Lightweight Authorization for EDHOC
draft-selander-lake-authz-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|
|---|---|---|---|
| Authors | Göran Selander , John Preuß Mattsson , Mališa Vučinić , Michael Richardson , Aurelio Schellenbaum | ||
| Last updated | 2022-10-19 | ||
| Replaced by | draft-ietf-lake-authz | ||
| RFC stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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| IESG | IESG state | I-D Exists | |
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draft-selander-lake-authz-00
LAKE Working Group G. Selander
Internet-Draft J. Preuß Mattsson
Intended status: Standards Track Ericsson AB
Expires: 22 April 2023 M. Vučinić
INRIA
M. Richardson
Sandelman Software Works
A. Schellenbaum
ZHAW
19 October 2022
Lightweight Authorization for EDHOC
draft-selander-lake-authz-00
Abstract
This document describes a procedure for augmenting the lightweight
authenticated Diffie-Hellman key exchange protocol EDHOC with third
party assisted authorization, targeting constrained IoT deployments
(RFC 7228).
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 22 April 2023.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Description . . . . . . . . . . . . . . . . . . . . . 3
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Device (U) . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Domain Authenticator (V) . . . . . . . . . . . . . . . . 4
3.3. Authorization Server (W) . . . . . . . . . . . . . . . . 5
4. The Protocol . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Reuse of EDHOC . . . . . . . . . . . . . . . . . . . . . 6
4.3. Device <-> Authorization Server (U <-> W) . . . . . . . . 8
4.4. Device <-> Authenticator (U <-> V) . . . . . . . . . . . 10
4.5. Authenticator <-> Authorization Server (V <-> W) . . . . 12
5. REST Interface at W . . . . . . . . . . . . . . . . . . . . . 14
5.1. HTTP URIs . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2. Voucher Request (/voucherrequest) . . . . . . . . . . . . 14
5.3. Certificate Request (/certrequest) . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. EDHOC External Authorization Data Registry . . . . . . . 16
7.2. The Well-Known URI Registry . . . . . . . . . . . . . . . 16
7.3. Well-Known Name Under ".arpa" Name Space . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Use with Constrained Join Protocol (CoJP) . . . . . 19
A.1. Network discovery . . . . . . . . . . . . . . . . . . . . 19
A.2. The enrollment protocol with parameter provisioning . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
For constrained IoT deployments [RFC7228] the overhead and processing
contributed by security protocols may be significant which motivates
the specification of lightweight protocols that are optimizing, in
particular, message overhead (see [I-D.ietf-lake-reqs]). This
document describes a procedure for augmenting the lightweight
authenticated Diffie-Hellman key exchange EDHOC [I-D.ietf-lake-edhoc]
with third party-assisted authorization.
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The procedure involves a device, a domain authenticator and an
authorization server. The device and authenticator perform mutual
authentication and authorization, assisted by the authorization
server which provides relevant authorization information to the
device (a "voucher") and to the authenticator.
The protocol assumes that authentication between device and
authenticator is performed with EDHOC, and defines the integration of
a lightweight authorization procedure using the External
Authorization Data (EAD) field defined in EDHOC.
In this document we consider the target interaction for which
authorization is needed to be "enrollment", for example joining a
network for the first time (e.g. [RFC9031]), but it can be applied
to authorize other target interactions.
The protocol enables a low message count by performing authorization
and enrollment in parallel with authentication, instead of in
sequence which is common for network access. It further reuses
protocol elements from EDHOC leading to reduced message sizes on
constrained links.
This protocol is applicable to a wide variety of settings, and can be
mapped to different authorization architectures.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to have an understanding of CBOR [RFC8949] and
EDHOC [I-D.ietf-lake-edhoc]. Appendix C.1 of [I-D.ietf-lake-edhoc]
contains some basic info about CBOR.
2. Problem Description
The (potentially constrained) device (U) wants to enroll into a
domain over a constrained link. The device authenticates and
enforces authorization of the (non-constrained) domain authenticator
(V) with the help of a voucher, and makes the enrollment request.
The domain authenticator (W) authenticates the device and authorizes
its enrollment. Authentication between device and domain
authenticator is made with the lightweight authenticated Diffie-
Hellman key exchange protocol EDHOC [I-D.ietf-lake-edhoc]. The
procedure is assisted by a (non-constrained) authorization server
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located in a non-constrained network behind the domain authenticator
providing information to the device and to the domain authenticator
as part of the protocol.
The objective of this document is to specify such a protocol which is
lightweight over the constrained link by reusing elements of EDHOC.
See illustration in Figure 1.
Voucher
EDHOC Info
+----------+ | | +---------------+ Voucher +---------------+
| | | | | | Request | |
| Device |--|----o-->| Domain |---------->| Authorization |
| |<-|---o----| Authenticator |<----------| Server |
| (U) |--|---|--->| (V) | Voucher | (W) |
| | | | | Response | |
+----------+ | +---------------+ +---------------+
Voucher
Figure 1: Overview of message flow. Link between U anv V is
constrained but link between V and W is not. Voucher_Info and
Voucher are sent in EDHOC External Authorization Data.
3. Assumptions
3.1. Device (U)
U takes the role as EDHOC Initiator with authentication credential
CRED_I. CRED_I may for example be an X.509 certificate or a CBOR Web
Token (CWT, [RFC8392]). For identification to W, U is provisioned
with an identifier ID_U, from which W shall be able to retrieve
CRED_I. ID_U is for example a reference to the device authentication
credential, or an identifier from a separate name space.
U is also provisioned with information about W:
* A static public DH key of W (G_W) used to protect communication
between device and authorization server (see Section 4.3).
* Location information about the authorization server (LOC_W) that
can be used by V. This is typically a URI but may be optimized,
e.g. only the domain name.
3.2. Domain Authenticator (V)
V takes the role as EDHOC Responder with authentication credential
CRED_R. CRED_R is a CWT Claims Set (CCS, [RFC8392]) containing the
public authentication key of V, PK_V, see Section 4.4.2.1
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V needs to establish secure communication with W based on information
in LOC_W. The communication between V and W is assumed to be
mutually authenticated and protected; authentication credentials and
communication security is out of scope, except for as specified below
in this section.
V may in principle use different credentials for authenticating to U
and to W (CRED_R is used for the former). However, V MUST prove
possession of private key of PK_V to W, since W is asserting (by
means of a voucher sent to U) that this credential belongs to V.
In this version of the draft is assumed that V authenticates to W
with the public key PK_V using some authentication protocol providing
proof of possession of the private key, for example TLS 1.3
[RFC8446]. A future version of this draft may specify explicit proof
of possession of the private key of PK_V in VREQ, e.g., by including
a signature of the contents of the voucher request made with the
private key corresponding to PK_V.
3.3. Authorization Server (W)
W has the private DH key corresponding to G_W, which is used to
secure the communication with U (see Section 4.3).
Authentication credentials and communication security used with V is
out of scope, except for the need to verify the possession of the
private key of PK_V as specified in Section 3.2.
W provides to U the authorization decision for enrollment with V in
the form of a voucher, see Section 4.3.2. W may provide V with the
authorization credential of U, CRED_I, after V has learnt the
identity of U.
W needs to be available during the execution of the protocol between
U and V.
4. The Protocol
4.1. Overview
Three security sessions are going on in parallel:
1. EDHOC [I-D.ietf-lake-edhoc] between device (U) and (domain)
authenticator (V)
2. Voucher Request/Response between authenticator (V) and
authorization server (W)
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3. An exchange of voucher-related information, including the voucher
itself, between device (U) and authorization server (W), mediated
by the authenticator (V).
Figure 2 provides an overview of the message flow detailed in this
section, for more details see Section 3.1 of [I-D.ietf-lake-edhoc].
U V W
| | |
| SUITES_I, G_X, EAD_1 | |
+------------------------------>| |
| EDHOC message_1 | H(m1), SS, G_X, ENC_ID, ?PoP_V |
| +--------------------------------->|
| | Voucher Request (VREQ) |
| | |
| | H(m1), Voucher |
| |<---------------------------------+
| | Voucher Response (VRES) |
| Enc(ID_CRED_R, SM_2, EAD_2) | |
|<------------------------------+ |
| EDHOC message_2 | |
| | |
| Enc(ID_CRED_I, SM_3) | |
+------------------------------>| |
| EDHOC message_3 | (Credential lookup:) |
| | ID_CRED_I |
| |--------------------------------->|
| |<---------------------------------|
| | CRED_I |
| | |
where
H(m1) = H(message_1)
EAD_1 contains Voucher_Info: LOC_W, ENC_ID
EAD_2 contains Voucher: MAC(H(message_1), CRED_R)
Figure 2: W-assisted authorization of U and V to each other:
EDHOC between U and V (only selected message fields shown for
simplicity), and Voucher Request/Response between V and W.
4.2. Reuse of EDHOC
The protocol illustrated in Figure 2 reuses several components of
EDHOC:
* G_X, the 'x' parameter of the ephemeral public Diffie-Hellman key
of party U, is also used in the protocol between U and W.
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* SUITES_I, the cipher suites relevant to U, which includes the
selected cipher suite - here denoted SS, also defines the
algorithms used between U and W. In particular SS contains
information about (see Section 3.6 of [I-D.ietf-lake-edhoc]):
- EDHOC AEAD algorithm: used to encrypt the identity of U
- EDHOC hash algorithm: used for key derivation and to calculate
the voucher
- EDHOC MAC length in bytes: length of the voucher
- EDHOC key exchange algorithm: used to calculate the shared
secret between U and W
* EAD_1, EAD_2 are the External Authorization Data message fields of
message_1 and message_2, respectively, see Section 3.8 of
[I-D.ietf-lake-edhoc]. This document specifies EAD items with
ead_label = TBD1, see Section 7.1).
* ID_CRED_I and ID_CRED_R are used to identify the authentication
credentials of U and V. As shown at the bottom of Figure 2, V may
use W to obtain CRED_I, the authentication credential of U. The
authentication credential of V, CRED_R, is transported in
ID_CRED_R in message_2, see Section 4.4.2.1.
* Signature_or_MAC_2 and Signature_or_MAC_3 (abbreviated SM_2 and
SM_3 in Figure 2), containing data generated using the private key
of V and U, respectively, are shown here just to be able to reason
about the use of credentials. The definition of these fields
depend on EDHOC method, see Section 5 of [I-D.ietf-lake-edhoc]).
The protocol also reuses the Extract and Expand key derivation from
EDHOC (Section 4 of [I-D.ietf-lake-edhoc]).
* The intermediate pseudo-random key PRK is derived using Extract():
- PRK = Extract(salt, IKM)
o where salt = 0x (the zero-length byte string)
o IKM is the ECDH shared secret G_XW (calculated from G_X and
W or G_W and X) as defined in Section 6.3.1 of [RFC9053].
The shared secret is derived using Expand() which is defined in terms
of the EDHOC hash algorithm of the selected cipher suite, see
Section 4.2. of [I-D.ietf-lake-edhoc]:
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* shared secret = Expand(PRK, info, length)
where
info = (
label : int,
context : bstr,
length : uint,
)
4.3. Device <-> Authorization Server (U <-> W)
The protocol between U and W is carried out via V with certain data
protected between the endpoints using the equivalent of a hybrid
public key encryption scheme such as [RFC9180]. U uses the public DH
key of the W, G_W, together with the private DH key corresponding to
ephemeral key G_X in EDHOC message_1, and vice versa for W. The
endpoints calculate a shared secret G_XW (see Section 4.2), which is
used to derive secret keys to protect data between U and W, as
detailed in this section.
The data exchanged between U and W is carried between U and V in
message_1 and message_2 (Section 4.4), and between V and W in the
Voucher Request/Response (Section 4.5).
4.3.1. Voucher Info
The external authorization data EAD_1 contains an EAD item with
ead_label = TBD1 and ead_value = Voucher_Info, which is a CBOR byte
string:
Voucher_Info = bstr .cbor Voucher_Info_Seq
Voucher_Info_Seq = (
LOC_W: tstr,
ENC_ID: bstr
)
where
* LOC_W is location information of W, used by V
* ENC_ID is the encrypted blob carrying an identifier of U passed on
from V to W, calculated as follows:
ENC_ID is 'ciphertext' of COSE_Encrypt0 (Section 5.2-5.3 of
[RFC9052]) computed from the following:
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* The encryption key K_1 and nonce IV_1 are derived as specified
below.
* 'protected' is a byte string of size 0
* 'plaintext and 'external_aad' as below:
plaintext = (
ID_U: bstr,
)
external_aad = (
SS: int,
)
where
* ID_U is an identity of the device, for example a reference to the
device authentication credential, see Section 3.1.
* SS is the selected cipher suite in SUITES_I.
The derivation of K_1 = Expand(PRK, info, length) uses the following
input to the info struct (Section 4.2):
* label = TBD1
* context = h''
* length is length of key of the EDHOC AEAD algorithm in bytes
The derivation of IV_1 = Expand(PRK, info, length) uses the following
input to the info struct (Section 4.2):
* label = TBD1
* context = h'00'
* length is length of nonce of the EDHOC AEAD algorithm in bytes
4.3.2. Voucher
The voucher is an assertion for U that W has performed the relevant
verifications and that U is authorized to continue the protocol with
V. The voucher is essentially a message authentication code which
binds the authentication credential of V to message_1 of EDHOC,
integrity protected with the shared secret context between U and W.
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The external authorization data EAD_2 contains an EAD item with
ead_label = TBD1 and ead_value = Voucher, which is a CBOR byte
string:
Voucher = bstr .cbor Expand(PRK, info, length)
calculated with the following input to the info struct (Section 4.2):
* label is TBD1
* context = bstr .cbor voucher_input
* length is EDHOC MAC length in bytes
where context is a CBOR bstr wrapping of the following CBOR sequence:
voucher_input = (
H(message_1): bstr,
CRED_R: bstr,
)
where
* H(message_1) is copied from the associated voucher request.
* CRED_R is a CWT Claims Set (CCS, [RFC8392]) containing the public
authentication key of V, PK_V, see Section 4.4.2.1
4.4. Device <-> Authenticator (U <-> V)
This section describes the processing in U and V, which execute the
EDHOC protocol using their respective authentication credentials, see
Figure 2. Normal EDHOC processing is omitted here.
4.4.1. Message 1
4.4.1.1. Processing in U
U composes EDHOC message_1 using authentication method, identifiers,
etc. according to an agreed application profile, see Section 3.9 of
[I-D.ietf-lake-edhoc]. The selected cipher suite, in this document
denoted SS, applies also to the interaction with W as detailed in
Section 4.2, in particular, to the key agreement algorithm which is
used with the static public DH key G_W of W. As part of the normal
EDHOC processing, U generates the ephemeral public key G_X which is
reused in the interaction with W, see Section 4.3.
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The device sends EDHOC message_1 with EAD item (-TBD1, Voucher_Info)
included in EAD_1, where Voucher_Info is specified in Section 4.3.
The negative sign indicates that the EAD item is critical, see
Section 3.8 in [I-D.ietf-lake-edhoc].
4.4.1.2. Processing in V
V receives EDHOC message_1 from U and processes it as specified in
Section 5.2.3 of [I-D.ietf-lake-edhoc], with the additional step of
processing the EAD item in EAD_1. Since the EAD item is critical, if
V does not recognize it or it contains information that V cannot
process, then V MUST discontinue EDHOC, see Section 3.8 in
[I-D.ietf-lake-edhoc]. Otherwise, the ead_label = TBD1, triggers the
voucher request to W as described in Section 4.5. The exchange
between V and W needs to be completed successfully for the EDHOC
exchange to be continued.
4.4.2. Message 2
4.4.2.1. Processing in V
V receives the voucher response from W as described in Section 4.5.
V sends EDHOC message_2 to U with the critical EAD item (-TBD1,
Voucher) included in EAD_2, where the Voucher is specified in
Section 4.3.
CRED_R is a CWT Claims Set (CCS, [RFC8392]) containing the public
authentication key of the authenticator PK_V encoded as a COSE_Key in
the 'cnf' claim, see Section 3.5.2 of [I-D.ietf-lake-edhoc].
ID_CRED_R contains the CCS with 'kccs' as COSE header_map, see
Section 9.6 of [I-D.ietf-lake-edhoc]. The Signature_or_MAC_2 field
calculated using the private key corresponding to PK_V is either a
signature or a MAC depending on EDHOC method.
4.4.2.2. Processing in U
U receives EDHOC message_2 from V and processes it as specified in
Section 5.3.2 of [I-D.ietf-lake-edhoc], with the additional step of
processing the EAD item in EAD_2.
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If U does not recognize the EAD item or the EAD item contains
information that U cannot process, then U MUST discontinue EDHOC, see
Section 3.8 in [I-D.ietf-lake-edhoc]. Otherwise U MUST verify the
Voucher by performing the same calculation as in Section 4.3.2 using
H(message_1) and CRED_R received in ID_CRED_R of message_2. If the
voucher calculated in this way is not identical to what was received
in message_2, then U MUST discontinue the protocol.
4.4.3. Message 3
4.4.3.1. Processing in U
If all verifications are passed, then U sends EDHOC message_3.
The Signature_or_MAC_3 field calculated using the private key
corresponding to PK_U is either a signature or a MAC depending on
EDHOC method.
EAD_3 MAY contain a certificate enrollment request, see e.g. CSR
specified in [I-D.mattsson-cose-cbor-cert-compress], or other request
which the device is now authorized to make.
EDHOC message_3 may be combined with an OSCORE request, see
[I-D.ietf-core-oscore-edhoc].
4.4.3.2. Processing in V
V performs the normal EDHOC verifications of message_3. V may
retrieve CRED_I from W, after V learnt ID_CRED_I from U.
4.5. Authenticator <-> Authorization Server (V <-> W)
V and W are assumed to be able to authenticate and set up a secure
connection, out of scope for this specification, for example TLS 1.3
authenticated with certificates. V is assumed to authenticate with
the public key PK_V, see Section 3.2.
This secure connection protects the Voucher Request/Response Protocol
(see protocol between V and W in Figure 2).
The hash of EDHOC message_1, H(message_1), acts as session identifier
of the Voucher Request/Response protocol, and binds together
instances of the two protocols (U<->V and V<->W).
4.5.1. Voucher Request
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4.5.1.1. Processing in V
Unless already in place, V and W establish a secure connection. V
uses H(message_1) as a session identifier associated to this
connection with W. If the same value of H(message_1) is already used
for a connection with this or other W, the protocol SHALL be
discontinued.
V sends the voucher request to W. The Voucher Request SHALL be a
CBOR array as defined below:
Voucher_Request = [
H(message_1): bstr,
SS: int,
G_X: bstr,
ENC_ID: bstr,
? PoP_V: bstr,
]
where the parameters are defined in Section 4.3, except:
* PoP_V is a proof-of-possession of public key PK_V using the
corresponding private key. PoP_V is optional.
Editor's note: Define PoP_V (include G_X, ENC_ID in the calculation
for binding to this EDHOC session). One case to study is when V
authenticates to U with static DH and to W with signature.
4.5.1.2. Processing in W
W receives the voucher request, verifies and decrypts ENC_ID, and
associates the session identifier H(message_1) to ID_U. If
H(message_1) is not unique among session identifiers associated to
this identity, the protocol SHALL be discontinued.
W uses the identity of the device, ID_U, to look up and verify the
associated authorization policies for U. This is out of scope for
the specification.
4.5.2. Voucher Response
4.5.2.1. Processing in W
W retrieves the public key of V, PK_V, used to authenticate the
secure connection with V, and constructs the CCS (see
Section 4.4.2.1) and the Voucher (see Section 4.3.2).
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Editor's note: Make sure the CCS is defined to allow W generate it
uniquely from PK_V.
W generates the voucher response and sends it to V over the secure
connection. The Voucher_Response SHALL be a CBOR array as defined
below:
Voucher_Response = [
H(message_1): bstr,
Voucher: bstr
]
where
* H(message_1) is copied from the associated voucher request.
* The Voucher is defined in Section 4.3.2.
4.5.2.2. Processing in V
V receives the voucher response from W over the secure connection.
If the received session identifier does not match the session
identifier H(message_1) associated to the secure connection, the
protocol SHALL be discontinued.
5. REST Interface at W
The interaction between V and W is enabled through a RESTful
interface exposed by W. V SHOULD access the resources exposed by W
through the protocol indicated by the scheme in LOC_W URI. In case
the scheme indicates "https", V SHOULD perform a TLS handshake with W
and use HTTP. In case the scheme indicates "coaps", V SHOULD perform
a DTLS handshake with W and access the same resources using CoAP. In
both cases, V MUST perform client authentication to authenticate to
W, using a certificate containing the PK_V public key.
5.1. HTTP URIs
W MUST support the use of the path-prefix "/.well-known/", as defined
in [RFC8615], and the registered name "lake-authz". A valid URI thus
begins with "https://www.example.com/.well-known/lake-authz". Each
operation specified in the following is indicated by a path-suffix.
5.2. Voucher Request (/voucherrequest)
To request a voucher, V MUST issue an HTTP request:
* Method is POST
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* Payload is the serialization of the Voucher Request object, as
specified in Section 4.5.1.
In case of successful processing at W, W MUST issue a 200 OK response
with payload containing the serialized Voucher Response object, as
specified in Section 4.5.2.
5.3. Certificate Request (/certrequest)
V requests the public key certificate of U from W through the
"/certrequest" path-suffix. To request U's authentication
credential, V MUST issue an HTTP request:
* Method is POST
* Payload is the serialization of the ID_CRED_I object, as received
in EDHOC message_3.
In case of a successful lookup of the authentication credential at W,
W MUST issue 200 OK response with payload containing the serialized
CRED_I.
6. Security Considerations
This specification builds on and reuses many of the security
constructions of EDHOC, e.g. shared secret calculation and key
derivation. The security considerations of EDHOC
[I-D.ietf-lake-edhoc] apply with modifications discussed here.
EDHOC provides identity protection of the Initiator, here the device.
The encryption of the device identity in the first message should
consider potential information leaking from the length of the
identifier ID_U, either by making all identifiers having the same
length or the use of a padding scheme.
Although W learns about the identity of U after receiving VREQ, this
information must not be disclosed to V, until U has revealed its
identity to V with ID_CRED_I in message_3. W may be used for lookup
of CRED_I from ID_CRED_I, or this credential lookup function may be
separate from the authorization function of W. The trust model used
here is that U decides to which V it reveals its identity. In an
alternative trust model where U trusts W to decide to which V it
reveal's U's identity, CRED_I could be sent in Voucher Response.
As noted Section 8.2 of [I-D.ietf-lake-edhoc] an ephemeral key may be
used to calculate several ECDH shared secrets. In this specification
the ephemeral key G_X is also used to calculate G_XW, the shared
secret with the authorization server.
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The private ephemeral key is thus used in the device for calculations
of key material relating to both the authenticator and the
authorization server. There are different options for where to
implement these calculations, one option is as an addition to EDHOC,
i.e., to extend the EDHOC API in the device with input of public key
of W (G_W) and identifier of U (ID_U), and produce the encryption of
ID_U which is included in Voucher_Info in EAD_1.
7. IANA Considerations
7.1. EDHOC External Authorization Data Registry
IANA has registered the following entry in the "EDHOC External
Authorization Data" registry under the group name "Ephemeral Diffie-
Hellman Over COSE (EDHOC)". The ead_label = TBD_1 corresponds to the
ead_value Voucher_Info in EAD_1, and Voucher in EAD_2 with processing
specified in Section 4.4.1 and Section 4.4.2, respectively, of this
document.
+-------+------------+-----------------+
| Label | Value Type | Description |
+-------+------------+-----------------+
| TBD1 | bstr | Voucher related |
| | | information |
+-------+------------+-----------------+
7.2. The Well-Known URI Registry
IANA has registered the following entry in "The Well-Known URI
Registry", using the template from [RFC8615]:
* URI suffix: lake-authz
* Change controller: IETF
* Specification document: [[this document]]
* Related information: None
7.3. Well-Known Name Under ".arpa" Name Space
This document allocates a well-known name under the .arpa name space
according to the rules given in [RFC3172] and [RFC6761]. The name
"lake-authz.arpa" is requested. No subdomains are expected, and
addition of any such subdomains requires the publication of an IETF
Standards Track RFC. No A, AAAA, or PTR record is requested.
8. References
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8.1. Normative References
[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J. P., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
Progress, Internet-Draft, draft-ietf-lake-edhoc-17, 12
October 2022, <https://www.ietf.org/archive/id/draft-ietf-
lake-edhoc-17.txt>.
[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>.
[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>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/info/rfc9052>.
[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>.
8.2. Informative References
[I-D.ietf-core-oscore-edhoc]
Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S.,
and G. Selander, "Profiling EDHOC for CoAP and OSCORE",
Work in Progress, Internet-Draft, draft-ietf-core-oscore-
edhoc-04, 11 July 2022, <https://www.ietf.org/archive/id/
draft-ietf-core-oscore-edhoc-04.txt>.
[I-D.ietf-lake-reqs]
Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carrillo, "Requirements for a Lightweight AKE for OSCORE",
Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04,
8 June 2020, <https://www.ietf.org/archive/id/draft-ietf-
lake-reqs-04.txt>.
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[I-D.mattsson-cose-cbor-cert-compress]
Raza, S., Höglund, J., Selander, G., Mattsson, J. P., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
mattsson-cose-cbor-cert-compress-08, 22 February 2021,
<https://www.ietf.org/archive/id/draft-mattsson-cose-cbor-
cert-compress-08.txt>.
[IEEE802.15.4]
IEEE standard for Information Technology, "IEEE Std
802.15.4 Standard for Low-Rate Wireless Networks", n.d..
[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>.
[RFC3172] Huston, G., Ed., "Management Guidelines & Operational
Requirements for the Address and Routing Parameter Area
Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
September 2001, <https://www.rfc-editor.org/info/rfc3172>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[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>.
[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>.
[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>.
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[RFC9180] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
February 2022, <https://www.rfc-editor.org/info/rfc9180>.
Appendix A. Use with Constrained Join Protocol (CoJP)
This section outlines how the protocol is used for network enrollment
and parameter provisioning. An IEEE 802.15.4 network is used as an
example of how a new device (U) can be enrolled into the domain
managed by the domain authenticator (V).
U V W
| | |
| | |
+- - - - - - - - - - - - - - - - - ->| |
| Optional network solicitation | |
|<-----------------------------------+ |
| Network discovery | |
| | |
+----------------------------------->| |
| EDHOC message_1 | |
| +----------------------------->|
| | Voucher Request (VREQ) |
| |<-----------------------------+
| | Voucher Response (VRES) |
|<-----------------------------------+ |
| EDHOC message_2 | |
| | |
| | |
+----------------------------------->| |
| EDHOC message_3 + CoJP request | |
| | |
+<-----------------------------------| |
| CoJP response | |
|
Figure 3: Use of draft-selander-lake-authz with CoJP.
A.1. Network discovery
When a device first boots, it needs to discover the network it
attempts to join. The network discovery procedure is defined by the
link-layer technology in use. In case of Time-slotted Channel
Hopping (TSCH) networks, a mode of [IEEE802.15.4], the device scans
the radio channels for Enhanced Beacon (EB) frames, a procedure known
as passive scan. EBs carry the information about the network, and
particularly the network identifier. Based on the EB, the network
identifier, the information pre-configured into the device, the
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device makes the decision on whether it should join the network
advertised by the received EB frame. This process is described in
Section 4.1. of [RFC9031]. In case of other, non-TSCH modes of IEEE
802.15.4 it is possible to use the active scan procedure and send
solicitation frames. These solicitation frames trigger the nearest
network coordinator to respond by emitting a beacon frame. The
network coordinator emitting beacons may be multiple link-layer hops
away from the domain authenticator (V), in which case it plays the
role of a Join Proxy (see [RFC9031]). Join Proxy does not
participate in the protocol and acts as a transparent router between
the device and the domain authenticator. For simplicity, Figure 3
illustrates the case when the device and the domain authenticator are
a single hop away and can communicate directly.
A.2. The enrollment protocol with parameter provisioning
A.2.1. Flight 1
Once the device has discovered the network it wants to join, it
constructs the EDHOC message_1, as described in Section 4.4. The
device SHALL map the message to a CoAP request:
* The request method is POST.
* The type is Confirmable (CON).
* The Proxy-Scheme option is set to "coap".
* The Uri-Host option is set to "lake-authz.arpa". This is an
anycast type of identifier of the domain authenticator (V) that is
resolved to its IPv6 address by the Join Proxy.
* The Uri-Path option is set to ".well-known/edhoc".
* The Content-Format option is set to "application/cid-edhoc+cbor-
seq"
* The payload is the (true, EDHOC message_1) CBOR sequence, where
EDHOC message_1 is constructed as defined in Section 4.4.
A.2.2. Flight 2
The domain authenticator receives message_1 and processes it as
described in Section 4.4. The message triggers the exchange with the
authorization server, as described in Section 4.5. If the exchange
between V and W completes successfully, the domain authenticator
prepares EDHOC message_2, as described in Section 4.4. The
authenticator SHALL map the message to a CoAP response:
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* The response code is 2.04 Changed.
* The Content-Format option is set to "application/edhoc+cbor-seq"
* The payload is the EDHOC message_2, as defined in Section 4.4.
A.2.3. Flight 3
The device receives EDHOC message_2 and processes it as described in
Section 4.4}. Upon successful processing of message_2, the device
prepares flight 3, which is an OSCORE-protected CoJP request
containing an EDHOC message_3, as described in
[I-D.ietf-core-oscore-edhoc]. EDHOC message_3 is prepared as
described in Section 4.4. The OSCORE-protected payload is the CoJP
Join Request object specified in Section 8.4.1. of [RFC9031]. OSCORE
protection leverages the OSCORE Security Context derived from the
EDHOC exchange, as specified in Appendix A of [I-D.ietf-lake-edhoc].
To that end, [I-D.ietf-core-oscore-edhoc] specifies that the Sender
ID of the client (device) must be set to the connection identifier
selected by the domain authenticator, C_R. OSCORE includes the
Sender ID as the kid in the OSCORE option. The network identifier in
the CoJP Join Request object is set to the network identifier
obtained from the network discovery phase. In case of IEEE 802.15.4
networks, this is the PAN ID.
The device SHALL map the message to a CoAP request:
* The request method is POST.
* The type is Confirmable (CON).
* The Proxy-Scheme option is set to "coap".
* The Uri-Host option is set to "lake-authz.arpa".
* The Uri-Path option is set to ".well-known/edhoc".
* The EDHOC option [I-D.ietf-core-oscore-edhoc] is set and is empty.
* The payload is prepared as described in Section 3.2. of
[I-D.ietf-core-oscore-edhoc], with EDHOC message_3 and the CoJP
Join Request object as the OSCORE-protected payload.
Note that the OSCORE Sender IDs are derived from the connection
identifiers of the EDHOC exchange. This is in contrast with
[RFC9031] where ID Context of the OSCORE Security Context is set to
the device identifier (pledge identifier). Since the device identity
is exchanged during the EDHOC handshake, and the certificate of the
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device is communicated to the authenticator as part of the Voucher
Response message, there is no need to transport the device identity
in OSCORE messages. The authenticator playing the role of the
[RFC9031] JRC obtains the device identity from the execution of the
authorization protocol.
A.2.4. Flight 4
Flight 4 is the OSCORE response carrying CoJP response message. The
message is processed as specified in Section 8.4.2. of [RFC9031].
Authors' Addresses
Göran Selander
Ericsson AB
Sweden
Email: goran.selander@ericsson.com
John Preuß Mattsson
Ericsson AB
Sweden
Email: john.mattsson@ericsson.com
Mališa Vučinić
INRIA
France
Email: malisa.vucinic@inria.fr
Michael Richardson
Sandelman Software Works
Canada
Email: mcr+ietf@sandelman.ca
Aurelio Schellenbaum
Institute of Embedded Systems, ZHAW
Switzerland
Email: aureliorubendario.schellenbaum@zhaw.ch
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