Internet DRAFT - draft-selander-lake-authz
draft-selander-lake-authz
LAKE Working Group G. Selander
Internet-Draft J. Preuß Mattsson
Intended status: Standards Track Ericsson AB
Expires: 8 January 2024 M. Vučinić
INRIA
M. Richardson
Sandelman Software Works
A. Schellenbaum
ZHAW
7 July 2023
Lightweight Authorization using Ephemeral Diffie-Hellman Over COSE
draft-selander-lake-authz-03
Abstract
This document describes a procedure for authorizing enrollment of new
devices using the lightweight authenticated key exchange protocol
Ephemeral Diffie-Hellman Over COSE (EDHOC). The procedure is
applicable to zero-touch onboarding of new devices to a constrained
network leveraging trust anchors installed at manufacture time.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://ericssonresearch.github.io/ace-ake-authz/draft-selander-lake-
authz.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-selander-lake-authz/.
Discussion of this document takes place on the Lightweight
Authenticated Key Exchange Working Group mailing list
(mailto:lake@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/lake/. Subscribe at
https://www.ietf.org/mailman/listinfo/lake/.
Source for this draft and an issue tracker can be found at
https://github.com/EricssonResearch/ace-ake-authz.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Problem Description . . . . . . . . . . . . . . . . . . . . . 4
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Device (U) . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Domain Authenticator (V) . . . . . . . . . . . . . . . . 6
3.3. Enrollment Server (W) . . . . . . . . . . . . . . . . . . 7
4. The Protocol . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Reuse of EDHOC . . . . . . . . . . . . . . . . . . . . . 9
4.3. Stateless Operation of V . . . . . . . . . . . . . . . . 11
4.4. Device <-> Enrollment Server (U <-> W) . . . . . . . . . 11
4.5. Device <-> Authenticator (U <-> V) . . . . . . . . . . . 14
4.6. Authenticator <-> Enrollment Server (V <-> W) . . . . . . 15
5. REST Interface at W . . . . . . . . . . . . . . . . . . . . . 17
5.1. Scheme "https" . . . . . . . . . . . . . . . . . . . . . 18
5.2. Scheme "coaps" . . . . . . . . . . . . . . . . . . . . . 18
5.3. Scheme "coap" . . . . . . . . . . . . . . . . . . . . . . 18
5.4. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
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7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7.1. EDHOC External Authorization Data Registry . . . . . . . 20
7.2. The Well-Known URI Registry . . . . . . . . . . . . . . . 21
7.3. Well-Known Name Under ".arpa" Name Space . . . . . . . . 21
7.4. Media Types Registry . . . . . . . . . . . . . . . . . . 21
7.5. CoAP Content-Formats Registry . . . . . . . . . . . . . . 22
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Use with Constrained Join Protocol (CoJP) . . . . . 24
A.1. Network Discovery . . . . . . . . . . . . . . . . . . . . 25
A.2. The Enrollment Protocol with Parameter Provisioning . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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.
The procedure involves a device, a domain authenticator, and an
enrollment server. The device and domain authenticator perform
mutual authentication and authorization, assisted by the enrollment
server which provides relevant authorization information to the
device (a "voucher") and to the authenticator. The high-level model
is similiar to BRSKI [RFC8995].
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 enrollment server may represent the manufacturer of the device,
or some other party with information about the device from which a
trust anchor has been pre-provisioned into the device. The (domain)
authenticator may represent the service provider or some other party
controlling access to the network in which the device is enrolling.
The protocol assumes that authentication between device and
authenticator is performed with EDHOC [I-D.ietf-lake-edhoc], and
defines the integration of a lightweight authorization procedure
using the External Authorization Data (EAD) fields defined in EDHOC.
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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 conveying authorization information.
The domain authenticator, in turn, authenticates the device and
authorizes its enrollment into the domain.
The procedure is assisted by a (non-constrained) enrollment server
(W) located in a non-constrained network behind the domain
authenticator, e.g. on the Internet, providing information to the
device (the voucher) 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
[I-D.ietf-lake-edhoc] and by shifting message overhead to the non-
constrained side of the network. See illustration in Figure 1.
Note the cardinality of the involved parties. It is expected that
the authenticator needs to handle a large unspecified number of
devices, but for a given device type or manufacturer it is expected
that one or a few nodes host enrollment servers.
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Voucher
Info
+----------+ | +---------------+ Voucher +---------------+
| | | | | Request | |
| Device +------o---->| Domain +---------->| Enrollment |
| |<---o-------+ Authenticator |<----------+ Server |
| (U) +----+------>| (V) | Voucher | (W) |
| | | | | Response | |
+----------+ | +---------------+ +---------------+
Voucher
Figure 1: Overview of message flow. EDHOC is used on the
constrained link between U and V. Voucher Info and Voucher are
sent in EDHOC External Authorization Data (EAD). The link
between V and W is not constrained.
3. Assumptions
The protocol is based on the following pre-existing relations between
the device (U), the domain authenticator (V) and the enrollment
server (W), see Figure 2.
* U and W have an explicit relation: U is configured with a public
key of W, see Section 3.1.
* V and W have an implicit relation, e.g., based on web PKI with
trusted CA certificates, see Section 3.2.
* U and V need not have any previous relation, this protocol
establishes a relation between U and V.
Each of the three parties have protected communication with the other
two during the protocol.
Explicit relation (e.g., from device manufacture)
| <---------------------------------------------------> |
| |
+----+-----+ +---------------+ +-------+-------+
| | | | non- | |
| Device | con- | Domain | con- | Enrollment |
| | stra- | Authenticator | stra- | Server |
| (U) | ined | (V) | ined | (W) |
| | | | | |
+----+-----+ +-------+-------+ +-------+-------+
| | |
| <----------------------> | <------------------------> |
No previous relation Implicit relation
(e.g., web PKI based)
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Figure 2: Overview of pre-existing relations.
3.1. Device (U)
To authenticate to V, the device (U) runs EDHOC in the role of
Initiator with authentication credential CRED_U, for example, an
X.509 certificate or a CBOR Web Token (CWT, [RFC8392]). CRED_U may,
for example, be carried in ID_CRED_I of EDHOC message_3 or be
provisioned to V over a non-constrained network, see bottom of
Figure 3.
U also needs to identify itself to W, this device identifier is
denoted by ID_U. The purpose of ID_U is for W to be able to
determine if the device with this identifier is authorized to enroll
with V. ID_U may be a reference to CRED_U, like ID_CRED_I in EDHOC
(see Section 3.5.2 of [I-D.ietf-lake-edhoc]), or a device identifier
from a different name space, such as EUI-64 identifiers.
U is also provisioned with information about W:
* A static public DH key of W (G_W) used to establish secure
communication with the enrollment server (see Section 4.4).
* Location information about the enrollment server (LOC_W) that can
be used by V to reach W. This is typically a URI but may
alternatively be only the domain name.
3.2. Domain Authenticator (V)
To authenticate to U, the domain authenticator (V) runs EDHOC in the
role of Responder with an authentication credential CRED_V, which is
a CWT Claims Set [RFC8392] containing a public key of V, see
Section 4.5.2.1. This proves to U the possession of the private key
corresponding to the public key of CRED_V. CRED_V typically needs to
be transported to U in EDHOC (using ID_CRED_R = CRED_V, see
Section 3.5.2 of [I-D.ietf-lake-edhoc]) since there is no previous
relation between U and V.
V and W need to establish a secure (confidentiality and integrity
protected) connection for the Voucher Request/Response protocol.
Furthermore, W needs access the same credential CRED_V as V used with
U, and V needs to prove to W the possession of the private key
corresponding to the public key of CRED_V. It is RECOMMENDED that V
authenticates to W using the same credential CRED_V as with U.
* V and W may protect the Voucher Request/Response protocol using
TLS 1.3 with client authentication [RFC8446] if CRED_V is an X.509
certificate of a signature public key. However, note that CRED_V
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may not be a valid credential to use with TLS 1.3, e.g., when U
and V run EDHOC with method 1 or 3, where the public key of CRED_V
is a static Diffie-Hellman key.
* V may run EDHOC with W using ID_CRED_I = CRED_V. In this case the
secure connection between V and W may be based on OSCORE
[RFC8613].
Note that both TLS 1.3 and EDHOC may be run between V and W during
this setup procedure. For example, W may authenticate to V using TLS
1.3 with server certificates signed by a CA trusted by V, and then V
may run EDHOC using CRED_V over the secure TLS connection to W, see
Figure 3.
Note also that the secure connection between V and W may be long
lived and reused for multiple voucher requests/responses.
Other details of proof-of-possession related to CRED_V and transport
of CRED_V are out of scope of this document.
3.3. Enrollment Server (W)
The enrollment server (W) is assumed to have the private DH key
corresponding to G_W, which is used to establish secure communication
with the device (see Section 4.4). W provides to U the authorization
decision for enrollment with V in the form of a voucher (see
Section 4.4.2). Authorization policies are out of scope for this
document.
Authentication credentials and communication security with V is
described in Section 3.2. To calculate the voucher, W needs access
to message_1 and CRED_V as used in the EDHOC session between U and V,
see Section 4.4.2.
* W MUST verify that CRED_V is bound to the secure connection
between W and V
* W MUST verify that V is in possession of the private key
corresponding to the public key of CRED_V
W needs to be available during the execution of the protocol between
U and V.
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4. The Protocol
4.1. Overview
The protocol consist of three security sessions going on in parallel:
1. The EDHOC session between device (U) and (domain) authenticator
(V)
2. Voucher Request/Response between authenticator (V) and enrollment
server (W)
3. An exchange of voucher-related information, including the voucher
itself, between device (U) and enrollment server (W), mediated by
the authenticator (V).
Figure 3 provides an overview of the message flow detailed in this
section. An outline of EDHOC is given in Section 3 of
[I-D.ietf-lake-edhoc].
U V W
| | |
| | |
| | Establish secure channel |
| +<--- --- --- --- --- --- --- -->|
| | (e.g., TLS with server cert.) |
| | |
| | Proof of possession w.r.t. CRED |
| +<--- --- --- --- --- --- --- -->|
| | (e.g., EDHOC) |
| | |
| | |
| | |
---------------------------------------------------------------------
CORE PROTOCOL
| | |
| EDHOC message_1 | |
+-------------------------->| |
| (EAD_1 = LOC_W, ENC_ID) | |
| | |
| | Voucher Request (VREQ) |
| +-------------------------------------->|
| | (message_1, ?opaque_state) |
| | |
| | Voucher Response (VRES) |
| |<--------------------------------------+
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| | (message_1, Voucher, ?opaque_state) |
| | |
| EDHOC message_2 | |
|<--------------------------+ |
| (EAD_2 = Voucher) | |
| | |
| | |
| EDHOC message_3 | |
+-------------------------->| |
| | |
---------------------------------------------------------------------
| |
| | Credential
| | Database
| | |
| | ID_CRED_I from message_3 |
| +--- --- --- --- --- --- --- -->|
| | |
| | CRED_U |
| |<-- --- --- --- --- --- --- ---+
| | |
| | |
Figure 3: Overview of the protocol: W-assisted authorization of U
and V to each other: EDHOC between U and V, and Voucher Request/
Response between V and W. Before the protocol, V and W are
assumed to have established a secure channel and performed proof-
of-possession of relevant keys. Credential lookup of CRED_U may
involve W or other credential database.
4.2. Reuse of EDHOC
The protocol illustrated in Figure 3 reuses several components of
EDHOC:
* G_X, the ephemeral public Diffie-Hellman key of U, is also used in
the protocol between U and W.
* SUITES_I includes the cipher suite for EDHOC selected by U, and
also defines the algorithms used between U and W (see Section 3.6
of [I-D.ietf-lake-edhoc]):
- EDHOC AEAD algorithm: used to encrypt ID_U
- EDHOC hash algorithm: used for key derivation and to calculate
the voucher
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- 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 the EAD items with
ead_label = TBD1, see Section 7.1).
* ID_CRED_I and ID_CRED_R are used to identify the authentication
credentials CRED_U and CRED_V, respectively. As shown at the
bottom of Figure 3, V may use W to obtain CRED_U. CRED_V is
transported in ID_CRED_R in message_2, see Section 4.5.2.1.
The protocol also reuses the EDHOC-Extract and EDHOC-Expand key
derivation from EDHOC (see Section 4 of [I-D.ietf-lake-edhoc]).
* The intermediate pseudo-random key PRK is derived using EDHOC-
Extract():
- PRK = EDHOC-Extract(salt, IKM)
o where salt = 0x (the zero-length byte string)
o IKM is computed as an ECDH cofactor Diffie-Hellman shared
secret from the public key of W, G_W, and the private key
corresponding to G_X (or v.v.), see Section 5.7.1.2 of
[NIST-800-56A].
The output keying material OKM is derived from PRK using EDHOC-
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]:
* OKM = EDHOC-Expand(PRK, info, length)
where
info = (
info_label : int,
context : bstr,
length : uint,
)
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4.3. Stateless Operation of V
V may act statelessly with respect to U: the state of the EDHOC
session started by U may be dropped at V until authorization from W
is received. Once V has received EDHOC message_1 from U and
extracted LOC_W from EAD_1, message_1 is forwarded unmodified to W in
the form of a Voucher Request. V encapsulates the internal state
that it needs to later respond to U, and sends that to W together
with EDHOC message_1. This state typically contains U's IP address
and port number, together with any other implementation-specific
parameter needed by V to respond to U. At this point, V can drop the
EDHOC session that was initiated by U.
V MUST encrypt and integrity protect the encapsulated state using a
uniformly-distributed (pseudo-)random key, known only to itself. How
V serializes and encrypts its internal state is out of scope of this
specification. For example, V may use the existing CBOR and COSE
libraries.
Editor's note: Consider to include an example of serialized internal
state.
W sends to V the voucher together with echoed message_1, as received
from U, and V's internal state. This allows V to act as a simple
message relay until it has obtained the authorization from W to
enroll U. The reception of a successful Voucher Response at V from W
implies the authorization for V to enroll U. At this point, V can
initialize a new EDHOC session with U, based on the message and the
state retrieved from the Voucher Response from W.
4.4. Device <-> Enrollment Server (U <-> W)
The protocol between U and W is carried between U and V in message_1
and message_2 (Section 4.5), and between V and W in the Voucher
Request/Response (Section 4.6). The data is protected between the
endpoints using secret keys derived from a Diffie-Hellman shared
secret (see Section 4.2) as further detailed in this section.
4.4.1. 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
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Voucher_Info_Seq = (
LOC_W: tstr,
ENC_ID: bstr
)
where
* LOC_W is a text string used by V to locate W, e.g., a URI or a
domain name.
* ENC_ID is a byte string containing an encrypted identifier of U,
calculated as follows:
ENC_ID is 'ciphertext' of COSE_Encrypt0 (Section 5.2 of [RFC9052])
computed from the following:
* 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 identifier of the device, see Section 3.1.
* SS is the selected cipher suite in SUITES_I of EDHOC message_1,
see Section 4.5.
Editor's note: Add more context to external_aad.
The derivation of K_1 = EDHOC-Expand(PRK, info, length) uses the
following input to the info struct (see Section 4.2):
* info_label = 0
* context = h'' (the empty CBOR string)
* length is length of key of the EDHOC AEAD algorithm in bytes
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The derivation of IV_1 = EDHOC-Expand(PRK, info, length) uses the
following input to the info struct (see Section 4.2):
* info_label = 1
* context = h'' (the empty CBOR string)
* length is length of nonce of the EDHOC AEAD algorithm in bytes
4.4.2. Voucher
The voucher is an assertion to U that W has authorized V. The
voucher is essentially a message authentication code which binds the
authentication credential of V, CRED_V, to message_1 of EDHOC.
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 EDHOC-Expand(PRK, info, length)
The voucher is calculated with the following input to the info struct
(see Section 4.2):
* info_label = 2
* context = bstr .cbor voucher_input
* length is EDHOC MAC length in bytes
where context is a CBOR byte string wrapping of the following CBOR
sequence:
voucher_input = (
H(message_1): bstr,
CRED_V: bstr,
)
where
* H(message_1) is the hash of EDHOC message_1, calculated from the
associated voucher request, see Section 4.6.1.
* CRED_V is the CWT Claims Set [RFC8392] containing the public
authentication key of V, see Section 4.5.2.1
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4.5. Device <-> Authenticator (U <-> V)
This section describes the processing in U and V, which include the
EDHOC protocol, see Figure 3. Normal EDHOC processing is omitted
here.
4.5.1. Message 1
4.5.1.1. 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, with respect to the Diffie Hellman key
agreement algorithm used between U and 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 4.4.
The device sends EDHOC message_1 with EAD item (-TBD1, Voucher_Info)
included in EAD_1, where Voucher_Info is specified in Section 4.4.
The negative sign indicates that the EAD item is critical, see
Section 3.8 of [I-D.ietf-lake-edhoc].
4.5.1.2. 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 abort the EDHOC session, see Section 3.8 of
[I-D.ietf-lake-edhoc]. Otherwise, the ead_label = TBD1, triggers the
voucher request to W as described in Section 4.6. The exchange
between V and W needs to be completed successfully for the EDHOC
session to be continued.
4.5.2. Message 2
4.5.2.1. Processing in V
V receives the voucher response from W as described in Section 4.6.
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 4.4.
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CRED_V is a CWT Claims Set [RFC8392] containing the public
authentication key of 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 CWT Claims Set with 'kccs' as COSE header_map,
see Section 9.6 of [I-D.ietf-lake-edhoc].
4.5.2.2. 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.
If U does not recognize the EAD item or the EAD item contains
information that U cannot process, then U MUST abort the EDHOC
session, see Section 3.8 of [I-D.ietf-lake-edhoc]. Otherwise U MUST
verify the Voucher by performing the same calculation as in
Section 4.4.2 using H(message_1) and CRED_V 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 abort the EDHOC session.
4.5.3. Message 3
4.5.3.1. Processing in U
If all verifications are passed, then U sends EDHOC message_3.
EDHOC message_3 may be combined with an OSCORE request, see
[I-D.ietf-core-oscore-edhoc].
4.5.3.2. Processing in V
V performs the normal EDHOC verifications of message_3. V may
retrieve CRED_U from a Credential Database, after having learnt
ID_CRED_I from U.
4.6. Authenticator <-> Enrollment Server (V <-> W)
It is assumed that V and W have set up a secure connection, W has
accessed the authentication credential CRED_V to be used in the EDHOC
session between V and with U, and that W has verified that V is in
possession of the private key corresponding to CRED_V, see
Section 3.2 and Section 3.3. V and W run the Voucher Request/
Response protocol over the secure connection.
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4.6.1. Voucher Request
4.6.1.1. Processing in V
V sends the voucher request to W. The Voucher Request SHALL be a
CBOR array as defined below:
Voucher_Request = [
message_1: bstr,
? opaque_state: bstr
]
where
* message_1 is the EDHOC message_1 as it was received from U.
* opaque_state is OPTIONAL and represents the serialized and
encrypted opaque state needed by V to statelessly respond to U
after the reception of Voucher_Response.
4.6.1.2. Processing in W
W receives and parses the voucher request received over the secure
connection with V. The voucher request essentially contains EDHOC
message_1 as sent by U to V. W SHALL NOT process message_1 as if it
was an EDHOC message intended for W.
W extracts from message_1:
* SS - the selected cipher suite, which is the (last) integer of
SUITES_I.
* G_X - the ephemeral public key of U
* ENC_ID - the encryption of the device identifier ID_U, contained
in the Voucher_Info field of the EAD item with ead_label = TBD1
(with minus sign indicating criticality)
W verifies and decrypts ENC_ID using the relevant algorithms of the
selected cipher suite SS (see Section 4.2), and obtains ID_U.
W calculates the hash of message_1 H(message_1), and associates this
session identifier to the device identifier ID_U. If H(message_1) is
not unique among session identifiers associated to this device
identifier of U, the EDHOC session SHALL be aborted.
W uses ID_U to look up the associated authorization policies for U
and enforces them. This is out of scope for the specification.
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4.6.2. Voucher Response
4.6.2.1. Processing in W
W retrieves CRED_V associated to the secure connection with V, and
constructs the the Voucher for the device with identifier ID_U (see
Section 4.4.2).
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 = [
message_1: bstr,
Voucher: bstr,
? opaque_state: bstr
]
where
* message_1 is the EDHOC message_1 as it was received from V.
* The Voucher is defined in Section 4.4.2.
* opaque_state is the echoed byte string opaque_state from
Voucher_Request, if present.
4.6.2.2. Processing in V
V receives the voucher response from W over the secure connection.
If present, V decrypts and verifies opaque_state as received from W.
If that verification fails then EDHOC is aborted. If the voucher
response is successfully received from W, then V responds to U with
EDHOC message_2 as described in Section 4.5.2.1.
5. REST Interface at W
The interaction between V and W is enabled through a RESTful
interface exposed by W. This RESTful interface MAY be implemented
using either HTTP or CoAP. V SHOULD access the resources exposed by
W through the protocol indicated by the scheme in LOC_W URI.
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5.1. Scheme "https"
In case the scheme indicates "https", V MUST perform a TLS handshake
with W and use HTTP. If the authentication credential CRED_V can be
used in a TLS handshake, e.g. an X.509 certificate of a signature
public key, then V SHOULD use it to authenticate to W as a client.
If the authentication credential CRED_V cannot be used in a TLS
handshake, e.g. if the public key is a static Diffie-Hellman key,
then V SHOULD first perform a TLS handshake with W using available
compatible keys. V MUST then perform an EDHOC session over the TLS
connection proving to W the possession of the private key
corresponding to CRED_V. Performing the EDHOC session is only
necessary if V did not authenticate with CRED_V in the TLS handshake
with W.
Editor's note: Clarify that performing TLS handshake is not necessary
for each device request; if there already is a TLS connection between
V and W that should be reused. Similar considerations for 5.2 and
5.3.
5.2. Scheme "coaps"
In case the scheme indicates "coaps", V SHOULD perform a DTLS
handshake with W and access the resources defined in Section 5.4
using CoAP. The normative requirements in Section 5.1 on performing
the DTLS handshake and EDHOC session remain the same, except that TLS
is replaced with DTLS.
5.3. Scheme "coap"
In case the scheme indicates "coap", V SHOULD perform an EDHOC
session with W, as specified in Appendix A of [I-D.ietf-lake-edhoc]
and access the resources defined in Section 5.4 using OSCORE and
CoAP. The authentication credential in this EDHOC session MUST be
CRED_V.
5.4. URIs
The URIs defined below are valid for both HTTP and CoAP. W MUST
support the use of the path-prefix "/.well-known/", as defined in
[RFC8615], and the registered name "lake-authz". A valid URI in case
of HTTP thus begins with
* "https://www.example.com/.well-known/lake-authz"
In case of CoAP with DTLS:
* "coaps://example.com/.well-known/lake-authz"
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In case of EDHOC and OSCORE:
* "coap://example.com/.well-known/lake-authz"
Each operation specified in the following is indicated by a path-
suffix.
5.4.1. Voucher Request (/voucherrequest)
To request a voucher, V MUST issue a request:
* Method is POST
* Payload is the serialization of the Voucher Request object, as
specified in Section 4.6.1.
* Content-Format (Content-Type) is set to "application/lake-authz-
voucherrequest+cbor"
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 4.6.2.
5.4.2. 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 a 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_U.
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.
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EDHOC provides identity protection of the Initiator, here the device.
The encryption of the device identifier ID_U in the first message
should consider potential information leaking from the length of
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_U from ID_CRED_I, or this credential lookup function may be
separate from the authorization function of W, see Figure 3. 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 reveals U's identity, CRED_U could be sent in Voucher
Response.
As noted in 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 enrollment server.
The private ephemeral key is thus used in the device for calculations
of key material relating to both the authenticator and the enrollment
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
device 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 4.5.1 and Section 4.5.2, respectively, of this
document.
+=======+============+=============================+
| Label | Value Type | Description |
+=======+============+=============================+
| TBD1 | bstr | Voucher related information |
+-------+------------+-----------------------------+
Table 1: Addition to the EDHOC EAD registry
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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.
7.4. Media Types Registry
IANA has added the media types "application/lake-authz-
voucherrequest+cbor" to the "Media Types" registry.
7.4.1. application/lake-authz-voucherrequest+cbor Media Type
Registration
* Type name: application
* Subtype name: lake-authz-voucherrequest+cbor
* Required parameters: N/A
* Optional paramaters: N/A
* Encoding considerations: binary
* Security cosniderations: See Section 6 of this document.
* Interoperability considerations: N/A
* Published specification: [[this document]] (this document)
* Application that use this media type: To be identified
* Fragment identifier considerations: N/A
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* Additional information:
- Magic number(s): N/A
- File extension(s): N/A
- Macintosh file type code(s): N/A
* Person & email address to contact for further information: See
"Authors' Addresses" section.
* Intended usage: COMMON
* Restrictions on usage: N/A
* Author: See "Authors' Addresses" section.
* Change Controller: IESG
7.5. CoAP Content-Formats Registry
IANA has added the media type "application/lake-authz-
voucherrequest+cbor" to the "CoAP Content-Formats" registry under the
registry group "Constrained RESTful Environments (CoRE) Parameters".
+================================+==========+======+============+
| Media Type | Encoding | ID | Reference |
+================================+==========+======+============+
| application/lake-authz- | - | TBD2 | [[this |
| voucherrequest+cbor | | | document]] |
+--------------------------------+----------+------+------------+
Table 2: Addition to the CoAP Content-Formats registry
8. References
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-20, 7 July
2023, <https://datatracker.ietf.org/api/v1/doc/document/
draft-ietf-lake-edhoc/>.
[NIST-800-56A]
Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Davis, "Recommendation for Pair-Wise Key-Establishment
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Schemes Using Discrete Logarithm Cryptography - NIST
Special Publication 800-56A, Revision 3", April 2018,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-56Ar3.pdf>.
[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>.
[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>.
[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>.
8.2. Informative References
[I-D.ietf-core-oscore-edhoc]
Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
G. Selander, "Using EDHOC with CoAP and OSCORE", Work in
Progress, Internet-Draft, draft-ietf-core-oscore-edhoc-07,
13 March 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-oscore-edhoc-07>.
[I-D.ietf-lake-reqs]
Vučinić, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carillo, "Requirements for a Lightweight AKE for OSCORE",
Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04,
8 June 2020, <https://datatracker.ietf.org/doc/html/draft-
ietf-lake-reqs-04>.
[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>.
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[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>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
[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>.
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).
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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 4: 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
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 4
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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 4.5. 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 4.5.
A.2.2. Flight 2
The domain authenticator receives message_1 and processes it as
described in Section 4.5. The message triggers the exchange with the
enrollment server, as described in Section 4.6. If the exchange
between V and W completes successfully, the domain authenticator
prepares EDHOC message_2, as described in Section 4.5. The
authenticator SHALL map the message to a CoAP response:
* 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 4.5.
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A.2.3. Flight 3
The device receives EDHOC message_2 and processes it as described in
Section 4.5}. 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 4.5. 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 session, 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 session. 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 session, and the certificate of the 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.
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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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