CoRE Working Group G. Selander
Internet-Draft M. Sethi
Intended Status: Informational Ericsson
Expires: April 24, 2014 L. Seitz
SICS Swedish ICT
October 21, 2013
Access Control Framework for Constrained Environments
draft-selander-core-access-control-01
Abstract
The Constrained Application Protocol (CoAP) is a light-weight web
transfer protocol designed to be used in constrained nodes and
constrained networks. Communication security support for CoAP,
including authentication, encryption, integrity protection, is
specified by means of a DTLS binding for CoAP, but authorization and
access control are not described in detail.
This document describes a generic and dynamic access control
framework suitable for constrained environments e.g. using CoAP. The
framework builds on standards and well known paradigms for access
control, externalizing authorization decision making to unconstrained
nodes while performing authorization decision enforcement and
verification of local conditions in constrained devices.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright and License Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Scope and Requirements . . . . . . . . . . . . . . . . . . . . 5
2.1 Resource Authorization and Protocol Authorization . . . . . 5
2.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
3 Outline of Access Control Framework . . . . . . . . . . . . . . 7
3.1 Rationale . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Message flow . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Access Tokens . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Access Token Protection . . . . . . . . . . . . . . . . . . 11
4.3 Access Token Transport . . . . . . . . . . . . . . . . . . 11
4.4 Access Token Reception . . . . . . . . . . . . . . . . . . 12
4.5 Access Token Enforcement . . . . . . . . . . . . . . . . . 13
5. Intermediary processing and notifications . . . . . . . . . . . 13
5.1 Intermediary nodes . . . . . . . . . . . . . . . . . . . . . 13
5.2 Mirror Server . . . . . . . . . . . . . . . . . . . . . . . 14
5.3 Observe . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1 Normative References . . . . . . . . . . . . . . . . . . . 17
9.2 Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Example Token Syntax . . . . . . . . . . . . . . . . 18
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Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The Constrained Application Protocol (CoAP) [I-D.ietf-core-coap] is a
light-weight web transfer protocol, suitable for applications in
embedded devices used in services such as smart energy, smart home,
building automation, remote patient monitoring etc. Due to the
nature of the these use cases including critical, unattended
infrastructure and the personal sphere, security and privacy are
critical components. Use cases for CoRE security are discussed in [I-
D.seitz-core-sec-usecases].
CoAP message exchanges can be protected with different security
protocols. The CoAP specification defines a DTLS binding for CoAP,
which provides communication security services including
authentication, encryption, integrity, and replay protection.
Authorization and access control - i.e. controlling who has access to
what - is addressed with access control lists, which are assumed to
have been provisioned to the devices and which contain lists of
identifiers that may start DTLS sessions with the devices.
There are some limitations inherent to such an approach:
1. By restricting the scope of access control to the granularity
of identifiers of requesting clients, it is not possible to
give different privileges to different entities that are
allowed to access the same device. For example, it may be
desirable to give some clients the right to GET resources but
others the right to POST or PUT resources to the same device;
or to give the same client different access rights for
different resources on the same device.
2. There are use cases [I-D.seitz-core-sec-usecases] where the
granularity of GET/PUT/POST/DELETE is not sufficient to specify
the relevant access restrictions. For example, an access
policy may depend on local conditions of the device such as
date and time, proximity, geo-location, detected effort (press
3 times), or other aspects of the current state of the device.
3. It is not defined how to change access privileges except by re-
provisioning. How such changes would be authorized is also
unclear.
This document proposes a framework that allows fine-grained and
flexible access control, applicable to a generic setting including
use cases with constrained devices [I-D.ietf-lwig-terminology].
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1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
Certain security-related terms are to be understood in the sense
defined in [RFC4949]. These terms include, but are not limited to,
"authentication", "authorization", "access control",
"confidentiality", "credential", "encryption", "sign", "signature",
"data integrity", and "verify".
Terminology for constrained environments is defined in [I-D.ietf-
lwig-terminology]. These terms include, but are not limited to,
"constrained device", "constrained network", and "device class".
2. Scope and Requirements
This section defines the scope and gives an overview of the
requirements that form the basis for the proposed Access Control
Framework.
2.1 Resource Authorization and Protocol Authorization
Access control is protection of system resources against unauthorized
access. There are different kinds of "system resources" that needs
protection and different kinds of protection mechanisms.
For the purpose of this memo, we distinguish between two types of
authorization: "Resource Authorization" and "Protocol
Authorization".
o Resource Authorization (RA) deals with the question whether the
server should allow a client requesting GET/PUT/POST/DELETE to
a resource (where "resource" is as defined in RFC 2616).
o Protocol Authorization (PA) deals with the question whether the
server should allow a client to run a certain protocol with it.
RA is mainly about granting only authorized requests for a resource,
and protecting resource related communication between authorized
client and server
PA is mainly about protecting the device hosting the resource and
avoiding unnecessary protocol processing e.g. to save battery /
computing resources or to protect against certain DoS attacks.
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Although there are overlapping and degenerate cases, we believe this
distinction is useful to understand the purpose of authorization.
There may be dependencies between PA and RA:
o RA typically imply some PA: If a client is authorized to access
a resource hosted on a server, then the client should be
allowed to run a protocol (say DTLS) with the server for
accessing the resource.
o PA access does not necessarily imply RA: Just because a client
is authorized to execute a protocol (say DTLS) with the server,
the client is not necessarily authorized to access any
resources hosted on the server.
The CoAP Security Modes [I-D.ietf-core-coap] and the Additional
Security Modes for CoAP [I-D.seitz-core-security-modes] define Access
Control Lists with information about what clients are allowed to run
DTLS with an origin server. This is by definition Protocol
Authorization. However, PA can be used to define RA: For example, by
allowing access to all resources for all clients successfully
executing the protocol.
The scope of the Access Control Framework defined in this draft is
primarily RA, but as is noted above, RA implies that complementing PA
needs to be defined.
2.2 Requirements
The Access Control Framework SHALL support
o access control in a constrained environment with constrained
devices or networks, in particular,
- additional messages exclusively for performing access control
SHOULD be kept at a minimum to reduce power consumption on
the constrained devices.
o access control applicable to a variety of use cases and access
purposes, in particular
- differentiated access rights for different requesting
entities,
- access control at least at the granularity of RESTful
resources,
- access policies based on local conditions (e.g. state of
device, time, position),
o changes to access policies without re-provisioning, and
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o interoperability between different system components and
providers, which is best achieved by the use of state-of-the-
art security standards and best practices (in particular end-
to-end security between resource and authorized client).
The Access Control Framework SHALL be compatible with a large variety
of client-server authentication methods, message protection
mechanisms (communication/object security), device key management
procedures and trust anchors (secret keys, raw public keys,
certificates).
3 Outline of Access Control Framework
In this section we present the rationale leading to our access
control framework, the resulting roles, the message flow, and the
access control procedure.
3.1 Rationale
Consider a generic setting where a CoAP client wants to access a
resource hosted on a CoAP server, which is potentially a constrained
device, and where the access rights are determined by the owner of
the resource. In this section we introduce some of the terms and
procedures and provide some rationale for those.
Managing and evaluating arbitrary access control policies is in
general too heavyweight for constrained devices. As a consequence
the main authorization decision is externalized to a less constrained
node, called the "authorization server", acting on behalf of the
resource owner.
On the other hand, access control enforcement should be performed in
a trusted environment associated to the resource and as close to the
resource as possible, in order to provide end-to-end security between
resource and authorized client.
Moreover, verifications of any local conditions should be performed
in conjunction with accessing the resource for the following reasons:
o Transporting information about local conditions in the device to
an authorization server for each policy decision (or on a
regular basis) introduces delays and/or adds additional
messages exclusively for the purpose of performing access
control.
o Local conditions may have changed at the time of enforcement.
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We therefore target enforcement and local decisions to take place in
the constrained device hosting the resource, or in a proxy-type
device offloading a severely constrained device hosting the resource.
We express local conditions as constraints under which an externally
granted authorization decision is valid, and which are verified at
the time and location of enforcement.
In order to convey the authorization decisions (including local
conditions) from the authorization server to the device where access
control is enforced, we use integrity protected data objects, which
we call "access tokens" (or just "tokens").
Access tokens are acquired from the authorization server and used to
gain access to the device. We denote by "access manager" the function
of requesting and receiving access tokens from an authorization
server. Constrained clients may need support to acquire tokens, in
which case the access manager is implemented on a separate node.
NOTES
1. The authorization server must be trusted by all involved
parties, in particular by the resource owner. We assume that
this trust relationship is manifested through trusted keys
established a priori in the constrained device and the
authorization server.
2. The existence of such a trust relationship, once introduced to
support authorization and access control, can be utilized to
optimize key establishment, authentication and message
protection between a client and the origin server.
3.2 Roles
The relevant roles involved in this access control framework are:
o A Resource Owner specifying the policies for access to the
resources.
o An Authorization Server (AS) performing the authorization
decision making, based on the access control policies, and
provisioned with one or more trusted keys from the Resource
Server.
o A potentially constrained Resource Server (RS) hosting resources
and provisioned with one or more trusted keys from the AS.
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o A potentially constrained Origin Client (OC) wishing to access
to a resource. As there may be client intermediaries, e.g.
forward proxies, the actual CoAP client requesting the RS may
be different from the origin client. When there are no other
clients to confuse with, we refer to the origin client simply
as "the client".
o An Access Manager (AM) which requests and receives access tokens
from an AS. The AM may be a standalone node or integrated/co-
located with the OC.
3.3 Message flow
The default procedure for resource access is described in
Figure 1, and works as follows:
Origin Access Authorization Resource
Client Manager Server Server
+ + + +
|---(1) AuthZ ---->| | |
| Request |<-(2) Authenticate ->| |
| | | |
| |-(3) Request token ->| |
| | | (4) |
| | | Evaluate |
| | | access |
| | | control |
| | | policies |
| |<---(5) Token, ------| |
| | Base Credentials | |
|<---(6) Token, ---| | |
| Base Credentials | | |
| + + |
|---------------(7) Store Token Request --------------->|
|<-------------------- Response ------------------------|
| |
|------------------(8) Resource Request --------------->|
|<-------------------- Response ------------------------|
Figure 1: Roles and access control procedure
The OC sends an authorization request to the AM (1).
The AM authenticates to the AS (2) on behalf of the OC. The AM then
requests an access token and optionally base credentials for a
specific security mode (3). The request contains the OC's subject
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identifier which is used to evaluate the access control policies.
The AS makes the authorization decision on behalf of the resource
owner (4) and, if granted, responds (5) to the AM with an access
token bound to the OC's subject identifier. Optionally it also sends
Base Credentials to be used in the message exchange between OC and
RS. A base credential may e.g. be the public key of the RS, a public
key certificate generated for the OC, or a derived key bootstrapping
the trust relation between the AS and RS [I-D.seitz-core-security-
modes].
The AM forwards the access token and base credentials to the OC (6).
The OC stores the token on the RS (7). The RS provides a well-known
resource for submitting and storing tokens used to authorize future
requests. After the token is verified by the RS it is stored and the
RS responds appropriately to the OC.
The OC submits Resource Request(s) (8), which are verified against
the stored tokens by the RS. If the RS finds a matching token, and
all local conditions are met, the request is processed and a response
is sent.
Request and Response messages need to be protected, either using
communication security, such as DTLS [RFC6347], or object security,
such as JWE [I-D.ietf-jose-json-web-encryption] and JWS [I-D.ietf-
jose-json-web-signature]. The base credentials that AS optionally
provides, can be used to establish the cryptographic keys for the
message protection scheme, and protocol authorization for
communication security establishment.
4. Access Tokens
The access token is a secure object containing authorization
information passed from the AS via the AM and OC to the RS. In this
section the content, protection and transport of an access token is
discussed.
4.1 Requirements
In order to enable the RS to enforce the authorization decision, the
access token MUST provide the following information:
o Which resource does the decision apply to.
o Which action (GET, PUT, POST, DELETE) does the decision apply
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to.
o Which OC does the decision apply to (subject identifier), and
how can this OC be authenticated (if necessary).
o Which AS has created this access token (issuer). This
information MAY be implicit from the signature of the token.
o Under what other conditions is the access token valid (local
conditions evaluated by the resource server at access time,
e.g. expiration, number of uses).
The access token SHALL include a sequence number which together with
the issuer, is unique for a given RS. The token MAY state a specific
allowed payload value, where applicable (e.g. for PUT/POST requests).
The access token MUST be integrity protected by the AS such that it
can be verified by the RS using a trusted key. An access token MAY
be protected with a message authentication code. The corresponding
symmetric key is then called the Access token Key (AK). An access
token MAY be signed with a private key in an asymmetric signature
scheme, for example the AS's private key (PrivK_AS). The RS, or
other nodes verifying the access token, MUST have access to the
relevant key (AK or PubK_AS) at the time of performing the
verification.
Using an asymmetric signature scheme is RECOMMENDED if intermediary
nodes, between OC and RS, are expected to verify the access token,
since it is less security critical to provision PubK_AS to the
intermediary nodes, rather than AK.
4.2 Access Token Protection
Since access tokens are to be consumed by constrained devices, the
protection of the access token must be lightweight and compact. This
specification RECOMMENDS the use of JSON Web Signatures (JWS) [I-
D.ietf-jose-json-web-signature] as a means of signing access tokens.
It is furthermore RECOMMENDED to use the JWS Compact Serialization in
order to further reduce the size of the protected access token
object.
In an object security setting, where the token may be transferred
over an insecure channel, it can be encrypted and integrity protected
using JWE [I-D.ietf-jose-json-web-encryption].
4.3 Access Token Transport
The access token can be transported from the OC to the RS in
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different ways.
A. One possibility is to extend the communication security
establishment protocol (e.g. using TLS authorization extensions
[RFC5878] in the DTLS/TLS handshake).
B. Another possibility is to use the application protocol (e.g.
CoAP) and send the tokens as regular requests.
In either case the access token is verified upon reception, and if it
is valid (see 4.4), stored for being used in a subsequent resource
request. If the access token is not valid (see Section 4.4) the RS
aborts the corresponding protocol to avoid unnecessary processing.
This saves resources in the case A above, since the communication
between RS and OC is still in a very early stage. However, early
abort of communication establishment can also be achieved by protocol
authorization, see e.g. [I-D.seitz-core-security-modes]. Moreover one
drawback with case A. is that a new session has to be established if
the same OC needs to submit a new access token to the RS.
For these reasons implementations SHALL at least support the
transport of access tokens in the application protocol. For this to
work, there needs to be a well-known location on the RS to which the
OC can send the access token. This resource SHALL have the local URI-
path './well-known/core/authz/'. Writing to this location SHALL NOT
require Resource Authorization (i.e. no access token is required).
4.4 Access Token Reception
Upon receiving an access token which is not already stored the RS
SHALL perform the following processing:
o Verify if the token is revoked
o Verify if the token is from a trusted issuer (i.e. the AS known
to the RS)
o Verify the signature of the token
In order to support token revocation the RS SHALL maintain a list of
sequence numbers per issuer, specifying the revoked tokens. If the
access token passes the verifications, we denote it 'valid'. The RS
SHALL only store valid access tokens. Revoked tokens SHALL be removed
from storage.
Optionally the RS can use the sequence number of the token, to
enforce token expiration. This can be done by rejecting sequence
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numbers that are significantly lower than the highest sequence number
the RS has received so far.
Optionally the RS can use the time lapse since received to enforce
token expiration. This can be done by storing together with the token
the local time as measured by the RS upon reception.
4.5 Access Token Enforcement
Upon receiving a request, the RS SHALL perform the following
processing on the relevant stored token:
o If there is information about expiry, verify if the stored token
has expired
o Verify that the stored token is bound to the requesting subject
o Verify that the stored token authorizes the received request
(including local conditions)
If no matching token is found, the request MUST be rejected using the
response code 4.03 Forbidden.
Keys or identifiers established in the communication security
protocol can be used to support subject binding verification. Table 1
shows examples of token subject identifiers based on different CoAP
security modes (see also section 9 of [I-D.ietf-core-coap], [RFC4279]
and [I-D.seitz-core-security-modes]).
+-----------------------------------------------+
| CoAP security mode | Token subject identifier|
+-----------------------------------------------+
| PreSharedKey | psk_identity |
| RawPublicKey | public key fingerprint |
| Certificate | Subject DN |
| DerivedKey | psk_identity |
| AuthorizedPublicKey | public key fingerprint |
+-----------------------------------------------+
Table 1: DTLS parameters as token subject identifiers
5. Intermediary processing and notifications
This section describes the security implications of intermediary
processing and notifications for access control.
5.1 Intermediary nodes
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There may be intermediary nodes between OC and RS, including forward
proxies, reverse proxies, cross-proxies, gateways, etc. From an
access control point of view the RS SHOULD be able to verify that a
received CoAP request is originating from the OC referenced in the
received access token. This has implications on the access token and
message protection profiles.
We distinguish between the end-to-end security setting where no
intermediary nodes need be trusted and the hop-by-hop security
setting where at least one intermediary node must be trusted.
DTLS generally needs to be hop-by-hop in case of proxies, this
requires some degree of trust in a proxy which may not be acceptable
for some applications. A RS sending back the response via the
forward proxy trusts the forward proxy with the plain text response
(e.g. a GET response) and that the proxy has established secure
communication with the OC.
In the hop-by-hop case, neither DTLS nor CoAP offers any means for RS
to authenticate the OC.
If the RS has established DTLS with a forward proxy which proxies
requests from an OC, then the access token MUST be signed by the OC
in addition to the AS integrity protection. The RS can not
authenticate the OC directly, but it can infer from a correctly
signed valid and fresh access token that the OC is authorized and has
an intent to perform the request.
5.2 Mirror Server
The access control framework can also be applied to the scenario
where a mirror server as defined in [I-D.vial-core-mirror-proxy] is
present. In such a scenario, each RS behaves as a client of the
mirror server. The access control enforcement in this case, would be
made at the mirror server instead of in a constrained RS, and the
trusted AS keys would have to be provisioned to the mirror server.
However, to a client wishing to access a resource, the mirror server
behaves as any other RS and is indistinguishable (transparent),
thereby requiring no change for the communication between client and
the mirror server. The communication between the mirror server and
the constrained RS may or may not be secured, and is oblivious to the
protocols used between the client and the mirror server.
5.3 Observe
The access control framework can also be applied, as it is, in the
case where the CoAP observe option [I-D.ietf-core-observe] is used.
With the observe option, clients can register an interest in a
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particular resource by sending a CoAP request containing the observe
option to a RS. The RS would in this case maintain the state
information for this expressed interest and send responses on state
changes only as long as the access token and local conditions
presented in the original interest request are valid. The local
conditions may need to be verified at each state change. Once the
access token expires, the RS will remove any state information for
the interest expressed. The OC would then have to send a new CoAP
request with an observe option expressing interest and a new access
token for demonstrating that it is allowed access.
6. Security Considerations
The present framework aims to protect the resources on RS, the
servers themselves, and the services offered. The means proposed to
protect these assets is to enforce granular access restrictions on
accessing the devices. Due to the setup of the framework, there is
also a need to protect the authorization decisions and the keys used
to protect the entire resource access procedure.
The AS is a Trusted Third Party from the point of view of the
resource owner. If the AS is compromised, it could e.g. issue access
tokens to unauthorized parties.
Since the AM requests tokens on behalf of the OC, the AS must be able
to verify that it really represents the OC.
In order to enforce a policy decision, the RS must authenticate the
OC, and match the identifier of the authenticated entity with the
subject identifier of the access token.
While DTLS offers bundled encryption and integrity protection of both
payload and headers, an object security approach allows for a trade-
off between protection against performance. Depending on the trust
model, access token and payload may need to be encrypted because
eavesdropping will reveal information about the OC's request, which
may be privacy sensitive. Wrapping of the payloads as secure objects
allows differentiated protection of the content based on its
sensitiveness.
A typical access token has a size in the order of hundreds of bytes.
If tokens can be sent to the RS by unauthenticated clients, care must
be taken to prevent that the processing and storage of the token
opens for Denial of Service attacks.
7. IANA Considerations
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<TBD: IANA considerations text>
8. Acknowledgements
The authors would like to thank Stefanie Gerdes, Mats Naeslund, and
John Mattsson for contributions and helpful comments.
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9. References
9.1 Normative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)", draft-ietf-
core-coap-18 (work in progress), June 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2 Informative References
[I-D.seitz-core-sec-usecases]
Seitz, L., Gerdes, S., and Selander, G., "Use cases for
CoRE security", draft-seitz-core-sec-usecases-00 (work in
progress), September 2013.
[I-D.ietf-lwig-terminology]
Bormann, C., Ersue, M., and Keranen, A., "Terminology for
Constrained Node Networks", draft-ietf-lwig-terminology-05
(work in progress), July 2013.
[I-D.seitz-core-security-modes]
Seitz, L., and Selander G., "Additional Security Modes for
CoAP", draft-seitz-core-security-modes-00 (work in
progress), October 2013
[I-D.ietf-jose-json-web-encryption]
Jones, M., Rescorla, E., and Hildebrand J., "JSON Web
Encryption (JWE)", draft-ietf-jose-json-web-encryption-17
(work in progress), October 2013.
[I-D.ietf-jose-json-web-signature]
Jones, M., Bradley, J., and Sakimura N., "JSON Web
Signature (JWS)", draft-ietf-jose-json-web-signature-17
(work in progress), October 2013.
[I-D.vial-core-mirror-proxy]
Vial, M., "CoRE Mirror Server", draft-vial-core-mirror-
proxy-01 (work in progress), July 2012.
[I-D.ietf-core-observe]
Hartke, K., "Observing Resources in CoAP", draft-ietf-
Selander, et al. Expires April 24, 2014 [Page 17]
INTERNET DRAFT CoRE Access Control October 21, 2013
core-observe-11 (work in progress), Octobe 2013.
[I-D.bormann-cbor] Bormann, C., and Hoffman P., "Concise Binary
Object Representation (CBOR)", draft-bormann-cbor-09 (work
in progress), September 2013.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI
36, RFC 4949, August 2007.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC5878] Brown, M. and R. Housley, "Transport Layer Security (TLS)
Authorization Extensions", RFC 5878, May 2010.
[RFC4279] Eronen, P., Ed., and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, December 2005.
Appendix A. Example Token Syntax
In this section we give an example of an access token using a compact
JSON notation.
01 {
02 "SN": "081d5ff7bb2c2d08",
03 "IS": "6f",
04 "SI": "435143a1b5fc8bb70a3aa9b10f6673a8",
05 "LCO": {
06 "NB":"09:00:00Z",
07 "NA":"17:00:00Z"
08 },
09 "ACT": "POST",
10 "VAL": "open",
11 "RES": "node346/doorLock"
12 }
+----------------------------------+
| Token element | Encoding |
+----------------------------------+
| Sequence number | SN |
| Issuer | IS |
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| Subject identifier | SI |
| Local conditions | LCO |
| Action | ACT |
| Allowed payload value | VAL |
| Resource | RES |
+----------------------------------+
Table 2: Token elements encoding
In this example the issuer is identified by a single byte, this is
possible because the token is for a specific RS, which is not
expected to have more than 256 distinct trusted AS.
The subject identifier is a public key fingerprint binding the token
to the corresponding public key, which in turn could be used to
establish a DTLS connection to the RS using the RawPublicKey security
mode (see section 9 of [I-D.ietf-core-coap]).
The local condition specifies a time frame during which the token is
valid (NB = not before, NA = not after). The syntax and semantics of
such conditions must be pre-defined on the consuming RS so that it
can parse and enforce them.
The action specifies the RESTful action (DELETE, GET, POST, PUT) that
this token authorizes, while the resource specifies the URI host and
URI path from the CoAP requests.
For actions including a payload (typically PUT and POST), the token
can specify a restriction on the allowed payload value.
Note that JSON is used here because it gives a human readable token
format, for production deployments one should consider using a more
compact representation format such as CBOR [I-D.bormann-cbor] to
reduce the token size.
Appendix B. Changelog
Changes from -00 to -01:
o The draft is significantly shortened, content is moved to
separate drafts and much informational content has been
removed.
o The limited use case descriptions are greatly expanded and moved
into a separate draft [I-D.seitz-core-sec-usecases].
o The key provisioning schemes are generalized to alternate CoAP
security modes and described in a separate draft [I-D.seitz-
core-security-modes]
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o The ACL categories are replaced by the distinction between
protocol authorization and resource authorization.
o The Access Manager functionality originally defined in draft-
gerdes-core-dcaf-authorize-00 is introduced.
o The communication security profile description is removed. For
a detailed DTLS based access control setting see [I-D.draft-
gerdes-core-dcaf-authorize].
o The object security profile is planned for a future draft.
Authors' Addresses
Goeran Selander
Ericsson
Farogatan 6
16480 Kista
SWEDEN
EMail: goran.selander@ericsson.com
Mohit Sethi
Ericsson
Hirsalantie 11
02420 Jorvas
FINLAND
EMail: mohit.m.sethi@ericsson.com
Ludwig Seitz
SICS Swedish ICT AB
Scheelevagen 17
22370 Lund
SWEDEN
EMail: ludwig@sics.se
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