RFC 1040 (rfc1040) - Page 2 of 29

Privacy enhancement for Internet electronic mail: Part I: Message encipherment and authentication procedures

RFC 1040        Privacy Enhancement for Electronic Mail     January 1988


   components and mail transport facilities is supported.

2.  Terminology

   For descriptive purposes, this RFC uses some terms defined in the OSI
   X.400 Message Handling System Model per the 1984 CCITT
   Recommendations.  This section replicates a portion of X.400's
   Section 2.2.1, "Description of the MHS Model: Overview" in order to
   make the terminology clear to readers who may not be familiar with
   the OSI MHS Model.

   In the [MHS] model, a user is a person or a computer application.  A
   user is referred to as either an originator (when sending a message)
   or a recipient (when receiving one).  MH Service elements define the
   set of message types and the capabilities that enable an originator
   to transfer messages of those types to one or more recipients.

   An originator prepares messages with the assistance of his User
   Agent.  A User Agent (UA) is an application process that interacts
   with the Message Transfer System (MTS) to submit messages.  The MTS
   delivers to one or more recipient UAs the messages submitted to it.
   Functions performed solely by the UA and not standardized as part of
   the MH Service elements are called local UA functions.

   The MTS is composed of a number of Message Transfer Agents (MTAs).
   Operating together, the MTAs relay messages and deliver them to the
   intended recipient UAs, which then make the messages available to the
   intended recipients.

   The collection of UAs and MTAs is called the Message Handling System
   (MHS).  The MHS and all of its users are collectively referred to as
   the Message Handling Environment.

3.  Services, Constraints, and Implications

   This RFC defines mechanisms to enhance privacy for electronic mail
   transferred in the Internet.  The facilities discussed in this RFC
   provide privacy enhancement services on an end-to-end basis between
   sender and recipient UAs.  No privacy enhancements are offered for
   message fields which are added or transformed by intermediate relay
   points.

   Authentication and integrity facilities are always applied to the
   entirety of a message's text.  No facility for confidentiality
   service without authentication is provided.  Encryption facilities
   may be applied selectively to portions of a message's contents; this
   allows less sensitive portions of messages (e.g., descriptive fields)
   to be processed by a recipient's delegate in the absence of the



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