ACE Working Group F. Palombini
Internet-Draft Ericsson AB
Intended status: Standards Track L. Seitz
Expires: December 20, 2020 Combitech
G. Selander
Ericsson AB
M. Gunnarsson
RISE
June 18, 2020
OSCORE profile of the Authentication and Authorization for Constrained
Environments Framework
draft-ietf-ace-oscore-profile-11
Abstract
This memo specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework. It
utilizes Object Security for Constrained RESTful Environments
(OSCORE) to provide communication security, server authentication,
and proof-of-possession for a key owned by the client and bound to an
OAuth 2.0 access token.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on December 20, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4
3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 6
3.1. C-to-AS: POST to token endpoint . . . . . . . . . . . . . 6
3.2. AS-to-C: Access Token . . . . . . . . . . . . . . . . . . 8
3.2.1. OSCORE_Security_Context Object . . . . . . . . . . . 13
4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 17
4.1. C-to-RS: POST to authz-info endpoint . . . . . . . . . . 18
4.1.1. The Nonce 1 Parameter . . . . . . . . . . . . . . . . 19
4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 19
4.2.1. The Nonce 2 Parameter . . . . . . . . . . . . . . . . 21
4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 21
4.4. Access rights verification . . . . . . . . . . . . . . . 22
5. Secure Communication with AS . . . . . . . . . . . . . . . . 22
6. Discarding the Security Context . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 25
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9.1. ACE OAuth Profile Registry . . . . . . . . . . . . . . . 25
9.2. OAuth Parameters Registry . . . . . . . . . . . . . . . . 26
9.3. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 26
9.4. OSCORE Security Context Parameters Registry . . . . . . . 26
9.5. CWT Confirmation Methods Registry . . . . . . . . . . . . 27
9.6. JWT Confirmation Methods Registry . . . . . . . . . . . . 28
9.7. Expert Review Instructions . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 30
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
This memo specifies a profile of the ACE framework
[I-D.ietf-ace-oauth-authz]. In this profile, a client and a resource
server use CoAP [RFC7252] to communicate. The client uses an access
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token, bound to a key (the proof-of-possession key) to authorize its
access to the resource server. Note that this profile uses a
symmetric-crypto-based scheme, where the symmetric secret is used as
input material for keying material derivation. In order to provide
communication security, proof of possession, and server
authentication the client and resource server use Object Security for
Constrained RESTful Environments (OSCORE) [RFC8613]. Note that the
proof of possession is not done by a dedicated protocol element, but
rather occurs implicitly, based on knowledge of the security keying
material.
OSCORE specifies how to use CBOR Object Signing and Encryption (COSE)
[RFC8152] to secure CoAP messages. Note that OSCORE can be used to
secure CoAP messages, as well as HTTP and combinations of HTTP and
CoAP; a profile of ACE similar to the one described in this document,
with the difference of using HTTP instead of CoAP as communication
protocol, could be specified analogously to this one.
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.
Certain security-related terms such as "authentication",
"authorization", "confidentiality", "(data) integrity", "message
authentication code", and "verify" are taken from [RFC4949].
RESTful terminology follows HTTP [RFC7231].
Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749], such as client (C), resource server (RS), and
authorization server (AS). It is assumed in this document that a
given resource on a specific RS is associated to a unique AS.
Concise Data Definition Language (CDDL) [RFC8610] is used in this
specification.
Note that the term "endpoint" is used here, as in
[I-D.ietf-ace-oauth-authz], following its OAuth definition, which is
to denote resources such as token and introspect at the AS and authz-
info at the RS. The CoAP [RFC7252] definition, which is "An entity
participating in the CoAP protocol" is not used in this memo.
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2. Protocol Overview
This section gives an overview on how to use the ACE Framework
[I-D.ietf-ace-oauth-authz] to secure the communication between a
client and a resource server using OSCORE [RFC8613]. The parameters
needed by the client to negotiate the use of this profile with the
authorization server, as well as OSCORE setup process, are described
in detail in the following sections.
The RS maintains a collection of OSCORE Security Contexts with
associated authorization information for all the clients that it is
communicating with. The authorization information is maintained as
policy that's used as input to processing requests from those
clients.
This profile requires a client to retrieve an access token from the
AS for the resource it wants to access on a RS, using the token
endpoint, as specified in section 5.6 of [I-D.ietf-ace-oauth-authz].
To determine the AS in charge of a resource hosted at the RS, the
client C MAY send an initial Unauthorized Resource Request message to
the RS. The RS then denies the request and sends the address of its
AS back to the client C as specified in section 5.1 of
[I-D.ietf-ace-oauth-authz]. The access token request and response
MUST be confidentiality-protected and ensure authenticity. This
profile RECOMMENDS the use of OSCORE between client and AS, but other
protocols (such as TLS or DTLS) can be used as well.
Once the client has retrieved the access token, it generates a nonce
N1 and posts both the token and N1 to the RS using the authz-info
endpoint and mechanisms specified in section 5.8 of
[I-D.ietf-ace-oauth-authz] and Content-Format = application/ace+cbor.
Note that, as specified in the ACE framework, the authz-info endpoint
is not a protected resource, so there is no cryptographic protection
to this request.
If the access token is valid, the RS replies to this request with a
2.01 (Created) response with Content-Format = application/ace+cbor,
which contains a nonce N2 in a CBOR map. Moreover, the server
concatenates the input salt, N1, and N2 to obtain the Master Salt of
the OSCORE Security Context (see section 3 of [RFC8613]). The RS
then derives the complete Security Context associated with the
received token from it plus the parameters received in the access
token from the AS, following section 3.2 of [RFC8613].
After receiving the nonce N2, the client concatenates the input salt,
N1 and N2 to obtain the Master Salt of the OSCORE Security Context
(see section 3 of [RFC8613]). The client then derives the complete
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Security Context from the nonces plus the parameters received from
the AS.
Finally, the client sends a request protected with OSCORE to the RS.
If the request verifies, the server stores the complete Security
Context state that is ready for use in protecting messages, and uses
it in the response, and in further communications with the client,
until token expiration. This Security Context is discarded when a
token (whether the same or different) is used to successfully derive
a new Security Context for that client.
The use of random nonces during the exchange prevents the reuse of an
AEAD nonces/key pair for two different messages. This situation
might occur when client and RS derive a new Security Context from an
existing (non-expired) access token, as might occur when either party
has just rebooted. Instead, by using random nonces as part of the
Master Salt, the request to the authz-info endpoint posting the same
token results in a different Security Context, by OSCORE
construction, since even though the Master Secret, Sender ID and
Recipient ID are the same, the Master Salt is different (see
Section 3.2.1 of [RFC8613]). Therefore, the main requirement for the
nonces is that they have a good amount of randomness. If random
nonces were not used, a node re-using a non-expired old token would
be susceptible to on-path attackers provoking the creation of OSCORE
messages using old AEAD keys and nonces.
After the whole message exchange has taken place, the client can
contact the AS to request an update of its access rights, sending a
similar request to the token endpoint that also includes an
identifier so that the AS can find the correct OSCORE security
material it has previously shared with the Client. This specific
identifier, which [I-D.ietf-ace-oauth-authz] encodes as a bstr, is
formatted to include two OSCORE identifiers, namely ID context and
client ID, that are necessary to determine the correct OSCORE
Security Context.
An overview of the profile flow for the OSCORE profile is given in
Figure 1.
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C RS AS
| [-- Resource Request --->] | |
| | |
| [<---- AS Request ------] | |
| Creation Hints | |
| | |
| ----- POST /token ----------------------------> |
| | |
| <---------------------------- Access Token ----- |
| + Access Information |
| ---- POST /authz-info ---> | |
| (access_token, N1) | |
| | |
| <--- 2.01 Created (N2) --- | |
| | |
/Sec Context /Sec Context |
Derivation/ Derivation/ |
| | |
| ---- OSCORE Request -----> | |
| | |
| <--- OSCORE Response ----- | |
| | |
| ---- OSCORE Request -----> | |
| | |
| <--- OSCORE Response ----- | |
| ... | |
Figure 1: Protocol Overview
3. Client-AS Communication
The following subsections describe the details of the POST request
and response to the token endpoint between client and AS.
Section 3.2 of [RFC8613] defines how to derive a Security Context
based on a shared master secret and a set of other parameters,
established between client and server, which the client receives from
the AS in this exchange. The proof-of-possession key (pop-key)
included in the response from the AS MUST be used as master secret in
OSCORE.
3.1. C-to-AS: POST to token endpoint
The client-to-AS request is specified in Section 5.6.1 of
[I-D.ietf-ace-oauth-authz].
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The client must send this POST request to the token endpoint over a
secure channel that guarantees authentication, message integrity and
confidentiality (see Section 5).
An example of such a request, with payload in CBOR diagnostic
notation without the tag and value abbreviations is reported in
Figure 2
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"req_aud" : "tempSensor4711",
"scope" : "read"
}
Figure 2: Example C-to-AS POST /token request for an access token
bound to a symmetric key.
If the client wants to update its access rights without changing an
existing OSCORE Security Context, it MUST include in its POST request
to the token endpoint a req_cnf object. The req_cnf MUST include a
kid field carrying a bstr-wrapped CBOR array object containing the
client's identifier (assigned as discussed in Section 3.2) and the
context identifier (if assigned as discussed in Section 3.2). The
CBOR array is defined in Figure 3, and follows the notation of
[RFC8610]. These identifiers, together with other information such
as audience, can be used by the AS to determine the shared secret
bound to the proof-of-possession token and therefore MUST identify a
symmetric key that was previously generated by the AS as a shared
secret for the communication between the client and the RS. The AS
MUST verify that the received value identifies a proof-of-possession
key that has previously been issued to the requesting client. If
that is not the case, the Client-to-AS request MUST be declined with
the error code 'invalid_request' as defined in Section 5.6.3 of
[I-D.ietf-ace-oauth-authz].
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kid_arr = [
clientId,
?IdContext
]
kid = bstr .cbor kid_arr
Figure 3: CDDL Notation of kid for Update of Access Rights
An example of such a request, with payload in CBOR diagnostic
notation without the tag and value abbreviations is reported in
Figure 4
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"req_aud" : "tempSensor4711",
"scope" : "write",
"req_cnf" : {
"kid" : << ["myclient","contextid1"] >>
}
Figure 4: Example C-to-AS POST /token request for updating rights to
an access token bound to a symmetric key.
3.2. AS-to-C: Access Token
After verifying the POST request to the token endpoint and that the
client is authorized to obtain an access token corresponding to its
access token request, the AS responds as defined in section 5.6.2 of
[I-D.ietf-ace-oauth-authz]. If the client request was invalid, or
not authorized, the AS returns an error response as described in
section 5.6.3 of [I-D.ietf-ace-oauth-authz].
The AS can signal that the use of OSCORE is REQUIRED for a specific
access token by including the "profile" parameter with the value
"coap_oscore" in the access token response. This means that the
client MUST use OSCORE towards all resource servers for which this
access token is valid, and follow Section 4.3 to derive the security
context to run OSCORE. Usually it is assumed that constrained
devices will be pre-configured with the necessary profile, so that
this kind of profile negotiation can be omitted.
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Moreover, the AS MUST send the following data:
o a master secret
o a server identifier
o a client identifier
Additionally, the AS MAY send the following data, in the same
response.
o a context identifier
o an AEAD algorithm
o an HKDF algorithm
o a salt
o the OSCORE version number
The OSCORE_Security_Context is a CBOR map object, defined in
Section 3.2.1. This object is transported in the 'cnf' parameter of
the access token response as defined in Section 3.2 of
[I-D.ietf-ace-oauth-params], as the value of a field named 'osc',
registered in Section 9.5 and Section 9.6. The master secret MUST be
communicated as the 'ms' field in the 'osc' field in the 'cnf'
parameter of the access token response as defined in Section 3.2 of
[I-D.ietf-ace-oauth-params]. The AEAD algorithm may be included as
the 'alg' parameter in the OSCORE_Security_Context; the HKDF
algorithm may be included as the 'hkdf' parameter of the
OSCORE_Security_Context, a salt may be included as the 'salt'
parameter of the OSCORE_Security_Context, and the OSCORE version
number may be included as the 'version' parameter of the
OSCORE_Security_Context.
The same parameters MUST be included as part of the access token.
This profile RECOMMENDS the use of CBOR web token (CWT) as specified
in [RFC8392]. If the token is a CWT, the same
OSCORE_Security_Context structure defined above MUST be placed in the
'osc' field of the 'cnf' claim of this token. The access token MUST
be encrypted, since it will be transferred from the client to the RS
over an unprotected channel.
The AS MUST also assign an identifier to the RS (serverId), and to
the client (clientId), and MAY assign an identifier to the context
(contextId). These identifiers are then used as Sender ID, Recipient
ID and ID Context in the OSCORE context as described in section 3.1
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of [RFC8613]. Applications need to consider that these identifiers
are sent in the clear and may reveal information about the endpoints,
as mentioned in section 12.8 of [RFC8613]. The pair (client
identifier, context identifier) MUST be unique in the set of all
clients for a single RS. Moreover, clientId, serverId and (when
assigned) contextId MUST be included in the OSCORE_Security_Context,
as defined in Section 3.2.1.
We assume in this document that a resource is associated to one
single AS, which makes it possible for the AS to enforce uniqueness
of identifiers for each client requesting a particular resource to a
RS. If this is not the case, collisions of identifiers may occur at
the RS, in which case the RS needs to have a mechanism in place to
disambiguate identifiers or mitigate the effect of the collisions.
Moreover, implementers of this specification need to be aware that if
other authentication mechanisms are used to set up OSCORE between the
same client and RS, that do not rely on AS assigning identifiers,
collisions may happen and need to be mitigated. A mitigation example
would be to use distinct namespaces of identifiers for different
authentication mechanisms.
Note that in Section 4.3 C sets the Sender ID of its Security Context
to the clientId value received and the Recipient ID to the serverId
value, and RS does the opposite.
Figure 5 shows an example of an AS response, with payload in CBOR
diagnostic notation without the tag and value abbreviations. The
access token has been truncated for readability.
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Header: Created (Code=2.01)
Content-Type: "application/ace+cbor"
Payload:
{
"access_token" : h'a5037674656d7053656e73 ...
(remainder of access token (CWT) omitted for brevity)',
"profile" : "coap_oscore",
"expires_in" : "3600",
"cnf" : {
"osc" : {
"alg" : "AES-CCM-16-64-128",
"clientId" : h'00',
"serverId" : h'01',
"ms" : h'f9af838368e353e78888e1426bd94e6f'
}
}
}
Figure 5: Example AS-to-C Access Token response with OSCORE profile.
Figure 6 shows an example CWT, containing the necessary OSCORE
parameters in the 'cnf' claim, in CBOR diagnostic notation without
tag and value abbreviations.
{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"exp" : "1360289224",
"scope" : "temperature_g firmware_p",
"cnf" : {
"osc" : {
"alg" : "AES-CCM-16-64-128",
"clientId" : h'00',
"serverId" : h'01',
"ms" : h'f9af838368e353e78888e1426bd94e6f'
}
}
Figure 6: Example CWT with OSCORE parameters.
The same CWT token as in Figure 6, using the value abbreviations
defined in [I-D.ietf-ace-oauth-authz] and [RFC8747] and encoded in
CBOR is shown in Figure 7.
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NOTE TO THE RFC EDITOR: before publishing, it should be checked (and
in case fixed) that the values used below (which are not yet
registered) are the final values registered in IANA.
A5 # map(5)
03 # unsigned(3)
76 # text(22)
74656D7053656E736F72496E4C6976696E67526F6F6D
# "tempSensorInLivingRoom"
06 # unsigned(6)
1A 5112D728 # unsigned(1360189224)
04 # unsigned(4)
1A 51145DC8 # unsigned(1360289224)
09 # unsigned(9)
78 18 # text(24)
74656D70657261747572655F67206669726D776172655F70
# "temperature_g firmware_p"
08 # unsigned(8)
A1 # map(1)
04 # unsigned(4)
A4 # map(4)
05 # unsigned(5)
0A # unsigned(10)
02 # unsigned(2)
46 # bytes(6)
636C69656E74 # "client"
03 # unsigned(3)
46 # bytes(6)
736572766572 # "server"
01 # unsigned(1)
50 # bytes(16)
F9AF838368E353E78888E1426BD94E6F
# "\xF9\xAF\x83\x83h\xE3S\xE7
\x88\x88\xE1Bk\xD9No"
Figure 7: Example CWT with OSCORE parameters.
If the client has requested an update to its access rights using the
same OSCORE Security Context, which is valid and authorized, the AS
MUST omit the 'cnf' parameter in the response, and MUST carry the
client identifier and the context identifier (if it was set and
included in the initial access token response by the AS) in the 'kid'
field in the 'cnf' parameter of the token, with the same structure
defined in Figure 3. These identifiers need to be included in the
token in order for the RS to identify the previously generated
Security Context.
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Figure 8 shows an example of such an AS response, with payload in
CBOR diagnostic notation without the tag and value abbreviations.
The access token has been truncated for readability.
Header: Created (Code=2.01)
Content-Type: "application/ace+cbor"
Payload:
{
"access_token" : h'a5037674656d7053656e73 ...
(remainder of access token (CWT) omitted for brevity)',
"profile" : "coap_oscore",
"expires_in" : "3600"
}
Figure 8: Example AS-to-C Access Token response with OSCORE profile,
for update of access rights.
Figure 9 shows an example CWT, containing the necessary OSCORE
parameters in the 'cnf' claim for update of access rights, in CBOR
diagnostic notation without tag and value abbreviations.
{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"exp" : "1360289224",
"scope" : "temperature_h",
"cnf" : {
"kid" : h'43814100'
}
}
Figure 9: Example CWT with OSCORE parameters for update of access
rights.
3.2.1. OSCORE_Security_Context Object
An OSCORE_Security_Context is an object that represents part or all
of an OSCORE Security Context, i.e., the local set of information
elements necessary to carry out the cryptographic operations in
OSCORE (Section 3.1 of [RFC8613]). In particular, the
OSCORE_Security_Context object is defined to be serialized and
transported between nodes, as specified by this document, but can
also be used by other specifications if needed. The
OSCORE_Security_Context object can either be encoded as a JSON object
or as a CBOR map. The set of common parameters that can appear in an
OSCORE_Security_Context object can be found in the IANA "OSCORE
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Security Context Parameters" registry (Section 9.4), defined for
extensibility, and is specified below. All parameters are optional.
Table 1 provides a summary of the OSCORE_Security_Context parameters
defined in this section.
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+-----------+-------+----------------+--------------+---------------+
| name | CBOR | CBOR type | registry | description |
| | label | | | |
+-----------+-------+----------------+--------------+---------------+
| version | 0 | int | | OSCORE |
| | | | | Version |
| | | | | |
| ms | 1 | bstr | | OSCORE Master |
| | | | | Secret value |
| | | | | |
| clientId | 2 | bstr | | OSCORE Sender |
| | | | | ID value of |
| | | | | the client, |
| | | | | OSCORE |
| | | | | Recipient ID |
| | | | | value of the |
| | | | | server |
| | | | | |
| serverId | 3 | bstr | | OSCORE Sender |
| | | | | ID value of |
| | | | | the server, |
| | | | | OSCORE |
| | | | | Recipient ID |
| | | | | value of the |
| | | | | client |
| | | | | |
| hkdf | 4 | tstr / int | COSE | OSCORE HKDF |
| | | | Algorithm | value |
| | | | Values | |
| | | | (HMAC-based) | |
| | | | | |
| alg | 5 | tstr / int | COSE | OSCORE AEAD |
| | | | Algorithm | Algorithm |
| | | | Values | value |
| | | | (AEAD) | |
| | | | | |
| salt | 6 | bstr | | OSCORE Master |
| | | | | Salt value |
| | | | | |
| contextId | 7 | bstr | | OSCORE ID |
| | | | | Context value |
+-----------+-------+----------------+--------------+---------------+
Table 1: OSCORE_Security_Context Parameters
version: This parameter identifies the OSCORE Version number, which
is an int. For more information about this field, see section 5.4
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of [RFC8613]. In JSON, the "version" value is an integer. In
CBOR, the "version" type is int, and has label 0.
ms: This parameter identifies the OSCORE Master Secret value, which
is a byte string. For more information about this field, see
section 3.1 of [RFC8613]. In JSON, the "ms" value is a Base64
encoded byte string. In CBOR, the "ms" type is bstr, and has
label 1.
clientId: This parameter identifies a client identifier as a byte
string. This identifier is used as OSCORE Sender ID in the client
and OSCORE Recipient ID in the server. For more information about
this field, see section 3.1 of [RFC8613]. In JSON, the "clientId"
value is a Base64 encoded byte string. In CBOR, the "clientId"
type is bstr, and has label 2.
serverId: This parameter identifies a server identifier as a byte
string. This identifier is used as OSCORE Sender ID in the server
and OSCORE Recipient ID in the client. For more information about
this field, see section 3.1 of [RFC8613]. In JSON, the "serverId"
value is a Base64 encoded byte string. In CBOR, the "serverId"
type is bstr, and has label 3.
hkdf: This parameter identifies the OSCORE HKDF Algorithm. For more
information about this field, see section 3.1 of [RFC8613]. The
values used MUST be registered in the IANA "COSE Algorithms"
registry and MUST be HMAC-based HKDF algorithms. The value can
either be the integer or the text string value of the HMAC-based
HKDF algorithm in the "COSE Algorithms" registry. In JSON, the
"hkdf" value is a case-sensitive ASCII string or an integer. In
CBOR, the "hkdf" type is tstr or int, and has label 4.
alg: This parameter identifies the OSCORE AEAD Algorithm. For more
information about this field, see section 3.1 of [RFC8613] The
values used MUST be registered in the IANA "COSE Algorithms"
registry and MUST be AEAD algorithms. The value can either be the
integer or the text string value of the HMAC-based HKDF algorithm
in the "COSE Algorithms" registry. In JSON, the "alg" value is a
case-sensitive ASCII string or an integer. In CBOR, the "alg"
type is tstr or int, and has label 5.
salt: This parameter identifies the OSCORE Master Salt value, which
is a byte string. For more information about this field, see
section 3.1 of [RFC8613]. In JSON, the "salt" value is a Base64
encoded byte string. In CBOR, the "salt" type is bstr, and has
label 6.
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contextId: This parameter identifies the security context as a byte
string. This identifier is used as OSCORE ID Context. For more
information about this field, see section 3.1 of [RFC8613]. In
JSON, the "contextID" value is a Base64 encoded byte string. In
CBOR, the "contextID" type is bstr, and has label 7.
An example of JSON OSCORE_Security_Context is given in Figure 10.
"osc" : {
"alg" : "AES-CCM-16-64-128",
"clientId" : b64'AA',
"serverId" : b64'AQ',
"ms" : b64'+a+Dg2jjU+eIiOFCa9lObw'
}
Figure 10: Example JSON OSCORE_Security_Context object
The CDDL grammar describing the CBOR OSCORE_Security_Context object
is:
OSCORE_Security_Context = {
? 0 => int, ; version
? 1 => bstr, ; ms
? 2 => bstr, ; clientId
? 3 => bstr, ; serverId
? 4 => tstr / int, ; hkdf
? 5 => tstr / int, ; alg
? 6 => bstr, ; salt
? 7 => bstr, ; contextId
* int / tstr => any
}
4. Client-RS Communication
The following subsections describe the details of the POST request
and response to the authz-info endpoint between client and RS. The
client generates a nonce N1, and posts it together with the token
that includes the materials (e.g., OSCORE parameters) received from
the AS to the RS. The RS then generates a nonce N2, and uses
Section 3.2 of [RFC8613] to derive a security context based on a
shared master secret and the two nonces, established between client
and server. The nonces are encoded as CBOR bstr if CBOR is used, and
as Base64 string if JSON is used. This security context is used to
protect all future communication between client and RS using OSCORE,
as long as the access token is valid.
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Note that the RS and client authenticates themselves by generating
the shared OSCORE Security Context using the pop-key as master
secret. An attacker posting a valid token to the RS will not be able
to generate a valid OSCORE context and thus not be able to prove
possession of the pop-key.
4.1. C-to-RS: POST to authz-info endpoint
The client MUST generate a nonce value very unlikely to have been
previously used with the same input keying material. This profile
RECOMMENDS to use a 64-bit long random number as nonce's value. The
client MUST store the nonce N1 as long as the response from the RS is
not received and the access token related to it is still valid. The
client MUST use CoAP and the Authorization Information resource as
described in section 5.8.1 of [I-D.ietf-ace-oauth-authz] to transport
the token and N1 to the RS.
Note that the use of the payload and the Content-Format is different
from what described in section 5.8.1 of [I-D.ietf-ace-oauth-authz],
which only transports the token without any CBOR wrapping. In this
profile, the client MUST wrap the token and N1 in a CBOR map. The
client MUST use the Content-Format "application/ace+cbor" defined in
section 8.14 of [I-D.ietf-ace-oauth-authz]. The client MUST include
the access token using the "access_token" parameter and N1 using the
'nonce1' parameter defined in Section 4.1.1.
The authz-info endpoint is not protected, nor are the responses from
this resource.
The access token MUST be encrypted, since it is transferred from the
client to the RS over an unprotected channel.
Note that a client may be required to re-POST the access token in
order to complete a request, since an RS may delete a stored access
token (and associated Security Context) at any time, for example due
to all storage space being consumed. This situation is detected by
the client when it receives an AS Request Creation Hints response.
Reposting the same access token will result in deriving a new OSCORE
Security Context to be used with the RS, as different nonces will be
used.
Figure 11 shows an example of the request sent from the client to the
RS, with payload in CBOR diagnostic notation without the tag and
value abbreviations. The access token has been truncated for
readability.
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Header: POST (Code=0.02)
Uri-Host: "rs.example.com"
Uri-Path: "authz-info"
Content-Format: "application/ace+cbor"
Payload:
{
"access_token": h'a5037674656d7053656e73 ...
(remainder of access token (CWT) omitted for brevity)',
"nonce1": h'018a278f7faab55a'
}
Figure 11: Example C-to-RS POST /authz-info request using CWT
If the client has already posted a valid token, has already
established a security association with the RS, and wants to update
its access rights, the client can do so by posting the new token
(retrieved from the AS and containing the update of access rights) to
the /authz-info endpoint. The client MUST protect the request using
the OSCORE Security Context established during the first token
exchange. The client MUST only send the access token in the payload,
no nonce is sent. After proper verification (see Section 4.2), the
RS will replace the old token with the new one, maintaining the same
Security Context.
4.1.1. The Nonce 1 Parameter
This parameter MUST be sent from the client to the RS, together with
the access token, if the ace profile used is coap_oscore. The
parameter is encoded as a byte string for CBOR-based interactions,
and as a string (Base64 encoded binary) for JSON-based interactions.
This parameter is registered in Section 9.2.
4.2. RS-to-C: 2.01 (Created)
The RS MUST follow the procedures defined in section 5.8.1 of
[I-D.ietf-ace-oauth-authz]: the RS must verify the validity of the
token. If the token is valid, the RS must respond to the POST
request with 2.01 (Created). If the token is valid but is associated
to claims that the RS cannot process (e.g., an unknown scope), or if
any of the expected parameters in the 'osc' is missing (e.g., any of
the mandatory parameters from the AS), or if any parameters received
in the 'osc' is unrecognized, the RS must respond with an error
response code equivalent to the CoAP code 4.00 (Bad Request). In the
latter two cases, the RS may provide additional information in the
error response, in order to clarify what went wrong. The RS may make
an introspection request to validate the token before responding to
the POST request to the authz-info endpoint.
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Additionally, the RS MUST generate a nonce N2 very unlikely to have
been previously used with the same input keying material, and send it
within the 2.01 (Created) response. The payload of the 2.01
(Created) response MUST be a CBOR map containing the 'nonce2'
parameter defined in Section 4.2.1, set to N2. This profile
RECOMMENDS to use a 64-bit long random number as nonce's value. The
RS MUST use the Content-Format "application/ace+cbor" defined in
section 8.14 of [I-D.ietf-ace-oauth-authz].
Figure 12 shows an example of the response sent from the RS to the
client, with payload in CBOR diagnostic notation without the tag and
value abbreviations.
Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"nonce2": h'25a8991cd700ac01'
}
Figure 12: Example RS-to-C 2.01 (Created) response
As specified in section 5.8.3 of [I-D.ietf-ace-oauth-authz], the RS
must notify the client with an error response with code 4.01
(Unauthorized) for any long running request before terminating the
session, when the access token expires.
If the RS receives the token in a OSCORE protected message, it means
that the client is requesting an update of access rights. The RS
MUST discard any nonce in the request, if any was sent. The RS MUST
check that the "kid" of the "cnf" parameter of the new access token
matches the OSCORE Security Context used to protect the message. If
that's the case, the RS MUST discard the old token and associate the
new token to the Security Context identified by "kid". The RS MUST
respond with a 2.01 (Created) response protected with the same
Security Context, with no payload. If any verification fails, the RS
MUST respond with a 4.01 (Unauthorized) error response.
As specified in section 5.8.1 of [I-D.ietf-ace-oauth-authz], when
receiving an updated access token with updated authorization
information from the client (see Section 3.1), it is recommended that
the RS overwrites the previous token, that is only the latest
authorization information in the token received by the RS is valid.
This simplifies for the RS to keep track of authorization information
for a given client.
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4.2.1. The Nonce 2 Parameter
This parameter MUST be sent from the RS to the Client if the ace
profile used is coap_oscore. The parameter is encoded as a byte
string for CBOR-based interactions, and as a string (Base64 encoded
binary) for JSON-based interactions. This parameter is registered in
Section 9.2
4.3. OSCORE Setup
Once receiving the 2.01 (Created) response from the RS, following the
POST request to authz-info endpoint, the client MUST extract the CBOR
bstr nonce N2 from the 'nonce2' parameter in the CBOR map in the
payload of the response. Then, the client MUST set the Master Salt
of the Security Context created to communicate with the RS to the
concatenation of salt, N1, and N2, in this order: Master Salt =
salt | N1 | N2, where | denotes byte string concatenation, where salt
was received from the AS in Section 3.2, and where N1 and N2 are the
two nonces encoded as CBOR bstr. The client MUST set the Master
Secret, Sender ID and Recipient ID from the parameters received from
the AS in Section 3.2. The client MUST set the AEAD Algorithm, ID
Context, HKDF, and OSCORE Version from the parameters received from
the AS in Section 3.2, if present. In case these parameters are
omitted, the default values are used as described in sections 3.2 and
5.4 of [RFC8613]. After that, the client MUST derive the complete
Security Context following section 3.2.1 of [RFC8613]. From this
point on, the client MUST use this Security Context to communicate
with the RS when accessing the resources as specified by the
authorization information.
If any of the expected parameters is missing (e.g., any of the
mandatory parameters from the AS, the client MUST stop the exchange,
and MUST NOT derive the Security Context. The client MAY restart the
exchange, to get the correct security material.
The client then uses this Security Context to send requests to RS
using OSCORE.
After sending the 2.01 (Created) response, the RS MUST set the Master
Salt of the Security Context created to communicate with the client
to the concatenation of salt, N1, and N2, in this order: Master Salt
= salt | N1 | N2, where | denotes byte string concatenation, where
salt was received from the AS in Section 4.2, and where N1 and N2 are
the two nonces encoded as CBOR bstr. The RS MUST set the Master
Secret, Sender ID and Recipient ID from the parameters, received from
the AS and forwarded by the client in the access token in Section 4.1
after validation of the token as specified in Section 4.2. The RS
MUST set the AEAD Algorithm, ID Context, HKDF, and OSCORE Version
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from the parameters received from the AS and forwarded by the client
in the access token in Section 4.1 after validation of the token as
specified in Section 4.2, if present. In case these parameters are
omitted, the default values are used as described in sections 3.2 and
5.4 of [RFC8613]. After that, the RS MUST derive the complete
Security Context following section 3.2.1 of [RFC8613], and MUST
associate this Security Context with the authorization information
from the access token.
The RS then uses this Security Context to verify requests and send
responses to C using OSCORE. If OSCORE verification fails, error
responses are used, as specified in section 8 of [RFC8613].
Additionally, if OSCORE verification succeeds, the verification of
access rights is performed as described in section Section 4.4. The
RS MUST NOT use the Security Context after the related token has
expired, and MUST respond with a unprotected 4.01 (Unauthorized)
error message to requests received that correspond to a Security
Context with an expired token.
4.4. Access rights verification
The RS MUST follow the procedures defined in section 5.8.2 of
[I-D.ietf-ace-oauth-authz]: if an RS receives an OSCORE-protected
request from a client, then the RS processes it according to
[RFC8613]. If OSCORE verification succeeds, and the target resource
requires authorization, the RS retrieves the authorization
information using the access token associated to the Security
Context. The RS then must verify that the authorization information
covers the resource and the action requested.
The response code must be 4.01 (Unauthorized) in case the client has
a valid token associated with that Security Context, but the Security
Context has not been used before, as the proof-of-possession in this
profile is performed by both parties verifying that they have
established the same Security Context.
5. Secure Communication with AS
As specified in the ACE framework (section 5.7 of
[I-D.ietf-ace-oauth-authz]), the requesting entity (RS and/or client)
and the AS communicates via the introspection or token endpoint. The
use of CoAP and OSCORE ([RFC8613]) for this communication is
RECOMMENDED in this profile, other protocols (such as HTTP and DTLS
or TLS) MAY be used instead.
If OSCORE is used, the requesting entity and the AS are expected to
have pre-established security contexts in place. How these security
contexts are established is out of scope for this profile.
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Furthermore the requesting entity and the AS communicate through the
introspection endpoint as specified in section 5.7 of
[I-D.ietf-ace-oauth-authz] and through the token endpoint as
specified in section 5.6 of [I-D.ietf-ace-oauth-authz].
6. Discarding the Security Context
There are a number of scenarios where a client or RS needs to discard
the OSCORE security context, and acquire a new one.
The client MUST discard the current Security Context associated with
an RS when:
o the Sequence Number space ends.
o the access token associated with the context expires.
o the client receives a number of 4.01 Unauthorized responses to
OSCORE requests using the same Security Context. The exact number
needs to be specified by the application.
o the client receives a new nonce in the 2.01 (Created) response
(see Section 4.2) to a POST request to the authz-info endpoint,
when re-posting a (non-expired) token associated to the existing
context.
The RS MUST discard the current Security Context associated with a
client when:
o the Sequence Number space ends.
o the access token associated with the context expires.
o the client has successfully replaced the current security context
with a newer one by posting an access token to the unprotected
/authz-info endpoint at the RS, e.g., by re-posting the same
token, as specified in Section 4.1.
Whenever one more access token is successfully posted to the RS, and
a new Security Context is derived between the client and RS, messages
in transit that were protected with the previous Security Context
might not pass verification, as the old context is discarded. That
means that messages sent shortly before the client posts one more
access token to the RS might not successfully reach the destination.
Analogously, implementations may want to cancel CoAP observations at
the RS registered before the Security Context is replaced, or
conversely they will need to implement a mechanism to ensure that
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those observation are to be protected with the newly derived Security
Context.
7. Security Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework
[I-D.ietf-ace-oauth-authz]. Thus the general security considerations
from the framework also apply to this profile.
Furthermore the general security considerations of OSCORE [RFC8613]
also apply to this specific use of the OSCORE protocol.
OSCORE is designed to secure point-to-point communication, providing
a secure binding between the request and the response(s). Thus the
basic OSCORE protocol is not intended for use in point-to-multipoint
communication (e.g., multicast, publish-subscribe). Implementers of
this profile should make sure that their usecase corresponds to the
expected use of OSCORE, to prevent weakening the security assurances
provided by OSCORE.
Since the use of nonces in the exchange guarantees uniqueness of AEAD
keys and nonces, it is REQUIRED that nonces are not reused with the
same input keying material even in case of re-boots. This document
RECOMMENDS the use of 64 bit random nonces. Considering the birthday
paradox, the average collision for each nonce will happen after 2^32
messages, which is considerably more token provisionings than
expected for intended applications. If applications use something
else, such as a counter, they need to guarantee that reboot and loss
of state on either node does not provoke re-use. If that is not
guaranteed, nodes are susceptible to re-use of AEAD (nonces, keys)
pairs, especially since an on-path attacker can cause the client to
use an arbitrary nonce for Security Context establishment by
replaying client-to-server messages.
This profile recommends that the RS maintains a single access token
for a client. The use of multiple access tokens for a single client
increases the strain on the resource server as it must consider every
access token and calculate the actual permissions of the client.
Also, tokens indicating different or disjoint permissions from each
other may lead the server to enforce wrong permissions. If one of
the access tokens expires earlier than others, the resulting
permissions may offer insufficient protection. Developers should
avoid using multiple access tokens for a client.
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8. Privacy Considerations
This document specifies a profile for the Authentication and
Authorization for Constrained Environments (ACE) framework
[I-D.ietf-ace-oauth-authz]. Thus the general privacy considerations
from the framework also apply to this profile.
As this document uses OSCORE, thus the privacy considerations from
[RFC8613] apply here as well.
An unprotected response to an unauthorized request may disclose
information about the resource server and/or its existing
relationship with the client. It is advisable to include as little
information as possible in an unencrypted response. When an OSCORE
Security Context already exists between the client and the resource
server, more detailed information may be included.
Although encrypted, the token is sent in the clear to the authz-info
endpoint, so if a client uses the same single token from multiple
locations with multiple Resource Servers, it can risk being tracked
by the token's value.
The nonces exchanged in the request and response to the authz-info
endpoint are also sent in the clear, so using random nonces is best
for privacy (as opposed to, e.g., a counter, that might leak some
information about the client).
The AS is the party tasked of assigning the identifiers used in
OSCORE, which are privacy sensitive (see Section 12.8 of [RFC8613]),
and which could reveal information about the client, or may be used
for correlating requests from one client.
Note that some information might still leak after OSCORE is
established, due to observable message sizes, the source, and the
destination addresses.
9. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[[this
specification]]" with the RFC number of this specification and delete
this paragraph.
9.1. ACE OAuth Profile Registry
The following registration is done for the ACE OAuth Profile Registry
following the procedure specified in section 8.7 of
[I-D.ietf-ace-oauth-authz]:
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o Profile name: coap_oscore
o Profile Description: Profile for using OSCORE to secure
communication between constrained nodes using the Authentication
and Authorization for Constrained Environments framework.
o Profile ID: TBD (value between 1 and 255)
o Change Controller: IESG
o Specification Document(s): [[this specification]]
9.2. OAuth Parameters Registry
The following registrations are done for the OAuth Parameters
Registry following the procedure specified in section 11.2 of
[RFC6749]:
o Parameter name: nonce1
o Parameter usage location: token request
o Change Controller: IESG
o Specification Document(s): [[this specification]]
o Parameter name: nonce2
o Parameter usage location: token response
o Change Controller: IESG
o Specification Document(s): [[this specification]]
9.3. OAuth Parameters CBOR Mappings Registry
The following registrations are done for the OAuth Parameters CBOR
Mappings Registry following the procedure specified in section 8.9 of
[I-D.ietf-ace-oauth-authz]:
o Name: nonce1
o CBOR Key: TBD1
o Value Type: bstr
o Reference: [[this specification]]
o Name: nonce2
o CBOR Key: TBD2
o Value Type: IESG
o Reference: [[this specification]]
9.4. OSCORE Security Context Parameters Registry
It is requested that IANA create a new registry entitled "OSCORE
Security Context Parameters" registry. The registry is to be created
as Expert Review Required. Guidelines for the experts is provided
Section 9.7. It should be noted that in addition to the expert
review, some portions of the registry require a specification,
potentially on standards track, be supplied as well.
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The columns of the registry are:
name The JSON name requested (e.g., "ms"). Because a core goal of
this specification is for the resulting representations to be
compact, it is RECOMMENDED that the name be short. This name is
case sensitive. Names may not match other registered names in a
case-insensitive manner unless the Designated Experts determine
that there is a compelling reason to allow an exception. The name
is not used in the CBOR encoding.
CBOR label The value to be used to identify this algorithm. Map key
labels MUST be unique. The label can be a positive integer, a
negative integer or a string. Integer values between -256 and 255
and strings of length 1 are designated as Standards Track Document
required. Integer values from -65536 to -257 and from 256 to
65535 and strings of length 2 are designated as Specification
Required. Integer values greater than 65535 and strings of length
greater than 2 are designated as expert review. Integer values
less than -65536 are marked as private use.
CBOR Type This field contains the CBOR type for the field.
registry This field denotes the registry that values may come from,
if one exists.
description This field contains a brief description for the field.
specification This contains a pointer to the public specification
for the field if one exists
This registry will be initially populated by the values in Table 1.
The specification column for all of these entries will be this
document and [RFC8613].
9.5. CWT Confirmation Methods Registry
The following registration is done for the CWT Confirmation Methods
Registry following the procedure specified in section 7.2.1 of
[RFC8747]:
o Confirmation Method Name: "osc"
o Confirmation Method Description: OSCORE_Security_Context carrying
the parameters for using OSCORE per-message security with implicit
key confirmation
o Confirmation Key: TBD (value between 4 and 255)
o Confirmation Value Type(s): map
o Change Controller: IESG
o Specification Document(s): Section 3.2.1 of [[this specification]]
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9.6. JWT Confirmation Methods Registry
The following registration is done for the JWT Confirmation Methods
Registry following the procedure specified in section 6.2.1 of
[RFC7800]:
o Confirmation Method Value: "osc"
o Confirmation Method Description: OSCORE_Security_Context carrying
the parameters for using OSCORE per-message security with implicit
key confirmation
o Change Controller: IESG
o Specification Document(s): Section 3.2.1 of [[this specification]]
9.7. Expert Review Instructions
The IANA registry established in this document is defined to use the
Expert Review registration policy. 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:
o 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.
o Specifications are required for the standards track range of point
assignment. Specifications should exist for specification
required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are
needed for the first-come, first-serve range 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.
o 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.
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10. References
10.1. Normative References
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-33
(work in progress), February 2020.
[I-D.ietf-ace-oauth-params]
Seitz, L., "Additional OAuth Parameters for Authorization
in Constrained Environments (ACE)", draft-ietf-ace-oauth-
params-13 (work in progress), April 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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/info/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/info/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
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10.2. Informative References
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016,
<https://www.rfc-editor.org/info/rfc7800>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>.
Appendix A. Profile Requirements
This section lists the specifications on this profile based on the
requirements on the framework, as requested in Appendix C of
[I-D.ietf-ace-oauth-authz].
o Optionally define new methods for the client to discover the
necessary permissions and AS for accessing a resource, different
from the one proposed in: Not specified
o Optionally specify new grant types: Not specified
o Optionally define the use of client certificates as client
credential type: Not specified
o Specify the communication protocol the client and RS the must use:
CoAP
o Specify the security protocol the client and RS must use to
protect their communication: OSCORE
o Specify how the client and the RS mutually authenticate:
Implicitly by possession of a common OSCORE security context
o Specify the proof-of-possession protocol(s) and how to select one,
if several are available. Also specify which key types (e.g.,
symmetric/asymmetric) are supported by a specific proof-of-
possession protocol: OSCORE algorithms; pre-established symmetric
keys
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o Specify a unique ace_profile identifier: coap_oscore
o If introspection is supported: Specify the communication and
security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE)
o Specify the communication and security protocol for interactions
between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE)
o Specify how/if the authz-info endpoint is protected, including how
error responses are protected: Not protected.
o Optionally define other methods of token transport than the authz-
info endpoint: Not defined
Acknowledgments
The authors wish to thank Jim Schaad and Marco Tiloca for the input
on this memo. Special thanks to the responsible area director
Benjamin Kaduk for his extensive review and contributed text. Ludwig
Seitz worked on this document as part of the CelticNext projects
CyberWI, and CRITISEC with funding from Vinnova.
Authors' Addresses
Francesca Palombini
Ericsson AB
Email: francesca.palombini@ericsson.com
Ludwig Seitz
Combitech
Djaeknegatan 31
Malmoe 211 35
Sweden
Email: ludwig.seitz@combitech.se
Goeran Selander
Ericsson AB
Email: goran.selander@ericsson.com
Martin Gunnarsson
RISE
Scheelevagen 17
Lund 22370
Sweden
Email: martin.gunnarsson@ri.se
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