OpenPGP Message Format
RFC 2440

Document Type RFC - Proposed Standard (November 1998; No errata)
Obsoleted by RFC 4880
Last updated 2013-03-02
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IESG IESG state RFC 2440 (Proposed Standard)
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Network Working Group                                         J. Callas
Request for Comments: 2440                           Network Associates
Category: Standards Track                                L. Donnerhacke
                                     IN-Root-CA Individual Network e.V.
                                                              H. Finney
                                                     Network Associates
                                                              R. Thayer
                                                        EIS Corporation
                                                          November 1998

                         OpenPGP Message Format

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

IESG Note

   This document defines many tag values, yet it doesn't describe a
   mechanism for adding new tags (for new features).  Traditionally the
   Internet Assigned Numbers Authority (IANA) handles the allocation of
   new values for future expansion and RFCs usually define the procedure
   to be used by the IANA.  However, there are subtle (and not so
   subtle) interactions that may occur in this protocol between new
   features and existing features which result in a significant
   reduction in over all security.  Therefore, this document does not
   define an extension procedure.  Instead requests to define new tag
   values (say for new encryption algorithms for example) should be
   forwarded to the IESG Security Area Directors for consideration or
   forwarding to the appropriate IETF Working Group for consideration.

Abstract

   This document is maintained in order to publish all necessary
   information needed to develop interoperable applications based on the
   OpenPGP format. It is not a step-by-step cookbook for writing an
   application. It describes only the format and methods needed to read,
   check, generate, and write conforming packets crossing any network.
   It does not deal with storage and implementation questions.  It does,

Callas, et. al.             Standards Track                     [Page 1]
RFC 2440                 OpenPGP Message Format            November 1998

   however, discuss implementation issues necessary to avoid security
   flaws.

   Open-PGP software uses a combination of strong public-key and
   symmetric cryptography to provide security services for electronic
   communications and data storage.  These services include
   confidentiality, key management, authentication, and digital
   signatures. This document specifies the message formats used in
   OpenPGP.

Table of Contents

            Status of this Memo                                       1
            IESG Note                                                 1
            Abstract                                                  1
            Table of Contents                                         2
   1.       Introduction                                              4
   1.1.     Terms                                                     5
   2.       General functions                                         5
   2.1.     Confidentiality via Encryption                            5
   2.2.     Authentication via Digital signature                      6
   2.3.     Compression                                               7
   2.4.     Conversion to Radix-64                                    7
   2.5.     Signature-Only Applications                               7
   3.       Data Element Formats                                      7
   3.1.     Scalar numbers                                            8
   3.2.     Multi-Precision Integers                                  8
   3.3.     Key IDs                                                   8
   3.4.     Text                                                      8
   3.5.     Time fields                                               9
   3.6.     String-to-key (S2K) specifiers                            9
   3.6.1.   String-to-key (S2k) specifier types                       9
   3.6.1.1. Simple S2K                                                9
   3.6.1.2. Salted S2K                                               10
   3.6.1.3. Iterated and Salted S2K                                  10
   3.6.2.   String-to-key usage                                      11
   3.6.2.1. Secret key encryption                                    11
   3.6.2.2. Symmetric-key message encryption                         11
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