RFC 9031: Constrained Join Protocol (CoJP) for 6TiSCH | RFC Editor

This document describes the minimal framework required for a new device, called a "pledge", to securely join a 6TiSCH (IPv6 over the Time-Slotted Channel Hopping mode of IEEE 802.15.4) network. The framework requires that the pledge and the JRC (Join Registrar/Coordinator, a central entity), share a symmetric key. How this key is provisioned is out of scope of this document. Through a single CoAP (Constrained Application Protocol) request-response exchange secured by OSCORE (Object Security for Constrained RESTful Environments), the pledge requests admission into the network, and the JRC configures it with link-layer keying material and other parameters. The JRC may at any time update the parameters through another request-response exchange secured by OSCORE. This specification defines the Constrained Join Protocol and its CBOR (Concise Binary Object Representation) data structures, and it describes how to configure the rest of the 6TiSCH communication stack for this join process to occur in a secure manner. Additional security mechanisms may be added on top of this minimal framework.¶
This is an Internet Standards Track document.¶
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9031.¶
Copyright (c) 2021 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.¶
This document defines a "secure join" solution for a new device, called a "pledge", to securely join a 6TiSCH network. The term "secure join" refers to network access authentication, authorization, and parameter distribution as defined in [RFC9030]. The Constrained Join Protocol (CoJP) defined in this document handles parameter distribution needed for a pledge to become a joined node. Mutual authentication during network access and implicit authorization are achieved through the use of a secure channel as configured according to this document. This document also specifies a configuration of different layers of the 6TiSCH protocol stack that reduces the Denial of Service (DoS) attack surface during the join process.¶
This document presumes a 6TiSCH network as described by [RFC7554] and [RFC8180]. By design, nodes in a 6TiSCH network [RFC7554] have their radio turned off most of the time in order to conserve energy. As a consequence, the link used by a new device for joining the network has limited bandwidth [RFC8180]. The secure join solution defined in this document therefore keeps the number of over-the-air exchanges to a minimum.¶
The microcontrollers at the heart of 6TiSCH nodes have small amounts of code memory. It is therefore paramount to reuse existing protocols available as part of the 6TiSCH stack. At the application layer, the 6TiSCH stack already relies on CoAP [RFC7252] for web transfer and on OSCORE [RFC8613] for its end-to-end security. The secure join solution defined in this document therefore reuses those two protocols as its building blocks.¶
CoJP is a generic protocol that can be used as-is in all modes of IEEE Std 802.15.4 [IEEE802.15.4], including the Time-Slotted Channel Hopping (TSCH) mode on which 6TiSCH is based. CoJP may also be used in other (low-power) networking technologies where efficiency in terms of communication overhead and code footprint is important. In such a case, it may be necessary to define through companion documents the configuration parameters specific to the technology in question. The overall process is described in Section 4, and the configuration of the stack is specific to 6TiSCH.¶
CoJP assumes the presence of a Join Registrar/Coordinator (JRC), a central entity. The configuration defined in this document assumes that the pledge and the JRC share a unique symmetric cryptographic key, called PSK (pre-shared key). The PSK is used to configure OSCORE to provide a secure channel to CoJP. How the PSK is installed is out of scope of this document: this may happen during the provisioning phase or by a key exchange protocol that may precede the execution of CoJP.¶
When the pledge seeks admission to a 6TiSCH network, it first synchronizes to it by initiating the passive scan defined in [IEEE802.15.4]. The pledge then exchanges CoJP messages with the JRC; for this end-to-end communication to happen, the messages are forwarded by nodes, called Join Proxies, that are already part of the 6TiSCH network. The messages exchanged allow the JRC and the pledge to mutually authenticate based on the properties provided by OSCORE. They also allow the JRC to configure the pledge with link-layer keying material, a short identifier, and other parameters. After this secure join process successfully completes, the joined node can interact with its neighbors to request additional bandwidth using the 6TiSCH Operation Sublayer (6top) Protocol [RFC8480] and can start sending application traffic.¶
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 onl