One document matched: draft-gerdes-ace-a2a-01.xml

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<rfc ipr="trust200902" docName="draft-gerdes-ace-a2a-01" category="info">

  <front>
    <title abbrev="ace-a2a">Managing the Authorization to Authorize in the Lifecycle of a Constrained Device</title>

    <author initials="S." surname="Gerdes" fullname="Stefanie Gerdes">
      <organization>Universität Bremen TZI</organization>
      <address>
        <postal>
          <street>Postfach 330440</street>
          <city>Bremen</city>
          <code>D-28359</code>
          <country>Germany</country>
        </postal>
        <phone>+49-421-218-63906</phone>
        <email>gerdes@tzi.org</email>
      </address>
    </author>

    <date year="2015" month="September" day="11"/>

    <area>Security</area>
    <workgroup>ACE Working Group</workgroup>
    <keyword>Internet-Draft</keyword>

    <abstract>


<t>Constrained nodes are devices which are limited in terms of
processing power, memory, non-volatile storage and transmission
capacity. Due to these constraints, commonly used security protocols
are not easily applicable. Nevertheless, an authentication and
authorization solution is needed to ensure the security of these
devices.</t>

<t>During the lifecycle of a constrained device, responsibility for
managing authorization policies for the constrained device 
may change several times. To ensure the security of the
constrained devices, the authorization to authorize must be
transferred to the new principal in a secure way.</t>

<t>Resource-constrained nodes benefit from delegating defined authentication- and
authorization-related tasks to less-constrained devices called
Authorization Managers, thus limiting the hardware requirements of the
security solution for the constrained devices.</t>

<t>This document defines how security relationships between constrained
nodes and their Authorization Managers can be established and managed
in a RESTful way, thus providing for a flexible authorization solution
for the whole lifecycle of a constrained node.</t>



    </abstract>


  </front>

  <middle>


<section anchor="introduction" title="Introduction">

<t>As shown in <xref target="I-D.ietf-ace-actors"/>, constrained nodes can benefit
from being closely coupled to a less constrained node called
Authorization Server or Authorization Manager (AM). The AM helps its
constrained node with authentication and authorization tasks.
Authorization solutions such as the
delegated CoAP Authentication and
Authorization Framework (DCAF) <xref target="I-D.gerdes-ace-dcaf-authorize"/>
define the communication flow between client, server and
their respective Authorization Managers, thus relieving constrained
nodes from managing keys for numerous devices while ensuring that the
constrained devices are able to enforce the authorization policies of
their principals.</t>

<t>Since the constrained devices strongly rely on their Authorization
Managers for security-related tasks, the connection between the
constrained device and its respective AM needs to be especially
protected. This is particularly difficult at transitions between
different phases in the lifecycle of a constrained device. These
transitions often comprise a change of the device ownership and
therefore might often entail that the principal that controls the
authorization policies changes. One way of transferring this
authorization to authorize is to change which Authorization Manager is
responsible for a constrained device.</t>

<t>This document defines how the security relationship between a
constrained node and its Authorization
Manager can be managed in a RESTful way, thus providing for a flexible
authorization solution for the whole lifecycle of a constrained
device.</t>

</section>
<section anchor="terminology" title="Terminology">

<t>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”,
“SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this
document are to be interpreted as described in RFC 2119 <xref target="RFC2119"/>.</t>

<t><list style="symbols">
  <t>Readers should be familiar with the concepts and terminology
introduced in <xref target="I-D.ietf-ace-actors"/> and
<xref target="I-D.gerdes-ace-dcaf-authorize"/></t>
</list></t>

</section>
<section anchor="authorization-to-authorize" title="Authorization to Authorize">

<t>The Authorization Manager helps its constrained node to determine
the authorization of
another node, e.g. if it is allowed to access an item of interest or
to provide information about such an item. Principals can easily
configure authorization information on the AM since it has the
necessary user interface. 
AM provides the authorization information to the constrained node: It is
authorized to define authorizations.</t>

<t>The constrained node needs keying material to determine if the
authorization information was really provided by its AM. We call this
keying material K_AM. Depending on the authorization solution,
symmetric or asymmetric keys can be used. For symmetric solutions, the
constrained node and the AM share a key. For asymmetric solutions,
K_AM is AM’s public key.</t>

<t>K_AM is stored in a resource which we call AM-Key, e.g. /am/key. The
key belongs to a URI which is the address of the AM.
The URI is stored in resource that we call AM-URI,
e.g. /am/uri.</t>

<t>The AM-key resource needs special protection because the entity which
controls K_AM is in control of the constrained node. Therefore, the
AM-key resource MUST be access-protected and SHOULD be write-only.</t>

</section>
<section anchor="AM_assign" title="Assigning a new Authorization Manager">

<t>To assign a new AM to a constrained node, the AM-key resource must
be changed. In this case, the constrained node always acts as the
server, even if it is otherwise used as a client. The client
in this communication SHOULD be the new AM.</t>

<t>To change the value of a resource representation, a ticket is
needed. To change the AM-key (/am/key) and AM-URI (/am/uri) resources, the
client needs a ticket that authorizes it to use PUT on these
resources. There are three possibilities for a client to get this ticket:</t>

<t><list style="symbols">
  <t>request a ticket from the former AM.</t>
  <t>use a preconfigured ticket.</t>
</list></t>

<t>With the help of the ticket, the constrained device can determine that
request is authorized. In DCAF, it can additionally be used to
establish a DTLS session between client and server. The new K_AM and
the URI of the new AM can then be securely transmitted to the Server.</t>

<t>The new K_AM MUST NOT be disclosed to others. If the authorization
ticket is requested from the former AM, the client MUST NOT include
the new K_AM in the Access Request Message.</t>

<t>If the client is not the new AM, the new K_AM MUST be transmitted
to the new AM and removed from the client.</t>

<!-- TODO: Example for message exchange -->

</section>
<section anchor="authorization-transitions-in-the-lifecycle-of-constrained-nodes" title="Authorization Transitions in the Lifecycle of Constrained Nodes">

<t>The lifecycle of a constrained node can be roughly divided into
six phases. The device is created in the manufacturing
phase. Devices are then sold to customers who introduce them to their
networks during the commissioning phase. In the operation phase,
constrained nodes fullfill their purpose in life, sometimes alternated
with a maintenance phase. Some nodes are sold during their lifetime
and need to be decommissioned and recommissioned in the handover
phase. At the end of the node’s lifecycle, the node is decommissioned
in the decommissioning phase.</t>

<t>Apart from the operation phase, mechanisms for
changing the authorization to authorize are needed in every phase of
the lifecycle. </t>

<section anchor="manufacturing" title="Manufacturing">

<t>In the manufacturing phase, the manufacturer can choose one of the
following options for the initial key provisioning:</t>

<t><list style="symbols">
  <t>Provisioning with AM service: K_AM is provisioned to the new node
and the manufacturer provides an Authorization Manager service.</t>
  <t>Provisioning only: K_AM is provisioned to the new node but the
manufacturer does not provide an Authorization Manager service.</t>
  <t>No provisioning: No K_AM is provisioned to the newly manufactured
node.</t>
</list></t>

<t>In the provisioning with AM service case, the manufacturer provides an
own AM service. Future principals can use the AM service to request a
ticket for their own AM or might even continue to use the
manufacturer’s AM if they don’t want to maintain their own. The node’s
AM-URI resource is set to the URI of the manufacturer’s
AM. Additionally, the manufacturer configures the K_AM keying material
on the AM and the constrained node. Depending on the used solution
shared symmetric keys or asymmetric key pairs are used. For symmetric
solutions, a shared secret must be generated and provided to
constrained node and AM. Each constrained node SHOULD be provisioned
with an individual unique key. For asymmetric solutions, key pairs
must be generated on the constrained node and the AM. The AM’s public
key is stored as K_AM in the AM-key resource.</t>

<t>In the provisioning only case, the manufacturer does not provide an AM
service. The AM-key resource is set to the initial K_AM. The AM-URI
resource is left empty. K_AM has to be made available to the new
principal, e.g. by encoding it into a QR code and printing it onto a sheet
of paper which is delivered with the device, or onto the device
itself. K_AM SHOULD be kept secret.</t>

<t>In the no provisioning case, the AM-key resource is not initialized and MUST
be unprotected. The new principal will then be able to write an AM-key
into this resource without the need for an authorization ticket.</t>

</section>
<section anchor="commissioning" title="Commissioning">

<t>In the commissioning phase, the principal of the node has
changed. The new principal needs to be able to take over the control over
the node by defining authorization policies. To achieve this, principals
will either use the Authorization Manager service of the manufacturer
(if available) or need to assign a new Authorization Manager to the
node (see also <xref target="AM_assign"/>).</t>

<t>To assign a new Authorization Manager, the procedure described in
<xref target="AM_assign"/> is used.</t>

<t>The constrained node MUST end all existing communications and delete
all Tickets that were issued by the former AM.</t>

</section>
<section anchor="decommissioning" title="Decommissioning">

<t>If a device is discarded or sold, the principal of the node
changes. To make sure that nobody who gets hold of the device
afterwards is able to misuse it, permissions for the node must be
revoked.</t>

<t>The constrained node must be deregistered from the AM. AM MUST NOT
issue any new tickets for the constrained node and SHOULD revoke
tickets on communication partners of this node.</t>

<t>Already existing tickets and session keys have to be removed from the
decommissioned node.</t>

</section>
<section anchor="handover" title="Handover">

<t>A change of ownership of a node often entails that the relationship
between the former AM and the constrained node must be canceled.</t>

<t>The exchange of the AM consists of a decomissioning as described in
<xref target="decommissioning"/> followed by a commissioning as described in
<xref target="commissioning"/>. Before the decommissioning, one of the mechanisms
described in <xref target="AM_assign"/> for the commissioning MUST be used to
create an authorization ticket for assigning the new AM.</t>

</section>
<section anchor="maintenance" title="Maintenance">

<t>During the lifecycle of a constrained node, Authorization Managers
sometimes need to be exchanged, e.g. because they are replaced by a
newer model. In this case, the former AM should issue a ticket for the
new AM before it is decommissioned. The AM-Key SHOULD be deleted from
the old AS to prevent it from issuing new tickets before the AM-Key is
changed. Old tickets issued by the AM do not need to be revoked.</t>

</section>
</section>
<section anchor="security-considerations" title="Security Considerations">

<t><list style="symbols">
  <t>What do we do if the key for changing the AM is lost?</t>
  <t>K_AM must be protected. The entity that has K_AM is in control of the
constrained node.</t>
  <t>It might be difficult to protect a preconfigured K_AM.</t>
  <t>If the PSK is printed onto the device, everyone who has access to
the device can use it.</t>
  <t>If a new AM-key is transmitted this transmission must be protected
very well.</t>
</list></t>

</section>
<section anchor="iana-considerations" title="IANA Considerations">

<t>None</t>

</section>


  </middle>

  <back>

    <references title='Normative References'>





<reference  anchor='RFC2119' target='http://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized. This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>



<reference anchor='I-D.gerdes-ace-dcaf-authorize'>
<front>
<title>Delegated CoAP Authentication and Authorization Framework (DCAF)</title>

<author initials='S' surname='Gerdes' fullname='Stefanie Gerdes'>
    <organization />
</author>

<author initials='O' surname='Bergmann' fullname='Olaf Bergmann'>
    <organization />
</author>

<author initials='C' surname='Bormann' fullname='Carsten Bormann'>
    <organization />
</author>

<date month='March' day='9' year='2015' />

<abstract><t>This specification defines a protocol for delegating client authentication and authorization in a constrained environment for establishing a Datagram Transport Layer Security (DTLS) channel between resource-constrained nodes.  The protocol relies on DTLS to transfer authorization information and shared secrets for symmetric cryptography between entities in a constrained network.  A resource- constrained node can use this protocol to delegate authentication of communication peers and management of authorization information to a trusted host with less severe limitations regarding processing power and memory.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-gerdes-ace-dcaf-authorize-02' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-gerdes-ace-dcaf-authorize-02.txt' />
</reference>




    </references>

    <references title='Informative References'>





<reference anchor='I-D.ietf-ace-actors'>
<front>
<title>An architecture for authorization in constrained environments</title>

<author initials='S' surname='Gerdes' fullname='Stefanie Gerdes'>
    <organization />
</author>

<author initials='L' surname='Seitz' fullname='Ludwig Seitz'>
    <organization />
</author>

<author initials='G' surname='Selander' fullname='Goran Selander'>
    <organization />
</author>

<author initials='C' surname='Bormann' fullname='Carsten Bormann'>
    <organization />
</author>

<date month='August' day='25' year='2015' />

<abstract><t>Constrained-node networks are networks where some nodes have severe constraints on code size, state memory, processing capabilities, user interface, power and communication bandwidth (RFC 7228).  This document provides terminology, and elements of an architecture / a problem statement, for authentication and authorization in these networks.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-ietf-ace-actors-00' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-ace-actors-00.txt' />
</reference>




    </references>



  </back>
</rfc>