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@ -1,23 +1,23 @@
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
<!ENTITY % ents SYSTEM 'xep.ent'>
<!ENTITY LABEL "&lt;label/&gt;">
<!ENTITY CATALOG "&lt;catalog/&gt;">
<!ENTITY SECURITYLABEL "&lt;securitylabel/&gt;">
<!ENTITY DISPLAYMARKING "&lt;displaymarking/&gt;">
<!ENTITY EQUIVALENTLABEL "&lt;equivalentlabel/&gt;">
<!ENTITY HEADLINE "&lt;headline/&gt;">
<!ENTITY IDENTITY "&lt;identity/&gt;">
<!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;
<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>Experimental</status>
<lastcall>2011-10-21</lastcall>
@ -37,87 +37,118 @@
<email>Kurt.Zeilenga@Isode.COM</email>
<jid>Kurt.Zeilenga@Isode.COM</jid>
</author>
<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 from attribute to catalog element for S2S requests. Make editorial changes.</p></remark>
<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>
<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>
<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>
<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; type= attribute. Clarify label catalog discovery. Clarify syntax of selector= attribute.</p></remark>
<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>
<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>
<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>
<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>
<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>
<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, 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>
<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>
<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>
@ -141,37 +172,34 @@
]]></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>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:
<ul>
<li>any mechanism for a client might discover the security policy
enforce 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>This document does not provide: <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> Such mechanisms may be introduced in subsequent documents.</p>
Such mechanisms may be introduced in subsequent documents.</p>
<p>This document does discuss how one might securely bind a security label to a stanza.
<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>
<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'
@ -194,10 +222,10 @@
]]></example>
</section1>
<section1 topic='Protocol' anchor='protocol'>
<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>
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>
@ -214,86 +242,74 @@
</securitylabel>
</message>
]]></example>
<p>The security label metadata 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 recepient 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>
<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>If catalog is restrictive, as indicated by the restrict attribute
with value of true, the client SHOULD use one of the labels
(or no label) offered by the catalog.</p>
<p>One and only one of the items may have a default 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 offers a choice of
sending a stanza without a label.</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 be include the
complete set of labels available for the use by the client in the
context.</p>
<blockquote>Note: 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
<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>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>
<blockquote>Note: 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.</blockquote>
<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 selector attribute. The
value of this attribute represents the item's placement in a
hierarchical organization of the items. If one item has a selector
attribute, all items should have a selector item. The value of the selector
attribute conforms to the selector-value ABNF production:
<blockquote>
<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: <blockquote><tt>
<![CDATA[
selector-value = (<item>"|")*<item>
]]>
</blockquote>
</tt></blockquote>
</p>
<p>where &lt;item&gt; 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>
<blockquote>Note: use of unnecessarily deep hierarchies should be
avoided.</blockquote>
<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>
<blockquote>Note: use of unnecessarily deep hierarchies should be avoided.</blockquote>
<example caption="Label Catalog Feature Discovery request"><![CDATA[
<iq type='get'
to='example.com'
@ -316,10 +332,10 @@ selector-value = (<item>"|")*<item>
]]></example>
<p>The following example pair illustrates catalog discovery. The
client directs the &IQ; to its server regardless of which catalog
it requests via the to= attribute of in &CATALOG; element. The
client SHOULD NOT provide a from= attribute in the &CATALOG; element.</p>
<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'>
@ -365,80 +381,75 @@ client SHOULD NOT provide a from= attribute in the &CATALOG; element.</p>
</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 from= attribute in the &CATALOG; element when
it desires a catalog to be prepared specifically for the user.
Otherwise the from= attribute in the &CATALOG; element is absent.
</p>
<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, or other formal specifications. Any other use of
&SECURITYLABEL; SHOULD be viewed as a protocol violation. The stanza SHOULD
be discarded with, if approrpriate, an error response. Such error responses
SHOULD NOT include content from the violating stanza, excepting that
necessary to well-formed error responses.</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 promiently
display the &DISPLAYMARKING; value. A policy-aware 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, chat rooms, pubsub
nodes.</p>
<section2 topic='Use in Instant Messaging' anchor='im-use'>
<p>A client may provide a &SECURITYLABEL; element in any &MESSAGE; it sends.</p>
<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>
@ -447,54 +458,47 @@ Otherwise the from= attribute in the &CATALOG; element is absent.
</p>
-->
</section2>
<section2 topic='Use in Group Chat and Multi-User Chat' anchor='muc-use'>
<p>A client may provide a &SECURITYLABEL; element in &MESSAGE; stanzas.</p>
<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>
<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>
<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>
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='Private Messages' anchor='muc-private'>
<p>Private messages are treated as discussed in the "Use in Instant Messaging"
section. (Should private messages be restricted by room's configuration?)</p>
<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='Invitations' anchor='muc-invite'>
<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='Changing Subject' anchor='muc-subject'>
<p>This section discusses semantics of &SECURITYLABEL; elements contained
in &MESSAGE; stanzas containing a &SUBJECT; element.</p>
<p>The presence of a &SECURITYLABEL; element indicates a request to change
the room's label, either to the provided label or, if the element is empty,
to unset the room's label. The server is to refuse the request if the
requestor is not authorized to change the subject, not cleared for the
requested label, or if the server is otherwise unwilling or unable to make
the change. If the label change is refused, so must the accompanied
subject change. Likewise, if the subject change is refused, so must the
accompanied label change.</p>
<p>Upon change of the room's label, the server MUST immediately kick
all members whom are not cleared for that label out of the room.</p>
<p>In absence of a &SECURITYLABEL; element, the label associated with the
room is unchanged.</p>
<p>The room's label can also be changed through room configuration (to be
discussed in later revision of this document).</p>
<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>
<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'
@ -527,14 +531,14 @@ Otherwise the from= attribute in the &CATALOG; element is absent.
</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>
<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'
@ -554,97 +558,21 @@ Otherwise the from= attribute in the &CATALOG; element is absent.
]]></example>
</section3>
</section2>
<section2 topic='Use in Presence' anchor='presence-use'>
<p>&SECURITYLABEL; elements are not to appear in &PRESENCE; stanzas. Server
SHALL treat any &PRESENCE; 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>
<section2 topic='Use in PubSub' anchor='pubsub-use'>
<section3 topic='Discovery' anchor='pubsub-disco'>
<p>A server SHOULD provide a label feature and information discovery for each node.</p>
<p>Clients SHOULD discover label feature and information on a per node basis.</p>
</section3>
<section3 topic='Publishing items with Security Labels' anchor='muc-send'>
<p>Each item may be individually labeled.</p>
<example caption="Publishing with a Security Label"><![CDATA[
<iq type='set'
from='hamlet@denmark.lit/blogbot'
to='pubsub.shakespeare.lit'
id='pub1'>
<pubsub xmlns='http://jabber.org/protocol/pubsub'>
<publish node='princely_musings'>
<item>
<entry xmlns='http://www.w3.org/2005/Atom'>
<title>Soliloquy</title>
<summary>
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them?
</summary>
<link rel='alternate' type='text/html'
href='http://denmark.lit/2003/12/13/atom03'/>
<id>tag:denmark.lit,2003:entry-32397</id>
<published>2003-12-13T18:30:02Z</published>
<updated>2003-12-13T18:30:02Z</updated>
</entry>
<securitylabel xmlns='urn:xmpp:sec-label:0'>
<displaymarking fgcolor='black' bgcolor='green'>UNCLASSIFIED</displaymarking>
<label>
<esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'>MQMGASk=</esssecuritylabel>
</label>
</securitylabel>
</item>
</publish>
</pubsub>
</iq>
]]></example>
<p>The service then notifies appropriately cleared subscribers.</p>
<example caption="Publishing with a Security Label"><![CDATA[
<message from='pubsub.shakespeare.lit' to='francisco@denmark.lit' id='foo'>
<event xmlns='http://jabber.org/protocol/pubsub#event'>
<items node=princely_musings'>
<item id='ae890ac52d0df67ed7cfdf51b644e901'>
<entry xmlns='http://www.w3.org/2005/Atom'>
<title>Soliloquy</title>
<summary>
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them?
</summary>
<link rel='alternate' type='text/html'
href='http://denmark.lit/2003/12/13/atom03'/>
<id>tag:denmark.lit,2003:entry-32397</id>
<published>2003-12-13T18:30:02Z</published>
<updated>2003-12-13T18:30:02Z</updated>
</entry>
<securitylabel xmlns='urn:xmpp:sec-label:0'>
<displaymarking fgcolor='black' bgcolor='green'>UNCLASSIFIED</displaymarking>
<label>
<esssecuritylabel xmlns='urn:xmpp:sec-label:ess:0'>MQMGASk=</esssecuritylabel>
</label>
</securitylabel>
</item>
</items>
</event>
</iq>
]]></example>
</section3>
<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 is extensible. In particular, the &LABEL; and &EQUIVALENTLABEL;
<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>
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>
<!--
@ -652,27 +580,29 @@ And by opposing end them?
<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>Certain XMPP stanzas, such as &PRESENCE; 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 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'>
<section1 topic="IANA Considerations" anchor="iana">
<p>This document requires no interaction with &IANA;.</p>
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<p>It is requested the &REGISTRAR; add the extension's namespaces
and schemas to appropriate XMPP registries.</p>
<section1 topic="XMPP Registrar Considerations" anchor="registrar">
<p>It is requested the &REGISTRAR; add the extension's namespaces and schemas to appropriate
XMPP registries.</p>
</section1>
<section1 topic='XML Schemas' anchor='schema'>
<section2 topic='Extension Schema' anchor='schema-sl'>
<section1 topic="XML Schemas" anchor="schema">
<section2 topic="Extension Schema" anchor="schema-sl">
<p>
<code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>
@ -771,14 +701,11 @@ And by opposing end them?
</xs:complexType>
</xs:element>
</xs:schema>
]]></code>
A copy of this schema is available at
<link url='http://www.xmpp.org/schemas/sec-label.xsd'>
http://www.xmpp.org/schemas/sec-label.xsd</link>.
</p>
]]></code> A copy of this schema is available at <link
url="http://www.xmpp.org/schemas/sec-label.xsd">
http://www.xmpp.org/schemas/sec-label.xsd</link>. </p>
</section2>
<section2 topic='&lt;catalog/&gt; schema' anchor='schema-catalog'>
<section2 topic="&lt;catalog/&gt; schema" anchor="schema-catalog">
<p>
<code><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
@ -874,14 +801,11 @@ And by opposing end them?
</xs:complexType>
</xs:element>
</xs:schema>
]]></code>
A copy of this schema is available at
<link url='http://www.xmpp.org/schemas/sec-label-catalog.xsd'>
http://www.xmpp.org/schemas/sec-label-catalog.xsd</link>.
</p>
]]></code> A copy of this schema is available at <link
url="http://www.xmpp.org/schemas/sec-label-catalog.xsd">
http://www.xmpp.org/schemas/sec-label-catalog.xsd</link>. </p>
</section2>
<section2 topic='&lt;esssecuritylabel/&gt; schema' anchor='schema-ess'>
<section2 topic="&lt;esssecuritylabel/&gt; schema" anchor="schema-ess">
<p>
<code><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
@ -899,12 +823,9 @@ And by opposing end them?
</xs:annotation>
</xs:element>
</xs:schema>
]]></code>
A copy of this schema is available at
<link url='http://www.xmpp.org/schemas/sec-label-ess.xsd'>
http://www.xmpp.org/schemas/sec-label-ess.xsd</link>.
</p>
]]></code> A copy of this schema is available at <link
url="http://www.xmpp.org/schemas/sec-label-ess.xsd">
http://www.xmpp.org/schemas/sec-label-ess.xsd</link>. </p>
</section2>
</section1>
</xep>