Notification of Revoked Access Tokens in the Authentication and Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-revoked-token-notification-08
| Document | Type | Active Internet-Draft (ace WG) | |
|---|---|---|---|
| Authors | Marco Tiloca , Francesca Palombini , Sebastian Echeverria , Grace Lewis | ||
| Last updated | 2024-07-11 (Latest revision 2024-06-24) | ||
| Replaces | draft-tiloca-ace-revoked-token-notification | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews |
IOTDIR Telechat review
by Niklas Widell
Ready w/nits
TSVART Last Call review
(of
-06)
by Joerg Ott
Ready w/nits
GENART Last Call review
(of
-06)
by Dale Worley
Ready w/issues
SECDIR Telechat Review due 2024-07-09
Incomplete
ARTART Last Call Review due 2024-04-11
Incomplete
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Göran Selander | ||
| Shepherd write-up | Show Last changed 2023-06-02 | ||
| IESG | IESG state | IESG Evaluation::Revised I-D Needed | |
| Action Holders | |||
| Consensus boilerplate | Yes | ||
| Telechat date |
(None)
Has a DISCUSS. Has enough positions to pass once DISCUSS positions are resolved. |
||
| Responsible AD | Paul Wouters | ||
| Send notices to | goran.selander@ericsson.com | ||
| IANA | IANA review state | IANA OK - Actions Needed | |
| IANA expert review state | Expert Reviews OK | ||
| IANA expert review comments | Custom Problem Detail Keys expert has approved the new registration. Passed on editorial note. |
draft-ietf-ace-revoked-token-notification-08
ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track F. Palombini
Expires: 26 December 2024 Ericsson AB
S. Echeverria
G. Lewis
CMU SEI
24 June 2024
Notification of Revoked Access Tokens in the Authentication and
Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-revoked-token-notification-08
Abstract
This document specifies a method of the Authentication and
Authorization for Constrained Environments (ACE) framework, which
allows an Authorization Server to notify Clients and Resource Servers
(i.e., registered devices) about revoked access tokens. As specified
in this document, the method allows Clients and Resource Servers to
access a Token Revocation List on the Authorization Server by using
the Constrained Application Protocol (CoAP), with the possible
additional use of resource observation. Resulting (unsolicited)
notifications of revoked access tokens complement alternative
approaches such as token introspection, while not requiring
additional endpoints on Clients and Resource Servers.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Authentication and
Authorization for Constrained Environments Working Group mailing list
(ace@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ace/.
Source for this draft and an issue tracker can be found at
https://github.com/ace-wg/ace-revoked-token-notification.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 26 December 2024.
Copyright Notice
Copyright (c) 2024 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/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
3. Token Hash . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Motivation for the Used Construction . . . . . . . . . . 10
3.1.1. Issuing of the Access Token to the Client . . . . . . 10
3.1.2. Provisioning of Access Tokens to the RS . . . . . . . 11
3.1.3. Design Rationale . . . . . . . . . . . . . . . . . . 12
3.2. Hash Input on the Client and the AS . . . . . . . . . . . 12
3.2.1. AS-to-Client Response Encoded in CBOR . . . . . . . . 12
3.2.2. AS-to-Client Response Encoded in JSON . . . . . . . . 13
3.3. HASH_INPUT on the RS . . . . . . . . . . . . . . . . . . 14
3.3.1. Access Tokens as CWTs . . . . . . . . . . . . . . . . 14
3.3.2. Access Tokens as JWTs . . . . . . . . . . . . . . . . 15
3.4. Computing the Token Hash . . . . . . . . . . . . . . . . 16
4. Token Revocation List (TRL) . . . . . . . . . . . . . . . . . 17
4.1. Update of the TRL . . . . . . . . . . . . . . . . . . . . 17
5. The TRL Endpoint . . . . . . . . . . . . . . . . . . . . . . 17
5.1. Error Responses with Problem Details . . . . . . . . . . 18
5.2. Supporting Diff Queries . . . . . . . . . . . . . . . . . 20
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5.2.1. Supporting the "Cursor" Extension . . . . . . . . . . 21
5.3. Query Parameters . . . . . . . . . . . . . . . . . . . . 23
6. Full Query of the TRL . . . . . . . . . . . . . . . . . . . . 25
7. Diff Query of the TRL . . . . . . . . . . . . . . . . . . . . 26
8. Response Messages when Using the "Cursor" Extension . . . . . 29
8.1. Response to Full Query . . . . . . . . . . . . . . . . . 30
8.2. Response to Diff Query . . . . . . . . . . . . . . . . . 30
8.2.1. Empty Collection . . . . . . . . . . . . . . . . . . 30
8.2.2. Cursor Not Specified in the Diff Query Request . . . 31
8.2.3. Cursor Specified in the Diff Query Request . . . . . 32
9. Registration at the Authorization Server . . . . . . . . . . 35
10. Notification of Revoked Access Tokens . . . . . . . . . . . . 36
10.1. Handling of Access Tokens and Token Hashes . . . . . . . 37
11. ACE Token Revocation List Parameters . . . . . . . . . . . . 39
12. ACE Token Revocation List Error Identifiers . . . . . . . . . 40
13. Security Considerations . . . . . . . . . . . . . . . . . . . 40
13.1. Content Retrieval from the TRL . . . . . . . . . . . . . 40
13.2. Size of the TRL . . . . . . . . . . . . . . . . . . . . 41
13.3. Communication Patterns . . . . . . . . . . . . . . . . . 41
13.4. Request of New Access Tokens . . . . . . . . . . . . . . 41
13.5. Vulnerable Time Window at the RS . . . . . . . . . . . . 42
13.6. Two Token Hashes at the RS using JWTs . . . . . . . . . 42
13.7. Additional Security Measures . . . . . . . . . . . . . . 43
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
14.1. Media Type Registrations . . . . . . . . . . . . . . . . 44
14.2. CoAP Content-Formats Registry . . . . . . . . . . . . . 45
14.3. Custom Problem Detail Keys Registry . . . . . . . . . . 45
14.4. ACE Token Revocation List Parameters Registry . . . . . 45
14.5. ACE Token Revocation List Errors . . . . . . . . . . . . 46
14.6. Expert Review Instructions . . . . . . . . . . . . . . . 47
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
15.1. Normative References . . . . . . . . . . . . . . . . . . 48
15.2. Informative References . . . . . . . . . . . . . . . . . 51
Appendix A. On using the Series Transfer Pattern . . . . . . . . 52
Appendix B. Local Supportive Parameters of the TRL Endpoint . . 52
Appendix C. Interaction Examples . . . . . . . . . . . . . . . . 54
C.1. Full Query with Observe . . . . . . . . . . . . . . . . . 55
C.2. Diff Query with Observe . . . . . . . . . . . . . . . . . 57
C.3. Full Query with Observe plus Diff Query . . . . . . . . . 59
C.4. Diff Query with Observe and "Cursor" . . . . . . . . . . 62
C.5. Full Query with Observe plus Diff Query with "Cursor" . . 65
Appendix D. CDDL Model . . . . . . . . . . . . . . . . . . . . . 71
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 71
E.1. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 71
E.2. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 71
E.3. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 72
E.4. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 73
E.5. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 73
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E.6. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 74
E.7. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 74
E.8. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 74
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 75
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 75
1. Introduction
Authentication and Authorization for Constrained Environments (ACE)
[RFC9200] is a framework that enforces access control on IoT devices
acting as Resource Servers. In order to use ACE, both Clients and
Resource Servers have to register with an Authorization Server (AS)
and become a registered device. Once registered, a Client can send a
request to the AS, to obtain an access token for a Resource Server
(RS). For a Client to access the RS, the Client must present the
issued access token at the RS, which then validates it before storing
it (see Section 5.10.1.1 of [RFC9200]).
Even though access tokens have expiration times, there are
circumstances by which an access token may need to be revoked before
its expiration time, such as: (1) a registered device has been
compromised, or is suspected of being compromised; (2) a registered
device is decommissioned; (3) there has been a change in the ACE
profile for a registered device; (4) there has been a change in
access policies for a registered device; and (5) there has been a
change in the outcome of policy evaluation for a registered device
(e.g., if policy assessment depends on dynamic conditions in the
execution environment, the user context, or the resource
utilization).
As discussed in Section 6.1 of [RFC9200], only client-initiated
revocation is currently specified [RFC7009] for OAuth 2.0 [RFC6749],
based on the assumption that access tokens in OAuth are issued with a
relatively short lifetime. However, this is not expected to be the
case for constrained, intermittently connected devices, that need
access tokens with relatively long lifetimes.
This document specifies a method for allowing registered devices to
access and possibly subscribe to a Token Revocation List (TRL) on the
AS, in order to obtain updated information about pertaining access
tokens that were revoked prior to their expiration. As specified in
this document, the registered devices use the Constrained Application
Protocol (CoAP) [RFC7252] to communicate with the AS and with one
another, and can subscribe to the TRL on the AS by using resource
observation for CoAP [RFC7641]. Other underlying protocols than CoAP
are not prohibited from being supported in the future, if they are
defined to be used in the ACE framework for Authentication and
Authorization.
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Unlike in the case of token introspection (see Section 5.9 of
[RFC9200]), a registered device does not provide an owned access
token to the AS for inquiring about its current state. Instead,
registered devices simply obtain updated information about pertaining
access tokens that were revoked prior to their expiration, as
efficiently identified by corresponding hash values.
The benefits of this method are that it complements token
introspection, and it does not require the registered devices to
support any additional endpoints (see Section 1.1). The only
additional requirements for registered devices are a request/response
interaction with the AS to access and possibly subscribe to the TRL
(see Section 2), and the lightweight computation of hash values to
use as access token identifiers (see Section 3).
The process by which access tokens are declared revoked is out of the
scope of this document. It is also out of scope the method by which
the AS determines or is notified of revoked access tokens, according
to which the AS consequently updates the TRL as specified in this
document.
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
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts
described in the ACE framework for Authentication and Authorization
[RFC9200], as well as with terms and concepts related to CBOR Web
Tokens (CWTs) [RFC8392] and JSON Web Tokens (JWTs) [RFC7519].
The terminology for entities in the considered architecture is
defined in OAuth 2.0 [RFC6749]. In particular, this includes Client,
Resource Server (RS), and Authorization Server (AS).
Readers are also expected to be familiar with the terms and concepts
related to CDDL [RFC8610], CBOR [RFC8949], JSON [RFC8259], CoAP
[RFC7252], CoAP Observe [RFC7641], and the use of hash functions to
name objects as defined in [RFC6920].
Note that the term "endpoint" is used here following its OAuth
definition [RFC6749], aimed at denoting resources such as /token and
/introspect at the AS, and /authz-info at the RS. This document does
not use the CoAP definition of "endpoint", which is "An entity
participating in the CoAP protocol."
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This specification also refers to the following terminology.
* Token hash: identifier of an access token, in binary format
encoding. The token hash has no relation to other access token
identifiers possibly used, such as the 'cti' (CWT ID) claim of
CBOR Web Tokens (CWTs) [RFC8392].
* Token Revocation List (TRL): a collection of token hashes such
that the corresponding access tokens have been revoked but are not
expired yet.
* TRL endpoint: an endpoint at the AS with a TRL as its
representation. The default name of the TRL endpoint in a url-
path is '/revoke/trl'. Implementations are not required to use
this name, and can define their own instead.
* Registered device: a device registered at the AS, i.e., as a
Client, or an RS, or both. A registered device acts as a
requester towards the TRL endpoint.
* Administrator: entity authorized to get full access to the TRL at
the AS, and acting as a requester towards the TRL endpoint. An
administrator is not necessarily a registered device as defined
above, i.e., a Client requesting access tokens or an RS consuming
access tokens.
* Pertaining access token:
- With reference to an administrator, an access token issued by
the AS.
- With reference to a registered device, an access token intended
to be owned by that device. An access token pertains to a
Client if the AS has issued the access token for that Client
following its request. An access token pertains to an RS if
the AS has issued the access token to be consumed by that RS.
* Token hash pertaining to a requester: a token hash corresponding
to an access token pertaining to that requester, i.e., an
administrator or a registered device.
* TRL update pertaining to a requester: an update to the TRL through
which token hashes pertaining to that requester have been added to
the TRL or removed from the TRL.
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Examples throughout this document are expressed in CBOR diagnostic
notation as defined in Section 8 of [RFC8949] and Appendix G of
[RFC8610]. Diagnostic notation comments are often used to provide a
textual representation of the numeric parameter names and values.
In the CBOR diagnostic notation used in this document, constructs of
the form e'SOME_NAME' are replaced by the value assigned to SOME_NAME
in the CDDL model shown in Figure 14 of Appendix D. For example,
{e'full_set': [], e'cursor': 3} stands for {0: [], 2: 3}.
Note to RFC Editor: Please delete the paragraph immediately preceding
this note. Also, in the CBOR diagnostic notation used in this
document, please replace the constructs of the form e'SOME_NAME' with
the value assigned to SOME_NAME in the CDDL model shown in Figure 14
of Appendix D. Finally, please delete this note.
2. Protocol Overview
This protocol defines how a CoAP-based Authorization Server informs
Clients and Resource Servers, i.e., registered devices, about
pertaining revoked access tokens. How the relationship between a
registered device and the AS is established is out of the scope of
this specification.
At a high level, the steps of this protocol are as follows.
* Upon startup, the AS creates a single TRL accessible through the
TRL endpoint. At any point in time, the TRL represents the list
of all revoked access tokens issued by the AS that are not expired
yet.
* When a device registers at the AS, it also receives the url-path
to the TRL endpoint.
At any time after the registration procedure is finished, the
registered device can send a GET request to the TRL endpoint at
the AS. When doing so, it can request for: the current list of
pertaining revoked access tokens (see Section 6); or the most
recent updates that occurred over the list of pertaining revoked
access tokens (see Section 7).
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In particular, the registered device can rely on Observation for
CoAP [RFC7641]. In such a case, the GET request sent to the TRL
endpoint includes the CoAP Observe Option set to 0 (register),
i.e., it is an Observation Request. By doing so, the registered
device effectively subscribes to the TRL, as interested in
receiving notifications about its update. Upon receiving the
Observation Request, the AS adds the registered device to the list
of observers of the TRL endpoint.
* When an access token is revoked, the AS adds the corresponding
token hash to the TRL. Also, when a revoked access token
eventually expires, the AS removes the corresponding token hash
from the TRL.
In either case, after updating the TRL, the AS sends Observe
notifications as per [RFC7641]. That is, an Observe notification
is sent to each registered device subscribed to the TRL and to
which the access token pertains.
Depending on the specific subscription established through the
Observation Request, the notification provides the current updated
list of revoked access tokens in the subset of the TRL pertaining
to that device (see Section 6), or the most recent TRL updates
occurred over that list of pertaining revoked access tokens (see
Section 7).
Further Observe notifications may be sent, consistently with
ongoing additional observations of the TRL endpoint.
* An administrator can access and subscribe to the TRL like a
registered device, while getting the content of the whole TRL (see
Section 6) or the most recent updates occurred to the whole TRL
(see Section 7).
Figure 1 shows a high-level overview of the service provided by this
protocol. For the sake of simplicity, the example shown in the
figure considers the simultaneous revocation of the three access
tokens t1, t2, and t3, whose corresponding token hashes are th1, th2,
and th3, respectively. Consequently, the AS adds the three token
hashes to the TRL at once, and sends Observe notifications to one
administrator and four registered devices. Each dotted line
associated with a pair of registered devices indicates the access
token that they both own.
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+----------------------+
| Authorization Server |
+-----------o----------+
/revoke/trl | TRL: (th1,th2,th3)
|
+-----------------+------------+------------+------------+
| | | | |
| th1,th2,th3 | th1,th2 | th1 | th3 | th2,th3
v v v v v
+---------------+ +----------+ +----------+ +----------+ +----------+
| Administrator | | Client 1 | | Resource | | Client 2 | | Resource |
| | | | | Server 1 | | | | Server 2 |
+---------------+ +----------+ +----------+ +----------+ +----------+
: : : : : :
: : t1 : : t3 : :
: :........: :............: :
: t2 :
:...........................................:
Figure 1: Protocol Overview
Appendix C provides examples of the protocol flow and message
exchanges between the AS and a registered device.
3. Token Hash
This section specifies how token hashes are computed.
First, Section 3.1 provides the motivation for the used construction.
Building on that, the value used as input to compute a token hash is
defined in Section 3.2 for the Client and the AS, and in Section 3.3
for the RS. Finally, Section 3.4 defines how such an input is used
for computing the token hash.
The process outlined below refers to the base64url encoding and
decoding without padding (see Section 5 of [RFC4648]), and denotes as
"binary representation" of a text string the corresponding UTF-8
encoding [RFC3629], which is the implied charset used in JSON (see
Section 8.1 of [RFC8259]).
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3.1. Motivation for the Used Construction
An access token can have one among different formats. The most
expected formats are CWT [RFC8392] and JWT [RFC7519], with the former
being the default format to use in the ACE framework (see Section 3
of [RFC9200]). While access tokens are opaque to Clients, an RS is
aware of whether access tokens that are issued for it to consume are
either CWTs or JWTs.
3.1.1. Issuing of the Access Token to the Client
There are two possible encodings that the AS can use for the AS-to-
Client response (see Section 5.8.2 of [RFC9200]), where the issued
access token is included and provided to the requester Client. The
RS may not be aware of which encoding is used for that response to
that particular requester Client.
* One way relies on CBOR, which is required if CoAP is used (see
Section 5 of [RFC9200]) and is recommended otherwise (see
Section 3 of [RFC9200]). That is, the AS-to-Client response has
media-type "application/ace+cbor".
This implies that, within the CBOR map specified as message
payload, the parameter 'access_token' is a CBOR data item of type
CBOR byte string and with value the binary representation BYTES of
the access token. In particular:
- If the access token is a CWT, then BYTES is the binary
representation of the CWT (i.e., of the CBOR array that encodes
the CWT).
- If the access token is a JWT, then BYTES is the binary
representation of the JWT (i.e., of the text string that
encodes the JWT).
* An alternative way relies on JSON. That is, the AS-to-Client
response has media-type "application/ace+json".
This implies that, within the JSON object specified as message
payload, the parameter 'access_token' has as value a text string
TEXT encoding the access token. In particular:
- If the access token is a JWT, then TEXT is the text string that
encodes the JWT.
- If the access token is a CWT, then TEXT is the base64url-
encoded text string of the binary representation of the CWT
(i.e., of the CBOR array that encodes the CWT).
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3.1.2. Provisioning of Access Tokens to the RS
In accordance with the used transport profile of ACE (e.g.,
[RFC9202], [RFC9203], [RFC9431]), the RS receives a piece of token-
related information hereafter denoted as TOKEN_INFO.
In particular:
* If the AS-to-Client response was encoded in CBOR, then TOKEN_INFO
is the value of the CBOR byte string conveyed by the
'access_token' parameter of that response. This is irrespective
of the access token being a CWT or a JWT. That is, TOKEN_INFO is
the binary representation of the access token.
* If the AS-to-Client response was encoded in JSON and the access
token is a JWT, then TOKEN_INFO is the binary representation of
the text string conveyed by the 'access_token' parameter of that
response. That is, TOKEN_INFO is the binary representation of the
access token.
* If the AS-to-Client response was encoded in JSON and the access
token is a CWT, then TOKEN_INFO is the binary representation of
the base64url-encoded text string that encodes the binary
representation of the access token. That is, TOKEN_INFO is the
binary representation of the base64url-encoded text string
conveyed by the 'access_token' parameter.
The following overviews how the above specifically applies to the
existing transport profiles of ACE.
* The access token can be uploaded to the RS by means of a POST
request to the /authz-info endpoint (see Section 5.10.1 of
[RFC9200]), using a CoAP Content-Format or HTTP media-type that
reflects the format of the access token, if available (e.g.,
"application/cwt" for CWTs), or "application/octet-stream"
otherwise. When doing so (e.g., like in [RFC9202]), TOKEN_INFO is
the payload of the POST request.
* The access token can be uploaded to the RS by means of a POST
request to the /authz-info endpoint, using the media-type
"application/ace+cbor". When doing so (e.g., like in [RFC9203]),
TOKEN_INFO is the value of the CBOR byte string conveyed by the
'access_token' parameter, within the CBOR map specified as payload
of the POST request.
* The access token can be uploaded to the RS during a DTLS session
establishment, e.g., like it is defined in Section 3.2.2 of
[RFC9202]. When doing so, TOKEN_INFO is the value of the
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'psk_identity' field of the ClientKeyExchange message (when using
DTLS 1.2 [RFC6347]), or of the 'identity' field of a PSKIdentity,
within the PreSharedKeyExtension of a ClientHello message (when
using DTLS 1.3 [RFC9147]).
* The access token can be uploaded to the RS within the MQTT CONNECT
packet, e.g., like it is defined in Section 2.2.4.1 of [RFC9431].
When doing so, TOKEN_INFO is specified within the 'Authentication
Data' field of the MQTT CONNECT packet, following the property
identifier 22 (0x16) and the token length.
3.1.3. Design Rationale
Considering the possible variants discussed above, it must always be
ensured that the same HASH_INPUT value is used as input for
generating the token hash of a given access token, by the AS that has
issued the access token and by the registered devices to which the
access token pertains (both Client and RS).
This is achieved by building HASH_INPUT according to the content of
the 'access_token' parameter in the AS-to-Client responses, since
that is what all among the AS, the Client, and the RS are able to
see.
3.2. Hash Input on the Client and the AS
The Client and the AS consider the content of the 'access_token'
parameter in the AS-to-Client response, where the access token is
included and provided to the requester Client.
The following defines how the Client and the AS determine the
HASH_INPUT value to use as input for computing the token hash of the
conveyed access token, depending on the AS-to-Client response being
encoded in CBOR (see Section 3.2.1) or in JSON (see Section 3.2.2).
Once determined HASH_INPUT, the Client and the AS use it to compute
the token hash of the conveyed access token as defined in
Section 3.4.
3.2.1. AS-to-Client Response Encoded in CBOR
If the AS-to-Client response is encoded in CBOR, then HASH_INPUT is
defined as follows:
* BYTES denotes the value of the CBOR byte string conveyed in the
parameter 'access_token'.
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With reference to the example in Figure 2, BYTES is the bytes
{0xd0 0x83 0x43 ... 0x64 0x3b}.
Note that BYTES is the binary representation of the access token,
irrespective of this being a CWT or a JWT.
* HASH_INPUT_TEXT is the base64url-encoded text string that encodes
BYTES.
* HASH_INPUT is the binary representation of HASH_INPUT_TEXT.
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 85800
Payload:
{
/ access_token / 1 : h'd08343a1010aa2044c53796d6d65
74726963313238054d99a0d7846e
762c49ffe8a63e0b5858b918a11f
d81e438b7f973d9e2e119bcb2242
4ba0f38a80f27562f400ee1d0d6c
0fdb559c02421fd384fc2ebe22d7
071378b0ea7428fff157444d45f7
e6afcda1aae5f6495830c5862708
7fc5b4974f319a8707a635dd643b',
/ token_type / 34 : 2 / PoP /,
/ expires_in / 2 : 86400,
/ ace_profile / 38 : 1 / coap_dtls /,
/ (remainder of the response omitted for brevity) /
}
Figure 2: Example of AS-to-Client CoAP response using CBOR
3.2.2. AS-to-Client Response Encoded in JSON
If the AS-to-Client response is encoded in JSON, then HASH_INPUT is
the binary representation of the text string conveyed by the
'access_token' parameter.
With reference to the example in Figure 3, HASH_INPUT is the binary
representation of "2YotnFZFEjr1zCsicMWpAA".
Note that:
* If the access token is a JWT, then HASH_INPUT is the binary
representation of the JWT.
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* If the access token is a CWT, then HASH_INPUT is the binary
representation of the base64url-encoded text string that encodes
the binary representation of the CWT.
HTTP/1.1 200 OK
Content-Type: application/ace+json
Cache-Control: no-store
Pragma: no-cache
Payload:
{
"access_token" : "2YotnFZFEjr1zCsicMWpAA",
"token_type" : "pop",
"expires_in" : 86400,
"ace_profile" : "1"
}
Figure 3: Example of AS-to-Client HTTP response using JSON
3.3. HASH_INPUT on the RS
The following defines how the RS determines the HASH_INPUT value to
use as input for computing the token hash of an access token,
depending on the RS using either CWTs (see Section 3.3.1) or JWTs
(see Section 3.3.2).
3.3.1. Access Tokens as CWTs
If the RS expects access tokens to be CWTs, then the RS performs the
following steps.
1. The RS receives the token-related information TOKEN_INFO, in
accordance with what is specified by the used profile of ACE (see
Section 3.1.2).
2. The RS assumes that the Client received the access token in an
AS-to-Client response encoded in CBOR (see Section 3.2.1).
Hence, the RS assumes TOKEN_INFO to be the binary representation
of the access token.
3. The RS verifies the access token as per Section 5.10.1.1 of
[RFC9200]. If the verification fails, then the RS does not
discard the access token yet, and it instead moves to step 4.
Otherwise, the RS stores the access token and computes the
corresponding token hash, as defined in Section 3.4. In
particular, the RS considers HASH_INPUT_TEXT as the base64url-
encoded text string that encodes TOKEN_INFO. Then, HASH_INPUT is
the binary representation of HASH_INPUT_TEXT.
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After that, the RS stores the computed token hash as associated
with the access token, and then terminates this algorithm.
4. The RS assumes that the Client received the access token in an
AS-to-Client response encoded in JSON (see Section 3.2.2).
Hence, the RS assumes TOKEN_INFO to be the binary representation
of HASH_INPUT_TEXT, which is the base64url-encoded text string
that encodes the binary representation of the access token.
5. The RS performs the base64url decoding of HASH_INPUT_TEXT, and
considers the result as the binary representation of the access
token.
6. The RS verifies the access token as per Section 5.10.1.1 of
[RFC9200]. If the verification fails, then the RS terminates
this algorithm.
Otherwise, the RS stores the access token and computes the
corresponding token hash, as defined in Section 3.4. In
particular, HASH_INPUT is TOKEN_INFO.
After that, the RS stores the computed token hash as associated
with the access token.
3.3.2. Access Tokens as JWTs
If the RS expects access tokens to be JWTs, then the RS performs the
following steps.
1. The RS receives the token-related information TOKEN_INFO, in
accordance with what is specified by the used profile of ACE (see
Section 3.1.2).
2. The RS verifies the access token as per Section 5.10.1.1 of
[RFC9200]. If the verification fails, then the RS terminates
this algorithm. Otherwise, the RS stores the access token.
3. The RS computes a first token hash associated with the access
token, as defined in Section 3.4.
In particular, the RS assumes that the Client received the access
token in an AS-to-Client response encoded in JSON (see
Section 3.2.2). Hence, HASH_INPUT is TOKEN_INFO.
After that, the RS stores the computed token hash as associated
with the access token.
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4. The RS computes a second token hash associated with the access
token, as defined in Section 3.4.
In particular, the RS assumes that the Client received the access
token in an AS-to-Client response encoded in CBOR (see
Section 3.2.1). Hence, HASH_INPUT is the binary representation
of HASH_INPUT_TEXT, which in turn is the base64url-encoded text
string that encodes TOKEN_INFO.
After that, the RS stores the computed token hash as associated
with the access token.
The RS skips step 3 only if it is certain that all its pertaining
access tokens are provided to any Client by means of AS-to-Client
responses encoded as CBOR messages. Otherwise, the RS MUST perform
step 3.
The RS skips step 4 only if it is certain that all its pertaining
access tokens are provided to any Client by means of AS-to-Client
responses encoded as JSON messages. Otherwise, the RS MUST perform
step 4.
If the RS performs both step 3 and step 4 above, then the RS MUST
store, maintain, and rely on both token hashes as associated with the
access token, consistent with what is specified in Section 10.1.
Section 13.6 discusses how computing and storing both token hashes
neutralizes an attack against the RS, where a dishonest Client can
induce the RS to compute a token hash different from the correct one.
3.4. Computing the Token Hash
Once determined HASH_INPUT as defined in Section 3.2 and Section 3.3,
a hash value of HASH_INPUT is generated as per Section 6 of
[RFC6920]. The resulting output in binary format is used as the
token hash. Note that the used binary format embeds the identifier
of the used hash function, in the first byte of the computed token
hash.
The specifically used hash function MUST be collision-resistant on
byte-strings, and MUST be selected from the "Named Information Hash
Algorithm" Registry [Named.Information.Hash.Algorithm].
The AS specifies the used hash function to registered devices during
their registration procedure (see Section 9).
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4. Token Revocation List (TRL)
Upon startup, the AS creates a single Token Revocation List (TRL),
encoded as a CBOR array.
Each element of the array is a CBOR byte string, with value the token
hash of an access token. The CBOR array MUST be treated as a set,
i.e., the order of its elements has no meaning.
The TRL is initialized as empty, i.e., its initial content MUST be
the empty CBOR array. The TRL is accessible through the TRL endpoint
at the AS.
4.1. Update of the TRL
The AS updates the TRL in the following two cases.
* When a non-expired access token is revoked, the token hash of the
access token is added to the TRL. That is, a CBOR byte string
with the token hash as its value is added to the CBOR array
encoding the TRL.
* When a revoked access token expires, the token hash of the access
token is removed from the TRL. That is, the CBOR byte string with
the token hash as its value is removed from the CBOR array
encoding the TRL.
The AS MAY perform a single update to the TRL such that one or more
token hashes are added or removed at once. For example, this can be
the case if multiple access tokens are revoked or expire at the same
time, or within an acceptably narrow time window.
5. The TRL Endpoint
Consistent with Section 6.5 of [RFC9200], all communications between
a requester towards the TRL endpoint and the AS MUST be encrypted, as
well as integrity and replay protected. Furthermore, responses from
the AS to the requester MUST be bound to the corresponding requests.
Following a request to the TRL endpoint, the corresponding, success
response messages sent by the AS use Content-Format "application/ace-
trl+cbor". Their payload is formatted as a CBOR map, and the CBOR
values used to abbreviate the parameters included therein are defined
in Section 11.
The AS MUST implement measures to prevent access to the TRL endpoint
by entities other than registered devices and authorized
administrators (see Section 9).
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The TRL endpoint supports only the GET method, and allows two types
of queries of the TRL.
* Full query: the AS returns the token hashes of the revoked access
tokens currently in the TRL and pertaining to the requester.
The AS MUST support this type of query. The processing of a full
query and the related response format are defined in Section 6.
* Diff query: the AS returns a list of diff entries. Each diff
entry is related to one update occurred to the TRL, and it
contains a set of token hashes pertaining to the requester. In
particular, all such token hashes were added to the TRL or removed
from the TRL at the update related to the diff entry in question.
The AS MAY support this type of query. In such a case, the AS
maintains the history of updates to the TRL as defined in
Section 5.2. The processing of a diff query and the related
response format are defined in Section 7.
If it supports diff queries, the AS MAY additionally support its
"Cursor" extension, which has two benefits. First, the AS can avoid
excessively long messages when several diff entries have to be
transferred, by delivering several diff query responses, each
containing one adjacent subset of diff entries at a time. Second, a
requester can retrieve diff entries associated with TRL updates that,
even if not the most recent ones, occurred after a TRL update
associated with a diff entry indicated as reference point.
If it supports the "Cursor" extension, the AS stores additional
information when maintaining the history of updates to the TRL, as
defined in Section 5.2.1. Also, the processing of full query
requests and diff query requests, as well as the related response
format, are further extended as defined in Section 8.
Appendix B provides an aggregated overview of the local supportive
parameters that the AS internally uses at its TRL endpoint, when
supporting diff queries and the "Cursor" extension.
5.1. Error Responses with Problem Details
Some error responses from the TRL endpoint at the AS can convey
error-specific information according to the problem-details format
defined in [RFC9290]. Such error responses MUST have Content-Format
set to "application/concise-problem-details+cbor". The payload of
these error responses MUST be a CBOR map specifying a Concise Problem
Details data item (see Section 2 of [RFC9290]). The CBOR map is
formatted as follows.
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* It MUST include the Custom Problem Detail entry 'ace-trl-error'
registered in Section 14.3 of this document. This entry is
formatted as a CBOR map, which includes the following fields.
- The field 'error-id' MUST be present. The map key used for
this field is the CBOR unsigned integer with value 0. The
value of this field is a CBOR integer specifying the error
occurred at the AS. This value is taken from the 'Value'
column of the "ACE Token Revocation List Errors" registry
defined in Section 14.5 of this document.
- The field 'cursor' MAY be present. The map key used for this
field is the CBOR unsigned integer with value 1. The value of
this field is a CBOR unsigned integer or the CBOR simple value
null (0xf6).
The CDDL notation [RFC8610] of the 'ace-trl-error' entry is given
below.
ace-trl-error = {
0: int, ; error-id
? 1: uint / null ; cursor
}
* It MAY include further Standard Problem Detail entries or Custom
Problem Detail entries (see [RFC9290]).
In particular, it can include the Standard Problem Detail entry
'detail' (map key -2), whose value is a CBOR text string that
specifies a human-readable, diagnostic description of the error
occurred at the AS. The diagnostic text is intended for software
engineers as well as for device and network operators, in order to
aid debugging and provide context for possible intervention. The
diagnostic message SHOULD be logged by the AS. The 'detail' entry
is unlikely relevant in an unattended setup where human
intervention is not expected.
An example of error response using the problem-details format is
shown in Figure 4.
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Header: Bad Request (Code=4.00)
Content-Format: application/concise-problem-details+cbor
Payload:
{
/ title / -1: "Invalid parameter value",
/ detail / -2: "Invalid value for 'cursor': -53",
/ ace-trl-error / e'ace-trl-error': {
/ error-id / 0: 0 / "Invalid parameter value" /,
/ cursor / 1: 42
}
}
Figure 4: Example of Error Response with Problem Details
The problem-details format in general and the Custom Problem Detail
entry 'ace-trl-error' in particular are OPTIONAL to support for
registered devices. A registered device supporting the entry 'ace-
trl-error' and able to understand the specified error may use that
information to determine what actions to take next.
5.2. Supporting Diff Queries
If the AS supports diff queries, it is able to transfer a list of
diff entries, each of which is related to one update occurred to the
TRL (see Section 5). That is, when replying to a diff query
performed by a requester, the AS specifies the diff entries related
to the most recent TRL updates pertaining to the requester.
The following defines how the AS builds and maintains an ordered list
of diff entries, for each registered device and administrator,
hereafter referred to as requesters. In particular, a requester's
diff entry associated with a TRL update contains a set of token
hashes pertaining to that requester, which were added to the TRL or
removed from the TRL at that update.
The AS defines the single, constant positive integer MAX_N >= 1. For
each requester, the AS maintains an update collection of maximum
MAX_N series items, each of which is a diff entry. For each
requester, the AS MUST keep track of the MAX_N most recent TRL
updates pertaining to the requester. If the AS supports diff
queries, the AS MUST provide requesters with the value of MAX_N, upon
their registration (see Section 9).
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The series items in the update collection MUST be strictly ordered in
a chronological fashion. That is, at any point in time, the current
first series item is the one least recently added to the update
collection and still retained by the AS, while the current last
series item is the one most recently added to the update collection.
The particular method used to achieve this is implementation-
specific.
Each time the TRL changes, the AS performs the following operations
for each requester.
1. The AS considers the subset of the TRL pertaining to that
requester. If the TRL subset is not affected by this TRL update,
the AS stops the processing for that requester. Otherwise, the
AS moves to step 2.
2. The AS creates two sets "trl_patch" of token hashes, i.e., one
"removed" set and one "added" set, as related to this TRL update.
3. The AS fills the two sets with the token hashes of the removed
and added access tokens, respectively, from/to the TRL subset
considered at step 1.
4. The AS creates a new series item, which includes the two sets
from step 3.
5. If the update collection associated with the requester currently
includes MAX_N series items, the AS MUST delete the oldest series
item in the update collection.
6. The AS adds the series item to the update collection associated
with the requester, as the last (most recent) one.
5.2.1. Supporting the "Cursor" Extension
If it supports the "Cursor" extension for diff queries, the AS
performs also the following actions.
The AS defines the single, constant unsigned integer MAX_INDEX <=
((2^64) - 1), where "^" is the exponentiation operator. The value of
MAX_INDEX is REQUIRED to be at least (MAX_N - 1), and is RECOMMENDED
to be at least ((2^32) - 1). MAX_INDEX SHOULD be orders of magnitude
greater than MAX_N.
The following applies separately for each requester's update
collection.
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* Each series item X in the update collection is also associated
with an unsigned integer 'index', whose minimum value is 0 and
whose maximum value is MAX_INDEX. The first series item ever
added to the update collection MUST have 'index' with value 0.
If i_X is the value of 'index' associated with a series item X,
then the following series item Y will take 'index' with value i_Y
= (i_X + 1) % (MAX_INDEX + 1). That is, after having added a
series item whose associated 'index' has value MAX_INDEX, the next
added series item will result in a wrap-around of the 'index'
value, and will thus take 'index' with value 0.
For example, assuming MAX_N = 3, the values of 'index' in the
update collection chronologically evolve as follows, as new series
items are added and old series items are deleted.
- ...
- (i_A = MAX_INDEX - 2, i_B = MAX_INDEX - 1, i_C = MAX_INDEX)
- (i_B = MAX_INDEX - 1, i_C = MAX_INDEX, i_D = 0)
- (i_C = MAX_INDEX, i_D = 0, i_E = 1)
- (i_D = 0, i_E = 1, i_F = 2)
- ...
* The unsigned integer 'last_index' is also defined, with minimum
value 0 and maximum value MAX_INDEX.
If the update collection is empty (i.e., no series items have been
added yet), the value of 'last_index' is not defined. If the
update collection is not empty, 'last_index' has the value of
'index' currently associated with the last series item in the
update collection.
That is, after having added V series items to the update
collection, the last and most recently added series item has
'index' with value 'last_index' = (V - 1) % (MAX_INDEX + 1).
As long as a wrap-around of the 'index' value has not occurred,
the value of 'last_index' is the absolute counter of series items
added to that update collection, minus 1.
When processing a diff query using the "Cursor" extension, the values
of 'index' are used as cursor information, as defined in Section 8.2.
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For each requester's update collection, the AS also defines a
constant, positive integer MAX_DIFF_BATCH <= MAX_N, whose value
specifies the maximum number of diff entries to be included in a
single diff query response. The specific value MAY depend on the
specific registered device or administrator associated with the
update collection in question. If supporting the "Cursor" extension,
the AS MUST provide registered devices and administrators with the
corresponding value of MAX_DIFF_BATCH, upon their registration (see
Section 9).
5.3. Query Parameters
A GET request to the TRL endpoint can include the following query
parameters. The AS MUST silently ignore unknown query parameters.
* 'diff': if included, it indicates to perform a diff query of the
TRL (see Section 7). Its value MUST be either:
- the integer 0, indicating that a (notification) response should
include as many diff entries as the AS can provide in the
response; or
- a positive integer strictly greater than 0, indicating the
maximum number of diff entries that a (notification) response
should include.
If the AS does not support diff queries, it ignores the 'diff'
query parameter when present in the GET request, and proceeds like
when processing a full query of the TRL (see Section 6).
Otherwise, the AS MUST return a 4.00 (Bad Request) response in
case the 'diff' query parameter of the GET request specifies a
value that is neither 0 nor a positive integer, irrespective of
the presence of the 'cursor' parameter and its value (see below).
The response MUST have Content-Format "application/concise-
problem-details+cbor" and its payload is formatted as defined in
Section 5.1. Within the Custom Problem Detail entry 'ace-trl-
error', the value of the 'error-id' field MUST be set to 0
("Invalid parameter value"), and the field 'cursor' MUST NOT be
present.
* 'cursor': if included, it indicates to perform a diff query of the
TRL together with the "Cursor" extension, as defined in
Section 8.2. Its value MUST be either 0 or a positive integer.
If the 'cursor' query parameter is included, then the 'diff' query
parameter MUST also be included.
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If included, the 'cursor' query parameter specifies an unsigned
integer value that was provided by the AS in a previous response
from the TRL endpoint (see Section 8.1, Section 8.2.2, and
Section 8.2.3).
If the AS does not support the "Cursor" extension, it ignores the
'cursor' query parameter when present in the GET request. In such
a case, the AS proceeds as specified elsewhere in this document,
i.e.: i) it performs a diff query of the TRL (see Section 7), if
it supports diff queries and the 'diff' query parameter is present
in the GET request; or ii) it performs a full query of the TRL
(see Section 6) otherwise.
If the AS supports both diff queries and the "Cursor" extension,
and the GET request specifies the 'cursor' query parameter, then
the AS MUST return a 4.00 (Bad Request) response in case any of
the conditions below holds.
The 4.00 (Bad Request) response MUST have Content-Format
"application/concise-problem-details+cbor" and its payload is
formatted as defined in Section 5.1.
- The GET request does not specify the 'diff' query parameter,
irrespective of the value of the 'cursor' parameter.
Within the Custom Problem Detail entry 'ace-trl-error', the
value of the 'error-id' field MUST be set to 1 ("Invalid set of
parameters"), and the field 'cursor' MUST NOT be present.
- The 'cursor' query parameter has a value that is neither 0 nor
a positive integer, or it has a value strictly greater than
MAX_INDEX (see Section 5.2.1).
Within the Custom Problem Detail entry 'ace-trl-error', the
value of the 'error-id' field MUST be set to 0 ("Invalid
parameter value"). The entry 'ace-trl-error' MUST include the
field 'cursor', whose value is either: the CBOR simple value
null (0xf6), if the update collection associated with the
requester is empty; or the corresponding current value of
'last_index' otherwise.
- All of the following hold: the update collection associated
with the requester is not empty; no wrap-around of its 'index'
value has occurred; and the 'cursor' query parameter has a
value strictly greater than the current 'last_index' on the
update collection (see Section 5.2.1).
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Within the Custom Problem Detail entry 'ace-trl-error', the
value of the 'error-id' field MUST be set to 2 ("Out of bound
cursor value"), and the field 'cursor' MUST NOT be present.
6. Full Query of the TRL
In order to produce a (notification) response to a GET request asking
for a full query of the TRL, the AS performs the following actions.
1. From the TRL, the AS builds a set HASHES such that:
* If the requester is a registered device, HASHES specifies the
token hashes currently in the TRL and associated with the
access tokens pertaining to that registered device. The AS
can always use the authenticated identity of the registered
device to perform the necessary filtering on the TRL content.
* If the requester is an administrator, HASHES specifies all the
token hashes currently in the TRL.
2. The AS sends a 2.05 (Content) response to the requester. The
response MUST have Content-Format "application/ace-trl+cbor".
The payload of the response is a CBOR map, which MUST be
formatted as follows.
* The 'full_set' parameter MUST be included and specifies a CBOR
array 'full_set_value'. Each element of 'full_set_value' is a
CBOR byte string, with value one of the token hashes from the
set HASHES. If the set HASHES is empty, the 'full_set'
parameter specifies the empty CBOR array.
The CBOR array MUST be treated as a set, i.e., the order of
its elements has no meaning.
* The 'cursor' parameter MUST be included if the AS supports
both diff queries and the related "Cursor" extension (see
Section 5.2 and Section 5.2.1). Its value is set as specified
in Section 8.1, and provides the requester with information
for performing a follow-up diff query using the "Cursor"
extension (see Section 8.2).
If the AS does not support both diff queries and the "Cursor"
extension, this parameter MUST NOT be included. In case the
requester does not support both diff queries and the "Cursor"
extension, it MUST silently ignore the 'cursor' parameter if
present.
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Figure 5 provides the CDDL definition [RFC8610] of the CBOR array
'full_set_value' specified in the response from the AS, as value of
the 'full_set' parameter.
token_hash = bytes
full_set_value = [* token_hash]
Figure 5: CDDL definition of 'full_set_value'
Figure 6 shows an example response from the AS, following a full
query request to the TRL endpoint. In this example, the AS does not
support diff queries nor the "Cursor" extension, hence the 'cursor'
parameter is not included in the payload of the response. Also, full
token hashes are omitted for brevity.
Header: Content (Code=2.05)
Content-Format: application/ace-trl+cbor
Payload:
{
e'full_set' : [
h'01fa51cc/...
(remainder of the token hash omitted for brevity)/',
h'01748190/...
(remainder of the token hash omitted for brevity)/'
]
}
Figure 6: Example of response following a full query request to
the TRL endpoint
7. Diff Query of the TRL
In order to produce a (notification) response to a GET request asking
for a diff query of the TRL, the AS performs the following actions.
Note that, if the AS supports both diff queries and the related
"Cursor" extension, the steps 3 and 4 defined below are extended as
defined in Section 8.2.
1. The AS defines the positive integer NUM as follows. If the value
N specified in the 'diff' query parameter in the GET request is
equal to 0 or greater than the pre-defined positive integer MAX_N
(see Section 5.2), then NUM takes the value of MAX_N. Otherwise,
NUM takes N.
2. The AS determines U = min(NUM, SIZE), where SIZE <= MAX_N. In
particular, SIZE is the number of diff entries currently stored
in the requester's update collection.
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3. The AS prepares U diff entries. If U is equal to 0 (e.g.,
because SIZE is equal to 0 at step 2), then no diff entries are
prepared.
The prepared diff entries are related to the U most recent TRL
updates pertaining to the requester, as maintained in the update
collection for that requester (see Section 5.2). In particular,
the first diff entry refers to the most recent of such updates,
the second diff entry refers to the second from last of such
updates, and so on.
Each diff entry is a CBOR array 'diff_entry', which includes the
following two elements.
* The first element is a 'trl_patch' set of token hashes,
encoded as a CBOR array 'removed'. Each element of the array
is a CBOR byte string, with value the token hash of an access
token such that: it pertained to the requester; and it was
removed from the TRL during the update associated with the
diff entry.
* The second element is a 'trl_patch' set of token hashes,
encoded as a CBOR array 'added'. Each element of the array is
a CBOR byte string, with value the token hash of an access
token such that: it pertains to the requester; and it was
added to the TRL during the update associated with the diff
entry.
The CBOR arrays 'removed' and 'added' MUST be treated as sets,
i.e., the order of their elements has no meaning.
4. The AS prepares a 2.05 (Content) response for the requester. The
response MUST have Content-Format "application/ace-trl+cbor".
The payload of the response is a CBOR map, which MUST be
formatted as follows.
* The 'diff_set' parameter MUST be present and specifies a CBOR
array 'diff_set_value' of U elements. Each element of
'diff_set_value' specifies one of the CBOR arrays 'diff_entry'
prepared above as a diff entry. Note that U might have value
0, in which case 'diff_set_value' is the empty CBOR array.
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Within 'diff_set_value', the CBOR arrays 'diff_entry' MUST be
sorted to reflect the corresponding updates to the TRL in
reverse chronological order. That is, the first 'diff_entry'
element of 'diff_set_value' relates to the most recent TRL
update pertaining to the requester. The second 'diff_entry'
element relates to the second from last most recent TRL update
pertaining to the requester, and so on.
* The 'cursor' parameter and the 'more' parameter MUST be
included if the AS supports both diff queries and the related
"Cursor" extension (see Section 5.2.1). Their values are set
as specified in Section 8.2, and provide the requester with
information for performing a follow-up query of the TRL (see
Section 8.2).
In case the AS supports diff queries but not the "Cursor"
extension, these parameters MUST NOT be included. In case the
requester supports diff queries but not the "Cursor"
extension, it MUST silently ignore the 'cursor' parameter and
the 'more' parameter if present.
Figure 7 provides the CDDL definition [RFC8610] of the CBOR array
'diff_set_value' specified in the response from the AS, as value of
the 'diff_set' parameter.
token_hash = bytes
trl_patch = [* token_hash]
diff_entry = [removed: trl_patch, added: trl_patch]
diff_set_value = [* diff_entry]
Figure 7: CDDL definition of 'diff_set_value'
Figure 8 shows an example response from the AS, following a diff
query request to the TRL endpoint, where U = 3 diff entries are
specified. In this example, the AS does not support the "Cursor"
extension, hence the 'cursor' parameter and the 'more' parameter are
not included in the payload of the response. Also, full token hashes
are omitted for brevity.
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Header: Content (Code=2.05)
Content-Format: application/ace-trl+cbor
Payload:
{
e'diff_set' : [
[
[ h'01fa51cc/...
(remainder of the token hash omitted for brevity)/',
h'01748190/...
(remainder of the token hash omitted for brevity)/'
],
[ h'01cdf1ca/...
(remainder of the token hash omitted for brevity)/',
h'01be41a6/...
(remainder of the token hash omitted for brevity)/'
]
],
[
[ h'0144dd12/...
(remainder of the token hash omitted for brevity)/',
h'01231fff/...
(remainder of the token hash omitted for brevity)/'
],
[]
],
[
[],
[ h'01ca986f/...
(remainder of the token hash omitted for brevity)/',
h'01fe1a2b/...
(remainder of the token hash omitted for brevity)/'
]
]
]
}
Figure 8: Example of response following a diff query request to
the TRL endpoint
Appendix A discusses how performing a diff query of the TRL is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
8. Response Messages when Using the "Cursor" Extension
If the AS supports both diff queries and the "Cursor" extension, it
composes a response to a full query request or diff query request as
defined in Section 8.1 and Section 8.2, respectively.
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The exact format of the response depends on the request being a full
query or diff query request, on the presence of the 'diff' and
'cursor' query parameters and their values in the diff query request,
and on the current status of the update collection associated with
the requester.
Error handling and the possible resulting error responses are as
defined in Section 5.3.
8.1. Response to Full Query
When processing a full query request to the TRL endpoint, the AS
composes a response as defined in Section 6.
In particular, the 'cursor' parameter included in the CBOR map
carried in the response payload specifies either the CBOR simple
value null (0xf6) or a CBOR unsigned integer.
The 'cursor' parameter MUST specify the CBOR simple value null in
case there are currently no TRL updates pertaining to the requester,
i.e., the update collection for that requester is empty. This is the
case from when the requester registers at the AS until the first
update pertaining to that requester occurs to the TRL.
Otherwise, the 'cursor' parameter MUST specify a CBOR unsigned
integer. This MUST take the 'index' value of the last series item in
the update collection associated with the requester (see
Section 5.2.1), as corresponding to the most recent TRL update
pertaining to the requester. Such a value is in fact the current
value of 'last_index' for the update collection associated with the
requester.
8.2. Response to Diff Query
When processing a diff query request to the TRL endpoint, the AS
composes a response as defined in the following.
8.2.1. Empty Collection
If the update collection associated with the requester has no
elements, the AS returns a 2.05 (Content) response. The response
MUST have Content-Format "application/ace-trl+cbor" and its payload
MUST be a CBOR map formatted as follows.
* The 'diff_set' parameter MUST be included and specifies the empty
CBOR array.
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* The 'cursor' parameter MUST be included and specifies the CBOR
simple value null (0xf6).
* The 'more' parameter MUST be included and specifies the CBOR
simple value false (0xf4).
Note that the above applies when the update collection associated
with the requester has no elements, regardless of whether the
'cursor' query parameter is included or not in the diff query
request, and irrespective of the specified unsigned integer value if
present.
8.2.2. Cursor Not Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request does not include the 'cursor' query
parameter, the AS performs the actions defined in Section 7, with the
following differences.
* At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 5.2.1), and prepares L = min(U, MAX_DIFF_BATCH) diff
entries.
If U <= MAX_DIFF_BATCH, the prepared diff entries are the last
series items in the update collection associated with the
requester, corresponding to the L most recent TRL updates
pertaining to the requester.
If U > MAX_DIFF_BATCH, the prepared diff entries are the eldest of
the last U series items in the update collection associated with
the requester, as corresponding to the first L of the U most
recent TRL updates pertaining to the requester.
* At step 4, the CBOR map to carry in the payload of the 2.05
(Content) response MUST be formatted as follows.
- The 'diff_set' parameter MUST be present and specifies a CBOR
array 'diff_set_value' of L elements. Each element of
'diff_set_value' specifies one of the CBOR arrays 'diff_entry'
prepared as a diff entry.
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- The 'cursor' parameter MUST be present and specifies a CBOR
unsigned integer. This MUST take the 'index' value of the
series item of the update collection included as first diff
entry in the 'diff_set_value' CBOR array, which is specified by
the 'diff_set' parameter. That is, the 'cursor' parameter
takes the 'index' value of the series item in the update
collection corresponding to the most recent TRL update
pertaining to the requester and returned in this diff query
response.
Note that the 'cursor' parameter takes the same 'index' value
of the last series item in the update collection when U <=
MAX_DIFF_BATCH.
- The 'more' parameter MUST be present and MUST specify the CBOR
simple value false (0xf4) if U <= MAX_DIFF_BATCH, or the CBOR
simple value true (0xf5) otherwise.
If the 'more' parameter in the payload of the received 2.05 (Content)
response has value true, the requester can send a follow-up diff
query request including the 'cursor' query parameter, with the same
value of the 'cursor' parameter specified in this diff query
response. As defined in Section 8.2.3, this would result in the AS
transferring the following subset of series items as diff entries,
thus resuming from where interrupted in the previous transfer.
8.2.3. Cursor Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request includes the 'cursor' query parameter with
value P, the AS proceeds as follows, depending on which of the
following two cases hold.
* Case A - The series item X with 'index' having value P and the
series item Y with 'index' having value (P + 1) % (MAX_INDEX + 1)
are both not found in the update collection associated with the
requester. This occurs when the item Y (and possibly further ones
after it) has been previously removed from the update collection
for that requester (see step 5 at Section 5.2).
In this case, the AS returns a 2.05 (Content) response. The
response MUST have Content-Format "application/ace-trl+cbor" and
its payload MUST be a CBOR map formatted as follows.
- The 'diff_set' parameter MUST be included and specifies the
empty CBOR array.
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- The 'cursor' parameter MUST be included and specifies the CBOR
simple value null (0xf6).
- The 'more' parameter MUST be included and specifies the CBOR
simple value true (0xf5).
With the combination ('cursor', 'more') = (null, true), the AS is
indicating that the update collection is in fact not empty, but
that one or more series items have been lost due to their removal.
These include the item with 'index' value (P + 1) % (MAX_INDEX +
1), that the requester wished to obtain as the first one following
the specified reference point with 'index' value P.
When receiving this diff query response, the requester SHOULD send
a new full query request to the AS. A successful response
provides the requester with the full, current pertaining subset of
the TRL, as well as with a valid value of the 'cursor' parameter
(see Section 8.1) to be possibly used as query parameter in a
following diff query request.
* Case B - The series item X with 'index' having value P is found in
the update collection associated with the requester; or the series
item X is not found and the series item Y with 'index' having
value (P + 1) % (MAX_INDEX + 1) is found in the update collection
associated with the requester.
In this case, the AS performs the actions defined in Section 7,
with the following differences.
- At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 5.2.1), and prepares L = min(SUB_U, MAX_DIFF_BATCH)
diff entries, where SUB_U = min(NUM, SUB_SIZE), and SUB_SIZE is
the number of series items in the update collection starting
from and including the series item added immediately after X.
If L is equal to 0 (e.g., because SUB_U is equal to 0), then no
diff entries are prepared.
If SUB_U <= MAX_DIFF_BATCH, the prepared diff entries are the
last series items in the update collection associated with the
requester, corresponding to the L most recent TRL updates
pertaining to the requester.
If SUB_U > MAX_DIFF_BATCH, the prepared diff entries are the
eldest of the last SUB_U series items in the update collection
associated with the requester, corresponding to the first L of
the SUB_U most recent TRL updates pertaining to the requester.
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- At step 4, the CBOR map to carry in the payload of the 2.05
(Content) response MUST be formatted as follows.
o The 'diff_set' parameter MUST be present and specifies a
CBOR array 'diff_set_value' of L elements. Each element of
'diff_set_value' specifies one of the CBOR arrays
'diff_entry' prepared as a diff entry. Note that L might
have value 0, in which case 'diff_set_value' is the empty
CBOR array.
o The 'cursor' parameter MUST be present and MUST specify a
CBOR unsigned integer. In particular:
+ If L is equal to 0, i.e., the series item X is the last
one in the update collection, then the 'cursor' parameter
MUST take the same 'index' value of the last series item
in the update collection. Such a value is in fact the
current value of 'last_index' for the update collection.
+ If L is different than 0, then the 'cursor' parameter
MUST take the 'index' value of the series element of the
update collection included as first diff entry in the
'diff_set' CBOR array. That is, the 'cursor' parameter
takes the 'index' value of the series item in the update
collection corresponding to the most recent TRL update
pertaining to the requester and returned in this diff
query response.
Note that the 'cursor' parameter takes the same 'index'
value of the last series item in the update collection when
SUB_U <= MAX_DIFF_BATCH.
o The 'more' parameter MUST be present and MUST specify the
CBOR simple value false (0xf4) if SUB_U <= MAX_DIFF_BATCH,
or the CBOR simple value true (0xf5) otherwise.
If the 'more' parameter in the payload of the received 2.05
(Content) response has value true, the requester can send a
follow-up diff query request including the 'cursor' query
parameter, with the same value of the 'cursor' parameter specified
in this diff query response. This would result in the AS
transferring the following subset of series items as diff entries,
thus resuming from where interrupted in the previous transfer.
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9. Registration at the Authorization Server
During the registration process at the AS, an administrator or a
registered device receives the following information as part of the
registration response.
* The url-path to the TRL endpoint at the AS.
* The hash function used to compute token hashes. This is specified
by identifying an entry in the "Named Information Hash Algorithm"
Registry [Named.Information.Hash.Algorithm]. The specific means
for this is outside the scope of this document.
* A positive integer MAX_N, if the AS supports diff queries of the
TRL (see Section 5.2 and Section 7).
* A positive integer MAX_DIFF_BATCH, if the AS supports diff queries
of the TRL as well as the related "Cursor" extension (see
Section 5.2.1 and Section 8).
When communicating with one another, the registered devices and the
AS have to use a secure communication association and be mutually
authenticated (see Section 5 of [RFC9200]).
In the same spirit, it MUST be ensured that communications between
the AS and an administrator are mutually authenticated, encrypted and
integrity protected, as well as protected against message replay.
Before starting its registration process at the AS, an administrator
has to establish such a secure communication association with the AS,
if they do not share one already. In particular, mutual
authentication is REQUIRED during the establishment of the secure
association. To this end, the administrator and the AS can rely,
e.g., on establishing a TLS or DTLS secure session with mutual
authentication [RFC8446][RFC9147], or an OSCORE Security Context
[RFC8613] by running the authenticated key exchange protocol EDHOC
[RFC9528].
When receiving authenticated requests from the administrator for
accessing the TRL endpoint, the AS can always check whether the
requester is authorized to take such a role, i.e., to access the full
TRL.
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To this end, the AS may rely on a local access control list or
similar, which specifies the authentication credentials of trusted,
authorized administrators. In particular, the AS verifies the
requester to the TRL endpoint as an authorized administrator, only if
the access control list includes the same authentication credential
used by the requester when establishing the mutually-authenticated
secure communication association with the AS.
Further details about the registration process at the AS are out of
scope for this specification. Note that the registration process is
also out of the scope of the ACE framework for Authentication and
Authorization (see Section 5.5 of [RFC9200]).
10. Notification of Revoked Access Tokens
Once registered at the AS, the administrator or registered device can
send a GET request to the TRL endpoint at the AS. The request can
express the wish for a full query (see Section 6) or a diff query
(see Section 7) of the TRL. Also, the request can include the CoAP
Observe Option set to 0 (register), in order to start an observation
of the TRL endpoint as per Section 3.1 of [RFC7641].
In case the request is successfully processed, the AS replies with a
response specifying the CoAP response code 2.05 (Content). In
particular, if the AS supports diff queries but not the "Cursor"
extension (see Section 5.2 and Section 5.2.1), then the payload of
the response is formatted as defined in Section 6 or in Section 7, in
case the GET request has yielded the execution of a full query or of
a diff query of the TRL, respectively. Instead, if the AS supports
both diff queries and the related "Cursor" extension, then the
payload of the response is formatted as defined in Section 8.
When the TRL is updated (see Section 4.1), the AS sends Observe
notifications to the observers whose pertaining subset of the TRL has
changed. Observe notifications are sent as per Section 4.2 of
[RFC7641]. If supported by the AS, an observer may configure the
behavior according to which the AS sends those Observe notifications.
To this end, a possible way relies on the conditional control
attribute "c.pmax" defined in [I-D.ietf-core-conditional-attributes],
which can be included as a "name=value" query parameter in an
Observation Request. This ensures that no more than c.pmax seconds
elapse between two consecutive notifications sent to that observer,
regardless of whether the TRL has changed or not.
Following a first exchange with the AS, an administrator or a
registered device can send additional GET (Observation) requests to
the TRL endpoint at any time, analogously to what is defined above.
When doing so, the requester towards the TRL endpoint can perform a
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full query (see Section 6) or a diff query (see Section 7) of the
TRL. In the latter case, the requester can additionally rely on the
"Cursor" extension (see Section 5.3 and Section 8.2).
As specified in Section 5.2, an AS supporting diff queries maintains
an update collection of maximum MAX_N series items for each
administrator or registered device, hereafter referred to as
requester. In particular, if an update collection includes MAX_N
series items, adding a further series item to that update collection
results in deleting the oldest series item from that update
collection.
From then on, the requester associated with the update collection
will not be able to retrieve the deleted series item, when sending a
new diff query request to the TRL endpoint. If that series item
reflected the revocation of an access token pertaining to the
requester, then the requester will not learn about that when
receiving the corresponding diff query response from the AS.
Sending a diff query request specifically as an Observation request,
and thus relying on Observe notifications, largely reduces the
chances for a requester to miss updates occurred to its associated
update collection altogether. In turn, this relies on the requester
successfully receiving the Observe notification responses from the
TRL (see also Section 13.3).
In order to limit the amount of time during which the requester is
unaware of pertaining access tokens that have been revoked but are
not expired yet, a requester SHOULD NOT rely solely on diff query
requests. In particular, a requester SHOULD also regularly send a
full query request to the TRL endpoint according to a related
application policy.
10.1. Handling of Access Tokens and Token Hashes
When receiving a response from the TRL endpoint, a registered device
MUST expunge every stored access token associated with a token hash
specified in the response. In case the registered device is an RS,
it MUST NOT delete the stored token hash after having expunged the
associated access token.
An RS MUST NOT accept and store an access token, if the corresponding
token hash is among the currently stored ones.
An RS MUST store the token hash th1 corresponding to an access token
t1 until both the following conditions hold.
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* The RS has received and seen t1, irrespective of having accepted
and stored it.
* The RS has gained knowledge that t1 has expired. This can be
achieved, e.g., through the following means.
- A response from the TRL endpoint indicating that t1 has expired
after its earlier revocation, i.e., the token hash th1 has been
removed from the TRL. This can be indicated, for instance, in
a response from the TRL endpoint following a diff query of the
TRL (see Section 7).
- The value of the 'exp' claim specified in t1 indicates that t1
has expired.
- The locally determined expiration time for t1 has passed, based
on the time at the RS when t1 was first accepted and on the
value of its 'exi' claim.
- The result of token introspection performed on t1 (see
Section 5.9 of [RFC9200]), if supported by both the RS and the
AS.
The RS MUST NOT delete the stored token hashes whose corresponding
access tokens do not fulfill both the two conditions above, unless it
becomes necessary due to memory limitations. In such a case, the RS
MUST delete the earliest stored token hashes first.
Retaining the stored token hashes as specified above limits the
impact from a (dishonest) Client whose pertaining access token: i)
specifies the 'exi' claim; ii) is uploaded at the RS for the first
time after it has been revoked and later expired; and iii) has the
sequence number encoded in the 'cti' claim greater than the highest
sequence number among the expired access tokens specifying the 'exi'
claim for the RS (see Section 5.10.3 of [RFC9200]). That is, the RS
would not accept such a revoked and expired access token as long as
it stores the corresponding token hash.
In order to further limit such a risk, when receiving an access token
that specifies the 'exi' claim and for which a corresponding token
hash is not stored, the RS can introspect the access token (see
Section 5.9 of [RFC9200]), if token introspection is implemented by
both the RS and the AS.
When, due to the stored and corresponding token hash th2, an access
token t2 that includes the 'exi' claim is expunged or is not accepted
upon its upload, the RS retrieves the sequence number sn2 encoded in
the 'cti' claim (see Section 5.10.3 of [RFC9200]). Then, the RS
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stores sn2 as associated with th2. If expunging or not accepting t2
yields the deletion of th2, then the RS MUST associate sn2 with th2
before continuing with the deletion of th2.
When deleting any token hash, the RS checks whether the token hash is
associated with a sequence number sn_th. In such a case, the RS
checks whether sn_th is greater than the highest sequence number sn*
among the expired access tokens specifying the 'exi' claim for the
RS. If that is the case, sn* MUST take the value of sn_th.
By virtue of what is defined in Section 5.10.3 of [RFC9200], this
ensures that, following the deletion of the token hash associated
with an access token specifying the 'exi' claim and uploaded for the
first time after it has been revoked and later expired, the RS will
not accept the access token at that point in time or in the future.
11. ACE Token Revocation List Parameters
This specification defines a number of parameters that can be
transported in the response from the TRL endpoint, when the response
payload is a CBOR map. Note that such a response MUST use the
Content-Format "application/ace-trl+cbor" defined in Section 14.2 of
this specification.
The table below summarizes the parameters. For each of them, it
specifies the value to use as CBOR key, i.e., as abbreviation in the
key of the map pair for the parameter, instead of the parameter's
name as a text string.
+==========+==========+==========================+
| Name | CBOR Key | CBOR Type |
+==========+==========+==========================+
| full_set | 0 | array |
+----------+----------+--------------------------+
| diff_set | 1 | array |
+----------+----------+--------------------------+
| cursor | 2 | Null or unsigned integer |
+----------+----------+--------------------------+
| more | 3 | True or False |
+----------+----------+--------------------------+
Table 1: CBOR abbreviations for the ACE Token
Revocation List parameters
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12. ACE Token Revocation List Error Identifiers
This specification defines a number of values that the AS can use as
error identifiers. These are used in error responses with Content-
Format "application/concise-problem-details+cbor", as values of the
'error-id' field within the Custom Problem Detail entry 'ace-trl-
error' (see Section 5.1).
+=======+===========================+
| Value | Description |
+=======+===========================+
| 0 | Invalid parameter value |
+-------+---------------------------+
| 1 | Invalid set of parameters |
+-------+---------------------------+
| 2 | Out of bound cursor value |
+-------+---------------------------+
Table 2: ACE Token Revocation
List Error Identifiers
13. Security Considerations
The protocol defined in this document inherits the security
considerations from the ACE framework for Authentication and
Authorization [RFC9200], from [RFC8392] as to the usage of CWTs, from
[RFC7519] as to the usage of JWTs, from [RFC7641] as to the usage of
CoAP Observe, and from [RFC6920] with regard to computing the token
hashes. The following considerations also apply.
13.1. Content Retrieval from the TRL
The AS MUST ensure that each registered device can access and
retrieve only its pertaining subset of the TRL. To this end, the AS
can always perform the required filtering based on the authenticated
identity of the registered device, i.e., a (non-public) identifier
that the AS can securely relate to the registered device and the
secure association that they use to communicate.
The AS MUST ensure that, other than registered devices accessing
their own pertaining subset of the TRL, only authorized and
authenticated administrators can retrieve the full TRL (see
Section 9).
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13.2. Size of the TRL
If many non-expired access tokens associated with a registered device
are revoked, the pertaining subset of the TRL could grow to a size
bigger than what the registered device is prepared to handle upon
reception of a response from the TRL endpoint, especially if relying
on a full query of the TRL (see Section 6).
This could be exploited by attackers to negatively affect the
behavior of a registered device. Therefore, in order to help reduce
the size of the TRL, the AS SHOULD refrain from issuing access tokens
with an excessively long expiration time.
13.3. Communication Patterns
The communication about revoked access tokens presented in this
specification is expected to especially rely on CoAP Observe
notifications sent from the AS to a requester (i.e., an administrator
or a registered device). The suppression of those notifications by
an external attacker that has access to the network would prevent
requesters from ever knowing that their pertaining access tokens have
been revoked.
In order to avoid this, a requester SHOULD NOT rely solely on the
CoAP Observe notifications. In particular, a requester SHOULD also
regularly poll the AS for the most current information about revoked
access tokens, by sending GET requests to the TRL endpoint according
to a related application policy.
13.4. Request of New Access Tokens
If a Client stores an access token that it still believes to be
valid, and it accordingly attempts to access a protected resource at
the RS, the Client may receive an unprotected 4.01 (Unauthorized)
response from the RS.
This can be due to a number of causes. For example, the access token
has been revoked, and the RS has become aware of it and has expunged
the access token, but the Client is not aware of it (yet). As
another example, the access token is still valid, but an on-path
active adversary might have injected a forged 4.01 (Unauthorized)
response, or the RS might have deleted the access token from its
local storage due to its dedicated storage space being all consumed.
In either case, if the Client believes that the access token is still
valid, it SHOULD NOT immediately ask for a new access token to the
Authorization Server upon receiving a 4.01 (Unauthorized) response
from the RS. Instead, the Client SHOULD send a request to the TRL
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endpoint at the AS. If the Client gains knowledge that the access
token is not valid anymore, the Client expunges the access token and
can ask for a new one. Otherwise, the Client can try again to upload
the same access token to the RS, or instead to request a new one.
13.5. Vulnerable Time Window at the RS
A Client may attempt to access a protected resource at an RS after
the access token allowing such an access has been revoked, but before
the RS is aware of the revocation.
In such a case, if the RS is still storing the access token, the
Client will be able to access the protected resource, even though it
should not. Such an access is a security violation, even if the
Client is not attempting to be malicious.
In order to minimize such a risk, if an RS relies solely on polling
through individual requests to the TRL endpoint to learn of revoked
access tokens, the RS SHOULD implement an adequate trade-off between
the polling frequency and the maximum length of the vulnerable time
window.
13.6. Two Token Hashes at the RS using JWTs
Section 3.3.2 defines that an RS using JWTs as access tokens has to
compute and store two token hashes associated with the same access
token. This is because, when using JWTs, the RS does not know for
sure if the AS provided the access token to the Client by means of an
AS-to-Client response encoded in CBOR or in JSON.
Taking advantage of that, a dishonest Client can attempt to perform
an attack against the RS. That is, the Client can first receive the
JWT in an AS-to-Client response encoded in CBOR (JSON). Then, the
Client can upload the JWT to the RS in a way that makes the RS
believe that the Client instead received the JWT in an AS-to-Client
response encoded in JSON (CBOR).
Consequently, the RS considers a HASH_INPUT different from the one
considered by the AS and the Client (see Section 3.2). Hence, the RS
computes a token hash h' different from the token hash h computed by
the AS and the Client. It follows that, if the AS revokes the access
token and advertises the right token hash h, then the RS will not
learn about the access token revocation and thus will not delete the
access token.
Fundamentally, this would happen because the HASH_INPUT used to
compute the token hash of a JWT depends on whether the AS-to-Client
response is encoded in CBOR or in JSON. This makes the RS vulnerable
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to the attack described above, when JWTs are used as access tokens.
Instead, this is not a problem if the access token is a CWT, since
the HASH_INPUT used to compute the token hash of a CWT does not
depend on whether the AS-to-Client response is encoded in CBOR or in
JSON.
While this asymmetry cannot be avoided altogether, the method defined
for the AS and the Client in Section 3.2 deliberately penalizes the
case where the RS uses JWTs as access tokens. In such a case, the RS
effectively neutralizes the attack described above, by computing and
storing two token hashes associated with the same access token (see
Section 3.3.2).
Conversely, this design deliberately favors the case where the RS
uses CWTs as access tokens, which is a preferable option for
resource-constrained RSs as well as the default case in the ACE
framework (see Section 3 of [RFC9200]). That is, if an RS uses CWTs
as access tokens, then the RS is not exposed to the attack described
above, and thus it safely computes and stores only one token hash per
access token (see Section 3.3.1).
13.7. Additional Security Measures
By accessing the TRL at the AS, registered devices and administrators
are able to learn that their pertaining access tokens have been
revoked. However, they cannot learn the reason why that happened,
including when that reason is the compromise, misbehavior, or
decommissioning of a registered device.
In fact, even the AS might not know that a registered device to which
a revoked access token pertains has been specifically compromised,
misbehaving, or decommissioned. At the same time, it might not be
acceptable to only revoke the access tokens pertaining to such a
registered device.
Therefore, in order to preserve the security of the system and
application, the entity that authoritatively declares a registered
device to be compromised, misbehaving, or decommissioned should also
promptly trigger the execution of additional revocation processes as
deemed appropriate. These include, for instance:
* The de-registration of the registered device from the AS, so that
the AS does not issue further access tokens pertaining to that
device.
* If applicable, the revocation of the public authentication
credential associated with the registered device (e.g., its public
key certificate).
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The methods by which these processes are triggered and carried out
are out of the scope of this document.
14. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
14.1. Media Type Registrations
IANA is asked to register the media type "application/ace-trl+cbor"
for messages of the protocol defined in this document encoded in
CBOR. This registration follows the procedures specified in
[RFC6838].
Type name: application
Subtype name: ace-trl+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: Must be encoded as a CBOR map containing the
protocol parameters defined in [RFC-XXXX].
Security considerations: See Section 13 of this document.
Interoperability considerations: N/A
Published specification: [RFC-XXXX]
Applications that use this media type: The type is used by
Authorization Servers, Clients, and Resource Servers that support the
notification of revoked access tokens, according to a Token
Revocation List maintained by the Authorization Server as specified
in [RFC-XXXX].
Fragment identifier considerations: N/A
Additional information: N/A
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)
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Intended usage: COMMON
Restrictions on usage: None
Author/Change controller: IETF
Provisional registration: No
14.2. CoAP Content-Formats Registry
IANA is asked to add the following entry to the "CoAP Content-
Formats" registry within the "Constrained RESTful Environments (CoRE)
Parameters" registry group.
Content Type: application/ace-trl+cbor
Content Coding: -
ID: TBD
Reference: [RFC-XXXX]
14.3. Custom Problem Detail Keys Registry
IANA is asked to register the following entry in the "Custom Problem
Detail Keys" registry within the "Constrained RESTful Environments
(CoRE) Parameters" registry group.
* Key Value: TBD
* Name: ace-trl-error
* Brief Description: Carry [RFC-XXXX] problem details in a Concise
Problem Details data item.
* Change Controller: IETF
* Reference: Section 5.1 of [RFC-XXXX]
14.4. ACE Token Revocation List Parameters Registry
IANA is asked to establish the "ACE Token Revocation List Parameters"
IANA registry within the "Authentication and Authorization for
Constrained Environments (ACE)" registry group.
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As registration policy, the registry uses either "Standards Action
with Expert Review", or "Specification Required" per Section 4.6 of
[RFC8126], or "Expert Review" per Section 4.5 of [RFC8126]. Expert
Review guidelines are provided in Section 14.6.
All assignments according to "Standards Action with Expert Review"
are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
with Expert Review additionally required per Section 4.5 of
[RFC8126]. The procedure for early IANA allocation of Standards
Track code points defined in [RFC7120] also applies. When such a
procedure is used, review and approval by the designated expert are
also required, in order for the WG chairs to determine that the
conditions for early allocation are met (see step 2 in Section 3.1 of
[RFC7120]).
The columns of this registry are:
* Name: This field contains a descriptive name that enables easier
reference to the item. The name MUST be unique and it is not used
in the encoding.
* CBOR Key: This field contains the value used as CBOR map key of
the item. The value MUST be unique. The value is an unsigned
integer or a negative integer. Different ranges of values use
different registration policies [RFC8126]. Integer values from
-256 to 255 are designated as "Standards Action With Expert
Review". Integer values from -65536 to -257 and from 256 to 65535
are designated as "Specification Required". Integer values
greater than 65535 are designated as "Expert Review". Integer
values less than -65536 are marked as "Private Use".
* CBOR Type: This field contains the allowable CBOR data types for
values of this item, or a pointer to the registry that defines its
type, when that depends on another item.
* Reference: This field contains a pointer to the public
specification for the item.
This registry has been initially populated by the values in
Section 11. The "Reference" column for all of these entries refers
to this document.
14.5. ACE Token Revocation List Errors
IANA is asked to establish the "ACE Token Revocation List Errors"
IANA registry within the "Authentication and Authorization for
Constrained Environments (ACE)" registry group.
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As registration policy, the registry uses either "Standards Action
with Expert Review", or "Specification Required" per Section 4.6 of
[RFC8126], or "Expert Review" per Section 4.5 of [RFC8126]. Expert
Review guidelines are provided in Section 14.6.
All assignments according to "Standards Action with Expert Review"
are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
with Expert Review additionally required per Section 4.5 of
[RFC8126]. The procedure for early IANA allocation of Standards
Track code points defined in [RFC7120] also applies. When such a
procedure is used, review and approval by the designated expert are
also required, in order for the WG chairs to determine that the
conditions for early allocation are met (see step 2 in Section 3.1 of
[RFC7120]).
The columns of this registry are:
* Value: The field contains the value to be used to identify the
error. The value MUST be unique. The value is an unsigned
integer or a negative integer. Different ranges of values use
different registration policies [RFC8126]. Integer values from
-256 to 255 are designated as "Standards Action With Expert
Review". Integer values from -65536 to -257 and from 256 to 65535
are designated as "Specification Required". Integer values
greater than 65535 are designated as "Expert Review". Integer
values less than -65536 are marked as "Private Use".
* Description: This field contains a brief description of the error.
* Reference: This field contains a pointer to the public
specification defining the error, if one exists.
This registry has been initially populated by the values in
Section 12. The "Reference" column for all of these entries refers
to this document.
14.6. Expert Review Instructions
The IANA registries established in this document are defined as
"Standards Action with Expert Review", "Specification Required", or
"Expert Review", depending on the range of values for which an
assignment is requested. This section gives some general guidelines
for what the experts should be looking for, but they are being
designated as experts for a reason so they should be given
substantial latitude.
Expert reviewers should take into consideration the following points:
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* Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
registered and that the point is likely to be used in deployments.
The zones tagged as private use are intended for testing purposes
and closed environments. Code points in other ranges should not
be assigned for testing.
* Specifications are required for the "Standards Action With Expert
Review" range of point assignment. Specifications should exist
for "Specification Required" ranges, but early assignment before a
specification is available is considered to be permissible. For
the "Expert Review" range of point assignment, specifications are
recommended, and are needed if they are expected to be used
outside of closed environments in an interoperable way. When
specifications are not provided, the description provided needs to
have sufficient information to identify what the point is being
used for.
* Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.
15. References
15.1. Normative References
[Named.Information.Hash.Algorithm]
IANA, "Named Information Hash Algorithm",
<https://www.iana.org/assignments/named-information/named-
information.xhtml>.
[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/rfc/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
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[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/rfc/rfc6347>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
Keranen, A., and P. Hallam-Baker, "Naming Things with
Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
<https://www.rfc-editor.org/rfc/rfc6920>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <https://www.rfc-editor.org/rfc/rfc7120>.
[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/rfc/rfc7252>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/rfc/rfc7519>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/rfc/rfc7641>.
[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/rfc/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/rfc/rfc8174>.
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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/rfc/rfc8259>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[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/rfc/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/rfc/rfc8613>.
[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/rfc/rfc8949>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/rfc/rfc9200>.
[RFC9202] 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)", RFC 9202,
DOI 10.17487/RFC9202, August 2022,
<https://www.rfc-editor.org/rfc/rfc9202>.
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[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/rfc/rfc9203>.
[RFC9290] Fossati, T. and C. Bormann, "Concise Problem Details for
Constrained Application Protocol (CoAP) APIs", RFC 9290,
DOI 10.17487/RFC9290, October 2022,
<https://www.rfc-editor.org/rfc/rfc9290>.
[RFC9431] Sengul, C. and A. Kirby, "Message Queuing Telemetry
Transport (MQTT) and Transport Layer Security (TLS)
Profile of Authentication and Authorization for
Constrained Environments (ACE) Framework", RFC 9431,
DOI 10.17487/RFC9431, July 2023,
<https://www.rfc-editor.org/rfc/rfc9431>.
[RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
DOI 10.17487/RFC9528, March 2024,
<https://www.rfc-editor.org/rfc/rfc9528>.
15.2. Informative References
[I-D.bormann-t2trg-stp]
Bormann, C. and K. Hartke, "The Series Transfer Pattern
(STP)", Work in Progress, Internet-Draft, draft-bormann-
t2trg-stp-03, 7 April 2020,
<https://datatracker.ietf.org/doc/html/draft-bormann-
t2trg-stp-03>.
[I-D.ietf-core-conditional-attributes]
Koster, M., Soloway, A., and B. Silverajan, "Conditional
Attributes for Constrained RESTful Environments", Work in
Progress, Internet-Draft, draft-ietf-core-conditional-
attributes-06, 14 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
conditional-attributes-06>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <https://www.rfc-editor.org/rfc/rfc7009>.
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Appendix A. On using the Series Transfer Pattern
Performing a diff query of the TRL as specified in Section 7 is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
That is, a diff query enables the transfer of a series of diff
entries, with the AS specifying U <= MAX_N diff entries as related to
the U most recent TRL updates pertaining to a requester, i.e., a
registered device or an administrator.
When responding to a diff query request from a requester (see
Section 7), 'diff_set' is a subset of the update collection
associated with the requester, where each 'diff_entry' record is a
series item from that update collection. Note that 'diff_set'
specifies the whole current update collection when the value of U is
equal to SIZE, i.e., the current number of series items in the update
collection.
The value N of the 'diff' query parameter in the GET request allows
the requester and the AS to trade the amount of provided information
with the latency of the information transfer.
Since the update collection associated with each requester includes
up to MAX_N series items, the AS deletes the oldest series item when
a new one is generated and added to the end of the update collection,
due to a new TRL update pertaining to that requester (see
Section 5.2). This addresses the question "When can the server
decide to no longer retain older items?" raised in Section 3.2 of
[I-D.bormann-t2trg-stp].
Furthermore, performing a diff query of the TRL together with the
"Cursor" extension as specified in Section 8 in fact relies on the
"Cursor" pattern of the Series Transfer Pattern (see Section 3.3 of
[I-D.bormann-t2trg-stp]).
Appendix B. Local Supportive Parameters of the TRL Endpoint
Table 3 provides an aggregated overview of the local supportive
parameters that the AS internally uses at its TRL endpoint, when
supporting diff queries (see Section 5) and the "Cursor" extension
(see Section 5.2.1).
Except for MAX_N defined in Section 5.2, all the other parameters are
defined in Section 5.2.1 and are used only if the AS supports the
"Cursor" extension.
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For each parameter, the columns of the table specify the following
information. Both a registered device and an administrator are
referred to as "requester".
* Name: parameter name. A name with letters in uppercase denotes a
parameter whose value does not change after its initialization.
* Single instance: "Y", if there is a single parameter instance
associated with the TRL; or "N", if there is one parameter
instance per update collection (i.e., per requester).
* Description: short parameter description.
* Values: the unsigned integer values that the parameter can assume,
where LB and UB denote the inclusive lower bound and upper bound,
respectively, and "^" is the exponentiation operator.
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+================+==========+====================+==================+
| Name | Single | Description | Values |
| | instance | | |
+================+==========+====================+==================+
| MAX_N | Y | Max number of | LB = 1 |
| | | series items in | |
| | | the update | If supporting |
| | | collection of | "Cursor", then |
| | | each requester | UB = MAX_INDEX+1 |
+----------------+----------+--------------------+------------------+
| MAX_DIFF_BATCH | N | Max number of | LB = 1 |
| | | diff entries | |
| | | included in a | UB = MAX_N |
| | | diff query | |
| | | response when | |
| | | using "Cursor" | |
+----------------+----------+--------------------+------------------+
| MAX_INDEX | Y | Max value of each | LB = MAX_N-1 |
| | | instance of the | |
| | | 'index' parameter | UB = (2^64)-1 |
+----------------+----------+--------------------+------------------+
| index | N | Value associated | LB = 0 |
| | | with a series | |
| | | item of an update | UB = MAX_INDEX |
| | | collection | |
+----------------+----------+--------------------+------------------+
| last_index | N | The 'index' value | LB = 0 |
| | | of the most | |
| | | recently added | UB = MAX_INDEX |
| | | series item in an | |
| | | update collection | |
+----------------+----------+--------------------+------------------+
Table 3: Local Supportive Parameters of the TRL Endpoint
Appendix C. Interaction Examples
This section provides examples of interactions between an RS as a
registered device and an AS. In the examples, all the access tokens
issued by the AS are intended to be consumed by the considered RS.
The AS supports both full queries and diff queries of the TRL, as
defined in Section 6 and Section 7, respectively.
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Registration is assumed to be done by the RS sending a POST request
with an unspecified payload to the AS, which replies with a 2.01
(Created) response. The payload of the registration response is
assumed to be a CBOR map, which in turn is assumed to include the
following entries:
* a 'trl_path' parameter, specifying the path of the TRL endpoint;
* a 'trl_hash' parameter, specifying the "Hash Name String" of the
hash function used to compute token hashes as defined in
Section 3;
* a 'max_n' parameter, specifying the value of MAX_N, i.e., the
maximum number of series items that the AS retains in the update
collection associated with a registered device (see Section 7);
* possible further parameters related to the registration process.
Furthermore, 'h(x)' refers to the hash function used to compute the
token hashes, as defined in Section 3 of this specification and
according to [RFC6920]. Assuming the usage of CWTs transported in
AS-to-Client responses encoded in CBOR (see Section 3.2.1),
'bstr.h(t1)' and 'bstr.h(t2)' denote the CBOR byte strings with value
the token hashes of the access tokens t1 and t2, respectively.
C.1. Full Query with Observe
Figure 9 shows an interaction example considering a CoAP observation
and a full query of the TRL.
In this example, the AS does not support the "Cursor" extension.
Hence, the 'cursor' parameter is not included in the payload of the
responses to a full query request.
RS AS
| |
| Registration: POST |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.01 Created |
| Payload: { |
| / ... / |
| "trl_path" : "/revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10 |
| } |
| |
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| GET coap://as.example.com/revoke/trl/ |
| Observe: 0 |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 42 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [] |
| } |
| |
| ... |
| |
| (Access tokens t1 and t2 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access token t1 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 53 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1)] |
| } |
| |
| ... |
| |
| (Access token t2 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 64 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1), bstr.h(t2)] |
| } |
| |
| ... |
| |
| (Access token t1 expires) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 75 |
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| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t2)] |
| } |
| |
| ... |
| |
| (Access token t2 expires) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 86 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [] |
| } |
| |
Figure 9: Interaction for full query with Observe
C.2. Diff Query with Observe
Figure 10 shows an interaction example considering a CoAP observation
and a diff query of the TRL.
The RS indicates N = 3 as value of the 'diff' query parameter, i.e.,
as the maximum number of diff entries to be specified in a response
from the AS.
In this example, the AS does not support the "Cursor" extension.
Hence, the 'cursor' parameter and the 'more' parameter are not
included in the payload of the responses to a diff query request.
RS AS
| |
| Registration: POST |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.01 Created |
| Payload: { |
| / ... / |
| "trl_path" : "/revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10 |
| } |
| |
| GET coap://as.example.com/revoke/trl?diff=3 |
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| Observe: 0 |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 42 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [] |
| } |
| |
| ... |
| |
| (Access tokens t1 and t2 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access token t1 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 53 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
| ... |
| |
| (Access token t2 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 64 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
| ... |
| |
| (Access token t1 expires) |
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| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 75 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
| ... |
| |
| (Access token t2 expires) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 86 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ] |
| } |
| |
Figure 10: Interaction for diff query with Observe
C.3. Full Query with Observe plus Diff Query
Figure 11 shows an interaction example considering a CoAP observation
and a full query of the TRL.
The example also considers one of the notifications from the AS to
get lost in transmission, and thus not reaching the RS.
When this happens, and after a waiting time defined by the
application has elapsed, the RS sends a GET request with no Observe
Option to the AS, to perform a diff query of the TRL. The RS
indicates N = 8 as value of the 'diff' query parameter, i.e., as the
maximum number of diff entries to be specified in a response from the
AS.
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In this example, the AS does not support the "Cursor" extension.
Hence, the 'cursor' parameter is not included in the payload of the
responses to a full query request. Also, the 'cursor' parameter and
the 'more' parameter are not included in the payload of the responses
to a diff query request.
RS AS
| |
| Registration: POST |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.01 Created |
| Payload: { |
| / ... / |
| "trl_path" : "/revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10 |
| } |
| |
| GET coap://as.example.com/revoke/trl/ |
| Observe: 0 |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 42 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [] |
| } |
| |
| ... |
| |
| (Access tokens t1 and t2 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access token t1 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 53 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1)] |
| } |
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| |
| ... |
| |
| (Access token t2 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 64 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1), bstr.h(t2)] |
| } |
| |
| ... |
| |
| (Access token t1 expires) |
| |
|<---------------------------------------------------+
| 2.05 Content |
| Observe: 75 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t2)] |
| } |
| |
| ... |
| |
| (Access token t2 expires) |
| |
| Lost X <------------------------------------------+
| 2.05 Content |
| Observe: 86 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [] |
| } |
| |
| ... |
| |
| (Enough time has passed since |
| the latest received notification) |
| |
| |
| GET coap://as.example.com/revoke/trl?diff=8 |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 Content |
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| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
Figure 11: Interaction for full query with Observe plus diff query
C.4. Diff Query with Observe and "Cursor"
In this example, the AS supports the "Cursor" extension. Hence, the
CBOR map conveyed as payload of the registration response
additionally includes a "max_diff_batch" parameter. This specifies
the value of MAX_DIFF_BATCH, i.e., the maximum number of diff entries
that can be included in a response to a diff query request from this
RS.
Figure 12 shows an interaction example considering a CoAP observation
and a diff query of the TRL.
The RS specifies the query parameter 'diff' with value 3, i.e., the
maximum number of diff entries to be specified in a response from the
AS.
After the RS has not received a notification from the AS for a
waiting time defined by the application, the RS sends a GET request
with no Observe Option to the AS, to perform a diff query of the TRL.
This is followed up by a further diff query request that specifies
the query parameter 'cursor'. Note that the payload of the
corresponding response differs from the payload of the response to
the previous diff query request.
RS AS
| |
| Registration: POST |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.01 Created |
| Payload: { |
| / ... / |
| "trl_path" : "/revoke/trl", |
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| "trl_hash" : "sha-256", |
| "max_n" : 10, |
| "max_diff_batch": 5 |
| } |
| |
| GET coap://as.example.com/revoke/trl?diff=3 |
| Observe: 0 |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Observe: 42 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [], |
| e'cursor' : null, |
| e'more' : false |
| } |
| |
| ... |
| |
| (Access tokens t1 and t2 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access token t1 is revoked) |
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Observe: 53 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [], [bstr.h(t1)] ] |
| ], |
| e'cursor' : 0, |
| e'more' : false |
| } |
| |
| ... |
| |
| (Access token t2 is revoked) |
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Observe: 64 |
| Content-Format: application/ace-trl+cbor |
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| Payload: { |
| e'diff_set' : [ |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ], |
| e'cursor' : 1, |
| e'more' : false |
| } |
| |
| ... |
| |
| (Access token t1 expires) |
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Observe: 75 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ], |
| e'cursor' : 2, |
| e'more' : false |
| } |
| |
| ... |
| |
| (Access token t2 expires) |
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Observe: 86 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ], |
| e'cursor' : 3, |
| e'more' : false |
| } |
| |
| ... |
| |
| (Enough time has passed since |
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| the latest received notification) |
| |
| |
| GET coap://as.example.com/revoke/trl?diff=3 |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ], |
| e'cursor' : 3, |
| e'more' : false |
| } |
| |
| GET coap://as.example.com/revoke/trl?diff=3&cursor=3 |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.05 Content |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [], |
| e'cursor' : 3, |
| e'more' : false |
| } |
| |
Figure 12: Interaction for diff query with Observe and "Cursor"
C.5. Full Query with Observe plus Diff Query with "Cursor"
In this example, the AS supports the "Cursor" extension. Hence, the
CBOR map conveyed as payload of the registration response
additionally includes a "max_diff_batch" parameter. This specifies
the value of MAX_DIFF_BATCH, i.e., the maximum number of diff entries
that can be included in a response to a diff query request from this
RS.
Figure 13 shows an interaction example considering a CoAP observation
and a full query of the TRL.
The example also considers some of the notifications from the AS to
get lost in transmission, and thus not reaching the RS.
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When this happens, and after a waiting time defined by the
application has elapsed, the RS sends a GET request with no Observe
Option to the AS, to perform a diff query of the TRL. In particular,
the RS specifies:
* The query parameter 'diff' with value 8, i.e., the maximum number
of diff entries to be specified in a response from the AS.
* The query parameter 'cursor' with value 2, thus requesting from
the update collection the series items following the one with
'index' value equal to 2 (i.e., following the last series item
that the RS successfully received in an earlier notification
response).
The response from the AS conveys a first batch of MAX_DIFF_BATCH = 5
series items from the update collection corresponding to the RS. The
AS indicates that further series items are actually available in the
update collection, by setting the 'more' parameter of the response to
true. Also, the 'cursor' parameter of the response is set to 7,
i.e., to the 'index' value of the most recent series item included in
the response.
After that, the RS follows up with a further diff query request
specifying the query parameter 'cursor' with value 7, in order to
retrieve the next and last batch of series items from the update
collection.
RS AS
| |
| Registration: POST |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.01 Created |
| Payload: { |
| / ... / |
| "trl_path" : "/revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10, |
| "max_diff_batch": 5 |
| } |
| |
| GET coap://as.example.com/revoke/trl/ |
| Observe: 0 |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.05 Content |
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| Observe: 42 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [], |
| e'cursor' : null |
| } |
| |
| ... |
| |
| (Access tokens t1, t2, t3 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access tokens t4, t5, t6 issued |
| and successfully submitted to RS) |
| |
| ... |
| |
| (Access token t1 is revoked) |
| |
|<--------------------------------------------------------------+
| 2.05 Content |
| Observe: 53 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1)], |
| e'cursor' : 0 |
| } |
| |
| ... |
| |
| (Access token t2 is revoked) |
| |
|<--------------------------------------------------------------+
| 2.05 Content |
| Observe: 64 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t1), bstr.h(t2)], |
| e'cursor' : 1 |
| } |
| |
| ... |
| |
| (Access token t1 expires) |
| |
|<--------------------------------------------------------------+
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| 2.05 Content |
| Observe: 75 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t2)], |
| e'cursor' : 2 |
| } |
| |
| ... |
| |
| (Access token t2 expires) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 86 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [], |
| e'cursor' : 3 |
| } |
| |
| ... |
| |
| (Access token t3 is revoked) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 88 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t3)], |
| e'cursor' : 4 |
| } |
| |
| ... |
| |
| (Access token t4 is revoked) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 89 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t3), bstr.h(t4)], |
| e'cursor' : 5 |
| } |
| |
| ... |
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| |
| (Access token t3 expires) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 90 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t4)], |
| e'cursor' : 6 |
| } |
| |
| ... |
| |
| (Access token t4 expires) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 91 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [], |
| e'cursor' : 7 |
| } |
| |
| ... |
| |
| (Access tokens t5 and t6 are revoked) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 92 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t5), bstr.h(t6)], |
| e'cursor' : 8 |
| } |
| |
| ... |
| |
| (Access token t5 expires) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 93 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [bstr.h(t6)], |
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| e'cursor' : 9 |
| } |
| |
| ... |
| |
| (Access token t6 expires) |
| |
| Lost X <-----------------------------------------------------+
| 2.05 Content |
| Observe: 94 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'full_set' : [], |
| e'cursor' : 10 |
| } |
| |
| ... |
| |
| (Enough time has passed since |
| the latest received notification) |
| |
| |
| GET coap://as.example.com/revoke/trl?diff=8&cursor=2 |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.05 Content |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t4)], [] ], |
| [ [bstr.h(t3)], [] ], |
| [ [], [bstr.h(t4)] ], |
| [ [], [bstr.h(t3)] ], |
| [ [bstr.h(t2)], [] ] |
| ], |
| e'cursor' : 7, |
| e'more' : true |
| } |
| |
| GET coap://as.example.com/revoke/trl?diff=8&cursor=7 |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.05 Content |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
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| [ [bstr.h(t6)], [] ], |
| [ [bstr.h(t5)], [] ], |
| [ [], [bstr.h(t5), bstr.h(t6)] ] |
| ], |
| e'cursor' : 10, |
| e'more' : false |
| } |
| |
Figure 13: Interaction for full query with Observe plus diff
query with "Cursor"
Appendix D. CDDL Model
This section is to be removed before publishing as an RFC.
full_set = 0
diff_set = 1
cursor = 2
more = 3
ace-trl-error = 1
Figure 14: CDDL model
Appendix E. Document Updates
This section is to be removed before publishing as an RFC.
E.1. Version -07 to -08
* Added definition of pertaining token hash.
* Added definition of pertaining TRL update.
* Rephrased example of token uploading to be more future ready.
* Consistent use of "TRL update" throughout the document.
* Editorial improvements.
E.2. Version -06 to -07
* RFC 9290 is used instead of the custom format for error responses.
* Avoided quotation marks when using CBOR simple values.
* CBOR diagnostic notation uses placeholders from a CDDL model.
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* Early mentioning that there is a single MAX_N value.
* Added more details on the authorization of administrators.
* Added recommendations for avoiding lost TRL updates from going
unnoticed.
* If diff queries are supported, the AS MUST provide MAX_N at
registration.
* If the "Cursor" extension is supported, the AS MUST provide
MAX_DIFF_BATCH at registration.
* Clarified that how the token revocation specifically happens is
out of scope.
* Clearer, upfront distinction between using CoAP Observe or not.
* Revised and extended method for computing the token hashes.
* Clearer presentation of invalid requests to the TRL endpoint.
* Clearer expected relation between MAX_INDEX and MAX_N values.
* Clarified meaning of registered parameters.
* Generalized security considerations on vulnerable time window at
the RS.
* Added security considerations on additional security measures.
* Fixes and improvements in the IANA considerations.
* Used AASVG in diagrams.
* Used actual tables instead of figures.
* Fixed notation in the examples.
* Clarifications and editorial improvements.
E.3. Version -05 to -06
* Clarified instructions for Expert Review in the IANA
considerations.
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E.4. Version -04 to -05
* Explicit focus on CoAP in the abstract and introduction.
* Removed terminology aliasing ("TRL endpoint" vs. "TRL resource").
* Use "requester" instead of "caller".
* Use "subset" instead of "portion".
* Revised presentation of how token hashes are computed.
* Improved error handling.
* Revised examples.
* More precise security considerations.
* Clarifications and editorial improvements.
* Updated author list.
E.5. Version -03 to -04
* Improved presentation of pre- and post-registration operations.
* Removed moot processing cases with the "Cursor" extension.
* Positive integers as CBOR abbreviations for all parameters.
* Renamed N_MAX as MAX_N.
* Access tokens are not necessarily uploaded through /authz-info.
* The use of the "c.pmax" conditional attribute is just an example.
* Revised handling of token hashes at the RS.
* Extended and improved security considerations.
* Fixed details in IANA considerations.
* New appendix overviewing parameters of the TRL endpoint.
* Examples of message exchange moved to an appendix.
* Added examples of message exchange with the "Cursor" extension.
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* Clarifications and editorial improvements.
E.6. Version -02 to -03
* Definition of MAX_INDEX for the "Cursor" extension.
* Handling wrap-around of 'index' when using the "Cursor" extension.
* Error handling for the case where 'cursor' > MAX_INDEX.
* Improved error handling in case 'index' is out-of-bound.
* Clarified parameter semantics, message content and examples.
* Editorial improvements.
E.7. Version -01 to -02
* Earlier mentioning of error cases.
* Clearer distinction between maintaining the history of TRL updates
and preparing the response to a diff query.
* Defined the use of "cursor" in the document body, as an extension
of diff queries.
* Both success and error responses have a CBOR map as payload.
* Corner cases of message processing explained more explicitly.
* Clarifications and editorial improvements.
E.8. Version -00 to -01
* Added actions to perform upon receiving responses from the TRL
endpoint.
* Fixed off-by-one error when using the "Cursor" pattern.
* Improved error handling, with registered error codes.
* Section restructuring (full- and diff-query as self-standing
sections).
* Renamed identifiers and CBOR parameters.
* Clarifications and editorial improvements.
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Acknowledgments
Ludwig Seitz contributed as a co-author of initial versions of this
document.
The authors sincerely thank Christian Amsüss, Carsten Bormann, Dhruv
Dhody, Rikard Höglund, Benjamin Kaduk, David Navarro, Joerg Ott,
Marco Rasori, Michael Richardson, Kyle Rose, Jim Schaad, Göran
Selander, Travis Spencer, Dale Worley, and Paul Wouters for their
comments and feedback.
The work on this document has been partly supported by the Sweden's
Innovation Agency VINNOVA and the Celtic-Next projects CRITISEC and
CYPRESS; and by the H2020 project SIFIS-Home (Grant agreement
952652).
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Kista
Sweden
Email: marco.tiloca@ri.se
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
SE-16440 Kista
Sweden
Email: francesca.palombini@ericsson.com
Sebastian Echeverria
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: secheverria@sei.cmu.edu
Grace Lewis
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: glewis@sei.cmu.edu
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