An Authorization Information Format (AIF) for ACE
draft-ietf-ace-aif-03
| Document | Type | Active Internet-Draft (ace WG) | |
|---|---|---|---|
| Author | Carsten Bormann | ||
| Last updated | 2021-10-06 (latest revision 2021-06-24) | ||
| Replaces | draft-bormann-core-ace-aif | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
| Stream | WG state | Submitted to IESG for Publication (wg milestone: Jul 2021 - Submission to the IE... ) | |
| Document shepherd | Loganaden Velvindron | ||
| Shepherd write-up | Show (last changed 2021-07-28) | ||
| IESG | IESG state | Publication Requested | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Benjamin Kaduk | ||
| Send notices to | loganaden@gmail.com | ||
ACE Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Informational 24 June 2021
Expires: 26 December 2021
An Authorization Information Format (AIF) for ACE
draft-ietf-ace-aif-03
Abstract
Constrained Devices as they are used in the "Internet of Things" need
security. One important element of this security is that devices in
the Internet of Things need to be able to decide which operations
requested of them should be considered authorized, need to ascertain
that the authorization to request the operation does apply to the
actual requester, and need to ascertain that other devices they place
requests on are the ones they intended.
To transfer detailed authorization information from an authorization
manager (such as an ACE-OAuth Authorization Server) to a device, a
compact representation format is needed. This document provides a
suggestion for such a format, the Authorization Information Format
(AIF). AIF is defined both as a general structure that can be used
for many different applications and as a specific refinement that
describes REST resources (potentially dynamically created) and the
permissions on them.
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 https://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 26 December 2021.
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Copyright Notice
Copyright (c) 2021 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 (https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Information Model . . . . . . . . . . . . . . . . . . . . . . 3
2.1. REST-specific Model . . . . . . . . . . . . . . . . . . . 4
2.2. Limitations . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Extended REST-specific Model . . . . . . . . . . . . . . 6
3. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Media Types . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Registries . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. Content-Format . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Constrained Devices as they are used in the "Internet of Things" need
security. One important element of this security is that devices in
the Internet of Things need to be able to decide which operations
requested of them should be considered authorized, need to ascertain
that the authorization to request the operation does apply to the
actual requester, and need to ascertain that other devices they place
requests on are the ones they intended.
To transfer detailed authorization information from an authorization
manager (such as an ACE-OAuth Authorization Server
[I-D.ietf-ace-oauth-authz]) to a device, a compact representation
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format is needed. This document provides a suggestion for such a
format, the Authorization Information Format (AIF). AIF is defined
both as a general structure that can be used for many different
applications and as a specific refinement that describes REST
resources (potentially dynamically created) and the permissions on
them.
1.1. Terminology
This memo uses terms from [RFC7252] and [RFC4949]; CoAP is used for
the explanatory examples as it is a good fit for Constrained Devices.
The shape of data is specified in CDDL [RFC8610]. Terminology for
Constrained Devices is defined in [RFC7228].
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. These words may also appear in this
document in lower case as plain English words, absent their normative
meanings.
(Note that this document is itself informational, but it is
discussing normative statements that MUST be put into concrete terms
in each specification that makes use of this document.)
The term "byte", abbreviated by "B", is used in its now customary
sense as a synonym for "octet".
2. Information Model
Authorizations are generally expressed through some data structures
that are cryptographically secured (or transmitted in a secure way).
This section discusses the information model underlying the payload
of that data (as opposed to the cryptographic armor around it).
For the purposes of this specification, the underlying access control
model will be that of an access matrix, which gives a set of
permissions for each possible combination of a subject and an object.
We do not concern the AIF format with the subject for which the AIF
data item is issued, so we are focusing the AIF data item on a single
row in the access matrix (such a row traditionally is also called a
capability list). As a consequence, AIF MUST be used in a way that
the subject of the authorizations is unambiguously identified (e.g.,
as part of the armor around it).
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The generic model of such a capability list is a list of pairs of
object identifiers and the permissions the subject has on the
object(s) identified.
AIF-Generic<Toid, Tperm> = [* [Toid, Tperm]]
Figure 1: Definition of Generic AIF
In a specific data model, the object identifier ("Toid") will often
be a text string, and the set of permissions ("Tperm") will be
represented by a bitset in turn represented as a number (see
Section 3).
AIF-Specific = AIF-Generic<tstr, uint>
Figure 2: Likely shape of a specific AIF
2.1. REST-specific Model
In the specific instantiation of the REST resources and the
permissions on them, for the object identifiers ("Toid"), we use the
URI of a resource on a CoAP server. More specifically, the parts of
the URI that identify the server ("authority" in [RFC3986]) are
considered the realm of the authentication mechanism (which are
handled in the cryptographic armor); we therefore focus on the "path-
absolute" and "query" parts of the URI (URI "local-part" in this
specification, as expressed by the Uri-Path and Uri-Query options in
CoAP). As a consequence, AIF MUST be used in a way that it is clear
who is the target (enforcement point) of these authorizations (note
that there may be more than one target that the same authorization
applies to, e.g., in a situation with homogeneous devices).
For the permissions ("Tperm"), we simplify the model permissions to
giving the subset of the CoAP methods permitted. This model is
summarized in Table 1.
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+============+================+
| local-part | Permission Set |
+============+================+
| /s/temp | GET |
+------------+----------------+
| /a/led | PUT, GET |
+------------+----------------+
| /dtls | POST |
+------------+----------------+
Table 1: An authorization
instance in the AIF
Information Model
In this example, a device offers a temperature sensor "/s/temp" for
read-only access and a LED actuator "/a/led" for read/write.
2.2. Limitations
This simple information model only allows granting permissions for
statically identifiable objects, e.g., URIs for the REST-specific
instantiation. One might be tempted to extend the model towards URI
templates [RFC6570] (for instance, to open up an authorization for
many parameter values as in "/s/temp{?any*}"), however, that requires
some considerations of the ease and unambiguity of matching a given
URI against a set of templates in an AIF object.
This simple information model also does not allow further
conditionalizing access based on state outside the identification of
objects (e.g., "opening a door is allowed if that is not locked").
Finally, the model does not provide any special access for a set of
resources that are specific to a subject, e.g., that the subject
created itself by previous operations (PUT, POST, or PATCH/iPATCH
[RFC8132]) or that were specifically created for the subject by
others.
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2.3. Extended REST-specific Model
The extended REST-specific model addresses the need to provide
defined access to dynamic resources that were created by the subject
itself, specifically, a resource that is made known to the subject by
providing Location-* options in a CoAP response or using the Location
header field in HTTP [RFC7231] (the Location-indicating mechanisms).
(The concept is somewhat comparable to "ACL inheritance" in NFSv4
[RFC8881], except that it does not use a containment relationship but
the fact that the dynamic resource was created from a resource to
which the subject had access.) In other words, it addresses the
third limitation mentioned in Section 2.2.
+================+===================================+
| local-part | Permission Set |
+================+===================================+
| /a/make-coffee | POST, Dynamic-GET, Dynamic-DELETE |
+----------------+-----------------------------------+
Table 2: An authorization instance in the AIF
Information Model
For a method X, the presence of a Dynamic-X permission means that the
subject holds permission to exercise the method X on resources that
have been returned by a Location-indicating mechanism to a request
that the subject made to the resource listed ("/a/make-coffee" in the
example shown in Table 2, which might return the location of a
resource that allows GET to find out about the status and DELETE to
cancel the coffee-making operation).
Since the use of the extension defined in this section can be
detected by the mentioning of the Dynamic-X permissions, there is no
need for another explicit switch between the basic and the extended
model; the extended model is always presumed once a Dynamic-X
permission is present.
3. Data Model
Different data model specializations can be defined for the generic
information model given above.
In this section, we will give the data model for basic REST
authorization as per Section 2.1 and Section 2.3. As discussed, in
this case the object identifier is specialized as a text string
giving a relative URI (local-part as absolute path on the server
serving as enforcement point). The permission set is specialized to
a single number by the following steps:
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* The entries in the table that specify the same local-part are
merged into a single entry that specifies the union of the
permission sets.
* The (non-dynamic) methods in the permission sets are converted
into their CoAP method numbers, minus 1.
* Dynamic-X permissions are converted into what the number would
have been for X, plus a Dynamic-Offset chosen as 32 (e.g., 35 for
Dynamic-DELETE).
* The set of numbers is converted into a single number by taking
each number to the power of two and computing the inclusive OR of
the binary representations of all the power values.
This data model could be interchanged in the JSON [RFC8259]
representation given in Figure 3.
[["/s/temp", 1], ["/a/led", 5], ["/dtls", 2]]
Figure 3: An authorization instance encoded in JSON (46 bytes)
In Figure 4, a straightforward specification of the data model
(including both the methods from [RFC7252] and the new ones from
[RFC8132], identified by the method code minus 1) is shown in CDDL
[RFC8610]:
AIF-REST = AIF-Generic<path, permissions>
path = tstr ; URI relative to enforcement point
permissions = uint .bits methods
methods = &(
GET: 0
POST: 1
PUT: 2
DELETE: 3
FETCH: 4
PATCH: 5
iPATCH: 6
Dynamic-GET: 32; 0 .plus Dynamic-Offset
Dynamic-POST: 33; 1 .plus Dynamic-Offset
Dynamic-PUT: 34; 2 .plus Dynamic-Offset
Dynamic-DELETE: 35; 3 .plus Dynamic-Offset
Dynamic-FETCH: 36; 4 .plus Dynamic-Offset
Dynamic-PATCH: 37; 5 .plus Dynamic-Offset
Dynamic-iPATCH: 38; 6 .plus Dynamic-Offset
)
Figure 4: AIF in CDDL
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A representation of this information in CBOR [RFC8949] is given in
Figure 5; again, several optimizations/improvements are possible.
83 # array(3)
82 # array(2)
67 # text(7)
2f732f74656d70 # "/s/temp"
01 # unsigned(1)
82 # array(2)
66 # text(6)
2f612f6c6564 # "/a/led"
05 # unsigned(5)
82 # array(2)
65 # text(5)
2f64746c73 # "/dtls"
02 # unsigned(2)
Figure 5: An authorization instance encoded in CBOR (28 bytes)
Note that choosing 32 as Dynamic-Offset means that all future CoAP
methods that can be registered can be represented both as themselves
and in the Dynamic-X variant, but only the dynamic forms of methods 1
to 21 are typically usable in a JSON form [RFC7493].
4. Media Types
This specification defines media types for the generic information
model, expressed in JSON ("application/aif+json") or in CBOR
("application/aif+cbor"). These media types have parameters for
specifying "Toid" and "Tperm"; default values are the values "local-
uri" for "Toid" and "REST-method-set" for "Tperm".
A specification that wants to use Generic AIF with different "Toid"
and/or "Tperm" is expected to request these as media type parameters
(Section 5.2) and register a corresponding Content-Format
(Section 5.3).
5. IANA Considerations
5.1. Media Types
IANA is requested to add the following Media-Types to the "Media
Types" registry.
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+==========+======================+=====================+
| Name | Template | Reference |
+==========+======================+=====================+
| aif+cbor | application/aif+cbor | RFC XXXX, Section 4 |
+----------+----------------------+---------------------+
| aif+json | application/aif+json | RFC XXXX, Section 4 |
+----------+----------------------+---------------------+
Table 3
// RFC Ed.: please replace RFC XXXX with this RFC number and remove
this note.
For "application/aif+cbor":
Type name: application
Subtype name: aif+cbor
Required parameters:
* "Toid": the identifier for the object for which permissions are
supplied. A value from the subregistry for "Toid". Default
value: "local-uri" (RFC XXXX).
* "Tperm": the data type of a permission set for the the object
identified via a "Toid". A value from the subregistry for
"Tperm". Default value: "REST-method-set" (RFC XXXX).
Optional parameters: none
Encoding considerations: binary (CBOR)
Security considerations: Section 6 of RFC XXXX
Interoperability considerations: none
Published specification: Section 4 of RFC XXXX
Applications that use this media type: No known applications
currently use this media type.
Fragment identifier considerations: The syntax and semantics of
fragment identifiers is as specified for "application/cbor". (At
publication of RFC XXXX, there is no fragment identification
syntax defined for "application/cbor".)
Person & email address to contact for further information: ACE WG
mailing list (ace@ietf.org), or IETF Applications and Real-Time
Area (art@ietf.org)
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IETF
Provisional registration: no
For "application/aif+json":
Type name: application
Subtype name: aif+json
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Required parameters:
* "Toid": the identifier for the object for which permissions are
supplied. A value from the subregistry for "Toid". Default
value: "local-uri" (RFC XXXX).
* "Tperm": the data type of a permission set for the the object
identified via a "Toid". A value from the subregistry for
"Tperm". Default value: "REST-method-set" (RFC XXXX).
Optional parameters: none
Encoding considerations: binary (JSON is UTF-8-encoded text)
Security considerations: Section 6 of RFC XXXX
Interoperability considerations: none
Published specification: Section 4 of RFC XXXX
Applications that use this media type: No known applications
currently use this media type.
Fragment identifier considerations: The syntax and semantics of
fragment identifiers is as specified for "application/json". (At
publication of RFC XXXX, there is no fragment identification
syntax defined for "application/json".)
Person & email address to contact for further information: ACE WG
mailing list (ace@ietf.org), or IETF Applications and Real-Time
Area (art@ietf.org)
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IETF
Provisional registration: no
5.2. Registries
IANA is requested to create a registry for AIF with two sub-
registries for "Toid" and "Tperm", populated with:
+=============+=================+=================================+
| Subregistry | name | Description/Specification |
+=============+=================+=================================+
| Toid | local-part | local-part of URI as specified |
| | | in RFC XXXX |
+-------------+-----------------+---------------------------------+
| Tperm | REST-method-set | set of REST methods represented |
| | | as specified in RFC XXXX |
+-------------+-----------------+---------------------------------+
Table 4
The registration policy is Specification required [RFC8126]. The
designated expert will engage with the submitter to ascertain the
requirements of this document are addressed.
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// RFC Ed.: please replace RFC XXXX with this RFC number and remove
this note.
5.3. Content-Format
IANA is requested to register Content-Format numbers in the "CoAP
Content-Formats" subregistry, within the "Constrained RESTful
Environments (CoRE) Parameters" Registry [IANA.core-parameters], as
follows:
+======================+================+======+===========+
| Media Type | Content Coding | ID | Reference |
+======================+================+======+===========+
| application/aif+cbor | - | TBD1 | RFC XXXX |
+----------------------+----------------+------+-----------+
| application/aif+json | - | TBD2 | RFC XXXX |
+----------------------+----------------+------+-----------+
Table 5
// RFC Ed.: please replace TBD1 and TBD2 with assigned IDs and remove
this note. // RFC Ed.: please replace RFC XXXX with this RFC number
and remove this note.
Note that applications that register "Toid" and "Tperm" values are
encouraged to also register Content-Formats for the relevant
combinations.
6. Security Considerations
The security considerations of [RFC7252] apply. Some wider issues
are discussed in [RFC8576].
When applying these formats, the referencing specification must be
careful to:
* ensure that the cryptographic armor employed around this format
fulfills the security objectives, and that the armor or some
additional information included in it with the AIF information
unambiguously identifies the subject to which the authorizations
shall apply, and
* ensure that the types used for "Toid" and "Tperm" provide the
appropriate granularity so that application requirements on the
precision of the authorization information are fulfilled, and that
all parties understand "Toid"/"Tperm" pairs to signify the same
operations.
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For the data formats, the security considerations of [RFC8259] and
[RFC8949] apply.
A generic implementation of AIF might implement just the basic REST
model as per Section 2.1. If it receives authorizations that include
permissions that use the Section 2.3, it needs to either reject the
AIF data item entirely or act only on the permissions that it does
understand. In other words, the usual principle "everything is
denied until it is explicitly allowed" needs to hold here as well.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
7.2. Informative References
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[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", Work in Progress, Internet-Draft,
draft-ietf-ace-oauth-authz-42, 8 June 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oauth-
authz-42.txt>.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters",
<http://www.iana.org/assignments/core-parameters>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
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[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8576] Garcia-Morchon, O., Kumar, S., and M. Sethi, "Internet of
Things (IoT) Security: State of the Art and Challenges",
RFC 8576, DOI 10.17487/RFC8576, April 2019,
<https://www.rfc-editor.org/info/rfc8576>.
[RFC8881] Noveck, D., Ed. and C. Lever, "Network File System (NFS)
Version 4 Minor Version 1 Protocol", RFC 8881,
DOI 10.17487/RFC8881, August 2020,
<https://www.rfc-editor.org/info/rfc8881>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
Acknowledgements
Jim Schaad, Francesca Palombini, Olaf Bergmann, Marco Tiloca, and
Christian Amsüss provided comments that shaped the direction of this
document. Alexey Melnikov pointed out that there were gaps in the
media type specifications, and Loganaden Velvindron provided a
shepherd review with further comments.
Author's Address
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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