ACE Working Group L. Seitz
SICS Swedish ICT
Internet-Draft July 18, 2016
Intended Status: Standards Track
Expires: January 19, 2017
OSCOAP profile of ACE
draft-seitz-ace-oscoap-profile-00
Abstract
This memo specifies a profile for the ACE framework for
Authentication and Authorization. It utilizes Object Security of
CoAP (OSCOAP) and Ephemeral Diffie-Hellman over COSE (EDHOC) to
provide communication security, server authentication, and proof-of-
possession for a key owned by the client and bound to an OAuth 2.0
access token.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Client to Resource Server . . . . . . . . . . . . . . . . . . . 4
2.1. Signalling the use of OSCOAP . . . . . . . . . . . . . . . 4
2.2. Key establishment for OSCOAP . . . . . . . . . . . . . . . 4
2.3. Securing the Resource Request . . . . . . . . . . . . . . . 6
2.4. Securing the Resource Server Response . . . . . . . . . . . 6
3. Client to Authorization Server . . . . . . . . . . . . . . . . 6
4. Resource Server to Authorization Server . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1 Normative References . . . . . . . . . . . . . . . . . . . 7
9.2 Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This memo specifies a profile of the ACE framework [I-D.ietf-ace-
oauth-authz]. In this profile, a client and a resource server use
CoAP to communicate. The client uses an access token, bound to a key
(the proof-of-possession key) to authorize its access to the resource
server. In order to provide communication security, proof of
possession, and server authentication they use Object Security of
CoAP (OSCOAP) [I-D.selander-ace-object-security] and Ephemeral
Diffie-Hellman Over COSE (EDHOC) [I-D.selander-ace-cose-ecdhe].
Optionally the client and the resource server may also use CoAP and
OSCOAP to communicate with the authorization server. The use of
EDHOC in this profile in addition to OSCOAP, provides perfect forward
secrecy (PFS) and the initial proof-of-possession, which ties the
proof-of-possession key to an OSCOAP security context.
OSCOAP specifies how to use CBOR Object Signing and Encryption (COSE)
[I-D.ietf-cose-msg] to secure CoAP messages. In order to provide
replay and reordering protection OSCOAP also introduces sequence
numbers that are used together with COSE. EDHOC specifies an
authenticated Diffie-Hellman protocol that allows two parties to use
COSE in order to establish a shared secret key with perfect forward
secrecy.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. These
words may also appear in this document in lowercase, absent their
normative meanings.
Certain security-related terms such as "authentication",
"authorization", "confidentiality", "(data) integrity", "message
authentication code", and "verify" are taken from [RFC4949].
Since we describe exchanges as RESTful protocol interactions HTTP
[RFC7231] offers useful terminology.
Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749] and [I-D.ietf-ace-actors], such as client (C), resource
server (RS), and authorization server (AS).
Note that the term "endpoint" is used here following its OAuth
definition, which is to denote resources such as /token and
/introspect at the AS and /authz-info at the RS. The CoAP [RFC7252]
definition, which is "An entity participating in the CoAP protocol"
is not used in this memo.
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2. Client to Resource Server
The use of OSCOAP for arbitrary CoAP messages is specified in [I-
D.selander-ace-object-security]. This section defines the specific
uses and their purpose for securing the communication between a
client and a resource server, and the parameters for to negotiating
the use of this profile with the token endpoint at the authorization
server as specified in section 6 of the ACE framework [I-D.ietf-ace-
oauth-authz].
2.1. Signalling the use of OSCOAP
A client requesting a token at an AS via the /token endpoint MAY
signal a preference for using OSCOAP by including the "profile"
parameter with the value "coap_oscoap" in it's access token request.
This follows the message formats specified in section 6.1 of the ACE
framework.
The AS responding to a successful access token request as defined in
section 6.2 of the ACE framework can signal that the use of OSCOAP is
REQUIRED for a specific access token by including the "profile"
parameter with the value "coap_oscoap" in the access token response.
This means that the client MUST use OSCOAP towards all resource
servers for which this access token is valid.
The error response procedures defined in section 6.3 of the ACE
framework are unchanged by this profile.
Note the the client and the authorization server MAY OPTIONALLY use
OSCOAP to protect the interaction via the /token endpoint. See
section 3 for details.
2.2. Key establishment for OSCOAP
Section 3.2 of OSCOAP [I-D.selander-ace-object-security] defines how
to derive a security context based on a pre-shared secret established
between client and server. If the proof-of-possession key is a
symmetric key, it MAY be directly used as shared secret with OSCOAP.
However to provide forward secrecy and mutual authentication in the
case of pre-established raw public keys or with X.509 certificates it
is RECOMMENDED to use EDHOC [I-D.selander-ace-cose-ecdhe] to generate
the initial shared key. EDHOC MUST be used as follows:
When the client sends the access token to the RS using the /authz-
info endpoint as specified in section 8.1 of the ACE framework, this
message MUST carry message_1 of the EDHOC protocol in the CoAP
payload, and the access token MUST be included in the COSE
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unprotected header of message_1 as a CBOR map with the key
'access_token'.
When the RS responds to this token submission request, if the access
token was valid the payload of the CoAP response MUST contain
message_2 of the EDHOC protocol. If the token was not valid, the
error response defined in the ACE framework is not modified. If the
EDHOC message_1 was not valid the RS MUST respond with error code
4.01 (Unauthorized).
In the case of EDHOC being used with symmetric pop-keys, the protocol
in section 3.4 of [I-D.selander-ace-cose-ecdhe] MUST be used. If the
pop-key is asymmetric, the RS MUST also use an asymmetric key for
authentication. This key is known to the client through the access
token response (see section 6.2 of the ACE framework). In this case
the protocol in section 3.5 of [I-D.selander-ace-cose-ecdhe] MUST be
used.
Note that if the OSCOAP profile is used, the /authz-info endpoint at
the Resource Server MUST be prepared to process and generate the
protocol messages of the EDHOC protocol as specified above. Hence
the use of EDHOC does not add any additional roundtrips to the ACE
message exchange.
Figure 1 illustrates the message exchanges for using EDHOC on the
/authz-info endpoint (step C in figure 1 of [I-D.ietf-ace-oauth-
authz]).
Resource
Client Server
| |
| |
C: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Content-Type: application/cose+cbor
| | Payload: EDHOC message_1 + access token
| |
|<--------+ Header: 2.04 Changed
| | Content-Type: application/cose+cbor
| 2.05 | Payload: EDHOC message_2
| |
Figure 1: Key establishment with EDHOC via the authz-info endpoint
Figure 2 shows an example of message_1 with an access token embedded
in the unprotected header.
997(
[
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/ protected / h'a201260444c150d41c',
/ 'alg' : 'ES256', 'kid' : 'kid_c' /
/ unprotected / {'access_token' : h'4a5015df6864286979'},
/ payload / h'83381a0c582fa120a50102024103200121582098f
50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b4d9
1d628022f5',
/ signature / h'eae868ecc1276883766c5dc5ba5b8dca25dab3c
2e56a51ce5705b793914348e14eea4aee6e0c9f09db4ef3ddeca8f3
506cd1a98a8fb64327be470355c9657ce0'
]
)
Figure 2: EDHOC message_1 with an access token
2.3. Securing the Resource Request
When the client wishes to send a request to the RS, it uses the steps
defined in section 6 of OSCOAP [I-D.selander-ace-object-security] to
generate an OSCOAP message out of the unsecured CoAP message.
2.4. Securing the Resource Server Response
When a RS responds to a client's request, it uses the steps defined
in section 6 of OSCOAP [I-D.selander-ace-object-security] to generate
an OSCOAP message out of the unsecured CoAP message.
3. Client to Authorization Server
As specified in the ACE framework section 5 [I-D.ietf-ace-oauth-
authz], the Client and AS can also use CoAP instead of HTTP to
communicate via the token endpoint. This section specifies how to
use OSCOAP between Client and AS together with CoAP. The use of
OSCOAP for this communication is OPTIONAL in this profile, other
security protocols (such as DTLS) MAY be used instead.
The client and the AS are expected to have pre-established
credentials (e.g. raw public keys). How these credentials are
established is out of scope for this profile. Furthermore the client
and the AS communicate using CoAP through the token endpoint as
specified in section 6 of [I-D.ietf-ace-oauth-authz]. At first point
of contact, prior to making the token request and response, the
client and the AS MUST perform an EDHOC exchange with the pre-
established credentials to create forward secret keying material for
use with OSCOAP. Subsequent requests and the responses MUST be
protected with OSCOAP.
4. Resource Server to Authorization Server
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As specified in the ACE framework section 5 [I-D.ietf-ace-oauth-
authz], the RS and AS can also use CoAP instead of HTTP to
communicate via the introspection endpoint. This section specifies
how to use OSCOAP between RS and AS together with CoAP. The use of
OSCOAP for this communication is OPTIONAL in this profile, other
security protocols (such as DTLS) MAY be used instead.
The RS and the AS are expected to have pre-established credentials
(e.g. symmetric keys). How these credentials are established is out
of scope for this profile. Furthermore the RS and the AS communicate
using CoAP through the introspection endpoint as specified in section
7 of [I-D.ietf-ace-oauth-authz]. At first point of contact, prior to
making the introspection request and response, the RS and the AS MUST
perform an EDHOC exchange with the pre-established credentials to
create forward secret keying material for use with OSCOAP.
Subsequent requests and the responses MUST be protected with OSCOAP.
5. Security Considerations
TBD.
6. Privacy Considerations
TBD.
7. IANA Considerations
FIXME: PoP alg: OSCOAP
8. Acknowledgements
The author wishes to thank Goeran Selander and Francesca Palombini
for the input on this memo.
9. References
9.1 Normative References
[I-D.selander-ace-object-security] Selander, G., Mattsson J.,
Palombini F., and L. Seitz. "Object Security of CoAP
(OSCOAP)", draft-selander-ace-object-security-04 (work in
progress), March 2016.
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[I-D.selander-ace-cose-ecdhe] Selander, G., Mattsson J.,
and F. Palombini. "Ephemeral Diffie-Hellman Over COSE
(EDHOC)", draft-selander-ace-cose-ecdhe-02 (work in
progress), June 2016.
[I-D.ietf-ace-oauth-authz] Seitz, L., Selander, G.,
Wahlstroem, E., Erdtmann, S., and H. Tschofenig.
"Authentication and Authorization for Constrained
Environments (ACE)", drart-ietf-ace-oauth-authz-02 (work
in progress), June 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997, <http://www.rfc-
editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, DOI
10.17487/RFC7252, June 2014, <http://www.rfc-
editor.org/info/rfc7252>.
9.2 Informative References
[I-D.gerdes-ace-actors]
Gerdes, S., Seitz, L., G. Selander, and C. Bormann (ed).
"An Arhitecture for Authorization in Constrained
Environments", draft-ietf-ace-actors-03 (work in
progress), March 2016.
[I-D.ietf-cose-msg] Schaad, J., "CBOR Object Signing and
Encryption (COSE)", draft-ietf-cose-msg-14 (work in
progress), June 2016.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI
36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<http://www.rfc-editor.org/info/rfc4949>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.
[RFC7231] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content",
RFC 7231, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
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Author's Address
Ludwig Seitz
SICS Swedish ICT AB
Scheelevagen 17
22370 Lund
SWEDEN
EMail: ludwig@sics.se
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