ACE Working Group F. Palombini
Internet-Draft Ericsson AB
Intended status: Standards Track L. Seitz
Expires: April 11, 2019 RISE SICS AB
G. Selander
Ericsson AB
M. Gunnarsson
RISE SICS AB
October 8, 2018
OSCORE profile of the Authentication and Authorization for Constrained
Environments Framework
draft-ietf-ace-oscore-profile-04
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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 11, 2019.
Copyright Notice
Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . . . 3
3. Client-AS Communication . . . . . . . . . . . . . . . . . . . 5
3.1. C-to-AS: POST /token . . . . . . . . . . . . . . . . . . 5
3.2. AS-to-C: Access Token . . . . . . . . . . . . . . . . . . 7
4. Client-RS Communication . . . . . . . . . . . . . . . . . . . 11
4.1. C-to-RS: POST /authz-info . . . . . . . . . . . . . . . . 12
4.2. RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . . 12
4.3. OSCORE Setup . . . . . . . . . . . . . . . . . . . . . . 13
4.4. Access rights verification . . . . . . . . . . . . . . . 15
5. Secure Communication with AS . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 19
Appendix B. Using the pop-key with EDHOC (EDHOC+OSCORE) . . . . 20
B.1. Using Asymmetric Keys . . . . . . . . . . . . . . . . . . 20
B.2. Using Symmetric Keys . . . . . . . . . . . . . . . . . . 22
B.3. Processing . . . . . . . . . . . . . . . . . . . . . . . 24
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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
token, bound to a key (the proof-of-possession key) to authorize its
access to the resource server. In order to provide communication
security, proof of possession, and server authentication they use
Object Security for Constrained RESTful Environments (OSCORE)
[I-D.ietf-core-object-security].
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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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. These
words may also appear in this document in lowercase, absent their
normative meanings.
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.
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
[I-D.ietf-core-object-security]. 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.
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
resource, 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 TLS
or DTLS MAY be used additionally or instead.
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Once the client has retrieved the access token, it posts it to the RS
using the authz-info resource and mechanisms specified in section 5.8
of [I-D.ietf-ace-oauth-authz]. If the access token is valid, the RS
replies to this request with a 2.01 (Created) response, which
contains a nonce N1.
After receiving the nonce N1, the client generates a nonce N2,
concatenates it with N1 and sets the ID Context in its Security
Context (see section 3 of [I-D.ietf-core-object-security]) to N1
concatenated with N2. The client then derives the complete Security
Context from the ID Context plus the parameters received from the AS.
Finally, the client sends a request protected with OSCORE to the RS.
This message contains the ID Context value. When receiving this
request after the 2.01 (Created) response, the server extract the ID
Context from it, verifies that the first part is equal to the nonce
N1 it previously sent, and if so, sets its own ID Context and derives
the complete Security Context from it plus the parameters received in
the AS, following section 3.2 of [I-D.ietf-core-object-security]. If
the request verifies, then this Security Context is stored in the
server, and used in the response, and in further communications with
the client, until token expiration. Once the client receives a valid
response, it does not continue to include the ID Context value in
further requests.
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 Information --] | |
| | |
| ----- POST /token ----------------------------> |
| | |
| <---------------------------- Access Token ----- |
| + RS Information |
| ---- POST /authz-info ---> | |
| | |
| <--- 2.01 Created (N1) --- | |
| | |
/Sec Context Derivation/ | |
| | |
| ---- OSCORE Request -----> | |
| (N1, N2) | |
| | |
| /Sec Context Derivation/ |
| | |
| <--- OSCORE Response ----- | |
| | |
| ---- OSCORE Request -----> | |
| | |
| <--- OSCORE Response ----- | |
| ... | |
Figure 1: Protocol Overview
3. Client-AS Communication
The following subsections describe the details of the POST /token
request and response between client and AS. Section 3.2 of
[I-D.ietf-core-object-security] 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) provisioned from the AS MUST be used as master secret in
OSCORE.
3.1. C-to-AS: POST /token
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 /token request over a secure channel
that guarantees authentication, message integrity and confidentiality
(see Section 5).
An example of such a request, 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:
{
"grant_type" : "client_credentials",
"client_id" : "myclient",
"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 /token
request a req_cnf object carrying the client's identifier (that was
assigned in section Section 3.2) in the kid field. This identifier
can be used by the AS to determine the shared secret to construct 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 and token
that have 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].
An example of such a request, in CBOR diagnostic notation without the
tag and value abbreviations is reported in Figure 3
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Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"grant_type" : "client_credentials",
"client_id" : "myclient",
"req_aud" : "tempSensor4711",
"scope" : "write",
"req_cnf" : {
"kid" : b64'Qg'
}
Figure 3: 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 /token request 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 signals 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.
Moreover, the AS MUST provision the following data:
o a master secret
o a client identifier
o a server identifier
Additionally, the AS MAY provision the following data, in the same
response.
o an AEAD algorithm
o an HKDF algorithm
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o a salt
o a replay window type and size
The master secret MUST be communicated as COSE_Key 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 COSE_Key; the HKDF algorithm MAY be
included as the 'hkdf' parameter of the COSE_Key and the salt MAY be
included as the 'slt' parameter of the COSE_Key as defined in
Figure 4.
The same parameters MUST be included as metadata 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 COSE_Key structure
defined above MUST be placed in the 'cnf' claim of this token.
The AS MUST also assign identifiers to both client and RS, which are
then used as Sender ID and Recipient ID in the OSCORE context as
described in section 3.1 of [I-D.ietf-core-object-security]. These
identifiers MUST be unique in the set of all clients and RS
identifiers for a certain AS. Moreover, these MUST be included in
the COSE_Key as header parameters, as defined in Figure 4.
We assume in this document that a resource is associated to one
single AS, which makes it possible to assume unique identifiers for
each client requesting a particular resource to a RS. If this is not
the case, collisions of identifiers may appear in the RS, in which
case the RS needs to have a mechanism in place to disambiguate
identifiers or mitigate their effect.
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.
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+----------+-------+--------------+------------+-------------------+
| name | label | CBOR type | registry | description |
+----------+-------+--------------+------------+-------------------+
| clientId | TBD1 | bstr | | Identifies the |
| | | | | client in an |
| | | | | OSCORE context |
| | | | | using this key |
| | | | | |
| serverId | TBD2 | bstr | | Identifies the |
| | | | | server in an |
| | | | | OSCORE context |
| | | | | using this key |
| | | | | |
| hkdf | TBD3 | bstr | | Identifies the |
| | | | | KDF algorithm in |
| | | | | an OSCORE context |
| | | | | using this key |
| | | | | |
| slt | TBD4 | bstr | | Identifies the |
| | | | | master salt in |
| | | | | an OSCORE context |
| | | | | using this key |
+----------+-------+--------------+------------+-------------------+
Figure 4: Additional COSE_Key Common Parameters
Figure 5 shows an example of such an AS response, in CBOR diagnostic
notation without the tag and value abbreviations.
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Header: Created (Code=2.01)
Content-Type: "application/cose+cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(remainder of access token omitted for brevity)',
"profile" : "coap_oscore",
"expires_in" : "3600",
"cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"alg" : "AES-CCM-16-64-128",
"clientId" : b64'qA',
"serverId" : b64'Qg',
"k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
}
}
}
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" : {
"COSE_Key" : {
"kty" : "Symmetric",
"alg" : "AES-CCM-16-64-128",
"clientId" : b64'Qg',
"serverId" : b64'qA',
"k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
}
}
Figure 6: 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 in the 'kid' field in the 'cnf' parameter of the
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token. The client identifier needs to be provisioned, in order for
the RS to identify the previously generated Security Context.
Figure 7 shows an example of such an AS response, in CBOR diagnostic
notation without the tag and value abbreviations.
Header: Created (Code=2.01)
Content-Type: "application/cose+cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(remainder of access token omitted for brevity)',
"profile" : "coap_oscore",
"expires_in" : "3600"
}
Figure 7: Example AS-to-C Access Token response with OSCORE profile,
for update of access rights.
Figure 8 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" : b64'Qg'
}
}
Figure 8: Example CWT with OSCORE parameters for update of access
rights.
4. Client-RS Communication
The following subsections describe the details of the POST /authz-
info request and response between client and RS. The client posts
the token that includes the materials provisioned by the AS to the
RS, which can then use Section 3.2 of [I-D.ietf-core-object-security]
to derive a security context based on a shared master secret and a
set of other parameters, established between client and server.
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Note that the proof-of-possession required to bind the access token
to the client is implicitly performed by generating the shared OSCORE
Security Context using the pop-key as master secret, for both client
and RS. An attacker using a stolen token 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 /authz-info
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 to the RS.
The authz-info resource 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, since
an RS may delete a stored access token, due to lack of memory.
Figure 9 shows an example of the request sent from the client to the
RS.
Header: POST (Code=0.02)
Uri-Host: "rs.example.com"
Uri-Path: "authz-info"
Content-Format: "application/cwt"
Payload:
b64'SlAV32hkKG ...
(remainder of access token omitted for brevity)',
Figure 9: Example C-to-RS POST /authz-info request using CWT
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) the RS
MUST respond with a response code equivalent to the CoAP code 4.00
(Bad Request). In the latter case 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
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token before responding to the POST request to the authz-info
resource.
Additionally, the RS MUST generate a nonce (N1) with a good amount of
randomness, and include it in the payload of the 2.01 (Created)
response as a CBOR byte string. This profile RECOMMENDS to use a
nonce of 64 bits. The RS MUST store this nonce as long as the access
token related to it is still valid.
Note that, when using this profile, an identifier of the token (e.g.,
the cti for a CWT) is not transported in the payload of this request,
as section 5.8.1 of [I-D.ietf-ace-oauth-authz] allows.
Figure 10 shows an example of the response sent from the RS to the
client.
Header: Created (Code=2.01)
Content-Format: "application/cbor"
Payload:
h'018a278f7faab55a',
Figure 10: Example RS-to-C 2.01 (Created) response
When receiving an updated access token with updated authorization
information from the client (see section 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.
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.
4.3. OSCORE Setup
Once receiving the 2.01 (Created) response from the RS, following the
POST /authz-info request, the client MUST extract the nonce N1 from
the CBOR byte string in the payload of the response. The client MUST
generate itself a nonce (N2) with a good amount of randomness. This
profile RECOMMENDS to use a nonce of 64 bits. Then, the client MUST
set the ID Context of the Security Context created to communicate
with the RS to the concatenation of N1 and N2, in this order: ID
Context = N1 | N2, where | denotes byte string concatenation. 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
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set the AEAD Algorithm, Master Salt, HKDF and Replay Window 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 section 3.2 of [I-D.ietf-core-object-security]. After
that, the client MUST derive the complete Security Context following
section 3.2.1 of [I-D.ietf-core-object-security]. 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.
The client then uses this Security Context to send requests to RS
using OSCORE. In the first request sent to the RS, the client MUST
include the kid context, with value ID Context, i.e. N1 concatenated
with N2. The client needs to make sure the RS receives the kid
context, possibly adding the kid context to later requests, until it
receives a valid OSCORE response from the RS using the same Security
Context.
When the RS receives this first OSCORE-protected request, it MUST
extract the kid context from the message first. Then, it needs to
verify that the first part of the kid context corresponds to the
nonce N1 it previously sent, and that it is followed by a non-zero-
length byte string. If that is verified, the RS MUST set the ID
Context to the kid context value. Then, the RS MUST set the Master
Secret, Sender ID and Recipient ID from the parameters received from
the client in the access token in Section 4.1. The RS MUST set the
AEAD Algorithm, Master Salt, HKDF and Replay Window from the
parameters received from the client in the access token in
Section 4.1, if present. In case these parameters are omitted, the
default values are used as described in section 3.2 of
[I-D.ietf-core-object-security]. After that, the RS MUST derive the
complete Security Context following section 3.2.1 of
[I-D.ietf-core-object-security], and MUST associate this Security
Context with the authorization information from the access token.
Then, the RS MUST delete the nonce N1 from memory.
The RS then uses this Security Context to verify the request and send
responses to RS using OSCORE. If OSCORE verification fails, error
responses are used, as specified in section 8 of
[I-D.ietf-core-object-security]. 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.
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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 it processes according to
[I-D.ietf-core-object-security]. If OSCORE verification succeeds,
and the target resource requires authorization, the RS retrieves the
authorization information from 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
not used the Security Context associated with the access token, or if
RS has no valid access token for the client. If RS has an access
token for the client but not for the resource that was requested, RS
MUST reject the request with a 4.03 (Forbidden). If RS has an access
token for the client but it does not cover the action that was
requested on the resource, RS MUST reject the request with a 4.05
(Method Not Allowed).
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 resource. The
use of CoAP and OSCORE 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.
Furthermore the requesting entity and the AS communicate using OSCORE
([I-D.ietf-core-object-security]) through the introspection resource
as specified in section 5.7 of [I-D.ietf-ace-oauth-authz] and through
the token resource as specified in section 5.6 of
[I-D.ietf-ace-oauth-authz].
6. 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
[I-D.ietf-core-object-security] also apply to this specific use of
the OSCORE protocol.
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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.
The use of nonces during the OSCORE Setup Section 4.3 prevents the
reuse of AEAD nonces in the RS Security Context, in case the RS loses
the Security Context associated with a client (e.g. in case of
unplanned reboot) and receives a replayed access token. In fact, by
using random nonces as ID Context, the POST /auth-info request
results in a different Security Context, since Master Secret, Sender
ID and Recipient ID are the same but ID Context is different.
Therefore, the main requirement for the nonces is that they have a
good amount of randomness. Moreover, the client echoes the nonce
created by the RS, which verifies it before deriving the Security
Context, and this protects against an adversary acting as a Man-in-
the-Middle and substituting the nonce in transit from client to RS to
provoke the creation of different Security Contexts in the client and
RS.
This profiles 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 may contradict each other which 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.
7. 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
[I-D.ietf-core-object-security] 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
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Security Context already exists between the client and the resource
server, more detailed information may be included.
Note that some information might still leak after OSCORE is
established, due to observable message sizes, the source, and the
destination addresses.
8. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[[this
specification]]" with the RFC number of this specification and delete
this paragraph.
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]:
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]]
The following registrations are done for the COSE Key Common
Parameter Registry specified in section 16.5 of [RFC8152]:
o Name: clientId
o Label: TBD1 (value between 1 and 255)
o CBOR Type: bstr
o Value Registry: N/A
o Description: Identifies the client in an OSCORE context
o Reference: [[this specification]]
o Name: serverId
o Label: TBD2 (value between 1 and 255)
o Value Type: bstr
o Value Registry: N/A
o Description: Identifies the server in an OSCORE context
o Reference: [[this specification]]
o Name: hkdf
o Label: TBD3 (value between 1 and 255)
o Value Type: bstr
o Value Registry: COSE Algorithms registry
o Description: Identifies the KDF algorithm to be used in an OSCORE
context
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o Reference: [[this specification]]
o Name: slt
o Label: TBD4 (value between 1 and 255)
o Value Type: bstr
o Value Registry: N/A
o Description: Identifies the master salt of to be used in an OSCORE
context
o Reference: [[this specification]]
9. References
9.1. 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-15
(work in progress), September 2018.
[I-D.ietf-ace-oauth-params]
Seitz, L., "Additional OAuth Parameters for Authorization
in Constrained Environments (ACE)", draft-ietf-ace-oauth-
params-00 (work in progress), September 2018.
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", draft-ietf-core-object-security-15 (work in
progress), August 2018.
[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>.
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[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>.
9.2. Informative References
[I-D.gerdes-ace-dcaf-authorize]
Gerdes, S., Bergmann, O., and C. Bormann, "Delegated CoAP
Authentication and Authorization Framework (DCAF)", draft-
gerdes-ace-dcaf-authorize-04 (work in progress), October
2015.
[I-D.selander-ace-cose-ecdhe]
Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
cose-ecdhe-10 (work in progress), September 2018.
[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>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
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 (Optional) discovery process of how the client finds the right AS
for an RS it wants to send a request to: Not specified
o communication protocol the client and the RS must use: CoAP
o security protocol the client and RS must use: OSCORE
o how the client and the RS mutually authenticate: Implicitly by
possession of a common OSCORE security context
o Content-format of the protocol messages: "application/cose+cbor"
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o proof-of-possession protocol(s) and how to select one; which key
types (e.g. symmetric/asymmetric) supported: OSCORE algorithms;
pre-established symmetric keys
o profile identifier: coap_oscore
o (Optional) how the RS talks to the AS for introspection: HTTP/CoAP
(+ TLS/DTLS/OSCORE)
o how the client talks to the AS for requesting a token: HTTP/CoAP
(+ TLS/DTLS/OSCORE)
o how/if the /authz-info endpoint is protected: Security protocol
above
o (Optional)other methods of token transport than the /authz-info
endpoint: no
Appendix B. Using the pop-key with EDHOC (EDHOC+OSCORE)
EDHOC specifies an authenticated Diffie-Hellman protocol that allows
two parties to use CBOR [RFC7049] and COSE in order to establish a
shared secret key with perfect forward secrecy. The use of Ephemeral
Diffie-Hellman Over COSE (EDHOC) [I-D.selander-ace-cose-ecdhe] in
this profile in addition to OSCORE, provides perfect forward secrecy
(PFS) and the initial proof-of-possession, which ties the proof-of-
possession key to an OSCORE security context.
If EDHOC is used together with OSCORE, and the pop-key (symmetric or
asymmetric) is used to authenticate the messages in EDHOC, then the
AS MUST provision the following data, in response to the access token
request:
o a symmetric or public key (associated to the RS)
o a key identifier;
How these parameters are communicated depends on the type of key
(asymmetric or symmetric). Moreover, the AS MUST signal the use of
OSCORE + EDHOC with the 'profile' parameter set to
"coap_oscore_edhoc".
Note that in the case described in this section, the 'expires_in'
parameter, defined in Section 4.2.2. of [RFC6749] defines the
lifetime in seconds of both the access token and the shared secret.
After expiration, C MUST acquire a new access token from the AS, and
run EDHOC again, as specified in this section
B.1. Using Asymmetric Keys
In case of an asymmetric key, C MUST communicate its own asymmetric
key to the AS in the 'req_cnf' parameter of the access token request,
as specified in Section 3.1 of [I-D.ietf-ace-oauth-params]; the AS
MUST communicate the RS's public key to C in the response, in the
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'rs_cnf' parameter, as specified in Section 3.2 of
[I-D.ietf-ace-oauth-params]. Note that the RS's public key MUST
include a 'kid' parameter, and that the value of the 'kid' MUST be
included in the access token, to let the RS know which of its public
keys C used. If the access token is a CWT [RFC8392], the key
identifier MUST be placed directly in the 'cnf' structure (if the key
is only referenced).
Figure 3 shows an example of such a request in CBOR diagnostic
notation without tag and value abbreviations.
Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cose+cbor"
Payload:
{
"grant_type" : "client_credentials",
"req_cnf" : {
"COSE_Key" : {
"kid" : "client_key"
"kty" : "EC",
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}
}
Figure 3: Example access token request (OSCORE+EDHOC, asymmetric).
Figure 4 shows an example of a corresponding response in CBOR
diagnostic notation without tag and value abbreviations.
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Header: Created (Code=2.01)
Content-Type: "application/cose+cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(contains "kid" : "client_key")',
"profile" : "coap_oscore_edhoc",
"expires_in" : "3600",
"cnf" : {
"COSE_Key" : {
"kid" : "server_key"
"kty" : "EC",
"crv" : "P-256",
"x" : b64'cGJ90UiglWiGahtagnv8usWxHK2PmfnHKwXPS54m0kT',
"y" : b64'reASjpkttcsz+1rb7btKLv8EX4IBOL+C3BttVivg+lS'
}
}
}
Figure 4: Example AS response (EDHOC+OSCORE, asymmetric).
B.2. Using Symmetric Keys
In the case of a symmetric key, the AS MUST communicate the key to
the client in the 'cnf' parameter of the access token response, as
specified in Section 3.2. of [I-D.ietf-ace-oauth-params]. The AS
MUST also select a key identifier, that MUST be included as the 'kid'
parameter of the COSE_key, as in figure 9 of
[I-D.ietf-ace-oauth-authz].
Figure 5 shows an example of the necessary parameters in the AS
response to the access token request when EDHOC is used. The example
uses CBOR diagnostic notation without tag and value abbreviations.
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Header: Created (Code=2.01)
Content-Type: "application/cose+cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(remainder of access token omitted for brevity)',
"profile" : "coap_oscore_edhoc",
"expires_in" : "3600",
"cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : b64'5tOS+h42dkw',
"k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
}
}
}
Figure 5: Example AS response (EDHOC+OSCORE, symmetric).
In both cases, the AS MUST also include the same key identifier as
'kid' parameter in the access token metadata. If the access token is
a CWT [RFC8392], the key identifier MUST be placed inside the 'cnf'
claim as 'kid' parameter of the COSE_Key or directly in the 'cnf'
structure (if the key is only referenced).
Figure 6 shows an example CWT containing the necessary EDHOC+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" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : b64'5tOS+h42dkw',
"k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
}
}
Figure 6: Example CWT with EDHOC+OSCORE, symmetric case.
All other parameters defining OSCORE security context are derived
from EDHOC message exchange, including the master secret (see
Appendix D.2 of [I-D.selander-ace-cose-ecdhe]).
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B.3. Processing
To provide forward secrecy and mutual authentication in the case of
pre-shared keys, pre-established raw public keys or with X.509
certificates it is RECOMMENDED to use EDHOC
[I-D.selander-ace-cose-ecdhe] to generate the keying material. EDHOC
MUST be used as defined in Appendix D of
[I-D.selander-ace-cose-ecdhe], with the following additions and
modifications.
The first EDHOC message is sent after the access token is posted to
the /authz-info resource of the RS as specified in Section 5.8.1 of
[I-D.ietf-ace-oauth-authz]. Then the EDHOC message_1 is sent and the
EDHOC protocol is initiated [I-D.selander-ace-cose-ecdhe]).
Before the RS continues with the EDHOC protocol and responds to this
token submission request, additional verifications on the access
token are done: the RS SHALL process the access token according to
[I-D.ietf-ace-oauth-authz]. If the token is valid then the RS
continues processing EDHOC following Appendix D of
[I-D.selander-ace-cose-ecdhe], otherwise it discontinues EDHOC and
responds with the error code as specified in
[I-D.ietf-ace-oauth-authz].
o In case the EDHOC verification fails, the RS MUST return an error
response to the client with code 4.01 (Unauthorized).
o If RS has an access token for C but not for the resource that C
has requested, RS MUST reject the request with a 4.03 (Forbidden).
o If RS has an access token for C but it does not cover the action C
requested on the resource, RS MUST reject the request with a 4.05
(Method Not Allowed).
o If all verifications above succeeds, further communication between
client and RS is protected with OSCORE, including the RS response
to the OSCORE request.
In the case of EDHOC being used with symmetric keys, the protocol in
Section 5 of [I-D.selander-ace-cose-ecdhe] MUST be used. If the key
is asymmetric, the RS MUST also use an asymmetric key for
authentication. This key is known to the client through the access
token response (see Section 5.6.2 of [I-D.ietf-ace-oauth-authz]). In
this case the protocol in Section 4 of [I-D.selander-ace-cose-ecdhe]
MUST be used.
Figure 7 illustrates the message exchanges for using OSCORE+EDHOC
(step C in figure 1 of [I-D.ietf-ace-oauth-authz]).
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Resource
Client Server
| |
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Content-Type: application/cbor
| | Payload: access token
| |
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| | Content-Type: application/edhoc
| | Payload: EDHOC message_1
| |
|<---------+ Header: 2.04 Changed
| 2.04 | Content-Type: application/edhoc
| | Payload: EDHOC message_2
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| | Content-Type: application/edhoc
| | Payload: EDHOC message_3
| |
|<---------+ Header: 2.04 Changed
| 2.04 |
| |
start of protected communication
| |
+--------->| CoAP request +
| OSCORE | Object-Security option
| request |
| |
|<---------+ CoAP response +
| OSCORE | Object-Security option
| response |
| |
Figure 7: Access token and key establishment with EDHOC
Acknowledgments
The authors wish to thank Jim Schaad and Marco Tiloca for the input
on this memo.
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Authors' Addresses
Francesca Palombini
Ericsson AB
Email: francesca.palombini@ericsson.com
Ludwig Seitz
RISE SICS AB
Scheelevagen 17
Lund 22370
Sweden
Email: ludwig.seitz@ri.se
Goeran Selander
Ericsson AB
Email: goran.selander@ericsson.com
Martin Gunnarsson
RISE SICS AB
Scheelevagen 17
Lund 22370
Sweden
Email: martin.gunnarsson@ri.se
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