RFC 8576
Internet of Things (IoT) Security: State of the Art and Challenges
Pages: 50
Informational
Informational
Part 1 of 3 – Pages 1 to 20
Internet Research Task Force (IRTF) O. Garcia-Morchon Request for Comments: 8576 Philips Category: Informational S. Kumar ISSN: 2070-1721 Signify M. Sethi Ericsson April 2019 Internet of Things (IoT) Security: State of the Art and ChallengesAbstract
The Internet of Things (IoT) concept refers to the usage of standard Internet protocols to allow for human-to-thing and thing-to-thing communication. The security needs for IoT systems are well recognized, and many standardization steps to provide security have been taken -- for example, the specification of the Constrained Application Protocol (CoAP) secured with Datagram Transport Layer Security (DTLS). However, security challenges still exist, not only because there are some use cases that lack a suitable solution, but also because many IoT devices and systems have been designed and deployed with very limited security capabilities. In this document, we first discuss the various stages in the lifecycle of a thing. Next, we document the security threats to a thing and the challenges that one might face to protect against these threats. Lastly, we discuss the next steps needed to facilitate the deployment of secure IoT systems. This document can be used by implementers and authors of IoT specifications as a reference for details about security considerations while documenting their specific security challenges, threat models, and mitigations. This document is a product of the IRTF Thing-to-Thing Research Group (T2TRG).
Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Research Task Force (IRTF). The IRTF publishes the results of Internet-related research and development activities. These results might not be suitable for deployment. Documents approved for publication by the IRSG are not candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8576. Copyright Notice Copyright (c) 2019 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. The Thing Lifecycle . . . . . . . . . . . . . . . . . . . . . 5 3. Security Threats and Managing Risk . . . . . . . . . . . . . 8 4. State of the Art . . . . . . . . . . . . . . . . . . . . . . 13 4.1. IP-Based IoT Protocols and Standards . . . . . . . . . . 13 4.2. Existing IP-Based Security Protocols and Solutions . . . 16 4.3. IoT Security Guidelines . . . . . . . . . . . . . . . . . 18 5. Challenges for a Secure IoT . . . . . . . . . . . . . . . . . 21 5.1. Constraints and Heterogeneous Communication . . . . . . . 21 5.1.1. Resource Constraints . . . . . . . . . . . . . . . . 21 5.1.2. Denial-of-Service Resistance . . . . . . . . . . . . 22 5.1.3. End-to-End Security, Protocol Translation, and the Role of Middleboxes . . . . . . . . . . . . . . . . . 23 5.1.4. New Network Architectures and Paradigm . . . . . . . 25 5.2. Bootstrapping of a Security Domain . . . . . . . . . . . 25 5.3. Operational Challenges . . . . . . . . . . . . . . . . . 25 5.3.1. Group Membership and Security . . . . . . . . . . . . 26 5.3.2. Mobility and IP Network Dynamics . . . . . . . . . . 27 5.4. Secure Software Update and Cryptographic Agility . . . . 27 5.5. End-of-Life . . . . . . . . . . . . . . . . . . . . . . . 30 5.6. Verifying Device Behavior . . . . . . . . . . . . . . . . 30 5.7. Testing: Bug Hunting and Vulnerabilities . . . . . . . . 31 5.8. Quantum-Resistance . . . . . . . . . . . . . . . . . . . 32 5.9. Privacy Protection . . . . . . . . . . . . . . . . . . . 33 5.10. Reverse-Engineering Considerations . . . . . . . . . . . 34 5.11. Trustworthy IoT Operation . . . . . . . . . . . . . . . . 35 6. Conclusions and Next Steps . . . . . . . . . . . . . . . . . 36 7. Security Considerations . . . . . . . . . . . . . . . . . . . 36 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 9. Informative References . . . . . . . . . . . . . . . . . . . 37 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction
The Internet of Things (IoT) denotes the interconnection of highly heterogeneous networked entities and networks that follow a number of different communication patterns, such as: human-to-human (H2H), human-to-thing (H2T), thing-to-thing (T2T), or thing-to-things (T2Ts). The term "IoT" was first coined in 1999 by the Auto-ID center [AUTO-ID], which had envisioned a world where every physical object has a radio-frequency identification (RFID) tag with a globally unique identifier. This would not only allow tracking of objects in real time but also allow querying of data about them over the Internet. However, since then, the meaning of the Internet of Things has expanded and now encompasses a wide variety of technologies, objects, and protocols. It is not surprising that the IoT has received significant attention from the research community to (re)design, apply, and use standard Internet technology and protocols for the IoT. The things that are part of the Internet of Things are computing devices that understand and react to the environment they reside in. These things are also often referred to as smart objects or smart devices. The introduction of IPv6 [RFC6568] and CoAP [RFC7252] as fundamental building blocks for IoT applications allows connecting IoT hosts to the Internet. This brings several advantages, including: (i) a homogeneous protocol ecosystem that allows simple integration with other Internet hosts; (ii) simplified development for devices that significantly vary in their capabilities; (iii) a unified interface for applications, removing the need for application-level proxies. These building blocks greatly simplify the deployment of the envisioned scenarios, which range from building automation to production environments and personal area networks. This document presents an overview of important security aspects for the Internet of Things. We begin by discussing the lifecycle of a thing in Section 2. In Section 3, we discuss security threats for the IoT and methodologies for managing these threats when designing a secure system. Section 4 reviews existing IP-based (security) protocols for the IoT and briefly summarizes existing guidelines and regulations. Section 5 identifies remaining challenges for a secure IoT and discusses potential solutions. Section 6 includes final remarks and conclusions. This document can be used by IoT standards specifications as a reference for details about security considerations that apply to the specified system or protocol. The first draft version of this document was submitted in March 2011. Initial draft versions of this document were presented and discussed during the meetings of the Constrained RESTful Environments (CORE) Working Group at IETF 80 and later. Discussions on security
lifecycle at IETF 92 (March 2015) evolved into more general security considerations. Thus, the draft was selected to address the T2TRG work item on the security considerations and challenges for the Internet of Things. Further updates of the draft were presented and discussed during the T2TRG meetings at IETF 96 (July 2016) and IETF 97 (November 2016) and at the joint interim meeting in Amsterdam (March 2017). This document has been reviewed by, commented on, and discussed extensively for a period of nearly six years by a vast majority of the T2TRG and related group members, the number of which certainly exceeds 100 individuals. It is the consensus of T2TRG that the security considerations described in this document should be published in the IRTF Stream of the RFC series. This document does not constitute a standard.2. The Thing Lifecycle
The lifecycle of a thing refers to the operational phases of a thing in the context of a given application or use case. Figure 1 shows the generic phases of the lifecycle of a thing. This generic lifecycle is applicable to very different IoT applications and scenarios. For instance, [RFC7744] provides an overview of relevant IoT use cases. In this document, we consider a Building Automation and Control (BAC) system to illustrate the lifecycle and the meaning of these different phases. A BAC system consists of a network of interconnected nodes that performs various functions in the domains of Heating, Ventilating, and Air Conditioning (HVAC), lighting, safety, etc. The nodes vary in functionality, and a large majority of them represent resource-constrained devices such as sensors and luminaries. Some devices may be battery operated or may rely on energy harvesting. This requires us to also consider devices that sleep during their operation to save energy. In our BAC scenario, the life of a thing starts when it is manufactured. Due to the different application areas (i.e., HVAC, lighting, or safety), nodes/things are tailored to a specific task. It is therefore unlikely that one single manufacturer will create all nodes in a building. Hence, interoperability as well as trust bootstrapping between nodes of different vendors is important. The thing is later installed and commissioned within a network by an installer during the bootstrapping phase. Specifically, the device identity and the secret keys used during normal operation may be provided to the device during this phase. Different subcontractors may install different IoT devices for different purposes. Furthermore, the installation and bootstrapping procedures may not be a discrete event and may stretch over an extended period. After being bootstrapped, the device and the system of things are in
operational mode and execute the functions of the BAC system. During this operational phase, the device is under the control of the system owner and used by multiple system users. For devices with lifetimes spanning several years, occasional maintenance cycles may be required. During each maintenance phase, the software on the device can be upgraded, or applications running on the device can be reconfigured. The maintenance tasks can be performed either locally or from a backend system. Depending on the operational changes to the device, it may be required to rebootstrap at the end of a maintenance cycle. The device continues to loop through the operational phase and the eventual maintenance phases until the device is decommissioned at the end of its lifecycle. However, the end-of-life of a device does not necessarily mean that it is defective; rather, it denotes a need to replace and upgrade the network to next-generation devices for additional functionality. Therefore, the device can be removed and recommissioned to be used in a different system under a different owner, thereby starting the lifecycle all over again. We note that the presented lifecycle represents to some extent a simplified model. For instance, it is possible to argue that the lifecycle does not start when a tangible device is manufactured but rather when the oldest bit of code that ends up in the device -- maybe from an open-source project or the operating system -- was written. Similarly, the lifecycle could also include an on-the-shelf phase where the device is in the supply chain before an owner/user purchases and installs it. Another phase could involve the device being rebadged by some vendor who is not the original manufacturer. Such phases can significantly complicate other phases such as maintenance and bootstrapping. Finally, other potential end states can be, e.g., a vendor that no longer supports a device type because it is at the end of its life or a situation in which a device is simply forgotten but remains functional.
_Manufactured _SW update _Decommissioned / / / | _Installed | _ Application | _Removed & | / | / reconfigured | / replaced | | _Commissioned | | | | | | / | | | | _Reownership & | | | _Application | | _Application | | / recommissioned | | | / running | | / running | | | | | | | | | | | | | \\ +##+##+###+#############+##+##+#############+##+##+##############>>> \/ \______________/ \/ \_____________/ \___/ time // / / \ \ \ Bootstrapping / Maintenance & \ Maintenance & / rebootstrapping \ rebootstrapping Operational Operational Figure 1: The Lifecycle of a Thing in the Internet of Things Security is a key requirement in any communication system. However, security is an even more critical requirement in real-world IoT deployments for several reasons. First, compromised IoT systems can not only endanger the privacy and security of a user but can also cause physical harm. This is because IoT systems often comprise sensors, actuators, and other connected devices in the physical environment of the user that could adversely affect the user if they are compromised. Second, a vulnerable IoT system means that an attacker can alter the functionality of a device from a given manufacturer. This not only affects the manufacturer's brand image but can also leak information that is very valuable for the manufacturer (such as proprietary algorithms). Third, the impact of attacking an IoT system goes beyond a specific device or an isolated system, since compromised IoT systems can be misused at scale. For example, they may be used to perform a Distributed Denial of Service (DDoS) attack that limits the availability of other networks and services. The fact that many IoT systems rely on standard IP protocols allows for easier system integration, but this also makes attacks on standard IP protocols widely applicable in other environments. This results in new requirements regarding the implementation of security. The term "security" subsumes a wide range of primitives, protocols, and procedures. For instance, it includes services such as confidentiality, authentication, integrity, authorization, source authentication, and availability. It often also includes augmented services such as duplicate detection and detection of stale packets (timeliness). These security services can be implemented through a combination of cryptographic mechanisms such as block ciphers, hash functions, and signature algorithms, as well as noncryptographic
mechanisms that implement authorization and other aspects of security-policy enforcement. For ensuring security in IoT networks, one should not only focus on the required security services but also pay special attention to how the services are realized in the overall system.3. Security Threats and Managing Risk
Security threats in related IP protocols have been analyzed in multiple documents, including Hypertext Transfer Protocol (HTTP) over Transport Layer Security (TLS) (HTTPS) [RFC2818], Constrained Application Protocol (CoAP) [RFC7252], IPv6 over Low-Power Wireless Personal Area Networks (6LoWPAN) [RFC4919], Access Node Control Protocol (ANCP) [RFC5713], Domain Name System (DNS) [RFC3833], IPv6 Neighbor Discovery (ND) [RFC3756], and Protocol for Carrying Authentication and Network Access (PANA) [RFC4016]. In this section, we specifically discuss the threats that could compromise an individual thing or the network as a whole. Some of these threats might go beyond the scope of Internet protocols, but we gather them here for the sake of completeness. The threats in the following list are not in any particular order, and some threats might be more critical than others, depending on the deployment scenario under consideration: 1. Vulnerable software/code: Things in the Internet of Things rely on software that might contain severe bugs and/or bad design choices. This makes the things vulnerable to many different types of attacks, depending on the criticality of the bugs, e.g., buffer overflows or lack of authentication. This can be considered one of the most important security threats. The large-scale Distributed Denial of Service (DDoS) attack, popularly known as the Mirai botnet [Mirai], was caused by things that had well-known or easy-to-guess passwords for configuration. 2. Privacy threat: The tracking of a thing's location and usage may pose a privacy risk to people around it. For instance, an attacker can infer privacy-sensitive information from the data gathered and communicated by individual things. Such information may subsequently be sold to interested parties for marketing purposes and targeted advertising. In extreme cases, such information might be used to track dissidents in oppressive regimes. Unlawful surveillance and interception of traffic to/ from a thing by intelligence agencies is also a privacy threat. 3. Cloning of things: During the manufacturing process of a thing, an untrusted factory can easily clone the physical characteristics, firmware/software, or security configuration of
the thing. Deployed things might also be compromised and their
software reverse engineered, allowing for cloning or software
modifications. Such a cloned thing may be sold at a cheaper
price in the market and yet can function normally as a genuine
thing. For example, two cloned devices can still be associated
and work with each other. In the worst-case scenario, a cloned
device can be used to control a genuine device or perform an
attack. One should note here that an untrusted factory may also
change functionality of the cloned thing, resulting in degraded
functionality with respect to the genuine thing (thereby
inflicting potential damage to the reputation of the original
thing manufacturer). Moreover, additional functionality can be
introduced in the cloned thing. An example of such
functionality is a backdoor.
4. Malicious substitution of things: During the installation of a
thing, a genuine thing may be replaced by a similar variant (of
lower quality) without being detected. The main motivation may
be cost savings, where the installation of lower-quality things
(for example, noncertified products) may significantly reduce
the installation and operational costs. The installers can
subsequently resell the genuine things to gain further financial
benefits. Another motivation may be to inflict damage to the
reputation of a competitor's offerings.
5. Eavesdropping attack: During the commissioning of a thing into a
network, it may be susceptible to eavesdropping, especially if
operational keying materials, security parameters, or
configuration settings are exchanged in the clear using a
wireless medium or if used cryptographic algorithms are not
suitable for the envisioned lifetime of the device and the
system. After obtaining the keying material, the attacker might
be able to recover the secret keys established between the
communicating entities, thereby compromising the authenticity
and confidentiality of the communication channel, as well as the
authenticity of commands and other traffic exchanged over this
communication channel. When the network is in operation, T2T
communication can be eavesdropped if the communication channel
is not sufficiently protected or if a session key is compromised
due to protocol weaknesses. An adversary may also be able to
eavesdrop if keys are not renewed or updated appropriately.
Lastly, messages can also be recorded and decrypted offline at a
later point of time. The VENONA project [venona-project] is one
such example where messages were recorded for offline
decryption.
6. Man-in-the-middle attack: Both the commissioning and operational
phases may be vulnerable to man-in-the-middle attacks. For
example, when keying material between communicating entities is
exchanged in the clear, the security of the key establishment
protocol depends on the tacit assumption that no third party can
eavesdrop during the execution of this protocol. Additionally,
device authentication or device authorization may be nontrivial
or need the support of a human decision process, since things
usually do not have a priori knowledge about each other and
cannot always differentiate friends and foes via completely
automated mechanisms.
7. Firmware attacks: When a thing is in operation or maintenance
phase, its firmware or software may be updated to allow for new
functionality or new features. An attacker may be able to
exploit such a firmware upgrade by maliciously replacing the
thing's firmware, thereby influencing its operational behavior.
For example, an attacker could add a piece of malicious code to
the firmware that will cause it to periodically report the
energy usage of the thing to a data repository for analysis.
The attacker can then use this information to determine when a
home or enterprise (where the thing is installed) is unoccupied
and break in. Similarly, devices whose software has not been
properly maintained and updated might contain vulnerabilities
that might be exploited by attackers to replace the firmware on
the device.
8. Extraction of private information: IoT devices (such as sensors,
actuators, etc.) are often physically unprotected in their
ambient environment, and they could easily be captured by an
attacker. An attacker with physical access may then attempt to
extract private information such as keys (for example, a group
key or the device's private key), data from sensors (for
example, healthcare status of a user), configuration parameters
(for example, the Wi-Fi key), or proprietary algorithms (for
example, the algorithm performing some data analytics task).
Even when the data originating from a thing is encrypted,
attackers can perform traffic analysis to deduce meaningful
information, which might compromise the privacy of the thing's
owner and/or user.
9. Routing attack: As highlighted in [Daniel], routing information in IoT networks can be spoofed, altered, or replayed, in order to create routing loops, attract/repel network traffic, extend/ shorten source routes, etc. A nonexhaustive list of routing attacks includes: a. Sinkhole attack (or blackhole attack), where an attacker declares himself to have a high-quality route/path to the base station, thus allowing him to do manipulate all packets passing through it. b. Selective forwarding, where an attacker may selectively forward packets or simply drop a packet. c. Wormhole attack, where an attacker may record packets at one location in the network and tunnel them to another location, thereby influencing perceived network behavior and potentially distorting statistics, thus greatly impacting the functionality of routing. d. Sybil attack, whereby an attacker presents multiple identities to other things in the network. We refer to [Daniel] for further router attacks and a more detailed description. 10. Elevation of privilege: An attacker with low privileges can misuse additional flaws in the implemented authentication and authorization mechanisms of a thing to gain more privileged access to the thing and its data. 11. Denial of Service (DoS) attack: Often things have very limited memory and computation capabilities. Therefore, they are vulnerable to resource-exhaustion attack. Attackers can continuously send requests to specific things so as to deplete their resources. This is especially dangerous in the Internet of Things since an attacker might be located in the backend and target resource-constrained devices that are part of a constrained-node network [RFC7228]. A DoS attack can also be launched by physically jamming the communication channel. Network availability can also be disrupted by flooding the network with a large number of packets. On the other hand, things compromised by attackers can be used to disrupt the operation of other networks or systems by means of a Distributed DoS (DDoS) attack.
To deal with the above threats, it is required to find and apply
suitable security mitigations. However, new threats and exploits
appear on a daily basis, and products are deployed in different
environments prone to different types of threats. Thus, ensuring a
proper level of security in an IoT system at any point of time is
challenging. To address this challenge, some of the following
methodologies can be used:
1. A Business Impact Analysis (BIA) assesses the consequences of the
loss of basic security attributes: confidentiality, integrity,
and availability in an IoT system. These consequences might
include the impact from lost data, reduced sales, increased
expenses, regulatory fines, customer dissatisfaction, etc.
Performing a business impact analysis allows a business to
determine the relevance of having a proper security design.
2. A Risk Assessment (RA) analyzes security threats to an IoT system
while considering their likelihood and impact. It also includes
categorizing each of them with a risk level. Risks classified as
moderate or high must be mitigated, i.e., the security
architecture should be able to deal with those threats.
3. A Privacy Impact Assessment (PIA) aims at assessing the
Personally Identifiable Information (PII) that is collected,
processed, or used in an IoT system. By doing so, the goal is to
fulfill applicable legal requirements and determine the risks and
effects of manipulation and loss of PII.
4. Procedures for incident reporting and mitigation refer to the
methodologies that allow becoming aware of any security issues
that affect an IoT system. Furthermore, this includes steps
towards the actual deployment of patches that mitigate the
identified vulnerabilities.
BIA, RA, and PIA should generally be realized during the creation of
a new IoT system or when deploying significant system/feature
upgrades. In general, it is recommended to reassess them on a
regular basis, taking into account new use cases and/or threats. The
way a BIA, RA, or PIA is performed depends on the environment and the
industry. More information can be found in NIST documents such as
[NISTSP800-34r1], [NISTSP800-30r1], and [NISTSP800-122].
4. State of the Art
This section is organized as follows. Section 4.1 summarizes the state of the art on IP-based IoT systems, within both the IETF and other standardization bodies. Section 4.2 summarizes the state of the art on IP-based security protocols and their usage. Section 4.3 discusses guidelines and regulations for securing IoT as proposed by other bodies. Note that the references included in this section are a representative of the state of the art at the point of writing, and they are by no means exhaustive. The references are also at varying levels of maturity; thus, it is advisable to review their specific status.4.1. IP-Based IoT Protocols and Standards
Nowadays, there exists a multitude of control protocols for IoT. For BAC systems, the ZigBee standard [ZB], BACNet [BACNET], and DALI [DALI] play key roles. Recent trends, however, focus on an all-IP approach for system control. In this setting, a number of IETF working groups are designing new protocols for resource-constrained networks of smart things. The 6LoWPAN Working Group [WG-6LoWPAN], for example, has defined methods and protocols for the efficient transmission and adaptation of IPv6 packets over IEEE 802.15.4 networks [RFC4944]. The CoRE Working Group [WG-CoRE] has specified the Constrained Application Protocol (CoAP) [RFC7252]. CoAP is a RESTful protocol for constrained devices that is modeled after HTTP and typically runs over UDP to enable efficient application-level communication for things. ("RESTful" refers to the Representational State Transfer (REST) architecture.) In many smart-object networks, the smart objects are dispersed and have intermittent reachability either because of network outages or because they sleep during their operational phase to save energy. In such scenarios, direct discovery of resources hosted on the constrained server might not be possible. To overcome this barrier, the CoRE Working Group is specifying the concept of a Resource Directory (RD) [RD]. The Resource Directory hosts descriptions of resources that are located on other nodes. These resource descriptions are specified as CoRE link format [RFC6690]. While CoAP defines a standard communication protocol, a format for representing sensor measurements and parameters over CoAP is required. "Sensor Measurement Lists (SenML)" [RFC8428] is a specification that defines media types for simple sensor measurements and parameters. It has a minimalistic design so that constrained
devices with limited computational capabilities can easily encode their measurements and, at the same time, servers can efficiently collect a large number of measurements. In many IoT deployments, the resource-constrained smart objects are connected to the Internet via a gateway that is directly reachable. For example, an IEEE 802.11 Access Point (AP) typically connects the client devices to the Internet over just one wireless hop. However, some deployments of smart-object networks require routing between the smart objects themselves. The IETF has therefore defined the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550]. RPL provides support for multipoint-to-point traffic from resource- constrained smart objects towards a more resourceful central control point, as well as point-to-multipoint traffic in the reverse direction. It also supports point-to-point traffic between the resource-constrained devices. A set of routing metrics and constraints for path calculation in RPL are also specified [RFC6551]. The IPv6 over Networks of Resource-constrained Nodes (6lo) Working Group of the IETF [WG-6lo] has specified how IPv6 packets can be transmitted over various link-layer protocols that are commonly employed for resource-constrained smart-object networks. There is also ongoing work to specify IPv6 connectivity for a Non-Broadcast Multi-Access (NBMA) mesh network that is formed by IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) links [ARCH-6TiSCH]. Other link- layer protocols for which the IETF has specified or is currently specifying IPv6 support include Bluetooth [RFC7668], Digital Enhanced Cordless Telecommunications (DECT) Ultra Low Energy (ULE) air interface [RFC8105], and Near Field Communication (NFC) [IPv6-over-NFC]. Baker and Meyer [RFC6272] identify which IP protocols can be used in smart-grid environments. They give advice to smart-grid network designers on how they can decide on a profile of the Internet protocol suite for smart-grid networks. The Low Power Wide-Area Network (LPWAN) Working Group [WG-LPWAN] is analyzing features, requirements, and solutions to adapt IP-based protocols to networks such as LoRa [LoRa], Sigfox [sigfox], NB-IoT [NB-IoT], etc. These networking technologies enable a smart thing to run for years on a single coin-cell by relying on a star network topology and using optimized radio modulation with frame sizes in the order of tens of bytes. Such networks bring new security challenges, since most existing security mechanism do not work well with such resource constraints.
JavaScript Object Notation (JSON) is a lightweight text- representation format for structured data [RFC8259]. It is often used for transmitting serialized structured data over the network. The IETF has defined specifications for encoding cryptographic keys, encrypted content, signed content, and claims to be transferred between two parties as JSON objects. They are referred to as JSON Web Keys (JWKs) [RFC7517], JSON Web Encryption (JWE) [RFC7516], JSON Web Signatures (JWSs) [RFC7515], and JSON Web Token (JWT) [RFC7519]. An alternative to JSON, Concise Binary Object Representation (CBOR) [RFC7049], is a concise binary data format that is used for serialization of structured data. It is designed for resource- constrained nodes, and therefore it aims to provide a fairly small message size with minimal implementation code and extensibility without the need for version negotiation. CBOR Object Signing and Encryption (COSE) [RFC8152] specifies how to encode cryptographic keys, message authentication codes, encrypted content, and signatures with CBOR. The Light-Weight Implementation Guidance (LWIG) Working Group [WG-LWIG] is collecting experiences from implementers of IP stacks in constrained devices. The working group has already produced documents such as [RFC7815], which defines how a minimal Internet Key Exchange Version 2 (IKEv2) initiator can be implemented. The Thing-2-Thing Research Group (T2TRG) [RG-T2TRG] is investigating the remaining research issues that need to be addressed to quickly turn the vision of IoT into a reality where resource-constrained nodes can communicate with each other and with other more capable nodes on the Internet. Additionally, industry alliances and other standardization bodies are creating constrained IP protocol stacks based on the IETF work. Some important examples of this include: 1. Thread [Thread]: Specifies the Thread protocol that is intended for a variety of IoT devices. It is an IPv6-based network protocol that runs over IEEE 802.15.4. 2. Industrial Internet Consortium [IIoT]: The consortium defines reference architectures and security frameworks for development, adoption, and widespread use of Industrial Internet technologies based on existing IETF standards. 3. IPSO Alliance (which subsequently merged with OMA SpecWorks [OMASpecWorks]): The alliance specifies a common object model that enables application software on any device to interoperate with other conforming devices.
4. OneM2M [OneM2M]: The standards body defines technical and API specifications for IoT devices. It aims to create a service layer that can run on any IoT device hardware and software. 5. Open Connectivity Foundation (OCF) [OCF]: The foundation develops standards and certifications primarily for IoT devices that use Constrained Application Protocol (CoAP) as the application-layer protocol. 6. Fairhair Alliance [Fairhair]: Specifies an IoT middleware to enable a common IP network infrastructure between different application standards used in building automation and lighting systems such as BACnet, KNX, and ZigBee. 7. OMA LwM2M [LWM2M]: OMA Lightweight M2M is a standard from the OMA SpecWorks for M2M and IoT device management. LwM2M relies on CoAP as the application-layer protocol and uses a RESTful architecture for remote management of IoT devices.4.2. Existing IP-Based Security Protocols and Solutions
There are three main security objectives for IoT networks: 1. protecting the IoT network from attackers 2. protecting IoT applications and thus the things and users 3. protecting the rest of the Internet and other things from attacks that use compromised things as an attack platform In the context of the IP-based IoT deployments, consideration of existing Internet security protocols is important. There are a wide range of specialized as well as general-purpose security solutions for the Internet domain, such as IKEv2/IPsec [RFC7296], Transport Layer Security (TLS) [RFC8446], Datagram Transport Layer Security (DTLS) [RFC6347], Host Identity Protocol (HIP) [RFC7401], PANA [RFC5191], Kerberos [RFC4120], Simple Authentication and Security Layer (SASL) [RFC4422], and Extensible Authentication Protocol (EAP) [RFC3748]. TLS provides security for TCP and requires a reliable transport. DTLS secures and uses datagram-oriented protocols such as UDP. Both protocols are intentionally kept similar and share the same ideology and cipher suites. The CoAP base specification [RFC7252] provides a description of how DTLS can be used for securing CoAP. It proposes three different modes for using DTLS: the PreSharedKey mode, where nodes have pre-provisioned keys for initiating a DTLS session with another node, RawPublicKey mode, where nodes have asymmetric-key
pairs but no certificates to verify the ownership, and Certificate mode, where public keys are certified by a certification authority. An IoT implementation profile is defined for TLS version 1.2 and DTLS version 1.2 that offers communication security for resource- constrained nodes [RFC7925]. There is ongoing work to define an authorization and access-control framework for resource-constrained nodes. The Authentication and Authorization for Constrained Environments (ACE) Working Group [WG-ACE] is defining a solution to allow only authorized access to resources that are hosted on a smart-object server and identified by a URI. The current proposal [ACE-OAuth] is based on the OAuth 2.0 framework [RFC6749], and it comes with profiles intended for different communication scenarios, e.g., "Datagram Transport Layer Security (DTLS) Profile for Authentication and Authorization for Constrained Environments (ACE)" [ACE-DTLS]. Object Security for Constrained RESTful Environments (OSCORE) [OSCORE] is a proposal that protects CoAP messages by wrapping them in the COSE format [RFC8152]. Thus, OSCORE falls in the category of object security, and it can be applied wherever CoAP can be used. The advantage of OSCORE over DTLS is that it provides some more flexibility when dealing with end-to-end security. Section 5.1.3 discusses this further. The Automated Certificate Management Environment (ACME) Working Group [WG-ACME] is specifying conventions for automated X.509 certificate management. This includes automatic validation of certificate issuance, certificate renewal, and certificate revocation. While the initial focus of the working group is on domain-name certificates (as used by web servers), other uses in some IoT deployments are possible. The Internet Key Exchange (IKEv2)/IPsec -- as well as the less used Host Identity protocol (HIP) -- reside at or above the network layer in the OSI model. Both protocols are able to perform an authenticated key exchange and set up the IPsec for secure payload delivery. Currently, there are also ongoing efforts to create a HIP variant coined Diet HIP [HIP-DEX] that takes constrained networks and nodes into account at the authentication and key-exchange level. Migault et al. [Diet-ESP] are working on a compressed version of IPsec so that it can easily be used by resource-constrained IoT devices. They rely on the Internet Key Exchange Protocol Version 2 (IKEv2) for negotiating the compression format. The Extensible Authentication Protocol (EAP) [RFC3748] is an authentication framework supporting multiple authentication methods.
EAP runs directly over the data link layer and thus does not require the deployment of IP. It supports duplicate detection and retransmission but does not allow for packet fragmentation. PANA is a network-layer transport for EAP that enables network access authentication between clients and the network infrastructure. In EAP terms, PANA is a UDP-based EAP lower layer that runs between the EAP peer and the EAP authenticator.4.3. IoT Security Guidelines
Attacks on and from IoT devices have become common in recent years -- for instance, large-scale DoS attacks on the Internet Infrastructure from compromised IoT devices. This fact has prompted many different standards bodies and consortia to provide guidelines for developers and the Internet community at large to build secure IoT devices and services. The following is a subset of the different guidelines and ongoing projects: 1. Global System for Mobile Communications Association (GSMA) IoT security guidelines [GSMAsecurity]: GSMA has published a set of security guidelines for the benefit of new IoT product and service providers. The guidelines are aimed at device manufacturers, service providers, developers, and network operators. An enterprise can complete an IoT Security Self- Assessment to demonstrate that its products and services are aligned with the security guidelines of the GSMA. 2. Broadband Internet Technical Advisory Group (BITAG) IoT Security and Privacy Recommendations [BITAG]: BITAG has published recommendations for ensuring the security and privacy of IoT device users. BITAG observes that many IoT devices are shipped from the factory with software that is already outdated and vulnerable. The report also states that many devices with vulnerabilities will not be fixed, either because the manufacturer does not provide updates or because the user does not apply them. The recommendations include that IoT devices should function without cloud and Internet connectivity and that all IoT devices should have methods for automatic secure software updates. 3. United Kingdom Department for Digital, Culture, Media and Sport (DCMS) [DCMS]: UK DCMS has released a report that includes a list of 13 steps for improving IoT security. These steps, for example, highlight the need for implementing a vulnerability disclosure policy and keeping software updated. The report is aimed at device manufacturers, IoT service providers, mobile application developers, and retailers.
4. Cloud Security Alliance (CSA) New Security Guidance for Early
Adopters of the IoT [CSA]: CSA recommendations for early
adopters of IoT encourage enterprises to implement security at
different layers of the protocol stack. It also recommends
implementation of an authentication/authorization framework for
IoT deployments. A complete list of recommendations is
available in the report [CSA].
5. United States Department of Homeland Security (DHS) [DHS]: DHS
has put forth six strategic principles that would enable IoT
developers, manufacturers, service providers, and consumers to
maintain security as they develop, manufacture, implement, or
use network-connected IoT devices.
6. National Institute of Standards and Technology (NIST)
[NIST-Guide]: The NIST special publication urges enterprise and
US federal agencies to address security throughout the systems
engineering process. The publication builds upon the
International Organization for Standardization
(ISO)/International Electrotechnical Commission (IEC) 15288
standard and augments each process in the system lifecycle with
security enhancements.
7. National Institute of Standards and Technology (NIST)
[NIST-LW-PROJECT] [NIST-LW-2016]: NIST is running a project on
lightweight cryptography with the purpose of: (i) identifying
application areas for which standard cryptographic algorithms
are too heavy, classifying them according to some application
profiles to be determined; (ii) determining limitations in those
existing cryptographic standards; and (iii) standardizing
lightweight algorithms that can be used in specific application
profiles.
8. Open Web Application Security Project (OWASP) [OWASP]: OWASP
provides security guidance for IoT manufacturers, developers,
and consumers. OWASP also includes guidelines for those who
intend to test and analyze IoT devices and applications.
9. IoT Security Foundation [IoTSecFoundation]: The IoT Security
Foundation has published a document that enlists various
considerations that need to be taken into account when
developing IoT applications. For example, the document states
that IoT devices could use a hardware root of trust to ensure
that only authorized software runs on the devices.
10. National Highway Traffic Safety Administration (NHTSA) [NHTSA]:
The US NHTSA provides guidance to the automotive industry for
improving the cyber security of vehicles. While some of the
guidelines are general, the document provides specific
recommendations for the automotive industry, such as how various
automotive manufacturers can share cybersecurity vulnerabilities
discovered.
11. "Best Current Practices for Securing Internet of Things (IoT)
Devices" [Moore]: This document provides a list of minimum
requirements that vendors of IoT devices should to take into
account while developing applications, services, and firmware
updates in order to reduce the frequency and severity of
security incidents that arise from compromised IoT devices.
12. European Union Agency for Network and Information Security
(ENISA) [ENISA-ICS]: ENISA published a document on
communication-network dependencies for Industrial Control
Systems (ICS)/Supervisory Control And Data Acquisition (SCADA)
systems in which security vulnerabilities, guidelines, and
general recommendations are summarized.
13. Internet Society Online Trust Alliance [ISOC-OTA]: The Internet
Society's IoT Trust Framework identifies the core requirements
that manufacturers, service providers, distributors, purchasers,
and policymakers need to understand, assess, and embrace for
effective security and privacy as part of the Internet of
Things.
Other guideline and recommendation documents may exist or may later
be published. This list should be considered nonexhaustive. Despite
the acknowledgment that security in the Internet is needed and the
existence of multiple guidelines, the fact is that many IoT devices
and systems have very limited security. There are multiple reasons
for this. For instance, some manufacturers focus on delivering a
product without paying enough attention to security. This may be
because of lack of expertise or limited budget. However, the
deployment of such insecure devices poses a severe threat to the
privacy and safety of users. The vast number of devices and their
inherently mobile nature also imply that an initially secure system
can become insecure if a compromised device gains access to the
system at some point in time. Even if all other devices in a given
environment are secure, this does not prevent external attacks caused
by insecure devices. Recently, the US Federal Communications
Commission (FCC) has stated the need for additional regulation of IoT
systems [FCC]. It is possible that we may see other such regional
regulations in the future.
(next page on part 2)