Internet DRAFT - draft-ietf-ace-revoked-token-notification
draft-ietf-ace-revoked-token-notification
ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track F. Palombini
Expires: 4 December 2023 Ericsson AB
S. Echeverria
G. Lewis
CMU SEI
2 June 2023
Notification of Revoked Access Tokens in the Authentication and
Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-revoked-token-notification-06
Abstract
This document specifies a method of the Authentication and
Authorization for Constrained Environments (ACE) framework, which
allows an Authorization Server to notify Clients and Resource Servers
(i.e., registered devices) about revoked access tokens. As specified
in this document, the method allows Clients and Resource Servers to
access a Token Revocation List on the Authorization Server by using
the Constrained Application Protocol (CoAP), with the possible
additional use of resource observation. Resulting (unsolicited)
notifications of revoked access tokens complement alternative
approaches such as token introspection, while not requiring
additional endpoints on Clients and Resource Servers.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Authentication and
Authorization for Constrained Environments Working Group mailing list
(ace@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ace/.
Source for this draft and an issue tracker can be found at
https://github.com/ace-wg/ace-revoked-token-notification.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
3. Token Hash . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Token Revocation List (TRL) . . . . . . . . . . . . . . . . . 10
4.1. Update of the TRL . . . . . . . . . . . . . . . . . . . . 10
5. The TRL Endpoint . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Supporting Diff Queries . . . . . . . . . . . . . . . . . 12
5.1.1. Supporting the "Cursor" Extension . . . . . . . . . . 13
5.2. Query Parameters . . . . . . . . . . . . . . . . . . . . 14
6. Full Query of the TRL . . . . . . . . . . . . . . . . . . . . 16
7. Diff Query of the TRL . . . . . . . . . . . . . . . . . . . . 18
8. Response Messages when Using the "Cursor" Extension . . . . . 21
8.1. Response to Full Query . . . . . . . . . . . . . . . . . 21
8.2. Response to Diff Query . . . . . . . . . . . . . . . . . 21
8.2.1. Empty Collection . . . . . . . . . . . . . . . . . . 22
8.2.2. Cursor Not Specified in the Diff Query Request . . . 22
8.2.3. Cursor Specified in the Diff Query Request . . . . . 23
9. Registration at the Authorization Server . . . . . . . . . . 26
10. Notification of Revoked Access Tokens . . . . . . . . . . . . 26
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10.1. Handling of Access Tokens and Token Hashes . . . . . . . 27
11. ACE Token Revocation List Parameters . . . . . . . . . . . . 29
12. ACE Token Revocation List Error Identifiers . . . . . . . . . 29
13. Security Considerations . . . . . . . . . . . . . . . . . . . 30
13.1. Content Retrieval from the TRL . . . . . . . . . . . . . 30
13.2. Size of the TRL . . . . . . . . . . . . . . . . . . . . 30
13.3. Communication Patterns . . . . . . . . . . . . . . . . . 30
13.4. Request of New Access Tokens . . . . . . . . . . . . . . 31
13.5. Dishonest Clients . . . . . . . . . . . . . . . . . . . 31
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
14.1. Media Type Registrations . . . . . . . . . . . . . . . . 32
14.2. CoAP Content-Formats Registry . . . . . . . . . . . . . 33
14.3. ACE Token Revocation List Parameters Registry . . . . . 33
14.4. ACE Token Revocation List Errors . . . . . . . . . . . . 34
14.5. Expert Review Instructions . . . . . . . . . . . . . . . 35
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
15.1. Normative References . . . . . . . . . . . . . . . . . . 35
15.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. On using the Series Transfer Pattern . . . . . . . . 38
Appendix B. Parameters of the TRL Endpoint . . . . . . . . . . . 38
Appendix C. Interaction Examples . . . . . . . . . . . . . . . . 40
C.1. Full Query with Observe . . . . . . . . . . . . . . . . . 40
C.2. Diff Query with Observe . . . . . . . . . . . . . . . . . 42
C.3. Full Query with Observe plus Diff Query . . . . . . . . . 45
C.4. Diff Query with Observe and "Cursor" . . . . . . . . . . 47
C.5. Full Query with Observe plus Diff Query with "Cursor" . . 51
Appendix D. Document Updates . . . . . . . . . . . . . . . . . . 56
D.1. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 56
D.2. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 57
D.3. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 57
D.4. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 58
D.5. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 58
D.6. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 58
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 59
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 59
1. Introduction
Authentication and Authorization for Constrained Environments (ACE)
[RFC9200] is a framework that enforces access control on IoT devices
acting as Resource Servers. In order to use ACE, both Clients and
Resource Servers have to register with an Authorization Server (AS)
and become a registered device. Once registered, a Client can send a
request to the AS, to obtain an access token for a Resource Server
(RS). For a Client to access the RS, the Client must present the
issued access token at the RS, which then validates it before storing
it (see Section 5.10.1.1 of [RFC9200]).
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Even though access tokens have expiration times, there are
circumstances by which an access token may need to be revoked before
its expiration time, such as: (1) a registered device has been
compromised, or is suspected of being compromised; (2) a registered
device is decommissioned; (3) there has been a change in the ACE
profile for a registered device; (4) there has been a change in
access policies for a registered device; and (5) there has been a
change in the outcome of policy evaluation for a registered device
(e.g., if policy assessment depends on dynamic conditions in the
execution environment, the user context, or the resource
utilization).
As discussed in Section 6.1 of [RFC9200], only client-initiated
revocation is currently specified [RFC7009] for OAuth 2.0 [RFC6749],
based on the assumption that access tokens in OAuth are issued with a
relatively short lifetime. However, this is not expected to be the
case for constrained, intermittently connected devices, that need
access tokens with relatively long lifetimes.
This document specifies a method for allowing registered devices to
access and possibly subscribe to a Token Revocation List (TRL) on the
AS, in order to obtain updated information about pertaining access
tokens that were revoked prior to their expiration. As specified in
this document, the registered devices use the Constrained Application
Protocol (CoAP) [RFC7252] to communicate with the AS and with one
another, and can subscribe to the TRL on the AS by using resource
observation for CoAP [RFC7641]. Other underlying protocols than CoAP
are not prohibited from being supported in the future, if they are
defined to use 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, as
efficiently identified by corresponding hash values.
The benefits of this method are that it complements token
introspection, and it does not require any additional endpoints on
the registered devices. The only additional requirements for
registered devices are a request/response interaction with the AS to
access and possibly subscribe to the TRL (see Section 2), and the
lightweight computation of hash values to use as Token identifiers
(see Section 3).
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1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
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 CBOR [RFC8949], JSON [RFC8259], the CoAP protocol
[RFC7252], CoAP Observe [RFC7641], and the use of hash functions to
name objects as defined in [RFC6920].
Note that, unless otherwise indicated, the term "endpoint" is used
here following its OAuth definition, 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 the following terminology.
* Token hash: identifier of an access token, in binary format
encoding. The token hash has no relation to other possibly used
token identifiers, 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 on the AS with a TRL as its
representation. The default name of the TRL endpoint in a url-
path is '/revoke/trl'. Implementations are not required to use
this name, and can define their own instead.
* Registered device: a device registered at the AS, i.e., as a
Client, or an RS, or both. A registered device acts as a
requester towards the TRL endpoint.
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* Administrator: entity authorized to get full access to the TRL at
the AS, and acting as a requester towards the TRL endpoint. An
administrator is not necessarily a registered device as defined
above, i.e., a Client requesting access tokens or an RS consuming
access tokens. How the administrator authorization is established
and verified is out of the scope of this specification.
* 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.
Examples throughout this document are expressed in CBOR diagnostic
notation without the tag and value abbreviations.
2. Protocol Overview
This protocol defines how a CoAP-based Authorization Server informs
Clients and Resource Servers, i.e., registered devices, about
pertaining revoked access tokens. How the relationship between a
registered device and the AS is established is out of the scope of
this specification.
At a high level, the steps of this protocol are as follows.
* Upon startup, the AS creates a single TRL accessible through the
TRL endpoint. At any point in time, the TRL represents the list
of all revoked access tokens issued by the AS that are not expired
yet.
* When a device registers at the AS, it also receives the url-path
to the TRL endpoint.
After the registration procedure is finished, the registered
device can send an Observation Request to the TRL endpoint as
described in [RFC7641], i.e., a GET request including the CoAP
Observe Option set to 0 (register). By doing so, the registered
device effectively subscribes to the TRL, as interested to receive
notifications about its update. Upon receiving the request, the
AS adds the registered device to the list of observers of the TRL
endpoint.
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At any time, the registered device can send a GET request to the
TRL endpoint. When doing so, it can request for: the current list
of pertaining revoked access tokens (see Section 6); or the most
recent updates occurred over the list of pertaining revoked access
tokens (see Section 7). In either case, the registered device may
also rely on an Observation Request for subscribing to the TRL as
discussed above.
* When an access token is revoked, the AS adds the corresponding
token hash to the TRL. Also, when a revoked access token
eventually expires, the AS removes the corresponding token hash
from the TRL.
In either case, after updating the TRL, the AS sends Observe
notifications as per [RFC7641]. That is, an Observe notification
is sent to each registered device subscribed to the TRL and to
which the access token pertains.
Depending on the specific subscription established through the
observation request, the notification provides the current updated
list of revoked access tokens in the subset of the TRL pertaining
to that device (see Section 6), or rather the most recent TRL
updates occurred over that list of pertaining revoked access
tokens (see Section 7).
Further Observe notifications may be sent, consistently with
ongoing additional observations of the TRL endpoint.
* An administrator can access and subscribe to the TRL like a
registered device, while getting the full updated content of the
TRL.
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, with token hash th1, th2 and th3, respectively.
Consistently, the AS adds the three token hashes to the TRL at once,
and sends Observe notifications to one administrator and four
registered devices. Each dotted line associated with a pair of
registered devices indicates the access token that they both own.
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+----------------------+
| Authorization Server |
+-----------o----------+
revoke/trl | TRL: (th1,th2,th3)
|
+-----------------+------------+------------+------------+
| | | | |
| th1,th2,th3 | th1,th2 | th1 | th3 | th2,th3
v v v v v
+---------------+ +----------+ +----------+ +----------+ +----------+
| Administrator | | Client 1 | | Resource | | Client 2 | | Resource |
| | | | | Server 1 | | | | Server 2 |
+---------------+ +----------+ +----------+ +----------+ +----------+
: : : : : :
: : t1 : : t3 : :
: :........: :............: :
: t2 :
:...........................................:
Figure 1: Protocol Overview
Appendix C provides examples of the protocol flow and message
exchange between the AS and a registered device.
3. Token Hash
The token hash of an access token is computed as follows.
1. The AS considers the content of the 'access_token' parameter in
the AS-to-Client response (see Section 5.8.2 of [RFC9200]), where
the Access Token was included and provided to the requesting
Client.
2. The AS defines HASH_INPUT as follows.
* If the content of the 'access_token' parameter from step 1 is
a CBOR byte string, then HASH_INPUT takes the binary
serialization of that CBOR byte string. This is the case
where CBOR was used to transport the Access Token (as a CWT or
JWT).
With reference to the example in Figure 2, and assuming the
string's length in bytes to be 119 (i.e., 0x77 in
hexadecimal), then HASH_INPUT takes the bytes {0x58 0x77 0xd0
0x83 0x44 0xa1 ...}, i.e., the raw content of the
'access_token' parameter.
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* If the content of the 'access_token' parameter from step 1 is
a text string, then HASH_INPUT takes the binary serialization
of that text string. This is the case where JSON was used to
transport the Access Token (as a CWT or JWT).
With reference to the example in Figure 3, HASH_INPUT is the
binary serialization of "2YotnFZFEjr1zCsicMWpAA", i.e., of the
raw content of the 'access_token' parameter.
In either case, HASH_INPUT results in the binary representation
of the raw content of the 'access_token' parameter from the AS-
to-Client response.
3. The AS generates a hash value of HASH_INPUT as per Section 6 of
[RFC6920]. The resulting output in binary format is used as the
token hash. Note that the used binary format embeds the
identifier of the used hash function, in the first byte of the
computed token hash.
The specifically used hash function MUST be collision-resistant
on byte-strings, and MUST be selected from the "Named Information
Hash Algorithm" Registry [Named.Information.Hash.Algorithm].
The AS specifies the used hash function to registered devices
during their registration procedure (see Section 9).
2.01 Created
Content-Format: application/ace+cbor
Max-Age: 85800
Payload:
{
"access_token" : h'd08344a1 ...
(remainder of the access token omitted for brevity) ...',
"token_type" : pop,
"expires_in" : 86400,
"profile" : coap_dtls,
(remainder of the response omitted for brevity)
}
Figure 2: Example of AS-to-Client response using CBOR
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
Payload:
{
"access_token" : "2YotnFZFEjr1zCsicMWpAA",
"token_type" : "pop",
"expires_in" : 86400,
"profile" : "coap_dtls",
(remainder of the response omitted for brevity)
}
Figure 3: Example of AS-to-Client response using JSON
4. Token Revocation List (TRL)
Upon startup, the AS creates a single Token Revocation List (TRL),
encoded as a CBOR array.
Each element of the array is a CBOR byte string, with value the token
hash of an access token. The CBOR array MUST be treated as a set,
i.e., the order of its elements has no meaning.
The TRL is initialized as empty, i.e., its initial content MUST be
the empty CBOR array. The TRL is accessible through the TRL endpoint
on the AS.
4.1. Update of the TRL
The AS updates the TRL in the following two cases.
* When a non-expired access token is revoked, the token hash of the
access token is added to the TRL. That is, a CBOR byte string
with the token hash as its value is added to the CBOR array
encoding the TRL.
* When a revoked access token expires, the token hash of the access
token is removed from the TRL. That is, the CBOR byte string with
the token hash as its value is removed from the CBOR array
encoding the TRL.
The AS MAY perform a single update to the TRL such that one or more
token hashes are added or removed at once. For example, this can be
the case if multiple access tokens are revoked or expire at the same
time, or within an acceptably narrow time window.
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5. The TRL Endpoint
Consistent with Section 6.5 of [RFC9200], all communications between
a requester towards the TRL endpoint and the AS MUST be encrypted, as
well as integrity and replay protected. Furthermore, responses from
the AS to the requester MUST be bound to the corresponding requests.
Following a request to the TRL endpoint, the messages defined in this
document that the AS sends as response use Content-Format
"application/ace-trl+cbor". Their payload is formatted as a CBOR
map, and the CBOR values for the parameters included therein are
defined in Section 11.
The AS MUST implement measures to prevent access to the TRL endpoint
by entities other than registered devices and authorized
administrators.
The TRL endpoint supports only the GET method, and allows two types
of queries of the TRL.
* Full query: the AS returns the token hashes of the revoked access
tokens currently in the TRL and pertaining to the requester.
The AS MUST support this type of query. The processing of a full
query and the related response format are defined in Section 6.
* Diff query: the AS returns a list of diff entries. Each diff
entry is related to one of the most recent updates, in the subset
of the TRL pertaining to the requester.
The entry associated with one of such updates contains a list of
token hashes, such that: i) the corresponding revoked access
tokens pertain to the requester; and ii) they were added to or
removed from the TRL at that update.
The AS MAY support this type of query. In such a case, the AS
maintains the history of updates to the TRL as defined in
Section 5.1. The processing of a diff query and the related
response format are defined in Section 7.
If it supports diff queries, the AS MAY additionally support its
"Cursor" extension, which has two benefits. First, the AS can avoid
excessively big latencies when several diff entries have to be
transferred, by delivering one adjacent subset at the time, in
different diff query responses. Second, a requester can retrieve
diff entries associated with TRL updates that, even if not the most
recent ones, occurred after a TRL update indicated as reference
point.
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If it supports the "Cursor" extension, the AS stores additional
information when maintaining the history of updates to the TRL, as
defined in Section 5.1.1. Also, the processing of full query
requests and diff query requests, as well as the related response
format, are further extended as defined in Section 8.
Appendix B provides an aggregated overview of the parameters used by
the TRL endpoint, when the AS supports diff queries and the "Cursor"
extension.
5.1. Supporting Diff Queries
If the AS supports diff queries, it is able to transfer a list of
diff entries, as a series of TRL updates. That is, when replying to
a diff query performed by a requester, the AS specifies the most
recent updates to the subset of the TRL pertaining to that requester.
The following defines how the AS builds and maintains consistent
histories of TRL updates for each registered device and
administrator, hereafter referred to as requesters.
For each requester, the AS maintains an update collection of maximum
MAX_N series items, where MAX_N is a pre-defined, constant positive
integer. The AS MUST keep track of the MAX_N most recent updates to
the subset of the TRL that pertains to each requester. The AS SHOULD
provide requesters with the value of MAX_N, upon their registration
(see Section 9).
The series items in the update collection MUST be strictly ordered in
a chronological fashion. That is, at any point in time, the current
first series item is the one least recently added to the update
collection and still retained by the AS, while the current last
series item is the one most recently added to the update collection.
The particular method used to achieve this is implementation-
specific.
Each time the TRL changes, the AS performs the following operations
for each requester.
1. The AS considers the subset of the TRL pertaining to that
requester. If the TRL subset is not affected by this TRL update,
the AS stops the processing for that requester. Otherwise, the
AS moves to step 2.
2. The AS creates two sets "trl_patch" of token hashes, i.e., one
"removed" set and one "added" set, as related to this TRL update.
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3. The AS fills the two sets with the token hashes of the removed
and added access tokens, respectively, from/to the TRL subset
considered at step 1.
4. The AS creates a new series item, which includes the two sets
from step 3.
5. If the update collection associated with the requester currently
includes MAX_N series items, the AS MUST delete the oldest series
item in the update collection.
This occurs when the number of TRL updates pertaining to the
requester and currently stored at the AS is equal to MAX_N.
6. The AS adds the series item to the update collection associated
with the requester, as the most recent one.
5.1.1. Supporting the "Cursor" Extension
If it supports the "Cursor" extension for diff queries, the AS
performs also the following actions.
The AS defines the constant, unsigned integer MAX_INDEX <= ((2^64) -
1), where "^" is the exponentiation operator. In particular, the
value of MAX_INDEX is REQUIRED to be at least (MAX_N - 1), and is
RECOMMENDED to be at least ((2^32) - 1). Note that MAX_INDEX is
practically expected to be order of magnitudes greater than MAX_N.
When maintaining the history of updates to the TRL, the following
applies separately for each update 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 'index' with value 0.
If i_X is the value of 'index' associated with a series item X,
then the following series item Y will take 'index' with value i_Y
= (i_X + 1) % (MAX_INDEX + 1). That is, after having added a
series item whose associated 'index' has value MAX_INDEX, the next
added series item will result in a wrap-around of the 'index'
value, and will thus take 'index' with value 0.
For example, assuming MAX_N = 3, the values of 'index' in the
update collection chronologically evolve as follows, as new series
items are added and old series items are deleted.
- ...
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- ( 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 latest added series item in
the update collection.
That is, after having added V series items to the update
collection, the last and most recently added series item has
'index' with value 'last_index' = (V - 1) % (MAX_INDEX + 1).
As long as a wrap-around of the 'index' value has not occurred,
the value of 'last_index' is the absolute counter of series items
added to that update collection until and including V, minus 1.
When processing a diff query using the "Cursor" extension, the values
of 'index' are used as cursor information, as defined in Section 8.2.
For each update collection, the AS also defines a constant, positive
integer MAX_DIFF_BATCH <= MAX_N, whose value specifies the maximum
number of diff entries to be included in a single diff query
response. The specific value depends on the specific registered
device or administrator associated with the update collection in
question. If supporting the "Cursor" extension, the AS SHOULD
provide registered devices and administrators with the value of
MAX_DIFF_BATCH, upon their registration (see Section 9).
5.2. Query Parameters
A GET request to the TRL endpoint can include the following query
parameters. The AS MUST silently ignore unknown query parameters.
* 'diff': if included, it indicates to perform a diff query of the
TRL (see Section 7). Its value MUST be either:
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- the integer 0, indicating that a (notification) response should
include as many diff entries as the AS can provide in the
response; or
- a positive integer strictly greater than 0, indicating the
maximum number of diff entries that a (notification) response
should include.
If the AS does not support diff queries, it ignores the 'diff'
query parameter when present in the GET request, and proceeds like
when processing a full query of the TRL (see Section 6).
Otherwise, the AS MUST return a 4.00 (Bad Request) response in
case the 'diff' query parameter of the GET request specifies a
value other than 0 or than a positive integer, irrespective of the
presence of the 'cursor' parameter and its value (see below). The
response MUST have Content-Format "application/ace-trl+cbor". The
payload of the response is a CBOR map, which MUST include the
'error' parameter with value 0 ("Invalid parameter value") and MAY
include the 'error_description' parameter to provide additional
context.
* 'cursor': if included, it indicates to perform a diff query of the
TRL together with the "Cursor" extension, as defined in
Section 8.2. Its value MUST be either 0 or a positive integer.
If included, the 'cursor' query parameter specifies an unsigned
integer value that was provided by the AS in a previous response
from the TRL endpoint (see Section 8.1, Section 8.2.2 and
Section 8.2.3).
If the AS does not support the "Cursor" extension, it ignores the
'cursor' query parameter when present in the GET request. In such
a case, the AS proceeds: i) like when processing a diff query of
the TRL (see Section 7), if it supports diff queries and the
'diff' query parameter is present in the GET request; or ii) like
when processing a full query of the TRL (see Section 6) otherwise.
If the AS supports both diff queries and the "Cursor" extension,
and the GET request specifies the 'cursor' query parameter, then
the AS MUST return a 4.00 (Bad Request) response in case any of
the conditions below holds.
The 4.00 (Bad Request) response MUST have Content-Format
"application/ace-trl+cbor". The payload of the response MUST be a
CBOR map, which MUST include the 'error' parameter and MAY include
the 'error_description' parameter to provide additional context.
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- The GET request does not specify the 'diff' query parameter,
irrespective of the value of the 'cursor' parameter.
The 'error' parameter within the CBOR map carried in the
payload of the 4.00 (Bad Request) response MUST have value 1
("Invalid set of parameters").
- The 'cursor' query parameter has a value other than 0 or than a
positive integer, or it has a value strictly greater than
MAX_INDEX (see Section 5.1.1).
The 'error' parameter within the CBOR map carried in the
payload of the 4.00 (Bad Request) response MUST have value 0
("Invalid parameter value"). The CBOR map MUST also include
the 'cursor' parameter, which MUST specify either: the CBOR
simple value "null" (0xf6), if the update collection associated
with the requester is empty; or the corresponding current value
of 'last_index' otherwise.
- All of the following hold: the update collection associated
with the requester is not empty; no wrap-around of its 'index'
value has occurred; and the 'cursor' query parameter has a
value strictly greater than the current 'last_index' on the
update collection (see Section 5.1.1).
The 'error' parameter within the CBOR map carried in the
payload of the 4.00 (Bad Request) response MUST have value 2
("Out of bound cursor value"). The CBOR map MUST also include
the 'cursor' parameter, which MUST specify the current value of
'last_index' for the update collection associated with the
requester.
6. Full Query of the TRL
In order to produce a (notification) response to a GET request asking
for a full query of the TRL, the AS performs the following actions.
1. From the TRL, the AS builds a set HASHES such that:
* If the requester is a registered device, HASHES specifies the
token hashes currently in the TRL and associated with the
access tokens pertaining to that registered device. The AS
can 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.
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2. The AS sends a 2.05 (Content) response to the requester. The
response MUST have Content-Format "application/ace-trl+cbor".
The payload of the response is a CBOR map, which MUST be
formatted as follows.
* The 'full_set' parameter MUST be included and specifies a CBOR
array 'full_set_value'. Each element of 'full_set_value'
specifies one of the token hashes from the set HASHES, encoded
as a CBOR byte string. If the set HASHES is empty, the
'full_set' parameter specifies the empty CBOR array.
The CBOR array MUST be treated as a set, i.e., the order of
its elements has no meaning.
* The 'cursor' parameter MUST be included if the AS supports
both diff queries and the related "Cursor" extension (see
Section 5.1 and Section 5.1.1). Its value is specified
according to what is defined in Section 8.1, and provides the
requester with information for performing a follow-up diff
query using the "Cursor" extension (see Section 8.2).
If the AS does not support both diff queries and the "Cursor"
extension, this parameter MUST NOT be included. In case the
requester does not support both diff queries and the "Cursor"
extension, it MUST silently ignore the 'cursor' parameter if
present.
Figure 4 provides the CDDL definition [RFC8610] of the CBOR array
'full_set_value' specified in the response from the AS, as value of
the 'full_set' parameter.
token_hash = bytes
full_set_value = [* token_hash]
Figure 4: CDDL definition of 'full_set_value'
Figure 5 shows an example of response from the AS, following a full
query request to the TRL endpoint. In this example, the AS does not
support diff queries nor the "Cursor" extension, hence the 'cursor'
parameter is not included in the payload of the response. Also, full
token hashes are omitted for brevity.
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2.05 Content
Content-Format: application/ace-trl+cbor
Payload:
{
"full_set" : [
h'01fa51cc ... ', h'01748190 ... '
]
}
Figure 5: Example of response following a Full Query request to
the TRL endpoint
7. Diff Query of the TRL
In order to produce a (notification) response to a GET request asking
for a diff query of the TRL, the AS performs the following actions.
Note that, if the AS supports both diff queries and the related
"Cursor" extension, the steps 3 and 4 defined below are extended as
defined in Section 8.2.
1. The AS defines the positive integer NUM as follows. If the value
N specified in the 'diff' query parameter in the GET request is
equal to 0 or greater than the pre-defined positive integer MAX_N
(see Section 5.1), then NUM takes the value of MAX_N. Otherwise,
NUM takes N.
2. The AS determines U = min(NUM, SIZE), where SIZE <= MAX_N is the
number of TRL updates pertaining to the requester and currently
stored at the AS.
3. The AS prepares U diff entries. If U is equal to 0 (e.g.,
because SIZE is equal to 0 at step 2), then no diff entries are
prepared.
The prepared diff entries are related to the U most recent TRL
updates pertaining to the requester, as maintained in the update
collection for that requester (see Section 5.1). In particular,
the first diff entry refers to the most recent of such updates,
the second diff entry refers to the second from last of such
updates, and so on.
Each diff entry is a CBOR array 'diff_entry', which includes the
following two elements.
* The first element is a 'trl_patch' set of token hashes,
encoded as a CBOR array 'removed'. Each element of the array
is a CBOR byte string, with value the token hash of an access
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token such that: it pertained to the requester; and it was
removed from the TRL during the update associated with the
diff entry.
* The second element is a 'trl_patch' set of token hashes,
encoded as a CBOR array 'added'. Each element of the array is
a CBOR byte string, with value the token hash of an access
token such that: it pertains to the requester; and it was
added to the TRL during the update associated with the diff
entry.
The CBOR arrays 'removed' and 'added' MUST be treated as sets,
i.e., the order of their elements has no meaning.
4. The AS prepares a 2.05 (Content) response for the requester. The
response MUST have Content-Format "application/ace-trl+cbor".
The payload of the response is a CBOR map, which MUST be
formatted as follows.
* The 'diff_set' parameter MUST be present and specifies a CBOR
array 'diff_set_value' of U elements. Each element of
'diff_set_value' specifies one of the CBOR arrays 'diff_entry'
prepared above as diff entry. Note that U might have value 0,
in which case 'diff_set_value' is the empty CBOR array.
Within 'diff_set_value', the CBOR arrays 'diff_entry' MUST be
sorted to reflect the corresponding updates to the TRL in
reverse chronological order. That is, the first 'diff_entry'
element of 'diff_set_value' relates to the most recent update
to the subset of the TRL pertaining to the requester. The
second 'diff_entry' element relates to the second from last
most recent update to that subset, and so on.
* The 'cursor' parameter and the 'more' parameter MUST be
included if the AS supports both diff queries and the related
"Cursor" extension (see Section 5.1.1). Their values are
specified according to what is defined in Section 8.2, and
provide the requester with information for performing a
follow-up query of the TRL (see Section 8.2).
In case the AS supports diff queries but not the "Cursor"
extension, these parameters MUST NOT be included. In case the
requester supports diff queries but not the "Cursor"
extension, it MUST silently ignore the 'cursor' parameter and
the 'more' parameter if present.
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Figure 6 provides the CDDL definition [RFC8610] of the CBOR array
'diff_set_value' specified in the response from the AS, as value of
the 'diff_set' parameter.
token_hash = bytes
trl_patch = [* token_hash]
diff_entry = [removed: trl_patch, added: trl_patch]
diff_set_value = [* diff_entry]
Figure 6: CDDL definition of 'diff_set_value'
Figure 7 shows an example of response from the AS, following a diff
query request to the TRL endpoint, where U = 3 diff entries are
specified. In this example, the AS does not support the "Cursor"
extension, hence the 'cursor' parameter and the 'more' parameter are
not included in the payload of the response. Also, full token hashes
are omitted for brevity.
2.05 Content
Content-Format: application/ace-trl+cbor
Payload:
{
"diff_set" : [
[
[ h'01fa51cc ... ', h'01748190 ... '],
[ h'01cdf1ca ... ', h'01be41a6 ... ']
],
[
[ h'0144dd12 ... ', h'01231fff ... '],
[]
],
[
[],
[ h'01ca986f ... ', h'01fe1a2b ... ']
]
]
}
Figure 7: Example of response following a Diff Query request to
the TRL endpoint
Appendix A discusses how performing a diff query of the TRL is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
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8. Response Messages when Using the "Cursor" Extension
If it supports both diff queries and the "Cursor" extension, the AS
composes a response to a full query request or diff query request as
defined in Section 8.1 and Section 8.2, respectively.
The exact format of the response depends on the request being a full
query or diff query request, on the presence of the 'diff' and
'cursor' query parameters and their values in the diff query request,
and on the current status of the update collection associated with
the requester.
Error handling and the possible resulting error responses are as
defined in Section 5.2.
8.1. Response to Full Query
When processing a full query request to the TRL endpoint, the AS
composes a response as defined in Section 6.
In particular, the 'cursor' parameter included in the CBOR map
carried in the response payload specifies either the CBOR simple
value "null" (0xf6) or a CBOR unsigned integer.
The 'cursor' parameter MUST specify the CBOR simple value "null" in
case there are currently no TRL updates pertinent 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 a first update
pertaining to that requester occurs to the TRL.
Otherwise, the 'cursor' parameter MUST specify a CBOR unsigned
integer. This MUST take the 'index' value of the last series item in
the update collection associated with the requester (see
Section 5.1.1), as corresponding to the most recent update pertaining
to the requester occurred to the TRL. Such a value is in fact the
current value of 'last_index' for the update collection associated
with the requester.
8.2. Response to Diff Query
When processing a diff query request to the TRL endpoint, the AS
composes a response as defined in the following.
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8.2.1. Empty Collection
If the update collection associated with the requester has no
elements, the AS returns a 2.05 (Content) response. The response
MUST have Content-Format "application/ace-trl+cbor" and its payload
MUST be a CBOR map formatted as follows.
* The 'diff_set' parameter MUST be included and specifies the empty
CBOR array.
* The 'cursor' parameter MUST be included and specifies the CBOR
simple value "null" (0xf6).
* The 'more' parameter MUST be included and specifies the CBOR
simple value "false" (0xf4).
Note that the above applies when the update collection associated
with the requester has no elements, regardless of whether the
'cursor' query parameter is included or not in the diff query
request, and irrespective of the specified unsigned integer value if
present.
8.2.2. Cursor Not Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request does not include the 'cursor' query
parameter, the AS performs the same actions defined in Section 7,
with the following differences.
* At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 5.1.1), 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.
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- 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 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 update pertaining
to the requester and returned in this diff query response.
Note that the 'cursor' parameter takes the same 'index' value
of the last series item in the update collection when U <=
MAX_DIFF_BATCH.
- The 'more' parameter MUST be present and MUST specify the CBOR
simple value "false" (0xf4) if U <= MAX_DIFF_BATCH, or the CBOR
simple value "true" (0xf5) otherwise.
If the 'more' parameter has value "true", the requester can
send a follow-up diff query request including the 'cursor'
query parameter, with the same value of the 'cursor' parameter
specified in this diff query response. As defined in
Section 8.2.3, this would result in the AS transferring the
following subset of series items as diff entries, thus resuming
from where interrupted in the previous transfer.
8.2.3. Cursor Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request includes the 'cursor' query parameter with
value P, the AS proceeds as follows, depending on which of the
following two cases hold.
* Case A - The series item X with 'index' having value P and the
series item Y with 'index' having value (P + 1) % (MAX_INDEX + 1)
are both not found in the update collection associated with the
requester. This occurs when the item Y (and possibly further ones
after it) has been previously removed from the history of updates
for that requester (see step 5 at Section 5.1).
In this case, the AS returns a 2.05 (Content) response. The
response MUST have Content-Format "application/ace-trl+cbor" and
its payload MUST be a CBOR map formatted as follows.
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- 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 signaling that the update collection is in fact not empty, but
that one or more series items have been lost due to their removal.
These include the item with 'index' value (P + 1) % (MAX_INDEX +
1), that the requester wished to obtain as the first one following
the specified reference point with 'index' value P.
When receiving this diff query response, the requester should send
a new full query request to the AS. A successful response
provides the requester with the full, current pertaining subset of
the TRL, as well as with a valid value of the 'cursor' parameter
(see Section 8.1) to be possibly used as query parameter in a
following diff query request.
* Case B - The series item X with 'index' having value P is found in
the update collection associated with the requester; or the series
item X is not found and the series item Y with 'index' having
value (P + 1) % (MAX_INDEX + 1) is found in the update collection
associated with the requester.
In this case, the AS performs the same actions defined in
Section 7, with the following differences.
- At step 3, the AS considers the value MAX_DIFF_BATCH (see
Section 5.1.1), and prepares L = min(SUB_U, MAX_DIFF_BATCH)
diff entries, where SUB_U = min(NUM, SUB_SIZE), and SUB_SIZE is
the number of series items in the update collection starting
from and including the series item added immediately after X.
If L is equal to 0 (e.g., because SUB_U is equal to 0), then no
diff entries are prepared.
If SUB_U <= MAX_DIFF_BATCH, the prepared diff entries are the
last series items in the update collection associated with the
requester, corresponding to the L most recent TRL updates
pertaining to the requester.
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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 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 diff entry. Note that L might have
value 0, in which case 'diff_set_value' is the empty CBOR
array.
o The 'cursor' parameter MUST be present and MUST specify a
CBOR unsigned integer. In particular:
+ If L is equal to 0, i.e., the series item X is the last
one in the update collection, then the 'cursor' parameter
MUST take the same 'index' value of the last series item
in the update collection. Such a value is in fact the
current value of 'last_index' for the update collection.
+ If L is different than 0, then the 'cursor' parameter
MUST take the 'index' value of the series element of the
update collection included as first diff entry in the
'diff_set' CBOR array. That is, the 'cursor' parameter
takes the 'index' value of the series item in the update
collection corresponding to the most recent 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 'more' has value "true", the requester can send a follow-
up diff query request including the 'cursor' query
parameter, with the same value of the 'cursor' parameter
specified in this diff query response. This would result in
the AS transferring the following subset of series items as
diff entries, thus resuming from where interrupted in the
previous transfer.
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9. Registration at the Authorization Server
During the registration process at the AS, an administrator or a
registered device receives the following information as part of the
registration response.
* The url-path to the TRL endpoint at the AS.
* The hash function used to compute token hashes. This is specified
as an integer or a text string, taking value from the "ID" or
"Hash Name String" column of the "Named Information Hash
Algorithm" Registry [Named.Information.Hash.Algorithm],
respectively.
* Optionally, a positive integer MAX_N, if the AS supports diff
queries of the TRL (see Section 5.1 and Section 7).
* Optionally, a positive integer MAX_DIFF_BATCH, if the AS supports
diff queries of the TRL as well as the related "Cursor" extension
(see Section 5.1.1 and Section 8).
Further details about the registration process at the AS are out of
scope for this specification. Note that the registration process is
also out of the scope of the ACE framework for Authentication and
Authorization (see Section 5.5 of [RFC9200]).
10. Notification of Revoked Access Tokens
Once completed the registration procedure at the AS, the
administrator or registered device can send a GET request to the TRL
endpoint at the AS. The request can express the wish for a full
query (see Section 6) or a diff query (see Section 7) of the TRL.
Also, the request can include the CoAP Observe Option set to 0
(register), in order to start an observation of the TRL endpoint as
per Section 3.1 of [RFC7641].
In case the request is successfully processed, the AS replies with a
response specifying the CoAP response code 2.05 (Content). In
particular, if the AS supports diff queries but not the "Cursor"
extension (see Section 5.1 and Section 5.1.1), then the payload of
the response is formatted as defined in Section 6 or in Section 7, in
case the GET request has yielded the execution of a full query or of
a diff query of the TRL, respectively. Instead, if the AS supports
both diff queries and the related "Cursor" extension, then the
payload of the response is formatted as defined in Section 8.
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When the TRL is updated (see Section 4.1), the AS sends Observe
notifications to the observers whose pertaining subset of the TRL has
changed. Observe notifications are sent as per Section 4.2 of
[RFC7641]. If supported by the AS, an observer may configure the
behavior according to which the AS sends those Observe notifications.
To this end, a possible way relies on the conditional control
attribute "c.pmax" defined in [I-D.ietf-core-conditional-attributes],
which can be included as a "name=value" query parameter in an
Observation Request. This ensures that no more than c.pmax seconds
elapse between two consecutive notifications sent to that observer,
regardless of whether the TRL has changed or not.
Following a first exchange with the AS, an administrator or a
registered device can send additional GET (Observation) requests to
the TRL endpoint at any time, analogously to what is defined above.
When doing so, the requester towards the TRL endpoint can perform a
full query (see Section 6) or a diff query (see Section 7) of the
TRL.
10.1. Handling of Access Tokens and Token Hashes
When receiving a response from the TRL endpoint, a registered device
MUST expunge every stored access token associated with a token hash
specified in the response. In case the registered device is an RS,
it MUST store the token hash.
An RS MUST NOT accept and store an access token, if the corresponding
token hash is among the currently stored ones.
An RS stores a token hash th1 corresponding to an access token t1
until both the following conditions 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.
- A response from the TRL endpoint indicating that t1 has expired
after its earlier revocation, i.e., the token hash th1 has been
removed from the TRL. This can be indicated, for instance, in
a response from the TRL endpoint following a diff query of the
TRL (see Section 7).
- The value of the 'exp' claim specified in t1 indicates that t1
has expired.
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- 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 the two conditions above, unless it
becomes necessary due to memory limitations. In such a case, the RS
MUST delete the earliest stored token hashes first.
Retaining the stored token hashes as specified above limits the
impact from a (dishonest) Client whose pertaining access token: i)
specifies the 'exi' claim; ii) is uploaded at the RS for the first
time after it has been revoked and later expired; and iii) has the
sequence number encoded in the 'cti' claim greater than the highest
sequence number among the expired access tokens specifying the 'exi'
claim for the RS (see Section 5.10.3 of [RFC9200]). That is, the RS
would not accept such a revoked and expired access token as long as
it stores the corresponding token hash.
In order to further limit such a risk, when receiving an access token
that specifies the 'exi' claim and for which a corresponding token
hash is not stored, the RS can introspect the access token (see
Section 5.9 of [RFC9200]), if token introspection is implemented by
both the RS and the AS.
When, due to the stored and corresponding token hash th2, an access
token t2 that includes the 'exi' claim is expunged or is not accepted
upon its upload, the RS retrieves the sequence number sn2 encoded in
the 'cti' claim (see Section 5.10.3 of [RFC9200]). Then, the RS
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.
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11. ACE Token Revocation List Parameters
This specification defines a number of parameters that can be
transported in the response from the TRL endpoint, when the response
payload is a CBOR map. Note that such a response MUST use the
Content-Format "application/ace-trl+cbor" defined in Section 14.2 of
this specification.
The table below summarizes them, and specifies the CBOR value to use
as abbreviation instead of the full descriptive name.
+-------------------+------------+------------------------+
| Name | CBOR Value | CBOR Type |
+-------------------+------------+------------------------+
| full_set | 0 | array |
+-------------------+------------+------------------------+
| diff_set | 1 | array |
+-------------------+------------+------------------------+
| cursor | 2 | unsigned integer / |
| | | simple value "null" |
+-------------------+------------+------------------------+
| more | 3 | simple value "false" / |
| | | simple value "true" |
+-------------------+------------+------------------------+
| error | 4 | integer |
+-------------------+------------+------------------------+
| error_description | 5 | text string |
+-------------------+------------+------------------------+
Figure 8: CBOR abbreviations for the ACE Token Revocation List
parameters
12. ACE Token Revocation List Error Identifiers
This specification defines a number of values that the AS can include
as error identifiers, in the 'error' parameter of an error response
from the TRL endpoint. This applies to error responses whose payload
is a CBOR map and whose Content-Format is "application/ace-trl+cbor".
+-------+---------------------------+
| Value | Description |
+-------+---------------------------+
| 0 | Invalid parameter value |
+-------+---------------------------+
| 1 | Invalid set of parameters |
+-------+---------------------------+
| 2 | Out of bound cursor value |
+-------+---------------------------+
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Figure 9: ACE Token Revocation List Error Identifiers
13. Security Considerations
Security considerations are inherited from the ACE framework for
Authentication and Authorization [RFC9200], from [RFC8392] as to the
usage of CWTs, from [RFC7519] as to the usage of JWTs, from [RFC7641]
as to the usage of CoAP Observe, and from [RFC6920] with regard to
computing the token hashes. The following considerations also apply.
13.1. Content Retrieval from the TRL
The AS MUST ensure that each registered device can access and
retrieve only its pertaining subset of the TRL. To this end, the AS
can 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.
Disclosing any information about revoked access tokens to entities
other than the intended registered devices may result in privacy
concerns. Therefore, the AS MUST ensure that, other than registered
devices accessing their own pertaining subset of the TRL, only
authorized and authenticated administrators can retrieve the full
TRL. To this end, the AS may rely on an access control list or
similar.
13.2. Size of the TRL
If many non-expired access tokens associated with a registered device
are revoked, the pertaining subset of the TRL could grow to a size
bigger than what the registered device is prepared to handle upon
reception, especially if relying on a full query of the TRL (see
Section 6).
This could be exploited by attackers to negatively affect the
behavior of a registered device. Issuing access tokens with not too
long expiration time could help reduce the size of the TRL, but an AS
SHOULD take measures to limit this size.
13.3. Communication Patterns
The communication about revoked access tokens presented in this
specification is expected to especially rely on CoAP Observe
notifications sent from the AS to a registered device. The
suppression of those notifications by an external attacker that has
access to the network would prevent registered devices from ever
knowing that their pertaining access tokens have been revoked.
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In order to avoid this, a registered device SHOULD NOT rely solely on
the CoAP Observe notifications. In particular, a registered device
SHOULD also regularly poll the AS for the most current information
about revoked access tokens, by sending GET requests to the TRL
endpoint according to a related application policy.
13.4. Request of New Access Tokens
If a Client stores an access token that it still believes to be
valid, and it accordingly attempts to access a protected resource at
the RS, the Client might anyway receive an unprotected 4.01
(Unauthorized) response from the RS.
This can be due to different reasons. For example, the access token
has actually been revoked and the Client is not aware about that yet,
while the RS has gained knowledge about that and has expunged the
access token. Also, an on-path, active adversary might have injected
a forged 4.01 (Unauthorized) response.
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, or instead to request a new one.
13.5. Dishonest Clients
A dishonest Client may attempt to exploit its early knowledge about a
revoked access token, in order to illegitimately continue accessing a
protected resource at the RS beyond the access token revocation.
That is, the Client might gain knowledge about the revocation of an
access token considerably earlier than the RS, e.g., if the Client
relies on CoAP Observe to access the TRL at the AS, while the RS
relies only on polling through individual requests.
This makes the RS vulnerable during a time interval that starts when
the Client gains knowledge of the revoked access token and ends when
the RS expunges the access token, e.g., after having gained knowledge
of its revocation. During such a time interval, the Client would be
able to illegitimately access protected resources at the RS, if this
still retains the access token without knowing about its revocation
yet.
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In order to mitigate the risk of such an abuse, if an RS relies
solely on polling through individual requests to the TRL endpoint,
the RS SHOULD enforce an adequate trade-off between the polling
frequency and the maximum length of the vulnerable time window.
14. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
14.1. Media Type Registrations
IANA is asked to register the media type "application/ace-trl+cbor"
for messages of the protocol defined in this document encoded in
CBOR. This registration follows the procedures specified in
[RFC6838].
Type name: application
Subtype name: ace-trl+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: Must be encoded as a CBOR map containing the
protocol parameters defined in [RFC-XXXX].
Security considerations: See Section 13 of this document.
Interoperability considerations: N/A
Published specification: [RFC-XXXX]
Applications that use this media type: The type is used by
Authorization Servers, Clients and Resource Servers that support the
notification of revoked access tokens, according to a Token
Revocation List maintained by the Authorization Server as specified
in [RFC-XXXX].
Fragment identifier considerations: N/A
Additional information: N/A
Person & email address to contact for further information:
<iesg@ietf.org>
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Intended usage: COMMON
Restrictions on usage: None
Author: Marco Tiloca <marco.tiloca@ri.se>
Change controller: IESG
14.2. CoAP Content-Formats Registry
IANA is asked to add the following entry to the "CoAP Content-
Formats" registry within the "CoRE Parameters" registry group.
Media Type: application/ace-trl+cbor
Encoding: -
ID: TBD
Reference: [RFC-XXXX]
14.3. ACE Token Revocation List Parameters Registry
IANA is asked to establish the "ACE Token Revocation List Parameters"
IANA registry within the "Authentication and Authorization for
Constrained Environments (ACE)" registry group.
The registry uses the "Expert Review" registration procedure
[RFC8126]. Expert Review guidelines are provided in Section 14.5.
It should be noted that, in addition to the Expert Review, some
portions of the registry require a specification, potentially a
Standards Track RFC, to be supplied as well.
The columns of this registry are:
* Name: This field contains a descriptive name that enables easier
reference to the item. The name MUST be unique. It is not used
in the encoding.
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* CBOR Value: This field contains the value used as CBOR
abbreviation of the item. These values MUST be unique. The value
can be 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 CBOR type of the item, or a
pointer to the registry that defines its type, when that depends
on another item.
* Reference: This field contains a pointer to the public
specification for the item.
This registry has been initially populated by the values in
Section 11. The "Reference" column for all of these entries refers
to this document.
14.4. ACE Token Revocation List Errors
IANA is asked to establish the "ACE Token Revocation List Errors"
IANA registry within the "Authentication and Authorization for
Constrained Environments (ACE)" registry group.
The registry uses the "Expert Review" registration procedure
[RFC8126]. Expert Review guidelines are provided in Section 14.5.
It should be noted that, in addition to the Expert Review, some
portions of the registry require a specification, potentially a
Standards Track RFC, to be supplied as well.
The columns of this registry are:
* Value: The field contains the value to be used to identify the
error. These values MUST be unique. The value can be 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.
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* Reference: This field contains a pointer to the public
specification defining the error, if one exists.
This registry has been initially populated by the values in
Section 12. The "Reference" column for all of these entries refers
to this document.
14.5. Expert Review Instructions
The IANA registries established in this document are defined as
"Expert Review". This section gives some general guidelines for what
the experts should be looking for, but they are being designated as
experts for a reason so they should be given substantial latitude.
Expert reviewers should take into consideration the following points:
* Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
registered and that the point is likely to be used in deployments.
The zones tagged as private use are intended for testing purposes
and closed environments. Code points in other ranges should not
be assigned for testing.
* Specifications are required for the "Standards Action With Expert
Review" range of point assignment. Specifications should exist
for "Specification Required" ranges, but early assignment before a
specification is available is considered to be permissible. For
the "Expert Review" range of point assignment, specifications are
recommended, and are needed if they are expected to be used
outside of closed environments in an interoperable way. When
specifications are not provided, the description provided needs to
have sufficient information to identify what the point is being
used for.
* Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.
15. References
15.1. Normative References
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[Named.Information.Hash.Algorithm]
IANA, "Named Information Hash Algorithm",
<https://www.iana.org/assignments/named-information/named-
information.xhtml>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
Keranen, A., and P. Hallam-Baker, "Naming Things with
Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
<https://www.rfc-editor.org/rfc/rfc6920>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/rfc/rfc7519>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/rfc/rfc7641>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
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[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[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>.
[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>.
[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>.
15.2. Informative References
[I-D.bormann-t2trg-stp]
Bormann, C. and K. Hartke, "The Series Transfer Pattern
(STP)", Work in Progress, Internet-Draft, draft-bormann-
t2trg-stp-03, 7 April 2020,
<https://datatracker.ietf.org/doc/html/draft-bormann-
t2trg-stp-03>.
[I-D.ietf-core-conditional-attributes]
Koster, M., Soloway, A., and B. Silverajan, "Conditional
Attributes for Constrained RESTful Environments", Work in
Progress, Internet-Draft, draft-ietf-core-conditional-
attributes-06, 14 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
conditional-attributes-06>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <https://www.rfc-editor.org/rfc/rfc7009>.
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Appendix A. On using the Series Transfer Pattern
Performing a diff query of the TRL as specified in Section 7 is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
That is, a diff query enables the transfer of a series of TRL
updates, with the AS specifying U <= MAX_N diff entries as the U most
recent updates to the subset of the TRL pertaining to a requester,
i.e., a registered device or an administrator.
When responding to a diff query request from a requester (see
Section 7), 'diff_set' is a subset of the update collection
associated with the requester, where each 'diff_entry' record is a
series item from that update collection. Note that 'diff_set'
specifies the whole current update collection when the value of U is
equal to SIZE, i.e., the current number of series items in the update
collection.
The value N of the 'diff' query parameter in the GET request allows
the requester and the AS to trade the amount of provided information
with the latency of the information transfer.
Since the update collection associated with each requester includes
up to MAX_N series items, the AS deletes the oldest series item when
a new one is generated and added to the end of the update collection,
due to a new TRL update pertaining to that requester (see
Section 5.1). This addresses the question "When can the server
decide to no longer retain older items?" raised in Section 3.2 of
[I-D.bormann-t2trg-stp].
Furthermore, performing a diff query of the TRL together with the
"Cursor" extension as specified in Section 8 in fact relies on the
"Cursor" pattern of the Series Transfer Pattern (see Section 3.3 of
[I-D.bormann-t2trg-stp]).
Appendix B. Parameters of the TRL Endpoint
Figure 10 provides an aggregated overview of the parameters used by
the TRL endpoint, when the AS supports diff queries (see Section 5)
and the "Cursor" extension (see Section 5.1.1).
Except for MAX_N defined in Section 5.1, all the other parameters are
defined in Section 5.1.1 and are used only if the AS supports the
"Cursor" extension.
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For each parameter, the columns of the table specify the following
information. Both a registered device and an administrator are
referred to as "requester".
* Name: parameter name. A name with letters in uppercase denotes a
parameter whose value does not change after its initialization.
* Single instance: "Y", if there is a single parameter instance
associated with the TRL; or "N", if there is one parameter
instance per update collection (i.e., per requester).
* Description: short parameter description.
* Values: the unsigned integer values that the parameter can assume,
where LB and UB denote the inclusive lower bound and upper bound,
respectively, and "^" is the exponentiation operator.
+----------------+----------+--------------------+--------------------+
| Name | Single | Description | Value |
| | instance | | |
+----------------+----------+--------------------+--------------------+
| MAX_N | Y | Max number of TRL | LB = 1 |
| | | updates stored per | |
| | | requester | If supporting |
| | | | "Cursor", then |
| | | | UB = (MAX_INDEX+1) |
+----------------+----------+--------------------+--------------------+
| MAX_DIFF_BATCH | N | Max number of diff | LB = 1 |
| | | entries included | |
| | | in a diff query | UB = MAX_N |
| | | 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 updated | 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 | |
+----------------+----------+--------------------+--------------------+
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Figure 10: Parameters of the TRL Endpoint
Appendix C. Interaction Examples
This section provides examples of interactions between an RS as a
registered device and an AS. In the examples, all the access tokens
issued by the AS are intended to be consumed by the considered RS.
The AS supports both full queries and diff queries of the TRL, as
defined in Section 6 and Section 7, respectively.
The details of the registration process are omitted, but it is
assumed that the RS sends an unspecified payload to the AS, which
replies with a 2.01 (Created) response.
The payload of the registration response is a CBOR map, which
includes the following entries:
* a 'trl_path' parameter, specifying the path of the TRL endpoint;
* a 'trl_hash' parameter, specifying the hash function used to
compute token hashes as defined in Section 3;
* a 'max_n' parameter, specifying the value of MAX_N, i.e., the
maximum number of TRL updates pertaining to each registered device
that the AS retains for that device (see Section 7);
* possible further parameters related to the registration process.
Furthermore, 'h(x)' refers to the hash function used to compute the
token hashes, as defined in Section 3 of this specification and
according to [RFC6920]. Assuming the usage of CWTs transported in
CBOR, 'bstr.h(t1)' and 'bstr.h(t2)' denote the byte-string
representations of the token hashes for the access tokens t1 and t2,
respectively.
C.1. Full Query with Observe
Figure 11 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.
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RS AS
| |
| Registration: POST |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl/ |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "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: { |
| "full_set" : [bstr.h(t1)] |
| } |
| . |
| . |
| . |
| |
| (Access token t2 is revoked) |
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| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1), bstr.h(t2)] |
| } |
| |
| . |
| . |
| . |
| |
| (Access token t1 expires) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access token t2 expires) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
| |
Figure 11: Interaction for Full Query with Observe
C.2. Diff Query with Observe
Figure 12 shows an interaction example considering a CoAP observation
and a diff query of the TRL.
The RS indicates N = 3 as value of the 'diff' query parameter, i.e.,
as the maximum number of diff entries to be specified in a response
from the AS.
In this example, the AS does not support the "Cursor" extension.
Hence the 'cursor' parameter and the 'more' parameter are not
included in the payload of the responses to a diff query request.
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RS AS
| |
| Registration: POST |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl?diff=3 |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "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: { |
| "diff_set" : [ |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| . |
| . |
| . |
| |
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| (Access token t2 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| . |
| . |
| . |
| |
| (Access token t1 expires) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "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: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ] |
| } |
| |
Figure 12: Interaction for Diff Query with Observe
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C.3. Full Query with Observe plus Diff Query
Figure 13 shows an interaction example considering a CoAP observation
and a full query of the TRL.
The example also considers one of the notifications from the AS to
get lost in transmission, and thus not reaching the RS.
When this happens, and after a waiting time defined by the
application has elapsed, the RS sends a GET request with no Observe
Option to the AS, to perform a diff query of the TRL. The RS
indicates N = 8 as value of the 'diff' query parameter, i.e., as the
maximum number of diff entries to be specified in a response from the
AS.
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 Observe: 0 |
| coap://as.example.com/revoke/trl/ |
+--------------------------------------------------->|
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
| . |
| . |
| . |
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| |
| (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: { |
| "full_set" : [bstr.h(t1)] |
| } |
| . |
| . |
| . |
| |
| (Access token t2 is revoked) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1), bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access token t1 expires) |
| |
|<---------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access token t2 expires) |
| |
| X<------------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
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| Payload: { |
| "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: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
Figure 13: Interaction for Full Query with Observe plus Diff Query
C.4. Diff Query with Observe and "Cursor"
In this example, the AS supports the "Cursor" extension. Hence, the
CBOR map conveyed as payload of the registration response
additionally includes a "max_diff_batch" parameter. This specifies
the value of MAX_DIFF_BATCH, i.e., the maximum number of diff entries
that can be included in a response to a diff query request from this
RS.
Figure 14 shows an interaction example considering a CoAP observation
and a diff query of the TRL.
The RS specifies the query parameter 'diff' with value 3, i.e., the
maximum number of diff entries to be specified in a response from the
AS.
After the RS has not received a notification from the AS for a
waiting time defined by the application, the RS sends a GET request
with no Observe Option to the AS, to perform a diff query of the TRL.
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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 Observe: 0 |
| coap://as.example.com/revoke/trl?diff=3 |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [], |
| "cursor" : null, |
| "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: { |
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| "diff_set" : [ |
| [ [], [bstr.h(t1)] ] |
| ], |
| "cursor" : 0, |
| "more" : false |
| } |
| . |
| . |
| . |
| |
| (Access token t2 is revoked) |
| |
|<-------------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ], |
| "cursor" : 1, |
| "more" : false |
| } |
| . |
| . |
| . |
| |
| (Access token t1 expires) |
| |
|<-------------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ], |
| "cursor" : 2, |
| "more" : false |
| } |
| . |
| . |
| . |
| |
| (Access token t2 expires) |
| |
|<-------------------------------------------------------+
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| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ], |
| "cursor" : 3, |
| "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: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ], |
| "cursor" : 3, |
| "more" : false |
| } |
| |
| GET |
| coap://as.example.com/revoke/trl?diff=3&cursor=3 |
+------------------------------------------------------->|
| |
|<-------------------------------------------------------+
| 2.05 CONTENT |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [], |
| "cursor" : 3, |
| "more" : false |
| } |
| |
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Figure 14: Interaction for Diff Query with Observe and "Cursor"
C.5. Full Query with Observe plus Diff Query with "Cursor"
In this example, the AS supports the "Cursor" extension. Hence, the
CBOR map conveyed as payload of the registration response
additionally includes a "max_diff_batch" parameter. This specifies
the value of MAX_DIFF_BATCH, i.e., the maximum number of diff entries
that can be included in a response to a diff query request from this
RS.
Figure 15 shows an interaction example considering a CoAP observation
and a full query of the TRL.
The example also considers some of the notifications from the AS to
get lost in transmission, and thus not reaching the RS.
When this happens, and after a waiting time defined by the
application has elapsed, the RS sends a GET request with no Observe
Option to the AS, to perform a diff query of the TRL. In particular,
the RS specifies:
* The query parameter 'diff' with value 8, i.e., the maximum number
of diff entries to be specified in a response from the AS.
* The query parameter 'cursor' with value 2, thus requesting from
the update collection the series items following the one with
'index' value equal to 2 (i.e., following the last series item
that the RS successfully received in an earlier notification
response).
The response from the AS conveys a first batch of MAX_DIFF_BATCH=5
series items from the update collection corresponding to the RS. The
AS indicates that further series items are actually available in the
update collection, by setting the 'more' parameter of the response to
"true". Also, the 'cursor' parameter of the response is set to 7,
i.e., to the 'index' value of the most recent series item included in
the response.
After that, the RS follows up with a further diff query request
specifying the query parameter 'cursor' with value 7, in order to
retrieve the next and last batch of series items from the update
collection.
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RS AS
| |
| Registration: POST |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "max_n" : 10, |
| "max_diff_batch": 5 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl/ |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [], |
| "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: { |
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| "full_set" : [bstr.h(t1)], |
| "cursor" : 0 |
| } |
| . |
| . |
| . |
| |
| (Access token t2 is revoked) |
| |
|<--------------------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1), bstr.h(t2)], |
| "cursor" : 1 |
| } |
| . |
| . |
| . |
| |
| (Access token t1 expires) |
| |
|<--------------------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t2)], |
| "cursor" : 2 |
| } |
| . |
| . |
| . |
| |
| (Access token t2 expires) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [], |
| "cursor" : 3 |
| } |
| . |
| . |
| . |
| |
| (Access token t3 is revoked) |
| |
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| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 88 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t3)], |
| "cursor" : 4 |
| } |
| . |
| . |
| . |
| |
| (Access token t4 is revoked) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 89 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t3), bstr.h(t4)], |
| "cursor" : 5 |
| } |
| . |
| . |
| . |
| |
| (Access token t3 expires) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 90 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t4)], |
| "cursor" : 6 |
| } |
| . |
| . |
| . |
| |
| (Access token t4 expires) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 91 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [], |
| "cursor" : 7 |
| } |
| . |
| . |
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| . |
| |
| (Access tokens t5 and t6 are revoked) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 92 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t5), bstr.h(t6)], |
| "cursor" : 8 |
| } |
| . |
| . |
| . |
| |
| (Access token t5 expires) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 93 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t6)], |
| "cursor" : 9 |
| } |
| . |
| . |
| . |
| |
| (Access token t6 expires) |
| |
| X<-----------------------------------------------------------+
| 2.05 CONTENT Observe: 94 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [], |
| "cursor" : 10 |
| } |
| . |
| . |
| . |
| |
| (Enough time has passed since |
| the latest received notification) |
| |
| GET |
| coap://as.example.com/revoke/trl?diff=8&cursor=2 |
+-------------------------------------------------------------->|
| |
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|<--------------------------------------------------------------+
| 2.05 CONTENT |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t4)], [] ], |
| [ [bstr.h(t3)], [] ], |
| [ [], [bstr.h(t4)] ], |
| [ [], [bstr.h(t3)] ], |
| [ [bstr.h(t2)], [] ] |
| ], |
| "cursor" : 7, |
| "more" : true |
| } |
| |
| GET |
| coap://as.example.com/revoke/trl?diff=8&cursor=7 |
+-------------------------------------------------------------->|
| |
|<--------------------------------------------------------------+
| 2.05 CONTENT |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t6)], [] ], |
| [ [bstr.h(t5)], [] ], |
| [ [], [bstr.h(t5), bstr.h(t6)] ] |
| ], |
| "cursor" : 10, |
| "more" : false |
| } |
| |
Figure 15: Interaction for Full Query with Observe plus Diff
Query with "Cursor"
Appendix D. Document Updates
RFC EDITOR: Please remove this section.
D.1. Version -05 to -06
* Clarified instructions for Expert Review in the IANA
considerations.
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D.2. 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.
D.3. Version -03 to -04
* Improved presentation of pre- and post-registration operations.
* Removed moot processing cases with the "Cursor" extension.
* Positive integers as CBOR abbreviations for all parameters.
* Renamed N_MAX as MAX_N.
* Access tokens are not necessarily uploaded through /authz-info.
* The use of the "c.pmax" conditional attribute is just an example.
* Revised handling of token hashes at the RS.
* Extended and improved security considerations.
* Fixed details in IANA considerations.
* New appendix overviewing parameters of the TRL endpoint.
* Examples of message exchange moved to an appendix.
* Added examples of message exchange with the "Cursor" extension.
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* Clarifications and editorial improvements.
D.4. 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.
D.5. 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.
D.6. Version -00 to -01
* Added actions to perform upon receiving responses from the TRL
endpoint.
* Fixed off-by-one error when using the "Cursor" pattern.
* Improved error handling, with registered error codes.
* Section restructuring (full- and diff-query as self-standing
sections).
* Renamed identifiers and CBOR parameters.
* Clarifications and editorial improvements.
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Acknowledgments
Ludwig Seitz contributed as a co-author of initial versions of this
document.
The authors sincerely thank Christian Amsüss, Carsten Bormann, Rikard
Höglund, Benjamin Kaduk, David Navarro, Marco Rasori, Michael
Richardson, Jim Schaad, Göran Selander and Travis Spencer for their
comments and feedback.
The work on this document has been partly supported by VINNOVA and
the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home
(Grant agreement 952652).
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Kista
Sweden
Email: marco.tiloca@ri.se
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
SE-16440 Kista
Sweden
Email: francesca.palombini@ericsson.com
Sebastian Echeverria
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: secheverria@sei.cmu.edu
Grace Lewis
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: glewis@sei.cmu.edu
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