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/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on December 6, 2015.
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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
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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).
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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
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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).
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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
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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
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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.
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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,
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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.
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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.
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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.
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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
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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.
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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).
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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.
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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
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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
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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
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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
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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.
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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).
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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.
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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
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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
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