ACE Working Group L. Seitz, Ed. Internet-Draft SICS Swedish ICT AB Intended status: Informational S. Gerdes, Ed. Expires: December 6, 2015 Universitaet Bremen TZI G. Selander Ericsson M. Mani Itron S. Kumar Philips Research June 04, 2015 ACE use cases draft-ietf-ace-usecases-04 Abstract Constrained devices are nodes with limited processing power, storage space and transmission capacities. These devices in many cases do not provide user interfaces and are often intended to interact without human intervention. This document comprises a collection of representative use cases for the application of authentication and authorization in constrained environments. These use cases aim at identifying authorization problems that arise during the lifecylce of a constrained device and are intended to provide a guideline for developing a comprehensive authentication and authorization solution for this class of scenarios. Where specific details are relevant, it is assumed that the devices use the Constrained Application Protocol (CoAP) as communication protocol, however most conclusions apply generally. 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). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Seitz, et al. Expires December 6, 2015 [Page 1] Internet-Draft ACE use cases June 2015 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." This Internet-Draft will expire on December 6, 2015. Copyright Notice Copyright (c) 2015 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Container monitoring . . . . . . . . . . . . . . . . . . 4 2.1.1. Bananas for Munich . . . . . . . . . . . . . . . . . 5 2.1.2. Authorization Problems Summary . . . . . . . . . . . 6 2.2. Home Automation . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. Controlling the Smart Home Infrastructure . . . . . . 7 2.2.2. Seamless Authorization . . . . . . . . . . . . . . . 7 2.2.3. Remotely letting in a visitor . . . . . . . . . . . . 7 2.2.4. Selling the house . . . . . . . . . . . . . . . . . . 8 2.2.5. Authorization Problems Summary . . . . . . . . . . . 8 2.3. Personal Health Monitoring . . . . . . . . . . . . . . . 9 2.3.1. John and the heart rate monitor . . . . . . . . . . . 10 2.3.2. Authorization Problems Summary . . . . . . . . . . . 11 2.4. Building Automation . . . . . . . . . . . . . . . . . . . 11 2.4.1. Device Lifecycle . . . . . . . . . . . . . . . . . . 12 2.4.2. Authorization Problems Summary . . . . . . . . . . . 14 2.5. Smart Metering . . . . . . . . . . . . . . . . . . . . . 15 2.5.1. Drive-by metering . . . . . . . . . . . . . . . . . . 15 2.5.2. Meshed Topology . . . . . . . . . . . . . . . . . . . 16 2.5.3. Advanced Metering Infrastructure . . . . . . . . . . 16 2.5.4. Authorization Problems Summary . . . . . . . . . . . 16 2.6. Sports and Entertainment . . . . . . . . . . . . . . . . 17 Seitz, et al. Expires December 6, 2015 [Page 2] Internet-Draft ACE use cases June 2015 2.6.1. Dynamically Connecting Smart Sports Equipment . . . . 17 2.6.2. Authorization Problems Summary . . . . . . . . . . . 18 2.7. Industrial Control Systems . . . . . . . . . . . . . . . 18 2.7.1. Oil Platform Control . . . . . . . . . . . . . . . . 19 2.7.2. Authorization Problems Summary . . . . . . . . . . . 19 3. Security Considerations . . . . . . . . . . . . . . . . . . . 19 3.1. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.2. Configuration of Access Permissions . . . . . . . . . . . 21 3.3. Design Considerations for Authorization Solutions . . . . 22 3.4. Proxies . . . . . . . . . . . . . . . . . . . . . . . . . 23 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 7. Informative References . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction Constrained devices [RFC7228] are nodes with limited processing power, storage space and transmission capacities. These devices are often battery-powered and in many cases do not provide user interfaces. Constrained devices benefit from being interconnected using Internet protocols. However, due to the devices' limitations, commonly used security protocols are not always easily applicable. As the devices are expected to be integrated in all aspects of everyday life, the application of adequate security mechanisms is required to prevent attackers from gaining control over data or functions important to our lives. This document comprises a collection of representative use cases for the application of authentication and authorization in constrained environments. These use cases aim at identifying authorization problems that arise during the lifecycle of a constrained device. Note that this document does not aim at collecting all possible use cases. We assume that the communication between the devices is based on the Representational State Transfer (REST) architectural style, i.e. a device acts as a server that offers resources such as sensor data and actuators. The resources can be accessed by clients, sometimes without human intervention (M2M). In some situations the communication will happen through intermediaries (e.g. gateways, proxies). Seitz, et al. Expires December 6, 2015 [Page 3] Internet-Draft ACE use cases June 2015 Where specific detail is necessary it is assumed that the devices communicate using CoAP [RFC7252], although most conclusions are generic. 1.1. Terminology Readers are required to be familiar with the terms defined in [RFC7228]. In addition, this document uses the following terminology: 2. Use Cases This section lists use cases involving constrained devices with certain authorization problems to be solved. Each use case first presents a general description of the application area, then one or more specific use cases, and finally a summary of the authorization- related problems users need to be solved. There are various reasons for assigning a function (client or server) to a device, e.g. which device initiates the conversation, how do devices find each other, etc. The definition of the function of a device in a certain use case is not in scope of this document. Readers should be aware that there might be reasons for each setting and that endpoints might even have different functions at different times. 2.1. Container monitoring The ability of sensors to communicate environmental data wirelessly opens up new application areas. The use of such sensor systems makes it possible to continuously track and transmit specific characteristics such as temperature, humidity and gas content during the transportation and storage of goods. The proper handling of the sensors in this scenario is not easy to accomplish. They have to be associated to the appropriate pallet of the respective container. Moreover, the goods and the corresponding sensors belong to specific customers. During the shipment to their destination the goods often pass stops where they are transloaded to other means of transportation, e.g. from ship transport to road transport. The transportation and storage of perishable goods is especially challenging since they have to be stored at a constant temperature and with proper ventilation. Additionally, it is very important for the vendors to be informed about irregularities in the temperature and ventilation of fruits to avoid the delivery of decomposed fruits Seitz, et al. Expires December 6, 2015 [Page 4] Internet-Draft ACE use cases June 2015 to their customers. The need for a constant monitoring of perishable goods has led to projects such as The Intelligent Container (http:// www.intelligentcontainer.com). 2.1.1. Bananas for Munich A fruit vendor grows bananas in Costa Rica for the German market. It instructs a transport company to deliver the goods via ship to Rotterdam where they are picked up by trucks and transported to a ripening facility. A Munich supermarket chain buys ripened bananas from the fruit vendor and transports them from the ripening facility to the individual markets with their own company trucks. The fruit vendor's quality management wants to assure the quality of their products and thus equips the banana boxes with sensors. The state of the goods is monitored consistently during shipment and ripening and abnormal sensor values are recorded (U1.2). Additionally, the sensor values are used to control the climate within the cargo containers (U1.1, U1.5, U1.7). The sensors therefore need to communicate with the climate control system. Since a wrong sensor value leads to a wrong temperature and thus to spoiled goods, the integrity of the sensor data must be assured (U1.2, U1.3). The banana boxes within a container will in most cases belong to the same owner. Adjacent containers might contain goods and sensors of different owners (U1.1). The personnel that transloads the goods must be able to locate the goods meant for a specific customer (U1.1, U1.6, U1.7). However the fruit vendor does not want to disclose sensor information pertaining to the condition of the goods to other companies and therefore wants to assure the confidentiality of this data (U1.4). Thus, the transloading personnel is only allowed to access logistic information (U1.1). Moreover, the transloading personnel is only allowed to access the data for the time of the transloading (U1.8). Due to the high water content of the fruits, the propagation of radio waves is hindered, thus often inhibiting direct communication between nodes [Jedermann14]. Instead, messages are forwarded over multiple hops (U1.9). The sensors in the banana boxes cannot always reach the Internet during the journey (U1.10). In the ripening facility bananas are stored until they are ready for selling. The banana box sensors are used to control the ventilation system and to monitor the degree of ripeness of the bananas. Ripe bananas need to be identified and sold before they spoil (U1.2, U1.8). Seitz, et al. Expires December 6, 2015 [Page 5] Internet-Draft ACE use cases June 2015 The supermarket chain gains ownership of the banana boxes when the bananas have ripened and are ready to leave the ripening facility. 2.1.2. Authorization Problems Summary o U1.1 Fruit vendors, transloading personnel and container owners want to grant different authorizations for their resources and/or endpoints to different parties. o U1.2 The fruit vendor requires the integrity of the sensor data that pertains the state of the goods for climate control and to ensure the quality of the monitored recordings. o U1.3 The container owner requires the integrity of the sensor data that is used for climate control. o U1.4 The fruit vendor requires the confidentiality of the sensor data that pertains the state of the goods and the confidentiality of location data, e.g., to protect them from targeted attacks from competitors. o U1.5 The fruit vendor may have several types of data that may be controlled by the same endpoint, e.g., sensor data and the data used for logistics. o U1.6 The fruit vendor and the transloading personnel require the integrity of the data that is used to locate the goods, in order to ensure that the good are correctly treated and delivered. o U1.7 The container owner and the fruit vendor may not be present at the time of access and cannot manually intervene in the authorization process. o U1.8 The fruit vendor, container owner and transloading company want to grant temporary access permissions to a party, in order to avoid giving permanent access to parties that are no longer involved in processing the bananas. o U1.9 Messages between client and resource server might need to be forwarded over multiple hops. o U1.10 The constrained devices might not always be able to reach the Internet. 2.2. Home Automation Automation of the home has the potential to become a big future market for the Internet of Things. One function of a home automation Seitz, et al. Expires December 6, 2015 [Page 6] Internet-Draft ACE use cases June 2015 system can be to connect devices in a house to the Internet and thus make them accessible and manageable remotely. Such devices might control for example heating, ventilation, lighting, home entertainment or home security. Such a system needs to accommodate a number of regular users (inhabitants, close friends, cleaning personnel) as well as a heterogeneous group of dynamically varying users (visitors, repairmen, delivery men). As the users are not typically trained in security (or even computer use), the configuration must use secure default settings, and the interface must be well adapted to novice users. 2.2.1. Controlling the Smart Home Infrastructure Alice and her husband Bob own a flat which is equipped with home automation devices such as HVAC and shutter control, and they have a motion sensor in the corridor which controls the light bulbs there (U2.5). Alice and Bob can control the shutters and the temperature in each room using either wall-mounted touch panels or an internet connected device (e.g. a smartphone). Since Alice and Bob both have a full- time job, they want to be able to change settings remotely, e.g. turn up the heating on a cold day if they will be home earlier than expected (U2.5). The couple does not want people in radio range of their devices, e.g. their neighbors, to be able to control them without authorization. Moreover, they don't want burglars to be able to deduce behavioral patterns from eavesdropping on the network (U2.8). 2.2.2. Seamless Authorization Alice buys a new light bulb for the corridor and integrates it into the home network, i.e. makes resources known to other devices in the network. Alice makes sure that the new light bulb and her other devices in the network get to know the authorization policies for the new device. Bob is not at home, but Alice wants him to be able to control the new device with his devices (e.g. his smartphone) without the need for additional administration effort (U2.7). She provides the necessary configurations for that (U2.9, U2.10). 2.2.3. Remotely letting in a visitor Seitz, et al. Expires December 6, 2015 [Page 7] Internet-Draft ACE use cases June 2015 Alice and Bob have equipped their home with automated connected door- locks and an alarm system at the door and the windows. The couple can control this system remotely. Alice and Bob have invited Alice's parents over for dinner, but are stuck in traffic and cannot arrive in time, while Alice's parents who use the subway will arrive punctually. Alice calls her parents and offers to let them in remotely, so they can make themselves comfortable while waiting (U2.1, U2.6). Then Alice sets temporary permissions that allow them to open the door, and shut down the alarm (U2.2). She wants these permissions to be only valid for the evening since she does not like it if her parents are able to enter the house as they see fit (U2.3, U2.4). When Alice's parents arrive at Alice's and Bob's home, they use their smartphone to communicate with the door-lock and alarm system (U2.5, U2.9). 2.2.4. Selling the house Alice and Bob have to move because Alice is starting a new job. They therefore decide to sell the house, and transfer control of all automated services to the new owners(U2.11). Before doing that they want to erase privacy relevant data from the logs of the automated systems, while the new owner is interested to keep some historic data e.g. pertaining to the behavior of the heating system (U2.12). 2.2.5. Authorization Problems Summary o U2.1 A home owner (Alice and Bob in the example above) wants to spontaneously provision authorization means to visitors. o U2.2 A home owner wants to spontaneously change the home's access control policies. o U2.3 A home owner wants to apply different access rights for different users. o U2.4 The home owners want to grant temporary access permissions to a party. o U2.5 The smart home devices need to be able to communicate with different control devices (e.g. wall-mounted touch panels, smartphones, electronic key fobs). o U2.6 The home owner wants to be able to configure authorization policies remotely. Seitz, et al. Expires December 6, 2015 [Page 8] Internet-Draft ACE use cases June 2015 o U2.7 Authorized Users want to be able to obtain access with little effort. o U2.8 The owners of the automated home want to prevent unauthorized entities from being able to deduce behavioral profiles from devices in the home network. o U2.9 Usability is particularly important in this scenario since the necessary authorization related tasks in the lifecycle of the device (commissioning, operation, maintenance and decommissioning) likely need to be performed by the home owners who in most cases have little knowledge of security. o U2.10 Home Owners want their devices to seamlessly (and in some cases even unnoticeably) fulfill their purpose. The administration effort needs to be kept at a minimum. o U2.11 Home Owners want to be able to transfer ownership of their automated systems when they sell the house. o U2.12 Home Owners want to be able to sanitize the logs of the automated systems, when transferring ownership, without deleting important operational data. 2.3. Personal Health Monitoring The use of wearable health monitoring technology is expected to grow strongly, as a multitude of novel devices are developed and marketed. The need for open industry standards to ensure interoperability between products has lead to initiatives such as Continua Alliance (continuaalliance.org) and Personal Connected Health Alliance (pchalliance.org). Personal health devices are typically battery driven, and located physically on the user. They monitor some bodily function, such as e.g. temperature, blood pressure, or pulse. They are connected to the Internet through an intermediary base-station, using wireless technologies. Through this connection they report the monitored data to some entity, which may either be the user herself, or some medical personnel in charge of the user. Medical data has always been considered as very sensitive, and therefore requires good protection against unauthorized disclosure. A frequent, conflicting requirement is the capability for medical personnel to gain emergency access, even if no specific access rights exist. As a result, the importance of secure audit logs increases in such scenarios. Since the users are not typically trained in security (or even computer use), the configuration must use secure default settings, Seitz, et al. Expires December 6, 2015 [Page 9] Internet-Draft ACE use cases June 2015 and the interface must be well adapted to novice users. Parts of the system must operate with minimal maintenance. Especially frequent changes of battery are unacceptable. 2.3.1. John and the heart rate monitor John has a heart condition, that can result in sudden cardiac arrests. He therefore uses a device called HeartGuard that monitors his heart rate and his position (U3.7). In case of a cardiac arrest it automatically sends an alarm to an emergency service, transmitting John's current location (U3.1). This requires the device to be close to a wireless access point, in order to be able to get an Internet connection (e.g. John's smartphone). To ensure Johns safety, the device is expected to be in constant operation (U3.3, U3.6). The device includes some authentication mechanism, in order to prevent other persons who get physical access to it from acting as the owner and messing up the access control and security settings (U3.8). John can configure additional persons that get notified in an emergency, for example his daughter Jill. Furthermore the device stores data on John's heart rate, which can later be accessed by a physician to assess the condition of John's heart (U3.2). However John is a privacy conscious person, and is worried that Jill might use HeartGuard to monitor his location while there is no emergency. Furthermore he doesn't want his health insurance to get access to the HeartGuard data, or even to the fact that he is wearing a HeartGuard, since they might refuse to renew his insurance if they decided he was too big a risk for them (U3.8). Finally John, while being comfortable with modern technology and able to operate it reasonably well, is not trained in computer security. He therefore needs an interface for the configuration of the HeartGuard security that is easy to understand and use (U3.5). If John does not understand the meaning of a setting, he tends to leave it alone, assuming that the manufacturer has initialized the device to secure settings (U3.4). NOTE: Monitoring of some state parameter (e.g. an alarm button) and the position of a person also fits well into an elderly care service. This is particularly useful for people suffering from dementia, where the relatives or caregivers need to be notified of the whereabouts of the person under certain conditions. In this case it is not the patient that decides about access. Seitz, et al. Expires December 6, 2015 [Page 10] Internet-Draft ACE use cases June 2015 2.3.2. Authorization Problems Summary o U3.1 The wearer of an eHealth device (John in the example above) wants to pre-configure special access rights in the context of an emergency. o U3.2 The wearer of an eHealth device wants to selectively allow different persons or groups access to medical data. o U3.3 The Security measures could affect battery lifetime of the device and changing the battery is very inconvenient. o U3.4 Devices are often used with default access control settings. o U3.5 Wearers of eHealth devices are often not trained in computer use, and especially computer security. o U3.6 Security mechanisms themselves could provide opportunities for denial of service attacks on the device. o U3.7 The device provides a service that can be fatal for the wearer if it fails. Accordingly, the wearer wants the device to have a high degree of resistance against attacks that may cause the device to fail to operate partially or completely. o U3.8 The wearer of an eHealth device requires the integrity and confidentiality of the data measured by the device. 2.4. Building Automation Buildings for commercial use such as shopping malls or office buildings nowadays are equipped increasingly with semi-automatic components to enhance the overall living quality and to save energy where possible. This includes for example heating, ventilation and air condition (HVAC) as well as illumination and security systems such as fire alarms. Different areas of these buildings are often exclusively leased to different companies. However they also share some of the common areas of the building. Accordingly, a company must be able to control the light and HVAC system of its own part of the building and must not have access to control rooms that belong to other companies. Some parts of the building automation system such as entrance illumination and fire alarm systems are controlled either by all parties together or by a service company. Seitz, et al. Expires December 6, 2015 [Page 11] Internet-Draft ACE use cases June 2015 2.4.1. Device Lifecycle 2.4.1.1. Installation and Commissioning A building is hired out to different companies for office space. This building features various automated systems, such as a fire alarm system, which is triggered by several smoke detectors which are spread out across the building. It also has automated HVAC, lighting and physical access control systems. A vacant area of the building has been recently leased to company A. Before moving into its new office, Company A wishes to replace the lighting with a more energy efficient and a better light quality luminaries. They hire an installation and commissioning company C to redo the illumination. Company C is instructed to integrate the new lighting devices, which may be from multiple manufacturers, into the existing lighting infrastructure of the building which includes presence sensors, switches, controllers etc (U4.1). Company C gets the necessary authorization from the service company to interact with the existing Building and Lighting Management System (BLMS) (U4.4). To prevent disturbance to other occupants of the building, Company C is provided authorization to perform the commissioning only during non-office hours and only to modify configuration on devices belonging to the domain of Company A's space (U4.5). After installation (wiring) of the new lighting devices, the commissioner adds the devices into the company A's lighting domain. Once the devices are in the correct domain, the commissioner authorizes the interaction rules between the new lighting devices and existing devices like presence sensors (U4.7). For this, the commissioner creates the authorization rules on the BLMS which define which lights form a group and which sensors/switches/controllers are allowed to control which groups (U4.8). These authorization rules may be context based like time of the day (office or non-office hours) or location of the handheld lighting controller etc (U4.5). 2.4.1.2. Operational Company A's staff move into the newly furnished office space. Most lighting is controlled by presence sensors which control the lighting of specific group of lights based on the authorization rules in the BLMS. Additionally employees are allowed to manually override the lighting brightness and color in their office by using the switches or handheld controllers. Such changes are allowed only if the authorization rules exist in the BLMS. For example lighting in the corridors may not be manually adjustable. Seitz, et al. Expires December 6, 2015 [Page 12] Internet-Draft ACE use cases June 2015 At the end of the day, lighting is dimmed down or switched off if no occupancy is detected even if manually overridden during the day. On a later date company B also moves into the same building, and shares some of the common spaces with company A (U4.2, U4.9). On a really hot day James who works for company A turns on the air condition in his office. Lucy who works for company B wants to make tea using an electric kettle. After she turned it on she goes outside to talk to a colleague until the water is boiling. Unfortunately, her kettle has a malfunction which causes overheating and results in a smoldering fire of the kettle's plastic case. Due to the smoke coming from the kettle the fire alarm is triggered. Alarm sirens throughout the building are switched on simultaneously (using a broadcast or multicast) to alert the staff of both companies (U4.8). Additionally, the ventilation system of the whole building is closed off to prevent the smoke from spreading and to withdraw oxygen from the fire. The smoke cannot get into James' office although he turned on his air condition because the fire alarm overrides the manual setting by sending commands (broadcast or multicast) to switch off all the air conditioning. The fire department is notified of the fire automatically and arrives within a short time. After inspecting the damage and extinguishing the smoldering fire a fire fighter resets the fire alarm because only the fire department is authorized to do that (U4.4, U4.5). 2.4.1.3. Maintenance Company A's staff are annoyed that the lights switch off too often in their rooms if they work silently in front of their computer. Company A notifies the commissioning Company C about the issue and asks them to increase the delay before lights switch off (U4.4). Company C again gets the necessary authorization from the service company to interact with the BLMS. The commissioner's tool gets the necessary authorization from BMLS to send a configuration change to all lighting devices in Company A's offices to increase their delay before they switch off. At some point the service company wants to update the firmware of lighting devices in order to eliminate software bugs. Before accepting the new firmware, each device checks the authorization of the service company to perform this update. 2.4.1.4. Decommissioning Seitz, et al. Expires December 6, 2015 [Page 13] Internet-Draft ACE use cases June 2015 Company A has noticed that the handheld controllers are often misplaced and hard to find when needed. So most of the time staff use the existing wall switches for manual control. Company A decides it would be better to completely remove handheld controllers and asks Company C to decommission them from the lighting system (U4.4). Company C again gets the necessary authorization from the service company to interact with the BLMS. The commissioner now deletes any rules that allowed handheld controllers authorization to control the lighting (U4.3, U4.6). Additionally the commissioner instructs the BLMS to push these new rules to prevent cached rules at the end devices from being used. 2.4.2. Authorization Problems Summary o U4.1 The building owner and the companies want to be able to add new devices to their administrative domain (commissioning). o U4.2 The building owner and the companies want to be able to integrate a device that formerly belonged to a different administrative domain to their own administrative domain (handover). o U4.3 The building owner and the companies want to be able to remove a device from their administrative domain (decommissioning). o U4.4 The building owner and the companies want to be able to delegate selected administration tasks for their devices to others. o U4.5 The building owner and the companies want to be able to define context-based authorization rules. o U4.6 The building owner and the companies want to be able to revoke granted permissions and delegations. o U4.7 The building owner and the companies want to allow authorized entities to send data to their endpoints (default deny). o U4.8 The building owner and the companies want to be able to authorize a device to control several devices at the same time using a multicast protocol. o U4.9 The companies want to be able to interconnect their own subsystems with those from a different operational domain while keeping the control over the authorizations (e.g. granting and revoking permissions) for their endpoints and devices. Seitz, et al. Expires December 6, 2015 [Page 14] Internet-Draft ACE use cases June 2015 2.5. Smart Metering Automated measuring of customer consumption is an established technology for electricity, water, and gas providers. Increasingly these systems also feature networking capability to allow for remote management. Such systems are in use for commercial, industrial and residential customers and require a certain level of security, in order to avoid economic loss to the providers, vulnerability of the distribution system, as well as disruption of services for the customers. The smart metering equipment for gas and water solutions is battery driven and communication should be used sparingly due to battery consumption. Therefore the types of meters sleep most of the time, and only wake up every minute/hour to check for incoming instructions. Furthermore they wake up a few times a day (based on their configuration) to upload their measured metering data. Different networking topologies exist for smart metering solutions. Based on environment, regulatory rules and expected cost, one or a mixture of these topologies may be deployed to collect the metering information. Drive-By metering is one of the most current solutions deployed for collection of gas and water meters. 2.5.1. Drive-by metering A service operator offers smart metering infrastructures and related services to various utility companies. Among these is a water provider, who in turn supplies several residential complexes in a city. The smart meters are installed in the end customer's homes to measure water consumption and thus generate billing data for the utility company, they can also be used to shut off the water if the bills are not paid (U5.1, U5.3). The meters do so by sending and receiving data to and from a base station (U5.2). Several base stations are installed around the city to collect the metering data. However in the denser urban areas, the base stations would have to be installed very close to the meters. This would require a high number of base stations and expose this more expensive equipment to manipulation or sabotage. The service operator has therefore chosen another approach, which is to drive around with a mobile base-station and let the meters connect to that in regular intervals in order to gather metering data (U5.4, U5.5, U5.7). Seitz, et al. Expires December 6, 2015 [Page 15] Internet-Draft ACE use cases June 2015 2.5.2. Meshed Topology In another deployment, the water meters are installed in a building that already has power meters installed, the latter are mains powered, and are therefore not subject to the same power saving restrictions. The water meters can therefore use the power meters as proxies, in order to achieve better connectivity. This requires the security measures on the water meters to work through intermediaries (U5.8). 2.5.3. Advanced Metering Infrastructure A utility company is updating its old utility distribution network with advanced meters and new communication systems, known as an Advanced Metering Infrastructure (AMI). AMI refers to a system that measures, collects and analyzes usage, and interacts with metering devices such as electricity meters, gas meters, heat meters, and water meters, through various communication media either on request (on-demand) or on pre-defined schedules. Based on this technology, new services make it possible for consumers to control their utility consumption (U5.2, U5.6) and reduce costs by supporting new tariff models from utility companies, and more accurate and timely billing. The technical solution is based on levels of data aggregation between smart meters located at the consumer premises and the Meter Data Management (MDM) system located at the utility company (U5.8). For reasons of efficiency and cost, end-to-end connectivity is not always feasible, so metering data is stored and aggregated in various intermediate devices before being forwarded to the utility company, and in turn accessed by the MDM. The intermediate devices may be operated by a third party service operator on behalf of the utility company (U5.6). One responsibility of the service operator is to make sure that meter readings are performed and delivered in a regular, timely manner. An example of a Service Level Agreement between the service operator and the utility company is e.g. "at least 95 % of the meters have readings recorded during the last 72 hours". 2.5.4. Authorization Problems Summary o U5.1 Devices are installed in hostile environments where they are physically accessible by attackers (including dishonest customers). The service operator and the utility company want to make sure that an attacker cannot use data from a captured device to attack other parts of their infrastructure. o U5.2 The utility company wants to control which entities are allowed to send data to, and read data from their endpoints. Seitz, et al. Expires December 6, 2015 [Page 16] Internet-Draft ACE use cases June 2015 o U5.3 The utility company wants to ensure the integrity of the data stored on their endpoints. o U5.4 The utility company wants to protect such data transfers to and from their endpoints. o U5.5 The devices may have intermittent Internet connectivity. o U5.6 Neither the service operator nor the utility company are always present at the time of access and cannot manually intervene in the authorization process. o U5.7 When authorization policies are updated it is impossible, or at least very inefficient to contact all affected endpoints directly. o U5.8 Messages between endpoints may need to be stored and forwarded over multiple nodes. 2.6. Sports and Entertainment In the area of leisure time activities, applications can benefit from the small size and weight of constrained devices. Sensors and actuators with various functions can be integrated into fitness equipment, games and even clothes. Users can carry their devices around with them at all times. Usability is especially important in this area since users will often want to spontaneously interconnect their devices with others. Therefore the configuration of access permissions must be simple and fast and not require much effort at the time of access (preferably none at all). The required level of security will in most cases be low since security breaches will likely have less severe consequences. The continuous monitoring of data might however enable an attacker to create behavioral or movement profiles. Moreover, the aggregation of data can seriously increase the impact on the privacy of the users. 2.6.1. Dynamically Connecting Smart Sports Equipment Jody is a an enthusiastic runner. To keep track of her training progress, she has smart running shoes that measure the pressure at various points beneath her feet to count her steps, detect irregularities in her stride and help her to improve her posture and running style. On a sunny afternoon, she goes to the Finnbahn track near her home to work out. She meets her friend Lynn who shows her the smart fitness watch she bought a few days ago. The watch can Seitz, et al. Expires December 6, 2015 [Page 17] Internet-Draft ACE use cases June 2015 measure the wearer's pulse, show speed and distance, and keep track of the configured training program. The girls detect that the watch can be connected with Jody's shoes and then can additionally display the information the shoes provide. Jody asks Lynn to let her try the watch and lend it to her for the afternoon. Lynn agrees but doesn't want Jody to access her training plan (U6.4). She configures the access policies for the watch so that Jody's shoes are allowed to access the display and measuring features but cannot read or add training data (U6.1, U6.2). Jody's shoes connect to Lynn's watch after only a press of a button because Jody already configured access rights for devices that belong to Lynn a while ago (U6.3). Jody wants the device to report the data back to her fitness account while she borrows it, so she allows it to access her account temporarily. After an hour, Jody gives the watch back and both girls terminate the connection between their devices. 2.6.2. Authorization Problems Summary o U6.1 Sports equipment owners want to be able to grant access rights dynamically when needed. o U6.2 Sports equipment owners want the configuration of access rights to work with very little effort. o U6.3 Sports equipment owners want to be able to pre-configure access policies that grant certain access permissions to endpoints with certain attributes (e.g. endpoints of a certain user) without additional configuration effort at the time of access. o U6.4 Sports equipment owners to protect the confidentiality of their data for privacy reasons. 2.7. Industrial Control Systems Industrial control systems (ICS) and especially supervisory control and data acquisition systems (SCADA) use a multitude of sensors and actuators in order to monitor and control industrial processes in the physical world. Example processes include manufacturing, power generation, and refining of raw materials. Since the advent of the Stuxnet worm it has become obvious to the general public how vulnerable this kind of systems are, especially when connected to the Internet. The severity of these vulnerabilities are exacerbated by the fact that many ICS are used to control critical public infrastructure, such as power, water Seitz, et al. Expires December 6, 2015 [Page 18] Internet-Draft ACE use cases June 2015 treatment of traffic control. Nevertheless the economical advantages of connecting such systems to the Internet can be significant if appropriate security measures are put in place (U7.5). 2.7.1. Oil Platform Control An oil platform uses an industrial control system to monitor data and control equipment. The purpose of this system is to gather and process data from a large number of sensors, and control actuators such as valves and switches to steer the oil extraction process on the platform. Raw data, alarms, reports and other information are also available to the operators, who can intervene with manual commands. Many of the sensors are connected to the controlling units by direct wire, but the operator is slowly replacing these units by wireless ones, since this makes maintenance easier (U7.4). Some of the controlling units are connected to the Internet, to allow for remote administration, since it is expensive and inconvenient to fly in a technician to the platform (U7.3). The main interest of the operator is to ensure the integrity of control messages and sensor readings (U7.1). Access in some cases needs to be restricted, e.g. the operator wants wireless actuators only to accept commands by authorized control units (U7.2). The owner of the platform also wants to collect auditing information for liability reasons (U7.1). 2.7.2. Authorization Problems Summary o U7.1 The operator of the platform wants to ensure the integrity and confidentiality of sensor and actuator data. o U7.2 The operator wants to ensure that data coming from sensors and commands sent to actuators are authentic. o U7.3 Some devices do not have direct Internet connection. o U7.4 Some devices have wired connection while others use wireless. o U7.5 The execution of unauthorized commands in an ICS can lead to significant financial damage, and threaten the availability of critical infrastructure services. Accordingly, the operator wants a security solution that provides a very high level of security. 3. Security Considerations Seitz, et al. Expires December 6, 2015 [Page 19] Internet-Draft ACE use cases June 2015 As the use cases listed in this document demonstrate, constrained devices are used in various application areas. The appeal of these devices is that they are small and inexpensive. That makes it easy to integrate them into many aspects of everyday life. Therefore such devices will see vast amounts of valuable data passing through and might even be in control of important functions. These assets need to be protected from unauthorized access. Even seemingly innocuous data and functions should be protected due to possible effects of aggregation: By collecting data or functions from several sources, attackers might be able to gain insights or a level of control not immediately obvious from each of these sources on its own. Not only the data on the constrained devices themselves is threatened, the devices might also be abused as an intrusion point to infiltrate a network. Once an attacker gained control over the device, it can be used to attack other devices as well. Due to their limited capabilities, constrained devices appear as the weakest link in the network and hence pose an attractive target for attackers. This section summarizes the security problems highlighted by the use cases above and provides guidelines for the design of protocols for authentication and authorization in constrained RESTful environments. 3.1. Attacks This document lists security problems that users of constrained devices want to solve. Further analysis of attack scenarios is not in scope of the document. However, there are attacks that must be considered by solution developers. Because of the expected large number of devices and their ubiquity, constrained devices increase the danger from Pervasive Monitoring [RFC7258] attacks. As some of the use cases indicate, constrained devices may be installed in hostile environments where they are physically accessible (see Section 2.5). Protection from physical attacks is not in the scope of ACE, but should be kept in mind by developers of authorization solutions. Denial of service (DoS) attacks threaten the availability of services a device provides. E.g., an attacker can induce a device to perform steps of a heavy weight security protocol (e.g. Datagram Transport Layer Security (DTLS) [RFC6347]) before authentication and authorization can be verified, thus exhausting the device's system resources. This leads to a temporary or - e.g. if the batteries are drained - permanent failure of the service. For some services of constrained devices, availability is especially important (see Seitz, et al. Expires December 6, 2015 [Page 20] Internet-Draft ACE use cases June 2015 Section 2.3). Because of their limitations, constrained devices are especially vulnerable to denial of service attacks. Solution designers must be particularly careful to consider these limitations in every part of the protocol. This includes: o Battery usage o Number of message exchanges required by security measures o Size of data that is transmitted (e.g. authentication and access control data) o Size of code required to run the protocol o Size of RAM memory and stack required to run the protocol Another category of attacks that needs to be considered by solution developers is session interception and hijacking. 3.2. Configuration of Access Permissions o The access control policies need to be enforced (all use cases): The information that is needed to implement the access control policies needs to be provided to the device that enforces the authorization and applied to every incoming request. o A single resource might have different access rights for different requesting entities (all use cases). Rationale: In some cases different types of users need different access rights, as opposed to a binary approach where the same access permissions are granted to all authenticated users. o A device might host several resources where each resource has its own access control policy (all use cases). o The device that makes the policy decisions should be able to evaluate context-based permissions such as location or time of access (see e.g. Section 2.2, Section 2.3, Section 2.4). Access may depend on local conditions, e.g. access to health data in an emergency. The device that makes the policy decisions should be able to take such conditions into account. Seitz, et al. Expires December 6, 2015 [Page 21] Internet-Draft ACE use cases June 2015 3.3. Design Considerations for Authorization Solutions o Devices need to be enabled to enforce authorization policies without human intervention at the time of the access request (see e.g. Section 2.1, Section 2.2, Section 2.4, Section 2.5). o Authorization solutions need to consider that constrained devices might not have internet access at the time of the access request (see e.g. Section 2.1, Section 2.3, Section 2.5, Section 2.6). o It should be possible to update access control policies without manually re-provisioning individual devices (see e.g. Section 2.2, Section 2.3, Section 2.5, Section 2.6). Rationale: Peers can change rapidly which makes manual re- provisioning unreasonably expensive. o Authorization policies may be defined to apply to a large number of devices that might only have intermittent connectivity. Distributing policy updates to every device for every update might not be a feasible solution (see e.g. Section 2.5). o It must be possible to dynamically revoke authorizations (see e.g. Section 2.4). o The authentication and access control protocol can put undue burden on the constrained system resources of a device participating in the protocol. An authorization solutions must take the limitations of the constrained devices into account (all use cases, see also Section 3.1). o Secure default settings are needed for the initial state of the authentication and authorization protocols (all use cases). Rationale: Many attacks exploit insecure default settings, and experience shows that default settings are frequently left unchanged by the end users. o Access to resources on other devices should only be permitted if a rule exists that explicitly allows this access (default deny) (see e.g. Section 2.4). o Usability is important for all use cases. The configuration of authorization policies as well as the gaining access to devices must be simple for the users of the devices. Special care needs to be taken for home scenarios where access control policies have to be configured by users that are typically not trained in security (see Section 2.2, Section 2.3, Section 2.6). Seitz, et al. Expires December 6, 2015 [Page 22] Internet-Draft ACE use cases June 2015 3.4. Proxies In some cases, the traffic between endpoints might go through intermediary nodes (e.g. proxies, gateways). This might affect the function or the security model of authentication and access control protocols e.g. end-to-end security between endpoints with DTLS might not be possible (see Section 2.5). 4. Privacy Considerations Many of the devices that are in focus of this document register data from the physical world (sensors) or affect processes in the physical world (actuators), which may involve data or processes belonging to individuals. To make matters worse the sensor data may be recorded continuously thus allowing to gather significant information about an individual subject through the sensor readings. Therefore privacy protection is especially important, and Authentication and Access control are important tools for this, since they make it possible to control who gets access to private data. Privacy protection can also be weighted in when evaluating the need for end-to-end confidentiality, since otherwise intermediary nodes will learn the content of potentially sensitive messages sent between endpoints and thereby threaten the privacy of the individual that may be subject of this data. In some cases, even the possession of a certain type of device can be confidential, e.g. individuals might not want to others to know that they are wearing a certain medical device (see Section 2.3). The personal health monitoring use case (see Section 2.3) indicates the need for secure audit logs which impose specific requirements on a solution. Auditing is not in the scope of ACE. However, if an authorization solution provides means for audit logs, it must consider the impact of logged data for the privacy of all parties involved. Suitable measures for protecting and purging the logs must be taken during operation, maintenance and decommissioning of the device. 5. Acknowledgments The authors would like to thank Olaf Bergmann, Sumit Singhal, John Mattson, Mohit Sethi, Carsten Bormann, Martin Murillo, Corinna Schmitt, Hannes Tschofenig, Erik Wahlstroem, Andreas Baeckman, Samuel Erdtman, Steve Moore, and Thomas Hardjono for reviewing and/or contributing to the document. Also, thanks to Markus Becker, Thomas Poetsch and Koojana Kuladinithi for their input on the container monitoring use case. Seitz, et al. Expires December 6, 2015 [Page 23] Internet-Draft ACE use cases June 2015 Ludwig Seitz and Goeran Selander worked on this document as part of EIT-ICT Labs activity PST-14056. 6. IANA Considerations This document has no IANA actions. 7. Informative References [Jedermann14] Jedermann, R., Poetsch, T., and C. LLoyd, "Communication techniques and challenges for wireless food quality monitoring", Philosophical Transactions of the Royal Society A Mathematical, Physical and Engineering Sciences, May 2014. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, January 2012. [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, May 2014. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, June 2014. [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, May 2014. Authors' Addresses Ludwig Seitz (editor) SICS Swedish ICT AB Scheelevaegen 17 Lund 223 70 Sweden Email: ludwig@sics.se Stefanie Gerdes (editor) Universitaet Bremen TZI Postfach 330440 Bremen 28359 Germany Phone: +49-421-218-63906 Email: gerdes@tzi.org Seitz, et al. Expires December 6, 2015 [Page 24] Internet-Draft ACE use cases June 2015 Goeran Selander Ericsson Faroegatan 6 Kista 164 80 Sweden Email: goran.selander@ericsson.com Mehdi Mani Itron 52, rue Camille Desmoulins Issy-les-Moulineaux 92130 France Email: Mehdi.Mani@itron.com Sandeep S. Kumar Philips Research High Tech Campus Eindhoven 5656 AA The Netherlands Email: sandeep.kumar@philips.com Seitz, et al. Expires December 6, 2015 [Page 25]