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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 7444

Network Working Group                                        K. Zeilenga
Internet-Draft                                               A. Melnikov
Intended status: Informational                             Isode Limited
Expires: October 07, 2013                                 April 05, 2013


                   Security Labels in Internet Email
                    draft-zeilenga-email-seclabel-05

Abstract

   This document describes a header field, SIO-Label, for use in
   Internet Mail to convey the sensitivity of the message.  This header
   field which may carry a textual representation (a display marking)
   and/or a structural representation (a security label) of the
   sensitivity of the message.  This document also describes a header
   field, SIO-Label-History, for recording changes in the message's
   label.

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 October 07, 2013.

Copyright Notice

   Copyright (c) 2013 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.  Relationship to Inline Sensitivity Markings . . . . . . .   3
     1.2.  Relationship to preexisting Security Label Header Fields    4
     1.3.  Relationship to Enhanced Security Services for S/MIME . .   4
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   5
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  The SIO-Label header field  . . . . . . . . . . . . . . . . .   6
   5.  The SIO-Label-History header field  . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   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 can be 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, an email message could have a EXAMPLE CONFIDENTIAL
   label, and hence requiring the sender and the receiver to have a
   clearance granting access to EXAMPLE CONFIDENTIAL labeled
   information.  X.841 [X.841] provides a discussion of security labels,
   clearances, and security policy.

   A display marking is a textual representation of the sensitivity of a
   piece of information.  For instance, "EXAMPLE CONFIDENTIAL" is a
   textual representation of the sensitivity.  A security policy can be
   used to generate display markings from security labels.  Display
   markings are generally expected to be prominently displayed whenever
   the content is displayed.

   Sensitivity-based authorization is used in networks which operate
   under a set of information classification rules, such as in
   government military agency networks.  The standardized formats for
   security labels, clearances, and security policy and associated
   authorization models are generalized and can be used in non-
   government deployments where appropriate.



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   Security labels may also be used for purposes other than
   authorization.  In particular, they may be used simply to convey the
   sensitivity of a piece information.  The security label could be
   used, for instance, to organize content in a content store.

   This document describes a protocol for conveying the sensitivity of a
   electronic mail message [RFC5322], as a whole.  In particular, this
   document describes a header field, SIO-Label, to carry a security
   label, a display marking, and display colors.  This document also
   describes a header field, SIO-Label-History, to record changes in the
   message's security label.

   This protocol is based in part upon Security Labels in XMPP [XEP258]
   protocol.

1.1.  Relationship to Inline Sensitivity Markings

   In environments requiring messages to be marked with an indication of
   their sensitivity, it is common to place a textual representation of
   the sensitivity, a display marking, within the body to the message
   and/or in the Subject header field.  For instance, the authors often
   receives messages of the form:

   To: author <author@example.com>;
   From: Some One <someone@example.net>;
   Subject: the subject (UNCLASSIFIED)

   UNCLASSIFIED

   Text of the message.

   UNCLASSIFIED


   Typically, when placed in the body of the message, the marking is
   inserted into the content such that it appears as the first line(s)
   of text of the body of the message.  This is known as a FLOT (First
   Line(s) of Text) marking.  The marking may or may not be surrounded
   by other text indicating the marking denotes the sensitivity of the
   message.  A FLOT may also accompanied by a LLOT (Last Line(s) of
   Text) marking.  The message above contains a two-line FLOT and a two-
   line LLOT (in both cases, a line providing the marking and a empty
   line between the marking and the original content).

   Typically, when placed in the Subject of the message, the marking is
   inserted before or after the original subject field contents
   surrounded with by parentheses or the like, and/or separated from the
   content by white space.



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   The particulars syntax and semantics of inline sensitivity markings
   is generally a local matter.  This hinders interoperability within an
   organization wanting to take actions based upon these markings, and
   hinders interoperability between cooperating organizations wanting to
   usefully share sensitivity information

   The authors expect such markings to be continued to widely used,
   especially in absence of ubiquitous support for a standardized header
   field indicating the sensitivity of the message.

   The authors hope that through the use of standardized header field,
   interoperability within organizations and between organizations can
   be improved.

1.2.  Relationship to preexisting Security Label Header Fields

   A number of non-standard header fields, such as the X-X411 field, are
   used to carry a representation of the sensitivity of the message,
   whether a structured representation or textual representation.

   The authors hope the use of non-standard header fields will be
   replaced, over time, with use of the header field described in this
   document.

1.3.  Relationship to Enhanced Security Services for S/MIME

   Enhanced Security Services for S/MIME (ESS) [RFC2634] provides,
   amongst other services, signature services "for content integrity,
   non-repudiation with the proof of origin, and [securely] binding
   attributes (such as a security label) to the original content.

   While it may be possible to utilize the protocol described in this
   document concurrently with ESS, this protocol should generally be
   viewed as an alternative to ESS.

   It is noted that in ESS, the security label applies to MIME [RFC2045]
   content, where in this protocol the label applies to the message as a
   whole.

   It is also noted that in ESS, security labels are securely bound to
   the MIME content through the use of digital signatures.  This
   protocol does not provide message signing services, and hence does
   not provide securely binding the label to the message, or for content
   integrity, or for non-repudiation of the proof of origin.

   This protocol is designed for situations/environments where message
   signing is not necessary to provide sufficient security.




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2.  Conventions Used in This Document

   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].

   The formal syntax specifications in this document use the Augmented
   Backus-Naur Form (ABNF) as described in [RFC5234].

   The term "base64 encoding" is used to refer to the Base 64 encoding
   defined in Section 4 of [RFC4648].  The term "BER encoding" is used
   to refer to encoding per the Basic Encoding Rules (BER) as defined in
   [X.690].

3.  Overview

   A Mail User Agent (MUAs) originating a message can, if so configured,
   offer the user with a menu of sensitivities to choose from and, upon
   selection, insert the display marking, foreground and background
   colors, and security label parameters associated with that selection
   into the SIO-Label header field of the message.

   Mail Submission Agents (MSAs), Mail Transfer Agents (MTAs), and Mail
   Delivery Agents (MDAs) then can, if so configured, use the provided
   (or lack thereof) sensitivity information in determining whether to
   accept, forward, or otherwise act on the message as submitted.  These
   agents, here after referred to as Service Agents (SAs), can, if so
   configured, modify the sensitivity information of the message, such
   as replacing the security label and/or display marking with an
   equivalent representations of the sensitivity of the message.  SAs
   which add or modify or delete the SIO-Label header field SHOULD add
   an SIO-Label-History header.

   Receiving MUAs which implement this extension SHALL, when displaying
   the message, also prominently display the marking, if any, conveyed
   in the SIO-Label header field or, if policy aware and configured to
   display locally generated markings, a marking generated by the
   conveyed label and the governing policy.  It is also desirable to
   display this marking in listings of messages.  In the case the
   conveyed marking is displayed, marking SHOULD be displayed using the
   foreground and background colors conveyed in the header field.  In
   the case the marking was generated from conveyed label and the
   governing policy, the marking SHOULD be displayed using the
   foreground and background colors conveyed by the governing policy.

   While MUAs are not expected to make authorization decisions based
   upon values of the SIO-Label header field, MUAs can otherwise use the
   provided (or lack thereof) sensitivity information in determining how



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   to act on the message.  For instance, the MUA may organize messages
   in its store of messages based upon the content of this header field.

4.  The SIO-Label header field

   The header field name is "SIO-Label" and its content is a set of key/
   value pairs, each referred to as a parameter.

   Formal header field syntax:

   sio-label = "SIO-Label:" [FWS] sio-label-parm-seq [FWS] CRLF

   sio-label-parm-seq = sio-label-parm
       [ [FWS] ";" [FWS] sio-label-parm-seq ]

   sio-label-parm = parameter


   where the parameter production is defined in [RFC2231], the FWS
   production are defined in [RFC2822], and the CRLF production is
   defined in [RFC5234].  It is noted that the RFC 2231 productions rely
   on [RFC0822] ABNF which implicitly allows for white space in certain
   cases.  In particular, white space is implicitly allowed in the
   parameter production immediately before and after the "=".  It is
   also noted that RFC 2231 allows for quoted-string values (of the
   parameter production) of substantial length and for string characters
   outside of US-ASCII, or other such cases.  Implementors should
   consult the referenced specifications for specifics.

   The "marking" parameter is a display string for use by
   implementations which are unable or unwilling to utilize the
   governing security policy to generate display markings.  The
   "marking" parameter SHOULD generally be provided in SIO-Label header
   fields.  It ought only be absent where an SA relies on other SA to
   generate the marking.

   The "fgcolor" and "bgcolor" parameters are tokens restricted to color
   production representing the foreground and background colors,
   respectively, for use in colorizing the display marking string.
   Their values are RGB colors in hexadecimal format (e.g., "#ff0000"),
   or one of the CSS color names (e.g., "red") given in named-color type
   below (the 16 HTML4 colors + "orange") [CSS3-Color].  The default
   foreground color is black.  The default background is white.  The
   "fgcolor" and "bgcolor" parameters SHALL be absent if the marking
   parameter is absent.

   Formal color syntax:




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   color = hex-color / named-color

   hex-color = "#" 6HEXDIG    ; Hex encoded RGB

   named-color =
              "aqua" /
              "black" /
              "blue" /
              "fuschia" /
              "gray" /
              "green" /
              "lime" /
              "maroon" /
              "navy" /
              "olive" /
              "purple" /
              "red" /
              "silver" /
              "teal" /
              "white" /
              "yellow" /
              "orange" ; named colors


   The "type" parameter is a quoted-string containing the string ":ess"
   or the string ":x411" or the string ":xml" or a URI [RFC3986]
   denoting the type and encoding of "label" parameter.  The "label"
   parameter value is a quoted string.  The "type" parameter SHALL be
   present if the "label" parameter is present.  The "label" parameter
   SHALL be present if the "type" parameter is present.  The absence of
   the "type" and "label" parameters indicates the message is handled,
   where sensitivity-based authorization is performed, under default
   handling rules (e.g., as if no SIO-Label was present).

   The string ":ess" indicates the "label" parameter value is the base64
   encoding of the BER encoding of an ESS security label [RFC2634].

   ESS Label Example:

   SIO-Label: marking="EXAMPLE CONFIDENTIAL";
       fgcolor=black; bgcolor=red;
       type=":ess"; label="MQYGASkCAQM="


   The string ":x411" indicates the "label" parameter value is the
   base64 encoding of the BER encoding of an X.411 security label
   [X.411].




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   X.411 Label Example:

   SIO-Label: marking="EXAMPLE CONFIDENTIAL";
       fgcolor=black; bgcolor=red;
       type=":x411"; label="MQYGASkCAQM="


   The string ":xml" indicates the "label" parameter value is the base64
   encoding of a security label represented using [XML].  The XML prolog
   SHOULD be absent unless specifically required (such as when the
   character encoding is not UTF-8).  The particular flavor of security
   label representation is indicated by the root element name and its
   name space.

   XML Label Example:

   SIO-Label: marking="EXAMPLE CONFIDENTIAL";
       fgcolor=black; bgcolor=red;
       type=":xml";
       label*0="PFNlY0xhYmVsIHhtbG5zPSJodHRwOi8vZXhhbX";
       label*1="BsZS5jb20vc2VjLWxhYmVsLzAiPjxQb2xpY3lJ";
       label*2="ZGVudGlmaWVyIFVSST0idXJuOm9pZDoxLjEiLz";
       label*3="48Q2xhc3NpZmljYXRpb24+MzwvQ2xhc3NpZmlj";
       label*4="YXRpb24+PC9TZWNMYWJlbD4=";


   The header field SHALL minimally contain a "marking" parameter or
   contain both the "type" and "label" parameters.

   This header field may be extended to include additional parameters by
   future document formally updating (or replacing) this document.
   Implementations SHOULD ignore additional parameters they do not
   recognize.  This recommendation is not a mandate so as to allow
   agents to process a message with an SIO-header field with
   unrecognized header fields differently than a message less those
   unrecongized header fields.

   Each message SHALL contain zero or one SIO-Label header field.

   Extended Example:

   SIO-Label: marking*=us-ascii'en'EXAMPLE%20CONFIDENTIAL;
       fgcolor = black ; bgcolor = red ;
       type=":ess"; label*0="MQYG";
       label*1="ASkCAQM="


   The Extended Example is equivalent to the ESS Label Example above.



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5.  The SIO-Label-History header field

   Any service agent MAY record label changes in an SIO-Label-History
   header.  This header field is intended to provide trace information
   (and only trace information).  For instance, it can be used to record
   the label change when an SIO-Label header is added, modify, or
   deleted by an service agent.  This field use can be used in other
   sitations as well.  For instance, an X.400 to Internet messagging
   gateway can use this header field to record labeling changes made
   while translating a message.

   The formal syntax of the SIO-Label-History header is the same as the
   SIO-Label, but with parameters as discussed here

   change - one of "add", "replace", "delete".

   changed-by - contains a string identify the agent, commonly the
   agent's fully qualified domain name.

   changed-at - contains a date-time string representing the date and
   time the header was rewritten.

   changed-comment - contains a string containing a comment.

   marking, fgcolor, bgcolor, type, label - records the message's label
   information prior to add, modify, delete of SIO-Label, using same
   parameter syntax used of SIO-Label.  These parameters are absent when
   the change action is add.

   new-marking, new-fgcolor, new-bgcolor, new-type, new-label - records
   the message's label information after add, modify, delete of SIO-
   Label, using same parameter syntax used for corresponding SIO-Label
   parameters.  These parameters are absent when the change type is
   delete.

   The header field SHALL minimally contain the "change", "changed-by",
   and "changed-at" parameters.

   This header field may be extended to include additional parameters by
   future document formally updating (or replacing) this document.

   Each message can contain zero or more SIO-Label-History header
   fields.  All SIO-Label-History header fields SHOULD immediately
   follow the the SIO-Label header field, if any, and be grouped
   together.  Additional SIO-Label-History header fields should be added
   immediately preceeding any existing SIO-Label-History header fields

   SIO Label History add, modify, delete example:



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   SIO-Label-History: marking="EXAMPLE CONFIDENTIAL";
       fgcolor=black; bgcolor=red;
       type=":xml";
       label*0="PFNlY0xhYmVsIHhtbG5zPSJodHRwOi8vZXhhbX";
       label*1="BsZS5jb20vc2VjLWxhYmVsLzAiPjxQb2xpY3lJ";
       label*2="ZGVudGlmaWVyIFVSST0idXJuOm9pZDoxLjEiLz";
       label*3="48Q2xhc3NpZmljYXRpb24+MzwvQ2xhc3NpZmlj";
       label*4="YXRpb24+PC9TZWNMYWJlbD4=";
       change=delete;
       changed-by="delete.example.com";
       changed-at="18 Feb 2013 9:24 PDT";
       changed-comment="delete"
   SIO-Label-History: marking="EXAMPLE CONFIDENTIAL";
       fgcolor=black; bgcolor=red;
       type=":ess"; label="MQYGASkCAQM=";
       new-marking="EXAMPLE CONFIDENTIAL";
       new-fgcolor=black; new-bgcolor=red;
       new-type=":xml";
       new-label*0="PFNlY0xhYmVsIHhtbG5zPSJodHRwOi8vZXhhbX";
       new-label*1="BsZS5jb20vc2VjLWxhYmVsLzAiPjxQb2xpY3lJ";
       new-label*2="ZGVudGlmaWVyIFVSST0idXJuOm9pZDoxLjEiLz";
       new-label*3="48Q2xhc3NpZmljYXRpb24+MzwvQ2xhc3NpZmlj";
       new-label*4="YXRpb24+PC9TZWNMYWJlbD4=";
       change=replace;
       changed-by="modify.example.net";
       changed-at="18 Feb 2013 8:24 PDT";
       changed-comment="replaced with XML variant"
   SIO-Label-History: new-marking="EXAMPLE CONFIDENTIAL";
       new-fgcolor=black; new-bgcolor=red;
       new-type=":ess"; new-label="MQYGASkCAQM=";
       change=add;
       changed-by="add.example.net";
       changed-at="18 Feb 2013 7:24 PDT";
       changed-comment="added label"


6.  IANA Considerations

   IANA is requested to add, as detailed below, the SIO-Label and SIO-
   Label-History header fields to the "Permanent Message Header Field
   Registry", defined by Registration Procedures for Message Header
   Fields [RFC3864].

   Header field name: SIO-Label
   Applicable protocol: mail [RFC5322]
   Status: informational
   Author/change controller: Kurt Zeilenga (kurt.zeilenga@isode.com)
   Specification document(s): [[this document]]



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   Header field name: SIO-Label-History
   Applicable protocol: mail [RFC5322]
   Status: informational
   Author/change controller: Kurt Zeilenga (kurt.zeilenga@isode.com)
   Specification document(s): [[this document]]

7.  Security Considerations

   Sensitive information should be appropriately protected (whether
   labeled or not).  For email messages, it is generally appropriate for
   the sending entity to authenticate the receiving entity and to
   establish transport level security, including both data integrity and
   data confidential protective services.  Where a receiving entity to
   make authorization decisions based upon assertions of the sending
   entity, including assertions of identity, it is generally appropriate
   for the receiving entity to authenticate the sending entity.

   This document provides a facility for expressing the sensitivity of
   an email message.  The mere expression of actual sensitivity of a
   generally does not elevate the sensitivity of the message, however
   expressions of sensitivities can themselves be regarded as sensitive
   information.  For instance, a marking of "BLACK PROJECT RESTRICTED"
   could disclose the existence of a sensitivity project.

   The SIO-Label header field expresses the sensitivity of the whole
   message, including the header and body.  This document does not
   provide a means to express the sensitivity of portions of an email
   message, such as the possibly different sensitivities of various MIME
   parts that the message may be composed of.  This approach used in
   this favors simplicity and ease of use of a single expression of
   sensitivity over the complexity and difficultly of use of portion
   marking and labeling.

   The expressed sensitivity can be used in determining how to handle a
   message.  For instance, the value of the SIO-Label header (or lack
   thereof) field can be used to determine if it appropriate to be
   forwarded to a particular entity and, if so, what the minimum
   security services are that which ought to be used in the forwarding
   exchange.  The mechanism for determining how to handle a message
   based expressed sensitivity is beyond the scope of this document.

   The actual content may be more or less sensitivity than indicated by
   the security label.  Agents should avoid lowering security
   requirements for message exchange with a particular entity based upon
   conveyed sensitivity.

   This protocol does not itself provide message signing services, such
   a used in providing message integrity protection, non-repudiation,



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   and binding of attributes, such the security label to the message.
   While it possible that this protocol could be used with a general
   message signing service, this document does not detail such use.

   While security label and display marking parameters are expected to
   express the same sensitivity, nothing in this specification ensures
   that the security label and display marking values express the same
   sensitivity.  For instance, an MUA could submit a message which
   contains security label which expresses one sensitivity and a display
   marking a different sensitivity, and by doing so, possibly cause an
   SA to inappropriately handle the message.  It is generally
   appropriate for each SA making use of the SIO-Label values to
   determine if the security label and display marking values express
   the same sensitivity and, if not, take appropriate action (such as
   rejecting the message).

   This document also provides a facility for expressing changes to the
   label of a message.  This is intended to be used for trace purposes
   only.  It is noted that this SIO-Label-History header field can
   include sensitive information and, as such, can be removed from the
   message where its inclusion would result in an inapprorpriate
   information disclosure.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2231]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded
              Word Extensions:
              Character Sets, Languages, and Continuations", RFC 2231,
              November 1997.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [RFC2634]  Hoffman, P., "Enhanced Security Services for S/MIME", RFC
              2634, June 1999.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.



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   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [XML]      Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
              and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

   [X.411]    International Telephone and Telegraph Consultative
              Committee, "Message Handling Systems (MHS) - Message
              Transfer System: Abstract Service Definition and
              Procedures", CCITT Recommendation X.411, June 1999.

   [X.690]    International Telephone and Telegraph Consultative
              Committee, "ASN.1 encoding rules: Specification of basic
              encoding Rules (BER), Canonical encoding rules (CER) and
              Distinguished encoding rules (DER)", CCITT Recommendation
              X.690, July 2002.

   [CSS3-Color]
              Celik, T. and C. Lilley, "CSS3 Color Module", World Wide
              Web Consortium CR CR-css3-color-20030514, May 2003,
              <http://www.w3.org/TR/2003/CR-css3-color-20030514>.

8.2.  Informative References

   [RFC0822]  Crocker, D.H., "Standard for the format of ARPA Internet
              text messages", STD 11, RFC 822, August 1982.

   [RFC2045]  Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [X.841]    International Telephone and Telegraph Consultative
              Committee, "Security information objects for access
              control", CCITT Recommendation X.841, October 2000.

   [XEP258]   Zeilenga, K., "XEP-0258: Security Labels in XMPP", XEP
              XMPP Extension Protocols, August 2011.





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Appendix A.  Acknowledgements

   The authors appreciate the review, comment, and text provided by
   community members, including Dave Cridland, Brad Hards, Steve Kille,
   Graeme Lunt, Alan Ross, Jim Schaad, and David Wilson.

Authors' Addresses

   Kurt Zeilenga
   Isode Limited

   EMail: Kurt.Zeilenga@isode.com


   Alexey Melnikov
   Isode Limited
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   EMail: Alexey.Melnikov@isode.com




























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