CoRE Working Group L. Seitz
Internet-Draft SICS Swedish ICT AB
Intended status: Informational S. Gerdes
Expires: March 20, 2014 Universitaet Bremen TZI
G. Selander
Ericsson
September 16, 2013
Use cases for CoRE security
draft-seitz-core-sec-usecases-00
Abstract
This document presents use cases for security measures in scenarios
involving constrained RESTful devices. Special focus is placed on
access control and authentication. Where specific details are
relevant, it is assumed that the devices use CoAP as communication
protocol, however most conclusions apply generally.
A number of security requirements are derived from the use cases,
which are intended as a guideline for developing a comprehensive
authentication and authorization approach for this class of
scenarios.
Status of this Memo
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This Internet-Draft will expire on March 20, 2014.
Copyright Notice
Copyright (c) 2013 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Container monitoring . . . . . . . . . . . . . . . . . . . 4
2.1.1. Bananas for Munich . . . . . . . . . . . . . . . . . . 4
2.1.2. Requirements . . . . . . . . . . . . . . . . . . . . . 5
2.2. Home Automation . . . . . . . . . . . . . . . . . . . . . 5
2.2.1. Remotely letting in a visitor . . . . . . . . . . . . 5
2.2.2. Requirements . . . . . . . . . . . . . . . . . . . . . 6
2.3. Personal Health Monitoring . . . . . . . . . . . . . . . . 6
2.3.1. John and the heart rate monitor . . . . . . . . . . . 7
2.3.2. Requirements . . . . . . . . . . . . . . . . . . . . . 7
2.4. Building Automation . . . . . . . . . . . . . . . . . . . 8
2.4.1. Fire Alarm . . . . . . . . . . . . . . . . . . . . . . 8
2.4.2. Requirements . . . . . . . . . . . . . . . . . . . . . 9
2.5. Industrial Control Systems . . . . . . . . . . . . . . . . 9
2.5.1. Water treatment plant . . . . . . . . . . . . . . . . 10
2.5.2. Requirements . . . . . . . . . . . . . . . . . . . . . 10
3. Requirements From The Use Cases . . . . . . . . . . . . . . . 12
3.1. General Security Requirements . . . . . . . . . . . . . . 12
3.2. Authentication Requirements . . . . . . . . . . . . . . . 13
3.3. Access Control Requirements . . . . . . . . . . . . . . . 13
4. Security Considerations . . . . . . . . . . . . . . . . . . . 15
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7. Informative References . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
This document presents use cases in an attempt to analyze the
security requirements especially on authentication and access control
in an Internet of Things setting. This setting features constrained
devices [I-D.ietf-lwig-terminology] communicating over the Internet.
Some of these devices may have very low capacity in terms of memory
and processing power, and may additionally be limited by the fact
that they run on battery power.
These devices offer resources such as sensor data and actuators,
which are accessed by clients, that may be users or other devices.
Where specific detail is necessary it is assumed that the devices
communicate using the CoAP protocol [I-D.ietf-core-coap], although
most conclusions are generic. Currently CoAP proposes to use DTLS
[RFC6347] for authentication, and access control lists on the
devices, that specify which clients may initiate a DTLS connection.
One goal of this document is to point out use cases where this
approach is not satisfactory.
1.1. Terminology
Resource Server (RS): The constrained device which hosts resources
the Client wants to access.
Client (C): A device which wants to access a resource on the Resource
Server. This could also be a constrained device.
Resource Owner (RO): The subject who owns the resource and controls
its access permissions.
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2. Use Cases
This section lists use cases involving constrained devices with
security requirements. Each use case first presents a general
description of the application area, then one or more specific use
cases, and finally the resulting security requirements.
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 transmit specific characteristics such as temperature,
humidity and gas content during 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.
2.1.1. Bananas for Munich
A Munich supermarket chain buys bananas from a Costa Rican fruit
vendor. It instructs a transport company to deliver the goods via
ship to Rotterdam where they are picked up by their own company
trucks.
The supermarket's quality management wants to assure the quality of
their products and thus uses the fruit vendor's service of equipping
the bananas with sensors. The state of the goods is monitored
consistently during the shipment and abnormal sensor values are
recorded. Additionally, the sensor values are used to control the
climate within the cargo containers.
The personnel of the transport company and the supermarket's delivery
service has to be able to locate the proper goods and match them to
the corresponding customer. The state of the cargo must not be
disclosed to them, however.
When the goods arrive at the supermarket in Munich, their state is
checked.
If no anomalies occurred during the transport, the bananas are
admitted for sale.
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2.1.2. Requirements
o U1.1 The supermarket chain must be able to allow the transport
company and the delivery service to access the position data on
the monitoring devices. Other state information must not be
accessible.
o U1.2 The climate regulation system in the containers must be able
to access the monitoring devices' state information to regulate
the climate accordingly.
o U1.3 The integrity and availability of the sensor data must be
assured for proper operation of climate control.
o U1.4 The supermarket chain must be able to allow the supermarket's
quality management to access the recorded state information on the
monitoring devices.
o U1.5 The supermarket chain will not want other companies to be
able to read sensor information so the confidentiality of the
monitoring devices' state information must be assured.
2.2. Home Automation
Automation of the home, housework or household activity is propagated
as a future market for the Internet of Things. A home automation
system integrates electrical devices in a house with each other, such
as heating, ventilation, lighting, home entertainment and 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).
The security required by the systems integrated in a automated home
varies, however it is clear that the security system controlling e.g.
the doors, alarms, and other critical systems needs to be at least as
secure as for a comparable unautomated home.
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. Remotely letting in a visitor
Jane is the owner of an automated home, that allows her to remotely
control all electrical devices through a web interface or mobile
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application.
Jane has invited over her acquaintance Jeffrey for dinner, but is
stuck in traffic and can not arrive in time, while Jeffrey who uses
the subway arrives punctually. Jane calls Jeffrey and offers him to
let him in remotely, so he can make himself comfortable and use
Jane's home entertainment system.
Jeffrey downloads an application that lets him communicate with
Jane's home, and Jane remotely instructs the door to open for him,
and the alarm to shut down. She gives Jeffrey access to lighting and
HVAC and also limited access to the home entertainment system,
allowing Jeffrey to all services except those that are pay-per-use or
those that Jane has marked as private.
2.2.2. Requirements
o U2.1 Jane needs to be able to spontaneously provision
authentication means to Jeffrey
o U2.2 Jane must be able to spontaneously change the access control
policies
o U2.3 Jane needs to be able to apply different rights for different
devices and users
o U2.4 Jane must be able to apply local conditions (presence, time)
to authorizations, and the device (e.g. the door) needs to be able
to verify these conditions
o U2.5 The different devices in Jane's home need to be able to
communicate with each other and with different control devices
o U2.6 The configuration of Jane's home needs to be secure by
default
o U2.7 It must be easy for Jane to edit the access control policies
for her home
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.
These 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, either through an intermediary base-station or directly,
using wireless technologies. Through this connection they report the
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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. Also the
system must require very little maintenance, so e.g. 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. In case of a cardiac arrest it
automatically sends an alarm to an emergency service, transmitting
John's current location. The device also functions as a implanted
cardioverter defibrilator, i.e. it can deliver a shock in order to
try and normalize Johns heart rate.
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 rather private 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, since they might refuse to renew his
insurance if they decided he was too big a risk for them.
2.3.2. Requirements
o U3.1 John must be able to selectively allow different persons or
groups to access the position data on condition that there is an
emergency.
o U3.2 John must be able to selectively allow different persons or
groups to access the heart rate data.
o U3.3 John must be able to block access to specific persons or
groups, if he mistrusts them.
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o U3.4 The device must operate in a way that does not require
frequent battery changes
o U3.5 The device must ensure that both incoming and outgoing
communication is confidentiality and integrity protected
o U3.6 The device must have secure settings by default
o U3.7 The device's security settings must be easy to configure
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 save energy
where possible. This includes for example heating, ventilation and
air condition (HVAC) as well as illumination and fire alarm systems.
These buildings are often used by more than one company who share
some parts of the building while other areas are used by each of them
exclusively. 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 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.
The building automation system has to provide for a security
mechanism which allows for authentication and fine-grained
authorization.
2.4.1. Fire Alarm
The Companies A and B share an office building which is equipped with
a fire alarm system. It is triggered by several smoke detectors
which are spread out across the building.
It is a really hot day and 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 notified and alert the staff
of both companies. Additionally, the ventilation system of the whole
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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.
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.
2.4.2. Requirements
o U4.1 The building control devices of company A must be able to
interoperate with those of company B. The devices might be
produced by different vendors and might be operated by different
service providers.
o U4.2 Only the smoke detectors must be able to trigger an alarm.
o U4.3 The availability and integrity of the smoke detector's alarm
messages have to be assured.
o U4.4 Only the fire department must be able to reset the fire
alarm.
o U4.5 James must be able to control the air conditioning in his
office.
o U4.6 The emergency system must be able to automatically close off
the ventilation system.
o U4.7 During fire alarm, the personnel must not be allowed to
regulate the climate control.
o U4.8 No unauthorized device must be able to access building
control devices.
o U4.9 Since replacing devices in the building is very work
intensive and thus expensive (there are many devices, and some are
in places that are hard to access), the devices and their
batteries should function for a very long time without
maintenance.
2.5. 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
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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. These 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.
2.5.1. Water treatment plant
The communal water treatment plant of a mid-sized city is controlled
by a networked ICS. Spread across the city are numerous nodes,
sensors (e.g. pollution meters, pressure indicators) and actuators
(e.g. valves, pumps) communicating via a wireless network. Since the
range of the network is limited, many nodes communicate through
intermediary proxies that relay communications to the administration
clients of the ICS.
Jenny is a technician whose job it is to monitor the plant and take
appropriate measure, if abnormal conditions are detected (e.g. if
water pollution is detected, or the pressure in a pump reaches
critical levels).
When Jenny is on holiday or sick-leave, the service company sends a
replacement worker from a pool of available, qualified persons.
Joshuah is a young, computer savvy kid with too much time at his
hands. He spends time wardriving and stumbles upon the wireless
network, used by the plant's sensors and actuators. Joshuah tries to
interact with the devices on this network and manages to stall a
valve controlling water flow to a part of the city. Jenny quickly
discovers the intrusion and is able to take appropriate measures to
prevent damage to the value and quickly restore normal service
conditions.
2.5.2. Requirements
o U5.1 The Integrity of the messages sent between the nodes in the
ICS must be protected.
o U5.2 The nodes must be resilient to denial of service attacks.
o U5.3 The security measures must cope with the presence of
intermediary proxies between the Resource Server and the Client.
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o U5.4 Since most of the processing capacity of the nodes and the
network load capacity must go towards production tasks, the
security measures must use minimal resources, both on the network
and on the nodes.
o U5.5 Since replacement workers can spontaneously jump in for
Jenny, the system needs to be able to handle authorization updates
without re-provisioning each node individually.
o U5.6 After a replacement worker has finished taking care of the
system, the corresponding authorization and authentication means
need to be revoked remotely.
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3. Requirements From The Use Cases
This section lists requirements derived from the use cases above.
Note that not every single requirement applies to every Resource
Server, however protocols should allow for all of these requirements
to be fulfilled.
3.1. General Security Requirements
The following requirements refer to general security measures, not
directly linked to authentication and authorization which are listed
in detail in the next sections.
o Integrity, confidentiality and replay protection of the message
exchanges between the Resource Server, the Client and other
involved parties (U1.3, U1.5, U3.5, U4.3, U5.1).
This may be achieved by either establishing a secure channel (such
as e.g. DTLS [RFC6347]) or object security applied to the
payloads (e.g. JWS/JWE [I-D.ietf-jose-json-web-signature],
[I-D.ietf-jose-json-web-encryption]).
o Protect the Resource Server against denial of service (U3.4, U4.3,
U5.2) - Minimize the number of protocol steps that an attacker can
induce a Resource Server to perform without proper authentication
and authorization.
* Note well that for constrained devices this includes attacks
that aim to drain the battery of the target.
o Security measures must work when traffic from the Client to the
Resource Server goes through intermediary nodes (U5.3).
Rationale: In many deployments, there will be gateways, proxies,
firewalls etc. between a Client and a Resource Server. Security
measures should therefore not require the Client to be directly
connected to the Resource Server.
o Use minimal resources for security measures (U3.4, U4.9, U5.4)
* Minimize battery usage
+ Minimize message exchanges only for security
+ Minimize the size of authorization and authentication data
that is transmitted
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+ Minimize the size of required software libraries
+ Minimize memory and stack usage on the devices
o Enable security by default (U2.6, U3.6)
Rationale: Many attacks exploit insecure default settings, and
experience shows that default settings are rarely changed by the
end users. Therefore the protocols for constrained devices should
require secure modes of use by default.
o Interoperability (U1.1, U1.2, U2.5, U4.1)
Rationale: Resource Owners may interact with Clients from various
manufacturers and vice-versa. In order to function correctly the
security mechanisms need to work together. This is best achieved
by standardization
o Usability (U2.7, U3.7)
* Keep response times reasonable
* Make the security measures transparent for human users where
possible
* Make the administration of security as simple as possible
3.2. Authentication Requirements
o Enable mutual authentication between the Client and the Resource
Server (U1.1, U1.2, U2.1, U4.4, U4.5, U4.6)
o Provision authentication means to Clients and Resource Servers
(U1.1, U1.2, U2.1, U4.4, U4.5, U4.6, U5.5)
* Optionally allow for remote provisioning.
o Enable remote revocation of authentication means (U3.3, U4.9,
U5.6)
3.3. Access Control Requirements
o Enforce the access control policies of the Resource Owner (U1.1,
U1.2, U1.4, U3.1, U3.2, U4.2, U4.4, U4.5, U4.6, U4.8) - Provision
access control policies set by the Resource Owner to the Policy
Decision Point (which may be on the Resource Server or on another
trusted entity) [RFC2904]. - Apply the access control policies to
incoming requests (this may be done by the Resource Server or by
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another trusted entity).
o Do not send additional messages just for access control (U3.4,
U5.4) Rationale: Sending and receiving is a much bigger battery
drainer, compared to processing on the device.
o Apply different rights for different requesting entities (U1.1,
U1.2, U2.3, U4.2, U4.4, U4.5, U4.6) Rationale: In some cases
different types of users require different access rights, as
opposed to all-or-nothing access control.
o Allow for fine-grained access control (U1.1, U1.2, U4.2, U4.4,
U4.5, U4.6) Resource Servers can host several resources, and a
resource (e.g. an actuator) can have different settings. In some
cases access rights need to be different at this level of
granularity.
o Apply local conditions (U2.4, U3.1, U4.7) Access may depend on
local conditions e.g. access to health data in an emergency. The
Policy Decision Point must be able to take such conditions into
account.
o Enable policy updates without re-provisioning the device (U2.2,
U4.9, U5.5, U5.6) Rationale: Clients can change rapidly and re-
provisioning might be prohibitively expensive.
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4. Security Considerations
This document lists security requirements for constrained devices,
motivated by specific use cases. Therefore the whole document deals
with security considerations.
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5. Acknowledgments
The authors would like to thank Olaf Bergmann, and Mohit Sethi for
contributing to the discussion and giving helpful comments. Also,
thanks to Markus Becker for his input on the container monitoring use
case.
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6. IANA Considerations
This document has no IANA actions.
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7. Informative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., and C. Bormann, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-18
(work in progress), June 2013.
[I-D.ietf-jose-json-web-encryption]
Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
Encryption (JWE)", draft-ietf-jose-json-web-encryption-16
(work in progress), September 2013.
[I-D.ietf-jose-json-web-signature]
Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature-16
(work in progress), September 2013.
[I-D.ietf-lwig-terminology]
Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained Node Networks", draft-ietf-lwig-terminology-05
(work in progress), July 2013.
[RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L.,
Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and
D. Spence, "AAA Authorization Framework", RFC 2904,
August 2000.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
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Authors' Addresses
Ludwig Seitz
SICS Swedish ICT AB
Scheelevaegen 17
Lund 22370
Sweden
Email: ludwig@sics.se
Stefanie Gerdes
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63906
Email: gerdes@tzi.org
Goeran Selander
Ericsson
Faroegatan 6
Kista 16480
Sweden
Email: goran.selander@ericsson.com
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