]> Lulea University of Technology

Lulea 97187 Sweden srevat@ltu.se

Lulea University of Technology

Lulea 97187 Sweden olov.schelen@ltu.se

Lulea University of Technology

Lulea 97187 Sweden ulf.bodin@ltu.se

General IOTOPS authorization onboarding web security Industrial network layer onboarding demands a technique that is efficient, scalable, and secure. In this document, we propose a delegation-based device onboarding technique using Power of Attorney (PoA) based authorization. This enables manufacturers to send the device to the right device owner manage the ownership transfer through the supply chain and eventually resell the device to a new owner.

Introduction Onboarding devices in industrial setting must be efficient, scalable, and secure. NIST guidelines on network layer onboarding explain essential features required by an ideal onboarding model. Many zero-touch onboarding models require the manufacturer to build and configure devices with specific onboarding features based on the destination network. It is complex to gather the onboarding requirements from multiple parties involved based on a centralized infrastructure, which makes it expensive and inefficient. There are different onboarding features that are established as part of the existing onboarding standards and there are different missing features that can improve the current onboarding technique. In this draft, we discuss different important onboarding features that can be obtained using delegation-based device onboarding. This can secure the device with unique onboarding credentials during deployment rather than at the time of manufacture (late binding). This approach is based on subgranting or delegation-based authorization, in which power or delegation can be granted to another entity for a limited time. This can be used between different parties in the supply chain and with integrators for ultimate onboarding in at the customer site. It can also be used in typical industrial subcontractor use cases where devices owned by subcontractors must/should temporarily (ie., for a limited time) be onboarded to an industrial site while the formal ownership is retained by the subcontractor. In the proposed model, we establish a trust chain between the manufacturer, device, device owner, and the onboarding controller for the automatic onboarding of devices using the power of attorney based authorization technique. This draft defines the protocol flow of the proposed onboarding technique defining the different entities part of the onboarding, mutual authorization between them, late binding, onboarding of devices without connectivity, transfer of ownership, and the sub-problem of reselling the device. With the use of CBOR and CoAP instead of JSON-based token formats, the proposed technique is suitable for use in constrained environments. Note that in this document we focus on the onboarding case using PoA while indeed PoA is completely generic and can be used in various other subgranting, and data sharing use cases, not covered in this document.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Onboarding basics

State of the art Device onboarding can be defined as an automated process of securely provisioning the device at the destination network from the manufacturer’s site via the supply chain. One aspect of onboarding is providing the device with network access . There are different definitions for onboarding; Intel zero-touch onboarding refers it as an ”Automated service that enables a device to be drop-shipped and powered on to dynamically provision to a customer’s IoT platform of choice in seconds”. According to Amazon Web Services (AWS), ”IoT device onboarding or provisioning refers to the process of configuring devices with unique identities, registering these identities with their IoT endpoint, and associating required permissions”. NIST guidelines are also referred by IETF , ”Onboarding is sometimes used as a synonym for bootstrapping and at other times is defined as a subprocess of bootstrapping”. According to the guidelines provided by NIST, onboarding can be performed in two different layers:

• Network layer onboarding
• Application layer onboarding.

The network layer onboarding may ensure device integrity and authorized ownership throughout the initial phases of onboarding. The information gathered during network layer onboarding is passed to application layer onboarding to make the device operational in the application layer.

Problem description The main issues in a device lifecycle are device ownership transfer, management of the device after bootstrapping such as installing the required software, its maintenance, and disposition of the device when transitioning to a new owner. Because of the large number of external devices and the security issues caused by their communication, device onboarding is considered as an important process. Multiple entities, transportation methods, sensitive data sharing, and other factors make the onboarding process difficult, necessitating automation and security. Hence, there is a need for an efficient onboarding procedure that secures devices with unique onboarding credentials during deployment rather than at the time of manufacture.

Delegation based Onboarding This document considers the network layer onboarding and subgranting the power to onboard from one entity to another in the bootstrapping stage. The different roles are:

• Manufacturer: The entity who built the device and is considered the very first owner of the device.
• Device: The device to be onboarded.
• Device Owner: The owner of the device, who is the last entry in the ownership voucher.
• Onboarding Controller: Part of the target network that provides network onboarding credentials to the device.

Figure 1 shows the Protocol flow diagram of the proposed model.

Protocol flow of Delegation based onboarding | I1 | .... | In | +------+ +------+ +------+ ^ | | |voucher | voucher | | v +---------+ +---------+ | | | | | Manufa-| | | | cturer | | Device | | (DO0) | | Owner | | | | | +---------+ +---------+ | ^ |1.Device onboarding | |credentials + hash | v 2.Mutual handshake with voucher| +---------+ + device identification | +----------+ | |<------------------------------ | | | | 3. PoA + Device onboarding cred. | | | Device |----------------------------------->|Onboarding| | | 4.Network onboarding cred. |Controller| | |<-----------------------------------| | +---------+ +----------+ ]]>

• 1) Manufacturer includes the device onboarding credentials to the device. This includes device ID, target network identifier (onboarding controller identifier), and device owner identifier, which can be in different forms such as certificates, pre-shared keys, and passwords.
• Parallel to step 1, the manufacturer sends the PoA-delegation voucher signed by the manufacturer to the first entity in the supply chain (this can be an integrator, retailer, etc). This PoA is transferred through the supply chain until it reaches the Device Owner entity. See section 5 for more details.
• 2) The device and the device owner are mutually authenticated and authorized by sharing the PoA-delegation voucher and device identification with each other. The device owner sends in the PoA-delegation voucher with the device identification details (device onboarding credentials hash) in it. The device matches the device onboarding credentials hash in the PoA-delegation voucher with the one it possesses. In addition, device verifies the signature on the PoA-delegation voucher using the device owner public key in its PoA-delegation voucher, to identify the right owner. Similarly, the device sends in the device identification details to the device owner, which is verified by the device owner.
• 3) The device sends the PoA-delegation voucher and the device onboarding credentials to the onboarding controller to obtain the credentials to onboard the device.
• 4) The onboarding controller provides the network onboarding credentials to the device on successful verification of the PoA-delegation voucher and other credentials. The network onboarding credentials include information required to bootstrap with the target network. Here, we assume that the network onboarding controller and the device owner have a pre-established trust relation.

The revocation of the PoA-delegation voucher can be accomplished by setting a low expiration time depending on the use case. In that case, the PoA-delegation voucher must be reissued periodically. Once the device obtains the network bootstrapping credentials, it can start communicating with the local cloud. This model for onboarding enables the subcontractor to onboard devices by subgranting his/her power to the device to act on behalf of the subcontractor. A proof of concept of the proposed model can be found at "https://github.com/sreelakshmivs/PoAimplementationinJava" under the MIT license.

PoA-Delegation Voucher Structure They are self-contained tokens that are structured in the compressed binary format CBOR. The entire voucher is first signed by the manufacturer using his/her private key. The various parameters included in a PoA-Delegation Voucher are the following:

Manufacturer Public Key

REQUIRED. The public key uniquely identifies the manufacturer who generates the PoA-delegation voucher. We assume that the public key is generated using a secure public-key algorithm by the principal. With this parameter, the authorization server can identify the person who generated the PoA-delegation voucher.

Manufacturer Name

OPTIONAL. The human-readable name of the manufacturer, which is additional information about the manufacturer.

Agent Public Key

REQUIRED. The public key, which uniquely identifies the agent or intermediate entity (Io, I1,.., In). This field is changed throughout the supply chain while transferring the voucher to the next agent in the supply chain.

Device Owner ID

REQUIRED. The unique identifier or the public key of the device owner.

Device Onboarding Credentials Hash

REQUIRED. The copy of the hash that is sent to the device by the manufacturer.

Signing Algorithm

OPTIONAL. The name of the signature algorithm used by the principal to digitally sign the PoA-delegation voucher.

Transferable

REQUIRED. It is a positive integer defining how many steps the PoA-delegation voucher can be transferred. The default is 0, which means that it is not transferable. A PoA-delegation voucher can be transferred by including it in another PoA-delegation voucher, i.e., it is signed in several delegation steps (where the number is decreased by one in each step).

iat (Issued at)

REQUIRED. The time at which the PoA-delegation voucher is issued by the principal to the agent.

eat (Expires at)

REQUIRED. The time at which the PoA-delegation voucher expires. This parameter is predefined by the manufacturer in the PoA-delegation voucher and it will be invalid after eat.

Metadata

OPTIONAL. The metadata is associated with the bootstrapping process if any. This parameter includes different sub- parameters that add specific information to the voucher.

Ownership Transfer using PoA based Delegation There are multiple ways of ownership transfer, and each of them has their strengths and limitations. In this draft, we define the transfer of owenrship based on delegation using the PoA based authorization technique. Here, the manufacturer is the first owner or DO0 of the device. The manufacturer signs the PoA-delegation voucher and sends it to the first entity in the supply chain. The existing ownership voucher techniques consider the intermediate parties between the manufacturer and the final device owner, that are part of the supply chain as device owners. In this technique, these intermediate entities are delegated to work on the device for a limited time or the PoA-delegation voucher allows them to work on behalf of the DO0 (manufacturer). The first voucher is signed by the manufacturer and the agent public key parameter is set to the public key or identification of the first entity (I0) in the supply chain. When I0 finish its task on the device, this field is changed to the public key of the next entity in the supply chain and the whole voucher is signed using the private key of I0. This process continues through the supply chain until it reaches the device owner, which is identified using the Device Owner Public Key parameter in the voucher. At this point, the PoA-delegation voucher would be signed with the private key of the last entity (In) in the supply chain. With each transfer of the ownership voucher (PoA-delegation voucher), the transferable parameter value is decremented. So, when it reaches the final device owner, the value of transferable in the voucher is 0. When the current owner resells the device in the future, they can set the transferable parameter value to an integer equal to the number of intermediate entities. With this approach, the intermediate entities such as integrators and retailers are not considered as device owners with full ownership of the device. Instead, they are delegated by the manufacturer, which allows them to work on the device for the time being. Here, the intermediate entities can be the trusted parties of the manufacturer or they can be also considered trustworthy from the other direction; which means they can be trusted parties of the device owner side. Either direction of the trust chain could be possible. With this approach, the reselling of the device can be done by transferring the PoA from the DO to the new owner without bothering the manufacturer. The current device owner issues a new PoA-delegation voucher to the new device owner by changing the device owner's public key parameter to the public key of the new owner. The device is fully reset without deleting the device onboarding credentials and adds the copy of the PoA-delegation voucher issued to the new owner, by the current owner of the device who sells the device.

Power of Attorney based authorization PoA-based authorization is a generic authorization technique used to authorize devices to access protected resources on behalf of the user, who owns the device (principal), even if the user is not online. The PoA model in its base form is completely decentralized (like for example Pretty Good Privacy (PGP)), where the user subgrants their power in the form of a self- contained PoA that contains public information such as public keys and a specific set of permissions for a predefined time. It is a decentralized authorization technique, where the different entities involved can access and verify the PoA using a downloadable image or library similar to PGP. Some centralization can be added by optional signatory registers and/or traditional Certificate Authorities (CA). The entities involved in PoA based authorization system are:

• Principal: The entity that generates and sends the PoA to the agent.
• Agent: The device that receives the PoA to sign on behalf of the principal with limited features for a pre-defined time.
• Resource server: The third party with a server that stores the information and credentials entitled to the principal. It serves agents according to subgrants defined in PoAs.
• Signatory registry: A database system where PoAs and system-related metadata are stored. It can serve as a trusted third party in certifying and verifying PoA. This component is optional.

The principal generates the PoA in advance to entitle an agent to autonomously execute tasks in the absence of the principal. The PoA is digitally signed by the principal and the agent uses the limited features of the principal’s account to execute tasks allowed by the PoA.

Related Works Fast IDentity Online Alliance (FIDO) defines an automatic onboarding protocol for IoT devices. With the late binding feature of this protocol, the IoT platform for the IoT device doesn't need to be selected in the early stage of its life cycle and reduces the cost and complexity in the supply chain. FIDO uses a rendezvous server for device registration and to find the device owner's location, by assuming that the device has an IP connectivity to the rendezvous server. An important feature of FIDO is the tracking of the transfer of ownership and the device's late-bound owner throughout the supply chain using the ownership voucher. FIDO Device Onboard-enabled Device is configured with required software and hardware along with a Restricted Operating Environment (ROE) and a Management Agent, that manages the device ownership voucher using the onboarding protocols. Another important parameter is the device credentials, it does not permanently identify the user and is only used for the purpose of the ownership transfer. FIDO expects that both the manufacturer and the owner will change their keys frequently. The main protocols in FIDO onboarding are the Device initialization protocol (DI), Transfer Ownership Protocol (TO0), TO1, and TO2. The function of DI is to insert FIDO Device Onboard credentials into the device during the manufacturing process. TO0 is used by the owner to identify itself to the rendezvous server, and similarly, TO1 is used by the device to identify itself and to interact with the rendezvous server using the device ROE. TO2 is used by the device ROE to contact and interact with the owner or device onboarding service. After TO2 successfully completed, the device onboarding credentials except the attestation key are replaced by the owner onboarding service. approach is similar to the PoA transferable parameter approach. A problem with the extended artifact approach is that the pledge should store all the previous delegation vouchers and they should attach them during the voucher request step. If modified using the PoA transferable approach, this could be a solution to the reselling problem of bootstrapping. provides a survey on different standards and protocols for onboarding. Onboarding is referred to by different names as part of the initial security setup of devices. This list of names includes bootstrapping, provisioning, enrollment, commissioning, initialization, and configuration. Most approaches rely on an external anchor such as a rendezvous server, bootstrap server, chip, or QR code. The communication protocol uses a home agent and a foreign agent to facilitate mobility. The home agent provides an anchor point for connectivity, while a mobile node can register with a foreign agent to get seamless connectivity at the visited network. This allows the user to move between different networks while having both the home and visitor IP addresses. However, this is primarily to obtain internet access, not to onboard a local realm. recognizes the need for an effective onboarding system in both network and application layers. This approach doesn't require much dependency on the manufacturer and the manufacturer's certificates. They define the flexibility of devices that are not resource-constrained such as Raspberry Pi and larger. The use of large smart devices enables executing functions that are not envisioned during their manufacturing. PoA based authorization can be added as a new grant type for OAuth protocol, which introduces a new role "principal" who controls the client, and enables the client to access resources through the OAuth authorization server on behalf of the principal, even if the principal is not available online . PoA-based authorization is an industrial authorization technique for CPS devices that is designed with different cryptographic algorithms and is similar work as the proxy signature with warrant . The proxy signature is a significant security cryptographic algorithm that strengthens its security by patching newer security loopholes. The main differences are seen in the applicability of the technique and the design methodology. In proxy signature, the agent or proxy signer is required to perform several cryptographic calculations to sign a message, as described in the warrant on behalf of the principal. PoA can be seen as a more industry-oriented technique, where the device acts/works on behalf of the principal as described in the PoA. Here, the agent is only required to verify and forward the PoA (received from the principal) to the resource owner and provide its strong identity, to obtain the resources on behalf of the principal. The different techniques mentioned above use a delegation-based authorization model for security, which relies on centralized servers or complex cryptographic algorithms, limiting their flexibility in the onboarding process. The PoA-based authorization technique, which does not rely on a centralized server and employs an industry-friendly PoA structure, enables a reliable and flexible onboarding process.

Security Considerations The security of the entire onboarding process relies on issues with security in different phases such as manufacturing, supply chain, bootstrapping, and application. The characteristics of these phases differ depending on the onboarding approach. The following are the different approaches:

• Use hardware manufacturer certificates. Using the manufacturing certificate, this method authenticates the device. However, there is no option to authorize the target network, which prevents the device from being onboarded to fraudulent networks.
• Tracking ownership transfers throughout the supply chain. This secure late binding to the management system/controller allows the controller to trust the device and ensure that it is not compromised during the supply chain transmission.
• Imprinting/configuring for/by the owner of the device. This approach configures the device for its future owner/controller by imprinting the future owner's identity. This method enables the device to only onboard to the trusted owner/controller. However, it requires the manufacturer to build devices with customized features based on their future owner/controller.
• PoA based onboarding. This decentralized approach employs the subgranting-based authorization technique, which enables the controller to grant authorization to the subcontractor (principal) and the device to obtain authorization from the subcontractor. The PoA approach compliments the above three approaches with the use of digitally signed PoAs that enable mutual authorization between the device and the controller, and the use of PoA to keep track of the ownership transfer, which is submitted to the controller on demand.

Attacks out of scope The payload data in the form of PoAs is immutable and protected by cryptographic signatures. Therefore, integrity threats like replay, message insertion, modification, and man in the middle are out of scope.

Attacks in scope Confidentiality threats like eavesdropping exist when PoAs are sent as clear data. However, this can be resolved by e2e encryption. For authentication, the PoAs rely on strong unique identities, e.g., the identity of a must be verified when it turns up with a PoA where it obtains some authorized credentials based on its public key. In some cases, a private key can serve to prove identity, but it should be noted that a private key can be stolen (Identity theft). This can be resolved by coupling the identity uniquely to the device, e.g., a device hash, X.509 certificate–DevID, Device Identifier Composition Engine [DICE], Compound Device Identifier [CDI], public key. The protocol interface for receiving and processing PoAs is susceptible to denial-of-service attacks, where potential overload attacks using meaningless or unacceptable PoAs could be issued. Possible resolutions to this threat will be addressed in future versions of this draft. We will conform to prefer industry standards e.g., as described in

References Normative References Informative References National Institute of Standards and Technology INTEL Internet Engineering Task Force Internet Engineering Task Force Fido Alliance Internet Engineering Task Force Internet Engineering Task Force Internet Engineering Task Force Internet Engineering Task Force

Contributors Thanks to all of the contributors.