Privacy enhancement for Internet electronic mail: Part I - message encipherment and authentication procedures
RFC 1113

Document Type RFC - Historic (August 1989; No errata)
Obsoleted by RFC 1421
Obsoletes RFC 1040, RFC 989
Last updated 2013-03-02
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Network Working Group                                            J. Linn
Request for Comments:  1113                                          DEC
Obsoletes RFCs: 989, 1040                         IAB Privacy Task Force
                                                             August 1989

           Privacy Enhancement for Internet Electronic Mail:
      Part I -- Message Encipherment and Authentication Procedures

STATUS OF THIS MEMO

   This RFC suggests a draft standard elective protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

ACKNOWLEDGMENT

   This RFC is the outgrowth of a series of IAB Privacy Task Force
   meetings and of internal working papers distributed for those
   meetings.  I would like to thank the following Privacy Task Force
   members and meeting guests for their comments and contributions at
   the meetings which led to the preparation of this RFC: David
   Balenson, Curt Barker, Jim Bidzos, Matt Bishop, Danny Cohen, Tom
   Daniel, Charles Fox, Morrie Gasser, Russ Housley, Steve Kent
   (chairman), John Laws, Steve Lipner, Dan Nessett, Mike Padlipsky, Rob
   Shirey, Miles Smid, Steve Walker, and Steve Wilbur.

Table of Contents

   1.  Executive Summary                                               2
   2.  Terminology                                                     3
   3.  Services, Constraints, and Implications                         3
   4.  Processing of Messages                                          7
   4.1  Message Processing Overview                                    7
   4.1.1  Types of Keys                                                7
   4.1.2  Processing Procedures                                        8
   4.2  Encryption Algorithms and Modes                                9
   4.3  Privacy Enhancement Message Transformations                   10
   4.3.1  Constraints                                                 10
   4.3.2  Approach                                                    11
   4.3.2.1  Step 1: Local Form                                        12
   4.3.2.2  Step 2: Canonical Form                                    12
   4.3.2.3  Step 3: Authentication and Encipherment                   12
   4.3.2.4  Step 4: Printable Encoding                                13
   4.3.2.5  Summary of Transformations                                15
   4.4  Encapsulation Mechanism                                       15
   4.5  Mail for Mailing Lists                                        17
   4.6  Summary of Encapsulated Header Fields                         18

Linn                                                            [Page 1]
RFC 1113                Mail Privacy: Procedures             August 1989

   4.6.1  Per-Message Encapsulated Header Fields                      20
   4.6.1.1  X-Proc-Type Field                                         20
   4.6.1.2  X-DEK-Info Field                                          21
   4.6.2  Encapsulated Header Fields Normally Per-Message             21
   4.6.2.1  X-Sender-ID Field                                         22
   4.6.2.2  X-Certificate Field                                       22
   4.6.2.3  X-MIC-Info Field                                          23
   4.6.3  Encapsulated Header Fields with Variable Occurrences        23
   4.6.3.1  X-Issuer-Certificate Field                                23
   4.6.4  Per-Recipient Encapsulated Header Fields                    24
   4.6.4.1  X-Recipient-ID Field                                      24
   4.6.4.2  X-Key-Info Field                                          24
   4.6.4.2.1  Symmetric Key Management                                24
   4.6.4.2.2  Asymmetric Key Management                               25
   5.  Key Management                                                 26
   5.1  Data Encrypting Keys (DEKs)                                   26
   5.2  Interchange Keys (IKs)                                        26
   5.2.1  Subfield Definitions                                        28
   5.2.1.1  Entity Identifier Subfield                                28
   5.2.1.2  Issuing Authority Subfield                                29
   5.2.1.3  Version/Expiration Subfield                               29
   5.2.2  IK Cryptoperiod Issues                                      29
   6.  User Naming                                                    29
   6.1  Current Approach                                              29
   6.2  Issues for Consideration                                      30
   7.  Example User Interface and Implementation                      30
   8.  Areas For Further Study                                        31
   9.  References                                                     32
   NOTES                                                              32

1.  Executive Summary

   This RFC defines message encipherment and authentication procedures,
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