Constrained Join Proxy for Bootstrapping Protocols

Constrained Join Proxy for Bootstrapping Protocols Sandelman Software Works

mcr+ietf@sandelman.ca

vanderstok consultancy

stokcons@bbhmail.nl

Cisco Systems

pkampana@cisco.com

Internet anima Working Group Internet-Draft This document extends the work of Bootstrapping Remote Secure Key Infrastructures (BRSKI) by replacing the Circuit-proxy between Pledge and Registrar by a stateless/stateful constrained Join Proxy. The constrained Join Proxy is a mesh neighbor of the Pledge and can relay a DTLS session originating from a Pledge with only link-local addresses to a Registrar which is not a mesh neighbor of the Pledge. This document defines a protocol to securely assign a Pledge to a domain, represented by a Registrar, using an intermediary node between Pledge and Registrar. This intermediary node is known as a "constrained Join Proxy". An enrolled Pledge can act as a constrained Join Proxy. About This Document Status information for this document may be found at . Discussion of this document takes place on the anima Working Group mailing list (), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction The Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol described in provides a solution for a secure zero-touch (automated) bootstrap of new (unconfigured) devices. In the context of BRSKI, new devices, called "Pledges", are equipped with a factory-installed Initial Device Identifier (IDevID) (see ), and are enrolled into a network. BRSKI makes use of Enrollment over Secure Transport (EST) with vouchers to securely enroll devices. A Registrar provides the security anchor of the network to which a Pledge enrolls. In this document, BRSKI is extended such that a Pledge connects to "Registrars" via a constrained Join Proxy. In particular, the underlying IP network is assumed to be a mesh network as described in , although other IP-over-foo networks are not excluded. An example network is shown in . A complete specification of the terminology is pointed at in . The specified solutions in and are based on POST or GET requests to the EST resources (/cacerts, /simpleenroll, /simplereenroll, /serverkeygen, and /csrattrs), and the brski resources (/requestvoucher, /voucher_status, and /enrollstatus). These requests use https and may be too large in terms of code space or bandwidth required for constrained devices. Constrained devices which may be part of constrained networks , typically implement the IPv6 over Low-Power Wireless personal Area Networks (6LoWPAN) and Constrained Application Protocol (CoAP) . CoAP can be run with the Datagram Transport Layer Security (DTLS) as a security protocol for authenticity and confidentiality of the messages. This is known as the "coaps" scheme. A constrained version of EST, using CoAP and DTLS, is described in . The extends with BRSKI artifacts such as voucher, request voucher, and the protocol extensions for constrained Pledges. 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 Pledge will not be IP routable over the mesh network until it is authenticated to the mesh network. A new Pledge can only initially use a link-local IPv6 address to communicate with a mesh neighbor until it receives the necessary network configuration parameters. The Pledge receives these configuration parameters from the Registrar. When the Registrar is not a direct neighbor of the Registrar but several hops away, the Pledge discovers a neighbor constrained Join Proxy, which transmits the DTLS protected request coming from the Pledge to the Registrar. The constrained Join Proxy must be enrolled previously such that the message from constrained Join Proxy to Registrar can be routed over one or more hops. During enrollment, a DTLS connection is required between Pledge and Registrar. An enrolled Pledge can act as constrained Join Proxy between other Pledges and the enrolling Registrar. This document specifies a new form of constrained Join Proxy and protocol to act as intermediary between Pledge and Registrar to relay DTLS messages between Pledge and Registrar. Two modes of the constrained Join Proxy are specified: This document is very much inspired by text published earlier in . outlined the various options for building a constrained Join Proxy. adopted only the Circuit Proxy method (1), leaving the other methods as future work. Similar to the difference between storing and non_storing Modes of Operations (MOP) in RPL , the stateful and stateless modes differ in the way that they store the state required to forward the return packet to the pledge. In the stateful method, the return forward state is stored in the join proxy. In the stateless method, the return forward state is stored in the network.

Terminology The following terms are defined in , and are used identically as in that document: artifact, imprint, domain, Join Registrar/Coordinator (JRC), Pledge, and Voucher. In this document, the term "Registrar" is used throughout instead of "Join Registrar/Coordinator (JRC)". The term "installation network" refers to all devices in the installation and the network connections between them. The term "installation IP_address" refers to an address out of the set of addresses which are routable over the whole installation network. The "Constrained Join Proxy" enables a pledge that is multiple hops away from the Registrar, to securely execute the BRSKI protocol over a secure channel. The term "join Proxy" is used interchangeably with the term "constrained Join Proxy" throughout this document.

Requirements Language 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 when, and only when, they appear in all capitals, as shown here.

constrained Join Proxy functionality As depicted in the , the Pledge (P), in a Low-Power and Lossy Network (LLN) mesh can be more than one hop away from the Registrar (R) and not yet authenticated into the network. In this situation, the Pledge can only communicate one-hop to its nearest neighbor, the constrained Join Proxy (J) using their link-local IPv6 addresses. However, the Pledge needs to communicate with end-to-end security with a Registrar to authenticate and get the relevant system/network parameters. If the Pledge, knowing the IP-address of the Registrar, initiates a DTLS connection to the Registrar, then the packets are dropped at the constrained Join Proxy since the Pledge is not yet admitted to the network or there is no IP routability to Pledge for any returned messages from the Registrar.

multi-hop enrollment. Without routing the Pledge cannot establish a secure connection to the Registrar over multiple hops in the network. Furthermore, the Pledge cannot discover the IP address of the Registrar over multiple hops to initiate a DTLS connection and perform authentication. To overcome the problems with non-routability of DTLS packets and/or discovery of the destination address of the Registrar, the constrained Join Proxy is introduced. This constrained Join Proxy functionality is configured into all authenticated devices in the network which may act as a constrained Join Proxy for Pledges. The constrained Join Proxy allows for routing of the packets from the Pledge using IP routing to the intended Registrar. An authenticated constrained Join Proxy can discover the routable IP address of the Registrar over multiple hops. The following specifies the two constrained Join Proxy modes. A comparison is presented in . When a mesh network is set up, it consists of a Registrar and a set of connected pledges. No constrained Join Proxies are present. The wanted end-state is a network with a Registrar and a set of enrolled devices. Some of these enrolled devices can act as constrained Join Proxies. Pledges can only employ link-local communication until they are enrolled. A Pledge will regularly try to discover a constrained Join Proxy or a Registrar with link-local discovery requests. The Pledges which are neighbors of the Registrar will discover the Registrar and be enrolled following the BRSKI protocol. An enrolled device can act as constrained Join Proxy. The Pledges which are not a neighbor of the Registrar will eventually discover a constrained Join Proxy and follow the BRSKI protocol to be enrolled. While this goes on, more and more constrained Join Proxies with a larger hop distance to the Registrar will emerge. The network should be configured such that at the end of the enrollment process, all pledges have discovered a neighboring constrained Join Proxy or the Registrar, and all Pledges are enrolled.

constrained Join Proxy specification A Join Proxy can operate in two modes:

Stateful mode
Stateless mode

A Join Proxy MUST implement both. A Registrar MUST implement the stateful mode and SHOULD implement the Stateless mode. A mechanism to switch between modes is out of scope of this document. It is recommended that a Join Proxy uses only one of these modes at any given moment during an installation lifetime. The advantages and disadvantages of the two modes are presented in .

Stateful Join Proxy In stateful mode, the Join Proxy forwards the DTLS messages to the Registrar. Assume that the Pledge does not know the IP address of the Registrar it needs to contact. The Join Proxy has been enrolled via the Registrar and learns the IP address and port of the Registrar, by using a discovery mechanism such as described in . The Pledge first discovers (see ) and selects the most appropriate Join Proxy. (Discovery can also be based upon section 4.1). The Pledge initiates its request as if the Join Proxy is the intended Registrar. The Join Proxy receives the message at a discoverable join-port. The Join Proxy constructs an IP packet by copying the DTLS payload from the message received from the Pledge, and provides source and destination addresses to forward the message to the intended Registrar. The Join Proxy stores the 4-tuple array of the messages received from the Registrar and copies it back to the header of the message returned to the Pledge. In the various steps of the message flow are shown, with 5684 being the standard coaps port. The columns "SRc_IP:port" and "Dst_IP:port" show the IP address and port values for the source and destination of the message.

Stateless Join Proxy The stateless Join Proxy aims to minimize the requirements on the constrained Join Proxy device. Stateless operation requires no memory in the Join Proxy device, and may also reduce the CPU impact as the device does not need to search through a state table. If an untrusted Pledge that can only use link-local addressing wants to contact a trusted Registrar, and the Registrar is more than one hop away, it sends its DTLS messages to the Join Proxy. When a Pledge attempts a DTLS connection to the Join Proxy, it uses its link-local IP address as its IP source address. This message is transmitted one-hop to a neighboring (Join Proxy) node. Under normal circumstances, this message would be dropped at the neighbor node since the Pledge is not yet IP routable or is not yet authenticated to send messages through the network. However, if the neighbor device has the Join Proxy functionality enabled; it routes the DTLS message to its Registrar of choice. The Join Proxy transforms the DTLS message to a JPY message which includes the DTLS data as payload, and sends the JPY message to the join-port of the Registrar. The JPY message payload consists of two parts:

Header (H) field: consisting of the source link-local address and port of the Pledge (P), and
Contents (C) field: containing the original DTLS payload.

On receiving the JPY message, the Registrar (or proxy) retrieves the two parts. The Registrar transiently stores the Header field information. The Registrar uses the Contents field to execute the Registrar functionality. However, when the Registrar replies, it also extends its DTLS message with the header field in a JPY message and sends it back to the Join Proxy. The Registrar SHOULD NOT assume that it can decode the Header Field, it should simply repeat it when responding. The Header contains the original source link-local address and port of the Pledge from the transient state stored earlier and the Contents field contains the DTLS payload. On receiving the JPY message, the Join Proxy retrieves the two parts. It uses the Header field to route the DTLS message containing the DTLS payload retrieved from the Contents field to the Pledge. In this scenario, both the Registrar and the Join Proxy use discoverable join-ports, for the Join Proxy this may be a default CoAP port. The depicts the message flow diagram:

Stateless Message structure The JPY message is constructed as a payload with media-type application/cbor Header and Contents fields together are one CBOR array of 5 elements:

header field: containing a CBOR array with the Pledge IPv6 Link Local address as a CBOR byte string, the Pledge's UDP port number as a CBOR integer, the IP address family (IPv4/IPv6) as a CBOR integer, and the proxy's ifindex or other identifier for the physical port as CBOR integer. The header field is not DTLS encrypted.
Content field: containing the DTLS payload as a CBOR byte string.

The address family integer is defined in with: The Join Proxy cannot decrypt the DTLS payload and has no knowledge of the transported media type.

CDDL representation of JPY message The contents are DTLS encrypted. In CBOR diagnostic notation the payload JPY[H(IP_P:p_P)], will look like: On reception by the Registrar, the Registrar MUST verify that the number of array elements is larger than or equal to 5, and reject the message when the number of array elements is smaller than 5. After replacing the 5th "content" element with the DTLS payload of the response message and leaving all other array elements unchanged, the Registrar returns the response message. Examples are shown in . The header field is completely opaque to the receiver. A Registrar MUST copy the header and return it unmodified in the return message. It is recommended to use the block option and make sure that the block size allows the addition of the JPY header without violating MTU sizes.

Discovery

Discovery operations by Join-Proxy In order to accomodate automatic configuration of the Join-Proxy, it must discover the location and a capabilities of the Registar. explains the basic mechanism, and this section explains the extensions required to discover if stateless operation is supported.

CoAP discovery describes how to use CoAP Discovery. The stateless Join Proxy requires a different end point that can accept the JPY encapsulation. The stateless Join Proxy can discover the join-port of the Registrar by sending a GET request to "/.well-known/core" including a resource type (rt) parameter with the value "brski.rjp" . Upon success, the return payload will contain the join-port of the Registrar. ; rt="brski.rjp" ]]>

GRASP discovery describes how to use GRASP discovery within the ACP to locate the stateful port of the Registrar. A join proxy which supports a stateless mode of operation using the mechanism described in must know where to send the encoded content from the pledge. The Registrar announces its willingness to use the stateless mechanism by including an additional objective in it's M_FLOOD'ed AN\_join\_registrar announcements, but with a different objective value. The following changes are necessary with respect to figure 10 of :

The transport-proto is IPPROTO_UDP
the objective is AN_join_registrar, identical to .
the objective name is "BRSKI_RJP".

Here is an example M_FLOOD announcing the Registrar on example port 5685, which is a port number chosen by the Registrar.

Example of Registrar announcement message Most Registrars will announce both a JPY-stateless and stateful ports, and may also announce an HTTPS/TLS service:

Example of Registrar announcing two services

Pledge discovers Join-Proxy Regardless of whether the Join Proxy operates in stateful or stateless mode, the Join Proxy is discovered by the Pledge identically. When doing constrained onboarding with DTLS as security, the Pledge will always see an IPv6 Link-Local destination, with a single UDP port to which DTLS messages are to be sent.

6tisch discovery The discovery of Join-Proxy by the Pledge uses the enhanced beacons as discussed in . However, 6tisch does not use DTLS and so this specification does not apply to it.

Comparison of stateless and stateful modes The stateful and stateless mode of operation for the Join Proxy have their advantages and disadvantages. This section should enable operators to make a choice between the two modes based on the available device resources and network bandwidth.

Comparison between stateful and stateless mode

Security Considerations All the concerns in section 4.1 apply. The Pledge can be deceived by malicious Join Proxy announcements. The Pledge will only join a network to which it receives a valid voucher . Once the Pledge joined, the payload between Pledge and Registrar is protected by DTLS. A malicious constrained Join Proxy has a number of routing possibilities:

It sends the message on to a malicious Registrar. This is the same case as the presence of a malicious Registrar discussed in RFC 8995.
It does not send on the request or does not return the response from the Registrar. This is the case of the not responding or crashing Registrar discussed in RFC 8995.
It uses the returned response of the Registrar to enroll itself in the network. With very low probability it can decrypt the response because successful enrollment is deemed unlikely.
It uses the request from the pledge to appropriate the pledge certificate, but then it still needs to acquire the private key of the pledge. This, too, is assumed to be highly unlikely.
A malicious node can construct an invalid Join Proxy message. Suppose, the destination port is the coaps port. In that case, a Join Proxy can accept the message and add the routing addresses without checking the payload. The Join Proxy then routes it to the Registrar. In all cases, the Registrar needs to receive the message at the join-port, checks that the message consists of two parts and uses the DTLS payload to start the BRSKI procedure. It is highly unlikely that this malicious payload will lead to node acceptance.
A malicious node can sniff the messages routed by the constrained Join Proxy. It is very unlikely that the malicious node can decrypt the DTLS payload. A malicious node can read the header field of the message sent by the stateless Join Proxy. This ability does not yield much more information than the visible addresses transported in the network packets.

It should be noted here that the contents of the CBOR array used to convey return address information is not DTLS protected. When the communication between JOIN Proxy and Registrar passes over an unsecure network, an attacker can change the CBOR array, causing the Registrar to deviate traffic from the intended Pledge. These concerns are also expressed in . It is also pointed out that the encryption in the source is a local matter. Similarly to , the use of AES-CCM with a 64-bit tag is recommended, combined with a sequence number and a replay window. If such scenario needs to be avoided, the constrained Join Proxy MUST encrypt the CBOR array using a locally generated symmetric key. The Registrar is not able to examine the encrypted result, but does not need to. The Registrar stores the encrypted header in the return packet without modifications. The constrained Join Proxy can decrypt the contents to route the message to the right destination. In some installations, layer 2 protection is provided between all member pairs of the mesh. In such an environment encryption of the CBOR array is unnecessary because the layer 2 protection already provide it.

IANA Considerations

Resource Type Attributes registry This specification registers two new Resource Type (rt=) Link Target Attributes in the "Resource Type (rt=) Link Target Attribute Values" subregistry under the "Constrained RESTful Environments (CoRE) Parameters" registry per the procedure.

service name and port number registry This specification registers two service names under the "Service Name and Transport Protocol Port Number" registry. Contact: IESG Description: Bootstrapping Remote Secure Key Infrastructure constrained Join Proxy Reference: [this document] Service Name: brski-rjp Transport Protocol(s): udp Assignee: IESG Contact: IESG Description: Bootstrapping Remote Secure Key Infrastructure Registrar join-port used by stateless constrained Join Proxy Reference: [this document] ]]>

Acknowledgements Many thanks for the comments by , , , , , , , , , , and .

Contributors , , and are the co-authors of the draft-kumar-dice-dtls-relay-02. Their draft has served as a basis for this document. Much text from their draft is copied over to this draft.

Changelog

11 to 10

10 to 09

09 to 07

06 to 07

05 to 06

04 to 05

03 to 04

02 to 03

01 to 02

Discovery of Join Proxy and Registrar ports

00 to 01

Registrar used throughout instead of EST server
Emphasized additional Join Proxy port for Join Proxy and Registrar
updated discovery accordingly
updated stateless Join Proxy JPY header
JPY header described with CDDL
Example simplified and corrected

00 to 00

copied from vanderstok-anima-constrained-join-proxy-05

References Normative References Datagram Transport Layer Security Version 1.2 This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] A Voucher Artifact for Bootstrapping Protocols This document defines a strategy to securely assign a pledge to an owner using an artifact signed, directly or indirectly, by the pledge's manufacturer. This artifact is known as a "voucher". This document defines an artifact format as a YANG-defined JSON document that has been signed using a Cryptographic Message Syntax (CMS) structure. Other YANG-derived formats are possible. The voucher artifact is normally generated by the pledge's manufacturer (i.e., the Manufacturer Authorized Signing Authority (MASA)). This document only defines the voucher artifact, leaving it to other documents to describe specialized protocols for accessing it. Bootstrapping Remote Secure Key Infrastructure (BRSKI) This document specifies automated bootstrapping of an Autonomic Control Plane. To do this, a Secure Key Infrastructure is bootstrapped. This is done using manufacturer-installed X.509 certificates, in combination with a manufacturer's authorizing service, both online and offline. We call this process the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol. Bootstrapping a new device can occur when using a routable address and a cloud service, only link-local connectivity, or limited/disconnected networks. Support for deployment models with less stringent security requirements is included. Bootstrapping is complete when the cryptographic identity of the new key infrastructure is successfully deployed to the device. The established secure connection can be used to deploy a locally issued certificate to the device as well. EST-coaps: Enrollment over Secure Transport with the Secure Constrained Application Protocol Consultant Cisco Systems Sandelman Software Works RISE SICS Enrollment over Secure Transport (EST) is used as a certificate provisioning protocol over HTTPS. Low-resource devices often use the lightweight Constrained Application Protocol (CoAP) for message exchanges. This document defines how to transport EST payloads over secure CoAP (EST-coaps), which allows constrained devices to use existing EST functionality for provisioning certificates. Constrained Bootstrapping Remote Secure Key Infrastructure (BRSKI) Sandelman Software Works vanderstok consultancy Cisco Systems IoTconsultancy.nl This document defines the Constrained Bootstrapping Remote Secure Key Infrastructure (Constrained BRSKI) protocol, which provides a solution for secure zero-touch bootstrapping of resource-constrained (IoT) devices into the network of a domain owner. This protocol is designed for constrained networks, which may have limited data throughput or may experience frequent packet loss. Constrained BRSKI is a variant of the BRSKI protocol, which uses an artifact signed by the device manufacturer called the "voucher" which enables a new device and the owner's network to mutually authenticate. While the BRSKI voucher is typically encoded in JSON, Constrained BRSKI defines a compact CBOR-encoded voucher. The BRSKI voucher is extended with new data types that allow for smaller voucher sizes. The Enrollment over Secure Transport (EST) protocol, used in BRSKI, is replaced with EST-over-CoAPS; and HTTPS used in BRSKI is replaced with CoAPS. Concise Binary Object Representation (CBOR) The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. GeneRic Autonomic Signaling Protocol (GRASP) This document specifies the GeneRic Autonomic Signaling Protocol (GRASP), which enables autonomic nodes and Autonomic Service Agents to dynamically discover peers, to synchronize state with each other, and to negotiate parameter settings with each other. GRASP depends on an external security environment that is described elsewhere. The technical objectives and parameters for specific application scenarios are to be described in separate documents. Appendices briefly discuss requirements for the protocol and existing protocols with comparable features. IEEE 802.1AR Secure Device Identifier IEEE Standard Address Family Numbers IANA Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Considerations for stateful vs stateless join router in ANIMA bootstrap Sandelman Software Works This document explores a number of issues affecting the decision to use a stateful or stateless forwarding mechanism by the join router (aka join assistant) during the bootstrap process for ANIMA. Encapsulation of 6TiSCH Join and Enrollment Information Elements Universidad Diego Portales Sandelman Software Works In the Time-Slotted Channel Hopping (TSCH) mode of IEEE Std 802.15.4, opportunities for broadcasts are limited to specific times and specific channels. Routers in a TSCH network transmit Enhanced Beacon (EB) frames to announce the presence of the network. This document provides a mechanism by which additional information critical for new nodes (pledges) and long-sleeping nodes may be carried within the EB in order to conserve use of broadcast opportunities. Constrained RESTful Environments (CoRE) Link Format This specification defines Web Linking using a link format for use by constrained web servers to describe hosted resources, their attributes, and other relationships between links. Based on the HTTP Link Header field defined in RFC 5988, the Constrained RESTful Environments (CoRE) Link Format is carried as a payload and is assigned an Internet media type. "RESTful" refers to the Representational State Transfer (REST) architecture. A well-known URI is defined as a default entry point for requesting the links hosted by a server. [STANDARDS-TRACK] Enrollment over Secure Transport This document profiles certificate enrollment for clients using Certificate Management over CMS (CMC) messages over a secure transport. This profile, called Enrollment over Secure Transport (EST), describes a simple, yet functional, certificate management protocol targeting Public Key Infrastructure (PKI) clients that need to acquire client certificates and associated Certification Authority (CA) certificates. It also supports client-generated public/private key pairs as well as key pairs generated by the CA. Terms Used in Routing for Low-Power and Lossy Networks This document provides a glossary of terminology used in routing requirements and solutions for networks referred to as Low-Power and Lossy Networks (LLNs). An LLN is typically composed of many embedded devices with limited power, memory, and processing resources interconnected by a variety of links. There is a wide scope of application areas for LLNs, including industrial monitoring, building automation (e.g., heating, ventilation, air conditioning, lighting, access control, fire), connected home, health care, environmental monitoring, urban sensor networks, energy management, assets tracking, and refrigeration. Terminology for Constrained-Node Networks The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks. DTLS Relay for Constrained Environments The 6LoWPAN and CoAP standards defined for resource-constrained devices are fast emerging as the de-facto protocols for enabling the Internet-of-Things (IoTs). Security is an important concern in IoTs and the DTLS protocol has been chosen as the preferred method for securing CoAP messages. DTLS is a point-to-point protocol relying on IP routing to deliver messages between the client and the server. However in some low-power lossy networks (LLNs) with multi-hop, a new "joining" device may not be initially IP-routable. Moreover, it exists in a separate, unauthenticated domain at the point of first contact and therefore cannot be initially trusted. This puts limitations on the ability to use DTLS as an authentication and confidentiality protocol at this stage. These devices being Resource-constrained often cannot accommodate more than one security protocol in their code memory. To overcome this problem we suggest DTLS as the single protocol and therefore, we present a DTLS Relay solution for the non-IP routable "joining" device to enable it to establish a secure DTLS connection with a DTLS Server. Furthermore we present a stateful and stateless mode of operation for the DTLS Relay. Transmission of IPv6 Packets over IEEE 802.15.4 Networks This document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifications include a simple header compression scheme using shared context and provisions for packet delivery in IEEE 802.15.4 meshes. [STANDARDS-TRACK] Counter with CBC-MAC (CCM) Counter with CBC-MAC (CCM) is a generic authenticated encryption block cipher mode. CCM is defined for use with 128-bit block ciphers, such as the Advanced Encryption Standard (AES). The Constrained Application Protocol (CoAP) The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) The IETF work in IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) defines 6LoWPANs such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow the traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non- transitive wireless links, as its reliance on the traditional IPv6 link concept and its heavy use of multicast make it inefficient and sometimes impractical in a low-power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, its addressing mechanisms, and duplicate address detection for Low- power Wireless Personal Area Networks and similar networks. The document thus updates RFC 4944 to specify the use of the optimizations defined here. [STANDARDS-TRACK] Block-Wise Transfers in the Constrained Application Protocol (CoAP) The Constrained Application Protocol (CoAP) is a RESTful transfer protocol for constrained nodes and networks. Basic CoAP messages work well for small payloads from sensors and actuators; however, applications will need to transfer larger payloads occasionally -- for instance, for firmware updates. In contrast to HTTP, where TCP does the grunt work of segmenting and resequencing, CoAP is based on datagram transports such as UDP or Datagram Transport Layer Security (DTLS). These transports only offer fragmentation, which is even more problematic in constrained nodes and networks, limiting the maximum size of resource representations that can practically be transferred. Instead of relying on IP fragmentation, this specification extends basic CoAP with a pair of "Block" options for transferring multiple blocks of information from a resource representation in multiple request-response pairs. In many important cases, the Block options enable a server to be truly stateless: the server can handle each block transfer separately, with no need for a connection setup or other server-side memory of previous block transfers. Essentially, the Block options provide a minimal way to transfer larger representations in a block-wise fashion. A CoAP implementation that does not support these options generally is limited in the size of the representations that can be exchanged, so there is an expectation that the Block options will be widely used in CoAP implementations. Therefore, this specification updates RFC 7252. Extended Tokens and Stateless Clients in the Constrained Application Protocol (CoAP) This document provides considerations for alleviating Constrained Application Protocol (CoAP) clients and intermediaries of keeping per-request state. To facilitate this, this document additionally introduces a new, optional CoAP protocol extension for extended token lengths. This document updates RFCs 7252 and 8323 with an extended definition of the "TKL" field in the CoAP message header. RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks Low-Power and Lossy Networks (LLNs) are a class of network in which both the routers and their interconnect are constrained. LLN routers typically operate with constraints on processing power, memory, and energy (battery power). Their interconnects are characterized by high loss rates, low data rates, and instability. LLNs are comprised of anything from a few dozen to thousands of routers. Supported traffic flows include point-to-point (between devices inside the LLN), point-to-multipoint (from a central control point to a subset of devices inside the LLN), and multipoint-to-point (from devices inside the LLN towards a central control point). This document specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL), which provides a mechanism whereby multipoint-to-point traffic from devices inside the LLN towards a central control point as well as point-to-multipoint traffic from the central control point to the devices inside the LLN are supported. Support for point-to-point traffic is also available. [STANDARDS-TRACK]

Stateless Proxy payload examples The examples show the request "GET coaps://192.168.1.200:5965/est/crts" to a Registrar. The header generated between Join Proxy and Registrar and from Registrar to Join Proxy are shown in detail. The DTLS payload is not shown. The request from Join Proxy to Registrar looks like: ]]> In CBOR Diagnostic: '] ]]> The response is: ]]> In CBOR diagnostic: '] ]]>