CoAP Usage for RELOAD: A Constrained Application Protocol (CoAP) Usage for REsource LOcation And Discovery (RELOAD)

Internet Engineering Task Force (IETF)                        J. Jimenez
Request for Comments: 7650                                      Ericsson
Category: Standards Track                                  J. Lopez-Vega
ISSN: 2070-1721                                    University of Granada
                                                              J. Maenpaa
                                                            G. Camarillo
                                                                Ericsson
                                                          September 2015


            A Constrained Application Protocol (CoAP) Usage
              for REsource LOcation And Discovery (RELOAD)

Abstract

   This document defines a Constrained Application Protocol (CoAP) Usage
   for REsource LOcation And Discovery (RELOAD).  The CoAP Usage
   provides the functionality to federate Wireless Sensor Networks
   (WSNs) in a peer-to-peer fashion.  The CoAP Usage for RELOAD allows
   CoAP nodes to store resources in a RELOAD peer-to-peer overlay,
   provides a lookup service, and enables the use of RELOAD overlay as a
   cache for sensor data.  This functionality is implemented in the
   RELOAD overlay itself, without the use of centralized servers.  The
   RELOAD AppAttach method is used to establish a direct connection
   between nodes through which CoAP messages are exchanged.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7650.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Registering CoAP URIs . . . . . . . . . . . . . . . . . . . .   7
   5.  Lookup  . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Forming a Direct Connection and Reading Data  . . . . . . . .   9
   7.  Caching Mechanisms  . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  ProxyCache  . . . . . . . . . . . . . . . . . . . . . . .  11
     7.2.  SensorCache . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  CoAP Usage Kinds Definition . . . . . . . . . . . . . . . . .  14
     8.1.  CoAP-REGISTRATION Kind  . . . . . . . . . . . . . . . . .  14
     8.2.  CoAP-CACHING Kind . . . . . . . . . . . . . . . . . . . .  15
   9.  Access Control Rules  . . . . . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     11.1.  CoAP-REGISTRATION Kind-ID  . . . . . . . . . . . . . . .  17
     11.2.  CoAP-CACHING Kind-ID . . . . . . . . . . . . . . . . . .  17
     11.3.  Access Control Policies  . . . . . . . . . . . . . . . .  17
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     12.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The Constrained Application Protocol (CoAP) Usage for REsource
   LOcation And Discovery (RELOAD) allows CoAP nodes to store resources
   in a RELOAD peer-to-peer overlay, provides a lookup service, and
   enables the use of RELOAD overlay as a cache for sensor data.  This
   functionality is implemented in the RELOAD overlay itself, without
   the use of centralized servers.

   This usage is intended for interconnected devices over a wide-area
   geographical coverage, such as in cases where multiple Wireless
   Sensor Networks (WSNs) need to be federated over some wider-area
   network.  These WSNs would interconnect by means of nodes that are
   equipped with long range modules (e.g., 2G, 3G, 4G) as well as short
   range ones (e.g., XBee, ZigBee, Bluetooth LE).

   Constrained devices are likely to be heterogeneous when it comes to
   their radio layer; however, we expect them to use a common
   application-layer protocol -- CoAP, which is a specialized web
   transfer protocol [RFC7252].  It realizes the Representational State
   Transfer (REST) architecture for the most constrained nodes, such as
   sensors and actuators.  CoAP can be used not only between nodes on
   the same constrained network but also between constrained nodes and
   nodes on the Internet.  The latter is possible since CoAP can be
   translated to Hypertext Transfer Protocol (HTTP) for integration with
   the web.  Application areas of CoAP include different forms of
   machine-to-machine (M2M) communication, such as home automation,
   construction, health care or transportation.  Areas with heavy use of
   sensor and actuator devices that monitor and interact with the
   surrounding environment.

   As specified in [RFC6940], RELOAD is fundamentally an overlay
   network.  It provides a layered architecture with pluggable
   application layers that can use the underlaying forwarding, storage,
   and lookup functionalities.  Figure 1 illustrates where the CoAP
   Usage is placed within the RELOAD architecture.

       Application

           +-------+
           | CoAP  |   ...
           | Usage |
           +-------+
       ------------------------------------ Messaging Service
       +------------------+     +---------+
       |     Message      |<--->| Storage |
       |    Transport     |     +---------+
       +------------------+           ^
              ^       ^               |
              |       v               v
              |     +-------------------+
              |     |    Topology       |
              |     |    Plug-in        |
              |     +-------------------+
              |         ^
              v         v
           +------------------+
           |  Forwarding &    |
           | Link Management  |
           +------------------+
       ------------------------------------ Overlay Link Service
            +-------+  +-------+
            |TLS    |  |DTLS   |  ...
            |Overlay|  |Overlay|
            |Link   |  |Link   |
            +-------+  +-------+

                          Figure 1: Architecture

   The CoAP Usage involves three basic functions:

   Registration: CoAP nodes that can use the RELOAD data storage
   functionality, can store a mapping from their CoAP URI to their Node-
   ID in the overlay.  They can also retrieve the Node-IDs of other
   nodes.  Nodes that are not RELOAD aware can use other mechanisms, for
   example [CORERESDIR] in their local network.

   Lookup: Once a CoAP node has identified the Node-ID for an URI it
   wishes to retrieve, it can use the RELOAD message routing system to
   set up a connection that can be used to exchange CoAP messages.
   Similarly as with the registration, nodes that are not RELOAD aware
   can use CoAP messages with a RELOAD Node (RN) that will in turn
   perform the lookup in the overlay.

   Caching: Nodes can use the RELOAD overlay as a caching mechanism for
   information about what CoAP resources are available on the node.
   This is especially useful for power-constrained nodes that can make
   their data available in the cache provided by the overlay while in
   sleep mode.

   For instance, a CoAP proxy (See Section 3) could register its Node-ID
   (e.g. "9996172") and a list of sensors (e.g. "/sensors/temp-1;
   /sensors/temp-2; /sensors/light, /sensors/humidity") under its URI
   (e.g. "coap://overlay-1.com/proxy-1/").

   When a node wants to discover the values associated with that URI, it
   queries the overlay for "coap://overlay-1.com/proxy-1/" and gets back
   the Node-ID of the proxy and the list of its associated sensors.  The
   requesting node can then use the RELOAD overlay to establish a direct
   connection with the proxy and to read sensor values.

   Moreover, the CoAP proxy can store the sensor information in the
   overlay.  In this way, information can be retrieved directly from the
   overlay without performing a direct connection to the storing proxy.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   We use the terminology and definitions from the RELOAD Base Protocol
   [RFC6940] extensively in this document.  Some of those concepts are
   further described in the "Concepts and Terminology for Peer to Peer
   SIP" [P2PSIP] document.

3.  Architecture

   In our architecture we extend the different nodes present in RELOAD
   (Peer, Client) and add support for sensor devices or other
   constrained devices.  Figure 2 illustrates the overlay topology.  The
   different nodes, according to their functionality, are:

   Client
      As specified in [RFC6940], clients are nodes that do not have
      routing or storage responsibilities in the Overlay.

   Peer
      As specified in [RFC6940], peers are nodes in the overlay that can
      route messages for nodes other than those to which it is directly
      connected.

   Sensor
      Devices capable of measuring a physical quantity.  Sensors usually
      acquire quantifiable information about their surrounding
      environment such as: temperature, humidity, electric current,
      moisture, radiation, and so on.

   Actuator
      Devices capable of interacting and affecting their environment
      such as: electrical motors, pneumatic actuators, electric
      switches, and so on.

   Proxy Node
      Devices having sufficient resources to run RELOAD either as client
      or peer.  These devices are located at the edge of the sensor
      network and, in case of Wireless Sensor Networks (WSN), act as
      coordinators of the network.

   Physical devices can have one or several of the previous functional
   roles.  According to the functionalities that are present in each of
   the nodes, they can be:

   Constrained Node
      A Constrained Node (CN) is a node with limited computational
      capabilities.  CN devices belong to classes of at least C1 and C2
      devices as defined in [RFC7228], their main constraint being the
      implementation of the CoAP protocol.  If the CN is wireless, then
      it will be part of a Low-Rate Wireless Personal Area Network
      (LR-WPAN), also termed Low-Power and Lossy Network (LLN).  Lastly,
      devices will usually be in sleep mode in order to prevent battery
      drain, and will not communicate during those periods.  A CN is NOT
      part of the RELOAD overlay, therefore it cannot act as a client,
      peer, nor proxy.  A CN is always either a Sensor or an Actuator.
      In the latter case, the node is often connected to a continuous
      energy power supply.

   RELOAD Node
      A RELOAD Node (RN) MUST implement the client functionality in the
      Overlay.  Additionally, the node will often be a full RELOAD peer.
      An RN may also be sensor or actuator since it can have those
      devices connected to it.

   Proxy Node
      A Proxy Node (PN) MUST implement the RN functionality and act as a
      sink for the LR-WPAN network.  The PN connects the short range
      Wireless Network to the Wide Area Network or the Internet.  A
      Proxy Node fulfills the "Proxy Node" role as described previously
      in the Architecture.

                  +------+
                  |      |
         +--------+  RN  +---------+
         |        |      |         |
     +---+--+     +------+      +--+---+
     |      |                   |      |
     |  RN  |                   |  RN  |
     |      |                   |      |   +------------+
     +---+--+                   +--+---+   |        WSN |
         |         RELOAD          |       |     +----+ |
         |         OVERLAY         |       | +---+ CN | |
     +---+--+                   +--+---+   | |   +----+ |
     |      |                   |      +-----+          |
     |  RN  |                   |  PN  |   |            |
     |      |                   |      +-----+          |
     +---+--+     +------+      +--+---+   | |   +----+ |
         |        |      |         |       | +---+ CN | |
         +--------+  PN  +---------+       |     +----+ |
                  |      |                 +------------+
                  +-+--+-+
                    |  |
           +--------|--|--------+
           |     +--+  +--+     |
           |     |        |     |
           |  +--+-+    +-+--+  |
           |  | CN |    | CN |  |
           |  +----+    +----+  |
           |                WSN |
           +--------------------+

                        Figure 2: Overlay Topology

4.  Registering CoAP URIs

   CoAP URIs are typically resolved using a DNS.  When CoAP is needed in
   a RELOAD environment, URI resolution is provided by the overlay as a
   whole.  Instead of registering a URI, a peer stores a
   CoAPRegistration structure under a hash of its own URI.  This uses
   the CoAP REGISTRATION Kind-ID, which is formally defined in
   Section 8.1 and uses a DICTIONARY data model.

   In this example, a CoAP proxy that is located in an overlay
   overlay-1.com using a Node-ID "9996172" wants to register four
   different sensors to the URI "coap://overlay-1.com/proxy-1/.well-
   known/".  We will be using the link format specified in [RFC6690] to
   store the following mapping in the overlay:

    Resource-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
    KEY =  9996172,

    VALUE = [
     </sensors/temp-1>;rt="temperature-c";if="sensor",
     </sensors/temp-2>;rt="temperature-c";if="sensor",
     </sensors/light>;rt="light-lux";if="sensor",
     </sensors/humidity>;rt="humidity-p";if="sensor"
        ]

   Note that the Resource-ID stored in the overlay is calculated as hash
   over the URI, that is -- h(URI), which in RELOAD is usually SHA-1.

   This would inform any other node performing a lookup for the previous
   URI "coap://overlay-1.com/proxy-1/.well-known" that the Node-ID value
   for proxy-1 is "9996172".  In addition, this mapping provides
   relevant information as to the number of sensors (CNs) and the URI
   path to connect to them using CoAP.

5.  Lookup

   The RELOAD overlay supports a rendezvous system that can be used for
   the lookup of other CoAP nodes.  This is done by fetching mapping
   information between CoAP URIs and Node-IDs.

   As an example, if a node RN located in the overlay overlay-1.com
   wishes to read which resources are served at an RN with URI
   coap://overlay-1.com/proxy-1/, it performs a fetch in the overlay.
   The Resource-ID used in this fetch is a SHA-1 hash over the URI
   "coap://overlay-1.com/proxy-1/.well-known/".

   After this fetch request, the overlay will return the following
   result:

    Resource-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
    KEY =  9996172,

    VALUE = [
     </sensors/temp-1>;rt="temperature-c";if="sensor",
     </sensors/temp-2>;rt="temperature-c";if="sensor",
     </sensors/light>;rt="light-lux";if="sensor",
     </sensors/humidity>;rt="humidity-p";if="sensor"
     ]

   The obtained KEY is the Node-ID of the RN responsible of this KEY/
   VALUE pair.  The VALUE is the set of URIs necessary to read data from
   the CNs associated with the RN.

   Using the RELOAD DICTIONARY model allows for multiple nodes to
   perform a store to the same Resource-ID.  This can be used, for
   example, to perform a store of resources of the same type or with
   similar characteristics.  After performing a lookup, this feature
   allows the fetching of those multiple RNs that host CNs of the same
   class.

   As an example, provided that the previous peer (9996172) and another
   peer (9996173) have stored the links to their respective temperature
   resources in this same Resource-ID (temperature), an RN (e.g.,
   node-A) can do a fetch to the URI "coap://overlay-1.com/
   temperature/.well-known/", obtaining the following results:

    Resource-ID = h(coap://overlay-1.com/temperature/.well-known/)

    KEY =  9996172,
    VALUE = [
     </sensors/temp-1>;rt="temperature-c";if="sensor",
     </sensors/temp-2>;rt="temperature-c";if="sensor",
      ]

    KEY = 9996173,
    VALUE = [
     </sensors/temp-a>;rt="temperature-c";if="sensor",
           </sensors/temp-b>;rt="temperature-c";if="sensor"
      ]

6.  Forming a Direct Connection and Reading Data

   Once an RN (e.g., node-A) has obtained the lookup information for a
   node in the overlay (e.g., proxy-1), it can directly connect to that
   node.  This is performed by sending an AppAttach request to the
   Node-ID obtained during the lookup process.

   After the AppAttach negotiation, node-A can access the values of the
   CNs at proxy-1 using the information obtained during the lookup.
   Following the example in Section 5, and according to [RFC6690], the
   requests for accessing the CNs at proxy-1 would be:

    REQ: GET /sensors/temp-1
    REQ: GET /sensors/temp-2
   Figure 3 shows a sample of a node reading temperature data.

   +-----+     +---------+    +-----+          +---+
   | PNA |     | OVERLAY |    | PNB |          |CNB|
   +-----+     +---------+    +-----+          +---+
      |             |            |                |
      |             |            |                |
      | 1.RELOAD    |            |                |
      | FetchReq    |            |                |
      |+----------->|            |                |
      |             |            |                |
      | 2.RELOAD    |            |                |
      | FetchAns    |            |                |
      |<-----------+|            |                |
      |             |            |                |
      | 3.RELOAD    |            |                |
      |  AppAttach  |            |                |
      |+----------->|            |                |
      |             | 4.RELOAD   |                |
      |             | AppAttach  |                |
      |             |+---------->|                |
      |             |            |                |
      |             | 5.RELOAD   |                |
      | 6.RELOAD    |AppAttachAns|                |
      |AppAttachAns |<----------+|                |
      |<-----------+|            |                |
      |             |            |                |
      |                          |                |
      |   ---------------------  |                |
      | /        7.ICE          \|                |
      | \   connectivity checks /|                |
      |   ---------------------  |                |
      |                          |                |
      |      8.CoAP CON          |                |
      |    GET /sensors/temp-1   |                |
      |+------------------------>|                |
      |                          |  9.CoAP  GET   |
      |                          |/sensors/temp-1 |
      |                          |+-------------->|
      |                          | 10.CoAP        |
      |     11.CoAP              |    ACK 200     |
      |        ACK 200           |<--------------+|
      |<------------------------+|                |
      |                          |                |

                Figure 3: An Example of a Message Sequence

7.  Caching Mechanisms

   The CoAP protocol itself supports the caching of sensor information
   in order to reduce the response time and network bandwidth
   consumption of future, equivalent requests.  CoAP caching is
   specified in Section 5 of [RFC7252].  It consists of reusing stored
   responses when new requests arrive.  This type of storage is done in
   CoAP proxies.

   This CoAP usage for RELOAD proposes an additional caching mechanism
   for storing sensor information directly in the overlay.  In order to
   do so, it is necessary to define how the data should be stored.  Such
   caching mechanism is primarily intended for CNs with sensor
   capabilities, not for RN sensors.  This is due to the battery
   constraints of CNs, forcing them to stay in sleep mode for long
   periods of time.

   Whenever a CN wakes up, it sends the most recent data from its
   sensors to its proxy (PN), which stores the data in the overlay using
   a RELOAD StoredData structure defined in Section 6 of [RFC6940].  We
   use the StoredDataValue structure defined in Section 6.2 of
   [RFC6940], in particular we use the SingleValue format type to store
   the cached values in the overlay.  From that structure length,
   storage_time, lifetime and Signature are used in the same way.  The
   only difference is DataValue, which in our case can be either a
   ProxyCache or a SensorCache:

   enum { reserved (0), proxy_cache(1), sensor_cache(2), (255) }
                CoAPCachingType;
   struct {
    CoAPCachingType coap_caching_type;

    select(coap_caching_type) {
     case proxy_cache: ProxyCache proxy_cache_entry;
     case sensor_cache: SensorCache sensor_cache_entry;
     /* extensions */

    }
   } CoAPCaching;

7.1.  ProxyCache

   ProxyCache is meant to store values and sensor information (e.g.,
   inactivity time) for all the sensors associated with a certain proxy,
   as well as their CoAP URIs.  SensorCache, on the other hand, is used
   for storing the information and cached value of only one sensor (CoAP
   URI is not necessary, as it is the same as the one used for
   generating the Resource-ID associated to that SensorCache entry).

   ProxyCache contains the Node-ID, length, and a series of SensorEntry
   types.

   struct {
    Node-ID  Node_ID;
    uint32   length;
    SensorEntry sensors[count];
   } ProxyCache;

   Node-ID
      The Node-ID of the Proxy Node (PN) responsible for different
      sensor devices;

   length
      The length of the rest of the structure;

   Sensor-Entry
      List of sensors in the form of SensorEntry types;

   SensorEntry contains the coap_uri, sensor_info, and a series of
   SensorValue types.

   struct {
    opaque  coap_uri;
    SensorInfo  sensor_info;
    uint32  length;
    SensorValue sensor_value[count];
   } SensorEntry;

   coap_uri
      CoAP name of the sensor device in question;

   sensor_info
      contains relevant sensor information;

   length
      The length of the rest of the structure;

   sensor_value
      contains a list of values stored by the sensor;

7.2.  SensorCache

   SensorCache: contains the information related to one sensor.

   struct {
    Node-ID  Node_ID;
    SensorInfo sensor_info;
    uint32  length;
    SensorValue sensor_value[count];
   } SensorCache;

   Node_ID
      identifies the Node-ID of the Proxy Node responsible for the
      sensor;

   sensor_info
      contains relevant sensor information;

   length
      The length of the rest of the structure;

   sensor_value
      contains a list of values stored by the sensor;

   SensorInfo contains relevant sensor information that is dependent on
   the use case.  As an example, we use the sensor manufacturer as
   relevant information.

   struct {
    opaque  dev_info;

    /* extensions */

   } SensorInfo;

   dev_info
      Contains specific device information as defined in [RFC6690] --
      for example, temperature, luminosity, etc.  It can also represent
      other semantic information about the device.

   SensorValue contains the measurement_time, lifetime, and value of the
   measurement.

   struct {
    uint32  measurement_time;
    uint32  lifetime;
    opaque  value;

    /* extensions */

   } SensorValue;

   measurement_time
      indicates the moment when the measure was taken, represented as
      the number of milliseconds elapsed since midnight Jan 1, 1970 UTC
      not counting leap seconds.

   lifetime
      indicates the validity time of that measured value in milliseconds
      since measurement_time.

   value
      indicates the actual value measured.  It can be of different types
      (integer, long, string); therefore, opaque has been used.

8.  CoAP Usage Kinds Definition

   This section defines the CoAP-REGISTRATION and CoAP-CACHING Kinds.

8.1.  CoAP-REGISTRATION Kind

   Kind-IDs
      The Resource Name for the CoAP-REGISTRATION Kind-ID is the CoAP
      URI.  The data stored is a CoAPRegistration, which contains a set
      of CoAP URIs.

   Data Model
      The data model for the CoAP-REGISTRATION Kind-ID is dictionary.
      The dictionary key is the Node-ID of the storing RN.  This allows
      each RN to store a single mapping.

   Access Control
      URI-NODE-MATCH.  The "coap:" prefix needs to be removed from the
      COAP URI before matching.

   Data stored under the COAP-REGISTRATION Kind is of type
   CoAPRegistration, defined below.

   struct {
    Node-ID Node_ID;
    uint16 coap_uris_length;
    opaque coap_uris (0..2^16-1);
   } CoAPRegistration;

8.2.  CoAP-CACHING Kind

   Kind-IDs
      The Resource Name for the CoAP-CACHING Kind-ID is the CoAP URI.
      The data stored is a CoAPCaching, which contains a cached value.

   Data Model
      The data model for the CoAP-CACHING Kind-ID is single value.

   Access Control
      URI-MATCH.  The "coap:" prefix needs to be removed from the COAP
      URI before matching.

   Data stored under the CoAP-CACHING Kind is of type CoAPCaching,
   defined in Section 7.

9.  Access Control Rules

   As specified in RELOAD Base [RFC6940], every Kind that is storable in
   an overlay must be associated with an access control policy.  This
   policy defines whether a request from a given node to operate on a
   given value should succeed or fail.  Usages can define any access
   control rules they choose, including publicly writable values.

   CoAP Usage for RELOAD requires an access control policy that allows
   multiple nodes in the overlay read and write access.  This access is
   for registering and caching information using CoAP URIs as
   identifiers.  Therefore, none of the access control policies
   specified in RELOAD Base [RFC6940] are sufficient.

   This document defines two access control policies, called URI-MATCH
   and URI-NODE-MATCH.  In the URI-MATCH policy, a given value MUST be
   written and overwritten if and only if the signer's certificate
   contains an uniformResourceIdentifier entry in the subjectAltName
   Extension [RFC5280] that in canonicalized form hashes to the
   Resource-ID for the resource.  As explained in Section 6.3 of
   [RFC7252] the "coap" and "coaps" schemes conform to the generic URI,
   thus they are normalized in the generic form as explained in
   Section 6 of [RFC3986].  The hash function used is specified in
   Section 10.2 of [RFC6940].  The certificate can be generated as
   specified in Section 9 of [RFC7252], using Certificate mode.

   In the URI-NODE-MATCH policy, a given value MUST be written and
   overwritten if and only if the condition for URI-MATCH is met and, in
   addition, the dictionary key is equal to the Node-ID in the
   certificate and that Node-ID is the one indicated in the
   SignerIdentity value cert_hash.

   These Access Control Policies are specified for IANA in Section 11.3.

10.  Security Considerations

   The security considerations of RELOAD [RFC6940] and CoAP [RFC7252]
   apply to this specification.  RELOAD's security model is based on
   public key certificates, which are used for signing messages and
   stored objects.  At the connection level, RELOAD can use either TLS
   or DTLS.  In the case of CoAP, several security modes have been
   defined.  Implementations of this specification MUST follow all the
   security-related rules specified in the RELOAD [RFC6940] and CoAP
   [RFC7252] specifications.

   Additionally, in RELOAD every Kind that is storable in an overlay
   must be associated with an access control policy.  This document
   specifies two new access control policies, which are specified in
   Section 9.  These policies cover the most typical deployment
   scenarios.

   During the phase of registration and lookup, security considerations
   relevant to RELOAD apply.  A CoAP node that advertises its existence
   via this mechanism, is more likely to be attacked, compared to a node
   (especially a sleepy node) that does not advertise its existence.
   Section 11 of [RFC7252] and Section 13 of [RFC6940] have more
   information about the kinds of attack and mitigation possible.

   The caching mechanism specified in this document is additional to the
   caching already done in CoAP.  Access control is handled by the
   RELOAD overlay, where the peer storing the data is responsible for
   validating the signature on the data being stored.

11.  IANA Considerations

11.1.  CoAP-REGISTRATION Kind-ID

   This document introduces a data Kind-ID to the "RELOAD Data Kind-ID"
   registry:

       +-------------------+------------+----------+
       | Kind              |    Kind-ID |      RFC |
       +-------------------+------------+----------+
       | CoAP-REGISTRATION |      0x105 | RFC 7650 |
       +-------------------+------------+----------+

   This Kind-ID was defined in Section 8.1.

11.2.  CoAP-CACHING Kind-ID

   This document introduces another data Kind-ID to the "RELOAD Data
   Kind-ID" registry:

       +--------------+------------+----------+
       | Kind         |    Kind-ID |      RFC |
       +--------------+------------+----------+
       | CoAP-CACHING |      0x106 | RFC 7650 |
       +--------------+------------+----------+

   This Kind-ID was defined in Section 8.2.

11.3.  Access Control Policies

   IANA has created a "CoAP Usage for RELOAD Access Control Policy"
   registry.  This registry has been added to the existing RELOAD
   registry.  Entries in this registry are strings denoting access
   control policies, as described in Section 9.  New entries in this
   registry are to be registered per the Specification Required policy
   in [RFC5226].  The initial contents of this registry are:

       +-----------------+----------+
       | Access Policy   |      RFC |
       +-----------------+----------+
       | URI-NODE-MATCH  | RFC 7650 |
       | URI-MATCH       | RFC 7650 |
       +-----------------+----------+

   This access control policy was described in Section 9.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <http://www.rfc-editor.org/info/rfc6690>.

   [RFC6940]  Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
              and H. Schulzrinne, "REsource LOcation And Discovery
              (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940,
              January 2014, <http://www.rfc-editor.org/info/rfc6940>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

12.2.  Informative References

   [CORERESDIR]
              Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE
              Resource Directory", Work in Progress, draft-ietf-core-
              resource-directory-04, July 2015.

   [P2PSIP]   Bryan, D., Matthews, P., Shim, E., Willis, D., and S.
              Dawkins, "Concepts and Terminology for Peer to Peer SIP",
              Work in Progress, draft-ietf-p2psip-concepts-07, May 2015.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <http://www.rfc-editor.org/info/rfc7228>.

Authors' Addresses

   Jaime Jimenez
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: jaime.jimenez@ericsson.com


   Jose M. Lopez-Vega
   University of Granada
   CITIC UGR Periodista Rafael Gomez Montero 2
   Granada  18071
   Spain

   Email: jmlvega@ugr.es


   Jouni Maenpaa
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: jouni.maenpaa@ericsson.com


   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: gonzalo.camarillo@ericsson.com