One document matched: draft-gerdes-ace-actors-02.txt
Differences from draft-gerdes-ace-actors-01.txt
ACE Working Group S. Gerdes
Internet-Draft Universitaet Bremen TZI
Intended status: Informational October 27, 2014
Expires: April 30, 2015
Actors in the ACE Architecture
draft-gerdes-ace-actors-02
Abstract
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.
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.
In this document, the required security related tasks are identified
as guidance for the development of authentication and authorization
solutions for constrained environments. Based on the tasks, an
architecture is developed to represent the relationships between the
logical functional entities involved.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 30, 2015.
Gerdes Expires April 30, 2015 [Page 1]
Internet-Draft ace-actors October 2014
Copyright Notice
Copyright (c) 2014 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
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
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Objectives . . . . . . . . . . . . . . . . . . . . . 5
4. Authentication and Authorization . . . . . . . . . . . . . . 6
5. Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Basic Scenario Tasks . . . . . . . . . . . . . . . . . . 7
5.2. Security-Related Tasks . . . . . . . . . . . . . . . . . 7
5.3. Authentication-Related Tasks . . . . . . . . . . . . . . 8
5.4. Authorization-Related Tasks . . . . . . . . . . . . . . . 8
6. Actors . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Constrained Level Actors . . . . . . . . . . . . . . . . 9
6.2. Principal Level Actors . . . . . . . . . . . . . . . . . 11
6.3. Less-Constrained Level Actors . . . . . . . . . . . . . . 11
7. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 13
7.1. Constrained Level Protocols . . . . . . . . . . . . . . . 13
7.1.1. Cross Level Support Protocols . . . . . . . . . . . . 14
7.2. Less-Constrained Level Protocols . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. List of Tasks . . . . . . . . . . . . . . . . . . . 15
A.1. Basic Scenario . . . . . . . . . . . . . . . . . . . . . 16
A.1.1. Processing Information . . . . . . . . . . . . . . . 16
A.1.2. Sending Information . . . . . . . . . . . . . . . . . 18
A.2. Security-Related Tasks . . . . . . . . . . . . . . . . . 20
A.2.1. Information Authenticity . . . . . . . . . . . . . . 20
A.2.2. Authorization Validation . . . . . . . . . . . . . . 21
Gerdes Expires April 30, 2015 [Page 2]
Internet-Draft ace-actors October 2014
A.2.3. Transmission Security . . . . . . . . . . . . . . . . 22
A.2.4. Obtain Authorization information . . . . . . . . . . 23
A.2.5. Attribute Binding . . . . . . . . . . . . . . . . . . 24
A.2.6. Configuration of Authorization Information . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
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.
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.
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. Moreover, these tasks need to be assigned to logical
functional entities which perform the tasks: the actors in the
architecture. Thus, relations between the actors and requirements
for protocols can be identified.
In this document, the required security related tasks are identified
as guidance for the development of authentication and authorization
solutions for constrained environments. Based on the tasks, an
architecture is developed to represent the relationships between the
logical functional entities involved.
1.1. Terminology
Readers are required to be familiar with the terms and concepts
defined in [RFC4949]. In addition, this document uses the following
terminology:
Resource (R): an item of interest, which is represented through an
interface. It might contain sensor or actuator values or other
information.
Gerdes Expires April 30, 2015 [Page 3]
Internet-Draft ace-actors October 2014
Constrained node: a constrained device in the sense of [RFC7228].
Actor: A logical functional entity that performs one or more tasks.
Depending on the tasks an actor must perform, the device that
contains the actor may need to have certain system resources
available. Multiple actors may share, i.e. be present within, a
device or even a piece of software.
Resource Server (RS): An entity which hosts and represents a
Resource.
Client (C): An entity which attempts to access a resource on a
Resource Server.
Resource Owner (RO): The principal that owns the resource and
controls its access permissions.
Client Owner (CO): The principal that owns the Client and controls
permissions concerning authorized representations of a Resource.
Server Authorization Manager (SAM): An entity that prepares and
endorses authentication and authorization data for a Resource
Server.
Client Authorization Manager (CAM): An entity that prepares and
endorses authentication and authorization data for a Client.
Attribute Binding Authority: An entity that is authorized to
validate claims about an entity.
2. Problem Statement
The scenario this document addresses can be summarized as follows:
o C wants to access R on a RS.
o A priori, C and RS do not necessarily know each other and have no
security relationship.
o C and / or RS are constrained.
------- --------
| C | -- requests resource ---> | RS |
------- <-- provides resource--- --------
Figure 1: Basic Scenario
Gerdes Expires April 30, 2015 [Page 4]
Internet-Draft ace-actors October 2014
There are some security requirements for this scenario including one
or more of:
o Rq0.1: No unauthorized entity has access to (or otherwise gains
knowledge of) R.
o Rq0.2: No unauthorized entity can provide C with a representation
of R (When C attempts to access R, that access reaches the proper
R).
Rq0.1 requires authorization on RS' side while Rq0.2 requires
authorization on C's side.
3. Security Objectives
The security objectives that can be addressed by an authorization
solution are confidentiality and integrity. Availability cannot be
achieved by authorization solutions. However, misconfigured or
wrongly designed authorization solutions can result in availability
breaches: Users might no longer be able to use data and services as
they are supposed to.
Authentication mechanisms can achieve additional security objectives
such as non-repudiation and accountability. They are not related to
authorization and thus are not in scope of this draft, but still
should be considered by Authenticated Authorization solutions. Non-
repudiation and accountability may require authentication on device
level, if it is necessary to determine which device performed an
action. In other cases it may be more important to find out who is
responsible for the device's actions.
The importance of a security objective depends on the application the
authorization mechanism is used for. [I-D.seitz-ace-usecases]
indicates that security objectives differ for the various constrained
environment use cases.
In many cases, one participating party might have different security
objectives than the other. However, to achieve a security objective,
both parties must participate in providing a solution. E.g., if CO
requires the integrity of sensor value representations RS is hosting,
RS needs to integrity-protect the transmitted data. Moreover, RS
needs to protect the access to the sensor representation to prevent
unauthorized users to manipulate the sensor values.
Gerdes Expires April 30, 2015 [Page 5]
Internet-Draft ace-actors October 2014
4. Authentication and Authorization
Authorization solutions aim at protecting the access to items of
interest, e.g. hardware or software resources or data: They enable
the owner of such a resource to control who can access it and how.
To determine if an entity is authorized to access a resource, an
authentication mechanism is needed. According to the Internet
Security Glossary [RFC4949], authentication is "the process of
verifying a claim that a system entity or system resource has a
certain attribute value." Examples for attribute values are the ID
of a device, the type of the device or the name of its owner.
The security objectives the authorization mechanism aims at can only
be achieved if the authentication and the authorization mechanism
work together correctly. We use the term _authenticated
authorization_ to refer to a synthesis of mechanism for
authentication and authorization.
If used for authorization, the authenticated attributes must be
meaningful for the purpose of the authorization, i.e. the
authorization policy grants access permissions based on these
attributes. If the authorization policy assigns permissions to an
individual entity, the authenticated attributes must be suitable to
uniquely identify this entity.
In scenarios where devices are communicating autonomously there is
less need to uniquely identify an individual device. For a resource
owner, the fact that the device belongs to a certain company or that
it has a specific type (e.g. light bulb) is likely more important
than that it has a unique identifier.
Resource and device owners need to decide about the required level of
granularity for the authorization, ranging from _device
authorization_ over _owner authorization_ to _binary authorization_
and _unrestricted authorization_. In the first case different access
permissions are granted to individual devices while in the second
case individual owners are authorized. If binary authorization is
used, all authenticated entities have the same access permissions.
Unrestricted authorization for an item of interest means that no
authorization mechanism is used (not even by authentication) and all
entities are able to access the item as they see fit. More fine-
grained authorization does not necessarily provide more security.
Resource and device owners need to consider that an entity should
only be granted the permissions it really needs to ensure the
confidentiality and integrity of resources.
Gerdes Expires April 30, 2015 [Page 6]
Internet-Draft ace-actors October 2014
For all cases where an authorization solution is needed (all but
Unrestricted Authorization), the authorizing party needs to be able
to authenticate the party that is to be authorized. Authentication
is therefore required for messages that contain representations of an
accessed item. More precisely, the authorizing party needs to make
sure that the receiver of a message containing a representation, and
the sender of a message containing a representation are authorized to
receive and send this message, respectively. To achieve this, the
integrity of these messages is required: Authenticity cannot be
assured if it is possible for an attacker to modify the message
during transmission.
5. Tasks
This section gives an overview of the tasks which must be performed
in the given scenario (see Section 2) to meet the security
requirements.
As described in the problem statement, either C or RS or both of them
are constrained. Therefore tasks which must be conducted by either C
or RS must be performable by constrained nodes.
5.1. Basic Scenario Tasks
This document does not assume a specific solution. We assume
however, that at least the following information is exchanged between
the client and the server:
o C transmits to RS which resource it requests to access, the kind
of action it wants to perform on the resource, and the parameters
needed for the action.
o RS transmits to C the result of the attempted access.
5.2. Security-Related Tasks
The reason for the communication is that C wants RS to process some
information. RS' 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.
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.
Gerdes Expires April 30, 2015 [Page 7]
Internet-Draft ace-actors October 2014
5.3. Authentication-Related Tasks
Several steps must be conducted for authenticating certain attributes
of an entity and validating the authenticity of an information:
1. 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.
Note: The attribute binding can be conducted using either symmetric
or asymmetric cryptography.
1. 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.
2. 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.
Step 1 is addressed in Appendix A.2.5. 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. Tasks
for step 2 and 3 are Information authenticity (see Appendix A.2.1)
and secure communication (see Appendix A.2.3).
5.4. Authorization-Related Tasks
Several steps must be conducted for explicit authorization:
1. Configuration of authorization information: The respective owners
(CO and RO) 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.
2. Obtaining authorization information: Authorization information
must be made available to the entity which enforces the
authorization.
Gerdes Expires April 30, 2015 [Page 8]
Internet-Draft ace-actors October 2014
3. 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.
4. Authorization enforcement: According to the result of the
authorization validation the access to a resource is granted or
denied.
Tasks for step 1 are defined in Appendix A.2.6. Appendix A.2.4
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. Appendix A.2.2
introduces tasks for these steps.
6. Actors
This section describes the various actors in the architecture. 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.
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.
The concept of actors is used to assign the tasks defined in
Appendix A to logical functional entities.
6.1. Constrained Level Actors
As described in the problem statement (see Section 2), either C or RS
or both of them may be located on a constrained node. We therefore
define that C and RS must be able to perform their tasks even if they
are located on a constrained node. Thus, C and RS are considered to
be Constrained Level Actors.
C performs the following tasks:
o Negotiate means for secure communication (Task TSecureComm, see
Appendix A.2.3).
Gerdes Expires April 30, 2015 [Page 9]
Internet-Draft ace-actors October 2014
o Validate that an entity is an authorized source for R (Task
TValSourceAuthz, see Appendix A.2.2).
o Securely transmit an access request (Task TSendReq, see
Appendix A.1.2).
o Validate that the response to an access request is authentic (Task
TAuthnResp, see Appendix A.2.1).
o Process the response to an access request (Task TProcResp, see
Appendix A.1.1).
RS performs the following tasks:
o Negotiate means for secure communication (Task TSecureComm, see
Appendix A.2.3).
o Validate the authenticity of an access request (Task TAuthnReq,
see Appendix A.2.1).
o Validate the authorization of the requester to access the
requested resource as requested (Task TValAccessAuthZ, see
Appendix A.2.2).
o Process an access request (Task TProcReq, see Appendix A.1.1).
o Securely transmit a response to an access request (Task TSendResp,
see Appendix A.1.2).
R is an item of interest such as a sensor or actuator value. R is
considered to be part of RS and not a separate actor. The device on
which RS is located might contain several resources of different
resource owners. For simplicity of exposition, these resources are
described as if they had separate RS.
As C and RS do not necessarily know each other they might belong to
different security domains.
------- --------
| C | -- requests resource ---> | RS | Constrained Level
------- <-- provides resource--- --------
Figure 2: Constrained Level Actors
Gerdes Expires April 30, 2015 [Page 10]
Internet-Draft ace-actors October 2014
6.2. Principal Level Actors
Our objective is that C and RS are under control of principals in the
physical world, the Client Owner (CO) and the Resource Owner (RO)
respectively. The owners decide about the security policies of their
respective devices and belong to the same security domain.
CO is in charge of C, i.e. CO specifies security policies for C,
e.g. with whom C is allowed to communicate. By definition, C and CO
belong to the same security domain.
CO must fulfill the following task:
o Configure for C authorization information for sources for R (Task
TConfigSourceAuthz, see Appendix A.2.6).
RO is in charge of R and RS. RO specifies authorization policies for
R and decides with whom RS is allowed to communicate. By definition,
R, RS and RO belong to the same security domain.
RO must fulfill the following task:
o Configure for RS authorization information for accessing R (Task
TConfigAccessAuthz, see Appendix A.2.6).
------ ------
| CO | | RO | Principal Level
------ ------
| |
in charge of in charge of
| |
V V
------- --------
| C | -- requests resource ---> | RS | Constrained Level
------- <-- provides resource--- --------
Figure 3: Constrained Level Actors and Principal Level Actors
6.3. Less-Constrained Level Actors
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 devices 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.
Gerdes Expires April 30, 2015 [Page 11]
Internet-Draft ace-actors October 2014
The Client Authorization Manager (CAM) belongs to the same security
domain as C and CO. CAM acts on behalf of CO. It assists C in
authenticating RS and determining if RS is an authorized source for
R. CAM can do that because for C, CAM is the authority for claims
about RS.
CAM performs the following tasks:
o Validate on the client side that an entity has certain attributes
(Task TValSourceAttr, see Appendix A.2.5).
o Obtain authorization information about an entity from C's owner
and provide it to C. (Task TObtainSourceAuthz, see
Appendix A.2.4).
o Negotiate means for secure communication to communicate with C
(Task TSecureComm, see Appendix A.2.3).
The Server Authorization Manager (SAM) belongs to the same security
domain as R, RS and RO. SAM acts on behalf of RO. It supports RS by
authenticating C and determining C's permissions on R. SAM can do
that because for RS, SAM is the authority for claims about C.
SAM performs the following tasks:
o Validate on the server side that an entity has certain attributes
(Task TValReqAttr, see Appendix A.2.5).
o Obtain authorization information about an entity from RS' owner
and provide it to RS (Task TObtainAccessAuthz, see
Appendix A.2.4).
o Negotiate means for secure communication to communicate with RS
(Task TSecureComm, see Appendix A.2.3).
Gerdes Expires April 30, 2015 [Page 12]
Internet-Draft ace-actors October 2014
------ ------
| CO | | RO | 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 ---> | RS | Constrained Level
------- <-- provides resource -- --------
Figure 4: Overview of all Complexity Levels
For more detailed graphics please consult the PDF version.
7. Protocol Requirements
Devices on the less-constrained level potentially are more powerful
than constrained level devices in terms of processing power, memory,
non-volatile storage. This results in different requirements for the
protocols used on these levels.
7.1. Constrained Level Protocols
A protocol is considered to be on the constrained level if it is used
between the actors C and RS which are considered to be constrained
(see Section 6.1). C and RS might not belong to the same security
domain. Therefore, constrained level protocols are required to work
between different security domains.
Commonly used Internet protocols can not in every case be applied to
constrained environments. In some cases, tweaking and profiling is
required. In other cases it is beneficial to define new protocols
which were designed with the special characteristics of constrained
environments in mind.
On the constrained level, protocols must be used which address the
specific requirements of constrained environments. The Constrained
Gerdes Expires April 30, 2015 [Page 13]
Internet-Draft ace-actors October 2014
Application Protocol (CoAP) [RFC7252] should be used as transfer
protocol if possible. CoAP defines a security binding to Datagram
Transport Layer Security Protocol (DTLS) [RFC6347]. Thus, DTLS
should be used for channel security.
Constrained devices have only limited storage space and thus cannot
store large numbers of keys. This is especially important because
constrained networks are expected to consist of thousands of nodes.
Protocols on the constrained level should keep this limitation in
mind.
7.1.1. Cross Level Support Protocols
Protocols which operate between a constrained device on one side and
the corresponding less constrained device on the other are considered
to be (cross level) support protocols. Protocols used between C and
CAM or RS and SAM are therefore support protocols.
Support protocols must consider the limitations of their constrained
endpoint and therefore belong to the constrained level protocols.
7.2. Less-Constrained Level Protocols
A protocol is considered to be on the less-constrained level if it is
used between the actors CAM and SAM. CAM and SAM might belong to
different security domains.
On the less-constrained level, HTTP [RFC7230] and Transport Layer
Security (TLS) [RFC5246] can be used alongside or instead of CoAP and
DTLS. Moreover, existing security solutions for authentication and
authorization such as the Web Authorization Protocol (OAuth)
[RFC6749] and Kerberos [RFC4120] can likely be used without
modifications and there are no limitations for the use of a Public
Key Infrastructure (PKI).
8. IANA Considerations
None
9. Security Considerations
This document discusses security requirements for the ACE
architecture.
Gerdes Expires April 30, 2015 [Page 14]
Internet-Draft ace-actors October 2014
10. Acknowledgments
The author would like to thank Carsten Bormann, Olaf Bergmann, Robert
Cragie and Klaus Hartke for their valuable input and feedback.
11. References
11.1. Normative References
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, May 2014.
11.2. Informative References
[I-D.seitz-ace-usecases]
Seitz, L., Gerdes, S., Selander, G., Mani, M., and S.
Kumar, "ACE use cases", draft-seitz-ace-usecases-02 (work
in progress), October 2014.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing", RFC 7230, June
2014.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014.
Appendix A. List of Tasks
This section defines the tasks which must be performed in the given
scenario (see Section 2) starting from communication related tasks
and then deriving the required security-related tasks. An overview
of the tasks can be found in Section 5.
Gerdes Expires April 30, 2015 [Page 15]
Internet-Draft ace-actors October 2014
A task has the following structure:
o The name of the task which has the form TXXX
o One or more Requirements (if applicable) of the form RqXXX
o One or more Preconditions (if applicable) of the form PreXXX
o One or more Postconditions (if applicable) of the form PostXXX
Requirements have to be met _while_ performing the task. They derive
directly from the scenario (see Section 2) or from the security
requirements defined for the scenario. Preconditions have to be
fulfilled _before_ conducting the task. Postconditions are the
_results_ of the completed task.
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).
Note: Regarding the communication, C and RS 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 RS. Several entities might have the same
attributes.
A.1. Basic Scenario
The intended result of the interaction between C and RS is that C has
successfully accessed R. C gets to know that its access request was
successful by receiving the answer from RS.
The transmission of information from C to RS 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.
A.1.1. Processing Information
The purpose of the communication between C and RS is C's intent to
access R. To achieve this, RS 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.
The confidentiality and integrity of R require that only authorized
entities are able to access R (see Rq0.1). Therefore, C and RS must
Gerdes Expires April 30, 2015 [Page 16]
Internet-Draft ace-actors October 2014
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 RS is an authorized source for R.
RS must validate that C is authorized to access R as requested.
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 RS might receive the information either from RS or
C directly or from a proxy which is authorized to speak for the
respective communication partner.
o 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 RS are
constrained).
Preconditions:
* PreProcResp.1: A response to an access request was sent (see
Appendix A.1.2).
* 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 Appendix A.1.2), i.e. RS or an
entity which is authorized to speak for RS (see Appendix A.2.1).
* PreProcResp.3 (required for Rq0.2): C validated that RS or the
entity which is authorized to speak for RS is an authorized source
for R (see Appendix A.2.2).
Postcondition:
* PostProcResp.1: C processed the response.
o Task TProcReq: Process an access request.
Description: RS 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 RS.
* RqProcReq.2: Must be performable by a constrained device
(derives from the problem statement: C and / or RS are
constrained).
Preconditions:
* PreProcReq.1: An access request was sent (see Appendix A.1.2).
Gerdes Expires April 30, 2015 [Page 17]
Internet-Draft ace-actors October 2014
* PreProcReq.2 (needed for Rq0.1): RS 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 Appendix A.2.1).
* PreProcReq.3 (needed for Rq0.1): RS validated the authorization
of C or the entity which is authorized to speak for C to access
the resource as requested (see Appendix A.2.2).
Postconditions:
* PostProcReq.1: The access request was processed (fulfills
PreSendResp.1, see Appendix A.1.2).
Note: The preconditions PreProcReq.2 and PreProcReq.3 must be
conducted together. RS 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.
A.1.2. Sending Information
The information needed for processing has to be transmitted at some
point. C has to transmit to RS which resource it wants to access
with which actions and parameters. RS 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.
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 RS might
transmit the message either to RS and C directly or to a proxy which
is authorized to speak for the respective communication partner.
o Task TSendReq: Securely transmit an access request.
Description: C wants to access a resource R hosted by the resource
server RS. To achieve this, it has to transmit some information
to RS 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 RS or to
an entity which is authorized to speak for RS. 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 RS are
constrained).
* RqSendReq.3: As the request might contain resource values, the
confidentiality and integrity of the request must be ensured
Gerdes Expires April 30, 2015 [Page 18]
Internet-Draft ace-actors October 2014
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 Appendix A.2.2).
* PreSendReq.2: To assure that the request reaches the proper RS,
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 RS (see
Appendix A.2.3).
Postconditions:
* PostSendReq.1: The request was sent securely to RS (necessary
for Rq0.1) (fulfills PreProcReq.1, see Appendix A.1.1).
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.
o Task TSendResp: Securely transmit a response to an access request.
Description: RS sends a response to an access request to inform C
about the result of the request. RS must assure that response
reaches the requesting C. RS might send the response to C or to
an entity which is authorized to speak for C. The response might
contain resource values. RS binds the request to RS's verifier to
ensure the integrity of the message. RS uses means to assure that
no unauthorized entity is able to access the information in the
response.
Requirements:
* RqSendResp.1: Is performed by RS (derives from the problem
statement).
* RqSendResp.2: Must be performable by a constrained device
(derives from the problem statement: C and / or RS 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
Appendix A.1.1).
* PreSendResp.2: If information about R is transmitted, validate
that the receiver is authorized to access R (see Appendix A.2.2).
* PreSendResp.3: RS 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 RS' verifier:
Means for secure communication were negotiated (see
Appendix A.2.3).
Gerdes Expires April 30, 2015 [Page 19]
Internet-Draft ace-actors October 2014
Postconditions:
* PostSendResp.1: A response to an access request was sent
(fulfills PreProcResp.1, see Appendix A.1.1).
A.2. Security-Related Tasks
A.2.1. Information Authenticity
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 RS (or an entity which is
authorized to speak for RS) and was not modified during transmission.
RS 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.
The entity which processes the information must be the entity which
is validating the source of the information.
C and RS must assure that the authenticated source of the information
is authorized to provide the information.
o 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
RS or an entity which is authorized to speak for RS.
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 RS are
constrained).
Preconditions:
* PreAuthnResp.1: Means for secure communication were negotiated
(see Appendix A.2.3).
Postconditions:
* PostAuthnResp.1: C knows that the response came from RS
(fulfills PreProcResp.2, see Appendix A.1.1).
o Task TAuthnReq: Validate the authenticity of a request.
Description: RS checks if the request stems from an entity in
possession of the respective verifier and is fresh. Thus, RS
validates that the request stems from C or an entity which is
authorized to speak for C.
Requirements:
Gerdes Expires April 30, 2015 [Page 20]
Internet-Draft ace-actors October 2014
* RqAuthnReq.1: Must be performed by RS.
* RqAuthnReq.2: Must be performable by a constrained device
(derives from the problem statement: C and / or RS are
constrained).
Preconditions:
* PreAuthnReq.1: Means for secure communication were negotiated
(see Appendix A.2.3).
Postconditions:
* PostAuthnReq.1: RS knows that the request is authentic (fulfills
PreProcReq.2, see Appendix A.1.1).
A.2.2. Authorization Validation
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 RS (or the entity which speaks for RS) is in
possession of attributes which are necessary for being an authorized
source for R. RS must validate that C (or the entity which speaks
for C) has attributes which are necessary for a permission to access
R as requested.
o Task TValSourceAuthz: Validate that an entity is an authorized
source for R.
Description: C checks if according to CO's authorization policy
and the authentication endorsement provided by the attribute
binding authority, RS (or an entity which speaks for RS) is
authorized to be a source for R. RS 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 RS are
constrained).
Preconditions:
* PreValSourceAuthz.1: Authorization information about the entity
is available. Requires obtaining authorization information about
the entity from C's owner (see Appendix A.2.4).
* PreValSourceAuthz.2: Means to validate that the entity has
certain attributes which are relevant for the authorization:
Requires validation of claims about RS (see Appendix A.2.5).
Postconditions:
* PostValSourceAuthz.1: The entity which performs the task knows
that an entity is an authorized source for R (fulfills
Gerdes Expires April 30, 2015 [Page 21]
Internet-Draft ace-actors October 2014
PreProcResp.3, see Appendix A.1.1 and PreSendReq.1, see
Appendix A.1.2).
o Task TValAccessAuthZ: Validate the authorization of the requester
to access the requested resource as requested.
Description: R's owner configures which clients are authorized to
perform which action on R. RS has to check if according to RO'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. RS assures that
requester's verifier is bound to certain attributes and the
authorization information refers to these attributes.
Requirements:
* RqValAccessAuthz.1: Is performed by RS
* RqValAccessAuthz.2: Must be performable by a constrained device
(derives from the problem statement: C and / or RS are
constrained).
Preconditions:
* PreValAccessAuthz.1: Authorization information about the entity
are available. Requires obtaining authorization information about
the entity from RS's owner (see Appendix A.2.4).
* 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 Appendix A.2.5).
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 Appendix A.1.1).
A.2.3. Transmission Security
To ensure the confidentiality and integrity of information during
transmission means for secure communication have to be negotiated
between the communicating parties.
o Task TSecureComm: Negotiate means for secure communication.
Description: To ensure the confidentiality and integrity of
transmitted information, means for secure communication 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 RS are
constrained).
Preconditions:
Gerdes Expires April 30, 2015 [Page 22]
Internet-Draft ace-actors October 2014
* PreSecureComm.1: Sender and receiver must be able to validate
that the entity in possession of a certain verifier has the
claimed attributes. (see Appendix A.2.5).
Postconditions:
* PostSecureComm.1: C and RS 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 Appendix A.1.2 as well as
PreAuthnResp.1 and PreAuthnReq.1, see Appendix A.2.1).
A.2.4. Obtain Authorization information
As described in Section 5.4, the authorization of an entity requires
several steps. The authorization information must be configured by
the owner and provided to the enforcing entity.
o Task TObtainSourceAuthz: Obtain authorization information about an
entity from C's owner.
Description: C's owner defines authorized sources for R. The
authorization information must be made available to C to enable it
to enforce CO's authorization information. To facilitate the
configuration for the owner 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 C's owner.
* RqObtainSourceAuthz.2: Must be performed by an entity which is
authorized to speak for C's owner 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 C's owner.
Preconditions:
* PreObtainSourceAuthz.1: C's owner configured authorized sources
for R (see Appendix A.2.6).
Postconditions:
* PostObtainSourceAuthz.1: C obtained RS' authorization to be a
source for R (fulfills PreValSourceAuthz.1, see Appendix A.2.2).
o Task TObtainAccessAuthz: Obtain authorization information about an
entity from RS' owner.
Description: RS' owner defines if and how C is authorized to
access R. The authorization information must be made available to
RS to enable it to enforce RO's authorization policies. To
Gerdes Expires April 30, 2015 [Page 23]
Internet-Draft ace-actors October 2014
facilitate the configuration for the owner this device should have
a user interface. The authorization information has to be made
available to RS in a secure way.
Requirements:
* RqObtainAccessAuthz.1: Must be performed by an entity which is
authorized by R's owner.
* RqObtainAccessAuthz.2: Must be performed by an entity which is
authorized to speak for R's owner 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 R's owner.
Preconditions:
* PreObtainAccessAuthz.1: R's owner configured authorization
information for the access to R (see Appendix A.2.6).
Postconditions:
* PostObtainAccessAuthz.1: RS obtained C's authorization for
accessing R (fulfills PreValAccessAuthz.1, see Appendix A.2.2).
A.2.5. Attribute Binding
As described in Section 5.3, several steps must be conducted for
authentication. This section addresses the binding of attributes to
a verifier.
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.
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.
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.
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).
Gerdes Expires April 30, 2015 [Page 24]
Internet-Draft ace-actors October 2014
o 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 C's owner to validate claims about RS.
* 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 Appendix A.2.2 and PreSecureComm.1, see Appendix A.2.3).
o 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 RS in a secure way. The
validating party states that an entity in possession of a certain
key has certain attributes and provides RS with means to validate
this endorsement.
Requirements:
* RqValReqAttr.1: Must be performed by an entity which is
authorized by RS' owner 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 RS in
form of a verifiable endorsement (fulfills PreValSourceAuthz.2,
see Appendix A.2.2 and PreSecureComm.1, see Appendix A.2.3).
A.2.6. Configuration of Authorization Information
As stated in Section 5.4, several steps have to be conducted for
authorization. This section is about the configuration of
authorization information.
The owner of a device or resource wants to be in control of her
device and her data. For that purpose, she has to configure
Gerdes Expires April 30, 2015 [Page 25]
Internet-Draft ace-actors October 2014
authorization information. C's owner might want to configure which
attributes an entity must have to be allowed to represent R. R's
owner might want to configure which attributes are required for
accessing R with a certain action.
o Task TConfigSourceAuthz: Configure for C authorization information
for sources for R.
Description: C's owner has to define authorized sources for R.
Requirements:
* RqConfigSourceAuthz.1: Must be provided by C's owner.
Postconditions:
* PostConfigSourceAuthz.1: The authorization information are
available to a device which performs TObtainSourceAuthz (fulfills
PreObtainSourceAuthz.1 see Appendix A.2.4).
o Task TConfigAccessAuthz: Configure for RS authorization
information for accessing R.
Description: R's owner has to configure if and how an entity with
certain attributes is allowed to access R.
Requirements:
* RqConfigAccessAuthz.1: Must be provided by R's owner.
Postconditions:
* PostConfigAccessAuthz.1: The authorization information are
available to the device which performs TObtainAccessAuthz
(fulfills PreObtainAccessAuthz.1, see Appendix A.2.4).
Author's Address
Stefanie Gerdes
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63906
Email: gerdes@tzi.org
Gerdes Expires April 30, 2015 [Page 26]
| PAFTECH AB 2003-2026 | 2026-04-22 13:35:40 |