openmobilealliance.org/release/LightweightM2M/
V1_2_1-20221209-A/OMA-TS-LightweightM2M_Core-
V1_2_1-20221209-A.pdf>.
[oma-transport]
Open Mobile Alliance, "Lightweight Machine to Machine
Technical Specification: Transport Bindings", Approved
Version 1.2.1, December 2022,
<https://www.openmobilealliance.org/release/
LightweightM2M/V1_2_1-20221209-A/OMA-TS-
LightweightM2M_Transport-V1_2_1-20221209-A.pdf>.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904,
DOI 10.17487/RFC2904, August 2000,
<https://www.rfc-editor.org/rfc/rfc2904>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/rfc/rfc4291>.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<https://www.rfc-editor.org/rfc/rfc5272>.
[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,
<https://www.rfc-editor.org/rfc/rfc6241>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/rfc/rfc7030>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/rfc/rfc7228>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/rfc/rfc7230>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/rfc/rfc8040>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/rfc/rfc8366>.
[RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
<https://www.rfc-editor.org/rfc/rfc8376>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/rfc/rfc8572>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/rfc/rfc8995>.
[RFC9140] Aura, T., Sethi, M., and A. Peltonen, "Nimble Out-of-Band
Authentication for EAP (EAP-NOOB)", RFC 9140,
DOI 10.17487/RFC9140, December 2021,
<https://www.rfc-editor.org/rfc/rfc9140>.
[RFC9148] van der Stok, P., Kampanakis, P., Richardson, M., and S.
Raza, "EST-coaps: Enrollment over Secure Transport with
the Secure Constrained Application Protocol", RFC 9148,
DOI 10.17487/RFC9148, April 2022,
<https://www.rfc-editor.org/rfc/rfc9148>.
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[Sethi14] Sethi, M., Oat, E., Di Francesco, M., and T. Aura, "Secure
Bootstrapping of Cloud-Managed Ubiquitous Displays",
Proceedings of ACM International Joint Conference on
Pervasive and Ubiquitous Computing (UbiComp 2014), pp.
739-750, Seattle, USA, September 2014,
<http://dx.doi.org/10.1145/2632048.2632049>.
[simpleconn]
Wi-Fi Alliance, "Wi-Fi Simple Configuration",
Version 2.0.7, 2019, <https://www.wi-
fi.org/download.php?file=/sites/default/files/private/Wi-F
i_Simple_Configuration_Technical_Specification_v2.0.7.pdf>
.
[threadcommissioning]
Thread Group, "Thread Commissioning", 2015.
Authors' Addresses
Mohit Sethi
Aalto University
FI-02150 Espoo
Finland
Email: mohit@iki.fi
Behcet Sarikaya
Email: sarikaya@ieee.org
Dan Garcia-Carrillo
University of Oviedo
33207 Oviedo
Spain
Email: garciadan@uniovi.es
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