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CoRE                                                     B. Greevenbosch
Internet-Draft                                       Huawei Technologies
Intended status: Informational                        September 06, 2013
Expires: March 10, 2014

Use cases and requirements for authentication and authorisation in CoAP


   This draft describes use cases and requirements for authenticated and
   authorised CoAP.  The draft especially focuses on threats and their


   Discussion and suggestions for improvement are requested, and should
   be sent to core@ietf.org.

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
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   This Internet-Draft will expire on March 10, 2014.

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   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Use cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Authorised and unauthorised devices . . . . . . . . . . .   3
     3.2.  Home security . . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  Illegal smart-meters  . . . . . . . . . . . . . . . . . .   4
     3.4.  Maintaining and extending a network of sensors and
           actuators . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.5.  Discovered compromised device . . . . . . . . . . . . . .   5
     3.6.  Vulnerability discovery in actuators in a chemical plant    5
     3.7.  Revocation of a non-compromised device  . . . . . . . . .   5
     3.8.  Mixing nodes from different vendors . . . . . . . . . . .   6
     3.9.  Privacy of medical communications . . . . . . . . . . . .   6
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Certificate authority . . . . . . . . . . . . . . . . . .   8
     5.2.  Expiry  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Time of revocation  . . . . . . . . . . . . . . . . . . .   8
   6.  Security considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   This draft describes use cases and requirements for secure
   authentication and authorisation, as well as their expiry and
   revocation, in CoAP.

   The draft consists of the following parts:

   o  The draft starts with several use cases.

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   o  A section with requirements related to the use cases follows.

   o  Discussion of the various security trade-offs that need to be made
      can be found in Section 5.

   The goal of the draft is to provide background material for usage
   when defining a solution for authorised CoAP.

3.  Use cases

3.1.  Authorised and unauthorised devices

   Company A produces sensor devices.  These devices are of high
   quality, and no vulnerabilities have been detected.  As such, they
   have been certified to be used in a wide area of applications.

   Company B produces also sensor devices.  However, these devices are
   of low quality, and have known security issues.  They failed the
   certification requirements.

   Company C is oblivious of this fact, and since it needs this kind of
   sensors to monitor its industrial process, it buys some to test.

   During installation of the sensors into Company C's monitoring
   network, the credentials of the sensors are verified by the system.
   The sensors from Company A install without problem.  However, for the
   sensors from Company B the authentication fails, and the installation
   of the sensors is refused.  The system informs the installation
   engineers about the reason of failure.

   Fortunately the authentication mechanism revealed that the sensors
   from Company B are not to be used.  This avoided a lot of trouble and
   potential security issues.

3.2.  Home security

   Henry has an advanced home security system.  The security system
   provides protection against burglary, as well as against fire.  It
   has sensors on doors, motion sensors, smoke detectors, cameras etc.
   It also has actuators for the electronic locks, a sprinkler system
   and actuators that can close the gas tap and cut the electricity.

   The system comes with tokens.  These tokens are used to turn on or
   off part of the system, and allow certain actions that need human
   interaction.  One of these actions is to open or close the front door
   lock.  Henry has provided a token to each of his family members.

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   The system has a solid authorisation and authentication model,
   ensuring that only Henry and his family's tokens can drive the
   system.  Even though the tokens can be bought in a regular store,
   only tokens that Henry has approved can be used in the system.

   Certain peripherals allow different access rights to different
   entities.  For example, the electricity closure can only be set by
   Henry and the master system, whereas its on/off status can be read by
   all family members.

   All peripherals are certified by an impartial certification body,
   which has specified minimum security requirements.  In this way,
   Henry is assured that when he adds a new peripheral and it is
   accepted by the system, it can be deemed reliable.

3.3.  Illegal smart-meters

   An electricity company depends on smart-meters to measure energy
   usage of the households it servers.  The gathered information is used
   for several purposes, billing being one of them.

   On the black market, there appear illegal smart-meters that only
   report 75% of the actual electricity usage.  These smart-meters are
   based on a clone of a valid public key.

   Once the electricity company discovers this, it revokes the
   associated public key, thereby ensuring that the illegal meters
   cannot be installed anymore.

3.4.  Maintaining and extending a network of sensors and actuators

   An agricultural company uses an IP network to ensure an optimal
   climate for the vegetables they grow in their green houses.  Sensors
   do measurements about e.g. humidity and sunlight, whereas actuators
   can drive artificial rain and supporting light.  A central controller
   is responsible for processing the sensor readings and driving the
   actuators accordingly.

   Sometimes, a sensor or actuator needs replacement as part of the
   normal maintenance cycle.  This is a routine task for the associated
   engineer, and involves simply disconnecting the old apparatus and
   connecting a new one.  The rest of the installation to the network
   happens automatically.

   As the agricultural company is doing good business, it decides to
   expand.  It buys another piece of land, and modernises the green
   house that was already built on the land.  The modernisation includes
   installing new sensors and actuators, which are seamlessly integrated

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   into the already existent network, such that they can work with the
   central controller too.

   The use case illustrates the need to be able to automatically install
   and update network nodes in an existing network.  It is also
   important to note, that installation of the network nodes includes
   proper authentication and authorisation.  After all, the agricultural
   company does not want outsiders to be able to influence the climate
   in the green houses, for example by driving the actuators or
   modifying the sensor readings.

3.5.  Discovered compromised device

   Company A has a certain type of actuators installed throughout its
   building.  On a certain time, some of these actuators start behaving
   funny.  It turns out that some hackers have been able to access the
   sensors, and drive them as they wish.

   Company A can't de-install the actuators immediately, after all, they
   are installed everywhere in the building.  Instead Company A has the
   actuators revoked, and then can replace them on a less hasty

3.6.  Vulnerability discovery in actuators in a chemical plant

   A chemical plant deploys sensors for the several properties of the
   substance being produced, and actuators that start certain processes
   when the substance is ready for the next step.

   A vulnerability in certain of the actuators is discovered; it would
   allow unauthorised third parties to take over the actuators and start
   processes at their will.

   After the discovery of the vulnerability, the chemical plant pro-
   actively de-activates the actuators and revokes their keys.  It then
   makes sure the vulnerability is resolved as quickly as possible, such
   that normal production can resume.

3.7.  Revocation of a non-compromised device

   Jack worked at the IT department of company E.

   However, due to a conflict with the company, Jack has been fired.
   When leaving, he smuggled out some tokens used to control several of
   the company's peripherals.

   When the company realises it misses the tokens, it revokes them to
   ensure they cannot be used to control the peripherals anymore.

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   Jack fails to wreak havoc as his revenge, and neither can he sell the
   tokens to other adversaries.

3.8.  Mixing nodes from different vendors

   A weather analysis and forecast agency needs global coverage for
   collection of temperature and air-pressure data.  It has contracts
   with several local authorities and companies for the placement of
   their sensors.

   For both logistic and economic reasons, the weather agency does not
   want to rely on one particular type of sensor from a single vendor.
   Instead, it wants to allow different sensors from different vendors,
   as long as these sensors meet certain criteria concerning precision,
   response time and reliability.

   To ensure the criteria are met, the weather agency performs several
   tests with new candidate sensors.  When the sensors pass the tests,
   the agency allows their usage in its network.  When the sensors fail
   the tests, the agency is ensured that they cannot be used for
   collecting data, lest the quality of the agency's analysis and
   forecast suffer from data of bad quality.

   In this use case, the vendor pro-actively controls which sensor types
   can be used in their network.  It uses an authentication and
   authorisation mechanism to automatically ensure that only those types
   it has approved can be installed.  The use case illustrates the need
   for interoperability in authentication between nodes manifactured by
   different vendors, as well as the need to exclude nodes that are not
   authorised to join the network.

3.9.  Privacy of medical communications

   Mr P has developed a heart problem.  To diagnose and monitor the
   condition of Mr P's heart, his cardiologist has requested Mr P to
   wear a sensor during the day.  The sensor measures the heartbeat and
   other vital functions.  The sensor transmits this information to the
   hospital, generally once every day.  When needed, e.g. when a
   situation occurs that requires extra attention, the sensor can also
   send information ad-hoc.

   Protecting the integrity of the sensor readings is important, even
   when it is unlikely that an adversary will tamper with the sensor
   readings.  After all, doing so would constitute a serious crime.
   Protecting Mr P's privacy adds significantly to the value of a solid
   security model in this use case.  In any case eavesdropping needs to
   be prevented, and that includes man-in-the-middle attacks.

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4.  Requirements

   This section lists requirements associated with authentication and
   authorisation in CoAP:

   1.   It SHALL be possible to verify the binding between the key and
        the entity associated with it.

   2.   It SHALL be possible to verify whether an entity is authorised
        to establish the connection.

   3.   It SHALL be possible to specify authorisation for a specific

   4.   It SHOULD be possible to specify authorisation based on the
        message type.

   5.   It SHALL NOT be possible for an unauthorised third party to
        establish a cryptographic relationship.

   6.   There SHALL be a mechanism that allows revocation of previously
        granted authorisation.

   7.   It SHALL be possible for a receiver to determine whether a key
        has been revoked.

   8.   It SHALL be possible to perform authentication, authorisation
        and revocation verification fully automatically.

   9.   The verification technology MUST NOT require much complexity on
        constrained entities.

   10.  The verification mechanism SHALL be scalable, allowing
        potentially millions of entities to verify authentication and

   11.  It SHOULD be possible to specify an expiry date for keys and/or

   12.  It SHALL be possible to revoke compromised keys.

   13.  Revocation SHALL NOT require physically unplugging the device.

   14.  There SHALL be protection against an unauthorised third party
        spoofing authorisation and/or revocation of keys and entities.

   15.  There SHOULD be protection against denial of service (DoS)
        attacks, as far as it is feasible.

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5.  Discussion

   In this section, we discuss the various trade-offs that need to be
   made, and implications they may have.

5.1.  Certificate authority

   Much of a traditional Public Key Infrastructure depends on a
   certificate authority.  The certificate authority (CA) signs the
   certificate of the device, or an intermediate certificate that signs
   the certificate of the device.

   This creates islands of trust, in which the CA has the power to
   revoke any key on its island.  Interoperability between devices of
   different CAs may still be possible, depending on which CAs the
   entities trust apart from their own CA.

5.2.  Expiry

   X.509 certificates [X.509] contain an expiry date.  This means that
   the certificates automatically become invalid after a time has
   passed.  Should the device's lifetime be longer than the validity
   period of the certificate, then the certificate has to be updated.

   The expiry date has the advantage that there is no need to keep track
   of revoked certificates infinitely.  After the certificate's
   expiration, the revocation status can be forgotten.

   However a major draw-back is that a mechanism is needed to update
   expired certificates, provided that the entities holding them should
   continue to be used.

5.3.  Time of revocation

   Authentication and revocation are normally checked when two entities
   meet each other for the first time.  But how about entities that are
   to be revoked later?

   The dealings with this highly depends on the security requirements of
   the employed system.  For example, home light-switches may have less
   stringent security requirements than actuators in a chemical plant.
   In the former, a revocation mechanism for deployed devices may not be
   needed, whereas in the latter it is essential.

6.  Security considerations

   This whole draft concerns security considerations.  It indicates use
   cases and requirements for authentication, authorisation and

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   associated expiry and revocation.  In addition it discusses several
   of the associated details and trade-offs.

   We refer to the rest of the draft for the complete picture.

7.  IANA considerations

   No IANA requests are required for this document.

8.  Acknowledgements

   Thanks to Rene Struik and Kepeng Li for their valuable feedback.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2.  Informative References

   [X.509]    , "Information technology - Open Systems Interconnection -
              The Directory: Public-key and attribute certificate
              frameworks.  ", ITU-T Recommendation X.509, ISO/IEC
              9594-8:2005, 2005.

Author's Address

   Bert Greevenbosch
   Huawei Technologies Co., Ltd.
   Huawei Industrial Base
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Phone: +86-755-28978088
   Email: bert.greevenbosch@huawei.com

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