Security Labels in Internet Email
RFC 7444

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Independent Submission                                       K. Zeilenga
Request for Comments: 7444                                   A. Melnikov
Category: Informational                                    Isode Limited
ISSN: 2070-1721                                            February 2015

                   Security Labels in Internet Email

Abstract

   This document describes a header field, SIO-Label, for use in
   Internet email to convey the sensitivity of the message.  This header
   field 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 document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7444.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   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.

Zeilenga & Melnikov           Informational                     [Page 1]
RFC 7444            Security Labels in Internet Email      February 2015

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 ............................................12
   7. Security Considerations ........................................12
   8. References .....................................................14
      8.1. Normative References ......................................14
      8.2. Informative References ....................................15
   Acknowledgements ..................................................16
   Authors' Addresses ................................................16

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 sensitive information
   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 an "EXAMPLE CONFIDENTIAL" label that
   requires the sender and the receiver to have a clearance granting
   access to information labeled "EXAMPLE CONFIDENTIAL".  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 that operate
   under a set of information classification rules, such as in
   government and military agency networks.  The standardized formats
   for security labels, clearances, security policy, and associated
   authorization models are generalized and can be used in non-
   government deployments where appropriate.

Zeilenga & Melnikov           Informational                     [Page 2]
RFC 7444            Security Labels in Internet Email      February 2015

   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