Internet Engineering Task Force (IETF) R. Marin-Lopez
Request for Comments: 9820 University of Murcia
Category: Standards Track D. Garcia-Carrillo
ISSN: 2070-1721 University of Oviedo
July
August 2025
Authentication Service Based on the Extensible Authentication Protocol
(EAP) for Use with the Constrained Application Protocol (CoAP)
Abstract
This document specifies an authentication service that uses the
Extensible Authentication Protocol (EAP) transported employing
Constrained Application Protocol (CoAP) messages. as a transport method to
carry the Extensible Authentication Protocol (EAP). As such, it
defines an EAP lower layer based on CoAP called "CoAP-EAP". One of
the main goals is to authenticate a CoAP-enabled Internet of Things
(IoT) device (EAP peer) that intends to join a security domain
managed by a Controller (EAP authenticator). Secondly, it allows
deriving key material to protect CoAP messages exchanged between them
based on Object Security for Constrained RESTful Environments
(OSCORE), enabling the establishment of a security association
between them.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9820.
Copyright Notice
Copyright (c) 2025 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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include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
1.1. Requirements Language
2. General Architecture
3. CoAP-EAP Operation
3.1. Discovery
3.2. Flow of Operation (OSCORE Establishment)
3.3. Re-Authentication
3.4. Managing the State of the Service
3.5. Error Handling
3.5.1. EAP Authentication Failure
3.5.2. Non-Responsive Endpoint
3.5.3. Duplicated Message with /.well-known/coap-eap
3.6. Proxy Operation in CoAP-EAP
4. CoAP-EAP Media Type Format
5. CBOR Objects in CoAP-EAP
6. Cipher Suite Negotiation and Key Derivation
6.1. Cipher Suite Negotiation
6.2. Deriving the OSCORE Security Context
7. Discussion
7.1. CoAP as the EAP Lower Layer
7.2. Size of the EAP Lower Layer vs. EAP Method Size
8. Security Considerations
8.1. Use of EAP Methods
8.2. Authorization
8.3. Allowing CoAP-EAP Traffic to Perform Authentication
8.4. Freshness of the Key Material
8.5. Channel-Binding Support
8.6. Additional Security Considerations
9. IANA Considerations
9.1. CoAP-EAP Cipher Suites
9.2. CDDL in CoAP-EAP Information Elements
9.3. The Well-Known URIs Registry
9.4. The EAP Lower Layers Registry
9.5. Media Types Registry
9.6. CoAP Content-Formats Registry
9.7. Resource Type (rt=) Link Target Attribute Values Registry
9.8. Expert Review Instructions
10. References
10.1. Normative References
10.2. Informative References
Appendix A. Flow of Operation (DTLS Establishment)
A.1. Deriving DTLS PSK DTLS_PSK and Identity
Appendix B. Using CoAP-EAP for Distributing Key Material for IoT
Networks
Appendix C. Example Use Case Scenarios
C.1. Example 1: CoAP-EAP Using ACE
C.2. Example 2: Multiple Domains with AAA Infrastructures
C.3. Example 3: Single Domain with a AAA Infrastructure
C.4. Example 4: Single Domain Without a AAA Infrastructure
C.5. Other Use Cases
C.5.1. CoAP-EAP for Network Access Authentication
C.5.2. CoAP-EAP for Service Authentication
Acknowledgments
Authors' Addresses
1. Introduction
This document specifies an authentication service (application) that
uses the Extensible Authentication Protocol (EAP) [RFC3748] and is
built on top of the Constrained Application Protocol (CoAP)
[RFC7252]; it is called "CoAP-EAP". CoAP-EAP is an application that
allows authenticating two CoAP endpoints by using EAP and
establishing an Object Security for Constrained RESTful Environments
(OSCORE) security association between them. More specifically, this
document specifies how CoAP can be used as a constrained, link-layer-
independent, reliable EAP lower layer [RFC3748] to transport EAP
messages between a CoAP server (acting as an EAP peer) and a CoAP
client (acting as an EAP authenticator) using CoAP messages. The
CoAP client has the option of contacting a backend Authentication,
Authorization, and Accounting (AAA) infrastructure to complete the
EAP negotiation, as described in the EAP specification [RFC3748].
In the case of this specification, the EAP methods that can be
transported with CoAP-EAP MUST export cryptographic material
[RFC5247]. Examples of such methods are the EAP Generalized Pre-
Shared Key (EAP-GPSK) [RFC5433], the EAP Method for Global System for
Mobile Communications (GSM) Subscriber Identity Modules (EAP-SIM)
[RFC4186], the EAP Method for 3rd Generation Authentication and Key
Agreement (EAP-AKA') [RFC5448], EAP-TLS 1.3 [RFC9190], EAP with
Ephemeral Diffie-Hellman over CBOR Object Signing and Encryption
(EAP-EDHOC) [EAP-EDHOC], etc. ("CBOR" stands for "Concise Binary
Object Representation".) In general, any EAP method designed in the
EAP Method Update (EMU) Working Group that exports the Master Session
Key (MSK) can be used with CoAP-EAP. The MSK is used as the basis
for further cryptographic derivations. This way, CoAP messages are
protected after authentication. After the CoAP-EAP operation, an
OSCORE security association is established between the endpoints of
the service. Using the keying material from the authentication,
other security associations could be generated. Appendix A shows how
to establish a (D)TLS security association using the keying material
from the EAP authentication.
One of the main applications of CoAP-EAP involves Internet of Things
(IoT) networks, where we can find very constrained links (e.g.,
limited bandwidth) and devices with limited capabilities. In these
IoT scenarios, we identify the IoT device as the entity that wants to
be authenticated by using EAP to join a domain that is managed by a
Controller. In these cases, the IoT device is the EAP peer and the
Controller is the entity steering the authentication (i.e., the EAP
authenticator); from now on, the IoT device will be referred to as
the EAP peer and the Controller will be referred to as the EAP
authenticator. In these cases, EAP methods with fewer exchanges,
shorter messages, and cryptographic algorithms suitable for
constrained devices are preferable. The benefits of the EAP
framework in IoT networks are highlighted in [EAP-Framework-IoT].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts
described in CoAP [RFC7252], EAP [RFC3748] [RFC5247], and OSCORE
[RFC8613].
2. General Architecture
Figure 1 illustrates the architecture defined in this document. In
this architecture, the EAP peer will act as a CoAP server for this
service and the domain EAP authenticator will act as a CoAP client.
The rationale behind this decision is that EAP requests will always
travel from the EAP server to the EAP peer. Accordingly, EAP
responses will always travel from the EAP peer to the EAP server.
It is worth noting that the EAP authenticator MAY interact with a
backend AAA infrastructure when EAP pass-through mode is used, which
will place the EAP server in the AAA server that contains the
information required to authenticate the EAP peer.
The protocol stack is described in Figure 2. CoAP-EAP is an
application built on top of CoAP. On top of the application, there
is an EAP state machine that can run any EAP method. In the case of
this specification, the EAP method MUST support key derivation and
export as specified in [RFC5247]: an MSK of at least 64 octets and an
Extended Master Session Key (EMSK) of at least 64 octets. CoAP-EAP
also relies on CoAP reliability mechanisms in CoAP to transport EAP:
CoAP over UDP with Confirmable messages [RFC7252] or CoAP over TCP,
TLS, or WebSockets [RFC8323].
+--------+ +--------------+ +----------+
| EAP | | EAP | | AAA/ |
| peer |<------>| authenticator|<----------->|EAP server|
+--------+ CoAP +--------------+ AAA +----------+
(optional)
<----(SCOPE
<---- SCOPE OF THIS DOCUMENT)----> DOCUMENT ---->
Figure 1: CoAP-EAP Architecture
+---------------------------------+
+-----------------------------------+
| EAP State Machine |
+---------------------------------+
+-----------------------------------+
| Application (CoAP-EAP) | <-- This Document
+---------------------------------+
+-----------------------------------+
| Request Requests / Responses / Signaling | RFC 7252 / RFC 8323
+---------------------------------+
+-----------------------------------+
| Message / Message Framing | RFC 7252 / RFC 8323
+---------------------------------+
+-----------------------------------+
| Unreliable / Reliable Transport | RFC 7252 / RFC 8323
+---------------------------------+
+-----------------------------------+
Figure 2: CoAP-EAP Stack
3. CoAP-EAP Operation
Because CoAP-EAP uses reliable delivery as defined in CoAP [RFC7252]
[RFC8323], EAP retransmission time is set to an infinite value, as
mentioned in [RFC3748]. To maintain ordering guarantees, CoAP-EAP
uses Hypermedia as the Engine of Application State (HATEOAS). Each
step during the EAP authentication accesses a new resource in the
CoAP server (EAP peer). The previous resource is removed once the
new resource is created, indicating the resource that will process
the next step of the EAP authentication.
One of the benefits of using EAP is that we can choose from a large
variety of authentication methods.
In CoAP-EAP, the EAP peer will only have one authentication session
with a specific EAP authenticator, and it will not process any other
EAP authentication in parallel (with the same EAP authenticator).
That is, a single ongoing EAP authentication is permitted for the
same EAP peer and the same EAP authenticator. It may be worth noting
that the EAP authenticator may have parallel EAP sessions with
multiple EAP peers.
To access the authentication service, this document defines the well-
known URI "coap-eap" (see Section 9.3). The /.well-known/coap-eap
URI is used with "coap", "coap+tcp", or "coap+ws".
3.1. Discovery
Before the CoAP-EAP exchange takes place, the EAP peer needs to
discover the EAP authenticator or the entity that will enable the
CoAP-EAP exchange (e.g., (i.e., an intermediary proxy). intermediary). The discovery process is
outside the scope of this document.
The CoAP-EAP application can be accessed through the URI "coap-eap"
for the trigger message (see Section 3.2, Step 0). The CoAP-EAP
service can be discovered by asking directly about the services
offered. This information can also be available in the resource
directory [RFC9176].
Implementation notes: There are different methods for discovering the
IPv6 address of the EAP authenticator or intermediary entity. For
example, in a 6LoWPAN network, the Border Router will typically act
as the EAP authenticator hence, authenticator. Hence, after receiving the Router
Advertisement (RA) messages from the Border Router, the EAP peer may
engage in the CoAP-EAP exchange.
3.2. Flow of Operation (OSCORE Establishment)
Figure 3 shows the general flow of operation for CoAP-EAP to
authenticate using EAP and establish an OSCORE security context. Security Context. The
flow does not show a specific EAP method. Instead, the chosen EAP
method is represented by using a generic name (EAP-X). The flow
assumes that the EAP peer knows the EAP authenticator implements the
CoAP-EAP service. A CoAP-EAP message has the media type
"application/coap-eap". See Section 9.5.
The steps for this flow of operation are as follows:
* Step 0. The EAP peer MUST start the CoAP-EAP process by sending a
"POST /.well-known/coap-eap" request (trigger message). This
message carries the 'No-Response' CoAP option [RFC7967] to avoid
waiting for a response that is not needed. This is the only
message where the EAP authenticator acts as a CoAP server and the
EAP peer acts as a CoAP client. The message also includes a URI
in the payload of the message to indicate the resource where the
EAP authenticator MUST send the next message. The name of the
resource is selected by the CoAP server.
Implementation notes: When generating the URI for a resource during a
step of the authentication, the resource could have the following
format as an example "path/eap/counter", where:
* "path" is some local path on the device to make the path unique.
This could be omitted if desired.
* "eap" is the name that indicates that the URI is for the EAP peer.
This has no meaning for the protocol but helps with debugging.
* "counter" is an incrementing unique number for every new EAP
request.
So, per Figure 3, the URI for the first resource would be "a/eap/1".
* Step 1. The EAP authenticator sends a POST message to the
resource indicated in Step 0 (e.g., '/a/eap/1'). The payload in
this message contains the first EAP message (EAP Request/Identity) (EAP-Request/Identity)
and the Recipient ID of the EAP authenticator (RID-C) for OSCORE,
and MAY contain a CBOR array with a list of proposed cipher suites
(CS-C) for OSCORE. If the cipher suite list is not included, the
default cipher suite for OSCORE is used. The details of the
cipher suite negotiation are discussed in Section 6.1.
* Step 2. The EAP peer processes the POST message sending the EAP
request (EAP-Req/Id) to the EAP peer state machine, which returns
an EAP response (EAP Resp/Id). (EAP-Resp/Id). Then, the CoAP-EAP application
assigns a new resource to the ongoing authentication process
(e.g., '/a/eap/2') and deletes the previous one ('/a/eap/1').
Finally, the CoAP-EAP application sends a '2.01 Created' response
with the new resource identifier in the Location-Path (and/or
Location-Query) options Options for the next step. The EAP response, the
Recipient ID of the EAP peer (RID-I), and the selected cipher
suite for OSCORE (CS-I) are included in the payload. In this
step, the EAP peer may create an OSCORE security
context Security Context (see
Section 6.2). The required MSK will be available once the EAP
authentication is successful (Step 7).
* Steps 3-6. From now on, the EAP authenticator and the EAP peer
will exchange EAP packets related to the EAP method (EAP-X),
transported in the CoAP message payload. The EAP authenticator
will use the POST method to send EAP requests to the EAP peer.
The EAP peer will use a CoAP response to carry the EAP response in
the payload. EAP requests and responses are represented in
Figure 3 using the nomenclature "EAP-X-Req" and "EAP-X-Resp",
respectively. When a POST message arrives (e.g., '/a/eap/1')
carrying an EAP request message, if processed correctly by the EAP
peer state machine, it returns an EAP Response. Along with each
EAP Response, a new resource is created (e.g., '/a/eap/3') for
processing the next EAP request and the ongoing resource (e.g.,
'/a/eap/2') is erased. This way, ordering guarantees are
achieved. Finally, an EAP response is sent in the payload of a
CoAP response that will also indicate the new resource in the
Location-Path (and/or Location-Query) Options. If an error occurs
while processing a legitimate message, the server will return a
"4.00
'4.00 Bad Request". Request'. Error handling is discussed in Section 3.5.
* Step 7. When the EAP authentication ends successfully, the EAP
authenticator obtains the MSK exported by the EAP method, an EAP
Success message, and some authorization information (e.g., session
lifetime)
Session-Lifetime) [RFC5247]. The EAP authenticator creates the
OSCORE
security context Security Context using the MSK and Recipient ID of both
entities exchanged in Steps 1 and 2. The establishment of the
OSCORE Security Context is defined in Section 6.2. Then, the EAP
authenticator sends the POST message protected with OSCORE for key
confirmation, including the EAP Success. The EAP authenticator
MAY also send a Session Lifetime, Session-Lifetime, in seconds, which is represented
by an unsigned integer in a CBOR object Object (see Section 5). If this
Session Lifetime
Session-Lifetime is not sent, the EAP peer assumes a default value
of 8 hours, as RECOMMENDED in [RFC5247]. The reception of the
OSCORE-protected POST message is considered by the EAP peer as an
alternate indication of success [RFC3748]. The EAP peer state
machine in the EAP peer interprets the alternate indication of
success (similarly to the arrival of an EAP Success) and returns
the MSK, which is used to create the OSCORE security context Security Context in
the EAP peer to process the protected POST message received from
the EAP authenticator.
* Step 8. If the EAP authentication and the verification of the
OSCORE-protected POST (Step 7) are successful, then the EAP peer
answers with an OSCORE-protected '2.04 Changed'. From this point
on, communication with the last resource (e.g., '/a/eap/(n)') MUST
be protected with OSCORE. If allowed by application policy, the
same OSCORE security context Security Context MAY be used to protect communication
to other resources between the same endpoints.
EAP peer EAP authenticator
------------- ------------
| POST /.well-known/coap-eap |
0)| No-Response |
| Payload("/a/eap/1") |
|---------------------------------------->|
| POST /a/eap/1 |
| Payload(EAP Req/Id||CS-C||RID-C) Payload(EAP-Req/Id||CS-C||RID-C) |
1)|<----------------------------------------|
| 2.01 Created Location-Path [/a/eap/2] |
| Payload(EAP Resp/Id||CS-I||RID-I) Payload(EAP-Resp/Id||CS-I||RID-I) |
2)|---------------------------------------->|
| POST /a/eap/2 |
| Payload(EAP-X Req) Payload(EAP-X-Req) |
3)|<----------------------------------------|
| 2.01 Created Location-Path [/a/eap/3] |
| Payload(EAP-X Resp) Payload(EAP-X-Resp) |
4)|---------------------------------------->|
....
| POST /a/eap/(n-1) |
| Payload(EAP-X Req) Payload(EAP-X-Req) |
5)|<----------------------------------------|
| 2.01 Created Location-Path [/a/eap/(n)] |
| Payload (EAP-X Resp) Payload(EAP-X-Resp) |
6)|---------------------------------------->|
| | MSK
| POST /a/eap/(n) | |
| OSCORE | | v
| Payload(EAP Success||*Session-Lifetime)| OSCORE
MSK 7)|<----------------------------------------| CTX
| | |
|
v | 2.04 Changed |
OSCORE | OSCORE |
CTX 8)|---------------------------------------->|
*Session-Lifetime is optional
Figure 3: CoAP-EAP Flow of Operation with OSCORE
3.3. Re-Authentication
When the CoAP-EAP state is close to expiring, the EAP peer may want
to start a new authentication process (re-authentication) to renew
the state. The main goal is to obtain new and fresh keying material
(MSK/EMSK) that, in turn, allows deriving a new OSCORE security
context, Security
Context, increasing the protection against key leakage. The keying
material MUST be renewed before the expiration of the Session-
Lifetime. By default, the EAP key management framework [RFC5247]
establishes a default value of 8 hours to refresh the keying
material. Certain EAP methods such as Nimble Out-of-Band
Authentication for EAP (EAP-NOOB) [RFC9140] or EAP-AKA' [RFC5448]
provide fast reconnect for quicker re-authentication. The EAP Re-
authentication Protocol (ERP) [RFC6696] MAY also be used to avoid the
repetition of the entire EAP exchange.
The re-authentication message flow will be the same as that shown in
Figure 3. Nevertheless, two different CoAP-EAP states will be active
during the re-authentication: the current CoAP-EAP state and the new
CoAP-EAP state, which will be created once the re-authentication has
finished successfully. Once the re-authentication is completed
successfully, the current CoAP-EAP state is deleted and replaced by
the new CoAP-EAP state. If for any reason the re-authentication
fails, the current CoAP-EAP state will be available until it expires,
or it will be renewed during a subsequent re-authentication attempt.
If the re-authentication fails, it is up to the EAP peer to decide
when to start a new re-authentication before the current EAP state
expires.
3.4. Managing the State of the Service
The EAP peer and the EAP authenticator keep state during the CoAP-EAP
negotiation. The CoAP-EAP state includes several important parts:
* A reference to an instance of the EAP (peer or authenticator/
server) state machine.
* The resource for the next message in the negotiation (e.g., '/a/
eap/2').
* The MSK, which is exported when the EAP authentication is
successful. CoAP-EAP can access the different variables via the
EAP state machine (see [RFC4137]).
* A reference to the OSCORE context.
Once created, the EAP authenticator MAY choose to delete the state as
described in Figure 4. Conversely, the EAP peer may need to renew
the CoAP-EAP state because the key material is close to expiring, as
mentioned in Section 3.3.
There are situations where the current CoAP-EAP state might need to
be removed. For instance, due to its expiration or forced removal,
the EAP peer has to be expelled from the security domain. Such an
exchange is illustrated in Figure 4.
If the EAP authenticator deems it necessary to remove the CoAP-EAP
state from the EAP peer before it expires, it can send a DELETE
command in a request to the EAP peer, referencing the last CoAP-EAP
state resource given by the CoAP server, whose identifier will be the
last one received (e.g., '/a/eap/(n)' in Figure 3). This message is
protected by the OSCORE security association to prevent forgery.
Upon reception of this message, the CoAP server sends a response to
the EAP authenticator with the code '2.02 Deleted', which is also
protected by the OSCORE security association. If a response from the
EAP peer does not arrive after EXCHANGE_LIFETIME, the EAP
authenticator will remove the state.
EAP peer EAP authenticator
------------- -------------
| |
| DELETE /a/eap/(n) |
| OSCORE |
|<--------------------------------------|
| |
| 2.02 Deleted |
| OSCORE |
|-------------------------------------->|
Figure 4: Deleting State
3.5. Error Handling
This section elaborates on how different errors are handled: EAP
authentication failure (Section 3.5.1), a non-responsive endpoint
(Section 3.5.2), and duplicated messages (Section 3.5.3).
3.5.1. EAP Authentication Failure
The EAP authentication may fail in different situations (e.g., wrong
credentials). The result is that the EAP authenticator will send an
EAP Failure message because of a failed EAP authentication (Step 7 in
Figure 3). In this case, the EAP peer MUST send a response '4.01
Unauthorized' in Step 8. Therefore, Steps 7 and 8 are not protected
in this case because no MSK is exported and the OSCORE security
context Security
Context is not yet generated.
If the EAP authentication fails during the re-authentication and the
EAP authenticator sends an EAP failure, Failure, the current CoAP-EAP state
will still be usable until it expires.
3.5.2. Non-Responsive Endpoint
If for any reason one of the entities becomes non-responsive, the
CoAP-EAP state SHOULD be removed after a stipulated amount of time.
The amount of time can be adjusted according to the policies
established by the application or use case where CoAP-EAP is used.
As a default value, the CoAP EXCHANGE_LIFETIME parameter, as defined
in CoAP [RFC7252], will be used.
The removal of the CoAP-EAP state in the EAP authenticator assumes
that the EAP peer will need to authenticate again.
According to CoAP, EXCHANGE_LIFETIME considers the time it takes
until a client stops expecting a response to a request. A timer is
reset every time a message is sent. By default, CoAP-EAP adopts the
value of EXCHANGE_LIFETIME as a timer in the EAP peer and
authenticator to remove the CoAP-EAP state if the authentication
process has not progressed in to completion during that time, in consequence, it has not
been completed. time.
The EAP peer will remove the CoAP-EAP state if either the
EXCHANGE_LIFETIME is triggered or the EAP peer state machine returns
an eapFail.
The EAP authenticator will remove the CoAP-EAP state if either the
EXCHANGE_LIFETIME is triggered or, when the EAP authenticator is
operating in pass-through mode (i.e., the EAP authentication is
performed against a AAA server), the EAP authenticator state machine
returns "aaaTimeout" [RFC4137].
3.5.3. Duplicated Message with /.well-known/coap-eap
The reception of the trigger message in Step (Step 0 in Figure 3) containing
the URI /coap-eap needs some additional considerations, as the
resource is always available in the EAP authenticator.
If a trigger message (Step 0) arrives at the EAP authenticator during an
ongoing authentication with the same EAP peer, the EAP authenticator
MUST silently discard this trigger message.
If an old "POST /.well-known/coap-eap" (Step 0) 0 in Figure 5) arrives
at the EAP authenticator and there is no authentication ongoing, the
EAP authenticator may understand that a new authentication process is
requested. Consequently, the EAP authenticator will start a new EAP
authentication. However, if the EAP peer did not start any
authentication and therefore,
authentication, it did not select any resource for the
EAP authentication. Thus, the EAP peer sends will send a '4.04 Not Found' in the response
(Figure 5).
EAP peer EAP authenticator
---------- ----------
| *POST /.well-known/coap-eap |
0) |
0)| No-Response |
| Payload("/a/eap/1") |
| ------------------------->|
| POST /a/eap/1 |
| Payload (EAP Req/Id||CS-C) Payload(EAP-Req/Id||CS-C) |
1) |<----------------------------------------|
1)|<----------------------------------------|
| |
| 4.04 Not Found |
|---------------------------------------->|
*Old
Figure 5: /.well-known/coap-eap with No Ongoing Authentication
from the EAP Authenticator
3.6. Proxy Operation in CoAP-EAP
The CoAP-EAP operation is intended to be compatible with the use of
intermediary entities between the EAP peer and the EAP authenticator
when direct communication is not possible. In this context, CoAP
proxies can be used as enablers of the CoAP-EAP exchange.
This specification is limited to using standard CoAP [RFC7252] as
well as standardized CoAP options [RFC8613]. It does not specify any
addition in the form of CoAP options. This is expected to ease the
integration of CoAP intermediaries in the CoAP-EAP exchange.
When using proxies in the CoAP-EAP exchange, it should be considered
that the exchange contains a role-reversal process at the beginning
of the exchange. In the first message, the EAP peer acts as a CoAP
client and the EAP authenticator acts as the CoAP server. After
that, in In the
remaining exchanges exchanges, the roles are reversed, being reversed (i.e., the EAP peer, peer acts
as the CoAP server, and the EAP authenticator, authenticator acts as the CoAP
client.
client). When using a proxy in the exchange, for Message 0, the proxy message 0 it will
act as forward, a forward proxy, and as a reverse proxy for the rest.
Additionally, in the first exchange, the EAP peer, as a CoAP client,
sends the URI for the next CoAP message in the payload of a request.
This is not the typical behavior, as URIs referring to new services/resources services/
resources appear in Location-Path and/or Location-Query Options in
CoAP responses. Hence, the proxy will have to treat the payload of
Message 0 as if it were a Location-Path Option of a CoAP response.
4. CoAP-EAP Media Type Format
In the CoAP-EAP exchange, the format specified by the "application/
coap-eap" media type will be used. See Section 9.5.
In CoAP-EAP, there are two different elements that can be sent over
the payload. The first one is a relative URI. This payload will be
present for the first message (0) in Figure 3.
In all the other cases, an EAP message will be followed by the CBOR
Object specified in Section 5. A visual example of the second case
can be found in Figure 7 (Section 6.1).
5. CBOR Objects in CoAP-EAP
In the CoAP-EAP exchange, there is information that needs to be exchanged between
the two entities. Examples of this information are entities -- for example, the cipher suites that need to be negotiated
negotiated, or authorization information (Session-lifetime). (Session-Lifetime). There
may also be a need to extend the information that has to be exchanged
in the future. This section specifies the CBOR data structure
[RFC8949] to exchange information between the EAP peer and the EAP
authenticator in the CoAP payload.
Figure 6 shows the specification of the CBOR Object to exchange
information in CoAP-EAP.
CoAP-EAP_Info = {
? 1 : [+ int], ; Cipher Suite (CS-C or CS-I)
? 2 : bstr, ; RID-C
? 3 : bstr, ; RID-I
? 4 : uint ; Session-Lifetime
}
Figure 6: CBOR Data Structure for CoAP-EAP
The parameters contain the following information:
1. Cipher Suite: An array with the list of proposed, or selected,
CBOR Object Signing and Encryption (COSE) algorithms for OSCORE.
If the field is carried over a request, a proposed cipher suite
is indicated; if it is carried over a response, it corresponds to
the agreed-upon cipher suite.
2. RID-C: The Recipient ID of the EAP authenticator. The EAP peer
uses this value as the Sender ID for its OSCORE Sender Context.
The EAP authenticator uses this value as the Recipient ID for its
Recipient Context.
3. RID-I: The Recipient ID of the EAP peer. The EAP authenticator
uses this value as the Sender ID for its OSCORE Sender Context.
The EAP peer uses this value as the Recipient ID for its
Recipient Context.
4. Session-Lifetime: The time that the session is valid, in seconds.
Other indexes can be used to carry additional values as needed, like
specific authorization parameters.
The indexes from 65001 to 65535 are reserved for experimentation.
6. Cipher Suite Negotiation and Key Derivation
6.1. Cipher Suite Negotiation
OSCORE runs after the EAP authentication, using the cipher suite
selected in the cipher suite negotiation (Steps 1 and 2). 2 in Figure 3).
To negotiate the cipher suite, CoAP-EAP follows a simple approach:
The EAP authenticator sends a list, in decreasing order of
preference, with the identifiers of the supported cipher suites (Step 1).
1 in Figure 8). In the response to that message (Step 2), 2 in
Figure 8), the EAP peer sends its choice.
This list is included in the payload after the EAP message through a
CBOR array. An example of how the fields are arranged in the CoAP
payload can be seen in Figure 7. An example exchange for the cipher
suite negotiation is shown in Figure 8, where it can be appreciated
the disposition of both the EAP-Request/Identity 8. The EAP request (EAP-
Request/Identity) and EAP-Response/
Identity, followed by EAP response (EAP-Response/Identity) are sent;
both messages include the CBOR object defined in Section 5, Object (Section 5) containing the
cipher suite field for the cipher suite negotiation.
+-----+-----------+-------+------++-------------+
|Code |Identifier |Length
+------+------------+--------+------+-----------------+
| Code | Identifier | Length | Data ||cipher suites|
+-----+-----------+-------+------++-------------+ | cipher suites |
+------+------------+--------+------+-----------------+
<---------- EAP packet Packet ----------> <-- CBOR array -->
Figure 7: Cipher Suites in the CoAP Payload
EAP peer EAP auth. Auth.
(CoAP server) (CoAP client)
------------- -------------
| |
| ... |
|---------------------------------------->|
| POST /a/eap/1 |
| Payload (EAP Req/Id, Payload(EAP-Req/Id, CBORArray[0,1,2]) |
1) |<----------------------------------------|
1)|<----------------------------------------|
| 2.01 Created Location-Path [/a/eap/2] |
| Payload (EAP Resp/Id, Payload(EAP-Resp/Id, CBORArray[0]) |
2) |---------------------------------------->|
2)|---------------------------------------->|
...
Figure 8: Cipher Suite Negotiation
If there is no CBOR array specifying the cipher suites, the default
cipher suites are applied. If the EAP authenticator sends a
restricted list of cipher suites that can be accepted, it MUST
include the default value 0, since it is mandatory to implement. The
EAP peer will have at least that option available.
The cipher suite requirements are inherited from those established by
OSCORE [RFC8613], which are COSE algorithms [RFC9053]. By default,
the HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
algorithm is SHA-256 and the Authenticated Encryption with Associated
Data (AEAD) algorithm is AES-CCM-16-64-128 [RFC9053]. ("HMAC" stands
for "Hashed Message Authentication Code".) Both are mandatory to
implement. The other supported and negotiated cipher suites are as
follows:
listed below; these hash algorithms are considered in cases where the
specification includes DTLS support in the future (TLS_SHA256,
TLS_SHA384, TLS_SHA512; see Appendix A):
* 0) AES-CCM-16-64-128, SHA-256 (default)
* 1) A128GCM, SHA-256
* 2) A256GCM, SHA-384
* 3) ChaCha20/Poly1305, SHA-256
* 4) ChaCha20/Poly1305, SHAKE256
This specification uses the HKDF as defined in [RFC5869] to derive
the necessary key material. Since the key derivation process uses
the MSK, which is considered fresh key material, the HKDF-Expand
function (shortened here as "KDF") will be used. See Section 8.1
regarding why the use of this function is enough and it is not
necessary to use KDF-Extract.
6.2. Deriving the OSCORE Security Context
The derivation of the OSCORE security context Security Context allows securing the
communication between the EAP peer and the EAP authenticator once the
MSK has been exported, providing confidentiality, integrity, key
confirmation (Steps 7 and 8), 8 in Figure 3), and detection of
downgrading attacks.
Once the Master Secret and Master Salt are derived, they can be used
to derive the rest of the OSCORE Security Context (see Section 3.2.1
of [RFC8613]). It should be noted that the ID Context is not
provided for the OSCORE Security Context derivation.
The Master Secret can be derived by using the chosen cipher suite and
the KDF as follows:
Master Secret = KDF(MSK, CS | "COAP-EAP OSCORE MASTER SECRET", length)
where:
* The MSK is exported by the EAP method. The use of the MSK for key
derivation is discussed in Section 8.
* CS is the concatenation of the content of the cipher suite
negotiation -- that is, the concatenation of two CBOR arrays CS-C
and CS-I (with CBOR ints as elements), as defined in Section 5.
If neither CS-C nor CS-I was sent (i.e., default algorithms are
used), the value used to generate CS will be the same as if the
default algorithms were explicitly sent in CS-C or CS-I (i.e., a
CBOR array with the cipher suite value of 0).
* "COAP-EAP OSCORE MASTER SECRET" is the ASCII code representation
of the non-NULL-terminated string (excluding the double quotes
around it).
* CS and "COAP-EAP OSCORE MASTER SECRET" are concatenated.
* length is the size of the output key material.
Similarly to the Master Secret, the Master Salt can be derived as
follows:
Master Salt = KDF(MSK, CS | "COAP-EAP OSCORE MASTER SALT", length)
where:
* The MSK is exported by the EAP method. The use of the MSK for key
derivation is discussed in Section 8.
* CS is the concatenation of the content of the cipher suite
negotiation -- that is, the concatenation of two CBOR arrays CS-C
and CS-I (with CBOR ints as elements), as defined in Section 5.
If neither CS-C nor CS-I was sent (i.e., default algorithms are
used), the value used to generate CS will be the same as if the
default algorithms were explicitly sent in CS-C or CS-I (i.e., a
CBOR array with the cipher suite value of 0).
* "COAP-EAP OSCORE MASTER SALT" is the ASCII code representation of
the non-NULL-terminated string (excluding the double quotes around
it).
* CS and "COAP-EAP OSCORE MASTER SALT" are concatenated.
* length is the size of the output key material.
Since the MSK is used to derive the Master Key, the correct
verification of the OSCORE-protected request (Step 7) and response
(Step 8) confirms that the EAP authenticator and the EAP peer have
the same Master Secret, achieving key confirmation.
To prevent a downgrading attack, the content of the cipher suite
(referred to here as "CS") negotiation is embedded in the Master
Secret derivation. If an attacker changes the value of the cipher
suite negotiation, the result will be different OSCORE security
contexts, Security
Contexts, which in turn will result in failure in Steps 7 and 8.
The EAP authenticator will use the Recipient ID of the EAP peer (RID-
I) as the Sender ID for its OSCORE Sender Context. The EAP peer will
use this value as the Recipient ID for its Recipient Context.
The EAP peer will use the Recipient ID of the EAP authenticator (RID-
C) as the Sender ID for its OSCORE Sender Context. The EAP
authenticator will use this value as the Recipient ID for its
Recipient Context.
7. Discussion
7.1. CoAP as the EAP Lower Layer
This section discusses the suitability of CoAP as the EAP lower layer
and reviews the requisites imposed by EAP on any protocol
transporting EAP. What EAP expects from its lower layers can be
found in Section 3.1 of [RFC3748], which is elaborated next:
Unreliable transport: EAP does not assume that lower layers are
reliable, but it can benefit from a reliable lower layer. In this
sense, CoAP provides a reliability mechanism (e.g., using
Confirmable messages).
Lower-layer error detection: EAP relies on lower-layer error
detection (e.g., CRC, checksum, Message Integrity Check (MIC),
etc.). For simplicity, CoAP-EAP delegates error detection to the
lower layers, such as the link layer or transport layer (e.g., UDP
over IPv6 or TCP).
Lower-layer security: EAP does not require security services from
the lower layers.
Minimum MTU: Lower layers need to provide an EAP MTU size of 1020
octets or greater. CoAP assumes an upper bound of 1024 octets for
its payload, which covers the EAP requirements when only the EAP
message is sent in the CoAP payload. In the case of Messages 1
and 2 in Figure 3, those messages have extra information apart
from EAP. Nevertheless, the EAP Req/Id EAP-Req/Id has a fixed length of 5
bytes. Message 2, with the EAP Resp/Id, EAP-Resp/Id, would limit the length of
the identity being used to the CoAP payload maximum size (1024) -
len( CS-I || RID-I ) - EAP Response header (5 bytes), which leaves
enough space for sending even lengthy identities. Nevertheless,
this limitation can be overcome by using CoAP block-wise transfers
[RFC7959]. Note: When EAP is proxied over a AAA framework, the
Access-Request packets in RADIUS MUST contain a Framed-MTU
attribute with a value of 1024 and, in Diameter, the Framed-MTU
Attribute-Value Pair (AVP) with a value of 1024. This information
signals the AAA server that it should limit its responses to 1024
octets.
Ordering guarantees: EAP relies on lower-layer ordering guarantees
for correct operation. Regarding message ordering, every time a
new message arrives at the authentication service hosted by the
EAP peer, a new resource is created, and this is indicated in a
"2.01 Created"
'2.01 Created' response code along with the name of the new
resource via Location-Path or Location-Query options. Options. This way,
the application shows that its state has advanced.
Although [RFC3748] states that "EAP provides its own support for
duplicate elimination and retransmission," EAP is also reliant on
lower-layer ordering guarantees. In this regard, [RFC3748] talks
about possible duplication and says, "Where the lower layer is
reliable, it will provide the EAP layer with a non-duplicated stream
of packets. However, while it is desirable that lower layers provide
for non-duplication, this is not a requirement." CoAP provides a
non-duplicated stream of packets and accomplishes the desirable non-
duplication. In addition, [RFC3748] says that when EAP runs over a
reliable lower layer "the authenticator retransmission timer SHOULD
be set to an infinite value, so that retransmissions do not occur at
the EAP layer."
7.2. Size of the EAP Lower Layer vs. EAP Method Size
Regarding the impact that an EAP lower layer will have on the number
of bytes of the whole authentication exchange, [CoAP-EAP] provides a
comparison with another network-layer-based EAP lower layer, the
Protocol for Carrying Authentication for Network Access (PANA) as
defined in [RFC5191].
The EAP method being transported will take most of the exchange.
However, the impact of the EAP lower layer cannot be ignored,
especially in very constrained communication technologies such as
those with limited capabilities (e.g., as can be found in IoT
networks).
Note: For scenarios involving To improve efficiency in environments with constrained devices
and networks, the
use of the latest versions of EAP methods (e.g., EAP-AKA'
[RFC5448], EAP-TLS 1.3 [RFC9190]) is are recommended in favor of over older versions with
the goal of economizing, or
versions. EAP methods more adapted for IoT networks (e.g., EAP-NOOB
[RFC9140], EAP-EDHOC [EAP-EDHOC], etc.). etc.) are also recommended.
8. Security Considerations
Security aspects to be considered include how authorization is
managed, the use of the MSK as key material, and how trust in the EAP
authenticator is established. Additional considerations such as EAP
channel binding as per [RFC6677] are also discussed here.
8.1. Use of EAP Methods
This document limits the use of EAP methods to those compliant with
[RFC4017], yielding strong and fresh session keys such as the MSK.
By this assumption, the HKDF-Expand function is used directly, as
clarified in [RFC5869].
8.2. Authorization
Authorization is part of bootstrapping. It serves to establish
whether the EAP peer can join and the set of conditions it must
adhere to. The authorization data will be gathered from the
organization that is responsible for the EAP peer and sent to the EAP
authenticator if a AAA infrastructure is deployed.
In standalone mode, the authorization information will be in the EAP
authenticator. If pass-through mode is used, authorization data
received from the AAA server can be delivered by the AAA protocol
(e.g., RADIUS or Diameter). Providing more fine-grained
authorization data can be done by transporting the data using the
Security Assertion Markup Language (SAML) in RADIUS [RFC7833]. After
bootstrapping, additional authorization information may be needed to
operate in the security domain. This can be taken care of by the
solutions proposed in the Authentication and Authorization for
Constrained Environments (ACE) WG, such as the use of OAuth
[RFC9200], among other solutions, to provide ACE.
8.3. Allowing CoAP-EAP Traffic to Perform Authentication
Since CoAP is an application protocol, CoAP-EAP assumes certain IP
connectivity in the link between the EAP peer and the EAP
authenticator to run. This link MUST only authorize exclusively unprotected IP
traffic to be sent between the EAP peer and the EAP authenticator
during the authentication with CoAP-EAP. Once the authentication is
successful, the key material generated by the EAP authentication
(MSK) and any other traffic can be authorized if it is protected. It
is worth noting that if the EAP authenticator is not in the same link
as the EAP peer and an intermediate entity (i.e., (e.g., a CoAP proxy) helps
with this process, this concept also applies to the communication
between the EAP peer and the intermediary.
Alternatively, the link layer MAY provide support to transport CoAP-
EAP without an IP address by using link-layer frames (e.g., by
defining a new Key Management Protocol ID per IEEE 802.15.9
[IEEE802159]).
8.4. Freshness of the Key Material
In CoAP-EAP, there is no nonce exchange to provide freshness to the
keys derived from the MSK. The MSKs and EMSKs are fresh key material
per [RFC5247]. Since only one authentication is established per EAP
authenticator, there is no need to generate additional key material.
If a new MSK is required, a re-authentication can be done by running
the process again or using a more lightweight EAP method to derive
additional key material as elaborated in Section 3.3.
8.5. Channel-Binding Support
According to [RFC6677], channel binding, as related to EAP, is sent
through the EAP method supporting it.
To satisfy the requirements of the this document, the EAP lower-layer
identifier (assigned for CoAP-EAP (10, as assigned by IANA) IANA; see Section 9.4)
needs to be sent, in the EAP Lower-
Layer Lower-Layer Attribute if RADIUS is used.
8.6. Additional Security Considerations
In the authentication process, it is possible for an entity to forge
messages to generate denial-of-service (DoS) attacks on any of the
entities involved. For instance, an attacker can forge multiple
initial messages to start an authentication (Step 0) 0 in Figure 3) with
the EAP authenticator as if they were sent by different EAP peers.
Consequently, the EAP authenticator will start an authentication
process for each message received in Step 0, sending the EAP Request/
Id EAP-Request/
Identity (Step 1).
To minimize the effects of this DoS attack, it is RECOMMENDED that
the EAP authenticator limit the rate at which it processes incoming
messages in Step 0 to provide robustness against DoS attacks. The
details of rate limiting are outside the scope of this specification.
Nevertheless, the rate of these messages is also limited by the
bandwidth available between the EAP peer and the EAP authenticator.
This bandwidth will be especially limited in constrained links (e.g.,
Low-Power WANs (LPWANs)). Lastly, it is also RECOMMENDED to reduce
at a minimum the state in the EAP authenticator at least until the
EAP Response/Id
EAP-Response/Identity is received by the EAP authenticator.
Another security-related concern is how to ensure that the EAP peer
joining the security domain can trust the EAP authenticator. This
issue is elaborated in [RFC5247]. In particular, the EAP peer knows
it can trust the EAP authenticator because the key that is used to
establish the security association is derived from the MSK. If the
EAP authenticator has the MSK, it is because the AAA server of the
EAP peer trusted the EAP authenticator.
9. IANA Considerations
9.1. CoAP-EAP Cipher Suites
IANA has created a new registry titled "CoAP-EAP Cipher Suites" under
a new registry group named "CoAP-EAP Protocol". "CoAP-EAP". The registration procedures
are "Specification Required", "Private Use", and "Standards Action
with Expert Review" (see [RFC8126]), as shown in Table 1.
+===============+=====================================+
| Range | Registration Procedures |
+===============+=====================================+
| -65536 to -25 | Specification Required |
+---------------+-------------------------------------+
| -24 to -21 | Private Use |
+---------------+-------------------------------------+
| -20 to 23 | Standards Action with Expert Review |
+---------------+-------------------------------------+
| 24 to 65535 | Specification Required |
+---------------+-------------------------------------+
Table 1: Registration Procedures for CoAP-EAP
Cipher Suites
The columns of the registry are Value, Algorithms, Description, and
Reference, where Value is an integer and the other columns are text
strings. The initial registrations are shown in Table 2.
+=======+============+=============================+===========+
| Value | Algorithms | Description | Reference |
+=======+============+=============================+===========+
| 0 | 10, -16 | AES-CCM-16-64-128, SHA-256 | RFC 9820 |
+-------+------------+-----------------------------+-----------+
| 1 | 1, -16 | A128GCM, SHA-256 | RFC 9820 |
+-------+------------+-----------------------------+-----------+
| 2 | 3, -43 | A256GCM, SHA-384 | RFC 9820 |
+-------+------------+-----------------------------+-----------+
| 3 | 24, -16 | ChaCha20/Poly1305, SHA-256 | RFC 9820 |
+-------+------------+-----------------------------+-----------+
| 4 | 24, -45 | ChaCha20/Poly1305, SHAKE256 | RFC 9820 |
+-------+------------+-----------------------------+-----------+
Table 2: CoAP-EAP Cipher Suites: Initial Registrations
9.2. CDDL in CoAP-EAP Information Elements
IANA has created a new registry titled "CoAP-EAP Information
Elements" under a new registry group named "CoAP-EAP Protocol". "CoAP-EAP". The
registration procedures are "Standards Action with Expert Review",
"Private Use", "Specification Required", and "Experimental Use" (see
[RFC8126]), as shown in Table 3.
+================+=====================================+
| Range | Registration Procedures |
+================+=====================================+
| 0 to 23 | Standards Action with Expert Review |
+----------------+-------------------------------------+
| 24 to 49 | Private Use |
+----------------+-------------------------------------+
| 50 to 65000 | Specification Required |
+----------------+-------------------------------------+
| 65001 to 65535 | Experimental Use |
+----------------+-------------------------------------+
Table 3: Registration Procedures for CoAP-EAP
Information Elements
The columns of the registry are Name, Label, CBOR Type, Description,
and Reference, where Label is an integer and the other columns are
text strings. The initial registrations are shown in Table 4.
+==================+=======+========+===============+===========+
| Name | Label | CBOR | Description | Reference |
| | | Type | | |
+==================+=======+========+===============+===========+
| Cipher Suite | 1 | CBOR | List of the | RFC 9820 |
| | | Array | proposed or | |
| | | | selected COSE | |
| | | | algorithms | |
| | | | for OSCORE | |
+------------------+-------+--------+---------------+-----------+
| RID-C | 2 | Byte | Contains the | RFC 9820 |
| | | String | Recipient ID | |
| | | | of the EAP | |
| | | | authenticator | |
+------------------+-------+--------+---------------+-----------+
| RID-I | 3 | Byte | Contains the | RFC 9820 |
| | | String | Recipient ID | |
| | | | of the EAP | |
| | | | peer | |
+------------------+-------+--------+---------------+-----------+
| Session-Lifetime | 4 | uint | Contains the | RFC 9820 |
| | | | time that the | |
| | | | session is | |
| | | | valid, in | |
| | | | seconds | |
+------------------+-------+--------+---------------+-----------+
Table 4: CoAP-EAP Information Elements: Initial Registrations
9.3. The Well-Known URIs Registry
IANA has added the well-known URI "coap-eap" to the "Well-Known URIs"
registry under the "Well-Known URIs" registry group defined by
[RFC8615].
URI Suffix: coap-eap
Reference: RFC 9820
Status: permanent
Change Controller: IETF
9.4. The EAP Lower Layers Registry
IANA has added the identifier "CoAP-EAP" to the "EAP Lower Layers"
registry (defined by [RFC6677]) under the "Extensible Authentication
Protocol (EAP) Registry".
Value: 10
Lower Layer: CoAP-EAP
Reference: RFC 9820
9.5. Media Types Registry
IANA has added the media type "application/coap-eap" to the "Media
Types" registry. Section 4 defines the format.
Type name: application
Subtype name: coap-eap
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See Section 8 of RFC 9820.
Interoperability considerations: N/A
Published specification: RFC 9820
Applications that use this media type: To be identified
Fragment identifier considerations: N/A
Additional information:
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person and email address to contact for further information:
ace@ietf.org
Intended usage: COMMON
Restrictions on usage: N/A
Author: See the "Authors' Addresses" section of RFC 9820.
Change Controller: IETF
9.6. CoAP Content-Formats Registry
IANA has added the media type "application/coap-eap" to the "CoAP
Content-Formats" registry under the "Constrained RESTful Environments
(CoRE) Parameters" registry group, following the specification in
Section 12.3 of [RFC7252].
+======================+==================+=====+===========+
| Media Type | Content Encoding | ID | Reference |
+======================+==================+=====+===========+
| application/coap-eap | - | 269 | RFC 9820 |
+----------------------+------------------+-----+-----------+
Table 5: CoAP Content-Formats Registry
9.7. Resource Type (rt=) Link Target Attribute Values Registry
IANA has added the resource type "core.coap-eap" to the "Resource
Type (rt=) Link Target Attribute Values" registry under the
"Constrained RESTful Environments (CoRE) Parameters" registry group.
+===============+===================+===========+
| Value | Description | Reference |
+===============+===================+===========+
| core.coap-eap | CoAP-EAP resource | RFC 9820 |
+---------------+-------------------+-----------+
Table 6: Resource Type (rt=) Link Target
Attribute Values Registry
9.8. Expert Review Instructions
The IANA registries established in this document apply the
"Specification Required", "Private Use", "Standards Action with
Expert Review", and "Experimental Use" policies. (See also
[RFC8126].) This section provides general guidelines for what
experts should focus on, but as they are designated experts for a
reason, they should be granted flexibility.
* When defining the use of CoAP-EAP Information Elements (IEs),
experts are expected to evaluate how the values are defined, their
scope, and whether they align with CoAP-EAP's functionality and
constraints. They are expected to assess whether the values are
clear, well structured, and follow CoAP and CoAP-EAP conventions,
such as concise encoding for constrained environments. They
should ensure that these IEs can seamlessly integrate with
existing CoAP implementations and extensions. Experts are also
expected to verify that IE values are protected from unauthorized
modification or misuse during transmission.
* When adding new cipher suites, experts must ensure that algorithm
values are sourced from the appropriate registry when required.
They should also consider seeking input from relevant IETF working
groups regarding the accuracy of registered parameters.
10. References
10.1. Normative References
[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>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<https://www.rfc-editor.org/info/rfc3748>.
[RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
RFC 5247, DOI 10.17487/RFC5247, August 2008,
<https://www.rfc-editor.org/info/rfc5247>.
[RFC6677] Hartman, S., Ed., Clancy, T., and K. Hoeper, "Channel-
Binding Support for Extensible Authentication Protocol
(EAP) Methods", RFC 6677, DOI 10.17487/RFC6677, July 2012,
<https://www.rfc-editor.org/info/rfc6677>.
[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>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[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>.
[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/info/rfc8323>.
[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>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
10.2. Informative References
[CoAP-EAP] Garcia-Carrillo, D. and R. Marin-Lopez, "Lightweight CoAP-
Based Bootstrapping Service for the Internet of Things",
Sensors, vol. 16, no. 3, DOI 10.3390/s16030358, 2016,
<https://www.mdpi.com/1424-8220/16/3/358>.
[EAP-EDHOC]
Garcia-Carrillo, D., Marin-Lopez, R., Selander, G., Preuß
Mattsson, J., and F. Lopez-Gomez, "Using the Extensible
Authentication Protocol (EAP) with Ephemeral Diffie-
Hellman over COSE (EDHOC)", Work in Progress, Internet-
Draft, draft-ietf-emu-eap-edhoc-04, 4 June 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-emu-eap-
edhoc-04>.
[EAP-Framework-IoT]
Sethi, M. and T. Aura, "Secure Network Access
Authentication for IoT Devices: EAP Framework vs.
Individual Protocols", IEEE Communications Standards
Magazine, vol. 5, no. 3, pp. 34-39,
DOI 10.1109/MCOMSTD.201.2000088, 2021,
<https://ieeexplore.ieee.org/document/9579387>.
[IEEE802159]
IEEE, "IEEE Standard for Transport of Key Management
Protocol (KMP) Datagrams", IEEE Std 802.15.9-2021,
DOI 10.1109/IEEESTD.2022.9690134, January 2022,
<https://doi.org/10.1109/IEEESTD.2022.9690134>.
[LO-CoAP-EAP]
Garcia-Carrillo, D., Marin-Lopez, R., Kandasamy, A., and
A. Pelov, "A CoAP-Based Network Access Authentication
Service for Low-Power Wide Area Networks: LO-CoAP-EAP",
Sensors, vol. 17, no. 11, DOI 10.3390/s17112646, 2017,
<https://www.mdpi.com/1424-8220/17/11/2646>.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, DOI 10.17487/RFC4017, March
2005, <https://www.rfc-editor.org/info/rfc4017>.
[RFC4137] Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba,
"State Machines for Extensible Authentication Protocol
(EAP) Peer and Authenticator", RFC 4137,
DOI 10.17487/RFC4137, August 2005,
<https://www.rfc-editor.org/info/rfc4137>.
[RFC4186] Haverinen, H., Ed. and J. Salowey, Ed., "Extensible
Authentication Protocol Method for Global System for
Mobile Communications (GSM) Subscriber Identity Modules
(EAP-SIM)", RFC 4186, DOI 10.17487/RFC4186, January 2006,
<https://www.rfc-editor.org/info/rfc4186>.
[RFC4764] Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: A
Pre-Shared Key Extensible Authentication Protocol (EAP)
Method", RFC 4764, DOI 10.17487/RFC4764, January 2007,
<https://www.rfc-editor.org/info/rfc4764>.
[RFC5191] Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H.,
and A. Yegin, "Protocol for Carrying Authentication for
Network Access (PANA)", RFC 5191, DOI 10.17487/RFC5191,
May 2008, <https://www.rfc-editor.org/info/rfc5191>.
[RFC5433] Clancy, T. and H. Tschofenig, "Extensible Authentication
Protocol - Generalized Pre-Shared Key (EAP-GPSK) Method",
RFC 5433, DOI 10.17487/RFC5433, February 2009,
<https://www.rfc-editor.org/info/rfc5433>.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, DOI 10.17487/RFC5448, May 2009,
<https://www.rfc-editor.org/info/rfc5448>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC6696] Cao, Z., He, B., Shi, Y., Wu, Q., Ed., and G. Zorn, Ed.,
"EAP Extensions for the EAP Re-authentication Protocol
(ERP)", RFC 6696, DOI 10.17487/RFC6696, July 2012,
<https://www.rfc-editor.org/info/rfc6696>.
[RFC7833] Howlett, J., Hartman, S., and A. Perez-Mendez, Ed., "A
RADIUS Attribute, Binding, Profiles, Name Identifier
Format, and Confirmation Methods for the Security
Assertion Markup Language (SAML)", RFC 7833,
DOI 10.17487/RFC7833, May 2016,
<https://www.rfc-editor.org/info/rfc7833>.
[RFC7967] Bhattacharyya, A., Bandyopadhyay, S., Pal, A., and T.
Bose, "Constrained Application Protocol (CoAP) Option for
No Server Response", RFC 7967, DOI 10.17487/RFC7967,
August 2016, <https://www.rfc-editor.org/info/rfc7967>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static
Context Header Compression (SCHC) for the Constrained
Application Protocol (CoAP)", RFC 8824,
DOI 10.17487/RFC8824, June 2021,
<https://www.rfc-editor.org/info/rfc8824>.
[RFC9031] Vučinić, M., Ed., Simon, J., Pister, K., and M.
Richardson, "Constrained Join Protocol (CoJP) for 6TiSCH",
RFC 9031, DOI 10.17487/RFC9031, May 2021,
<https://www.rfc-editor.org/info/rfc9031>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/info/rfc9053>.
[RFC9140] Aura, T., Sethi, M., and A. Peltonen, "Nimble Out-of-Band
Authentication for EAP (EAP-NOOB)", RFC 9140,
DOI 10.17487/RFC9140, December 2021,
<https://www.rfc-editor.org/info/rfc9140>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and
P. van der Stok, "Constrained RESTful Environments (CoRE)
Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April
2022, <https://www.rfc-editor.org/info/rfc9176>.
[RFC9190] Preuß Mattsson, J. and M. Sethi, "EAP-TLS 1.3: Using the
Extensible Authentication Protocol with TLS 1.3",
RFC 9190, DOI 10.17487/RFC9190, February 2022,
<https://www.rfc-editor.org/info/rfc9190>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/info/rfc9200>.
[THREAD] Thread Group, Kumar, S. and E. Dijk, "Thread Specification 1.3", 2023. 1.4 Features White Paper",
September 2024,
<https://www.threadgroup.org/Portals/0/Documents/
Thread_1.4_Features_White_Paper_September_2024.pdf>.
[TS133.501]
ETSI, "5G; Security architecture and procedures for 5G
System", V15.2.0, V18.9.0, ETSI TS 133 501, 2018.
[ZigbeeIP] Zigbee Alliance, "Zigbee IP Specification (Zigbee Document
095023r34)", 2014. April 2025,
<https://www.etsi.org/deliver/
etsi_ts/133500_133599/133501/18.09.00_60/
ts_133501v180900p.pdf>.
Appendix A. Flow of Operation (DTLS Establishment)
CoAP-EAP makes it possible to derive a Pre-Shared Key (PSK) from the
MSK to allow (D)TLS PSK-based authentication between the EAP peer and
the EAP authenticator instead of using OSCORE. In the case of using
(D)TLS to establish a security association, there is a limitation on
the use of intermediaries between the EAP peer and the EAP
authenticator, as (D)TLS breaks the end-to-end communications when
using intermediaries such as proxies.
Figure 9 shows the last steps of the flow of operation for CoAP-EAP
when (D)TLS is used to protect the communication between the EAP peer
and the EAP authenticator using the keying material exported by the
EAP authentication. The general flow is essentially the same as in
the case of OSCORE, except that DTLS negotiation is established in
Step 7. Once DTLS negotiation has finished successfully, the EAP
peer is granted access to the domain. Step 7 MUST be interpreted by
the EAP peer as an alternate success indication, which will end up
with the MSK and the DTLS_PSK derivation for the (D)TLS
authentication based on the PSK.
EAP peer EAP authenticator
------------- -------------
...
| 2.01 Created Location-Path [/a/eap/(n)] |
| Payload (EAP-X Resp) Payload(EAP-X-Resp) |
6) |---------------------------------------->|
6)|---------------------------------------->|
| | MSK
| (D)TLS 1.3 Client Hello | |
MSK 7) |<----------------------------------------| V 7)|<----------------------------------------| v
| | | DTLS_PSK
V |===============DTLS handshake============|
v |============= DTLS handshake ============|
DTLS_PSK | |
<-(Protected
<-- Protected with (D)TLS)-> (D)TLS -->
Figure 9: CoAP-EAP Flow of Operation with DTLS
According to [RFC8446], the provision of the PSK out of band also
requires the provision of the KDF hash algorithm and the PSK
identity. To simplify the design in CoAP-EAP, the KDF hash algorithm
can be included in the list of cipher suites exchanged in Steps 1 and
2 (Figure 8) if DTLS one wants to be used use DTLS instead of OSCORE. For the
same reason, the PSK identity is derived from (RID-C) (RID-I) RID-C || RID-I as
defined in Appendix A.1.
Analogous to how the cipher suite is negotiated for OSCORE
(Section 6.1), the EAP authenticator sends a list, in decreasing
order of preference, with the identifiers of the hash algorithms
supported (Step 1). In the response, the EAP peer sends its choice.
This list is included in the payload after the EAP message with a
CBOR array that contains the cipher suites. This CBOR array is
enclosed as one of the elements of the CBOR Object used for
transporting information in CoAP-EAP (see Section 5). An example of
how the fields are arranged in the CoAP payload can be seen in
Figure 7.
If there is no CBOR array specifying the cipher suites, the default
cipher suites are applied. If the EAP authenticator sends a
restricted list of cipher suites that can be accepted, it MUST
include the default value 0, since it is mandatory to implement. The
EAP peer will have at least that option available.
For DTLS, the negotiated cipher suite is used to determine the hash
function to be used to derive the "DTLS PSK" "DTLS_PSK" from the MSK. The
following hash algorithms are considered: considered in cases where the
specification includes DTLS support in the future (TLS_SHA256,
TLS_SHA384, TLS_SHA512):
* 5) TLS_SHA256
* 6) TLS_SHA384
* 7) TLS_SHA512
The inclusion of these values, apart from indicating the hash
algorithm, indicates that the EAP authenticator intends to establish
an OSCORE security association or a DTLS security association after
the authentication is completed. If both options appear in the
cipher suite negotiation, the OSCORE security association will be
preferred over DTLS.
A.1. Deriving DTLS PSK DTLS_PSK and Identity
To enable DTLS after an EAP authentication, Identity and the PSK for
DTLS are defined. Identity in this case is generated by
concatenating the exchanged Sender ID and the Recipient ID.
CoAP-EAP PSK Identity = RID-C || RID-I
It is also possible to derive a PSK for DTLS [RFC9147], referred to
here as "DTLS PSK", "DTLS_PSK", from the MSK between both the EAP peer and EAP
authenticator if required. The length of the DTLS PSK DTLS_PSK will depend on
the cipher suite. To have keying material with sufficient length, a
key of 32 bytes is derived that can be truncated later if needed:
DTLS PSK
DTLS_PSK = KDF(MSK, "CoAP-EAP DTLS PSK", DTLS_PSK", length)
where:
* The MSK is exported by the EAP method.
* "CoAP-EAP DTLS PSK" DTLS_PSK" is the ASCII code representation of the non-
NULL-terminated string (excluding the double quotes around it).
* length is the size of the output key material.
Appendix B. Using CoAP-EAP for Distributing Key Material for IoT
Networks
Similarly to the example in Appendix A.1, where a shared key PSK for DTLS is
derived, it is possible to provide key material to different link
layers after the CoAP-EAP authentication is complete.
For example, CoAP-EAP could be used to derive the PSK required to run
the Constrained Join Protocol (CoJP) for IPv6 over the TSCH mode of
IEEE 802.15.4e (6TiSCH) [RFC9031]. ("TSCH" stands for "Time-Slotted
Channel Hopping".)
Another example would be when a shared Network Key is required by the
devices that join a network. An example of this Network Key can be
found in Zigbee IP [ZigbeeIP] or the THREAD protocol [THREAD]. After CoAP-EAP execution, a
security association based on OSCORE protects any exchange between
the EAP peer and the EAP authenticator. This security association
can be used for distributing the Network Key securely and other
required parameters. How the Network Key is distributed after a
successful CoAP-EAP authentication is outside the scope of this
document.
How a particular link-layer technology uses the MSK to derive further
key material for protecting the link layer or uses OSCORE protection
to distribute key material is outside the scope of this document.
Appendix C. Example Use Case Scenarios
In IoT networks, for an EAP peer to act as a trustworthy entity
within a security domain, certain key material needs to be shared
between the EAP peer and the EAP authenticator.
Next, examples of different use case scenarios will be elaborated on
as related to the usage of CoAP-EAP.
Generally, four entities are involved:
* Two EAP peers (A and B).
* One EAP authenticator (C). The EAP authenticator manages a domain
where EAP peers can be deployed. In IoT networks, it can be
considered a more powerful machine than the EAP peers.
* One AAA server. Optional. The AAA server is not constrained.
Here, the EAP authenticator is operating in pass-through mode.
Generally, any EAP peer wanting to join the domain managed by the EAP
authenticator MUST perform a CoAP-EAP authentication with the EAP
authenticator (C). This authentication MAY involve an external AAA
server. This means that the EAP peers (A and B), once deployed, will
run CoAP-EAP once, as a bootstrapping phase, to establish a security
association with C. Moreover, any other entity that wants to join
and establish communications with EAP peers under C's domain must
also do the same.
By using EAP, the flexibility of having different types of
credentials can be achieved. For instance, if a device that is not
battery dependent and not very constrained is available, a heavier
authentication method could be used. With varied EAP peers and
networks, authentication methods that are more lightweight (e.g.,
EAP-NOOB [RFC9140], EAP-AKA' [RFC5448], EAP-PSK [RFC4764], EAP-EDHOC
[EAP-EDHOC], etc.) and are able to adapt to different types of
devices according to organization policies or device capabilities
might need to be used.
C.1. Example 1: CoAP-EAP Using ACE
When using ACE, the process of client registration and provisioning
of credentials to the client is not specified. The process of client
registration and provisioning can be achieved using CoAP-EAP. Once
the process of authentication with EAP is completed, the fresh key
material is shared between the EAP peer and the EAP authenticator.
With ACE, the EAP authenticator and the Authorization Server (AS) can
be co-located.
Next, a general way to exemplify how client registration can be
performed using CoAP-EAP is presented, to allow two EAP peers (A and
B) to communicate and interact after a successful client
registration.
EAP peer A wants to communicate with EAP peer B (e.g., to activate a
light switch). The overall process is divided into three phases.
* In the first phase, EAP peer A does not yet belong to EAP
authenticator C's domain. Then, it communicates with C and
authenticates with CoAP-EAP, which, optionally, communicates with
the AAA server to complete the authentication process. If the
authentication is successful, a fresh MSK is shared between C and
EAP peer A. This key material allows EAP peer A to establish a
security association with C. Some authorization information may
also be provided in this step. If EAP is used in standalone mode,
the AS itself, having information about the devices, can be the
entity providing said authorization information.
If authentication and authorization are correct, EAP peer A is
enrolled in EAP authenticator C's domain for some period of time.
In particular, [RFC5247] recommends 8 hours, though the entity
providing the authorization information can establish this
lifetime. In the same manner, B needs to perform the same process
with CoAP-EAP to be part of EAP authenticator C's domain.
* In the second phase, when EAP peer A wants to talk to EAP peer B,
it contacts EAP authenticator C for authorization to access EAP
peer B and obtain all the required information to do that securely
(e.g., keys, tokens, authorization information, etc.). This phase
does NOT require the usage of CoAP-EAP. The details of this phase
are outside the scope of this document; the ACE framework is used
for this purpose. See [RFC9200].
* In the third phase, EAP peer A can access EAP peer B with the
credentials and information obtained from EAP authenticator C
during the second phase. This access can be repeated without
contacting the EAP authenticator, while as long as the credentials given
to A are still valid. The details of this phase are outside the
scope of this document.
It is worth noting that the first phase with CoAP-EAP is required to join EAP authenticator C's domain. domain, the
first phase (authentication via CoAP-EAP) is required. Once it is
performed successfully, the communications are local to EAP
authenticator C's domain and there is no need to perform a new EAP
authentication as long as the key material is still valid. When the
keys are about to expire, the EAP peer can engage in a re-authentication re-
authentication to renew the key material, as explained in
Section 3.3.
C.2. Example 2: Multiple Domains with AAA Infrastructures
A device (A) of the domain acme.org uses a specific kind of
credential (e.g., AKA) and intends to join the um.es domain. This user does not
belong to this domain, for which it first performs a client
registration using CoAP-EAP. To do this, it interacts with the EAP
authenticator's domain, which in turn communicates with a AAA
infrastructure (acting as a AAA client). Through Then, the local AAA server communicate
communicates with the home AAA server to complete the
authentication and integrate authentication.
This way, the device can be considered as a trustworthy entity into within
EAP authenticator C's domain. In this scenario, the AS, in the role
of the EAP authenticator, receives the key material from the AAA
infrastructure.
C.3. Example 3: Single Domain with a AAA Infrastructure
In this scenario, a university campus has several faculty buildings,
where each building has its criteria or policies in place to manage
EAP peers under an AS. All buildings belong to the same domain
(e.g., um.es). All these buildings are managed with a AAA
infrastructure. A new device (A) with credentials from the domain
(e.g., um.es) will be able to perform the device registration with an
EAP authenticator (C) of any building if they are managed by the same
general domain.
C.4. Example 4: Single Domain Without a AAA Infrastructure
In another case, without a AAA infrastructure, with an EAP
authenticator that has co-located the EAP server, and using EAP
standalone mode, all the devices can be managed within the same
domain locally. Client registration of an EAP peer (A) with a
Controller (C) can also be performed in the same manner.
C.5. Other Use Cases
C.5.1. CoAP-EAP for Network Access Authentication
One of the first steps for an EAP peer is to perform the
authentication to gain access to the network. To do so, the device
must first be authenticated and granted authorization to gain access
to the network. Additionally, security parameters such as
credentials can be derived from the authentication process, allowing
the trustworthy operation of the EAP peer in a particular network by
joining the security domain. By using EAP, this can be achieved with
flexibility and scalability, because of the different EAP methods
available and the ability to rely on AAA infrastructures if needed to
support multi-domain scenarios, which is a key feature when the EAP
peers deployed under the same security domain belong, for example, to
different organizations.
The following two cases apply to the process of joining a network:
1) the node has an IPv6 address (e.g., link-local IPv6 or IPv6 global
address) and 2) the node does not have an IPv6 address.
In networks where the device is in place but no IP support is
available until the EAP peer is authenticated, specific support for
this EAP lower layer has to be defined to allow CoAP-EAP messages to
be exchanged between the EAP peer and the EAP authenticator. For
example, in IEEE 802.15.4 networks, a new Key Management Protocol
(KMP) ID can be defined to add such support in the case of IEEE
802.15.9 [IEEE802159], where it can be assumed that the device has at
least a link-layer IPv6 address.
When the EAP peer intends to be admitted into the network, it would
search for an entity that offers the CoAP-EAP service, be it directly
via the EAP authenticator or through an intermediary (i.e., (e.g., proxy).
See Section 3.1.
CoAP-EAP will run between the EAP peer and the EAP authenticator or
through an intermediary entity such as a proxy, as happens in a mesh
network, where the EAP authenticator could be placed one or more hops
away from the EAP peer. In the case that a proxy participates in
CoAP-EAP, it will be because it is already a trustworthy entity
within the domain and communicates through a secure channel with the
EAP authenticator, as illustrated by Figure 10.
If the EAP peer cannot connect to the EAP authenticator directly, the
EAP peer can follow the same process as that described in Section 3.6
to perform the authentication (i.e., can connect via an intermediary
entity (proxy) (e.g., proxy) that is already part of the network (already
shares key material and communicates through a secure channel with
the authenticator) and can aid in running CoAP-EAP).
When CoAP-EAP is completed and the OSCORE security association is
established with the EAP authenticator, the EAP peer receives the
local configuration parameters for the network (e.g., a network key) Network Key)
and can configure a global IPv6 address. Moreover, there is no need
for a CoAP proxy an intermediary entity after a successful authentication.
For removal, if the EAP authenticator decides to remove a particular
EAP peer from the network or the peer itself intends to leave, either
the EAP peer or the EAP authenticator can directly send a DELETE
command to explicitly express that the network access state is
removed, and the device will no longer belong to the network. Thus,
any state related to the EAP peer is removed in the EAP
authenticator. Forced removal can be done by sending new specific
key material to the devices that still belong to the network,
excluding the removed device, following a model similar to CoJP for
6TiSCH [RFC9031] or Zigbee IP [ZigbeeIP]. [RFC9031]. The specifics on how this process is to be done
are outside the scope of this document.
+-------+ +--------+ +--------------+
| EAP | | CoAP | | EAP |
| peer |<------>| proxy |<------------------------->| authenticator|
+-------+ CoAP +--------+ CoAP +--------------+
OSCORE/DTLS
<--(security association)-->
<-- security association -->
Figure 10: CoAP-EAP Through CoAP Proxy
Given that EAP is also used for network access authentication, this
service can be adapted to other technologies -- for instance, to
provide network access control to very constrained technologies
(e.g., Long Range (LoRa) networks). The authors of [LO-CoAP-EAP]
provide a study of a minimal version of CoAP-EAP for LPWANs, with
interesting results. In this specific case, compression as provided
by Static Context Header Compression (SCHC) for CoAP [RFC8824] can be
leveraged.
C.5.2. CoAP-EAP for Service Authentication
It is not uncommon that the infrastructure where the device is
deployed and the services of the EAP peer are managed by different
organizations. Therefore, in addition to the authentication for
network access control, the possibility of a secondary authentication
to access different services has to be considered. This process of
authentication, for example, will provide the necessary key material
to establish a secure channel and interact with the entity in charge
of granting access to different services.
In 5G, for example, consider primary and secondary authentication
using EAP [TS133.501].
Acknowledgments
We would like to thank the reviewers of this work: Paul Wouters,
Heikki Vatiainen, Josh Howlett, Deb Cooley, Eliot Lear, Alan DeKok,
Carsten Bormann, Mohit Sethi, Benjamin Kaduk, Christian Amsüss, John
Preuß Mattsson, Göran Selander, Alexandre Petrescu, Pedro Moreno-
Sanchez, and Eduardo Ingles-Sanchez.
We would also like to thank Gabriel Lopez-Millan for the first review
of this document, Ivan Jimenez-Sanchez for the first proof-of-concept
implementation of this idea, Julian Niklas Schimmelpfennig for the
implementation of the Erbium-based IoT device implementation, and
Daniel Menendez Gonzalez for the Python implementation.
Thanks also to Alexander Pelov and Laurent Toutain for their valuable
comments, especially regarding the potential optimizations of CoAP-
EAP.
This work was supported in part by Grant PID2020-112675RB-C44 funded
by MCIN/AEI/10.13039/5011000011033 (ONOFRE-3-UMU) and in part by the
H2020 EU project IoTCrawler under contract 779852.
Authors' Addresses
Rafa Marin-Lopez
University of Murcia
Campus de Espinardo S/N, Faculty of Computer Science
30100 Murcia
Spain
Email: rafa@um.es
Dan Garcia-Carrillo
University of Oviedo
Calle Luis Ortiz Berrocal S/N, Edificio Polivalente
33203 Gijon Asturias
Spain
Email: garciadan@uniovi.es