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Versions: 00

ACE Working Group                                            G. Selander
Internet-Draft                                               Ericsson AB
Intended status: Standards Track                                 S. Raza
Expires: September 6, 2018                                     RISE SICS
                                                              M. Furuhed
                                                                   Nexus
                                                              M. Vucinic
                                                University of Montenegro
                                                          March 05, 2018


                  Protecting EST payloads with OSCORE
                 draft-selander-ace-coap-est-oscore-00

Abstract

   This document specifies public key certificate enrollment procedures
   protected with application-layer security protocols suitable for
   Internet of Things (IoT) deployments.  The protocols leverage payload
   formats defined in Enrolment over Secure Transport (EST) and existing
   IoT standards including the Constrained Application Protocol (CoAP),
   Concise Binary Object Representation (CBOR) and the CBOR Object
   Signing and Encryption (COSE) format.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 6, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  EST-CoAPs operational differences . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Protocol Design and Layering  . . . . . . . . . . . . . . . .   4
   3.  Discovery and URI . . . . . . . . . . . . . . . . . . . . . .   5
   4.  OSCORE-Based Security . . . . . . . . . . . . . . . . . . . .   5
   5.  Proxying  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   One of the challenges with deploying a Public Key Infrastructure
   (PKI) for the Internet of Things (IoT) is certificate enrolment,
   because existing enrolment protocols are not optimized for
   constrained environments [RFC7228].

   One optimization of certificate enrollment targeting IoT deployments
   is specified in EST-CoAPs ([I-D.ietf-ace-coap-est]), which defines a
   version of Enrolment over Secure Transport [RFC7030] for transporting
   EST payloads over CoAP [RFC7252] and DTLS [RFC6347], instead of
   secured HTTP.

   This document describes a method for protecting EST payloads over
   CoAP or HTTP with OSCORE [I-D.ietf-core-object-security].  OSCORE
   specifies an extension to CoAP which protects the application layer
   message and can be applied independently of how CoAP messages are
   transported.  OSCORE can also be applied to CoAP-mappable HTTP which
   enables end-to-end security for mixed CoAP and HTTP transfer of
   application layer data.  Hence EST payloads can be protected end-to-




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   end independent of underlying transport and through proxies
   translating between between CoAP and HTTP.

   OSCORE is designed for constrained environments, building on IoT
   standards such as CoAP, CBOR [RFC7049] and COSE [RFC8152], and has in
   particular gained traction in settings where message sizes and the
   number of exchanged messages needs to be kept at a minimum, see e.g.
   [I-D.ietf-6tisch-minimal-security], or for securing multicast CoAP
   messages [I-D.ietf-core-oscore-groupcomm].  Where OSCORE is
   implemented and used for communication security, the reuse of OSCORE
   for other purposes, such as enrolment, reduces the implementation
   footprint.

   In order to protect certificate enrolment with OSCORE, the necessary
   keying material (notably, the OSCORE Master Secret, see
   [I-D.ietf-core-object-security]) needs to be established between CoAP
   client and server, e.g. using a key exchange protocol; a trusted
   third party; or pre-established keys.  Different options are allowed
   and with different properties as is detailed in the next section.

   Yet other optimizations to certificate based enrolment are possible
   further improve the performance of certificate enrolment and
   certificate based authentication, in particular the use of more
   compact representations of X.509 certificates.

1.1.  EST-CoAPs operational differences

   This specification builds on EST-CoAPs [I-D.ietf-ace-coap-est] but
   transport layer security provided by DTLS is replaced, or
   complemented, by protection of the application layer data.  This
   specification deviates from EST-CoAPs in the following respects:

   o  The DTLS record layer is replaced, or complemented, with OSCORE.

   o  The DTLS handshake is replaced, or complemented, with an
      alternative key establishment, for example:

      *  A key exchange protocol, such as EDHOC
         [I-D.selander-ace-cose-ecdhe].  The use of a key exchange
         protocol completes the analogy with EST-CoAPs, and provides
         perfect forward secrecy (PFS) of the keys used to protect the
         EST messages.  However, PFS is not necessary for the enrolment
         procedure and adds significant overhead in terms of message
         size and round trips.

      *  Trusted third party (TTP) based provisioning, such as the
         OSCORE profile of ACE [I-D.ietf-ace-oscore-profile].  This
         assumes existing security associations between the client and



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         the TTP, and between the server and the TTP, and reduces the
         message size and round trips compared to a key exchange
         protocol.

      *  Pre-shared keys (PSK).  Although one reason for using PKI is to
         avoid managing PSK, applying OSCORE directly with PSK
         specifically during deployment gives a one round-trip enrolment
         protocol with low message overhead, thereby further reducing
         the network load and time for commissioning.

   o  EST payloads protected by OSCORE can be proxied between
      constrained networks supporting CoAP/CoAPs and non-constrained
      networks supporting HTTP/HTTPs with a CoAP-HTTP proxy protection
      without any security processing in the proxy.

1.2.  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.

   This document uses terminology from [I-D.ietf-ace-coap-est] which in
   turn is based on [RFC7030] and, in turn, on [RFC5272].

2.  Protocol Design and Layering

   EST-oscore uses CoAP [RFC7252] and Block-Wise [RFC7959] to transfer
   EST messages in the same way as [I-D.ietf-ace-coap-est].  Figure 1
   below shows the layered EST-oscore architecture.

            +------------------------------------------------+
            |          EST request/response messages         |
            +------------------------------------------------+
            |   CoAP with OSCORE   |   HTTP with OSCORE      |
            +------------------------------------------------+
            |   UDP  |  DTLS/UDP   |        TLS/TCP          |
            +------------------------------------------------+


                   Figure 1: EST protected with OSCORE.

   EST-oscore follows closely the EST-coaps and EST design.  The message
   types for simple enroll, reenroll, CA certificate retrieval, CSR
   Attributes request messages and Server-side key generation messages
   apply.




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   The payload format, message bindings and CoAP response codes
   specified in Section 3.1 - 3.3, as well as the new Content-Formats
   defined in Section 8.1 of [I-D.ietf-ace-coap-est] apply.  Message
   fragmentation based on CoAP Block options specified in section 3.4 is
   also applicable with OSCORE.  The same deployment limitation
   considerations as listed in section 3.5 applies.

3.  Discovery and URI

   The discovery of EST resources defined in Section 4 of
   [I-D.ietf-ace-coap-est], as well as the new Resource Type defined in
   Section 8.1 of [I-D.ietf-ace-coap-est] apply to EST-oscore.  Support
   for OSCORE is indicated by the "osc" attribute defined in Section 9
   of [I-D.ietf-core-object-security], for example:

        REQ: GET /.well-known/core?rt=ace.est

        RES: 2.05 Content
      </est>; rt="ace.est";osc


   The abbreviated EST-coaps URI paths defined in Section 4 of
   [I-D.ietf-ace-coap-est] also apply.

4.  OSCORE-Based Security

   EST-oscore depends on the application layer security provided by
   OSCORE for protecting CoAP and CoAP-mappable HTTP independent of
   transport.  The establishment of keys for OSCORE defines many of the
   properties of the protocol.

   If a key exchange protocols is used, fragmentation of the protocol
   messages needs to be handled.  EDHOC [I-D.selander-ace-cose-ecdhe]
   may be carried in CoAP in which case Block fragmentation can be used.

   (Editor's note: Compare and complete with the analogous Section 5 in
   EST-coaps)

5.  Proxying

   Section 6 of [I-D.ietf-ace-coap-est] describes the real-world
   deployment setting where a constrained EST client with a CoAP stack
   needs to communicate securely outside the CoAP boundary with an EST
   server implementing HTTP/TLS.  This section describes the analogous
   setting with OSCORE protected EST payloads.

   Since OSCORE is applicable to CoAP-mappable HTTP the EST payloads can
   be protected end-to-end between EST client and EST server independent



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   of transport layer security which is terminated in the proxy, see
   Figure Figure 2.  The mappings between CoAP and HTTP referred to in
   Section 6 of [I-D.ietf-ace-coap-est] applies and the additional
   mappings resulting from the use of OSCORE are specified in
   Section 10.4 of [I-D.ietf-core-object-security].

                                           Constrained-Node Network
                         .---------.    .----------------------------.
                         |   RA    |    |.--------------------------.|
                         '---------'    ||                          ||
                               |        ||                          ||
       .------.  HTTP   .-----------------.   CoAP   .-----------.  ||
       | EST  |<------->|  CoAP-to-HTTP   |<-------->| EST Client|  ||
       |Server| (over   |      Proxy      |          '-----------'  ||
       '------'  TLS)   '-----------------'                         ||
                                        ||                          ||
           <------------------------------------------------>       ||
                              OSCORE    |'--------------------------'|
                                        '----------------------------'

            Figure 2: CoAP-to-HTTP proxy at the CoAP boundary.

6.  Security Considerations

   TBD

7.  Privacy Considerations

   TBD

8.  IANA Considerations

9.  Acknowledgments

10.  References

10.1.  Normative References

   [I-D.ietf-ace-coap-est]
              Stok, P., Kampanakis, P., Kumar, S., Richardson, M.,
              Furuhed, M., and S. Raza, "EST over secure CoAP (EST-
              coaps)", draft-ietf-ace-coap-est-00 (work in progress),
              February 2018.








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   [I-D.ietf-core-object-security]
              Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", draft-ietf-core-object-security-08 (work in
              progress), January 2018.

   [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>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7959]  Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
              the Constrained Application Protocol (CoAP)", RFC 7959,
              DOI 10.17487/RFC7959, August 2016,
              <https://www.rfc-editor.org/info/rfc7959>.

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

10.2.  Informative References

   [I-D.ietf-6tisch-minimal-security]
              Vucinic, M., Simon, J., Pister, K., and M. Richardson,
              "Minimal Security Framework for 6TiSCH", draft-ietf-
              6tisch-minimal-security-04 (work in progress), October
              2017.

   [I-D.ietf-ace-oscore-profile]
              Seitz, L., Palombini, F., and M. Gunnarsson, "OSCORE
              profile of the Authentication and Authorization for
              Constrained Environments Framework", draft-ietf-ace-
              oscore-profile-00 (work in progress), December 2017.

   [I-D.ietf-core-oscore-groupcomm]
              Tiloca, M., Selander, G., Palombini, F., and J. Park,
              "Secure group communication for CoAP", draft-ietf-core-
              oscore-groupcomm-01 (work in progress), March 2018.




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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-07 (work in progress), July 2017.

   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <https://www.rfc-editor.org/info/rfc5272>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <https://www.rfc-editor.org/info/rfc7030>.

   [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>.

Appendix A.  Examples

   TBD

Authors' Addresses

   Goeran Selander
   Ericsson AB

   Email: goran.selander@ericsson.com


   Shahid Raza
   RISE SICS

   Email: shahid.raza@ri.se


   Martin Furuhed
   Nexus

   Email: martin.furuhed@nexusgroup.com






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   Malisa Vucinic
   University of Montenegro

   Email: malisav@ac.me















































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