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Versions: (draft-seitz-ace-ocsoap-profile) 00 01 02 03 04 05 06 draft-ietf-ace-oscore-profile

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

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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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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   Provisions Relating to IETF Documents
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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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