| ACE Working Group | L. Seitz, Ed. |
| Internet-Draft | SICS Swedish ICT AB |
| Intended status: Informational | S. Gerdes, Ed. |
| Expires: August 9, 2015 | Universität Bremen TZI |
| G. Selander | |
| Ericsson | |
| M. Mani | |
| Itron | |
| S. Kumar | |
| Philips Research | |
| February 05, 2015 |
ACE use cases
draft-ietf-ace-usecases-02
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 access control 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.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 9, 2015.
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
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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).
Where specific detail is necessary it is assumed that the devices communicate using CoAP [RFC7252], although most conclusions are generic.
Readers are required to be familiar with the terms defined in [RFC7228]. In addition, this document uses the following terminology:
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 principals 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.
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 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).
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. Additionally, the sensor values are used to control the climate within the cargo containers. 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. The banana boxes within a container will in most cases belong to the same principal. Adjacent containers might contain goods and sensors of different principals.
The personnel that transloads the goods must be able to locate the goods meant for a specific customer. 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. Thus, the transloading personnel is only allowed to access logistic information. Moreover, the transloading personnel is only allowed to access the data for the time of the transloading.
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. The sensors in the banana boxes cannot always reach the Internet during the journey.
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.
The supermarket chain gains ownership of the banana boxes when the bananas have ripened and are ready to leave the ripening facility.
Automation of the home has the potential to become a big future market for the Internet of Things. A home automation system connects devices in a house to the Internet and thus makes 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.
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.
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.
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.
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. She provides the necessary configurations for that.
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. Then Alice sets temporary permissions that allow them to open the door, and shut down the alarm. 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.
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.
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, 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.
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. In case of a cardiac arrest it automatically sends an alarm to an emergency service, transmitting John’s current location. 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).
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.
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.
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.
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. 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.
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.
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.
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.
Company C gets the necessary authorization from the service company to interact with the existing Building and Lighting Management System (BLMS). 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. 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. 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. 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.
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.
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. 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 broadcastor multicast) to alert the staff of both companies. 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.
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.
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.
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.
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. Additionally the commissioner instructs the BLMS to push these new rules to prevent cached rules at the end devices from being used.
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.
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. The meters do so by sending data to a base station. 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.
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.
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 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. Two possible intermediate levels are:
For reasons of efficiency and cost end-to-end connectivity is not always feasible, so metering data is stored in batches in DC for some time before being forwarded to the HES, and in turn accessed by the MDM. The HES and the DC units may be operated by a third party service operator on behalf of the utility company. One responsibility of the service operator is to make sure that meter readings are performed and delivered to the HES. 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”.
In the area of leisure time activities, applications can benefit from the small size and weight of constrained devices. Sensors and actuators with various functionalities can be integrated into fitness equipment, games and even clothes. Principals can carry their devices around with them at all times.
Usability is especially important in this area since principals 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 principals.
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 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. 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. 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.
After an hour, Jody gives the watch back and both girls terminate the connection between their devices.
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 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.
An oil platform uses an industrical 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.
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.
The main interest of the operator is to ensure the integrity of control messages and sensor readings. The access to some resources needs to be restricted to certain clients, e.g. the operator wants wireless actuators only to accept commands by authorized control units.
The owner of the platform also wants to collect auditing information for liability reasons.
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, the devices will be entrusted with vast amounts of valuable data or even control functions, that need to be protected from unauthorized access. Moreover, the aggregation of data must be considered: attackers might not only collect data from a single device but from many devices, thus increasing the potential damage.
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.
This document lists security problems that principals 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 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:
Another category of attacks that needs to be considered by solution developers is session interception and hijacking.
In some cases, the traffic between Client and Resource Server 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 Client and Resource Server with DTLS might not be possible (see Section 2.5).
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 a client and a resource server and thereby endanger 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. principals 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 the principal and other parties involved. Suitable measures for protecting and purging the logs must be taken during operation, maintenance and decommissioning of the device.
The authors would like to thank Olaf Bergmann, Sumit Singhal, John Mattson, Mohit Sethi, Carsten Bormann, Martin Murillo, Corinna Schmitt, Hannes Tschofenig, Erik Wahlstroem, and Andreas Backman for reviewing and/or contributing to the document. Also, thanks to Markus Becker, Thomas Pötsch and Koojana Kuladinithi for their input on the container monitoring use case.
Ludwig Seitz and Göran Selander worked on this document as part of EIT-ICT Labs activity PST-14056.
This document has no IANA actions.
| [Jedermann14] | Jedermann, R., Pötsch, 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. |