Evolution of Endpoint Security - A Taxonomy for Endpoints
The information below is for an old version of the document.
|Document||Type||This is an older version of an Internet-Draft whose latest revision is Expired|
|Stream||Stream state||(No stream defined)|
|RFC Editor Note||(None)|
|IESG||IESG state||I-D Exists|
|Send notices to||(None)|
Individual Submission M McFadden Internet Draft internet policy advisors ltd Intended status: Informational February 14, 2021 Expires: August 14, 2021 Evolution of Endpoint Security - A Taxonomy for Endpoints draft-mcfadden-opsec-endp-taxonomy-00 Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on August 14, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract McFadden Expires August 14, 2021 [Page 1] Internet-Draft A Taxonomy for Endpoints February 2021 A separate document [I-D:draft-mcfadden-opsec-endp-evolve] attempts to establish the capabilities and limitations of endpoint-only security solutions and explore potential alternative approaches. That document discusses endpoints in general terms. It has been suggested that there are classes of endpoints that have different characteristics. Those classes may have completely different threat landscapes and the endpoints may have completely different security capabilities. As a companion to the endpoint evolution draft, this document provides a taxonomy of endpoints that is intended to provide a foundation for further work on endpoint security evolution and research on approaches to providing endpoint security alternatives in a diverse group of settings. Table of Contents 1. Introduction...................................................3 2. Conventions used in this document..............................4 3. Problem Statement..............................................4 4. The Endpoint in the EVOLVE draft...............................4 5. Taxonomy and Hierarchy.........................................5 6. Taxonomy.......................................................6 6.1. Traditional and Enterprise Computing Equipment [TECE].....6 6.1.1. Description..........................................6 6.1.2. Endpoint characteristics.............................6 6.2. Personal Computing Equipment..............................7 6.2.1. Description..........................................7 6.2.2. Endpoint characteristics.............................8 6.3. Human Interface Devices...................................8 6.3.1. Endpoint description.................................8 6.3.2. Endpoint characteristics.............................9 6.4. Human Sensor Devices.....................................10 6.4.1. Endpoint characteristics............................10 6.5. Non-human Sensor Devices.................................11 6.5.1. Endpoint Description................................11 6.5.2. Endpoint characteristics............................11 6.6. Peripheral Computing Equipment and Embedded Endpoints....12 6.6.1. Endpoint Description................................12 6.6.2. Endpoint characteristics............................12 6.7. Application Layer Endpoints..............................13 6.7.1. Description.........................................13 6.7.2. Endpoint Characteristics............................13 6.8. Edge Network and Acquisition Endpoints...................14 6.8.1. Description.........................................14 6.8.2. Endpoint characteristics............................15 7. Security Considerations.......................................15 8. IANA Considerations...........................................16 McFadden, M. Expires August 14, 2021 [Page 2] Internet-Draft A Taxonomy for Endpoints February 2021 9. References....................................................16 9.1. Informative References ..................................16 10. Acknowledgments..............................................16 Appendix A. Document History.....................................17 1. Introduction A document entitled "Evolution of Endpoint Security - An Operational Perspective (EVOLVE) [I-D. draft-mcfadden-opsec-endp-evolve-00] attempts to initiate research into the limits of endpoint-only security solutions. The EVOLVE introduction focuses on endpoints that are User Equipment rather than hosts. Even so, this encompasses an enormous variety of possible endpoints. EVOLVE takes a unified view of endpoints - seeing them all as one type. However, it seems reasonable to suggest that, in the huge variety of types of endpoints, there are categories of similarity. These categories are important because categories of endpoint devices may share particular advantages or limitations for endpoint security. While EVOLVE provides a clear model for understanding some of the limitations of endpoint security in today's networks, it is very likely that more specificity is needed. This draft attempts to suggest a Taxonomy of Endpoints as a foundation for further work on the EVOLVE draft. The goal is to identify classes of endpoints with similar characteristics. Those characteristics may lead to the discovery that the devices in a particular category share similar characteristics for endpoint security. It is essential to understand that this taxonomy is intended as a foundation for work on the EVOLVE draft and is not an all-purpose guide to the enormous breadth of devices that are or could be endpoints on public or private networks. Others have attempted to provide classifications for end devices, but they are not focused on the issues related to endpoint security. In addition, most are almost immediately out-of-date when published. This document takes a different approach: the taxonomy here is intended to support the work of the EVOLVE draft and provide a classification system that may make it possible to group endpoints in related categories for the purpose of discussing their security characteristics. While a general-purpose taxonomy of Internet endpoints might be useful in a variety of settings, it is not the intended goal of this document. McFadden, M. Expires August 14, 2021 [Page 3] Internet-Draft A Taxonomy for Endpoints February 2021 In addition, this document does not attempt to assess and document the endpoint security characteristics of each part of the taxonomy. The work of identifying advantages and limitations of specific classes of endpoints is envisioned as future work on the EVOLVE draft. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Problem Statement The EVOLVE draft attempts to provide an analysis of the current state of the provision of endpoint security. It does that by providing a provisional definition of an endpoint and then examining the advantages and limitations of providing security at that endpoint. The original approach to the EVOLVE draft divides the universe of endpoints into User Equipment (UE) and hosts - and then focuses entirely on User Equipment. User Equipment encompasses a very broad set of endpoints. It may be possible to provide a stronger set of device type groupings. Endpoints in the same groups may share security characteristics that are particular to that group. The fundamental question is: can a taxonomy of endpoint devices be created that allows for grouping of endpoints that have similar security characteristics? If it is possible to answer that question in the affirmative, then research can be done on the security characteristics of each category and influence the development of protocols that have the greatest impact for those type of devices. 4. The Endpoint in the EVOLVE draft The EVOLVE draft simplifies the representation of an endpoint by providing the following model: McFadden, M. Expires August 14, 2021 [Page 4] Internet-Draft A Taxonomy for Endpoints February 2021 +------------------------------------------------+ | | | Application | | | |------------------------------------------------| | | | OS / Execution Environment | | | |------------------------------------------------| | | | Hardware | | | +------------------------------------------------+ Figure 1 Endpoint Generalization in the EVOLVE draft This simplification means that there are many combinations of hardware, operating systems, execution environments and applications. It also means that any of these three layers can be an endpoint for the purposes of a discussion of endpoint security. The EVOLVE draft suggests that we consider endpoints including those which have a variety of power, computational, storage and network capacities. It is possible that grouping devices with similar characteristics will help in identifying categories of devices that share similar endpoint security characteristics. 5. Taxonomy and Hierarchy One suggestion for the taxonomy for endpoints is to consider a hierarchy of endpoints that collects similar endpoint types in large categories and then distinguishes between them in "sub-groups" or lower levels of the taxonomy. The advantage to using both the taxonomy and the EVOLVE draft is that the groupings may provide a way to categorize threats and mitigations to large classes of endpoints on the Internet while providing the ability for differentiation. An example might be a class of endpoints characterized as "constrained devices." As an example, "constrained devices" might be further subdivided into sub-classes such as sensors, embedded processors, specific (or, special) purpose single-use processors, mesh gateways, and so forth. It can even be imagined that the second level of the hierarchy could be further subdivided by further distinguishing the endpoint types. McFadden, M. Expires August 14, 2021 [Page 5] Internet-Draft A Taxonomy for Endpoints February 2021 The current version of the draft does not take this approach. One of the goals of the endpoint taxonomy is to provide enough differentiation and specificity to ensure that a later version of the EVOLVE draft can successfully discuss common threats and mitigations for each of the categories in the taxonomy. By providing an ever greater hierarchy of endpoint types, it becomes difficult to scale the EVOLVE document that discusses threats and mitigations to the highly specific endpoint types. 6. Taxonomy Others have attempted to provide general-purpose taxonomy and device classification guides (informative references to be provided in a later draft version). In some settings automated detection and classification of devices provides an essential step in providing appropriate access control and security services. General-purpose classification systems tend to ossify or become enormously complex. Classification has come from commercial entities, computer science organizations, the academic community and even regional collections of cooperating national governments. For the purposes of providing a taxonomy for the EVOLVE draft, we limit the discussion to a taxonomy for endpoints only. We divide endpoints into eight different classes and then attempt to carefully describe the characteristics of devices in each class. 6.1. Traditional and Enterprise Computing Equipment [TECE] 6.1.1. Description Traditional and Enterprise Computing Equipment is characterized by its extremely high-capacity for transactional volume, storage and shared user population. TECE forms the backbone of high-volume, high-availability transactional computing and is provided in both physical and virtualized forms. Traditional computing endpoints are shared computing environments characterized by centralized, shared computing. These endpoints are often in large scale data centers. These endpoints are capable of high-availability, substantial requirements for power and environmental control. These endpoints are also characterized by very complex operating systems and user environments. 6.1.2. Endpoint characteristics o Cost - these endpoints are characterized by extremely high cost. McFadden, M. Expires August 14, 2021 [Page 6] Internet-Draft A Taxonomy for Endpoints February 2021 o Physical size - these are very large endpoints, not suitable or intended for use by an individual. o Network link characteristics - capable of supporting extremely high bandwidth. o User interface - very complex and shared among multiple individuals. o Processing power - extremely high processing capability. o Physical power - requires substantial provision of electrical power and environmental controls. o Code complexity - Extremely high support for very complex code including parallelism, multitasking and multithreaded execution. 6.2. Personal Computing Equipment 6.2.1. Description These are endpoints designed or intended to be used by an individual. They can be delivered as fixed, portable or virtual instantiations of the endpoint. It should be noted that virtual instantiations of endpoints introduce complexities in defining the characteristics of the endpoints. In each case, the device supports a mechanism for human-interface and has the capability for both local storage and processing. The personal computing equipment class is also characterized by relatively low cost and power requirements. This class of endpoint is also characterized by the devices supporting multiple purpose use. This class is divided into two sub-classes: fixed and mobile endpoints. The mobile subclass is further divided into four other subclasses: laptops, tablets, intelligent phones, and ultraportable personal computing equipment. Personal computing endpoints usually have at least one, and often many, network links - often supporting a variety of network connectivity technologies. These endpoints are also characterized by having a human interface - either integral to the computing device itself or supplied externally to the computing device. McFadden, M. Expires August 14, 2021 [Page 7] Internet-Draft A Taxonomy for Endpoints February 2021 6.2.2. Endpoint characteristics o Cost - these endpoints have a huge range of costs, from extremely inexpensive for simple "personal computer on a board" endpoints to moderately expensive for specially configured laptop and fixed devices. o Physical size - the physical size of these devices range from handheld to a small cabinet for fixed, desktop units. o Network link characteristics - personal computing endpoints are often characterized by supporting multiple connectivity technologies. o User interface - personal computing endpoints are characterized by having user interfaces designed for an individual. The interface varies from simple, text-based interaction to gesture, touch and voice control. o Processing power - these endpoints are characterized by a significant range of processing power: from single CPU units to endpoints that can support multiple concurrent processes. o Physical power - personal computing endpoints are characterized by using either traditional mains power or power supplied by a battery. o Code complexity - personal computing endpoints support complex code and often parallel and multithreaded execution of code. 6.3. Human Interface Devices 6.3.1. Endpoint description Human interface transactions begin with a task-related goal for a user. This leads to a user behavior (such as pointing, typing or touching) which occurs in the current computing environment. The user's action then should trigger an event in the current computing environment. Early computer science research breaks the taxonomy for Human Interface Devices into four large categories: input devices, pointing devices, indirect pointing and speech recognition. More recent research adds neural interfaces, VR sensors, and human attribute sensors. In all of these cases, the endpoints have the goal of providing a mechanism for user navigation, interconnection, form filling, menu interaction, data entry or sensing of human input McFadden, M. Expires August 14, 2021 [Page 8] Internet-Draft A Taxonomy for Endpoints February 2021 (although not to be confused with the following category in the taxonomy). The result is that this category of the taxonomy has been characterized by extremely limited computing capability in the past. In contemporary networks the human interface devices are far more complex and, as a result, subject to a wider collections of risks as endpoints. Since human interface devices are often the mechanism that provides control of a computing resource, attacks on those devices are of particular concern. In the past, the idea that there was an external threat to a mouse or a pointing device would be ignored. In contrast, today's voice actuated input devices and VR interfaces are sophisticated enough to represent a real platform for attack. 6.3.2. Endpoint characteristics o Cost - these endpoints are typically low in cost compared to traditional computing equipment. They are often closer in cost to simple peripheral equipment rather than endpoints that provide general purpose computing platforms. o Physical size - these devices are meant to provide a human interface and are sized appropriately to that use case. Examples include those devices that are small enough to be handheld or worn. o Network link characteristics - human interface devices are connected in a variety of ways. Early devices were wired to the device to which they provided connectivity. More recently, these devices have a network connection between them and the connected device. Examples of this connection use Bluetooth or other, very local network connections. These devices may have connections to wider networks to support applications such as augmented reality. o User interface - generally these devices provide a user interface rather than having a distinct user interface of their own. More complex human interface devices have limited interfaces for settings and control of the device, and its connectivity and function. o Processing power - these devices are characterized by having limited processing power. o Physical power - most human interface devices are characterized by having limited power requirements. They are sometimes powered by their connection to the device. In other cases, they are powered by a battery. McFadden, M. Expires August 14, 2021 [Page 9] Internet-Draft A Taxonomy for Endpoints February 2021 o Code complexity - human interface devices tend to have either no or very limited capabilities to execute code. Modern interface devices which support presentation of a virtual physical environment are capable of executing the code needed to provide the interface between the presentation of visual (and other) stimuli while responding to gestures and movement of the person using the device. 6.4. Human Sensor Devices Description These are endpoints whose primary purpose is to sense, store, transmit or process information about a human being. These endpoints are characterized as having use cases in health and wellness monitoring, human performance enhancement, personalized medicine and human safety. The endpoints are characterized as sensor devices with the capacity to sense, store and report on data collected on an individual. The sensor may be multimodal. These endpoints are almost always characterized by have a battery for power and having limited storage, networking and processing capabilities. 6.4.1. Endpoint characteristics o Cost - Human Sensor Endpoints can range in cost from very low (for instance a heartbeat sensor) to quite expensive (a sensor built into an implanted device). o Physical size - human sensors are very small and almost always portable. o Network link characteristics - human sensors usually have a single network like technology available and are capable of very limited bandwidth utilization on that link. o User interface - human sensors have extremely limited, or no, user interface. o Processing power - human sensors are characterized by having limited processing power - often incorporating only the ability to collect store and forward sensed information. o Physical power - human sensors are characterized by being powered by internal batteries McFadden, M. Expires August 14, 2021 [Page 10] Internet-Draft A Taxonomy for Endpoints February 2021 o Code complexity - human sensors are not usually capable of running complex code. Often, the capability of the endpoint is to simply sense, store and forward data without reporting and analysis of that data. 6.5. Non-human Sensor Devices 6.5.1. Endpoint Description These endpoints are capable of sensing, storage, communication and possibly some computation. They are characterized by having very low bandwidth radios, a battery for power, sensor technology and a small processor. Unlike in Section 5.4, these devices are not intended to sense human-related information. Compared with Human Sensors, non-human sensors often have a variety of communications technologies available - for instance, self- organizing into mesh networks. 6.5.2. Endpoint characteristics o Cost - Non-human Sensor Endpoints can range in cost from very low (for instance, a simple temperature sensor) to quite expensive (a sensor built into an implanted device. o Physical size - Non-human sensors are often small and almost always portable. o Network link characteristics - Non-human sensors usually have a single network like technology available but the topology of those network links can be highly varied. Quite often these devices are capable of very limited bandwidth utilization on the link to which they are attached. o User interface - non-human sensors have extremely limited, or no, user interface. o Processing power - non-human sensors are characterized by having limited processing power - often incorporating only the ability to collect store and forward sensed information. Some non-human sensors have the capability to process stored data, but usually this is limited. o Physical power - non-human sensors often require very limited amounts of power - very often provided by a battery. McFadden, M. Expires August 14, 2021 [Page 11] Internet-Draft A Taxonomy for Endpoints February 2021 o Code complexity - non-human sensors are not usually capable of running complex code. Often, the capability of the endpoint is to simply sense, store and forward data without reporting and analysis of that data. 6.6. Peripheral Computing Equipment and Embedded Endpoints 6.6.1. Endpoint Description These are endpoints that are "embedded" in devices that may have a different primary function. An example is a network endpoint in a printer that supports remote access, configuration and printing. Another example is an endpoint in an appliance that has a different primary function (for instance, a refrigerator). In either case, the endpoint is characterized as being added to another system, machine or peripheral. These devices are characterized as being specialized for their particular use case and function. Their specific characteristics often depend upon the system, device or peripheral in which they are being hosted. As an example, the embedded endpoint gets its physical power and networking capabilities from the device in which it is connected. 6.6.2. Endpoint characteristics o Cost - almost never available as a standalone device - instead, always embedded into the peripheral or system which is hosting it. o Physical size - almost always very small - to be embedded into some other system or device. o Network link characteristics - dependent on network services available from the host device and not always IP-based. o User interface - almost always provided by the "hosting" device. Many embedded endpoints share a user interface with the configuration and control tool for the underlying device. o Processing power - usually limited and constrained by the use case. Some embedded endpoints provide remote access to the underlying resources provided by the processor. o Physical power - generally supplied by the "host" system or device. McFadden, M. Expires August 14, 2021 [Page 12] Internet-Draft A Taxonomy for Endpoints February 2021 o Code complexity - limited and almost always constrained by use case. 6.7. Application Layer Endpoints 6.7.1. Description A significant trend in the contemporary public Internet is to have applications act as completely independent agents - a situation where the application itself provides the necessary infrastructure (for instance, domain name resolution) to provide services. An example would be a web browser that independently resolved domain names and established secure communication channels independently. The traffic between the application and the servers it uses might not be available for analysis by security software. As a result, application-based endpoints would have the characteristic of having to provide security services (for instance, traffic security or malware detection) for itself. This type of endpoint also has the characteristic of potentially having adverse impacts on other applications running on the same platform. For example, if several applications are provisioning their own infrastructure services, then those services are being duplicated on that platform. For security related infrastructure there would be no common, platform-wide approach to securing the applications or the traffic generated between the application and external servers. 6.7.2. Endpoint Characteristics o Cost - applications vary widely in cost and some are free. o Physical size - based on code, application endpoints do not have physical characteristics (e.g. size, power requirements, etc.). o Network link characteristics - applications often use network facilities provided by lower layers of the stack. In particular, many application endpoints use the network services provided by the underlying operating system that acts as the host for the application. An emerging trend in both wired and wireless networks is for the application to interface with the network link to control or provide some of the network link services for itself. An example of this would be an application that does DNS resolution services for itself rather then depending on the underlying operating system to provide that service. McFadden, M. Expires August 14, 2021 [Page 13] Internet-Draft A Taxonomy for Endpoints February 2021 o User interface - the application usually provides its own user interface which can be minimal (for instance, command line driven) or complex (windows or VR driven). o Processing power - always dependent on the device on which the application is hosted. o Physical power - based on code, application endpoints do not have physical requirements (e.g. power) o Code complexity - highly variable. Applications can be very simple or highly complex depending on the application's requirements. 6.8. Edge Network and Acquisition Endpoints 6.8.1. Description The emergence of intelligent devices and things has led to new network designs where data is aggregated at points topologically close to where the data is gathered. The gathered data can then have the option to flow to nearby gateways, or a Wi-Fi/W-LAN (SD- WAN) router/equipment, or the telco tower/rooftop towers. These often perform an acquisition function that includes both aggregation and data condensation. They usually have some level of processing capability. The main task for these devices is to collect the data from various other endpoints and send the processed data upstream. In doing so, they often perform some low-level data processing, such as data filtering (which determines what data is sent/blocked) and data analytics. The acquisition systems are often architected to talk to distributed data centers and end devices; for instance, on a factory shop floor, a CDN's edge PoP (Point of Presence), an edge colocation local, or a metro regional datacenter for a Telco or IT Service Provider. In all cases, these edge computing devices represent a newer class of endpoints. These are endpoints that are not at the extreme edge of the network, but provide services to the devices at those edges (especially for those devices in the class discussed in section 6.4 and 6.5 above). The threats and mitigations for this class of device is expected to be significantly different from those in sections 6.4 and 6.5. McFadden, M. Expires August 14, 2021 [Page 14] Internet-Draft A Taxonomy for Endpoints February 2021 6.8.2. Endpoint characteristics o Cost - highly variable. Edge network devices in 5G networks can be very expensive. Aggregation nodes in sensor networks can be very inexpensive. o Physical size - highly variable. Edge network devices in 5G networks can be larger than personal computing equipment. Aggregation nodes in sensor networks can be as small as a circuit board, battery and radio. o Network link characteristics - by their nature, these devices have at least a pair of network links. One of these links faces toward the network where the data is being aggregated. The other faces toward the network where the data is being processed, analyzed or reported upon. o User interface - these devices usually have a limited user interface, characterized by the need to configure the device, provide security and allow for management of the network links. o Processing power - usually these devices have limited processing power: their emphasis is on aggregation and management of data flows between networks. o Physical power - highly variable. Edge network devices in 5G networks can require significant sources of secure and consistent power. Aggregation nodes in sensor networks can often be supported by a small battery. o Code complexity - usually these devices have limited ability to load and execute code. Since their emphasis is on aggregation and management of data flows between networks, these devices usually have minimal ability to run general purpose code. 7. Security Considerations This draft is non-normative and simply attempts to provide a taxonomy for endpoints. The goal of the taxonomy is to document that there are classes of endpoints that have different characteristics. Those classes may have completely different threat landscapes and the endpoints may have completely different security capabilities. In support of the work on the EVOLVE draft [I-D:draft-mcfadden- opsec-endp-evolve-00], this draft provides a taxonomy of endpoints that is intended to provide a foundation for further work on the McFadden, M. Expires August 14, 2021 [Page 15] Internet-Draft A Taxonomy for Endpoints February 2021 EVOLVE draft and research on approaches to providing endpoint security alternatives in a diverse group of settings. 8. IANA Considerations This memo contains no instructions or requests for IANA. The authors continue to appreciate the efforts of IANA staff in support of the IETF. 9. References 9.1. Informative References [I-D. draft-mcfadden-opsec-endp-evolve-00], McFadden, M., "Evolution of Endpoint Security - An Operational Perspective", Internet Draft (work in progress), February 2021 10. Acknowledgments The original idea for this draft came from another, now expired draft. The authors of that draft intended a comprehensive discussion of endpoint security and a clear description of how the evolution of the Internet made endpoint security - on its own - insufficient. The author thanks those previous contributors: Arnaud Taddei, Bret Jordan, Candid Wueest, Chris Larsen, Andre Engel, Kevin Roundy, Yugiong Sun, and David Wells. The author also extends his appreciation to the discussions in the IAB Activity called model-t where the future of the Internet's threat landscape has also been discussed. This document was prepared using 2-Word-v2.0.template.dot. McFadden, M. Expires August 14, 2021 [Page 16] Internet-Draft A Taxonomy for Endpoints February 2021 Appendix A. Document History [[ To be removed from the final document ]] -00 Initial Internet Draft McFadden, M. Expires August 14, 2021 [Page 17] Internet-Draft A Taxonomy for Endpoints February 2021 Authors' Addresses Mark McFadden Internet policy advisors ltd uk 6 Bridge Street Chepstow, Wales NP16 5EY United Kingdom Phone: +44 2921 25 3649 Email: firstname.lastname@example.org McFadden, M. Expires August 14, 2021 [Page 18]