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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
                                                      September 16, 2013

                      Use cases for CoRE security


   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

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
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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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   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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

   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
   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

   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

   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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   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

   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

   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

   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

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

   o  U4.5 James must be able to control the air conditioning in his

   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

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

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],

   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

      *  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,

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

   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

   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

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6.  IANA Considerations

   This document has no IANA actions.

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7.  Informative References

              Shelby, Z., Hartke, K., and C. Bormann, "Constrained
              Application Protocol (CoAP)", draft-ietf-core-coap-18
              (work in progress), June 2013.

              Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
              Encryption (JWE)", draft-ietf-jose-json-web-encryption-16
              (work in progress), September 2013.

              Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", draft-ietf-jose-json-web-signature-16
              (work in progress), September 2013.

              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

   Email: ludwig@sics.se

   Stefanie Gerdes
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359

   Phone: +49-421-218-63906
   Email: gerdes@tzi.org

   Goeran Selander
   Faroegatan 6
   Kista  16480

   Email: goran.selander@ericsson.com

Seitz, et al.            Expires March 20, 2014                [Page 19]

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