ACE Working Group
Internet Engineering Task Force (IETF) M. Tiloca
Internet-Draft
Request for Comments: 9770 RISE AB
Intended status:
Category: Standards Track F. Palombini
Expires: 26 March 2025
ISSN: 2070-1721 Ericsson AB
S. Echeverria
G. Lewis
CMU SEI
22 September 2024
April 2025
Notification of Revoked Access Tokens in the Authentication and
Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-revoked-token-notification-09
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 (TRL) 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.
Internet-Drafts are working documents an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 March 2025.
https://www.rfc-editor.org/info/rfc9770.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
3. Issuing of Access Tokens at the AS . . . . . . . . . . . . . 9
4. Token Hash . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Motivation for the Used Construction . . . . . . . . . . 12
4.1.1. Issuing of the Access Token to the Client . . . . . . 12
4.1.2. Provisioning of Access Tokens to the RS . . . . . . . 13
4.1.3. Design Rationale . . . . . . . . . . . . . . . . . . 14
4.2. Hash Input on the Client and the AS . . . . . . . . . . . 14
4.2.1. AS-to-Client Response Encoded in CBOR . . . . . . . . 15
4.2.2. AS-to-Client Response Encoded in JSON . . . . . . . . 15
4.3. HASH_INPUT on the RS . . . . . . . . . . . . . . . . . . 17
4.3.1. Access Tokens as CWTs . . . . . . . . . . . . . . . . 17
4.3.2. Access Tokens as JWTs . . . . . . . . . . . . . . . . 18
4.4. Computing the Token Hash . . . . . . . . . . . . . . . . 19
5. Token Revocation List (TRL) . . . . . . . . . . . . . . . . . 19
5.1. Update of the TRL . . . . . . . . . . . . . . . . . . . . 20
6. The TRL Endpoint . . . . . . . . . . . . . . . . . . . . . . 20
6.1. Error Responses with Problem Details . . . . . . . . . . 21
6.2. Supporting Diff Queries . . . . . . . . . . . . . . . . . 23
6.2.1. Supporting the "Cursor" Extension . . . . . . . . . . 24
6.3. Query Parameters . . . . . . . . . . . . . . . . . . . . 25
7. Full Query of the TRL . . . . . . . . . . . . . . . . . . . . 27
8. Diff Query of the TRL . . . . . . . . . . . . . . . . . . . . 29
9. Response Messages when Using the "Cursor" Extension . . . . . 32
9.1. Response to Full Query . . . . . . . . . . . . . . . . . 32
9.2. Response to Diff Query . . . . . . . . . . . . . . . . . 32
9.2.1. Empty Collection . . . . . . . . . . . . . . . . . . 33
9.2.2. Cursor Not Specified in the Diff Query Request . . . 33
9.2.3. Cursor Specified in the Diff Query Request . . . . . 34
10. Registration at the Authorization Server . . . . . . . . . . 37
11. Notification of Revoked Access Tokens . . . . . . . . . . . . 38
11.1. Handling of Revoked Access Tokens and Token Hashes . . . 40
12. ACE Token Revocation List Parameters . . . . . . . . . . . . 42
13. ACE Token Revocation List Error Identifiers . . . . . . . . . 43
14. Security Considerations . . . . . . . . . . . . . . . . . . . 43
14.1. Content Retrieval from the TRL . . . . . . . . . . . . . 43
14.2. Size of the TRL . . . . . . . . . . . . . . . . . . . . 44
14.3. Communication Patterns . . . . . . . . . . . . . . . . . 44
14.4. Request of New Access Tokens . . . . . . . . . . . . . . 45
14.5. Vulnerable Time Window at the RS . . . . . . . . . . . . 45
14.6. Preventing Unnoticed Manipulation of Access Tokens . . . 46
14.7. Two Token Hashes at the RS using Using JWTs . . . . . . . . . 47
14.8. Additional Security Measures . . . . . . . . . . . . . . 48
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
15.1. Media Type Registrations . . . . . . . . . . . . . . . . 48
15.2. CoAP Content-Formats Registry . . . . . . . . . . . . . 49
15.3. Custom Problem Detail Keys Registry . . . . . . . . . . 50
15.4. ACE Token Revocation List Parameters Registry . . . . . 50
15.5. ACE Token Revocation List Errors . . . . . . . . . . . . 51
15.6. Expert Review Instructions . . . . . . . . . . . . . . . 52
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 53
16.1. Normative References . . . . . . . . . . . . . . . . . . 53
16.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. On using Using the Series Transfer Pattern . . . . . . . . 57
Appendix B. Local Supportive Parameters of the TRL Endpoint . . 58
Appendix C. Interaction Examples . . . . . . . . . . . . . . . . 59
C.1. Full Query with Observe . . . . . . . . . . . . . . . . . 60
C.2. Diff Query with Observe . . . . . . . . . . . . . . . . . 62
C.3. Full Query with Observe plus Plus Diff Query . . . . . . . . . 64
C.4. Diff Query with Observe and "Cursor" . . . . . . . . . . 67
C.5. Full Query with Observe plus Plus Diff Query with "Cursor" . . 70
Appendix D. CDDL Model . . . . . . . . . . . . . . . . . . . . . 76
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 76
E.1. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 76
E.2. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 77
E.3. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 78
E.4. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 79
E.5. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 79
E.6. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 79
E.7. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 80
E.8. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 80
E.9. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 80
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 81
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 81
1. Introduction
Authentication and Authorization for Constrained Environments (ACE)
[RFC9200] is a framework that enforces access control on IoT Internet of
Things (IoT) devices acting as resource servers Resource Servers (RSs). In order to
use ACE, both clients and RSs have to register with an authorization server Authorization
Server (AS) and become
a registered device. devices. Once registered, a client
can send a request to the AS, AS to obtain an access token for an 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) as when:
1. a registered device has been
compromised, compromised or is suspected of being
compromised; (2)
2. a registered device is decommissioned; (3)
3. there has been a change in the ACE profile for a registered
device; (4)
4. there has been a change in access policies for a registered
device; and (5)
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, 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,
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,
another and can subscribe to the TRL on the AS by using resource
observation for CoAP [RFC7641]. Other underlying Underlying protocols other 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.
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, expiration as
efficiently identified by corresponding hash values.
The benefits of this method are that it complements token
introspection,
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), 2) and the lightweight computation of hash values to use
as access token identifiers (see Section 4).
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 the Concise Data Definition Language (CDDL) [RFC8610], CBOR
Concise Binary Object Representation (CBOR) [RFC8949], JSON
[RFC8259], COSE CBOR Object Signing and Encryption (COSE) [RFC9052], 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."
This specification also refers to uses the following terminology.
* 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, 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: an entity that is authorized to get full access to
the TRL at the AS, AS and acting that acts 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.
An administrator might also be authorized to perform further
administrative operations at the AS, e.g., through a dedicated
admin interface that is out of the scope of this document. By
considering the token hashes retrieved from the TRL together with
other information obtained from the AS, the administrator becomes
able to derive additional information, e.g., the fact that
accesses have been revoked for specific registered devices.
*
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.
*
Full query: a type of query to the TRL, TRL where the AS returns the
token hashes of the revoked access tokens currently in the TRL and
pertaining to the requester. Further details are specified in
Section
Sections 6 and Section 7.
*
Diff query: a type of query to the TRL, TRL where the AS returns a list
of diff entries, each related to one update occurred to the TRL and
containing a set of token hashes pertaining to the requester.
Further details are specified in Section Sections 6 and
Section 8.
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 15 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 15
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.
* follows:
1. 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.
*
2. 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 following: the current
list of pertaining revoked access tokens (see Section 7); 7) or the
most recent updates that occurred over the list of pertaining
revoked access tokens (see Section 8).
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.
*
3. 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 7), or the most recent TRL
updates that occurred over that list of pertaining revoked access
tokens (see Section 8).
Further Observe notifications may be sent, consistently consistent with
ongoing additional observations of the TRL endpoint.
*
4. An administrator can access and subscribe to the TRL like a
registered device, device while getting the content of the whole TRL (see
Section 7) or the most recent updates occurred to the whole TRL (see
Section 8).
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, t3 whose corresponding token hashes are th1, th2,
and th3, respectively. Consequently, the AS adds the three token
hashes to the TRL at once, 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.
+----------------------+
| 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. Issuing of Access Tokens at the AS
An AS that supports the method defined in this document MUST adhere
to the following rules when issuing an access token. token:
* All the intended header parameters in the access token MUST be
specified within integrity-protected fields.
* If the access token is a CWT, the following applies. applies:
- Any "unprotected" field MUST be empty, i.e., its value MUST be
encoded as the empty CBOR map (0xa0). This applies to: to the
top-level top-
level "unprotected" field of the COSE object used for the
CWT; CWT,
the "unprotected" field of each element of the "signatures" array;
array, and the "unprotected" field of each element of any
"recipients" array (see Sections 2, 3, 4, 5, and 6 of
[RFC9052]).
- Consistent with the specific COSE object used for the CWT, the
corresponding tagged structure in the set COSE_Tagged_Message
MUST be used (see Section 2 of [RFC9052]). That is, the CBOR
array that encodes the CWT MUST be tagged by using the COSE
CBOR tag corresponding to the used COSE object. Table 1 in
Section 2 of [RFC9052] specifies the tag numbers in question.
In turn, the resulting tagged data item MUST be tagged by using
the CWT CBOR tag with tag number 61 (see Section 6 of
[RFC8392]). After that, the resulting data item MUST NOT be
further tagged.
Encoding of the tag numbers MUST be done using definite
lengths, and the length of the encoded tag numbers MUST be the
minimum possible length. This means that the tag number 16 is
encoded as 0xd0 and not as 0xd810.
The example in Figure 2 shows a CWT that uses the COSE object
COSE_Encrypt0 (see Section 5.2 of [RFC9052]).
* If, like for JWTs [RFC7519], the access token relies on a JSON
object for encoding its claims, the following applies. applies:
Consistent with the ACE framework for Authentication and
Authorization [RFC9200], this document specifically considers
JWTs, which are always represented using the JWS JSON Web Signature
(JWS) Compact Serialization from [RFC7515] or the JWE JSON Web
Encryption (JWE) Compact Serialization from [RFC7516].
Consequently, all the header parameters are specified within
integrity-protected fields.
In case alternative access tokens were used, the following
applies:
- If the access token uses the JWS JSON Compact Serialization from
[RFC7515], it MUST NOT include the JWS Unprotected Header.
- If the access token uses the JWE JSON Compact Serialization from
[RFC7516], it MUST NOT include the JWE Shared Unprotected
Header and it MUST NOT include the "header" member in any of
the elements of the "recipients" array.
/ CWT CBOR tag / 61(
/ COSE_Encrypt0 CBOR tag / 16(
/ COSE_Encrypt0 object / [
/ protected / h'a3010a044c53796d6d65747269633132
38054d99a0d7846e762c49ffe8a63e0b',
/ unprotected / {},
/ ciphertext / h'b918a11fd81e438b7f973d9e2e119bcb
22424ba0f38a80f27562f400ee1d0d6c
0fdb559c02421fd384fc2ebe22d70713
78b0ea7428fff157444d45f7e6afcda1
aae5f6495830c58627087fc5b4974f31
9a8707a635dd643b'
]
)
)
Figure 2: Example of CWT Using COSE_Encrypt0
Section 14.6 discusses how adhering to the rules above neutralizes an
attack against the RS, RS where an active adversary can induce the RS to
compute a token hash different from the correct one.
4. Token Hash
This section specifies how token hashes are computed.
First, Section 4.1 provides the motivation for the used construction.
Building on that, the value used as input to compute a token hash is
defined in Section 4.2 for the client and the AS, AS and in Section 4.3
for the RS. Finally, Section 4.4 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]), [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]).
Consistent with Section 3.4 of [RFC8949], the term "tag" is used for
the entire CBOR data item consisting of both a tag number and the tag
content: the tag content is the CBOR data item that is being tagged.
Also, "tagged access token" is used to denote nested CBOR tags
(possibly a single one), with the innermost tag content being a CWT.
4.1. 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 for
Authentication and Authorization (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.
4.1.1. 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]), [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 method of encoding 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 a value of BYTES. 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 untagged CWT) or of a tagged access token with the CWT as
the innermost tag content.
- 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 method of encoding 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 a value a text string
TEXT. 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 BYTES, which is the binary
representation of the CWT (i.e., of the CBOR array that encodes
the untagged CWT) or of a tagged access token with the CWT as
the innermost tag content.
4.1.2. 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. That is, TOKEN_INFO is
the binary representation of the (tagged) 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 (tagged) 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. ACE:
* The (tagged) 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 (tagged) 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 (tagged) 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
'psk_identity' field of the ClientKeyExchange message (when using
DTLS 1.2 [RFC6347]), [RFC6347]) or of the 'identity' field of a PSKIdentity,
within the PreSharedKeyExtension of a ClientHello message (when
using DTLS 1.3 [RFC9147]).
* The (tagged) 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.
4.1.3. 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 responses because
that is what all among the AS, the client, and the RS are all able to see.
4.2. 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 in which the (tagged) 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 4.2.1) or in JSON (see Section 4.2.2).
Once determined HASH_INPUT, the HASH_INPUT is determined, the client and the AS use it to
compute the token hash of the conveyed access token as defined in
Section 4.4.
4.2.1. 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'.
With reference to the example in Figure 3, BYTES is the bytes
{0xd8 0x3d 0xd0 ... 0x64 0x3b}.
Note that BYTES is the binary representation of the tagged access
token if this is a CWT (as per Section 3), 3) or of the access token
if this is 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'd83dd0835820a3010a044c53796d6d
6574726963313238054d99a0d7846e
762c49ffe8a63e0ba05858b918a11f
d81e438b7f973d9e2e119bcb22424b
a0f38a80f27562f400ee1d0d6c0fdb
559c02421fd384fc2ebe22d7071378
b0ea7428fff157444d45f7e6afcda1
aae5f6495830c58627087fc5b4974f
319a8707a635dd643b',
/ token_type / 34 : 2 / PoP /,
/ expires_in / 2 : 86400,
/ ace_profile / 38 : 1 / coap_dtls /,
/ (remainder of the response omitted for brevity) /
}
Figure 3: Example of AS-to-Client CoAP response using Response Using CBOR
4.2.2. 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 4, HASH_INPUT is the binary
representation of "eyJh...YFiA". When showing the access token,
Figure 4 uses line breaks for display purposes only.
Note that:
* If the access token is a JWT, then HASH_INPUT is the binary
representation of the JWT.
* If the access token is a CWT, then HASH_INPUT is the binary
representation of a base64url-encoded text string, which encodes
the binary representation of a tagged access token with the CWT as
the innermost tag content (as per Section 3).
HTTP/1.1 200 OK
Content-Type: application/ace+json
Cache-Control: no-store
Pragma: no-cache
Payload:
{
"access_token" : "eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJB
MTI4Q0JDLUhTMjU2In0.
QR1Owv2ug2WyPBnbQrRARTeEk9kDO2w8
qDcjiHnSJflSdv1iNqhWXaKH4MqAkQtM
oNfABIPJaZm0HaA415sv3aeuBWnD8J-U
i7Ah6cWafs3ZwwFKDFUUsWHSK-IPKxLG
TkND09XyjORj_CHAgOPJ-Sd8ONQRnJvW
n_hXV1BNMHzUjPyYwEsRhDhzjAD26ima
sOTsgruobpYGoQcXUwFDn7moXPRfDE8-
NoQX7N7ZYMmpUDkR-Cx9obNGwJQ3nM52
YCitxoQVPzjbl7WBuB7AohdBoZOdZ24W
lN1lVIeh8v1K4krB8xgKvRU8kgFrEn_a
1rZgN5TiysnmzTROF869lQ.
AxY8DCtDaGlsbGljb3RoZQ.
MKOle7UQrG6nSxTLX6Mqwt0orbHvAKeW
nDYvpIAeZ72deHxz3roJDXQyhxx0wKaM
HDjUEOKIwrtkHthpqEanSBNYHZgmNOV7
sln1Eu9g3J8.
fiK51VwhsxJ-siBMR-YFiA",
"token_type" : "pop",
"expires_in" : 86400,
"ace_profile" : "1"
}
Figure 4: Example of AS-to-Client HTTP response using Response Using JSON
4.3. 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 4.3.1) or JWTs
(see Section 4.3.2).
4.3.1. Access Tokens as CWTs
If the RS expects access tokens to be CWTs, then the RS performs the
following steps. 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 4.1.2).
2. The RS assumes that the client received the access token in an
AS-to-Client response encoded in CBOR (see Section 4.2.1).
Hence, the RS assumes TOKEN_INFO to be the binary representation
of the tagged access token with the CWT as the innermost tag
content (as per Section 3).
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 yet; instead, it instead moves to step 4.
Otherwise, the RS stores the access token and computes the
corresponding token hash, hash as defined in Section 4.4. 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.
After that, the RS stores the computed token hash as associated
with the access token, and then token; then, it 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 4.2.2).
Hence, the RS assumes TOKEN_INFO to be the binary representation
of HASH_INPUT_TEXT. In turn, HASH_INPUT_TEXT is the base64url-
encoded text string that encodes the binary representation of the
tagged access token with the CWT as the innermost tag content (as
per Section 3).
5. The RS performs the base64url decoding of HASH_INPUT_TEXT, HASH_INPUT_TEXT and
considers the result as to be the binary representation of the
tagged 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, hash as defined in Section 4.4. In
particular, HASH_INPUT is TOKEN_INFO.
After that, the RS stores the computed token hash as associated
with the access token.
4.3.2. Access Tokens as JWTs
If the RS expects access tokens to be JWTs, then the RS performs the
following steps. 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 4.1.2).
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,
token as defined in Section 4.4.
In particular, the RS assumes that the client received the access
token in an AS-to-Client response encoded in JSON (see
Section 4.2.2). Hence, HASH_INPUT is TOKEN_INFO.
After that, the RS stores the computed token hash as associated
with the access token.
4. The RS computes a second token hash associated with the access
token,
token as defined in Section 4.4.
In particular, the RS assumes that the client received the access
token in an AS-to-Client response encoded in CBOR (see
Section 4.2.1). Hence, HASH_INPUT is the binary representation
of HASH_INPUT_TEXT, which which, in turn 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 steps 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 11.1.
Section 14.7 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.
4.4. Computing the Token Hash
Once determined HASH_INPUT is determined as defined in Section Sections 4.2 and Section 4.3, 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, function in the first byte of the computed token hash.
The specifically used specific hash function used MUST be collision-resistant collision resistant on
byte-strings, byte
strings and MUST be selected from the "Named Information Hash
Algorithm" Registry [Named.Information.Hash.Algorithm].
Algorithm Registry" [IANA.Hash.Algorithms]. Consistent with the
compliance requirements in Section 2 of [RFC6920], the hash function
sha-256 as specified in [SHA-256] is mandatory to implement.
The AS specifies the used hash function to registered devices during
their registration procedure (see Section 10).
5. Token Revocation List (TRL)
Upon startup, the AS creates a single Token Revocation List (TRL), (TRL)
encoded as a CBOR array.
Each element of the array is a CBOR byte string, 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.
5.1. Update of the TRL
The AS updates the TRL in the following two cases. 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,
time or within an acceptably narrow time window. frame.
6. 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, 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 12.
The AS MUST implement measures to prevent access to the TRL endpoint
by entities other than registered devices and authorized
administrators (see Section 10).
The TRL endpoint supports only the GET method, and allows two types
of queries of the TRL.
* TRL:
1. 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 7.
*
2. 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 6.2. The processing of a diff query and the related
response format are defined in Section 8.
If it supports diff queries, the AS MAY additionally support its
"Cursor" extension, which has two benefits. First, the benefits:
1. The AS can avoid excessively long messages when several diff
entries have to be
transferred, transferred by delivering several diff query
responses, each containing one adjacent subset of diff entries at
a time. Second, a
2. 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 a reference
point.
If it supports the "Cursor" extension, the AS stores additional
information when maintaining the history of updates to the TRL, TRL as
defined in Section 6.2.1. 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 9.
Appendix B provides an aggregated overview of the local supportive
parameters that the AS internally uses at its TRL endpoint, endpoint when
supporting diff queries and the "Cursor" extension.
6.1. 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. follows:
* It MUST include the Custom Problem Detail entry 'ace-trl-error'
registered in Section 15.3 of this document. This entry is
formatted as a CBOR map, which includes the following fields. fields:
- The field 'error-id' field MUST be present. The map key used for
this field is the CBOR unsigned integer with a value of 0. The
value of this field is a CBOR integer specifying the error that
occurred at the AS. This value is taken from the 'Value'
column of the "ACE Token Revocation List Errors" registry
defined in Section 15.5 of this document.
- The field 'cursor' field MAY be present. The map key used for this
field is the CBOR unsigned integer with a value of 1. The
value of this field is a CBOR unsigned integer or the CBOR
simple value null (0xf6). The use of this field is defined in
Section 6.3.
The CDDL notation [RFC8610] of the 'ace-trl-error' entry is given
below.
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, human-readable diagnostic description of the error
that occurred at the AS. The diagnostic text is intended for
software engineers as well as for device and network operators, operators in
order to aid in debugging and provide context for possible
intervention. The diagnostic message SHOULD be logged by the AS.
The 'detail' entry is unlikely to be relevant in an unattended
setup where human intervention is not expected.
An example of an error response using the problem-details format is
shown in Figure 5.
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 5: 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 that is able to understand the specified error may use
that information to determine what actions to take next.
6.2. 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 that occurred to
the TRL (see Section 6). 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. "requesters". In particular, a requester's
diff entry associated with a TRL update contains a set of token
hashes pertaining to that requester, each of which were was added to the
TRL or removed from the TRL at that update.
The AS defines the single, single constant positive integer MAX_N >= 1. For
each requester, the AS maintains an update updated 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, MAX_N upon
their registration (see Section 10).
The series of items in the update collection MUST be strictly ordered in
a chronological fashion.
chronologically ordered. That is, at any point in time, the current first
series item is would be the one least recently added to the update
collection and still retained by the AS, while AS; the current last series item is would
be the one most recently added to the update collection. The
particular method used to achieve this is implementation- implementation specific.
Each time the TRL changes, the AS performs the following operations
for each requester. 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 item that 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, requester as the last (most recent) one. entry.
6.2.1. Supporting the "Cursor" Extension
If it supports the "Cursor" extension for diff queries, the AS
performs also
performs the following actions. actions:
The AS defines the single, 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), 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.
collection:
* 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 an 'index' with a value
of 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 a value of
i_Y = (i_X + 1) % (MAX_INDEX + 1). That is, after having added a
series item whose associated 'index' has a value of MAX_INDEX, the
next added series item will result in a wrap-around wraparound of the 'index'
value, and
value; thus, it will thus take an 'index' with a value of 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. 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 an
'index' with a value of 'last_index' = (V - 1) % (MAX_INDEX + 1).
As long as a wrap-around wraparound 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 9.2.
For each requester's update collection, the AS also defines a
constant,
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, MAX_DIFF_BATCH upon their registration (see
Section 10).
6.3. 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 8). 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, request and proceeds like
when processing a full query of the TRL (see Section 7).
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 set to "application/concise-
problem-details+cbor"
problem-details+cbor", and its payload is formatted as defined in
Section 6.1. 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' field 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 9.2. 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.
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 Sections 9.1, Section 9.2.2, and
Section 9.2.3).
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)
that is:
1. it performs a diff query of the TRL (see Section 8), if it
supports diff queries and the 'diff' query parameter is
present in the GET request; or ii)
2. it performs a full query of the TRL (see Section 7) otherwise. 7).
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" set to
"application/concise-problem-details+cbor", and its payload is
formatted as defined in Section 6.1.
- 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' field MUST NOT be present.
- The 'cursor' query parameter has a value that is neither 0 nor
a positive integer, or integer; otherwise, it has a value strictly greater
than MAX_INDEX (see Section 6.2.1).
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',
'cursor' field, whose value is either:
o the CBOR simple value null (0xf6), if the update collection
associated with the requester is empty; or
o the corresponding current value of
'last_index' otherwise. 'last_index'.
- All of the following hold: the update collection associated
with the requester is not empty; no wrap-around wraparound 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 6.2.1).
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' field MUST NOT be present.
7. 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. actions:
1. From the TRL, the AS builds a set of 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". set to "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, string with a value of 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
Sections 6.2 and Section 6.2.1). Its value is set as specified in
Section 9.1, 9.1 and provides the requester with information for
performing a follow-up diff query using the "Cursor" extension
(see Section 9.2).
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.
Figure 6 provides the CDDL definition [RFC8610] of the CBOR array
'full_set_value' specified in the response from the AS, AS as the value
of the 'full_set' parameter.
token_hash = bytes
full_set_value = [* token_hash]
Figure 6: CDDL definition Definition of 'full_set_value'
Figure 7 shows an example response from the AS, AS following a full query
request to the TRL endpoint. In this example, the AS does not
support diff queries nor the "Cursor" extension, 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...4819', / elided for brevity /
h'01748190...223d' / elided for brevity /
]
}
Figure 7: Example of response following Response Following a full query request Full Query Request to
the TRL endpoint Endpoint
8. 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. 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 9.2.
1. The AS defines the positive integer NUM as follows. If 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 predefined positive integer MAX_N
(see Section 6.2), 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.
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 6.2). 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 elements:
a. A 'trl_patch' set of token hashes, hashes encoded as a CBOR array
'removed'. Each element of the array is a CBOR byte string, string
with value the token hash of an access token such that: that it pertained
pertains to the requester; requester and it was removed from the TRL during
the update associated with the diff entry.
* The second element is a
b. A 'trl_patch' set of token hashes, hashes encoded as a CBOR array
'added'. Each element of the array is a CBOR byte string, string
with value the token hash of an access token such that: that it
pertains to the requester; 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". set to "application/ace-
trl+cbor". The payload of the response is a CBOR map, which MUST
be formatted as follows. 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 a
value
0, of 0; in which case this case, 'diff_set_value' is the empty CBOR
array.
Within 'diff_set_value', the any 'diff_entry' 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 second-to-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 6.2.1). Their values are set
as specified in Section 9.2, 9.2 and provide the requester with
information for performing a follow-up query of the TRL (see
Section 9.2).
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 included, and the "Cursor"
extension, it AS
MUST silently ignore the 'cursor' parameter and the 'more'
parameter if present.
Figure 8 provides the CDDL definition [RFC8610] of the CBOR array
'diff_set_value' specified in the response from the AS, as the 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 8: CDDL definition Definition of 'diff_set_value'
Figure 9 shows an example response from the AS, 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 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.
Header: Content (Code=2.05)
Content-Format: application/ace-trl+cbor
Payload:
{
e'diff_set' : [
[
[ h'01fa51cc...0f6a', / elided for brevity /
h'01748190...8bce' / elided for brevity /
],
[ h'01cdf1ca...563d', / elided for brevity /
h'01be41a6...a057' / elided for brevity /
]
],
[
[ h'0144dd12...77bc', / elided for brevity /
h'01231fff...a2ce' / elided for brevity /
],
[]
],
[
[],
[ h'01ca986f...ffc1', / elided for brevity /
h'01fe1a2b...def0' / elided for brevity /
]
]
]
}
Figure 9: Example of response following Response Following a diff query request Diff Query Request to
the TRL endpoint Endpoint
Appendix A discusses how performing a diff query of the TRL is is, in
fact
fact, a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
[STP].
9. 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 Sections 9.1 and Section 9.2, respectively.
The exact format of the response depends on 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 6.3.
9.1. Response to Full Query
When processing a full query request to the TRL endpoint, the AS
composes a response as defined in Section 7.
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 (0xf6)
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 6.2.1), 6.2.1) as corresponding to the most recent TRL update
pertaining to the requester. Such In fact, such a value is in fact the current
value of 'last_index' for the update collection associated with the
requester.
9.2. Response to Diff Query
When processing a diff query request to the TRL endpoint, the AS
composes a response as defined in the following. following subsections.
9.2.1. 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" set to "application/ace-trl+cbor", and its
payload MUST be a CBOR map formatted as follows. follows:
* The 'diff_set' parameter MUST be included and specifies the empty
CBOR array.
* 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 or not the
'cursor' query parameter is included or not in the diff query
request, request and
irrespective of the specified unsigned integer value if present.
9.2.2. 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 8, with the
following differences. differences:
* At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 6.2.1), 6.2.1) 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. 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.
- 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, 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 a value of true, the requester can send a follow-up diff
query request including the 'cursor' query parameter, parameter with the same
value of the 'cursor' parameter specified in this diff query
response. As defined in Section 9.2.3, 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.
9.2.3. 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.
* hold:
Case A - 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 6.2).
In this case, the AS returns a 2.05 (Content) response. The
response MUST have Content-Format "application/ace-trl+cbor" set to "application/ace-
trl+cbor", and its payload MUST be a CBOR map formatted as follows.
-
follows:
* The 'diff_set' parameter MUST be included and specifies
the empty CBOR array.
-
* 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 is, in fact 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), 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, full
current pertaining subset of the TRL, TRL as well as with a valid
value of the 'cursor' parameter (see Section 9.1) to be possibly be,
possibly, used as query parameter in a following diff query
request.
*
Case B - B: The series item X with 'index' having value P is found in
the update collection associated with the requester; 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 8, 8 with the following differences.
- differences:
* At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 6.2.1), 6.2.1) and prepares L = min(SUB_U,
MAX_DIFF_BATCH) diff entries, where SUB_U = min(NUM, SUB_SIZE),
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.
-
* At step 4, the CBOR map to carry in the payload of the
2.05 (Content) response MUST be formatted as follows.
o 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. 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:
+
o 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
In fact, such a value is in fact the current value of
'last_index' for the update collection.
+
o 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,
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 thus, resuming from where interrupted in the
previous transfer.
10. 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. 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]. Algorithm
Registry" [IANA.Hash.Algorithms]. 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 Sections 6.2 and Section 8).
* A positive integer MAX_DIFF_BATCH, if the AS supports diff queries
of the TRL as well as the related "Cursor" extension (see
Section Sections
6.2.1 and Section 9).
Once completed the registration process, process is completed, the AS maintains the
registration and related information until a possible deregistration
occurs, hence hence, keeping track of active administrators and registered
devices. The particular way to achieve this is implementation- implementation
specific. Such In any case, such a mechanism to maintain registrations is
enforced in
any case at the AS, AS in order to ensure that requests sent by clients
to the /token endpoint (see Section 5.8 of [RFC9200]) and by RSs to
the /introspect endpoint (see Section 5.9 of [RFC9200]) are processed
as intended.
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 MUST be ensured to be mutually authenticated, encrypted
encrypted, and integrity protected, 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], (see [RFC8446] and [RFC9147]) or an OSCORE Object Security
for Constrained RESTful Environments (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
content of the whole TRL.
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, administrator only if
the access control list includes the same authentication credential
used by the requester when establishing the mutually-authenticated 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]).
11. 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 7) or a diff query
(see Section 8) of the TRL. Also, the request can include the CoAP
Observe Option set to 0 (register), (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 Sections 6.2 and Section 6.2.1), then the payload of the
response is formatted as defined in Section Sections 7 or in Section 8, 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 9.
In case a requester does not receive a response from the TRL endpoint
or it receives an error response from the TRL endpoint, the requester
does not make any assumption assumptions or draw any conclusion conclusions regarding the
revocation or expiration of its pertaining access tokens. The
requester MAY try again by sending a new request to the TRL endpoint.
When the TRL is updated (see Section 5.1), 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], [CoRE-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 or not the TRL has changed or not. changed.
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
full query (see Section 7) or a diff query (see Section 8) of the
TRL. In the latter case, the requester can additionally rely on the
"Cursor" extension (see Section Sections 6.3 and Section 9.2).
As specified in Section 6.2, 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. a
"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, 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 Request,
and, thus, relying on Observe notifications, largely reduces the
chances for a requester to miss updates occurred to its associated update collection altogether.
collection. In turn, this relies on the requester successfully
receiving the Observe notification responses from the TRL (see also
Section 14.3).
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.
11.1. Handling of Revoked 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.
If an RS uses the method defined in this document with the AS that
has issued an access token, then the RS MUST NOT accept and store
that access token if any of the following holds.
* The token hash corresponding to the access token is among the
currently stored ones.
* The access token is a CWT and any of the following holds. holds:
- The access token includes a non-empty "unprotected" field,
i.e., the value of the field is not encoded as the empty CBOR
map (0xa0). This applies to: to the top-level "unprotected" field
of the COSE object used for the CWT; CWT, the "unprotected" field of
each element of the "signatures" array; array, and the "unprotected"
field of each element of any "recipients" array.
- The received CBOR data item that embodies the access token does
not comply with what is defined in Section 3. This concerns:
o the use of exactly two nested CBOR tags, where the outer tag
is the CWT CBOR tag and the inner tag is one of the COSE
CBOR tags;
o the tag numbers encoded with the minimum possible length;
and
o the access token being the innermost tag content of the
received CBOR data item.
- In the received CBOR data item that embodies the access token,
the inner tag has a tag number that is not consistent with the
actual COSE data item to process. For instance, the inner tag
number is 16 (COSE_Encrypt0), (COSE_Encrypt0) but the CWT is actually a
COSE_Sign data item.
* The access token relies on a JSON object for encoding its claims,
but it is not a JWT [RFC7519] and any of the following holds. holds:
- The access token uses the JWS JSON Serialization from
[RFC7515], [RFC7515]
and it includes the JWS Unprotected Header.
- The access token uses the JWE JSON Serialization from
[RFC7516], [RFC7516]
and it includes the JWE Shared Unprotected Header and/or includes
the "header" member in any of the elements of the "recipients"
array.
An RS MUST store the token hash th1 corresponding to an access token
t1 until both the following conditions hold. hold:
* 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. 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 8).
- 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)
1. specifies the 'exi' claim; ii) claim,
2. is uploaded at the RS for the first time after it has been
revoked and later expired; expired, and iii)
3. has the sequence number encoded in the 'cti' claim (for CWTs) or
in the 'jti' claim (for JWTs) 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 (for CWTs) or in the 'jti' claim (for JWTs) (see
Section 5.10.3 of [RFC9200]). Then, the RS 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.
12. 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 15.2 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 Abbreviations for the ACE Token
Revocation List parameters Parameters
13. 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 6.1).
+=======+===========================+
| 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
14. 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, CWTs from
[RFC7519] and [RFC8725] as to [RFC8392], the usage
of JWTs, JWTs from [RFC7641] as to [RFC7519] and [RFC8725], the usage of CoAP Observe, and Observe from [RFC6920] with regard to
computing
[RFC7641], and computation of the token hashes. hashes from [RFC6920]. The
following considerations also apply.
14.1. 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 access the content of the whole TRL
(see Section 10).
Note that the TRL endpoint supports only the GET method (see
Section 6). Therefore, as detailed in Section Sections 7 and Section 8,
accesses access to
the TRL endpoint are is performed only by means of protected and
authenticated GET requests, which which, by definition definition, are safe in the
REST sense and do not alter the content of the TRL. That is,
registered devices and administrators can perform exclusively read-
only operations when accessing the TRL endpoint.
In fact, the two circumstances described in Section 5.1, the content of the
TRL can be updated only internally by the
AS, in the two circumstances described in Section 5.1. AS. Therefore, an
adversary that is not in control of the AS cannot manipulate the
content of the TRL, e.g., by removing a token hash and thereby
fraudulently allowing a client to access protected resources in spite
of a revoked access token, token or by adding a token hash and thereby
fraudulently stopping a client from accessing protected resources in
spite of an access token being still valid.
14.2. 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 7).
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.
14.3. 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, tokens by sending GET requests to the TRL endpoint. Specific
strategies and schedules for polling the AS are to be defined by a
related application policy, policy and by also taking into account the expected
operational and availability patterns adopted by the requester (e.g.,
in the interest of energy saving and other optimizations).
14.4. 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, causes, for example:
* the access token has been revoked, and the RS has become aware of it it,
and the RS has expunged the access token, but the client is not
aware of it this (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, 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
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, RS or instead to request a new one.
14.5. 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, 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, 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.
14.6. Preventing Unnoticed Manipulation of Access Tokens
As defined in Section 3, issued access tokens MUST NOT rely on
unprotected headers to specify information as header parameters.
Also, when issued access tokens are CWTs, they MUST be tagged by
using the COSE CBOR tag corresponding to the used COSE object, object.
Further, the result MUST be in turn tagged by using the CWT CBOR tag, and tag; no further
tagging is performed.
This ensures that the RS always computes the correct token hash
corresponding to an access token, i.e., the same token hash computed
by the AS and C for that access token.
By construction, the rules defined in Section 3 prevent an active
adversary from successfully performing an attack against the RS,
which would otherwise be possible in case the access token is
uploaded to the RS over an unprotected communication channel.
In such an attack, the adversary intercepts the access token when
this is sent en route
to the RS. Then, the adversary manipulates the access token in a way which
that is going to be unnoticed by the RS, RS but without preventing the successful,
successful cryptographic validation of the access token at the RS.
To this end, the adversary has two possible options:
* Adding and/or removing fields within the unprotected header(s) of
the access token, as long as those fields do not play a role in
the cryptographic validation of the access token.
* Specifically when the access token is a CWT, adding/removing adding, removing, or
manipulating possible CBOR tag(s) tags enclosing the access token.
After that, the adversary sends the manipulated access token to the
RS.
After having successfully validated the manipulated access token, the
RS computes a corresponding token hash different from the one
computed and stored by C and the AS. Finally, the RS stores the
manipulated access token and the corresponding wrong token hash.
Later on, if the access token is revoked and the AS provides the RS
with the corresponding correct token hash, the RS does not recognize
the received token hash among the stored ones, and therefore ones; therefore, it does not
delete the revoked access token.
14.7. Two Token Hashes at the RS using Using JWTs
Section 4.3.2 defines states 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 4.2). 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 revocation; thus, it 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
to the attack described above, above when JWTs are used as access tokens.
Instead,
However, this is not a problem if the access token is a CWT, 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 4.2 deliberately penalizes the
case where the RS uses JWTs as access tokens. In such a case, the RS
effectively neutralizes the attack described above, above by computing and
storing two token hashes associated with the same access token (see
Section 4.3.2).
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 for Authentication and Authorization (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 above; thus, it safely
computes and stores only one token hash per access token (see
Section 4.3.1).
14.8. 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, why, 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, 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).
The methods by which these processes are triggered and carried out
are out of the scope of this document.
15. IANA Considerations
This document has the following
The IANA 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. document are described in the following
subsections.
15.1. Media Type Registrations
IANA is asked to register has registered 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]. RFC 9770.
Security considerations: See Section 14 of this document.
Interoperability considerations: N/A
Published specification: [RFC-XXXX] RFC 9770
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, tokens according to a Token
Revocation List maintained by the authorization server as
specified in [RFC-XXXX]. RFC 9770.
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)
Intended usage: COMMON
Restrictions on usage: None
Author/Change controller: IETF
Provisional registration: No
15.2. CoAP Content-Formats Registry
IANA is asked to add has added the following entry to the "CoAP Content-
Formats" Content-Formats"
registry within the "Constrained RESTful Environments (CoRE)
Parameters" registry group.
Content Type: application/ace-trl+cbor
Content Coding: -
ID: TBD 262
Reference: [RFC-XXXX] RFC 9770
15.3. Custom Problem Detail Keys Registry
IANA is asked to register has registered the following entry in the "Custom Problem Detail
Keys" registry within the "Constrained RESTful Environments (CoRE)
Parameters" registry group.
*
Key Value: TBD
* 1
Name: ace-trl-error
*
Brief Description: Carry [RFC-XXXX] RFC 9770 problem details in a Concise
Problem Details data item.
*
Change Controller: IETF
*
Reference: Section 6.1 of [RFC-XXXX] RFC 9770
15.4. ACE Token Revocation List Parameters Registry
IANA is asked to establish has established the "ACE Token Revocation List Parameters"
IANA
registry within the "Authentication and Authorization for Constrained
Environments (ACE)" registry group.
As registration policy,
One of the registry uses either following registration policies is used: "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 15.6.
All assignments according to "Standards Action with Expert Review"
are made on a "Standards Action" basis per Section 4.9 of [RFC8126], [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, IANA will ask the designated expert(s) to approve
the early allocation before registration. In addition, WG chairs are
encouraged to consult the expert(s) early during the process outlined
in Section 3.1 of [RFC7120].
The columns of this registry are: are as follows:
* Name: This field contains a descriptive name that enables easier
reference to the item. The name MUST be unique 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, 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 12. The "Reference" column for all of these entries refers
to this document.
15.5. ACE Token Revocation List Errors
IANA is asked to establish has established the "ACE Token Revocation List Errors"
IANA registry
within the "Authentication and Authorization for Constrained
Environments (ACE)" registry group.
As registration policy,
One of the registry uses either following registration policies is used: "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 15.6.
All assignments according to "Standards Action with Expert Review"
are made on a "Standards Action" basis per Section 4.9 of [RFC8126], [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, IANA will ask the designated expert(s) to approve
the early allocation before registration. In addition, WG chairs are
encouraged to consult the expert(s) early during the process outlined
in Section 3.1 of [RFC7120].
The columns of this registry are: are as follows:
* 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 13. The "Reference" column for all of these entries refers
to this document.
15.6. Expert Review Instructions
The IANA registries established in by this document are defined as use "Standards
Action with Expert Review", "Specification Required", or "Expert Review",
Review" registration procedures 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 reason, so they should be given
substantial latitude.
Expert reviewers should take into consideration the following points:
* 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 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,
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.
16. References
16.1. Normative References
[Named.Information.Hash.Algorithm]
[IANA.Hash.Algorithms]
IANA, "Named Information Hash Algorithm",
<https://www.iana.org/assignments/named-information/named-
information.xhtml>. Algorithm Registry",
<https://www.iana.org/assignments/named-information>.
[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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/rfc3629>.
[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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/rfc/rfc7515>. <https://www.rfc-editor.org/info/rfc7515>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/rfc/rfc7516>.
<https://www.rfc-editor.org/info/rfc7516>.
[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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. <https://www.rfc-editor.org/info/rfc8174>.
[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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>. <https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc8613>.
[RFC8725] Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
Current Practices", BCP 225, RFC 8725,
DOI 10.17487/RFC8725, February 2020,
<https://www.rfc-editor.org/rfc/rfc8725>.
<https://www.rfc-editor.org/info/rfc8725>.
[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>.
<https://www.rfc-editor.org/info/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
<https://www.rfc-editor.org/info/rfc9052>.
[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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc9202>.
[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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/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>.
<https://www.rfc-editor.org/info/rfc9528>.
[SHA-256] NIST, "Secure Hash Standard", NIST FIPS 180-3 , October 2008,
<http://csrc.nist.gov/publications/fips/fips180-3/
fips180-3_final.pdf>. PUB 180-4,
DOI 10.6028/NIST.FIPS.180-4, August 2015,
<https://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.180-4.pdf>.
16.2. 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]
[CoRE-ATTRIBUTES]
Silverajan, B., Koster, M., Soloway, A., and B. Silverajan, A. Soloway, "Conditional
Attributes
Query Parameters for Constrained RESTful Environments", CoAP Observe", Work in Progress,
Internet-Draft, draft-ietf-core-conditional-
attributes-07, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
conditional-attributes-07>. draft-ietf-core-conditional-attributes-11,
16 March 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-conditional-attributes-11>.
[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>. <https://www.rfc-editor.org/info/rfc7009>.
[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>.
Appendix A. On using Using the Series Transfer Pattern
Performing a diff query of the TRL as specified in Section 8 is is, in
fact
fact, a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
[STP].
That is, a diff query enables the transfer of a series of diff
entries,
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 8), 'diff_set' is a subset of the update collection
associated with the requester, 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 6.2). 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].
[STP].
Furthermore, performing a diff query of the TRL together with the
"Cursor" extension extension, as specified in Section 9 9, in fact fact, relies on the
"Cursor" pattern of the Series Transfer Pattern STP (see Section 3.3 of
[I-D.bormann-t2trg-stp]). [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, endpoint when
supporting diff queries (see Section 6) and the "Cursor" extension
(see Section 6.2.1).
Except for MAX_N defined in Section 6.2, all the other parameters are
defined in Section 6.2.1 and are used only if the AS supports the
"Cursor" extension.
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: The parameter name. A name with letters in uppercase denotes
a parameter whose value does not change after its initialization.
*
Single instance: "Y", "Y" if there is a single parameter instance
associated with the TRL; TRL or "N", "N" if there is one parameter instance
per update collection (i.e., per requester).
*
Description: A short parameter description.
* Values: description of the parameter.
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.
+================+==========+====================+==================+
| 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 Sections 7 and Section 8, respectively.
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 which, in turn turn, is assumed to include the
following entries:
* a 'trl_path' parameter, parameter specifying the path of the TRL endpoint;
* a 'trl_hash' parameter, parameter specifying the "Hash Name String" of the
hash function used to compute token hashes as defined in
Section 4;
* a 'max_n' parameter, 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 8);
* 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 4 of this specification and
according to [RFC6920]. Assuming the usage of CWTs transported in
AS-to-Client responses encoded in CBOR (see Section 4.2.1),
'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 10 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 |
| } |
| |
| 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 |
| 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 10: Interaction for full query Full Query with Observe
C.2. Diff Query with Observe
Figure 11 shows an interaction example considering of a CoAP observation and a
diff query of the TRL.
The RS indicates N = 3 as the 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 |
| 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) |
| |
|<---------------------------------------------------+
| 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 11: Interaction for diff query Diff Query with Observe
C.3. Full Query with Observe plus Plus Diff Query
Figure 12 shows an interaction example considering of a CoAP observation and a
full query of the TRL.
The example also considers shows one of the notifications from the AS to
get getting
lost in transmission, and thus transmission; thus, it does not reaching reach 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, AS to perform a diff query of the TRL. The RS
indicates N = 8 as the 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 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)] |
| } |
| |
| ... |
| |
| (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 |
| Content-Format: application/ace-trl+cbor |
| Payload: { |
| e'diff_set' : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
Figure 12: Interaction for full query Full Query with Observe plus diff query 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 13 shows an interaction example considering of a CoAP observation and a
diff query of the TRL.
The RS specifies the query parameter 'diff' with a value of 3, i.e.,
the maximum number of diff entries to be specified in a response from
the AS.
After
If the RS has not received a notification from the AS for after a waiting
time defined by the application, the RS sends a GET request with no
Observe Option to the AS, 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", |
| "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 |
| 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 |
| 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 13: Interaction for diff query Diff Query with Observe and "Cursor"
C.5. Full Query with Observe plus 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 14 shows an interaction example considering of a CoAP observation and a
full query of the TRL.
The example also considers shows some of the notifications from the AS to
get getting
lost in transmission, and thus transmission; thus, they do not reaching reach 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. In particular,
the RS specifies:
* The query parameter 'diff' with a value of 8, i.e., the maximum
number of diff entries to be specified in a response from the AS.
* The query parameter 'cursor' with a value of 2, thus requesting
from the update collection the series items following the one with
the '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, 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 a value 7, of 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 |
| 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) |
| |
|<--------------------------------------------------------------+
| 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 |
| } |
| |
| ... |
| |
| (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)], |
| 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' : [ |
| [ [bstr.h(t6)], [] ], |
| [ [bstr.h(t5)], [] ], |
| [ [], [bstr.h(t5), bstr.h(t6)] ] |
| ], |
| e'cursor' : 10, |
| e'more' : false |
| } |
| |
Figure 14: Interaction for full query Full Query with Observe plus diff
query 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 15: CDDL model
Appendix E. Document Updates
This section is to be removed before publishing as an RFC.
E.1. Version -08 to -09
* Terminology:
- Improved definition of "administrator".
- Added early definitions of "Full query" and "Diff query".
* Rephrased "full TRL" to avoid confusion with "full query".
* Consistent with RFC 6920, defined sha-256 as mandatory to
implement.
* Prevented an attack to the RS by:
- Using only Protected Headers in access tokens.
- Using canonical CBOR tagging of CWTs.
* Clarifications:
- Handling of access tokens with 'exi' for both CWTs and JWTs.
- Registrations of devices are persisted and tracked at the AS.
- No response or error response from the TRL endpoint yields no
assumption.
- Rationale of application policies in defining strategies and
schedules for polling the AS.
* Security considerations:
- Added reference to RFC 8725.
- Improved considerations on content retrieval from the TRL.
* IANA:
- Added a pointer to where the use of the field 'cursor' in
problem-details is defined.
- Revised text on Expert Review when using early allocation per
RFC 7120.
* Split elision and comments in examples with CBOR Diagnostic
Notation.
* Lowercase capitalization for "client", "resource server", and
"authorization server".
* Editorial improvements.
E.2. 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.3. 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.
* 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.4. Version -05 to -06
* Clarified instructions for Expert Review in the IANA
considerations.
E.5. 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.6. 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.
* Clarifications and editorial improvements.
E.7. 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.8. 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.9. 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. Model
Acknowledgments
Ludwig Seitz contributed as a co-author coauthor of initial versions of this
document.
The authors sincerely thank Christian Amsüss, Carsten Bormann, Deb
Cooley, Roman Danyliw, Dhruv Dhody, Rikard Höglund, Benjamin Kaduk,
David Navarro, Joerg Ott, Marco Rasori, Michael Richardson, Kyle
Rose, Zaheduzzaman Sarker, Jim Schaad, Göran Selander, Travis
Spencer, Orie Steele, Éric Vyncke, Niklas Widell, 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, PA 15213-2612
United States of America
Email: secheverria@sei.cmu.edu
Grace Lewis
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, PA 15213-2612
United States of America
Email: glewis@sei.cmu.edu