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Versions: (draft-appala-mile-xmpp-grid) 00 01 02 03

MILE                                                  N. Cam-Winget, Ed.
Internet-Draft                                                 S. Appala
Intended status: Standards Track                                 S. Pope
Expires: January 4, 2018                                   Cisco Systems
                                                            July 3, 2017


       Using XMPP Protocol and its Extensions for Use with IODEF
                      draft-ietf-mile-xmpp-grid-03

Abstract

   This document describes how the Extensible Messaging and Presence
   Protocol (XMPP) [RFC7590] can be used as the framework as transport
   protocol for collecting and distributing any security telemetry
   information between any network connected device.  As an example,
   this document describes how XMPP can be used to transport the
   Incident Object Description Exchange Format (IODEF) information.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Glossary of Terms . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Overview of XMPP-Grid . . . . . . . . . . . . . . . . . .   4
     1.3.  Benefits of XMPP-Grid . . . . . . . . . . . . . . . . . .   5
   2.  XMPP-Grid Architecture  . . . . . . . . . . . . . . . . . . .   6
     2.1.  Using XMPP  . . . . . . . . . . . . . . . . . . . . . . .   7
     2.2.  XMPP-Grid Requirements for enabling Information Sharing .   8
   3.  Example use of XMPP-Grid for IODEF  . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     5.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  Network . . . . . . . . . . . . . . . . . . . . . . .  12
       5.1.2.  XMPP-Grid Nodes . . . . . . . . . . . . . . . . . . .  12
       5.1.3.  XMPP-Grid Controller  . . . . . . . . . . . . . . . .  12
       5.1.4.  Certification Authority . . . . . . . . . . . . . . .  12
     5.2.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.1.  Network Attacks . . . . . . . . . . . . . . . . . . .  13
       5.2.2.  XMPP-Grid Nodes . . . . . . . . . . . . . . . . . . .  14
       5.2.3.  XMPP-Grid Controllers . . . . . . . . . . . . . . . .  15
       5.2.4.  Certification Authority . . . . . . . . . . . . . . .  16
     5.3.  Countermeasures . . . . . . . . . . . . . . . . . . . . .  17
       5.3.1.  Securing the XMPP-Grid Transport Protocol . . . . . .  17
       5.3.2.  Securing XMPP-Grid Nodes  . . . . . . . . . . . . . .  18
       5.3.3.  Securing XMPP-Grid Controllers  . . . . . . . . . . .  18
       5.3.4.  Limit on search result size . . . . . . . . . . . . .  19
       5.3.5.  Cryptographically random session-id and
               authentication checks for ARC . . . . . . . . . . . .  19
       5.3.6.  Securing the Certification Authority  . . . . . . . .  20
     5.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  20
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   XMPP-Grid is intended for use as a secure transport and
   communications ecosystem for devices, applications and organizations
   to interconnect, forming an information grid for the exchange of
   formatted data (e.g.  XML, JSON, etc).  This document describes how
   XMPP [RFC7590] serves as the framework and protocols for securely



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   collecting and distributing security telemetry information between
   and among network platforms, endpoints, and most any network
   connected device.

   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 [RFC2119].

1.1.  Glossary of Terms

   Capability Provider

      Providers who are capable of sharing information on XMPP-Grid.

   Publisher

      A capability provider sharing content information to other devices
      participating on XMPP-Grid.

   Subscriber

      A device participating in XMPP-Grid and subscribing or consuming
      information published by Publishers on XMPP-Grid.

   Topics

      Contextual information channel created on XMPP-Grid where a
      published message by the Publisher will be propagated by XMPP in
      real-time to a set of subscribed devices.

   XMPP-Grid

      Set of standards-based XMPP messages with extensions, intended for
      use as a transport and communications protocol framework between
      devices forming an information grid for sharing information.

   XMPP-Grid Controller

      Centralized component of XMPP-Grid responsible for managing all
      control plane operations.

   XMPP-Grid Node

      Platform or device that implements XMPP to connect to XMPP-Grid
      and share or consume security data.






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1.2.  Overview of XMPP-Grid

   XMPP-Grid employs publish/subscribe/query operations brokered by a
   controller, which enforces access control in the system.  This XMPP-
   based architecture controls what platforms can connect to the "Grid"
   to share ("publish") and/or consume ("subscribe" or "query")
   contextual information ("Topics") such as security data needed to
   support MILE.

   Leveraging the XMPP architecture, XMPP-Grid uses the XMPP server to
   act as a controller, affecting the authentication and authorization
   of participating XMPP-Grid nodes (Node).  Security information may
   only be published or consumed by authenticated and authorized Nodes
   using the XMPP publish/subscribe extension defined in [XEP-0060].

   The components of XMPP-Grid are:

   o  XMPP-Grid Controller (Controller): The Controller manages the
      control plane of XMPP-Grid operations.  As such it authenticates
      and authorizes platforms connecting to the data exchange grid and
      controls whether or not they can publish, subscribe or query
      Topics of security data.

   o  XMPP-Grid Node (Node): A Node is a platform or application that
      has mutually authenticated with the Controller and obtained
      authorization by the Controller to share and/or consume security
      data.

   o  Data Repository: This is the source of security data available on
      the Grid and may be a network security platform, management
      console, endpoint, etc.  XMPP-Grid does not mandate a specific
      information model, but instead remains open to transport
      structured or unstructured data.  Data may be supplied by the
      security platform itself or by an external information repository.

   o  Topic: An XMPP-Grid Topic defines a type of security data that a
      platform wants to share with other platform(s) and a specified
      interface by which the data can be obtained.

   As enabled by the XMPP architecture, XMPP-Grid is used to exchange
   security context data between systems on a 1-to-1, 1-to-many, or
   many-to-many basis.  Security data shared between these systems may
   use pre-negotiated non-standard/native data formats or may utilize an
   optional common information repository with a standardized data
   format, such as IODEF.  XMPP-Grid is data format agnostic and
   accommodates transport of whatever format the end systems agree upon.

   XMPP-Grid can operate in the following deployment architectures:



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   o  Broker-Flow: An XMPP-Grid control plane brokers the authorization
      and redirects the Topic subscriber to Topic publisher directly.
      In this architecture, the Controller only manages the connection;
      the security data flow is directly between Nodes using data
      formats negotiated out-of-band.

   o  Centralized Data-Flow: An XMPP-Grid maintains the data within its
      optional centralized database.  In this architecture, the
      Controller provides a common information structure for use in
      formatting and storing security context data, such as IODEF, and
      directly responds to Node publish and Subscribe requests.

   o  Proxy-Flow: An XMPP-Grid is acting as proxy, collecting the data
      from the publisher(s) and presenting it to the subscriber
      directly.  This is used for ad-hoc queries.

   Within the deployment architecture, XMPP-Grid may be used in any
   combination of the following data exchange modes.  The flexibility
   afforded by the different modes enables security information to be
   exchanged between systems in the method most suitable for serving a
   given use-case.

   o  Continuous Topic update stream: This mode delivers in real-time
      any data published to a Topic to the Nodes that are subscribed to
      that Topic.

   o  Directed query: This mode enables Nodes to request a specific set
      of security information regarding a specific asset, such as a
      specific user endpoint.

   o  Bulk historic data query: This mode enables Nodes to request
      transfer of past output from a Topic over a specific span of time.

1.3.  Benefits of XMPP-Grid

   Currently, security information standards such as IODEF [RFC7970]
   defines a data models that has no explicit transport defined and
   typically are carried over HTTPS as defined in RID [RFC6545].

   As security solutions are expanding to expose and share information
   asynchronously and across network boundaries there is a need for an
   architecture that facilitates federation, discovery of the different
   information available, the interfaces used to obtain the information
   and the need for near real-time exchange of data.

   Based on XMPP, XMPP-Grid has been defined to meet those requirements.





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2.  XMPP-Grid Architecture

   XMPP-Grid is an XMPP-based communication fabric that facilitates
   secure sharing of information between network elements and networked
   applications connected to the fabric both in real time and on demand
   (see figure below).

                         +--------------------------------------+
                         | +--------------------------------------+
                         | | +--------------------------------------+
                         | | |                                      |
                         +-| |               Node(s)                |
                           +-|                                      |
                             +--------------------------------------+
                               /   \         /   \            /   \
                              /  C  \       /     \          /     \
                              -  o  -       -  d  -          -     -
                               ||n||A        | a  |B          |   |C
                               ||t||         | t  |           |   |
                              -  r  -       -  a  -           |   |
                              \  o  /       \     /           |   |
                               \ l /         \   /            |   |
                            /|---------------------|\         |   |
                     /|----/                         \--------| d |--|\
                    /     /        XMPP-Grid          \ ctrl  | a |    \
                    \     \        Controller         / plane | t |    /
                     \|----\                         /--------| a |--|/
                            \|---------------------|/         |   |
                               /   \         /   \            |   |
                              /  C  \       /     \           |   |
                              -  o  -       -  d  -           |   |
                               ||n||A        | a |B           |   |C
                               ||t||         | t |            |   |
                              -  r  -       -  a  -          -     -
                              \  o  /       \     /          \     /
                               \ l /         \   /            \   /
                             +------------------------------------+
                             |                                    |-+
                             |             Node(s)                | |
                             |                                    | |-+
                             +------------------------------------+ | |
                               +------------------------------------+ |
                                 +------------------------------------+




                     Figure 1: XMPP-Grid Architecture



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   Nodes must connect to the XMPP-Grid controller to authenticate and
   establish appropriate authorizations, with appropriate authorization
   privileges.  The control plane messaging is established through XMPP
   and shown as "A" (Control plane interface) in Figure 1.  Authorized
   nodes may then share data either thru the XMPP-Grid Controller (shown
   as "B" in Figure 1) or directly (shown as "C" in Figure 1).  The data
   messaging enable Nodes to:

   o  Receive real-time events of the published messages from the
      publisher through Topic subscriptions

   o  Make directed queries to other Nodes in the XMPP-Grid with
      appropriate authorization from the Controller

   o  Negotiate out-of-band secure file transfer channel with the peer

2.1.  Using XMPP

   XMPP is used as the foundation message routing protocol for
   exchanging security data between systems across XMPP-Grid.  XMPP is a
   communications protocol for message-oriented middleware based on XML.
   Designed to be extensible, the protocol uses de-centralized client-
   server architecture where the clients connect to the servers securely
   and the messages between the clients are routed through the XMPP
   servers deployed within the cluster.  XMPP has been used extensively
   for publish-subscribe systems, file transfer, video, VoIP, Internet
   of Things, Smart Grid Software Defined Networks (SDN) and other
   collaboration and social networking applications.  The following are
   the 4 IETF specifications produced by the XMPP working group:

   o  [RFC7590] Extensible Messaging and Presence Protocol (XMPP): Core

   o  [RFC6121] Extensible Messaging and Presence Protocol (XMPP):
      Instant Messaging and Presence

   o  [RFC3922] Mapping the Extensible Messaging and Presence Protocol
      (XMPP) to Common Presence and Instant Messaging (CPIM)

   o  [RFC3923] End-to-End Signing and Object Encryption for the
      Extensible Messaging and Presence Protocol (XMPP)

   XMPP offers several of the following salient features for building a
   security data interexchange protocol:

   o  Open - standards-based, decentralized and federated architecture,
      with no single point of failure





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   o  Security - Supports domain segregations and federation.  Offers
      strong security via Simple Authentication and Security Layer
      (SASL) [RFC4422] and Transport Layer Security (TLS) [RFC5246].

   o  Real-time event management/exchange - using publish, subscribe
      notifications

   o  Flexibility and Extensibility - XMPP is XML based and is easily
      extensible to adapt to new use-cases.  Custom functionality can be
      built on top of it.

   o  Multiple information exchanges - XMPP offers multiple information
      exchange mechanisms between the participating clients -

   o

      *  Real-time event notifications through publish and subscribe.

      *  On-demand or directed queries between the clients communicated
         through the XMPP server

      *  Facilitates out-of-band, direct communication between
         participating clients

   o  Bi-directional - avoids firewall tunneling and avoids opening up a
      new connection in each direction between client and server.

   o  Scalable - supports cluster mode deployment with fan-out and
      message routing

   o  Peer-to-peer communications also enables scale - directed queries
      and out-of-band file transfer support

   o  XMPP offers Node availability, Node service capability discovery,
      and Node presence within the XMPP network.  Nodes ability to
      detect the availability, presence and capabilities of other
      participating nodes eases turnkey deployment.

   The XMPP extensions used in XMPP-Grid are now part (e.g. publish/
   subscribe) of the main XMPP specification [RFC7590] and the presence
   in [RFC6121].  A full list of XMPP Extension Protocols (XEPs)
   [RFC7590] can be found in http://xmpp.org/extensions/xep-0001.html .

2.2.  XMPP-Grid Requirements for enabling Information Sharing

   This section summarizes the requirements and the extensions used to
   facilitate the secure sharing of information using XMPP.  Knowledge




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   of the XMPP Protocol and extensions is required to understand this
   section.

   o  Authentication and Authorization: Nodes participating in XMPP-Grid
      MUST mutually authenticate to the controller using XMPP's
      authentication mechanisms.  Authorization is affected by the
      controller.

   o  Topic Discovery: to facilitate dynamic discovery, Nodes SHOULD
      support the XMPP Service Discovery [XEP-0030].

   o  Publish/Subscribe: to facilitate unsolicited notifications to new
      or updated security information, Nodes MUST support the XMPP
      Publish/Subscribe protocol as defined in [RFC7590].

   Once a Node has authenticated with the XMPP-Grid controller, it may
   further register a topic (e.g. information type) to be shared or use
   the discovery mechanism for determining topics to be consumed.
   Sharing Information: security information may be shared using
   registered topics.  An example for sharing or consuming the IODEF 1.0
   is defined in [XEP-0268].

3.  Example use of XMPP-Grid for IODEF

   A Node follows the standard XMPP workflow for connecting to the
   Controller as well as using the XMPP discovery mechanisms to discover
   the availability to consume IODEF information.  The general workflow
   is summarized in the figure below:























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        |----------------|                   |----------------|                |----------------|
        | IODEF Client   |                   | XMPP Server    |                | IODEF Service  |
        |  (Subscriber)  |                   | (Controller)   |                |  (Publisher)   |
        |----------------|                   |----------------|                |----------------|
                |                                    |                                   |
                |     IODEF Client Authentication    |                                   |
                |<---------------------------------->|                                   |
                |                                    |   IODEF Service Authentication    |
                |                                    |<--------------------------------->|
                |                                    | Create IODEFas a Topic (XEP-0060) |
                |                                    |<----------------------------------|
                |                                    | Topic Creation Success            |
                |                                    |---------------------------------->|
                | Topic Discovery (XEP-0030)         |                                   |
                |----------------------------------->|                                   |
                | Discovery Response with Topics     |                                   |
                |<-----------------------------------|                                   |
                |                                    |                                   |
                | Subscribe to IODEF Topic (XEP-0060)|                                   |
                |----------------------------------->|                                   |
                | Subscription Success               |                                   |
                |<-----------------------------------|                                   |
                |                                    | IODEF Incident Publish (XEP-0268) |
                |       IODEF Incident Publish       |<----------------------------------|
                |<-----------------------------------|                                   |
                |                                    |                                   |


                   Figure 2: IODEF Example XMPP Workflow

   An example XMPP discovery request for an IODEF 1.0 topic is shown
   below:

               <iq type='get'
               from='iodefclientabc@company.com'
               to='pubsub.company.com'
               id='nodes1'>
               <query xmlns='http://jabber.org/protocol/disco#items'/>
               </iq>

   An example XMPP discovery response for an IODEF 1.0 topic is shown
   below:









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               <iq type='result'
               from='pubsub.company.com'
               to='iodefclientabc@company.com'
               id='nodes1'>
               <query xmlns='http://jabber.org/protocol/disco#items'>
               <item jid='pubsub.company.com'
               node='incident'
               name='IODEF incident report'/>
               </query>
               </iq>

4.  IANA Considerations

   IODEF extensions as defined in [XEP-0268] may require IANA
   considerations and assignment thru the IODEF IANA rules.

5.  Security Considerations

   An XMPP-Grid Controller serves as an controlling broker for XMPP-Grid
   Nodes such as Enforcement Points, Policy Servers, CMDBs, and Sensors,
   using a publish-subscribe-search model of information exchange and
   lookup.  By increasing the ability of XMPP-Grid Nodes to learn about
   and respond to security-relevant events and data, XMPP-Grid can
   improve the timeliness and utility of the security system.  However,
   this integrated security system can also be exploited by attackers if
   they can compromise it.  Therefore, strong security protections for
   XMPP-Grid are essential.

   This section provides a security analysis of the XMPP-Grid transport
   protocol and the architectural elements that employ it, specifically
   with respect to their use of this protocol.  Three subsections define
   the trust model (which elements are trusted to do what), the threat
   model (attacks that may be mounted on the system), and the
   countermeasures (ways to address or mitigate the threats previously
   identified).

5.1.  Trust Model

   The first step in analyzing the security of the XMPP-Grid transport
   protocol is to describe the trust model, listing what each
   architectural element is trusted to do.  The items listed here are
   assumptions, but provisions are made in the Threat Model and
   Countermeasures sections for elements that fail to perform as they
   were trusted to do.







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5.1.1.  Network

   The network used to carry XMPP-Grid messages is trusted to:

   o  Perform best effort delivery of network traffic

   The network used to carry XMPP-Grid messages is not expected
   (trusted) to:

   o  Provide confidentiality or integrity protection for messages sent
      over it

   o  Provide timely or reliable service

5.1.2.  XMPP-Grid Nodes

   Authorized XMPP-Grid Nodes are trusted to:

   o  Preserve the confidentiality of sensitive data retrieved via the
      XMPP-Grid Controller

5.1.3.  XMPP-Grid Controller

   The XMPP-Grid Controller is trusted to:

   o  Broker requests for data and enforce authorization of access to
      this data throughout its lifecycle

   o  Perform service requests in a timely and accurate manner

   o  Create and maintain accurate operational attributes

   o  Only reveal data to and accept service requests from authorized
      parties

   The XMPP-Grid Controller is not expected (trusted) to:

   o  Verify the truth (correctness) of data

5.1.4.  Certification Authority

   The Certification Authority (CA) that issues certificates for the
   XMPP-Grid Controller and/or XMPP-Grid Nodes (or each CA, if there are
   several) is trusted to:

   o  Ensure that only proper certificates are issued and that all
      certificates are issued in accordance with the CA's policies




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   o  Revoke certificates previously issued when necessary

   o  Regularly and securely distribute certificate revocation
      information

   o  Promptly detect and report any violations of this trust so that
      they can be handled

   The CA is not expected (trusted) to:

   o  Issue certificates that go beyond the XMPP-Grid needs or other
      constraints imposed by a relying party.

5.2.  Threat Model

   To secure the XMPP-Grid transport protocol and the architectural
   elements that implement it, this section identifies the attacks that
   can be mounted against the protocol and elements.

5.2.1.  Network Attacks

   A variety of attacks can be mounted using the network.  For the
   purposes of this subsection the phrase "network traffic" should be
   taken to mean messages and/or parts of messages.  Any of these
   attacks may be mounted by network elements, by parties who control
   network elements, and (in many cases) by parties who control network-
   attached devices.

   o  Network traffic may be passively monitored to glean information
      from any unencrypted traffic

   o  Even if all traffic is encrypted, valuable information can be
      gained by traffic analysis (volume, timing, source and destination
      addresses, etc.)

   o  Network traffic may be modified in transit

   o  Previously transmitted network traffic may be replayed

   o  New network traffic may be added

   o  Network traffic may be blocked, perhaps selectively

   o  A "Man In The Middle" (MITM) attack may be mounted where an
      attacker interposes itself between two communicating parties and
      poses as the other end to either party or impersonates the other
      end to either or both parties




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   o  Resist attacks (including denial of service and other attacks from
      XMPP-Grid Nodes)

   o  Undesired network traffic may be sent in an effort to overload an
      architectural component, thus mounting a denial of service attack

5.2.2.  XMPP-Grid Nodes

   An unauthorized XMPP-Grid Nodes (one which is not recognized by the
   XMPP-Grid Controller or is recognized but not authorized to perform
   any actions) cannot mount any attacks other than those listed in the
   Network Attacks section above.

   An authorized XMPP-Grid Node, on the other hand, can mount many
   attacks.  These attacks might occur because the XMPP-Grid Node is
   controlled by a malicious, careless, or incompetent party (whether
   because its owner is malicious, careless, or incompetent or because
   the XMPP-Grid Node has been compromised and is now controlled by a
   party other than its owner).  They might also occur because the XMPP-
   Grid Node is running malicious software; because the XMPP-Grid Node
   is running buggy software (which may fail in a state that floods the
   network with traffic); or because the XMPP-Grid Node has been
   configured improperly.  From a security standpoint, it generally
   makes no difference why an attack is initiated.  The same
   countermeasures can be employed in any case.

   Here is a list of attacks that may be mounted by an authorized XMPP-
   Grid Node:

   o  Cause many false alarms or otherwise overload the XMPP-Grid
      Controller or other elements in the network security system
      (including human administrators) leading to a denial of service or
      disabling parts of the network security system

   o  Omit important actions (such as posting incriminating data),
      resulting in incorrect access

   o  Use confidential information obtained from the XMPP-Grid
      Controller to enable further attacks (such as using endpoint
      health check results to exploit vulnerable endpoints)

   o  Advertise data crafted to exploit vulnerabilities in the XMPP-Grid
      Controller or in other XMPP-Grid Nodes, with a goal of
      compromising those systems

   o  Issue a search request or set up a subscription that matches an
      enormous result, leading to resource exhaustion on the XMPP-Grid
      Controller, the publishing XMPP-Grid Node, and/or the network



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   o  Establish a communication channel using another XMPP-Grid Node's
      session-id

   Dependencies of or vulnerabilities of authorized XMPP-Grid Nodes may
   be exploited to effect these attacks.  Another way to effect these
   attacks is to gain the ability to impersonate an XMPP-Grid Node
   (through theft of the XMPP-Grid Node's identity credentials or
   through other means).  Even a clock skew between the XMPP-Grid Node
   and XMPP-Grid Controller can cause problems if the XMPP-Grid Node
   assumes that old XMPP-Grid Node data should be ignored.

5.2.3.  XMPP-Grid Controllers

   An unauthorized XMPP-Grid Controller (one which is not trusted by
   XMPP-Grid Nodes) cannot mount any attacks other than those listed in
   the Network Attacks section above.

   An authorized XMPP-Grid Controller can mount many attacks.  Similar
   to the XMPP-Grid Node case described above, these attacks might occur
   because the XMPP-Grid Controller is controlled by a malicious,
   careless, or incompetent party (either an XMPP-Grid Controller
   administrator or an attacker who has seized control of the XMPP-Grid
   Controller).  They might also occur because the XMPP-Grid Controller
   is running malicious software, because the XMPP-Grid Controller is
   running buggy software (which may fail in a state that corrupts data
   or floods the network with traffic), or because the XMPP-Grid
   Controller has been configured improperly.

   All of the attacks listed for XMPP-Grid Node above can be mounted by
   the XMPP-Grid Controller.  Detection of these attacks will be more
   difficult since the XMPP-Grid Controller can create false operational
   attributes and/or logs that imply some other party created any bad
   data.

   Additional XMPP-Grid Controller attacks may include:

   o  Expose different data to different XMPP-Grid Nodes to mislead
      investigators or cause inconsistent behavior

   o  Mount an even more effective denial of service attack than a
      single XMPP-Grid Node could

   o  Obtain and cache XMPP-Grid Node credentials so they can be used to
      impersonate XMPP-Grid Nodes even after a breach of the XMPP-Grid
      Controller is repaired






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   o  Obtain and cache XMPP-Grid Controller administrator credentials so
      they can be used to regain control of the XMPP-Grid Controller
      after the breach of the XMPP-Grid Controller is repaired

   Dependencies of or vulnerabilities of the XMPP-Grid Controller may be
   exploited to obtain control of the XMPP-Grid Controller and effect
   these attacks.

5.2.4.  Certification Authority

   A Certification Authority trusted to issue certificates for the XMPP-
   Grid Controller and/or XMPP-Grid Nodes can mount several attacks:

   o  Issue certificates for unauthorized parties, enabling them to
      impersonate authorized parties such as the XMPP-Grid Controller or
      an XMPP-Grid Node.  This can lead to all the threats that can be
      mounted by the certificate's subject.

   o  Issue certificates without following all of the CA's policies.
      Because this can result in issuing certificates that may be used
      to impersonate authorized parties, this can lead to all the
      threats that can be mounted by the certificate's subject.

   o  Fail to revoke previously issued certificates that need to be
      revoked.  This can lead to undetected impersonation of the
      certificate's subject or failure to revoke authorization of the
      subject, and therefore can lead to all of the threats that can be
      mounted by that subject.

   o  Fail to regularly and securely distribute certificate revocation
      information.  This may cause a relying party to accept a revoked
      certificate, leading to undetected impersonation of the
      certificate's subject or failure to revoke authorization of the
      subject, and therefore can lead to all of the threats that can be
      mounted by that subject.  It can also cause a relying party to
      refuse to proceed with a transaction because timely revocation
      information is not available, even though the transaction should
      be permitted to proceed.

   o  Allow the CA's private key to be revealed to an unauthorized
      party.  This can lead to all the threats above.  Even worse, the
      actions taken with the private key will not be known to the CA.

   o  Fail to promptly detect and report errors and violations of trust
      so that relying parties can be promptly notified.  This can cause
      the threats listed earlier in this section to persist longer than
      necessary, leading to many knock-on effects.




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5.3.  Countermeasures

   Below are countermeasures for specific attack scenarios to the XMPP-
   Grid infrastructure.

5.3.1.  Securing the XMPP-Grid Transport Protocol

   To address network attacks, the XMPP-Grid transport protocol
   described in this document requires that the XMPP-Grid messages MUST
   be carried over TLS (minimally TLS 1.2 [RFC5246]) as described in
   [RFC2818].  The XMPP-Grid Node MUST verify the XMPP-Grid Controller's
   certificate and determine whether the XMPP-Grid Controller is trusted
   by this XMPP-Grid Node before completing the TLS handshake.  The
   XMPP-Grid Controller MUST authenticate the XMPP-Grid Node either
   using mutual certificate-based authentication in the TLS handshake or
   using Basic Authentication as described in IETF RFC 2617.  XMPP-Grid
   Controller MUST use Simple Authentication and Security Layer (SASL),
   described in [RFC4422], to support the aforesaid authentication
   mechanisms.  SASL offers authentication mechanism negotiations
   between the XMPP-Grid Controller and XMPP-Grid node during the
   connection establishment phase.  XMPP-Grid Nodes and XMPP-Grid
   Controllers using mutual certificate-based authentication SHOULD each
   verify the revocation status of the other party's certificate.  All
   XMPP-Grid Controllers and XMPP-Grid Nodes MUST implement both mutual
   certificate-based authentication and Basic Authentication.  The
   selection of which XMPP-Grid Node authentication technique to use in
   any particular deployment is left to the administrator.

   An XMPP-Grid Controller MAY also support a local, configurable set of
   Basic Authentication userid-password pairs.  If so, it is
   implementation dependent whether an XMPP-Grid Controller ends a
   session when an administrator changes the configured password.  Since
   Basic Authentication has many security disadvantages (especially the
   transmission of reusable XMPP-Grid Node passwords to the XMPP-Grid
   Controller), it SHOULD only be used when absolutely necessary.  Per
   the HTTP specification, when basic authentication is in use, an XMPP-
   Grid Controller MAY respond to any request that lacks credentials
   with an error code similar to HTTP code 401.  An XMPP-Grid Node
   SHOULD avoid this code by submitting basic auth credentials with
   every request when basic authentication is in use.  If it does not do
   so, an XMPP-Grid Node MUST respond to this code by resubmitting the
   same request with credentials (unless the XMPP-Grid Node is shutting
   down).

   As XMPP uses TLS as the transport and security mechanisms, it is
   understood that best practices such as those in
   [I-D.ietf-uta-tls-bcp] are followed.




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   These protocol security measures provide protection against all the
   network attacks listed in the above document section except denial of
   service attacks.  If protection against these denial of service
   attacks is desired, ingress filtering, rate limiting per source IP
   address, and other denial of service mitigation measures may be
   employed.  In addition, an XMPP-Grid Controller MAY automatically
   disable a misbehaving XMPP-Grid Node.

5.3.2.  Securing XMPP-Grid Nodes

   XMPP-Grid Nodes may be deployed in locations that are susceptible to
   physical attacks.  Physical security measures may be taken to avoid
   compromise of XMPP-Grid Nodes, but these may not always be practical
   or completely effective.  An alternative measure is to configure the
   XMPP-Grid Controller to provide read-only access for such systems.
   The XMPP-Grid Controller SHOULD also include a full authorization
   model so that individual XMPP-Grid Nodes may be configured to have
   only the privileges that they need.  The XMPP-Grid Controller MAY
   provide functional templates so that the administrator can configure
   a specific XMPP-Grid Node as a DHCP server and authorize only the
   operations and metadata types needed by a DHCP server to be permitted
   for that XMPP-Grid Node.  These techniques can reduce the negative
   impacts of a compromised XMPP-Grid Node without diminishing the
   utility of the overall system.

   To handle attacks within the bounds of this authorization model, the
   XMPP-Grid Controller MAY also include rate limits and alerts for
   unusual XMPP-Grid Node behavior.  XMPP-Grid Controllers SHOULD make
   it easy to revoke an XMPP-Grid Node's authorization when necessary.
   Another way to detect attacks from XMPP-Grid Nodes is to create fake
   entries in the available data (honeytokens) which normal XMPP-Grid
   Nodes will not attempt to access.  The XMPP-Grid Controller SHOULD
   include auditable logs of XMPP-Grid Node activities.

   To avoid compromise of XMPP-Grid Node, XMPP-Grid Node SHOULD be
   hardened against attack and minimized to reduce their attack surface.
   They should be well managed to minimize vulnerabilities in the
   underlying platform and in systems upon which the XMPP-Grid Node
   depends.  Personnel with administrative access should be carefully
   screened and monitored to detect problems as soon as possible.

5.3.3.  Securing XMPP-Grid Controllers

   Because of the serious consequences of XMPP-Grid Controller
   compromise, XMPP-Grid Controllers SHOULD be especially well hardened
   against attack and minimized to reduce their attack surface.  They
   should be well managed to minimize vulnerabilities in the underlying
   platform and in systems upon which the XMPP-Grid Controller depends.



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   Network security measures such as firewalls or intrusion detection
   systems may be used to monitor and limit traffic to and from the
   XMPP-Grid Controller.  Personnel with administrative access should be
   carefully screened and monitored to detect problems as soon as
   possible.  Administrators should not use password-based
   authentication but should instead use non-reusable credentials and
   multi-factor authentication (where available).  Physical security
   measures SHOULD be employed to prevent physical attacks on XMPP-Grid
   Controllers.

   To ease detection of XMPP-Grid Controller compromise should it occur,
   XMPP-Grid Controller behavior should be monitored to detect unusual
   behavior (such as a reboot, a large increase in traffic, or different
   views of an information repository for similar XMPP-Grid Nodes).
   XMPP-Grid Nodes should log and/or notify administrators when peculiar
   XMPP-Grid Controller behavior is detected.  To aid forensic
   investigation, permanent read-only audit logs of security-relevant
   information (especially administrative actions) should be maintained.
   If XMPP-Grid Controller compromise is detected, a careful analysis
   should be performed of the impact of this compromise.  Any reusable
   credentials that may have been compromised should be reissued.

5.3.4.  Limit on search result size

   While XMPP-Grid is designed for high scalability to 100,000s of
   Nodes, an XMPP-Grid Controller MAY establish a limit to the amount of
   data it is willing to return in search or subscription results.  This
   mitigates the threat of an XMPP-Grid Node causing resource exhaustion
   by issuing a search or subscription that leads to an enormous result.

5.3.5.  Cryptographically random session-id and authentication checks
        for ARC

   An XMPP-Grid Controller SHOULD ensure that the XMPP-Grid Node
   establishing an Authenticated Results Chain (ARC) is the same XMPP-
   Grid Node as the XMPP-Grid Node that established the corresponding
   Synchronization Source Identifier (SSRC).  The XMPP-Grid Controller
   SHOULD employ both of the following strategies:

   o  session-ids SHOULD be cryptographically random

   o  The HTTPS transport for the SSRC and the ARC SHOULD be
      authenticated using the same credentials.  SSL session resumption
      MAY be used to establish the ARC based on the SSRC SSL session.







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5.3.6.  Securing the Certification Authority

   As noted above, compromise of a Certification Authority (CA) trusted
   to issue certificates for the XMPP-Grid Controller and/or XMPP-Grid
   Nodes is a major security breach.  Many guidelines for proper CA
   security have been developed: the CA/Browser Forum's Baseline
   Requirements, the AICPA/CICA Trust Service Principles, etc.  The CA
   operator and relying parties should agree on an appropriately
   rigorous security practices to be used.

   Even with the most rigorous security practices, a CA may be
   compromised.  If this compromise is detected quickly, relying parties
   can remove the CA from their list of trusted CAs, and other CAs can
   revoke any certificates issued to the CA.  However, CA compromise may
   go undetected for some time, and there's always the possibility that
   a CA is being operated improperly or in a manner that is not in the
   interests of the relying parties.  For this reason, relying parties
   may wish to "pin" a small number of particularly critical
   certificates (such as the certificate for the XMPP-Grid Controller).
   Once a certificate has been pinned, the relying party will not accept
   another certificate in its place unless the Administrator explicitly
   commands it to do so.  This does not mean that the relying party will
   not check the revocation status of pinned certificates.  However, the
   Administrator may still be consulted if a pinned certificate is
   revoked, since the CA and revocation process are not completely
   trusted.

5.4.  Summary

   XMPP-Grid's considerable value as a broker for security-sensitive
   data exchange distribution also makes the protocol and the network
   security elements that implement it a target for attack.  Therefore,
   strong security has been included as a basic design principle within
   the XMPP-Grid design process.

   The XMPP-Grid transport protocol provides strong protection against a
   variety of different attacks.  In the event that an XMPP-Grid Node or
   XMPP-Grid Controller is compromised, the effects of this compromise
   have been reduced and limited with the recommended role-based
   authorization model and other provisions, and best practices for
   managing and protecting XMPP-Grid systems have been described.  Taken
   together, these measures should provide protection commensurate with
   the threat to XMPP-Grid systems, thus ensuring that they fulfill
   their promise as a network security clearing-house.







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6.  Privacy Considerations

   XMPP-Grid Nodes may publish information about endpoint health,
   network access, events (which may include information about what
   services an endpoint is accessing), roles and capabilities, and the
   identity of the end user operating the endpoint.  Any of this
   published information may be queried by other XMPP-Grid Nodes and
   could potentially be used to correlate network activity to a
   particular end user.

   Dynamic and static information brokered by an XMPP-Grid Controller,
   ostensibly for purposes of correlation by XMPP-Grid Nodes for
   intrusion detection, could be misused by a broader set of XMPP-Grid
   Nodes which hitherto have been performing specific roles with strict
   well-defined separation of duties.

   Care should be taken by deployers of XMPP-Grid to ensure that the
   information published by XMPP-Grid Nodes does not violate agreements
   with end users or local and regional laws and regulations.  This can
   be accomplished either by configuring XMPP-Grid Nodes to not publish
   certain information or by restricting access to sensitive data to
   trusted XMPP-Grid Nodes.  That is, the easiest means to ensure
   privacy or protect sensitive data, is to omit or not share it at all.

   Another consideration for deployers is to enable end-to-end
   encryption to ensure the data is protected from the data layer to
   data layer and thus protect it from the transport layer.

7.  Acknowledgements

   The authors would like to acknowledge the contributions, authoring
   and/or editing of the following people: Joseph Salowey, Lisa
   Lorenzin, Clifford Kahn, Henk Birkholz, Jessica Fitzgerald-McKay,
   Steve Hanna, and Steve Venema.  In addition, we want to thank Takeshi
   Takahashi, Panos Kampanakis, Adam Montville and Chris Inacio for
   reviewing and providing valuable comments.

8.  References

8.1.  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>.






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   [RFC3922]  Saint-Andre, P., "Mapping the Extensible Messaging and
              Presence Protocol (XMPP) to Common Presence and Instant
              Messaging (CPIM)", RFC 3922, DOI 10.17487/RFC3922, October
              2004, <http://www.rfc-editor.org/info/rfc3922>.

   [RFC3923]  Saint-Andre, P., "End-to-End Signing and Object Encryption
              for the Extensible Messaging and Presence Protocol
              (XMPP)", RFC 3923, DOI 10.17487/RFC3923, October 2004,
              <http://www.rfc-editor.org/info/rfc3923>.

   [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
              Authentication and Security Layer (SASL)", RFC 4422,
              DOI 10.17487/RFC4422, June 2006,
              <http://www.rfc-editor.org/info/rfc4422>.

   [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 6121, DOI 10.17487/RFC6121, March 2011,
              <http://www.rfc-editor.org/info/rfc6121>.

   [RFC7590]  Saint-Andre, P. and T. Alkemade, "Use of Transport Layer
              Security (TLS) in the Extensible Messaging and Presence
              Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June
              2015, <http://www.rfc-editor.org/info/rfc7590>.

   [XEP-0030]
              Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
              Andre, "Service Discovery", XSF XEP 0030, July 2010.

   [XEP-0060]
              Millard, P. and P. Saint-Andre, "Publish-Subscribe",
              XSF XEP 0060, December 2016.

   [XEP-0268]
              Hefczyc, A., Jensen, F., Remond, M., Saint-Andre, P., and
              M. Wild, "Service Discovery", XSF XEP 0268, MY 2012.

8.2.  Informative References

   [I-D.ietf-mile-rolie]
              Field, J., Banghart, S., and D. Waltermire, "Resource-
              Oriented Lightweight Information Exchange", draft-ietf-
              mile-rolie-07 (work in progress), May 2017.

   [I-D.ietf-uta-tls-bcp]
              Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of TLS and DTLS", draft-
              ietf-uta-tls-bcp-11 (work in progress), February 2015.



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   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC6545]  Moriarty, K., "Real-time Inter-network Defense (RID)",
              RFC 6545, DOI 10.17487/RFC6545, April 2012,
              <http://www.rfc-editor.org/info/rfc6545>.

   [RFC6546]  Trammell, B., "Transport of Real-time Inter-network
              Defense (RID) Messages over HTTP/TLS", RFC 6546,
              DOI 10.17487/RFC6546, April 2012,
              <http://www.rfc-editor.org/info/rfc6546>.

   [RFC7970]  Danyliw, R., "The Incident Object Description Exchange
              Format Version 2", RFC 7970, DOI 10.17487/RFC7970,
              November 2016, <http://www.rfc-editor.org/info/rfc7970>.

Authors' Addresses

   Nancy Cam-Winget (editor)
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: ncamwing@cisco.com


   Syam Appala
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: syam1@cisco.com











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   Scott Pope
   Cisco Systems
   5400 Meadows Road
   Suite 300
   Lake Oswego, OR  97035
   USA

   Email: scottp@cisco.com











































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