xeps/xep-0258.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
  <!ENTITY % ents SYSTEM 'xep.ent'>
  <!ENTITY LABEL "<tt>&lt;label/&gt;</tt>">
  <!ENTITY CATALOG "<tt>&lt;catalog/&gt;</tt>">
  <!ENTITY ITEM "<tt>&lt;item/&gt;</tt>">
  <!ENTITY SECURITYLABEL "<tt>&lt;securitylabel/&gt;</tt>">
  <!ENTITY DISPLAYMARKING "<tt>&lt;displaymarking/&gt;</tt>">
  <!ENTITY EQUIVALENTLABEL "<tt>&lt;equivalentlabel/&gt;</tt>">
  <!ENTITY HEADLINE "<tt>&lt;headline/&gt;</tt>">
  <!ENTITY IDENTITY "<tt>&lt;identity/&gt;</tt>">
%ents;
]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
    <header>
        <title>Security Labels in XMPP</title>
        <abstract>This document describes the use of security labels in XMPP. The document specifies
            how security label meta-data is carried in XMPP, when this meta-data should or should
            not be provided, and how the meta-data is to be processed.</abstract> &LEGALNOTICE;
            <number>0258</number>
        <status>Draft</status>
        <type>Standards Track</type>
        <sig>Standards</sig>
        <approver>Council</approver>
        <dependencies>
            <spec>XMPP Core</spec>
            <spec>XEP-0001</spec>
        </dependencies>
        <supersedes/>
        <supersededby/>
        <shortname>sec-label</shortname>
  <schemaloc>
    <ns>extension</ns>
    <url>http://xmpp.org/schemas/sec-label.xsd</url>
  </schemaloc>
  <schemaloc>
    <ns>catalog</ns>
    <url>http://xmpp.org/schemas/sec-label-catalog.xsd</url>
  </schemaloc>
  <schemaloc>
    <ns>esssecuritylabel</ns>
    <url>http://xmpp.org/schemas/sec-label-ess.xsd</url>
  </schemaloc>
        <author>
            <firstname>Kurt</firstname>
            <surname>Zeilenga</surname>
            <email>Kurt.Zeilenga@Isode.COM</email>
            <jid>Kurt.Zeilenga@Isode.COM</jid>
        </author>
  <revision>
    <version>1.1</version>
    <date>2013-04-08</date>
    <initials>kdz</initials>
    <remark><p>Clarify catalogs are temporal objects.  Offer client handling suggestions.</p></remark>
  </revision>
  <revision>
    <version>1.0</version>
    <date>2011-11-10</date>
    <initials>psa</initials>
    <remark><p>Per a vote of the XMPP Council, advanced specification to Draft; corrected version of catalog namespace in schema.</p></remark>
  </revision>
        <revision>
            <version>0.10</version>
            <date>2011-11-03</date>
            <initials>kdz</initials>
            <remark>
                <p>Address last call comments.</p>
            </remark>
        </revision>
        <revision>
            <version>0.9</version>
            <date>2011-09-21</date>
            <initials>kdz</initials>
            <remark>
                <p>Add optional <tt>from=</tt> attribute to catalog element for S2S requests. Make
                    editorial changes.</p>
            </remark>
        </revision>
        <revision>
            <version>0.8</version>
            <date>2011-08-11</date>
            <initials>kdz</initials>
            <remark>
                <p>Correct catalog schema.</p>
            </remark>
        </revision>
        <revision>
            <version>0.7</version>
            <date>2011-03-08</date>
            <initials>kdz</initials>
            <remark>
                <p>Illustrate XEP Multi-User Chat room security label configuration. Make
                    clarifications and minor editorial changes.</p>
            </remark>
        </revision>
        <revision>
            <version>0.6</version>
            <date>2010-07-30</date>
            <initials>kdz</initials>
            <remark>
                <p>Extend catalog handling. Minor editorial changes.</p>
            </remark>
        </revision>
        <revision>
            <version>0.5</version>
            <date>2009-07-27</date>
            <initials>kdz</initials>
            <remark>
                <p>Remove &LABEL;/&EQUIVALENTLABEL; <tt>type=</tt> attribute. Clarify label catalog
                    discovery. Clarify syntax of <tt>selector=</tt> attribute.</p>
            </remark>
        </revision>
        <revision>
            <version>0.4</version>
            <date>2009-07-23</date>
            <initials>kdz</initials>
            <remark>
                <p>Update label catalogs to include user input selector.</p>
            </remark>
        </revision>
        <revision>
            <version>0.3</version>
            <date>2009-03-20</date>
            <initials>kdz</initials>
            <remark>
                <p>Add text regarding default bg/fg colors. Correct examples.</p>
            </remark>
        </revision>
        <revision>
            <version>0.2</version>
            <date>2009-03-10</date>
            <initials>kdz</initials>
            <remark>
                <p>Reworked discovery and various updates.</p>
            </remark>
        </revision>
        <revision>
            <version>0.1</version>
            <date>2009-01-05</date>
            <initials>psa</initials>
            <remark>
                <p>Initial published version.</p>
            </remark>
        </revision>
        <revision>
            <version>0.0.081203</version>
            <date>2008-12-03</date>
            <initials>kdz</initials>
            <remark>
                <p>Initial draft.</p>
            </remark>
        </revision>
    </header>

    <section1 topic="Introduction" anchor="intro">
        <p>A security label, sometimes referred to as a confidentiality label, is a structured
            representation of the sensitivity of a piece of information. A security label is used in
            conjunction with a clearance, a structured representation of what information
            sensitivities a person (or other entity) is authorized to access, and a security policy
            to control access to each piece of information. For instance, a message could be labeled
            as "SECRET", and hence requiring the sender and the receiver to each have a clearance
            granting access to "SECRET" information. &X.841; provides a discussion of security
            labels, clearances, and security policy.</p>
        <p>Sensitivity-based authorization is used in networks which operate under a set of
            information classification rules, such as in government agency networks. The
            standardized formats for security labels, clearances, and security policy are
            generalized and do have application in non-government networks.</p>
        <p>This document describes the use of security labels in &xmpp;. The document specifies how
            security label meta-data is carried in XMPP. It standardizes a mechanism for carrying
            ESS Security Labels in XMPP, as well as provides for use of other label formats. ESS
            Security Labels are specified in &rfc2634;. ESS Security Labels are commonly used in
            conjunction with &X.500; clearances and either X.841 or &SDN.801c; security
            policies.</p>
        <example caption="Message with ESS Security Label"><![CDATA[
<message to='romeo@example.net' from='juliet@example.com/balcony'>
    <body>This content is classified.</body>
    <securitylabel xmlns='urn:xmpp:sec-label:0'>
        <displaymarking fgcolor='black' bgcolor='red'>SECRET</displaymarking>
        <label><esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'>
            MQYCAQQGASk=
        </esssecuritylabel></label>
    </securitylabel>
</message>
]]></example>
        <example caption="Message with IC-ISM Label"><![CDATA[
<message to='romeo@example.net' from='juliet@example.com/balcony'>
    <body>This content is classified.</body>
    <securitylabel xmlns='urn:xmpp:sec-label:0'>
        <displaymarking fgcolor='black' bgcolor='red'>SECRET</displaymarking>
        <label><icismlabel xmlns='http://example.gov/IC-ISM/0' classification='S'
            ownerProducer='USA'/></label>
    </securitylabel>
</message>
]]></example>
        <p>Note: The &IC-ISM; label example is for <em>illustrative purposes only</em>.</p>

        <p>The document details when security label meta-data should or should not be provided, and
            how this meta-data is to be processed.</p>

          <p>This document does not provide:</p>
          <ul>
            <li>any mechanism for a client to discover the security policy in force at its home
              server, or any other server;</li>
            <li>any mechanism for a client to discover the user's clearance, or the clearance of
              associated with any resource; nor</li>
            <li>any administrative mechanism for a client to configure configure policy,
              clearance, and labels of any resource.</li>
          </ul>
          <p>Such mechanisms may be introduced in subsequent documents.</p>

        <p>This document does not discuss how one might securely bind a security label to a stanza.
            It is expected a subsequent document will tackle this topic.</p>
    </section1>

    <section1 topic="Discovering Feature Support" anchor="disco">
        <p>An entity (client or server) which supports the XMPP Security Label protocol MUST report
            that fact by including a service discovery feature of "<tt>urn:xmpp:sec-label:0</tt>" in
            response to a &xep0030; information request.</p>
        <p>Clients wishing to include a XMPP Security Label element in any stanza they generate
            SHOULD determine if their server supports the XMPP Security Label protocol. If their
            server does not support XMPP Security Label, the client SHOULD NOT generate XMPP
            Security Labels as the server not supporting this protocol will generally ignore XMPP
            Security Labels as they would any other unrecognized element.</p>
        <p>As each service domain may have different support for security labels, servers should
            advertise and clients should perform appropriate discovery lookups on a per service
            basis.</p>
        <example caption="Service Discovery information request"><![CDATA[
<iq type='get'
    from='user@example.com/Work'
    to='example.com'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
]]></example>
        <example caption="Service Discovery information response"><![CDATA[
<iq type='result'
    from='example.com'
    to='user@example.com/Work'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:sec-label:0'/>
    ...
  </query>
</iq>
]]></example>
    </section1>

    <section1 topic="Protocol" anchor="protocol">
        <p>An element, &SECURITYLABEL;, is defined to carry security label meta-data. This meta-data
            includes a security label, zero or more equivalent security labels, and optionally
            display marking data.</p>
        <example caption="Labeled Message"><![CDATA[
<message to='romeo@example.net' from='juliet@example.com/balcony'>
    <body>This content is classified.</body>
    <securitylabel xmlns='urn:xmpp:sec-label:0'>
        <displaymarking fgcolor='black' bgcolor='red'>SECRET</displaymarking>
        <label>
            <esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'
                >MQYCAQIGASk=</esssecuritylabel>
        </label>
        <equivalentlabel>
            <esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'
                >MRUCAgD9DA9BcXVhIChvYnNvbGV0ZSk=</esssecuritylabel>
        </equivalentlabel>
    </securitylabel>
</message>
]]></example>
        <p>The security label meta-data is carried in an &SECURITYLABEL; element. The
            &SECURITYLABEL; element which contains one and only one &LABEL; element, zero or more
            &EQUIVALENTLABEL; elements, and an optional &DISPLAYMARKING; element.</p>
        <p>The &LABEL; provides the primary security label. It is commonly issued by the sender
            under the security policy of that they and their home server operating under. The
            &LABEL; contains either a single element representing the primary security label or is
            empty to indicate use of a default.</p>
        <p>Each &EQUIVALENTLABEL; represents an equivalent security label under other policies. Each
            &EQUIVALENTLABEL; contains a single element representing the equivalent label. This
            element might be used when a recipient is known to hold a clearance under a different
            policy than the sender.</p>
        <p>The &DISPLAYMARKING; element contains a display string for use by implementations which
            are unable to utilize the applicable security policy to generate display markings. The
            element may optionally contain two attributes, <tt>fgcolor=</tt> and <tt>bgcolor=</tt>,
            whose values are HTML color strings (e.g., '<tt>red</tt>' or '<tt>#ff0000</tt>'), for
            use in colorizing the display marking. The <tt>fgcolor=</tt> default is <tt>black</tt>.
            The <tt>bgcolor=</tt> default is <tt>white</tt>. </p>
    </section1>

    <section1 topic="Label Catalog Discovery" anchor="label-catalog">
        <p>A client can request a catalog for a particular JID by sending a catalog discovery
            request to the client's server. Where the JID is hosted by some other server, the
            client's server is expected to produce a suitable catalog (or fail the request). The
            client's server may, as needed, query catalogs from other servers in order to fulfill
            the client's request.</p>
        <p>While this specification does not preclude a client from directing a catalog request
            elsewhere, it is noted that catalog returned by a party other than its server may not be
            directly usable by the client. For instance, the client's server might require a
            particular only-locally-known label be used in messages to a particular remote JID.</p>
        <p>It is RECOMMENDED the server publish catalogs of security label for use by clients.</p>
        <p>Two identical catalog requests may return different results, even for the same
	    requester, as the results may depend on numerous factors.  It is suggested that clients
	    request a catalog for use in a short-lived context, such as short-lived 1-to-1 chat
	    session, for all use in stanzas of that session.  For use in long-lived context, such
	    as a long-lived Multi-User Chat session, it is suggested the client request the
	    current catalog when the user becomes present after a period of extended absence.
	    Alternatively, a client could simply cache catalog results for a configurable amount of
	    time.  With either approach, it is also suggested clients provide a means for the user
	    to request an immediate refresh of all catalogs in all contexts.  This is useful where
	    the user made changes to a personal label catalog which the XMPP server uses as input
	    in processing catalog requests.  Note: there is no requirement that XMPP servers
	    support 'personal label catalogs' (such details are beyond the scope of this document).</p>
        <p>If catalog is restrictive, as indicated by the <tt>restrict=</tt> attribute with value of
            true, the client SHOULD restrict the user to choosing one of the items from the catalog
            and use the label of that item (or no label if the selected item is empty).</p>
        <p>One and only one of the items may have a <tt>default=</tt> attribute with value of true.
            The client should default the label selection to this item in cases where the user has
            not selected an item.</p>
        <p>An item may have no security label. Such an item explicitly offers a choice of sending a
            stanza without a label. A non-restrictive catalog implicitly offers this choice when it
            does not contain an empty item.</p>
        <p>Each catalog provided should only contain labels for which the client is allowed to use
            (based upon the user's authorization) in a particular context (such as in chat room). A
            catalog may not include the complete set of labels available for the use by the client
            in the context.</p>
          <p><em>Note:</em> the single catalog per context approach used here is likely inadequate in
            environments where there are a large number of labels in use. It is expected that a more
            sophisticated approach will be introduced in a subsequent revision of this
            specification.</p>
        <p>As each service domain may have different support for security labels, servers should
            advertise and clients should perform appropriate discovery lookups on a per service
            basis.</p>
        <p>To indicate the support for label catalog discovery, a server advertises the
                <tt>urn:xmpp:sec-label:catalog:2</tt> feature. The following pair of examples
            illustrates this feature discovery.</p>
        <p>Items in the catalog may contain a <tt>selector=</tt> attribute. The value of this
            attribute represents the item's placement in a hierarchical organization of the items.
            If one item has a <tt>selector=</tt> attribute, all items should have a
                <tt>selector=</tt> attribute. The value of the <tt>selector=</tt> attribute conforms
                to the <tt>selector-value</tt> ABNF production:
        </p>
        <code><![CDATA[selector-value = (<item>"|")*<item>]]></code>
        <p>where &ITEM; is a sequence of characters not including "|".</p>
        <p>A value of "X|Y|Z" indicates that this item is "Z" in the the "Y" subset of the "X"
            subset of items. This information may be used, for instance, in generating label
            selection menus in graphical user interfaces.</p>
        <p><em>Note:</em> use of unnecessarily deep hierarchies should be avoided.</p>
        <example caption="Label Catalog Feature Discovery request"><![CDATA[
<iq type='get'
    to='example.com'
    from='user@example.com/Work'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
]]></example>
        <example caption="Label Information Feature Discovery response"><![CDATA[
<iq type='result'
    from='example.com'
    to='user@example.com/Work'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:sec-label:catalog:2'/>
    ...
  </query>
</iq>
]]></example>


        <p>The following example pair illustrates catalog discovery. The client directs the <tt>&IQ;</tt> to
            its server regardless of which catalog it requests via the <tt>to=</tt> attribute of in
            &CATALOG; element. The client SHOULD NOT provide a <tt>from=</tt> attribute in the
            &CATALOG; element.</p>

        <example caption="Label Catalog request"><![CDATA[
<iq to='example.com' type='get' id='cat1'>
  <catalog xmlns='urn:xmpp:sec-label:catalog:2' to='example.com'/>
</iq>
]]></example>

        <example caption="Label Catalog Get response"><![CDATA[
<iq type='result' to='user@example.com/Work' id='cat1'>
  <catalog xmlns='urn:xmpp:sec-label:catalog:2'
      to='example.com' name='Default'
      desc='an example set of labels'
	  restrict='false'>
	<item selector="Classified|SECRET">
            <securitylabel xmlns='urn:xmpp:sec-label:0'>
                <displaymarking fgcolor='black' bgcolor='red'>SECRET</displaymarking>
                <label>
                    <esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'
                        >MQYCAQQGASk=</esssecuritylabel>
                </label>
            </securitylabel>
	</item>
	<item selector="Classified|CONFIDENTIAL">
            <securitylabel xmlns='urn:xmpp:sec-label:0'>
                <displaymarking fgcolor='black' bgcolor='navy'>CONFIDENTIAL</displaymarking>
                <label>
                    <esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'
                        >MQYCAQMGASk</esssecuritylabel>
                </label>
            </securitylabel>
	</item>
	<item selector="Classified|RESTRICTED">
            <securitylabel xmlns='urn:xmpp:sec-label:0'>
                <displaymarking fgcolor='black' bgcolor='aqua'>RESTRICTED</displaymarking>
                <label>
                    <esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'
                        >MQYCAQIGASk=</esssecuritylabel>
                </label>
            </securitylabel>
	</item>
	<item selector="UNCLASSIFIED" default="true"/>
  </catalog>
</iq>
]]></example>

        <p> Where the server needs to obtain a catalog from another server in order to respond to
            its client, it can send an &IQ; to that server requesting that catalog. The requesting
            server provides the bare JID of the requesting user in the <tt>from=</tt> attribute in
            the &CATALOG; element when it desires a catalog to be prepared specifically for the
            user. Otherwise the <tt>from=</tt> attribute in the &CATALOG; element is absent. </p>

    </section1>

    <section1 topic="Use in XMPP" anchor="xmpp-use">
        <p>The sensitivity-based access control decisions discussed herein are to be made
            independently of other access control decisions or other facilities. That is, the
            sensitivity-based access control decisions are not conditional on other factors.</p>
        <p>It is intended that &SECURITYLABEL; elements are only used as prescribed by this
            document, documents extending this document, or other formal specifications. Any other
            use of &SECURITYLABEL; SHOULD be viewed as a protocol violation. The stanza SHOULD be
            discarded with, if appropriate, an error response. Such error responses SHOULD NOT
            include content from the violating stanza, excepting that necessary to well-formed error
            responses. Error responses MUST NOT contain a &SECURITYLABEL; element. Any such error
            response violates this protocol and MUST be discarded by servers implementing this
            specification. Error responses MUST NOT be subjected to security label authorization
            checks. However, this prohibition does not preclude a server from taking appropriate
            action to prevent the disclosure of sensitive information, such as closing the
            stream.</p>
        <p>When use of a &SECURITYLABEL; element is prescribed, that use is RECOMMENDED. Absence of
            a &SECURITYLABEL; element implies the stanza has the default label as specified in the
            governing security policy. Given that the governing policy may not specify a default
            label, hence denying access to the stanza, supporting clients SHOULD provide a
            &SECURITYLABEL; element where prescribed.</p>
        <p>Typically, a client would allow the user to choose populate the &SECURITYLABEL; from one
            of from a small set of security labels selections known to it (through configuration
            and/or discovery and/or other means), such as from a pull-down menu. That selection
            would include appropriate values for the &LABEL;, &DISPLAYMARKING;, and
            &EQUIVALENTLABEL; elements.</p>
        <p>A policy-aware client may provide the user with an interface allowing the user to produce
            custom labeling data for inclusion in this set. A policy-aware client SHOULD preclude
            the user from producing &LABEL; values which the user's own clearance does not grant
            access to, and SHOULD preclude sending any label which the user's own clearance does not
            grant access to. Each &EQUIVALENTLABEL; value, if any, MUST be equivalent under an
            equivalent policy to the &LABEL;. The &DISPLAYMARKING; element SHOULD be set the display
            marking prescribed for the &LABEL; under the governing policy, or, if the governing
            policy prescribes no display marking for the &LABEL;, absent.</p>
        <p>A client which receives a stanza with &SECURITYLABEL; element is to prominently display
            the &DISPLAYMARKING; value. A policy-aware client may alternatively prominently display
            the marking for the &LABEL; prescribed by the governing policy.</p>
        <p>Each server is expected to make a number of sensitivity-based authorization decisions.
            Each decision is made by evaluating an Access Control Decision Function (ACDF) with a
            governing policy, a clearance, and a security label. The ACDF yields either
                <em>Grant</em> or <em>Deny</em>.</p>
        <p>If the user holds a valid clearance (known to the server) under the governing policy, the
            clearance input is the user's clearance. Otherwise, if the governing policy provides a
            default clearance, the clearance input is the default clearance. Otherwise, the
            clearance input is the nil clearance. The nil clearance is a clearance for which the
            ACDF always returns Deny when given as the clearance input.</p>
        <p>If the stanza contains a &SECURITYLABEL; element and the either the &LABEL; element or
            one of the &EQUIVALENTLABEL; elements contain an appropriate label, that label input is
            that label. Otherwise, the label input is the default label provided the governing
            policy or, if no default label is provided, the nil label. The nil label is a label for
            which the ACDF always returns Deny when given as the label input.</p>
        <p>The term "effective clearance" and "effective label" refer, respectively, to the
            clearance and label provided as input to the ACDF.</p>
        <p>Not all sensitivity-based authorization decisions an XMPP server might make involve a
            user clearance and/or stanza label. A server may only provide service to users which
            hold an appropriate clearance as determined by calling the ACDF with the user's
            clearance and a label associated with the service. A clearance might also be associated
            with the service to restrict the set of labels may be used in labeling stanzas. Labels
            and clearances can also be associated with network interfaces, remote servers, and chat
            rooms.</p>
        <section2 topic="Use in Instant Messaging" anchor="im-use">
            <p>A client may provide a &SECURITYLABEL; element in any <tt>&MESSAGE;</tt> it sends.</p>
            <!--
    <p>The server will make, at a minimum, the following accessing control decisions:
    <ul>
    <li>TBD</li>
    </ul>
    </p>
-->
        </section2>
        <section2 topic="Use in Group Chat and Multi-User Chat" anchor="muc-use">
            <p>A client may provide a &SECURITYLABEL; element in <tt>&MESSAGE;</tt> stanzas.</p>

            <section3 topic="Discovery" anchor="muc-disco">
                <p>A server SHOULD provide a label feature and information discovery for the
                    room.</p>
                <p>Clients SHOULD discover label feature and information on a per room basis.</p>
            </section3>

            <section3 topic="Sending Messages" anchor="muc-send">
                <p>Sending groupchat messages is similar to sending normal messages, however their
                    are a few differences.</p>
                <p>Groupchat messages are addressed to the room. The room clearance must be suitable
                    for the message label, else it should be rejected.</p>
                <p>The room's clearance may allow a variety of labels to be used. Not all
                    participants may be cleared for all labels allowed in the room. The server MUST
                    only deliver messages to participants for which they are cleared to receive.</p>
            </section3>
            <section3 topic="Room History" anchor="muc-history">
                <p>The server MUST only deliver messages to participants for which they are cleared
                    to receive.</p>
            </section3>
            <section3 topic="Private Messages" anchor="muc-private">
                <p>Private messages SHOULD be handled much like groupchat messages, including
                    rejection of messages for a label not suitable for the room. The server MUST NOT
                    deliver messages to participants for which they are cleared to receive.</p>
            </section3>
            <section3 topic="Invitations" anchor="muc-invite">
                <p>Invitations may be labeled.</p>
            </section3>
            <section3 topic="Room Subject" anchor="muc-subject">
                <p>A stanza intended to change the room subject SHOULD not carry a security label
                    and SHOULD NOT be subject to security-label authorization checks. Such a stanza
                    does not have any impact on the security-label parameters associated with the
                    room.</p>
            </section3>
            <section3 topic="Room Configuration" anchor="muc-config">
                <p>The server may allow for configuration of security label parameters via room
                    configuration mechanisms. The approach is intended to be ad-hoc. Hence this
                    section is intended to be illustrative of one possible approach. Implementations
                    are free to utilize other approaches.</p>
                <example caption="Room Configuration Form"><![CDATA[
<iq from='room@muc.example.com'
    id='create1'
    to='user@example.com/Work'
    type='result'>
<query xmlns='http://jabber.org/protocol/muc#owner'>
    <x xmlns='jabber:x:data' type='form'>
       <title>"darkcave" room configuration</title>
       ...
       <field label='Room Label' type='list-single' var='sec-label#label'>
       <value>Catalog:UNCLASSIFIED</value>
       <option label='SECRET'><value>Catalog:SECRET</value></option>
       <option label='CONFIDENTIAL'><value>Catalog:CONFIDENTIAL</value></option>
       <option label='UNCLASSIFED'><value>Catalog:UNCLASSIFIED</value></option>
       <option label='Custom'><value>Custom</value></option>
       </field>
       <field label='Custom Room Label' type='text-single'
            var='sec-label#custom-label'/>

       <field label='Room Allowed Markings' type='list-multi' var='sec-label#clearance'>
       <value>Catalog:UNCLASSIFIED</value>
       <option label='SECRET'><value>Catalog:SECRET</value></option>
       <option label='CONFIDENTIAL'><value>Catalog:CONFIDENTIAL</value></option>
       <option label='UNCLASSIFED'><value>Catalog:UNCLASSIFIED</value></option>
       <option label='Custom'><value>Custom</value></option>
       </field>
       <field label='Custom Room Clearance' type='text-single'
            var='sec-label#custom-clearance'/>
    </x>
</query>
</iq>
]]></example>
                <p>In the above example, the server allows the room label to be set to one of to a
                    subset of labels from the label catalog (see below), using the display name for
                    selection, as well as custom label support. For custom label choice support, the
                    server offers an single text box for entry of an appropriate text string
                    indicating the label to use. Likewise for the room clearance and default room
                    clearance.</p>
                <p>Though offering choices from the label catalog is often desirable, a server could
                    only offer custom label and/or clearance support.</p>
                <example caption="Room Configuration Form"><![CDATA[
<iq from='room@muc.example.com'
    id='create1'
    to='user@example.com/Work'
    type='result'>
<query xmlns='http://jabber.org/protocol/muc#owner'>
    <x xmlns='jabber:x:data' type='form'>
       <title>"darkcave" room configuration</title>
       ...
       <field label='Room Label' type='text-single'
            var='sec-label#custom-label'/>
       <field label='Room Clearance' type='text-single'
            var='sec-label#custom-clearance'/>
    </x>
</query>
</iq>
]]></example>
            </section3>
        </section2>
        <section2 topic="Use in Presence" anchor="presence-use">
            <p>&SECURITYLABEL; elements are not to appear in <tt>&PRESENCE;</tt> stanzas. Server SHALL treat
                any <tt>&PRESENCE;</tt> stanza that contains a &SECURITYLABEL; as a protocol violation.</p>
            <p>Presence information is subject to sensitivity-base authorization decisions, however
                these decisions are made are made using a label associated with the presence
                resource, such as a chat room's label.</p>
        </section2>
    </section1>

    <section1 topic="Extension Considerations" anchor="exts">
        <p> This extension is itself extensible. In particular, the &LABEL; and &EQUIVALENTLABEL;
            elements are designed to hold a range of security labels formats. XML name spaces SHOULD
            be used to avoid name clashes. </p>
        <p> Future documents may specify how security-labels are used in other areas of XMPP, such
            as PubSub.</p>
    </section1>

    <!--
<section1 topic='Implementation Notes' anchor='impl'>
  <p>OPTIONAL.</p>
</section1>
-->
    <section1 topic="Security Considerations" anchor="security">
        <p>This document is all about authorization, a key aspect of security. Hence, security
            considerations are discussed through this document.</p>
	<p>Nothing in this document ensures appropriate labeling the sensitivity of a piece of
	    information.  Addressing inappropriate labeling of information is beyond the scope of
	    this document.</p>
        <p>Certain XMPP stanzas, such as <tt>&PRESENCE;</tt> stanzas, are not themselves subject to any
            sensitivity-based authorization decisions, and may be forwarded throughout the XMPP
            network. The content of these stanzas should not contain information requiring
            sensitivity-based dissemination controls.</p>
        <p>It is desirable to securely bind the security label to the object it labels. This may be
            accomplished through use of digital signatures. Specification of such is left to a
            future document. </p>
    </section1>
    <section1 topic="IANA Considerations" anchor="iana">
        <p>This document requires no interaction with &IANA;.</p>
    </section1>
    <section1 topic="XMPP Registrar Considerations" anchor="registrar">
        <section2 topic='Protocol Namespaces' anchor='registrar-ns'>
            <p>This specification defines the following XML namespaces:</p>
            <ul>
                <li>urn:xmpp:sec-label:0</li>
                <li>urn:xmpp:sec-label:catalog:2</li>
                <li>urn:xmpp:sec-label:ess:0</li>
            </ul>
            <p>The &REGISTRAR; includes the foregoing namespaces in the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
        </section2>
        <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
          &NSVER;
        </section2>
    </section1>
    <section1 topic="XML Schemas" anchor="schema">
        <section2 topic="Extension Schema" anchor="schema-sl">
                <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:xmpp:sec-label:0"
    xmlns="urn:xmpp:sec-label:0" elementFormDefault="qualified">

    <xs:annotation>
      <xs:documentation>
        The protocol documented by this schema is defined in
        XEP-0258: http://xmpp.org/extensions/xep-0258.html
      </xs:documentation>
    </xs:annotation>

    <xs:simpleType name="colorCSS">
        <xs:annotation>
            <xs:documentation>CSS colors (W3C colors + "orange")</xs:documentation>
        </xs:annotation>
        <xs:restriction base="xs:string">
            <xs:enumeration value="aqua"/>
            <xs:enumeration value="black"/>
            <xs:enumeration value="blue"/>
            <xs:enumeration value="fuschia"/>
            <xs:enumeration value="gray"/>
            <xs:enumeration value="green"/>
            <xs:enumeration value="lime"/>
            <xs:enumeration value="maroon"/>
            <xs:enumeration value="navy"/>
            <xs:enumeration value="olive"/>
            <xs:enumeration value="purple"/>
            <xs:enumeration value="red"/>
            <xs:enumeration value="silver"/>
            <xs:enumeration value="teal"/>
            <xs:enumeration value="white"/>
            <xs:enumeration value="yellow"/>
            <xs:enumeration value="orange"/>
        </xs:restriction>
    </xs:simpleType>

    <xs:simpleType name="colorRGB">
        <xs:annotation>
            <xs:documentation>Hex encoded RGB</xs:documentation>
        </xs:annotation>
        <xs:restriction base="xs:string">
            <xs:pattern value="#[0-9A-Fa-f]{6}"/>
        </xs:restriction>
    </xs:simpleType>

    <xs:simpleType name="color">
        <xs:annotation>
            <xs:documentation>Color</xs:documentation>
        </xs:annotation>
        <xs:union memberTypes="colorCSS colorRGB"/>
    </xs:simpleType>

    <xs:complexType name="displaymarking">
        <xs:annotation>
            <xs:documentation>Display Marking</xs:documentation>
            <xs:documentation>String to be prominently displayed along with labeled
                object.</xs:documentation>
        </xs:annotation>
        <xs:simpleContent>
            <xs:extension base="xs:string">
                <xs:attribute name="bgcolor" type="color" use="optional" default="white"/>
                <xs:attribute name="fgcolor" type="color" use="optional" default="black"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>

    <xs:complexType name="label">
        <xs:choice minOccurs="0">
            <xs:any namespace="##other" processContents="lax"/>
        </xs:choice>
    </xs:complexType>

    <xs:element name="securitylabel">
        <xs:annotation>
            <xs:documentation>A Security Label</xs:documentation>
        </xs:annotation>
        <xs:complexType>
            <xs:sequence>
                <xs:element name="displaymarking" type="displaymarking">
                    <xs:annotation>
                        <xs:documentation>A Display Marking</xs:documentation>
                        <xs:documentation>To be prominently displayed</xs:documentation>
                    </xs:annotation>
                </xs:element>
                <xs:element name="label" type="label">
                    <xs:annotation>
                        <xs:documentation>The Primary Label</xs:documentation>
                    </xs:annotation>
                </xs:element>
                <xs:element name="equivalentlabel" type="label" minOccurs="0" maxOccurs="unbounded">
                    <xs:annotation>
                        <xs:documentation>An Equivalent Label</xs:documentation>
                    </xs:annotation>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>
]]></code>
<p>A copy of this schema is available at <link
    url="http://xmpp.org/schemas/sec-label.xsd">
    http://xmpp.org/schemas/sec-label.xsd</link>.</p>
        </section2>
        <section2 topic="&lt;catalog/&gt; schema" anchor="schema-catalog">
                <code><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:sl="urn:xmpp:sec-label:0"
    xmlns="urn:xmpp:sec-label:catalog:2" targetNamespace="urn:xmpp:sec-label:catalog:2"
    elementFormDefault="qualified">

    <xs:annotation>
      <xs:documentation>
        The protocol documented by this schema is defined in
        XEP-0258: http://xmpp.org/extensions/xep-0258.html
      </xs:documentation>
    </xs:annotation>

    <xs:import schemaLocation="sec-label.xsd" namespace="urn:xmpp:sec-label:0"/>

    <xs:attribute name="to" type="xs:string">
        <xs:annotation>
            <xs:documentation>Target JabberId</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="from" type="xs:string">
        <xs:annotation>
            <xs:documentation>Target JabberId</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="name" type="xs:string">
        <xs:annotation>
            <xs:documentation>Name</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="desc" type="xs:string">
        <xs:annotation>
            <xs:documentation>Description</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="id" type="xs:string">
        <xs:annotation>
            <xs:documentation>Identifer for current revision, commonly a hash</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="size" type="xs:integer">
        <xs:annotation>
            <xs:documentation>Number of items</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="restrict" type="xs:boolean">
        <xs:annotation>
            <xs:documentation>Restrictive</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="selector" type="xs:string">
        <xs:annotation>
            <xs:documentation>User input selector</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:attribute name="default" type="xs:boolean">
        <xs:annotation>
            <xs:documentation>default selection</xs:documentation>
        </xs:annotation>
    </xs:attribute>

    <xs:element name="catalog">
        <xs:annotation>
            <xs:documentation>A Catalog of Labels</xs:documentation>
        </xs:annotation>

        <xs:complexType>
            <xs:sequence>
                <xs:element name="item" minOccurs="0" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:sequence minOccurs="0">
                            <xs:element ref="sl:securitylabel"/>
                        </xs:sequence>
                        <xs:attribute ref="selector" use="optional"/>
                        <xs:attribute ref="default" use="optional"/>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
            <xs:attribute ref="to" use="optional"/>
            <xs:attribute ref="from" use="optional"/>
            <xs:attribute ref="name" use="optional"/>
            <xs:attribute ref="desc" use="optional"/>
            <xs:attribute ref="id" use="optional"/>
            <xs:attribute ref="size" use="optional"/>
            <xs:attribute ref="restrict" use="optional"/>
        </xs:complexType>
    </xs:element>
</xs:schema>
]]></code>
<p>A copy of this schema is available at <link
    url="http://xmpp.org/schemas/sec-label-catalog.xsd">
    http://xmpp.org/schemas/sec-label-catalog.xsd</link>.</p>
        </section2>
        <section2 topic="&lt;esssecuritylabel/&gt; schema" anchor="schema-ess">
                <code><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:xmpp:sec-label:ess:0"
    xmlns="urn:xmpp:sec-label:ess:0" elementFormDefault="qualified">

    <xs:annotation>
      <xs:documentation>
        The protocol documented by this schema is defined in
        XEP-0258: http://xmpp.org/extensions/xep-0258.html
      </xs:documentation>
    </xs:annotation>

    <xs:element name="esssecuritylabel" type="xs:base64Binary">
        <xs:annotation>
            <xs:documentation>An S/MIME ESS SecurityLabel [RFC2634]</xs:documentation>
            <xs:documentation>Value is the base64 encoding of the BER/DER encoding of an ASN.1
                ESSSecurityLabel type as defined in RFC 2634. </xs:documentation>
        </xs:annotation>
    </xs:element>
</xs:schema>
]]></code>
<p>A copy of this schema is available at <link
    url="http://xmpp.org/schemas/sec-label-ess.xsd">
    http://xmpp.org/schemas/sec-label-ess.xsd</link>.</p>
        </section2>
    </section1>
</xep>