| anima Working Group | M. Richardson |
| Internet-Draft | Sandelman Software Works |
| Intended status: Standards Track | P. van der Stok |
| Expires: April 2, 2019 | vanderstok consultancy |
| P. Kampanakis | |
| Cisco Systems | |
| September 29, 2018 |
Constrained Join Proxy for Bootstrapping Protocols
draft-vanderstok-constrained-anima-dtls-join-proxy-00
This document defines a protocol to securely assign a pledge to an owner, using an intermediary node between pledge and owner. This intermediary node is known as a "constrained-join-proxy".
This document extends the work of [I-D.ietf-anima-bootstrapping-keyinfra] by replacing the Circuit-proxy by a stateless constrained join-proxy, that uses IP encapsulation.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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Enrolment of new nodes into constrained networks with constrained nodes present is described in [I-D.ietf-anima-bootstrapping-keyinfra] and makes use of Enrolment over Secure Transport (EST) [RFC7030]. The specified solutions use https and may be too large in terms of code space or bandwidth required. Constrained devices in constrained networks [RFC7228] typically implement the IPv6 over Low-Power Wireless personal Area Networks (6LoWPAN) [RFC4944] and Constrained Application Protocol (CoAP) [RFC7252].
CoAP has chosen Datagram Transport Layer Security (DTLS) [RFC6347] as the preferred security protocol for authenticity and confidentiality of the messages. A constrained version of EST, using Coap and DTLS, is described in [I-D.ietf-ace-coap-est].
DTLS is a client-server protocol relying on the underlying IP layer to perform the routing between the DTLS Client and the DTLS Server. However, the new "joining" device will not be IP routable until it is authenticated to the network. A new "joining" device can only initially use a link-local IPv6 address to communicate with a neighbour node using neighbour discovery [RFC6775] until it receives the necessary network configuration parameters. However, before the device can receive these configuration parameters, it needs to authenticate itself to the network to which it connects. In [I-D.ietf-anima-bootstrapping-keyinfra] Enrolment over Secure Transport (EST) [RFC7030] is used to authenticate the joining device. However, IPv6 routing is necessary to establish a connection between joining device and the EST server.
This document specifies a Join-proxy and protocol to act as intermediary between joining device and EST server to establish a connection between joining device and EST server.
This document is very much inspired by text published earlier in [I-D.kumar-dice-dtls-relay].
The following terms are defined in [RFC8366], and are used identically as in that document: artifact, imprint, domain, Join Registrar/Coordinator (JRC), Manufacturer Authorized Signing Authority (MASA), pledge, Trust of First Use (TOFU), and Voucher.
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant STuPiD implementations.
As depicted in the Figure 1, the joining Device, or pledge (P), is more than one hop away from the EST server (E) and not yet authenticated into the network. At this stage, it can only communicate one-hop to its nearest neighbour, the Join proxy (J) using their link-local IPv6 addresses. However, the Device needs to communicate with end-to-end security with a Registrar hosting the EST server (E) to authenticate and get the relevant system/network parameters. If the Pledge (P) initiates a DTLS connection to the EST server whose IP address has been pre-configured, then the packets are dropped at the Join Proxy (J) since the Pledge (P) is not yet admitted to the network or there is no IP routability to Pledge (P) for any returned messages.
++++
|E |---- +--+ +--+
| | \ |J |........|P |
++++ \-----| | | |
EST server +--+ +--+
REgistrar Join Proxy PLedge
"Joining" Device
Figure 1: multi-hop enrolment.
Furthermore, the Pledge (P) may wish to establish a secure connection to the EST server (E) in the network assuming appropriate credentials are exchanged out-of-band, e.g. a hash of the Pledge (P)'s raw public key could be provided to the EST server (E). However, the Pledge (P) is unaware of the IP address of the EST-server (E) to initiate a DTLS connection and perform authentication with.
An DTLS connection is required between Pledge and EST server. To overcome the problems with non-routability of DTLS packets and/ or discovery of the destination address of the EST Server to contact, the Join Proxy is introduced. This Join-Proxy functionality is configured into all authenticated devices in the network which may act as the Join Proxy (J) for newly joining nodes. The Join Proxy allows for routing of the packets from the Pledge (P) using IP routing to the intended EST Server.
In this section, the constrained Join Proxy functionality is specified using DTLS and coaps. When a joining device as a client attempts a DTLS connection to the EST server, it uses its link- local IP address as its IP source address. This message is transmitted one-hop to a neighbour node. Under normal circumstances, this message would be dropped at the neighbour node since the joining device is not yet IP routable or it is not yet authenticated to send messages through the network. However, if the neighbour device has the Join Proxy functionality enabled, it routes the DTLS message to a specific EST Server. Additional security mechanisms need to exist to prevent this routing functionality being used by rogue nodes to bypass any network authentication procedures.
The Join-proxy is stateless to minimize the requirements on the constrained Join-proxy device.
If an untrusted DTLS Client that can only use link-local addressing wants to contact a trusted end-point EST Server, it sends the DTLS message to the Join Proxy. The Join Proxy encapsulates this message into a new type of message called Join ProxY (JPY) message. The JPY message consists of two parts:
On receiving the JPY message, the EST Server decapsulates it to retrieve the two parts. It uses the Header field information to transiently store the DTLS Client's address and port. The EST Server then performs the normal DTLS operations on the DTLS message from the Contents field. However, when the EST Server replies, it also encapsulates its DTLS message in a JPY message back to the Join Proxy. The Header contains the original source link-local address and port of the DTLS Client from the transient state stored earlier (which can now be discarded) and the Contents field contains the DTLS message.
On receiving the JPY message, the Join Proxy decapsulates it to retrieve the two parts. It uses the Header field to route the DTLS message retrieved from the Contents field to the joining node.
The Figure 2 depicts the message flow diagram when the EST Server end-point address is known only to the Join Proxy:
+--------------+------------+---------------+-----------------------+ | EST Client | Join Proxy | EST server | Message | | (P) | (J) | (E) |Src_IP:port|Dst_IP:port| +--------------+------------+---------------+-----------+-----------+ | --ClientHello--> | IP_C:p_C |IP_Ra:5684 | | --JPY[H(IP_C:p_C),--> | IP_Rb:p_Rb|IP_S:5684 | | C(ClientHello)] | | | | <--JPY[H(IP_C:p_C),-- | IP_S:5684 |IP_Rb:p_Rb | | C(ServerHello)] | | | | <--ServerHello-- | IP_Ra:5684|IP_C:p_C | | : | | | | : | : | : | | | : | : | | --Finished--> | IP_C:p_C |IP_Ra:5684 | | --JPY[H(IP_C:p_C),--> | IP_Rb:p_Rb|IP_S:5684 | | C(Finished)] | | | | <--JPY[H(IP_C:p_C),-- | IP_S:5684 |IP_Rb:p_Rb | | C(Finished)] | | | | <--Finished-- | IP_Ra:5684|IP_C:p_C | | : | : | : | +-------------------------------------------+-----------+-----------+ IP_C:p_C = Link-local IP address and port of DTLS Client IP_S:5684 = IP address and coaps port of DTLS Server IP_Ra:5684 = Link-local IP address and coaps port of DTLS Relay IP_Rb:p_Rb = IP address(can be same as IP_Ra) and port of DTLS Relay JPY[H(),C()] = Join Proxy message with header H and content C
Figure 2: constrained joining message flow.
The JPY message is constructed as a single untagged [RFC7049] CBOR map. The contents of the map include:
(INSERT CDDL notation)
It should be noted here that the contents of the CBOR map are not protected, but that the communication is between the Proxy and a known registrar (a connected UDP socket), and that messages from other origins are ignored.
This document needs to create a registry for key indexes in the CBOR map. It should be given a name, and the amending formula should be IETF Specification.
Much of this text is inspired by [I-D.kumar-dice-dtls-relay].
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