6tisch Working Group M. Richardson
Internet-Draft Sandelman Software Works
Intended status: Informational B. Damm
Expires: March 1, 2018 Silver Spring Networks
August 28, 2017

6tisch Zero-Touch Secure Join protocol


This document describes a zero-touch mechanism to enroll a new device (the "pledge") into a IEEE802.15.4 TSCH network using the 6tisch signaling mechanisms. The resulting device will obtain a domain specific credential that can be used with either 802.15.9 per-host pair keying protocols, or to obtain the network-wide key from a coordinator. The mechanism describe her is an augmentation to the one-touch mechanism described in [I-D.ietf-6tisch-minimal-security].

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 March 1, 2018.

Copyright Notice

Copyright (c) 2017 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

Enrollment of new nodes into LLNs present unique challenges. The constrained nodes has no user interfaces, and even if they did, configuring thousands of such nodes manually is undesireable from a human resources issue, as well as the difficulty in getting consistent results.

This document is about a standard way to introduce new nodes into a 6tisch network that does not involve any direct manipulation of the nodes themselves. This act has been called "zero-touch" provisioning, and it does not occur by chance, but requires coordination between the manufacturer of the node, the service operator running the LLN, and the installers actually taking the devices out of the shipping boxes.

This document is a constrained profile of [I-D.ietf-anima-bootstrapping-keyinfra]. The above document/protocol is referred by by it's acronym: BRSKI. The pronounciation of which is "brew-ski", a common north american slang for beer with a pseudo-polish ending.

This document follows the same structure as it's parent in order to emphasize the similarities, but specializes a number of things to constrained networks of constrained devices. Like ANIMA's BRSKI, the networks which are in scope for this protocol are deployed by a professional operator. The deterministic mechanisms which have been designed into 6tisch have been created to satisfy the operational needs of industrial settings.

This document builds upon the "one-touch" provisioning described in [I-D.ietf-6tisch-minimal-security], reusing the OSCOAP Join Request mechanism when appropriate. In addition, it uses the CoAP adaption of EST defined in [I-D.vanderstok-ace-coap-est] in an identical way.

Otherwise, this document follows BRSKI with the following high-level changes:

802.1AR Client certificates are retained, but optionally are specified by reference rather than value.

It is expected that the back-end network operator infrastructure would be able to bootstrap ANIMA BRSKI-type devices over ethernet, while also being able bootstrap 6tisch devices over 802.15.4 with few changes.

1.1. Terminology

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.

The reader is expected to be familiar with the terms and concepts defined in [I-D.ietf-6tisch-terminology], [RFC7252], [I-D.ietf-core-object-security], and [I-D.ietf-anima-bootstrapping-keyinfra]. The following terms are imported: drop ship, imprint, enrollment, pledge, join proxy, ownership voucher, join registrar/coordinator. The following terms are repeated here for readability, but this document is not authoritative for their definition:

the prospective device, which has the identity provided to at the factory. Neither the device nor the network knows if the device yet knows if this device belongs with this network.
Joined Node
the prospective device, after having completing the join process, often just called a Node.
Join Proxy (JP):
a stateless relay that provides connectivity between the pledge and the join registrar/coordinator.
Join Registrar/Coordinator (JRC):
central entity responsible for authentication and authorization of joining nodes.
Audit Token
A signed token from the manufacturer authorized signing authority indicating that the bootstrapping event has been successfully logged. This has been referred to as an "authorization token" indicating that it authorizes bootstrapping to proceed.
Ownership Voucher
A signed voucher from the vendor vouching that a specific domain "owns" the new entity as defined in [I-D.ietf-anima-voucher].
manufacturer installed certificate. An [ieee802-1AR] identity. Not to be confused with a (cryptographic) "Message Integrity Check"

1.2. Other Bootstrapping Approaches

BRSKI describes a more general, more flexible approach for bootstrapping devices into an ISP or Enterprise network.

[I-D.ietf-6tisch-minimal-security] provides an extremely streamlined approach to enrolling from hundreds to thousands of devices into a network, provided that a unique secret key can be installed in each device.

1.3. Scope of solution

The solution described in this document is appropriate to enrolling between hundreds to hundreds of thousands of diverse devices into a network without any prior contact with the devices. The devices could be shipped by the manufacturer directly to the customer site without ever being seen by the operator of the network. As described in BRSKI, in the audit-mode of operation the device will be claimed by the first network that sees it. In the tracked owner mode of operation, sales channel integration provides a strong connection that the operator of the network is the legitimate owner of the device.

2. Architectural Overview

Section 2 of BRSKI has a diagram with all of the components shown together. There are no significant changes to the diagram.

The use of a circuit proxy is not mandated. Instead the IPIP mechanism described in appendix C ("IPIP Join Proxy mechanism") SHOULD be be used instead as it supports both DTLS, EDHOC and OSCOAP protocols. The CoAP proxy mechanism MAY be implemented instead: the decision depends upon the capabilities of the Registrar and the proxy. A mechanism is included for the Registrar to announce it's capabilities (XXX).

2.1. Secure Imprinting using Vouchers

As in BRSKI, the format and cryptographic mechansim of vouchers is described in detail in [I-D.ietf-anima-voucher]. As described in section YYY, the physical format for vouchers in this document differs from that of BRSKI, in that it uses [I-D.ietf-ace-cbor-web-token] to encode the voucher and to sign it.

2.2. Initial Device Identifier

The essential component of the zero-touch operation is that the pledge is provisioned with an 802.1AR (PKIX) certificate installed during the manufacturing process.

It is expected that constrained devices will use a signature algorithm corresponding to the hardware acceleration that they have, if they have any. The anticipated algorithms are the ECDSA P-256 (secp256p1) as SHOULD-, while newer devices SHOLD+ begin to appear using EdDSA curves using the 25519 curves. (EDNOTE details here)

There are a number of simplications detailed later on in this document designed to eliminate the need for an ASN.1 parser in the pledge.

The pledge should consider it's 802.1AR certificate to be an opaque blob of bytes, to be inserted into protocols at appropriate places. The pledge SHOULD have access to it's public and private keys in the most useable native format for computation.

The pledge MUST have the public key of the MASA built in a manufacturer time. This is a seemingly identical requirement as for BRSKI, but rather than being an abstract trust anchor that can be augmented with a certificate chain, the pledge MUST be provided with the Raw Public Key that the MASA will use to sign vouchers for that pledge.

There are a number of security concerns with use of a single MASA signing key, and section Section 6.1 addresses some of them with some operational suggestions.

BRSKI places some clear requirements upon the contents of the IDevID, but leaves the exact origin of the voucher serial-number open. This document restricts the process to being the hwSerialNum OCTET STRING. As CWT can handle binary formats, no base64 encoding is necessary.

The use of the MASA-URL extension is encouraged if the certificate is sent at all.

[[EDNOTE here belongs text about sending only a reference to the IDevID rather than the entire certificate]]

2.3. Protocol Flow

The diagram from BRSKI is reproduced with some edits:

   +--------+         +---------+    +------------+     +------------+
   | Pledge |         | IPIP    |    | Domain     |     | Vendor     |
   |        |         | Proxy   |    | Registrar  |     | Service    |
   |        |         |         |    |            |     | (Internet  |
   +--------+         +---------+    +------------+     +------------+
     |                     |                   |                    |
     |<-RFC4862 IPv6 adr   |                   |                    |
     |                     |                   |                    |
     |<--------------------|                   |                    |
     | Enhanced Beacon     |                   |                    |
     |   periodic broadcast|                   |                    |
     |                     |                   |                    |
     |<------------------->C<----------------->|                    |
     |             DTLS via the IPIP    Proxy  |                    |
     |<--Registrar DTLS server authentication--|                    |
   [PROVISIONAL accept of server cert]         |                    |
     P---X.509 client authentication---------->|                    |
     P                     |                   |                    |
     P---Voucher Request (include nonce)------>|                    |
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |              [accept device?]          |
     P                     |              [contact Vendor]          |
     P                     |                   |--Pledge ID-------->|
     P                     |                   |--Domain ID-------->|
     P                     |                   |--nonce------------>|
     P                     |                   |     [extract DomainID]
     P                     |                   |                    |
     P                     |                   |     [update audit log]
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |                   |<-device audit log--|
     P                     |                   |<- voucher ---------|
     P                     |                   |                    |
     P                     |                   |                    |
     P                     |       [verify audit log and voucher]   |
     P                     |                   |                    |
     P<------voucher---------------------------|                    |
   [verify voucher ]       |                   |                    |
   [verify provisional cert|                   |                    |
     |                     |                   |                    |
     |<--------------------------------------->|                    |
     | Continue with RFC7030 enrollment        |                    |
     | using now bidirectionally authenticated |                    |
     | DTLS session.       |                   |                    |
     |                     |                   |                    |
     |                     |                   |                    |
     |                     |                   |                    |

Noteable changes are:

  1. no IPv4 support/options.
  2. no mDNS steps, 6tisch only uses Enhanced Beacon
  3. nonce-full option is always recommended

2.4. Lack of realtime clock

For the constrained situation it is assumed that devices have no real time clock. These nodes do have access to a monotonically increasing clock that will not go backwards in the form of the Absolute Sequence Number. Synchronization to the ASN is required in order to transmit/receive data and most nodes will maintain it in hardware.

The heuristic described in BRSKI under this section SHOULD be applied if there are dates in the CWT format voucher.

Voucher requests SHOULD include a nonce. For devices intended for off-line deployment, the vouchers will have been generated in advance and no nonce-ful operation will not be possible.

2.5. Cloud Registrar

In 6tisch, the pledge never has network connectivity until it is enrolled, so no alternate registrar is ever possible.

3. Protocol Details

BRSKI is specified to run over HTTPS. This document respecifies it to run over CoAP with either DTLS or EDHOC-provided OSCOAP security. There is an emerging (hybrid) possibility of DTLS-providing the OSCOAP security, but such a specification does not yet exist.

[I-D.vanderstok-ace-coap-est] specifies that CoAP specifies the use of CoAP Block-Wise Transfer ("Block") [RFC7959] to fragment EST messages at the application layer.

BRSKI introduces the concept of a provisional state for EST. The same situation must also be added to DTLS: a situation where the connection is active but the identity of the Registar has not yet been confirmed. The DTLS MUST validate that the exchange has been signed by the Raw Public Key that is presented by the Server, even though there is as yet no trust in that key. Such a key is often available through APIs that provide for channel binding, such as described in [RFC5056].

As in [I-D.vanderstok-ace-coap-est], support for Observe CoAP options [RFC7641] with BRSKI is not supported in the current BRSKI/EST message flows. Observe options could be used by the server to notify clients about a change in the cacerts or csr attributes (resources) and might be an area of future work.

Redirection as described in [RFC7030] section 3.2.1 is NOT supported.

3.1. Discovery

Only IPv6 operations using Link-Local addresses are supported. Use of a temporary address is NOT encouraged as the critial resource on the Proxy device is the number of Neighbour Cache Entries that can be used for untrusted pledge entries.

3.1.1. Proxy Discovery Protocol Details

The Proxy is discovered using the enhanced beacon defined in [I-D.richardson-6tisch-join-enhanced-beacon].

3.1.2. Registrar Discovery Protocol Details

The Registrar is not discovered by the Proxy. Any device that is expected to be able to operate as a Registrar MAY be told the address of the Registrar when that device joins the network. The address MAY be included in the [I-D.ietf-6tisch-minimal-security] Join Response. If the address is NOT included, then Proxy may assume that the Registrar can be found at the DODAG root, which is well known in the 6tisch's use of the RPL protocol.

3.2. Pledge Requests Voucher from the Registrar

The voucher request and response as defined by BRSKI is modified slightly. In order to simplify the pledge, the use of a certificate (and chain) for the Registrar is not supported. Instead the newly defined pinned-domain-subject-public-key-info must contain the (raw) public key info for the Registrar. It MUST be byte for byte identical to that which is transmitted by the Registrar during the TLS ServerCertificate handshake.

BRSKI permits the voucher request to be signed or unsigned. This document defines the voucher request to be unsigned.

/* -*- c -*- */
module ietf-cwt-voucher {
  yang-version 1.1;

  prefix "vcwt";

  import ietf-restconf {
    prefix rc;
      "This import statement is only present to access
       the yang-data extension defined in RFC 8040.";
    reference "RFC 8040: RESTCONF Protocol";

  import ietf-voucher {
    prefix "v";

   "IETF 6tisch Working Group";

   "WG Web:   <http://tools.ietf.org/wg/6tisch/>
    WG List:  <mailto:6tisch@ietf.org>
    Author:   Michael Richardson

   "This module defines the format for a voucher, which is produced by
    a pledge's manufacturer or delegate (MASA) to securely assign one
    or more pledges to an 'owner', so that the pledges may establish a
    secure connection to the owner's network infrastructure.

    This version provides a very restricted subset appropriate
    for very constrained devices.
    In particular, it assumes that nonce-ful operation is
    always required, that expiration dates are rather weak, as no
    clocks can be assumed, and that the Registrar is identified
    by a pinned Raw Public Key.

    The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
    the module text are to be interpreted as described in RFC 2119.";

  revision "YYYY-MM-DD" {
     "Initial version";
     "RFC XXXX: Voucher Profile for Constrained Devices";

  // Grouping defined for future usage
  grouping voucher-cwt-grouping {
      "Grouping to allow reuse/extensions in future work.";

    uses v:voucher-artifact-grouping {
      augment "voucher" {
        description "Base the CWT voucher upon the regular one";
        leaf pinned-domain-subject-public-key-info {
          type binary;
            "The pinned-domain-subject replaces the
         pinned-domain-certificate in constrained uses of
         the voucher.  The pinned-domain-public-key-info is the
         Raw Public Key of the Registrar. This field is encoded
         as specified in RFC7250, section 3.
         The ECDSA algorithm MUST be supported.
         The EdDSA algorithm as specified in
         draft-ietf-tls-rfc4492bis-17 SHOULD be supported.
         Support for the DSA algorithm is not recommended.
         Support for the RSA algorithm is a MAY.";

This definition, translated via the rules in [I-D.ietf-core-yang-cbor] produces the following CDDL for an unsigned voucher (request):

This is a PLACEHOLDER for a CDDL definition derived from the YANG model.
SID experimental base 60100 is used.

dictionary keys are:
60100      ietf-cwt-voucher
60101      assertion
60102      created-on
60103      domain-cert-revocation-checks
60104      expires-on
60105      idevid-issuer
60106      last-renewal-date
60107      nonce
60108      pinned-domain-cert
60109      pinned-domain-subject-public-key-info
60110      prior-signed-voucher
60111      serial-number

3.3. Registrar Requests Voucher from MASA

There are no change from BRSKI, as this step is between two non-constrained devices. The format of the voucher is CWT, which implies changes to both the Registrar and the MASA, but semantically the content is the same.

The manufacturer will know what algorithms are supported by the pledge, and will issue a 406 (Conflict) error to the Registrar if the Registar's public key format is not supported by the pledge.

3.4. Voucher Response

The voucher response MUST have an additional header called: "pinned-domain-rpk".

3.4.1. Completing authentication of Provisional TLS connection

In order to simplify the pledge as much as possible, the voucher response

3.5. Voucher Status Telemetry


3.6. MASA authorization log Request


3.6.1. MASA authorization log Response


3.7. EST Integration for PKI bootstrapping


3.7.1. EST Distribution of CA Certificates


3.7.2. EST CSR Attributes


3.7.3. EST Client Certificate Request


3.7.4. Enrollment Status Telemetry


3.7.5. EST over CoAP


4. Reduced security operational modes


4.1. Trust Model


4.2. Pledge security reductions


4.3. Registrar security reductions


4.4. MASA security reductions


5. IANA Considerations


5.1. MIME-Type Registry


6. Security Considerations

6.1. Security of MASA voucher signing key(s)

7. Privacy Considerations


8. Acknowledgements

9. References

9.1. Normative References

[cullenCiscoPhoneDeploy] Jennings, C., "Transitive Trust Enrollment for Constrained Devices", 2012.
[I-D.ietf-6lo-privacy-considerations] Thaler, D., "Privacy Considerations for IPv6 Adaptation Layer Mechanisms", Internet-Draft draft-ietf-6lo-privacy-considerations-04, October 2016.
[I-D.ietf-6tisch-minimal] Vilajosana, X., Pister, K. and T. Watteyne, "Minimal 6TiSCH Configuration", Internet-Draft draft-ietf-6tisch-minimal-21, February 2017.
[I-D.ietf-6tisch-minimal-security] Vucinic, M., Simon, J., Pister, K. and M. Richardson, "Minimal Security Framework for 6TiSCH", Internet-Draft draft-ietf-6tisch-minimal-security-03, June 2017.
[I-D.ietf-6tisch-terminology] Palattella, M., Thubert, P., Watteyne, T. and Q. Wang, "Terminology in IPv6 over the TSCH mode of IEEE 802.15.4e", Internet-Draft draft-ietf-6tisch-terminology-09, June 2017.
[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-08, August 2017.
[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-07, July 2017.
[I-D.ietf-anima-grasp] Bormann, C., Carpenter, B. and B. Liu, "A Generic Autonomic Signaling Protocol (GRASP)", Internet-Draft draft-ietf-anima-grasp-15, July 2017.
[I-D.ietf-anima-voucher] Watsen, K., Richardson, M., Pritikin, M. and T. Eckert, "Voucher Profile for Bootstrapping Protocols", Internet-Draft draft-ietf-anima-voucher-05, August 2017.
[I-D.ietf-core-comi] Veillette, M., Stok, P., Pelov, A. and A. Bierman, "CoAP Management Interface", Internet-Draft draft-ietf-core-comi-01, July 2017.
[I-D.ietf-core-object-security] Selander, G., Mattsson, J., Palombini, F. and L. Seitz, "Object Security of CoAP (OSCOAP)", Internet-Draft draft-ietf-core-object-security-04, July 2017.
[I-D.ietf-core-yang-cbor] Veillette, M., Pelov, A., Somaraju, A., Turner, R. and A. Minaburo, "CBOR Encoding of Data Modeled with YANG", Internet-Draft draft-ietf-core-yang-cbor-05, August 2017.
[I-D.ietf-netconf-keystore] Watsen, K., "Keystore Model", Internet-Draft draft-ietf-netconf-keystore-02, June 2017.
[I-D.richardson-6tisch-join-enhanced-beacon] Dujovne, D. and M. Richardson, "IEEE802.15.4 Informational Element encapsulation of 6tisch Join Information", Internet-Draft draft-richardson-6tisch-join-enhanced-beacon-02, July 2017.
[I-D.richardson-6tisch-minimal-rekey] Richardson, M., "Minimal Security rekeying mechanism for 6TiSCH", Internet-Draft draft-richardson-6tisch-minimal-rekey-02, August 2017.
[I-D.richardson-anima-6join-discovery] Richardson, M., "GRASP discovery of Registrar by Join Assistant", Internet-Draft draft-richardson-anima-6join-discovery-00, October 2016.
[I-D.selander-ace-cose-ecdhe] Selander, G., Mattsson, J. and F. Palombini, "Ephemeral Diffie-Hellman Over COSE (EDHOC)", Internet-Draft draft-selander-ace-cose-ecdhe-07, July 2017.
[I-D.vanderstok-ace-coap-est] Kumar, S., Stok, P., Kampanakis, P., Furuhed, M. and S. Raza, "EST over secure CoAP (EST-coaps)", Internet-Draft draft-vanderstok-ace-coap-est-02, June 2017.
[iec62591] IEC, ., "62591:2016 Industrial networks - Wireless communication network and communication profiles - WirelessHART", 2016.
[ieee802-1AR] IEEE Standard, ., "IEEE 802.1AR Secure Device Identifier", 2009.
[ieee802154] IEEE Standard, ., "802.15.4-2015 - IEEE Standard for Low-Rate Wireless Personal Area Networks (WPANs)", 2015.
[ieee802159] IEEE Standard, ., "802.15.9-2016 - IEEE Approved Draft Recommended Practice for Transport of Key Management Protocol (KMP) Datagrams", 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)", RFC 7217, DOI 10.17487/RFC7217, April 2014.
[RFC7228] Bormann, C., Ersue, M. and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014.
[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.
[RFC7252] Shelby, Z., Hartke, K. and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014.
[RFC7959] Bormann, C. and Z. Shelby, "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016.

9.2. Informative References

[duckling] Stajano, F. and R. Anderson, "The resurrecting duckling: security issues for ad-hoc wireless networks", 1999.
[I-D.ietf-ace-actors] Gerdes, S., Seitz, L., Selander, G. and C. Bormann, "An architecture for authorization in constrained environments", Internet-Draft draft-ietf-ace-actors-05, March 2017.
[I-D.ietf-core-sid] Veillette, M., Pelov, A., Turner, R., Minaburo, A. and A. Somaraju, "YANG Schema Item iDentifier (SID)", Internet-Draft draft-ietf-core-sid-01, May 2017.
[I-D.ietf-roll-useofrplinfo] Robles, I., Richardson, M. and P. Thubert, "When to use RFC 6553, 6554 and IPv6-in-IPv6", Internet-Draft draft-ietf-roll-useofrplinfo-16, July 2017.
[ISA100] "The Technology Behind the ISA100.11a Standard", June 2010.
[PFS] Wikipedia, ., "Forward Secrecy", August 2016.
[pledge] Dictionary.com, ., "Dictionary.com Unabridged", 2015.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, November 2005.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006.
[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007.
[RFC7554] Watteyne, T., Palattella, M. and L. Grieco, "Using IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the Internet of Things (IoT): Problem Statement", RFC 7554, DOI 10.17487/RFC7554, May 2015.
[RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015.
[RFC7731] Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731, February 2016.

Appendix A. One-Touch Assumptions

This document interacts with the one-touch solution described in [I-D.ietf-6tisch-minimal-security].

A.1. Factory provided credentials (if any)

When a manufacturer installed certificate is provided as the IDevID, it SHOULD contain a number of fields. [I-D.ietf-anima-bootstrapping-keyinfra] provides a detailed set of requirements.

A manufacturer unique serial number MUST be provided in the serialNumber SubjectAltName extension, and MAY be repeated in the Common Name. There are no sequential or numeric requirements on the serialNumber, it may be any unique value that the manufacturer wants to use. The serialNumber SHOULD be printed on the packaging and/or on the device in a discrete way so that failures can be physically traced to the relevant device.

A.1.1. Credentials to be introduced

The goal of the bootstrap process is to introduce one or more new locally relevant credentials:

  1. a certificate signed by a local certificate authority/registrar. This is the LDevID of [ieee802-1AR].
  2. alternatively, a network-wide key to be used to secure L2 traffic.
  3. alternatively, a network-wide key to be used to authenticate per-peer keying of L2 traffic using a mechanism such as provided by [ieee802159].

A.2. Network Assumptions

This document is about enrollment of constrained devices [RFC7228] to a constrained network. Constrained networks is such as [ieee802154], and in particular the time-slotted, channel hopping (tsch) mode, feature low bandwidths, and limited opportunities to transmit. A key feature of these networks is that receivers are only listening at certain times.

A.2.1. Security above and below IP

802.15.4 networks have three kinds of layer-2 security:

Setting up the credentials to bootstrap one of these kinds of security, (or directly configuring the key itself for the first case) is required. This is the security below the IP layer.

Security is required above the IP layer: there are three aspects which the credentials in the previous section are to be used.

A.2.1.1. Perfect Forward Secrecy

Perfert Forward Secrecy (PFS) is the property of a protocol such that complete knowledge of the crypto state (for instance, via a memory dump) at time X does not imply that data from a disjoint time Y can also be recovered. ([PFS]).

PFS is important for two reasons: one is that it offers protection against the compromise of a node. It does this by changing the keys in a non-deterministic way. This second property also makes it much easier to remove a node from the network, as any node which has not participated in the key changing process will find itself no longer connected.

A.2.2. Join network assumptions

The network which the new pledge will connect to will have to have the following properties:

A.2.3. Number and cost of round trips


A.2.4. Size of packets, number of fragments

A.3. Target end-state for join process

At the end of the zero-touch join process there will be a symmetric key protected channel between the Join Registrar/Coordinator and the pledge, now known as a Joined Node. This channel may be rekeyed via new exchange of asymmetric exponents (ECDH for instance), authenticated using the domain specific credentials created during the join process.

This channel is in the form of an OSCOAP protected connection with [I-D.ietf-core-comi] encoded objects. This document includes definition of a [I-D.ietf-netconf-keystore] compatible objects for encoding of the relevant [I-D.ietf-anima-bootstrapping-keyinfra] objects.

Appendix B. Join Protocol

The pledge join protocol state machine is described in [I-D.ietf-6tisch-minimal-security], in section XYZ. The pledge recognizes that it is in zero-touch configuration by the following situation:

All of these conditions MUST be true. If any of these are not true, then the pledge has either been connected to the wrong network, or it has already been bootstrapped into a different network, and it should wait until it finds that network.

The zero-touch process consists of three stages:

  1. the key agreement process
  2. the provisional enrollment process
  3. the key distribution process

B.1. Key Agreement process

The key agreement process is identical to [I-D.ietf-6tisch-minimal-security]. The process uses EDHOC with certificates.

The pledge will have to trust the JRC provisionally, as described in [I-D.ietf-anima-bootstrapping-keyinfra], section 3.1.2, and in section 4.1.1 of [RFC7030].

The JRC will be able to validate the IDevID of the pledge using the manufacturer's CA.

The pledge may not know if it is in a zero-touch or one-touch situation: the pledge may be able to verify the JRC based upon trust anchors that were installed at manufacturing time. In that case, the pledge runs the simplified one-touch process.

The pledge signals in the EDHOC message_2 if it has accepted the JRC certificate. The JRC will in general, not trust the pledge with the network keys until it has provided the pledge with a voucher. The pledge will notice the absence of the provisioning keys.

XXX - there could be some disconnect here. May need additional signals here.

B.2. Provisional Enrollment process

When the pledge determines that it can not verify the certificate of the JRC using built-in trust anchors, then it enters a provisional state. In this state, it keeps the channel created by EDHOC open.

A new EDHOC key derivation is done by the JRC and pledge using a new label, "6tisch-provisional".

The pledge runs as a passive CoMI server, leaving the JRC to drive the enrollment process. The JRC can interrogate the pledge in a variety of fashions as shown below: the process terminates when the JRC provides the pledge with an ownership voucher and the pledge leaves the provisional state.

A typical interaction involves the following requests:

    +-----------+ +----------+ +-----------+ +----------+
    |           | |          | | Circuit   | | New      |
    |  Vendor   | | Registrar| |  Proxy    | | Entity   |
    |  (MASA)   | |          | |           | |          |
    ++----------+ +--+-------+ +-----------+ +----------+
     |               |     GET  request voucher       |
     |               |-------------------------------->
     |               <----------voucher-token---------|
     |/requestvoucher|                                |
     <---------------+                                |
     +--------------->                                |
     |/requestlog    |                                |
     <---------------+                                |
     +--------------->                                |
     |               |        POST voucher            |
     |               |-------------------------------->
     |               <------------2.05 OK ------------+
     |               |                                |
     |               |        POST csr attributes     |
     |               |-------------------------------->
     |               <------------2.05 OK ------------+
     |               |                                |
     |               |        GET  cert request       |
     |               |-------------------------------->
     |     ????      <------------2.05 OK ------------+
     |<--------------|              CSR               |
     |-------------->|                                |
     |               |        POST certificate        |
     |               |-------------------------------->
     |               <------------2.05 OK ------------+
     |               |                                |

B.3. Key Distribution Process

The key distribution process utilizes the protocol described [I-D.richardson-6tisch-minimal-rekey]. The process starts with the initial key, rather than an actual rekey.

This protocol remains active for subsequent rekey operations.

Appendix C. YANG model for BRSKI objects

module ietf-6tisch-brski { yang-version 1.1;

namespace "urn:ietf:params:xml:ns:yang:6tisch-brski"; prefix "ietf6brski";

//import ietf-yang-types { prefix yang; } //import ietf-inet-types { prefix inet; }

organization "IETF 6tisch Working Group";

contact "WG Web: http://tools.ietf.org/wg/6tisch/ WG List: 6tisch@ietf.org Author: Michael Richardson mcr+ietf@sandelman.ca";

description "This module defines an interface to set and retrieve BRSKI objects using CoMI. This interface is used as part of an enrollment process for constrained nodes and networks.";

revision "2017-03-01" { description "Initial version"; reference "RFC XXXX: 6tisch zero-touch bootstrap"; }

// top-level container container ietf6brski { leaf requestnonce { type binary; length XX; // how big can/should it be? mandatory true; description "Request Nonce."; } leaf voucher { type binary; description "The voucher as a serialized COSE object"; }

leaf csrattributes {
  type binary;
  description "A list of attributes that MUST be in the CSR";

leaf certificaterequest {
  type binary;
  description "A PKIX format Certificate Request";

leaf certificate {
  type binary;
  description "The LDevID certificate";
}   } }

C.1. Description of Pledge States in Join Process


Appendix D. Definition of managed objects for zero-touch bootstrap

The following is relevant YANG for use in the bootstrap protocol. The objects identified are identical in format to the named objects from [I-D.ietf-anima-bootstrapping-keyinfra].

Appendix E. Privacy Considerations

[I-D.ietf-6lo-privacy-considerations] details a number of privacy considerations important in Resource Constrained nodes. There are two networks and three sets of constrained nodes to consider. They are: 1. the production nodes on the production network. 2. the new pledges, which have yet to enroll, and which are on a join network. 3. the production nodes which are also acting as proxy nodes.

E.1. Privacy Considerations for Production network

The details of this are out of scope for this document.

E.2. Privacy Considerations for New Pledges

New Pledges do not yet receive Router Advertisements with PIO options, and so configure link-local addresses only based upon layer-2 addresses using the normal SLAAC mechanisms described in [RFC4191].

These link-local addresses are visible to any on-link eavesdropper (who is synchronized to the same Join Assistant), so regardless of what is chosen they can be seen. This link-layer traffic is encapsulated by the Join Assistant into IPIP packets and carried to the JCE. The traffic SHOULD never leave the operator's network, and no outside traffic should enter, so it should not be possible to do any ICMP scanning as described in [I-D.ietf-6lo-privacy-considerations].

The join process described herein requires that some identifier meaningful to the network operator be communicated to the JCE via the Neighbor Advertisement's ARO option. This need not be a manufacturer created EUI-64 as assigned by IEEE; it could be another value with higher entropy and less interesting vendor/device information. Regardless of what is chosen, it can be used to track where the device attaches.

For most constrained device, network attachment occurs very infrequently, often only once in their lifetime, so tracking opportunities may be rare.

Further, during the enrollment process, a DTLS connection connection will be created. Unless TLS1.3 is used, the device identity will be visible to passive observers in the 802.11AR IDevID certificate that is sent. Even when TLS1.3 is used, an active attacker could collect the information by simply connecting to the device; it would not have to successful complete the negotiation either, or even attempt to Man-In-The-Middle the device.

There is, at the same time, significant value in avoiding a link-local DAD process by using an IEEE assigned EUI-64, and there is also significant advantage to the operator being able to see what the vendor of the new device is.

E.2.1. EUI-64 derived address for join time IID

It is therefore suggested that the IID used in the link-local address used during the join process be a vendor assigned EUI-64. After the join process has concluded, the device SHOULD be assigned a unique randomly generated long address, and a unique short address (not based upon the vendor EUI-64) for use at link-layer. At that point, all layer-3 content is encrypted by the layer-2 key.

E.3. Privacy Considerations for Join Assistant

Appendix F. Security Considerations

Appendix G. IANA Considerations

This document allocates one value from the subregistry "Address Registration Option Status Values": ND_NS_JOIN_DECLINED Join Assistant, JOIN DECLINED (TBD-AA)

Appendix H. Protocol Definition

Appendix I. Acknowledgements

Kristofer Pister helped with many non-IETF references.

Authors' Addresses

Michael Richardson Sandelman Software Works EMail: mcr+ietf@sandelman.ca
Benjamin Damm Silver Spring Networks EMail: bdamm@ssni.com