]> Sandelman Software Works

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vanderstok consultancy

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Cisco Systems

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Internet anima Working Group Internet-Draft This document extends the work of Bootstrapping Remote Secure Key Infrastructures (BRSKI) by replacing the (stateful) TLS Circuit proxy between Pledge and Registrar with a stateless or stateful Circuit proxy using CoAP which is called the 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. Like the BRSKI Circuit proxy, this constrained Join Proxy eliminates the need of Pledges to have routeable IP addresses before enrolment by utilizing link-local addresses. Use of the constrained Join Proxy also eliminates the need of the Pledge to authenticate to the network or perform network-wide Registrar discover before enrolment. 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, this solution is intended to support mesh networks as described in . The constrained Join Proxy as specified in this document is one of the Join Proxy options referred to in section 2.5.2 as future work. 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 that use CoAP. However, in networks that require authentication, such as those using , 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 that is operating the constrained Join Proxy, which forwards DTLS protected messages between Pledge and 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. An enrolled Pledge can act as constrained Join Proxy between other Pledges and the enrolling 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 using the CoAP extended token in a way identical to that described in .

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. 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 "Constrained Join Proxy" enables a Pledge that is multiple hops away from the Registrar, to execute the BRSKI protocol using a secure channel. The term "Join Proxy" is used interchangeably with the term "constrained Join Proxy" throughout this document. The Circuit Proxy is referred to as a TCP circuit Join Proxy.

constrained Join Proxy functionality As depicted in the , the Pledge (P), in a network such as 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 link-local IPv6 addresses. However, the Pledge needs to communicate using end-to-end security with a Registrar in order to onboard, 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 the Pledge for any returned messages from the Registrar.

multi-hop enrollment.

Without a routeable IPv6 address, the Pledge (P) cannot exchange IPv6/UDP/DTLS traffic with the Registrar (R), over multiple hops in the network. Furthermore, the Pledge may not even be able to 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 the discovery of the destination address of the Registrar, the constrained Join Proxy is introduced. This constrained Join Proxy functionality is also (auto) 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. Only some of these Pledges may be neighbors of the Registrar. Others would need for their traffic to be routed across one or more enrolled devices to reach the Registrar. The desired state of the installation is a network with a Registrar and all Pledges becoming 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 constrained 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 constrained 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. The constrained Join Proxy is as a packet-by-packet proxy for UDP packets between Pledge and Registrar. The constrained BRSKI protocol between Pledge and Registrar described in which this Join Proxy supports uses UDP messages with DTLS payload, but the Join Proxy as described here is unaware of this payload. It can therefore potentially also work for other UDP based protocols as long as they are agnostic to (or can be made to work with) the change of IP header by the constrained Join Proxy. In both Stateless and Stateful mode, the Join Proxy needs to be configured with or dynamically discover a Registrar to perform its service. This specification does not discuss how a constrained Join Proxy selects a Registrar when it discovers 2 or more.

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

• Stateful mode
• Stateless mode

The advantages and disadvantages of the two modes are presented in . A Registrar MUST implement both the stateful mode and the Stateless mode, but an operator MAY configure it to announce only one. A Join Proxy MUST implement the stateless mode, but SHOULD implement the stateful mode if it has sufficient memory. For a Join Proxy to be operational, the node on which it is running has to be able to talk to a Registrar (exchange UDP messages with it). This can happen fully automatically by the Join Proxy node first enrolling itself as a Pledge, and then learning the IP address, the UDP port and the mode(s) (Stateful and/or Stateless) of the Registrar, through a discovery mechanism such as those described in Section 6. In mesh LLN networks like those based upon RPL (), it would not be unusual for the 6LBR (the DODAG root) to have a wired network interface on which the Registrar can be found. Or the Registrar may in fact be co-located with the 6LBR. This 6LBR then becomes the first Join Proxy, and additional nodes attach to it in a concentric fashion. Other methods, such as provisioning the Join Proxy are out of scope of this document but equally feasible. Once the Join Proxy is operational, its mode is determined by the mode of the Registrar. If the Registrar offers both Stateful and Stateless mode, the Join Proxy MUST use the stateless mode. Independent of the mode of the Join Proxy, the Pledge first discovers (see Section 6) and selects the most appropriate Join Proxy. From the discovery, the Pledge learns the Join Proxies link-local scope IP address and UDP (join) port. This discovery can also be based upon section 4.1. If the discovery method does not support discovery of the join-port, then the Pledge assumes the default CoAP over DTLS UDP port (5683).

Stateful Join Proxy In stateful mode, the Join Proxy acts as a UDP "circuit" proxy that does not change the UDP payload (data octets according to ) but only rewrites the IP and UDP headers of each packet it receives from Pledge and Registrar. The stateful Join Proxy operates as a 'pseudo' UDP circuit proxy creating and utilizing connection mapping state to rewrite the IP address and UDP port number packet header fields of UDP packets that it forwards between Pledge and Registrar. depiects how this state is used.

constrained stateful joining message flow with Registrar address known to Join Proxy. | IP_P:p_P | IP_Jl:p_Jl | | --ClientHello--> | IP_Jr:p_Jr| IP_R:5684 | | | | | | <--ServerHello-- | IP_R:5684 | IP_Jr:p_Jr | | : | | | | <--ServerHello-- : | IP_Jl:p_Jl| IP_P:p_P | | : : | | | | [DTLS messages] | : | : | | : : | : | : | | --Finished--> : | IP_P:p_P | IP_Jl:p_Jl | | --Finished--> | IP_Jr:p_Jr| IP_R:5684 | | | | | | <--Finished-- | IP_R:5684 | IP_Jr:p_Jr | | <--Finished-- | IP_Jl:p_Jl| IP_P:p_P | | : : | : | : | +---------------------------------------+-------------+------------+ IP_P:p_P = Link-local IP address and port of Pledge (DTLS Client) IP_R:5684 = Routable IP address and coaps port of Registrar IP_Jl:p_Jl = Link-local IP address and join-port of Join Proxy IP_Jr:p_Jr = Routable IP address and client port of Join Proxy ]]>

Because UDP does not have the notion of a connection, this document calls this a 'pseudo' connection, whose establishment is solely triggered by receipt of a packet from a Pledge with an IP_p%IF:p_P source for which no mapping state exists, and that is termined by a connection expiry timer E. 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 proxy receives an ICMP error message from the Registrar or Plege, for which mapping state exist, the proxy SHOULD map the ICMP message as it would map a UDP message and forward the ICMP message to the Registrar / Pledge. Processing of ICMP messages SHOULD NOT reset the connection expiry timer. To protect itself and the Registrar against malfunctioning Pledges and or denial of service attacks, the join proxy SHOULD limit the number of simultaneous mapping states on per ip address to 2 and the number of simultaneous mapping states per interface to 10. When mapping state can not be built due to exhausted state, the proxy SHOULD return an ICMP error (1), "Destination Port Unreachable" message with code (1), "Communication with destination administratively prohibited".

Stateless Join Proxy Stateless Join Proxy operation eliminates the need and complexity to maintain per UDP connection mapping state on the proxy and the state machinery to build, maintain and remove this mapping state. It also removes the need to protect this mapping state against DoS attacks and may also reduce memory and CPU requirements on the proxy. Stateless Join Proxy operations works by encapsulating the DTLS messages into a new CoAP header . This new CoAP header is designed to be as minimalistic as possible. The use of CoAP here costs a XXX bytes more than a custom encapsulation, but simplies much of the operation, as well as permitting the result to pass through CoAP proxies, CoAP to HTTP proxies, and other mechanisms that might be introduced into a network. This also eliminates custom code that is only rarely used, which may reduce bugs. The CoAP payload is configured much as specifies:

• The request method is POST.
• The type is Confirmable (CON).
• The Proxy-Scheme option is set to "coap".
• No Uri_Host option is included, as none is technically required.
• No Uri-Path option is included.
• The payload is the DTLS payload as received from the Pledge.
• An extended token is included to contain some encrypted state that allows replies to be returned to the Pledge.

shows an example CoAP header, assuming a 16-byte extended token, with the resulting overhead of 28 bytes. When the Join Proxy receives a UDP message from a Pledge, it encodes the Pledges link-local IP address, interface and UDP (source) port of the packet into the extended token. The result is sent to the Registrar from a fixed source UDP port. As described in , when the Registrar sends packets for the Pledge, it MUST return the token field unchanged. This allows the Join Proxy to decode the saved Pledge state, and reconstruct the Pledges link-local IP address, interace and UDP (destination) port for the return packet. shows this per-packet mapping on the Join Proxy. The Registrar transiently stores the extended token field information in case it needs to generate additional messages as a result of DTLS processing. The Registrar uses the payload field to execute the Registrar functionality. 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 CoAP message, the Join Proxy processes the CoAP header. It uses the extended token field to route the payload as a DTLS message to the Pledge. In the stateless Join Proxy mode, both the Registrar and the Join Proxy use discoverable UDP join-ports. For the Join Proxy this may be a default CoAP port.

constrained stateless joining message flow. | IP_P:p_P |IP_Jl:p_Jl | | --JPY[H(IP_P:p_P),--> | IP_Jr:p_Jr|IP_R:p_Ra | | C(ClientHello)] | | | | <--JPY[H(IP_P:p_P),-- | IP_R:p_Ra |IP_Jr:p_Jr | | C(ServerHello)] | | | | <--ServerHello-- | IP_Jl:p_Jl|IP_P:p_P | | : | | | | [ DTLS messages ] | : | : | | : | : | : | | --Finished--> | IP_P:p_P |IP_Jr:p_Jr | | --JPY[H(IP_P:p_P),--> | IP_Jl:p_Jl|IP_R:p_Ra | | C(Finished)] | | | | <--JPY[H(IP_P:p_P),-- | IP_R:p_Ra |IP_Jr:p_Jr | | C(Finished)] | | | | <--Finished-- | IP_Jl:p_Jl|IP_P:p_P | | : | : | : | +-------------------------------------------+-----------+-----------+ IP_P:p_P = Link-local IP address and port of the Pledge IP_R:p_Ra = Routable IP address and join-port of Registrar IP_Jl:p_Jl = Link-local IP address and join-port of Join Proxy IP_Jr:p_Jr = Routable IP address and port of Join Proxy JPY[H(),C()] = Join Proxy message with header H and content C ]]>

Constraucting the extended token The Join Proxy cannot decrypt the DTLS payload and has no knowledge of the transported media type. The contents are DTLS encrypted. The extended token payload is to be reflected by the Registrar when sending reply packets to the Join Proxy. The extended token content is not standardized, but this section provides an non-normative example. As explained in , the Join Proxy SHOULD encrypt the extended token with a symmetric key known only to the Join Proxy. This key need not persist on a long term basis, and MAY be changed periodically. This is intended to be identical to the mechanism described in . However, since the CoAP layer is inside of the DTLS layer (which is between the Pledge and the Registrar), it is not possible for the Join Proxy to act as an actual CoAP proxy. The context that is stored into the extended token might be constructed with the following CDDL grammar: (This is illustrative only: the contents are not subject to standardization) This results in a total of 96 bits, or 12 bytes. The structure stores the srcport, the originating IPv6 Link-Local address, the IPv4/IPv6 family (as a single bit) and an ifindex to provide the link-local scope. This fits nicely into a single AES128 CBC block for instance, resulting in a 16 byte token. The Join Proxy MUST maintain the same context block for all communications from the same Pledge. This implies that any encryption key either does not change during the communication, or that when it does, it is acceptable to break any onboarding connections which have not yet completed. If using a context parameter like defined above, it should be easy for the Join Proxy to meet this requirement without maintaining any local state about the Pledge. Note: when IPv6 is used only the lower 64-bits of the origin IP need to be recorded, because they are all IPv6 Link-Local addresses, so the upper 64-bits are just "fe80::". For IPv4, a Link-Local IPv4 address would be used, and it would fit into 64-bits. On media where the IID is not 64-bits, a different arrangement will be necessary. For the join messages relayed to a particular Registrar, the Join Proxy SHOULD use the same UDP source port for all messages related to all Pledges. A Join Proxy MAY change the UDP source port, but doing so creates more local state. But, a Join Proxy with multiple CPUs (unlikely in a constrained system, but possible in some future) could, for instance, use different source port numbers to demultiplex connections across CPUs.

Processing by Registrar On reception of a CoAP encapsulated join message by the Registrar, the Registrar processes the CoAP header and extracts the extended token. The extended token will need to be provided as input to a DTLS library , as the 5-tuple of the UDP connection alone does not provide enough context for the Registrar to pick an appropriate context. Note that the socket will need to be used for multiple DTLS flows, which is atypical for how DTLS usually uses sockets. As an alternative, the Registrar could split out the state processing from the DTLS processing, creating new sockets that it maintains, but this just duplicates state across many places. It may still be an advantage for some architectures. Examples are shown in . At the CoAP level, within the Constrained BRSKI and the EST-COAP level, the block option is often used. The Registrar and the Pledge MUST select a block size that would allow the addition of the additional CoAP 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 second CoAP header encapsulation and extended token. 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 a port that contain process the CoAP encalsulated DTLS messages. ;rt=brski.rjp ]]> In the link format, and , the authority attribute can not include a port number unless it also includes the IP address. The returned join-port is expected to process the CoAP encapsulated DTLS messages described in section . The scheme is now CoAP, as the outside protocol is CoAP and could be subject to further CoAP operations. An EST/Registrar server running at address 2001:db8:0:abcd::52, with the CoAP processing on port 7634, and the stateful Registrar on port 5683 could reply to a multicast query as follows: ;rt=brski.rjp, ;rt=brski, ;rt=brski.rv;ct=836, ;rt=brski.vs;ct="50 60", ;rt=brski.es;ct="50 60", ]]>

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 CoAP-stateless and stateful ports, and may also announce an HTTPS/TLS service:

Example of Registrar announcing three 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.

CoAP discovery In the context of a CoAP network without Autonomic Network support, discovery follows the standard CoAP policy. The Pledge can discover a Join Proxy by sending a link-local multicast message to ALL CoAP Nodes with address FF02::FD. Multiple or no nodes may respond. The handling of multiple responses and the absence of responses follow section 4 of . The join-port of the Join Proxy is discovered by sending a GET request to "/.well-known/core" including a resource type (rt) parameter with the value "brski.jp" . Upon success, the return payload will contain the join-port. The example below shows the discovery of the join-port of the Join Proxy. ; rt="brski.jp" ]]> Port numbers are assumed to be the default numbers 5683 and 5684 for coap and coaps respectively (sections 12.6 and 12.7 of ) when not shown in the response. Discoverable port numbers are usually returned for Join Proxy resources in the <URI-Reference> of the payload (see section 4.1 of ).

GRASP discovery This section is normative for uses with an ANIMA ACP. In the context of autonomic networks, the Join-Proxy uses the DULL GRASP M_FLOOD mechanism to announce itself. Section 4.1.1 of discusses this in more detail. The following changes are necessary with respect to figure 10 of :

• The transport-proto is IPPROTO_UDP
• the objective is AN_Proxy

The Registrar announces itself using ACP instance of GRASP using M_FLOOD messages. Autonomic Network Join Proxies MUST support GRASP discovery of Registrar as described in section 4.3 of . Here is an example M_FLOOD announcing the Join-Proxy at fe80::1, on standard coaps port 5684.

Example of Registrar announcement message

6tisch discovery The discovery of Join-Proxy by the Pledge uses the enhanced beacons as discussed in . 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.

Properties	Stateful mode	Stateless mode
State Information	The Join Proxy needs additional storage to maintain mapping between the address and port number of the Pledge and those of the Registrar.	No information is maintained by the Join Proxy. Registrar needs to store the packet header.
Packet size	The size of the forwarded message is the same as the original message.	Size of the forwarded message is bigger than the original, it includes additional information
Specification complexity	The Join Proxy needs additional functionality to maintain state information, and specify the source and destination addresses of the DTLS handshake messages	CoAP message to encapsulate DTLS payload. The Registrar and the Join Proxy have to understand the CoAP header in order to process it.
Ports	Join Proxy needs discoverable join-port	Join Proxy and Registrar need discoverable join-ports

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 by the Join Proxy 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.

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.

Changelog

14 to 13

• incorporated review comments from TTE
• jpy message changed to CoAP header

13 to 12

12 to 11

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 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] 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. 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. This document specifies version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection / non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document obsoletes RFC 6347. 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. 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. 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. 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 Standard IANA 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] 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. 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. 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 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. 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. 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. 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. 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. Philips Research University of Glasgow Singapore Philips Research 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. 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) 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 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] 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. 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. 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] This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. 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. To participate in wide-area IP networking, a host needs to be configured with IP addresses for its interfaces, either manually by the user or automatically from a source on the network such as a Dynamic Host Configuration Protocol (DHCP) server. Unfortunately, such address configuration information may not always be available. It is therefore beneficial for a host to be able to depend on a useful subset of IP networking functions even when no address configuration is available. This document describes how a host may automatically configure an interface with an IPv4 address within the 169.254/16 prefix that is valid for communication with other devices connected to the same physical (or logical) link. IPv4 Link-Local addresses are not suitable for communication with devices not directly connected to the same physical (or logical) link, and are only used where stable, routable addresses are not available (such as on ad hoc or isolated networks). This document does not recommend that IPv4 Link-Local addresses and routable addresses be configured simultaneously on the same interface. [STANDARDS-TRACK] A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]

Stateless CoAP payload examples This section shows how the CoAP header is arranged by the stateless proxy. The Option is Proxy-Scheme, with a value 39, and must be encoded as an Option Delta of 13, followed by a single byte of (39-13=) 26. The total size of the header is 4,1+16,6,1 is 28 bytes. A CBOR header would have taken 4+16 bytes or 20 bytes, for a difference of 8 bytes.

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. NOTE THESE ARE OLD. The request from Join Proxy to Registrar looks like: ]]> In CBOR Diagnostic: '] ]]> The response is: ]]> In CBOR diagnostic: '] ]]>