Internet DRAFT - draft-bormann-core-ace-aif
draft-bormann-core-ace-aif
Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Informational 28 June 2020
Expires: 30 December 2020
An Authorization Information Format (AIF) for ACE
draft-bormann-core-ace-aif-09
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
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 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
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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 30 December 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Information Model . . . . . . . . . . . . . . . . . . . . . . 3
2.1. REST-specific model . . . . . . . . . . . . . . . . . . . 4
2.2. Limitations . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Extended REST-specific model . . . . . . . . . . . . . . 5
3. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Media Types . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Registries . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Content-Format . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
(See Abstract.)
1.1. Terminology
This memo uses terms from [RFC7252] and [RFC4949].
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.
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(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 strawman, 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
object is issued, focusing the AIF object 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).
The generic model of a 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
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2.1. REST-specific model
In the specific instantiation of the REST resources and the
permissions on them, for the object identifiers ("Toid"), we simply
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
unambiguous who is the target (enforcement point) of these
authorizations.
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.
+============+================+
| local-part | Permission Set |
+============+================+
| /s/light | GET |
+------------+----------------+
| /a/led | PUT, GET |
+------------+----------------+
| /dtls | POST |
+------------+----------------+
Table 1: An authorization
instance in the AIF
Information Model
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], 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 doesn't allow further
conditionalizing access based on state outside the identification of
objects (e.g., "opening a door is allowed if that isn't locked").
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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 that were
specifically created for the subject by others.
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 result or using the Location
header field in HTTP [RFC7231] (the Location-indicating mechanisms).
(The concept is somewhat comparable to "ACL inheritance" in NFSv4
[rfc5661], 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.)
+================+===================================+
| 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, 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.
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In this section, we will give the data model for basic REST
authorization. As discussed, 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:
* 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/light", 1], ["/a/led", 5], ["/dtls", 2]]
Figure 3: An authorization instance encoded in JSON (46 bytes)
In CDDL [RFC8610], 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:
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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
A representation of this information in CBOR [RFC7049] is given in
Figure 5; again, several optimizations/improvements are possible.
83 # array(3)
82 # array(2)
68 # text(8)
2f732f6c69676874 # "/s/light"
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 (29 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].
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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".
[Insert lots of boilerplate here]
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
See Section 4.
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 [RFCthis] |
+-------------+-----------------+---------------------------------+
| Tperm | REST-method-set | set of REST methods represented |
| | | as specified in [RFCthis] |
+-------------+-----------------+---------------------------------+
Table 3
The registration policy is Specification required [RFC8126]. The
designated expert will engage with the submitter to ascertain the
requirements of this document are addressed.
5.3. Content-Format
IANA is requested to register Content-Format numbers in the CoRE
Parameters Registry [IANA.core-parameters], as follows:
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6. Security Considerations
(TBD. Some issues are already discussed in the security
considerations of [RFC7252] and in [RFC8576].)
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>.
[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>.
[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
[I-D.ietf-ace-dtls-authorize]
Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", Work in Progress,
Internet-Draft, draft-ietf-ace-dtls-authorize-11, 18 June
2020, <http://www.ietf.org/internet-drafts/draft-ietf-ace-
dtls-authorize-11.txt>.
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[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE profile of the Authentication and Authorization
for Constrained Environments Framework", Work in Progress,
Internet-Draft, draft-ietf-ace-oscore-profile-11, 18 June
2020, <http://www.ietf.org/internet-drafts/draft-ietf-ace-
oscore-profile-11.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>.
[rfc5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
<https://www.rfc-editor.org/info/rfc5661>.
[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>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[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>.
Acknowledgements
Jim Schaad and Francesca Palombini provided comments that shaped the
direction of this document.
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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