[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00

TBD                                                        M. Sahni, Ed.
Internet-Draft                                        Palo Alto Networks
Intended status: Standards Track                            June 4, 2020
Expires: December 6, 2020


                        CoAP Transport for CMPV2
               draft-msahni-tbd-cmpv2-coap-transport-00

Abstract

   This document specifies how to use Constrained Application Protocol
   (CoAP) as a Transport Medium for the Certificate management protocol
   version 2 (CMPv2) and Lightweight CMP Profile
   [Lightweight-CMP-Profile] which is a subset of CMPv2 defined for
   Constrained devices.  The CMPv2 defines the interaction between
   various PKI entities for the purpose of certificate creation and
   management.  The CoAP is an HTTP like client-server protocol used by
   various constrained devices in the IoT and industrial scenarios.
   Constrained devices are devices that have low memory or CPU or power
   constraints and avoid the use of complex protocols like TCP to save
   resources.

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 December 6, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of



Sahni                   Expires December 6, 2020                [Page 1]


Internet-Draft          CoAP Transport for CMPV2               June 2020


   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  CoAP Transport For CMPv2  . . . . . . . . . . . . . . . . . .   3
     2.1.  CoAP URI Format . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  CoAP Request Format . . . . . . . . . . . . . . . . . . .   3
     2.3.  CoAP Content-Format . . . . . . . . . . . . . . . . . . .   3
     2.4.  Announcement PKIMessage . . . . . . . . . . . . . . . . .   4
     2.5.  CoAP Block Wise Transfer Mode . . . . . . . . . . . . . .   4
     2.6.  Multicast CoAP  . . . . . . . . . . . . . . . . . . . . .   4
   3.  Using CoAP over DTLS  . . . . . . . . . . . . . . . . . . . .   4
   4.  Proxy support . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  CoAP to HTTP Proxy  . . . . . . . . . . . . . . . . . . .   5
     4.2.  CoAPs to HTTPs Proxy  . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
     8.3.  URL References  . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The CMPv2 is used by the entities in PKI for the generation and
   management of the certificate.  One of the requirements of CMPv2
   [RFC4210] is to be usable over a variety of protocols.  The CoAP
   [RFC7252] and [RFC7959] is a client-server protocol like HTTP that is
   designed to be used by constrained devices over constrained networks
   (low power lossy networks).  This document specifies the use of CoAP
   as a transport medium for the CMPv2 and Lightweight CMP Profile
   [Lightweight-CMP-Profile].  This document, in general, follows the
   HTTP transport specifications for CMPv2 defined in [RFC6712] and
   specifies the additional requirements for CoAP transport.  This
   document also provides guidance on how to use a "CoAP to HTTP" proxy
   for a better adaptation of CoAP transport without significant changes
   to the existing PKI entities.  Although CoAP transport can be used
   for communication between RAs and CAs or between CAs, the scope of
   this document is for communication between EEs and RAs or EEs and



Sahni                   Expires December 6, 2020                [Page 2]


Internet-Draft          CoAP Transport for CMPV2               June 2020


   CAs.This document is applicable only when the CoAP transport is being
   used for the CMPv2 transactions.

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.

2.  CoAP Transport For CMPv2

   CMPv2 transaction consists of passing PKIMesssage [RFC4210] between
   the PKI End Entities (EEs), Registration Authorities (RAs), and
   Certification Authorities (CAs). if the EEs are constrained devices
   then they will prefer, as a client, the use of CoAP over the HTTP as
   a transport medium, while the RAs and CAs, in general, are not
   constrained and can support both CoAP and HTTP Client and Server
   implementation.  This section describes how to use CoAP as transport
   for CMPv2 or Lightweight CMP Profile [Lightweight-CMP-Profile].

2.1.  CoAP URI Format

   The CoAP URI MUST follow the guidelines defined in section 3.6 of
   [RFC6712] for CMPv2 protocol.  Implementations supporting the
   Lightweight CMP Profile [Lightweight-CMP-Profile] MUST follow the
   guidelines specified for HTTP transport defined in section 7.1 of
   Lightweight CMP Profile [Lightweight-CMP-Profile].  The URI's for
   CoAP resources should start of coap:// instead of http:// and
   coaps:// instead of https://

2.2.  CoAP Request Format

   The CMPv2 PKIMessage MUST be DER encoded and sent as the body of the
   CoAP POST request.  If the CoAP request is successful then the server
   should return a "2.05 Content" response code.  If the CoAP request is
   not successful then an appropriate CoAP Client Error 4.xx or a Server
   Error 5.xx response code MUST be returned.

2.3.  CoAP Content-Format

   When transferring CMPv2 PKIMesssage over CoAP the media type
   application/pkixcmp MUST be used.







Sahni                   Expires December 6, 2020                [Page 3]


Internet-Draft          CoAP Transport for CMPV2               June 2020


2.4.  Announcement PKIMessage

   When using the CoAP protocol, a PKI entity SHOULD poll for the
   possible changes via PKI Information request using General Message
   defined in a PKIMessage for various type of changes like CA key
   update or to get current CRL to check revocation or using Support
   messages defined in section 5.4 of Lightweight CMP Profile
   [Lightweight-CMP-Profile].  This will make use of a CoAP to HTTP
   proxy transparent to the client.

2.5.  CoAP Block Wise Transfer Mode

   Since the CMPv2 PKIMesssage consists of a header body and optional
   fields, when using CoAP as transport for the CMPv2 protocol the Block
   Wise transfer [RFC7959] mode MUST be used for the CMPv2 Transaction.
   If a CoAP to HTTP proxy is in the path between EEs and CA or EEs and
   RA then, it MUST receive the entire body from the client before
   sending the HTTP request to the server.  This will avoid unnecessary
   errors in case the entire content of the PKIMesssage is not received
   and Proxy opens a connection with the server.

2.6.  Multicast CoAP

   CMPv2 PKIMessage request messages sent from EEs to RAs or from EEs to
   CAs over CoAP transport MUST not use a Multicast destination address.

3.  Using CoAP over DTLS

   When the end to end secrecy is desired for CoAP transport, CoAP over
   DTLS [RFC6347] as a transport medium should be used.  Section 9.1 of
   [RFC7252] defines how to use DTLS [RFC6347] for securing the CoAP.
   For CMPv2 and Lightweight CMP Profile [Lightweight-CMP-Profile] the
   clients should follow specifications defined in section 7.1 and
   section 7.2 of Lightweight CMP Profile [Lightweight-CMP-Profile] for
   setting up DTLS [RFC6347] connection either using certificates or
   shared secret for setting up DLTS connection.  Once a DTLS [RFC6347]
   connection is established it SHOULD be used for as long as possible
   to avoid the frequent overhead of using DTLS [RFC6347] connection for
   constrained devices

4.  Proxy support

   The use of a CoAP to HTTP proxy is recommended to avoid significant
   changes in the implementation of the CAs and RAs.  However, if a
   proxy is in place then Announcements Messages cannot be passed to EEs
   efficiently.





Sahni                   Expires December 6, 2020                [Page 4]


Internet-Draft          CoAP Transport for CMPV2               June 2020


4.1.  CoAP to HTTP Proxy

   If a CoAP to HTTP proxy is used then it MUST be positioned between
   EEs and RAs or between EEs and CAs when RA is not part of CMPv2
   transactions.  The use of a CoAP to HTTP proxy between CAs and RAs is
   not recommended.  The implementation of a CoAP to HTTP proxy is
   specified in Section 10 of [RFC7252].  The CoAP to HTTP proxy will
   also protect the CAs and RAs from UDP based Denial of Service
   attacks.

4.2.  CoAPs to HTTPs Proxy

   A CoAPS to HTTPS proxy (DTLS [RFC6347] transport to TLS [RFC8446]
   transport proxy) SHOULD not be used as it can be insecure for the
   client to trust the Man in the Middle (MiTM) certificate issued by
   the proxy to share client and server shared secret with the proxy.
   If a server requires Mutual TLS [MTLS] then a proxy will not work.

5.  Security Considerations

   The CMPv2 protocol itself does not require secure transport and
   depends upon various mechanisms in the protocol itself to make sure
   that the transactions are secure.  However, the CoAP protocol which
   uses UDP as layer 4 transport is vulnerable to many issues due to the
   connectionless characteristics of UDP itself.  The Security
   considerations for CoAP protocol are mentioned in the [RFC7252].
   Using a CoAP to HTTP proxy mitigates some of the risks as the
   requests from the EE's can terminate inside the trusted network and
   will not require the server to listen on a UDP port making it safe
   from UDP based address spoofing, Denial of Service, and amplification
   attacks due to the characteristics of TCP.

6.  IANA Considerations

   This document requires a new entry to the CoAP Content-Formats
   Registry code for the content-type application/pkixcmp

7.  Acknowledgments

   The author would like to thank Hendrik Brockhaus, David von Oheimb,
   and Andreas Kretschmer for their guidance in writing the content of
   this document and providing valuable feedback.

8.  References







Sahni                   Expires December 6, 2020                [Page 5]


Internet-Draft          CoAP Transport for CMPV2               June 2020


8.1.  Normative References

   [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>.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [RFC6712]  Kause, T. and M. Peylo, "Internet X.509 Public Key
              Infrastructure -- HTTP Transfer for the Certificate
              Management Protocol (CMP)", RFC 6712,
              DOI 10.17487/RFC6712, September 2012,
              <https://www.rfc-editor.org/info/rfc6712>.

   [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>.

   [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>.

8.2.  Informative References

   [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>.

   [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>.

8.3.  URL References







Sahni                   Expires December 6, 2020                [Page 6]


Internet-Draft          CoAP Transport for CMPV2               June 2020


   [Lightweight-CMP-Profile]
              Brockhaus, H., Fries, S., and D. von Oheimb, "Lightweight
              CMP Profile", 2020, <https://tools.ietf.org/html/draft-
              brockhaus-lamps-lightweight-cmp-profile-03>.

   [MTLS]     Rescorla, E., "Mutual TLS", August 2018,
              <https://tools.ietf.org/html/rfc8446#section-4.3.2>.

Author's Address

   Mohit Sahni (editor)
   Palo Alto Networks
   3000 Tannery Way
   Santa Clara, CA  95054
   US

   EMail: msahni@paloaltonetworks.com


































Sahni                   Expires December 6, 2020                [Page 7]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/