One document matched: draft-gerdes-ace-tasks-00.xml
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<rfc ipr="trust200902" docName="draft-gerdes-ace-tasks-00" category="info">
<front>
<title abbrev="ace-tasks">Authorization-Related Tasks in Constrained Environments</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="29"/>
<area>Security</area>
<workgroup>ACE Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>Constrained nodes are small 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>Due to the limitations of the constrained nodes it is especially
important to develop a light-weight security solution which is
adjusted to the relevant security objectives of each participating
party in this environment. Necessary security measures must be
identified and applied where needed.</t>
<t>In this document, the required security related tasks are identified
as guidance for the development of authentication and authorization
solutions for constrained environments.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>Constrained nodes are small devices with limited abilities which in
many cases are made to fulfill a single simple task. They have limited
hardware resources such as processing power, memory, non-volatile storage and
transmission capacity and additionally in most cases do not have user
interfaces and displays. Due to these constraints, commonly used
security protocols are not always easily applicable.</t>
<t>Constrained nodes are expected to be integrated in all aspects of
everyday life and thus will be entrusted with vast amounts of
data. Without appropriate security mechanisms attackers might gain
control over things relevant to our lives. Authentication and
authorization mechanisms are therefore
prerequisites for a secure Internet of Things.</t>
<t>The limitations of the constrained nodes ask for security mechanisms
which take the special characteristics of constrained environments
into account. Therefore, it is crucial to identify the
tasks which must be performed to meet the security requirements in
constrained scenarios.</t>
<t>In this document, the required authorization-related tasks are identified
as guidance for the development of authentication and authorization
solutions for constrained environments.</t>
<section anchor="terminology" title="Terminology">
<t>Readers are required to be familiar with the terms and concepts
defined in <xref target="RFC4949"/> and <xref target="I-D.ietf-ace-actors"/>.</t>
</section>
</section>
<section anchor="ps" title="Problem Statement">
<t>The scenario this document addresses can be summarized as
follows:</t>
<t><list style="symbols">
<t>C wants to access R on a S.</t>
<t>A priori, C and S do not necessarily know each other and have no security
relationship.</t>
<t>C and / or S are constrained.</t>
</list></t>
<figure title="Basic Scenario" anchor="figbasic"><artwork><![CDATA[
------- -------
| C | -- requests resource ---> | S |
------- <-- provides resource--- -------
]]></artwork></figure>
<!-- graphic: request.png -->
<t>The security requirements of any specific version of this scenario
will include one or more of:</t>
<t><list style="symbols">
<t>Rq0.1: No unauthorized entity has access to (or otherwise
gains knowledge of) R.</t>
<t>Rq0.2: C is exchanging status updates of a resource only with
authorized resources. (When C attempts to access R, that access
reaches an authorized R).</t>
</list></t>
<t>Rq0.1 requires authorization on the server side while Rq0.2 requires
authorization on the client side.</t>
</section>
<section anchor="task_overview" title="Tasks">
<t>This section gives an overview of the tasks which must be performed in
the given scenario (see <xref target="ps"/>) to meet any specific security requirements.</t>
<t>Either C or S or both of them
are constrained. Therefore tasks which must be conducted by either C
or S must be performable by constrained nodes.</t>
<section anchor="basic-scenario-tasks" title="Basic Scenario Tasks">
<t>This document does not assume a specific transfer protocol. We assume however,
that at least the following information is exchanged between the
client and the server:</t>
<t><list style="symbols">
<t>C transmits to S which resource it requests to access, the kind of
action it wants to perform on the resource, and the parameters
needed for the action.</t>
<t>S transmits to C the result of the attempted access.</t>
</list></t>
</section>
<section anchor="security-related-tasks" title="Security-Related Tasks">
<t>The reason for the communication is that C wants S to process some
information. S’ reaction to C’s access request might be processed by
C. The reason for using an authorization solution is to validate that
the entity that sent the information used for processing is authorized
to provide it.</t>
<t>To validate if a sender is authorized to send a received piece of
information, the receiver must determine the sender’s
authorization. Correspondingly, to validate if a receiver is allowed
to receive a message, the sender must determine its
authorization. This can only be achieved with the help of an
authentication mechanism.</t>
</section>
<section anchor="authn_tasks" title="Authentication-Related Tasks">
<t>Several steps must be conducted for authenticating certain attributes
of an entity and validating the authenticity of an information:</t>
<t><list style="numbers">
<t>Attribute binding: The attribute that shall be verifiable must be
bound to a verifier,
e.g. a key. To achieve this, an entity that is authorized to conduct the
attribute binding, the attribute binding authority, checks if an
entity actually has the attributes it claims to have and then
binds them to a verifier. The binding authority must provide some
kind of endorsement information which enables other entities to
validate this binding.</t>
</list></t>
<t>Note: The attribute binding can be conducted using either symmetric or
asymmetric cryptography.</t>
<t><list style="numbers">
<t>Verifier validation: The entity that wants to authenticate the
source of an information checks the attribute-verifier-binding
using the endorsement provided by the attribute binding authority.</t>
<t>Authentication: The verifier is used for authenticating the source
of a data item, i.e. it is checked whether the data item is bound
to the verifier. Thus the attributes of the source can be determined.</t>
</list></t>
<t>Step 1 is addressed in <xref target="claim_val"/>. After the first step is
conducted, step 2 and step 3 can be performed when needed. They must
be performed together and thus are examined together as well. <!--
{{val_endorse}} introduces the tasks for step 2. --> Tasks for step 2
and 3 are Information authenticity (see <xref target="inf_authn"/>) and secure
communication (see <xref target="secure_comm"/>).</t>
</section>
<section anchor="authz_tasks" title="Authorization-Related Tasks">
<t>Several steps must be conducted for explicit authorization:</t>
<t><list style="numbers">
<t>Configuration of authorization information: The respective principals
(COP and ROP) must configure the authorization information according
to their authorization policy. An authorization information must
contain one or more permissions and the attribute an entity must
have to apply to this authorization.</t>
<t>Obtaining authorization information: Authorization information
must be made available to the entity which enforces the
authorization.</t>
<t>Authorization validation: The authorization of an entity with
certain attributes must be confirmed by applying the request in
conjunction with authenticated attributes to the policy provided
by the authorization information.</t>
<t>Authorization enforcement: According to the result of the
authorization validation the access to a resource is granted or
denied.</t>
</list></t>
<t>Tasks for step 1 are defined in <xref target="config_authz"/>. <xref target="obtain_authz"/>
addresses step 2. After step 1 and step 2 are conducted, step 3 and
step 4 can be performed when needed. Step 3 and step 4 must be
performed together and thus are examined together. <xref target="authz_val"/>
introduces tasks for these steps.</t>
</section>
</section>
<section anchor="actors" title="Actors">
<t>This section describes how the tasks defined in <xref target="tasks"/> are mapped
to the various actors in the architecture (see also
<xref target="I-D.ietf-ace-actors"/>). An
actor consists of a set of tasks and additionally has an security
domain (client domain or server domain) and a level (constrained,
principal, less-constrained). Tasks are assigned to actors according
to their security domain and required level.</t>
<t>Note: Actors are a concept to understand the security requirements for
constrained devices. The architecture of an actual solution might
differ as long as the security requirements that derive from the
relationship between the identified actors are considered. Several actors
might share a single device or even be combined in a single piece of software.
Interfaces between actors may be realized as protocols or be internal
to such a piece of software.</t>
<t>The concept of actors is used to assign the tasks defined in <xref target="tasks"/>
to logical functional entities.</t>
<section anchor="cla" title="Constrained Level Actors">
<t>As described in the problem statement (see <xref target="ps"/>), either C or S or both of
them may be located on a constrained node. We therefore define that C
and S must be able to perform their tasks even if they are located on
a constrained node. Thus, C and S are considered to be Constrained
Level Actors.</t>
<t>C performs the following tasks:</t>
<t><list style="symbols">
<t>Negotiate means for secure communication (Task TSecureComm, see
<xref target="secure_comm"/>).</t>
<t>Validate that an entity is an authorized source for R (Task
TValSourceAuthz, see <xref target="authz_val"/>).</t>
<t>Securely transmit an access request (Task TSendReq, see <xref target="send_info"/>).</t>
<t>Validate that the response to an access request is authentic (Task
TAuthnResp, see <xref target="inf_authn"/>).</t>
<t>Process the response to an access request (Task TProcResp, see
<xref target="proc_info"/>).</t>
</list></t>
<t>S performs the following tasks:</t>
<t><list style="symbols">
<t>Negotiate means for secure communication (Task TSecureComm, see
<xref target="secure_comm"/>).</t>
<t>Validate the authenticity of an access request (Task TAuthnReq, see
<xref target="inf_authn"/>).</t>
<t>Validate the authorization of the requester to access the requested
resource as requested (Task TValAccessAuthZ, see <xref target="authz_val"/>).</t>
<t>Process an access request (Task TProcReq, see <xref target="proc_info"/>).</t>
<t>Securely transmit a response to an access request (Task
TSendResp, see <xref target="send_info"/>).</t>
</list></t>
<t>R is an item of interest such as a sensor or actuator value. R is
considered to be part of S and not a separate actor. The device
on which S is located might
contain several resources of different ROPs. For
simplicity of exposition, these resources are described as if they had
separate S.</t>
<t>As C and S do not necessarily know each other they might belong to
different security domains.</t>
<!-- Graphic: constrained_level_small.png -->
<figure title="Constrained Level Actors" anchor="figcl"><artwork><![CDATA[
------- -------
| C | -- requests resource ---> | S | Constrained Level
------- <-- provides resource--- -------
]]></artwork></figure>
</section>
<section anchor="principal-level-actors" title="Principal Level Actors">
<t>Our objective is that C and S are under control of principals in the physical world, the Client Overseeing Principal (COP)
and the Resource Overseeing Principal (ROP) respectively. The principals decide about the
security policies of their respective endpoints and belong to the same
security domain.</t>
<t>COP is in charge of C, i.e. COP specifies security policies for C,
e.g. with whom C is allowed to communicate. By definition, C and COP
belong to the same security domain.</t>
<t>COP must fulfill the following task:</t>
<t><list style="symbols">
<t>Configure for C authorization information for sources for R (Task
TConfigSourceAuthz, see <xref target="config_authz"/>).</t>
</list></t>
<t>ROP is in charge of R and S. ROP specifies authorization policies for R
and decides with whom S is allowed to communicate. By definition, R, S and ROP
belong to the same security domain.</t>
<t>ROP must fulfill the following task:</t>
<t><list style="symbols">
<t>Configure for S authorization information for accessing R (Task
TConfigAccessAuthz, see <xref target="config_authz"/>).</t>
</list></t>
<!-- Graphic security_domains_owners.png -->
<figure title="Constrained Level Actors and Principal Level Actors" anchor="figclandpl"><artwork><![CDATA[
------- -------
| COP | | ROP | Principal Level
------- -------
| |
in charge of in charge of
| |
V V
------- -------
| C | -- requests resource ---> | S | Constrained Level
------- <-- provides resource--- -------
]]></artwork></figure>
</section>
<section anchor="lcl" title="Less-Constrained Level Actors">
<t>Constrained level actors
can only fulfill a limited number of tasks and may not have network
connectivity all the time. To relieve them from
having to manage keys for numerous endpoints and conducting
computationally intensive tasks, another complexity level for actors is
introduced. An actor on the less-constrained level belongs to the
same security domain as its respective constrained level actor. They
also have the same principal.</t>
<t>The Client Authorization Server (CAM) belongs to the same security domain as
C and COP. CAM acts on behalf of COP. It assists C in authenticating S
and determining if S is an authorized source for R. CAM can do that
because for C, CAM is the authority for claims about S.</t>
<t>CAM performs the following tasks:</t>
<t><list style="symbols">
<t>Validate on the client side that an entity has certain attributes
(Task TValSourceAttr, see <xref target="claim_val"/>).</t>
<t>Obtain authorization information about an entity from C’s principal (COP) and
provide it to C. (Task TObtainSourceAuthz, see <xref target="obtain_authz"/>).</t>
<t>Negotiate means for secure communication to communicate with C
(Task TSecureComm, see <xref target="secure_comm"/>).</t>
</list></t>
<t>The Authorization Server (SAM) belongs to the same security domain as
R, S and ROP. SAM acts on behalf of ROP. It supports S by
authenticating C and determining C’s permissions on R. SAM can do that
because for S, SAM is the authority for claims about C.</t>
<t>SAM performs the following tasks:</t>
<t><list style="symbols">
<t>Validate on the server side that an entity has certain attributes
(Task TValReqAttr, see <xref target="claim_val"/>).</t>
<t>Obtain authorization information about an entity from S’ principal (ROP) and
provide it to S (Task TObtainAccessAuthz, see <xref target="obtain_authz"/>).</t>
<t>Negotiate means for secure communication to communicate with S
(Task TSecureComm, see <xref target="secure_comm"/>).</t>
</list></t>
<!-- Graphic: eierlegendewollmilchsau2.png -->
<figure title="Overview of all Complexity Levels" anchor="figalllevels"><artwork><![CDATA[
------- -------
| COP | | ROP | Principal Level
------- -------
| |
in charge of in charge of
| |
V V
---------- ---------
| CAM | <- AuthN and AuthZ -> | SAM | Less-Constrained Level
---------- ---------
| |
authentication authentication
and authorization and authorization
support support
| |
V V
------- -------
| C | -- requests resource ---> | S | Constrained Level
------- <-- provides resource -- -------
]]></artwork></figure>
<t>For more detailed graphics please consult the PDF version.</t>
</section>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<t>None</t>
</section>
<section anchor="security-considerations" title="Security Considerations">
<t>This document discusses authorization-related tasks for constrained
environments and describes how these tasks can be mapped to actors in
the architecture.</t>
</section>
<section anchor="acknowledgments" title="Acknowledgments">
<t>The author would like to thank Carsten Bormann, Olaf Bergmann, Robert
Cragie and Klaus Hartke for their valuable input and feedback.</t>
</section>
</middle>
<back>
<references title='Informative References'>
<reference anchor='RFC4949' target='http://www.rfc-editor.org/info/rfc4949'>
<front>
<title>Internet Security Glossary, Version 2</title>
<author initials='R.' surname='Shirey' fullname='R. Shirey'><organization /></author>
<date year='2007' month='August' />
<abstract><t>This Glossary provides definitions, abbreviations, and explanations of terminology for information system security. The 334 pages of entries offer recommendations to improve the comprehensibility of written material that is generated in the Internet Standards Process (RFC 2026). The recommendations follow the principles that such writing should (a) use the same term or definition whenever the same concept is mentioned; (b) use terms in their plainest, dictionary sense; (c) use terms that are already well-established in open publications; and (d) avoid terms that either favor a particular vendor or favor a particular technology or mechanism over other, competing techniques that already exist or could be developed. This memo provides information for the Internet community.</t></abstract>
</front>
<seriesInfo name='FYI' value='36'/>
<seriesInfo name='RFC' value='4949'/>
<seriesInfo name='DOI' value='10.17487/RFC4949'/>
</reference>
<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>
<section anchor="tasks" title="List of Tasks">
<t>This section defines the tasks which must be performed in the given
scenario (see <xref target="ps"/>) starting from communication related tasks and
then deriving the required security-related tasks. An overview of the
tasks can be found in <xref target="task_overview"/>.</t>
<t>A task has the following structure:</t>
<t><list style="symbols">
<t>The name of the task which has the form TXXX</t>
<t>One or more Requirements (if applicable) of the form RqXXX</t>
<t>One or more Preconditions (if applicable) of the form PreXXX</t>
<t>One or more Postconditions (if applicable) of the form PostXXX</t>
</list></t>
<t>Requirements have to be met <spanx style="emph">while</spanx> performing the task. They derive
directly from the scenario (see <xref target="ps"/>) or from the security
requirements defined for the scenario. Preconditions have to be
fulfilled <spanx style="emph">before</spanx> conducting the task. Postconditions are the
<spanx style="emph">results</spanx> of the completed task.</t>
<t>We start our analysis with the processing tasks and define which preconditions
need to be fulfilled before these tasks can be conducted. We then
determine which tasks therefore need to be performed first (have
postconditions which match the respective preconditions).</t>
<t>Note: Regarding the communication, C and S are defined as entities
each having their set of attributes and a verifier which is bound to
these attributes. Attributes are not necessarily usable to identify an
individual C or S. Several entities might have the same attributes.</t>
<section anchor="basic-scenario" title="Basic Scenario">
<t>The intended result of the interaction between C and S is that C has
successfully accessed R. C gets to know that its access
request was successful by receiving the answer from S.</t>
<t>The transmission of information from C to S comprises two parts:
sending the information on one side and receiving and processing it on
the other. Security has to be considered at each of these steps.</t>
<section anchor="proc_info" title="Processing Information">
<t>The purpose of the communication between C and S is C’s intent to
access R. To achieve this, S must process the information about the
requested access and C
must process the information in the response to a requested access. The
request and the response might both contain resource values.</t>
<t>The confidentiality and integrity of R require that only
authorized entities are able to access R (see Rq0.1). Therefore, C and
S must check that the information is authentic and that the source of
the information is authorized to provide it, before the information
can be processed. C must validate that S is an authorized source for
R. S must validate that C is authorized to access R as requested.</t>
<t>If proxies are used, it depends on the type of proxy how they are
integrated into the communication and what kind of security
relationships need to be established.
A future version of this document will provide more
details on this topic. At this point we assume that C and S might
receive the information either from S or C directly or from a proxy
which is authorized to speak for the respective communication partner.</t>
<t><list style="symbols">
<t>Task TProcResp: Process the response to an access request.
Description: C processes the response to an access request
according to the reason for requesting the resource in the first
place. The response might include resource values or information
about the results of a request.
Requirements:
* RqProcResp.1: Is performed by C (derives from the problem
statement).
* RqProcResp.2: Must be performable by a constrained device
(derives from the problem statement: C and / or S are
constrained).
Preconditions:
* PreProcResp.1: A response to an access request was sent (see
<xref target="send_info"/>).
* PreProcResp.2 (required for Rq0.2): C validated that the
response to an access request is authentic, i.e. it stems
from the entity requested in TSendReq (see <xref target="send_info"/>),
i.e. S or an entity which is authorized to speak for S
(see <xref target="inf_authn"/>).
* PreProcResp.3 (required for Rq0.2): C validated that S or the
entity which is authorized to speak for S is an authorized
source for R (see <xref target="authz_val"/>).
Postcondition:
* PostProcResp.1: C processed the response.</t>
<t>Task TProcReq: Process an access request.
Description: S either performs an action on the resource according
to the information in the request, or determines the reason for not
performing an action.
Requirements:
* RqProcReq.1: Is performed by S.
* RqProcReq.2: Must be performable by a constrained device
(derives from the problem statement: C and / or S are
constrained).
Preconditions:
* PreProcReq.1: An access request was sent (see <xref target="send_info"/>).
* PreProcReq.2 (needed for Rq0.1): S validated that the
request is authentic, i.e. it stems from C or an entity
which is authorized to speak for C and is fresh. (see
<xref target="inf_authn"/>).
* PreProcReq.3 (needed for Rq0.1): S validated the
authorization of C or the entity which is authorized to
speak for C to access the resource as requested
(see <xref target="authz_val"/>).
Postconditions:
* PostProcReq.1: The access request was processed (fulfills
PreSendResp.1, see <xref target="send_info"/>).</t>
</list></t>
<t>Note: The preconditions PreProcReq.2 and PreProcReq.3 must be
conducted together. S must assure that the response is bound to a
verifier, the verifier is bound to certain attributes and
the authorization information refers to these attributes.</t>
</section>
<section anchor="send_info" title="Sending Information">
<t>The information needed for processing has to be transmitted at some
point. C has to transmit to S which resource it wants to access with
which actions and parameters. S has to transmit to C the result of
the request. The request and the response might both contain resource
values. To fulfill Rq0.1, the confidentiality and integrity of the
transmitted data has to be assured.</t>
<t>If proxies are used, it depends on the type of proxy how they need to
be handled. A future version of this document will provide more
details on this topic. At this point we assume that C and S might
transmit the message either to S and C directly or to a proxy which
is authorized to speak for the respective communication partner.</t>
<t><list style="symbols">
<t>Task TSendReq: Securely transmit an access request.
Description: C wants to access a resource R hosted by the resource
server S. To achieve this, it has to transmit some information to
S such as the resource to be accessed, the action to be performed
on the resource and, if a writing access is requested, the value to
write. C might send the request directly to S or to an entity
which is authorized to speak for S. C assures that the request
reaches the proper R. C binds the request to C’s verifier to ensure
the integrity of the message. C uses means to assure that no
unauthorized entity is able to access the information in the
request.
Requirements:
* RqSendReq.1: Is performed by C (derives from problem statement).
* RqSendReq.2: Must be performable by a constrained device
(derives
from the problem statement: C and / or S are constrained).
* RqSendReq.3: As the request might contain resource values,
the confidentiality and integrity of the request must be
ensured during transmission. Only authorized parties must be
able to read or modify the request (derives from Rq0.1).
Preconditions:
* PreSendReq.1: Validate that the receiver is an authorized
source for R (see <xref target="authz_val"/>).
* PreSendReq.2: To assure that the request reaches the proper
S, that no unauthorized party is able to access the request, and
that the information in the request is bound to C’s verifier
it is necessary to negotiate means for secure communication
with S (see <xref target="secure_comm"/>).
Postconditions:
* PostSendReq.1: The request was sent securely to S
(necessary for Rq0.1) (fulfills PreProcReq.1, see
<xref target="proc_info"/>).</t>
</list></t>
<t>Note: The preconditions PreSendReq.1 and PreSendReq.2 must be
conducted together. C must assure that the request reaches an entity
with certain attributes and that the authorization information refers
to these attributes.</t>
<t><list style="symbols">
<t>Task TSendResp: Securely transmit a response to an access request.
Description: S sends a response to an access request to inform C
about the result of the request. S must assure that response
reaches the requesting C. S might send the response to C or to an
entity which is authorized to speak for C. The response might
contain resource values. S binds the request to S’s verifier to ensure
the integrity of the message. S uses means to assure that no
unauthorized entity is able to access the information in the
response.
Requirements:
* RqSendResp.1: Is performed by S (derives from the
problem statement).
* RqSendResp.2: Must be performable by a constrained
device (derives from the problem statement: C and / or S
are constrained).
* RqSendResp.3: As the response might contain resource
values, the confidentiality and integrity of the response
must be ensured during transmission. Only authorized parties
must be able to read or modify the response (derives from
Rq0.1).
Preconditions:
* PreSendResp.1: An access request was processed (see
<xref target="proc_info"/>).
* PreSendResp.2: If information about R is transmitted,
validate that the receiver is authorized
to access R (see <xref target="authz_val"/>).
* PreSendResp.3: S must assure that the response reaches the
requesting C, no unauthorized party is able to access the
response and the information in the response is bound to S’
verifier: Means for secure communication were
negotiated (see <xref target="secure_comm"/>).
Postconditions:
* PostSendResp.1: A response to an access request was sent
(fulfills PreProcResp.1, see <xref target="proc_info"/>).</t>
</list></t>
</section>
</section>
<section anchor="security-related-tasks-1" title="Security-Related Tasks">
<section anchor="inf_authn" title="Information Authenticity">
<t>This section addresses information authentication, i.e. using the
verifier to validate the source of an information. Information
authentication must be conducted before processing received
information. C must validate that a response to
an access request is fresh, really stems from the queried S (or an
entity which is authorized to speak for S) and was not modified during
transmission. S must validate that the information in the access
request is fresh, really stems from C (or an entity which is authorized
to speak for C) and was not modified during transmission.</t>
<!-- TODO: explain freshness requirement -->
<t>The entity which processes the information must be the entity which is
validating the source of the information.</t>
<t>C and S must assure that the authenticated source of the information
is authorized to provide the information.</t>
<!-- TODO: mention endorsement validation -->
<t><list style="symbols">
<t>Task TAuthnResp: Validate that the response to an access request
is authentic.
Description: C checks if the response to an access request stems
from an entity in possession of the respective verifier and is
fresh. Thus, C validates that the response stems from the queried S or an
entity which is authorized to speak for S.
Requirements:
* RqAuthnResp.1: Must be performed by C.
* RqAuthnResp.2: Must be performable by a constrained
device (derives from the problem statement: C and / or S
are constrained).
Preconditions:
* PreAuthnResp.1: Means for secure communication were
negotiated (see <xref target="secure_comm"/>).
Postconditions:
* PostAuthnResp.1: C knows that the response came from S
(fulfills PreProcResp.2, see <xref target="proc_info"/>).</t>
<t>Task TAuthnReq: Validate the authenticity of a request.
Description: S checks if the request stems from an entity in
possession of the respective verifier and is fresh. Thus, S
validates that the request stems from C or an entity which is
authorized to speak
for C.
Requirements:
* RqAuthnReq.1: Must be performed by S.
* RqAuthnReq.2: Must be performable by a constrained device
(derives from the problem statement: C and / or S are
constrained).
Preconditions:
* PreAuthnReq.1: Means for secure communication were
negotiated (see <xref target="secure_comm"/>).
Postconditions:
* PostAuthnReq.1: S knows that the request is authentic
(fulfills PreProcReq.2, see <xref target="proc_info"/>).</t>
</list></t>
</section>
<section anchor="authz_val" title="Authorization Validation">
<!-- We differentiate the configuration of authorization information,
the obtaining of the authorization information and the validation of
the authorization. -->
<t>This section addresses the validation of the authorization of an
entity. The entity which processes the information must validate that
the source of the information is authorized to provide it. The
processing entity has to verify that the source of the information has
certain attributes which authorize it to provide the information: C
must validate that S (or the entity which speaks for S) is in
possession of attributes which are necessary for being an authorized
source for R. S must validate that C (or the entity which speaks for
C) has attributes which are necessary for a permission to access R as
requested.</t>
<!-- TODO: mention authorization enforcement -->
<t><list style="symbols">
<t>Task TValSourceAuthz: Validate that an entity is an authorized source for
R.
Description: C checks if according to COP’s
authorization policy and the authentication endorsement provided by
the attribute binding authority, S (or an entity which speaks for
S) is authorized to be a source for R. S assures that
the entity’s verifier is bound to certain attributes and the
authorization information refers to these attributes.
Requirements:
* RqValSourceAuthz.1: Is performed by C
* RqValSourceAuthz.2: Must be performable by a constrained device
(derives from the problem statement: C and / or S are
constrained).
Preconditions:
* PreValSourceAuthz.1: Authorization information about the entity
is available. Requires obtaining authorization information
about the entity from COP (see <xref target="obtain_authz"/>).
* PreValSourceAuthz.2: Means to validate that the entity has
certain attributes which are relevant for the authorization:
Requires validation of claims about S (see <xref target="claim_val"/>).
Postconditions:
* PostValSourceAuthz.1: The entity which performs the task
knows that an entity is an authorized source for R (fulfills
PreProcResp.3, see <xref target="proc_info"/> and PreSendReq.1, see
<xref target="send_info"/>).</t>
<t>Task TValAccessAuthZ: Validate the authorization of the requester
to access
the requested resource as requested.
Description: ROP configures which clients are authorized to
perform which action on R. S has to check if according to ROP’s
authorization policy and the authentication endorsement provided by
the attribute binding authority, C (or an entity which speaks for
C) is authorized to access R as requested. S assures that
requester’s verifier is bound to certain attributes and the
authorization information refers to these attributes.
Requirements:
* RqValAccessAuthz.1: Is performed by S
* RqValAccessAuthz.2: Must be performable by a constrained
device (derives from the problem statement: C and / or S
are
constrained).
Preconditions:
* PreValAccessAuthz.1: Authorization information about the entity
are available. Requires obtaining authorization information
about the entity from ROP (see <xref target="obtain_authz"/>).
* PreValAccessAuthz.2: Means to validate that the entity has
certain attributes which are relevant for the authorization:
Requires validation of claims about C or the entity which
speaks for C (see <xref target="claim_val"/>).
Postconditions:
* PostValAccessAuthz.1: The entity which performs the task knows
that an entity is authorized to access R with the requested
action (fulfills PreProcReq.3, see <xref target="proc_info"/>).</t>
</list></t>
</section>
<section anchor="secure_comm" title="Transmission Security">
<t>To ensure the confidentiality and integrity of information during
transmission means for secure communication have to be negotiated
between the communicating parties.</t>
<t><list style="symbols">
<t>Task TSecureComm: Negotiate means for secure communication.
Description: To ensure the confidentiality and integrity of
transmitted information, means for secure communication
(e.g. session keys, used cipher suites, etc.) have to be
negotiated. Channel security as well as object security solutions
are possible. Details depend on the used solution and are not in
the scope of this document.
Requirements:
* RqSecureComm.1: Must be performable by a constrained device
(derives from the problem statement: C and / or S are
constrained).
Preconditions:
* PreSecureComm.1: Sender and receiver must be able to
validate that the entity in possession of a certain
verifier has the claimed attributes. (see <xref target="claim_val"/>).
Postconditions:
* PostSecureComm.1: C and S can communicate securely: The
integrity and confidentiality of information is ensured
during transmission. The sending entity can use means to
assure that the information reaches the intended receiver
so that no unauthorized party is able to access the
information. The sending entity can bind the information to
the entity’s verifier (fulfills PreSendResp.3 and
PreSendReq.2, see <xref target="send_info"/> as well as
PreAuthnResp.1 and PreAuthnReq.1, see <xref target="inf_authn"/>).</t>
</list></t>
</section>
<section anchor="obtain_authz" title="Obtain Authorization information">
<t>As described in <xref target="authz_tasks"/>, the authorization of an entity
requires several steps. The authorization information must be
configured by the principal and provided to the enforcing entity.</t>
<t><list style="symbols">
<t>Task TObtainSourceAuthz: Obtain authorization information about an entity
from C’s principal (COP).
Description: COP defines authorized sources for R. The
authorization information must be made available to C to enable it
to enforce COP’s authorization information. To facilitate the
configuration for the principal this device should have a user
interface. The authorization information has to be made available
to C in a secure way.
Requirements:
* RqObtainSourceAuthz.1: Must be performed by an entity which
is authorized by COP.
* RqObtainSourceAuthz.2: Must be performed by an entity which
is authorized to speak for COP concerning authorized
sources for R.
* RqObtainSourceAuthz.3: Should be performed by a device which
can provide some sort of user interface to facilitate the
configuration of authorization information for COP.
Preconditions:
* PreObtainSourceAuthz.1: COP configured authorized
sources for R (see <xref target="config_authz"/>).
Postconditions:
* PostObtainSourceAuthz.1: C obtained S’ authorization to be
a source for R (fulfills PreValSourceAuthz.1, see
<xref target="authz_val"/>).</t>
<t>Task TObtainAccessAuthz: Obtain authorization information about an entity
from S’ principal (ROP).
Description: ROP defines if and how C is
authorized to access R. The authorization information must be made
available to S to enable it to enforce ROP’s authorization
policies. To facilitate the configuration for the principal this device
should have a user interface. The authorization information has to
be made available to S in a secure way.
Requirements:
* RqObtainAccessAuthz.1: Must be performed by an entity which
is authorized by ROP.
* RqObtainAccessAuthz.2: Must be performed by an entity which
is authorized to speak for ROP concerning
authorization of access to R.
* RqObtainAccessAuthz.3: Should be performed by a device which
can provide some sort of user interface to facilitate the
configuration of authorization information for ROP.
Preconditions:
* PreObtainAccessAuthz.1: ROP configured authorization
information for the access to R (see <xref target="config_authz"/>).
Postconditions:
* PostObtainAccessAuthz.1: S obtained C’s authorization for
accessing R (fulfills PreValAccessAuthz.1, see
<xref target="authz_val"/>).</t>
</list></t>
</section>
<section anchor="claim_val" title="Attribute Binding">
<t>As described in <xref target="authn_tasks"/>, several steps must be conducted for
authentication. This section addresses the binding of attributes to a
verifier.</t>
<t>For authentication it is necessary to validate if an
entity has certain attributes. An example for such an attribute
in the physical world is the name of a person or her age. In
constrained environments, attributes might be the name of the owner or
the type of device. Authorizations are bound to such attributes.</t>
<t>The possession of attributes must be verifiable. For that purpose,
attributes must be bound to a verifier. An example for a verifier in
the physical world is a passport. In constrained environments, a
verifier will likely be the knowledge of a secret.</t>
<t>At some point, an authority has to check if an entity in possession of
the verifier really possesses the claimed attributes. In the physical
world, government agencies check your name and age before they give
you a passport.</t>
<t>The entity that validates the claims has to provide some kind of seal
to make its endorsement verifiable for other entities and thus bind
the attributes to the verifier. In the physical world passports are
stamped by the issuing government agencies (and must only be provided by
government agencies anyway).</t>
<t><list style="symbols">
<t>Task TValSourceAttr: Validate on the client side that an entity has
certain attributes.
Description: The claim that an entity has certain attributes has to
be checked and made available for C in a secure way. The validating
party states that an entity in possession of a certain key has
certain attributes and provides C with means to validate this
endorsement.
Requirements:
* RqValSourceAttr.1: Must be performed by an entity which
is authorized by COP to validate claims about S.
* RqValSourceAttr.3: The executing entity must have the means
to fulfill the task (e.g. enough storage space,
computational power, a user interface to facilitate the
configuration of authentication policies).
Postconditions:
* PostValSourceAttr.1: Means for authenticating (validating
the attribute-verifier-binding of) other entities were given
to C in form of a verifiable endorsement (fulfills
PreValSourceAuthz.2, see <xref target="authz_val"/> and PreSecureComm.1,
see <xref target="secure_comm"/>).</t>
<t>Task TValReqAttr: Validate on the server side that an entity has
certain attributes.
Description: The claim that an entity has certain attributes has to
be checked and made available for S in a secure way. The
validating party states that an entity in possession of a certain
key has certain attributes and provides S with means to validate
this endorsement.
Requirements:
* RqValReqAttr.1: Must be performed by an entity which is
authorized by ROP to validate claims about C.
* RqValReqAttr.2: The executing entity must have the means to fulfill
the task (e.g. enough storage space, computational power, a
user interface to facilitate the configuration of
authentication policies).
Postconditions:
* PostValReqAttr.1: Means for authenticating (validating the
attribute-verifier-binding of) other entities were given to
S in form of a verifiable endorsement (fulfills
PreValSourceAuthz.2, see <xref target="authz_val"/> and PreSecureComm.1,
see <xref target="secure_comm"/>).</t>
</list></t>
</section>
<section anchor="config_authz" title="Configuration of Authorization Information">
<t>As stated in <xref target="authz_tasks"/>, several steps have to be conducted for
authorization. This section is about the configuration of
authorization information.</t>
<t>The principal of an endpoint or resource wants to be in control of her device
and her data. For that purpose, she has to configure authorization
information. COP might want to configure which attributes an entity
must have to be allowed to represent R. ROP might want to configure
which attributes are required for accessing R with a certain action.</t>
<t><list style="symbols">
<t>Task TConfigSourceAuthz: Configure for C authorization information for
sources for R.
Description: COP has to define authorized sources for R.
Requirements:
* RqConfigSourceAuthz.1: Must be provided by COP.
Postconditions:
* PostConfigSourceAuthz.1: The authorization information are
available to an endpoint which performs TObtainSourceAuthz
(fulfills PreObtainSourceAuthz.1 see <xref target="obtain_authz"/>).</t>
<t>Task TConfigAccessAuthz: Configure for S authorization information for
accessing R.
Description: ROP has to configure if and how an entity with
certain attributes is allowed to access R.
Requirements:
* RqConfigAccessAuthz.1: Must be provided by ROP.
Postconditions:
* PostConfigAccessAuthz.1: The authorization information are
available to the endpoint which performs TObtainAccessAuthz
(fulfills PreObtainAccessAuthz.1, see <xref target="obtain_authz"/>).</t>
</list></t>
</section>
</section>
</section>
</back>
</rfc>
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