anima Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Standards Track P. van der Stok
Expires: April 2, 2019 vanderstok consultancy
P. Kampanakis
Cisco Systems
September 29, 2018

Constrained Join Proxy for Bootstrapping Protocols
draft-vanderstok-constrained-anima-dtls-join-proxy-00

Abstract

This document defines a protocol to securely assign a pledge to an owner, using an intermediary node between pledge and owner. This intermediary node is known as a "constrained-join-proxy".

This document extends the work of [I-D.ietf-anima-bootstrapping-keyinfra] by replacing the Circuit-proxy by a stateless constrained join-proxy, that uses IP encapsulation.

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 April 2, 2019.

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 (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

Enrolment of new nodes into constrained networks with constrained nodes present is described in [I-D.ietf-anima-bootstrapping-keyinfra] and makes use of Enrolment over Secure Transport (EST) [RFC7030]. The specified solutions use https and may be too large in terms of code space or bandwidth required. Constrained devices in constrained networks [RFC7228] typically implement the IPv6 over Low-Power Wireless personal Area Networks (6LoWPAN) [RFC4944] and Constrained Application Protocol (CoAP) [RFC7252].

CoAP has chosen Datagram Transport Layer Security (DTLS) [RFC6347] as the preferred security protocol for authenticity and confidentiality of the messages. A constrained version of EST, using Coap and DTLS, is described in [I-D.ietf-ace-coap-est].

DTLS is a client-server protocol relying on the underlying IP layer to perform the routing between the DTLS Client and the DTLS Server. However, the new "joining" device will not be IP routable until it is authenticated to the network. A new "joining" device can only initially use a link-local IPv6 address to communicate with a neighbour node using neighbour discovery [RFC6775] until it receives the necessary network configuration parameters. However, before the device can receive these configuration parameters, it needs to authenticate itself to the network to which it connects. In [I-D.ietf-anima-bootstrapping-keyinfra] Enrolment over Secure Transport (EST) [RFC7030] is used to authenticate the joining device. However, IPv6 routing is necessary to establish a connection between joining device and the EST server.

This document specifies a Join-proxy and protocol to act as intermediary between joining device and EST server to establish a connection between joining device and EST server.

This document is very much inspired by text published earlier in [I-D.kumar-dice-dtls-relay].

2. Terminology

The following terms are defined in [RFC8366], and are used identically as in that document: artifact, imprint, domain, Join Registrar/Coordinator (JRC), Manufacturer Authorized Signing Authority (MASA), pledge, Trust of First Use (TOFU), and Voucher.

3. Requirements Language

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant STuPiD implementations.

4. Join Proxy functionality

As depicted in the Figure 1, the joining Device, or pledge (P), is more than one hop away from the EST server (E) and not yet authenticated into the network. At this stage, it can only communicate one-hop to its nearest neighbour, the Join proxy (J) using their link-local IPv6 addresses. However, the Device needs to communicate with end-to-end security with a Registrar hosting the EST server (E) to authenticate and get the relevant system/network parameters. If the Pledge (P) initiates a DTLS connection to the EST server whose IP address has been pre-configured, then the packets are dropped at the Join Proxy (J) since the Pledge (P) is not yet admitted to the network or there is no IP routability to Pledge (P) for any returned messages.

                      ++++
                      |E |----       +--+        +--+
                      |  |    \      |J |........|P |
                      ++++     \-----|  |        |  |
                   EST server        +--+        +--+
                   REgistrar       Join Proxy   PLedge
                                                "Joining" Device

Figure 1: multi-hop enrolment.

Furthermore, the Pledge (P) may wish to establish a secure connection to the EST server (E) in the network assuming appropriate credentials are exchanged out-of-band, e.g. a hash of the Pledge (P)'s raw public key could be provided to the EST server (E). However, the Pledge (P) is unaware of the IP address of the EST-server (E) to initiate a DTLS connection and perform authentication with.

An DTLS connection is required between Pledge and EST server. To overcome the problems with non-routability of DTLS packets and/ or discovery of the destination address of the EST Server to contact, the Join Proxy is introduced. This Join-Proxy functionality is configured into all authenticated devices in the network which may act as the Join Proxy (J) for newly joining nodes. The Join Proxy allows for routing of the packets from the Pledge (P) using IP routing to the intended EST Server.

5. Join Proxy specification

In this section, the constrained Join Proxy functionality is specified using DTLS and coaps. When a joining device as a client attempts a DTLS connection to the EST server, it uses its link- local IP address as its IP source address. This message is transmitted one-hop to a neighbour node. Under normal circumstances, this message would be dropped at the neighbour node since the joining device is not yet IP routable or it is not yet authenticated to send messages through the network. However, if the neighbour device has the Join Proxy functionality enabled, it routes the DTLS message to a specific EST Server. Additional security mechanisms need to exist to prevent this routing functionality being used by rogue nodes to bypass any network authentication procedures.

The Join-proxy is stateless to minimize the requirements on the constrained Join-proxy device.

If an untrusted DTLS Client that can only use link-local addressing wants to contact a trusted end-point EST Server, it sends the DTLS message to the Join Proxy. The Join Proxy encapsulates this message into a new type of message called Join ProxY (JPY) message. The JPY message consists of two parts:

On receiving the JPY message, the EST Server decapsulates it to retrieve the two parts. It uses the Header field information to transiently store the DTLS Client's address and port. The EST Server then performs the normal DTLS operations on the DTLS message from the Contents field. However, when the EST Server replies, it also encapsulates its DTLS message in a JPY message back to the Join Proxy. The Header contains the original source link-local address and port of the DTLS Client from the transient state stored earlier (which can now be discarded) and the Contents field contains the DTLS message.

On receiving the JPY message, the Join Proxy decapsulates it to retrieve the two parts. It uses the Header field to route the DTLS message retrieved from the Contents field to the joining node.

The Figure 2 depicts the message flow diagram when the EST Server end-point address is known only to the Join Proxy:

+--------------+------------+---------------+-----------------------+
| EST  Client  | Join Proxy |    EST server |        Message        |
|     (P)      |     (J)    |      (E)      |Src_IP:port|Dst_IP:port|
+--------------+------------+---------------+-----------+-----------+
|      --ClientHello-->                     | IP_C:p_C  |IP_Ra:5684 |
|                    --JPY[H(IP_C:p_C),-->  | IP_Rb:p_Rb|IP_S:5684  |
|                          C(ClientHello)]  |           |           |
|                    <--JPY[H(IP_C:p_C),--  | IP_S:5684 |IP_Rb:p_Rb |
|                         C(ServerHello)]   |           |           |
|      <--ServerHello--                     | IP_Ra:5684|IP_C:p_C   |
|              :                            |           |           |
|              :                            |     :     |    :      |
|                                           |     :     |    :      |
|      --Finished-->                        | IP_C:p_C  |IP_Ra:5684 |
|                    --JPY[H(IP_C:p_C),-->  | IP_Rb:p_Rb|IP_S:5684  |
|                          C(Finished)]     |           |           |
|                    <--JPY[H(IP_C:p_C),--  | IP_S:5684 |IP_Rb:p_Rb |
|                         C(Finished)]      |           |           |
|      <--Finished--                        | IP_Ra:5684|IP_C:p_C   |
|              :                            |     :     |    :      |
+-------------------------------------------+-----------+-----------+
IP_C:p_C = Link-local IP address and port of DTLS Client
IP_S:5684 = IP address and coaps port of DTLS Server
IP_Ra:5684 = Link-local IP address and coaps port of DTLS Relay
IP_Rb:p_Rb = IP address(can be same as IP_Ra) and port of DTLS Relay

JPY[H(),C()] = Join Proxy message with header H and content C

Figure 2: constrained joining message flow.

6. Protocol

The JPY message is constructed as a single untagged [RFC7049] CBOR map. The contents of the map include:

1:
the pledge IPv6 Link Local address as a 16-byte binary value.
2:
the pledge's UDP port number, if different from 5684, as a CBOR integer.
3:
the proxy's ifindex or other identifier for the physical port on which the pledge is connected.
4:
the contents of the UDP (DTLS) message received from the pledge.

(INSERT CDDL notation)

7. Security Considerations

It should be noted here that the contents of the CBOR map are not protected, but that the communication is between the Proxy and a known registrar (a connected UDP socket), and that messages from other origins are ignored.

8. IANA Considerations

This document needs to create a registry for key indexes in the CBOR map. It should be given a name, and the amending formula should be IETF Specification.

9. Acknowledgements

Much of this text is inspired by [I-D.kumar-dice-dtls-relay].

10. Changelog

empty

11. References

11.1. Normative References

[I-D.ietf-ace-cbor-web-token] Jones, M., Wahlstroem, E., Erdtman, S. and H. Tschofenig, "CBOR Web Token (CWT)", Internet-Draft draft-ietf-ace-cbor-web-token-15, March 2018.
[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)", Internet-Draft draft-ietf-ace-coap-est-05, July 2018.
[I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S. and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", Internet-Draft draft-ietf-anima-bootstrapping-keyinfra-16, June 2018.
[I-D.ietf-core-object-security] Selander, G., Mattsson, J., Palombini, F. and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", Internet-Draft draft-ietf-core-object-security-15, August 2018.
[ieee802-1AR] IEEE Standard, ., "IEEE 802.1AR Secure Device Identifier", 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013.
[RFC7250] Wouters, P., Tschofenig, H., Gilmore, J., Weiler, S. and T. Kivinen, "Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, June 2014.
[RFC7950] Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M. and T. Eckert, "A Voucher Artifact for Bootstrapping Protocols", RFC 8366, DOI 10.17487/RFC8366, May 2018.

11.2. Informative References

[duckling] Stajano, F. and R. Anderson, "The resurrecting duckling: security issues for ad-hoc wireless networks", 1999.
[I-D.kumar-dice-dtls-relay] Kumar, S., Keoh, S. and O. Garcia-Morchon, "DTLS Relay for Constrained Environments", Internet-Draft draft-kumar-dice-dtls-relay-02, October 2014.
[pledge] Dictionary.com, ., "Dictionary.com Unabridged", 2015.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J. and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E. and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, November 2012.
[RFC7030] Pritikin, M., Yee, P. and D. Harkins, "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013.
[RFC7228] Bormann, C., Ersue, M. and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014.
[RFC7252] Shelby, Z., Hartke, K. and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014.

Authors' Addresses

Michael Richardson Sandelman Software Works EMail: mcr+ietf@sandelman.ca
Peter van der Stok vanderstok consultancy EMail: consultancy@vanderstok.org
Panos Kampanakis Cisco Systems EMail: pkampana@cisco.com