PGP Message Exchange Formats
RFC 1991

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Network Working Group                                          D. Atkins
Request for Comments: 1991                                           MIT
Category: Informational                                     W. Stallings
                                                    Comp-Comm Consulting
                                                           P. Zimmermann
                                            Boulder Software Engineering
                                                             August 1996

                      PGP Message Exchange Formats

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Table of Contents

   1.    Introduction............................................2
   2.    PGP Services............................................2
   2.1   Digital signature.......................................3
   2.2   Confidentiality.........................................3
   2.3   Compression.............................................4
   2.4   Radix-64 conversion.....................................4
   2.4.1 ASCII Armor Formats.....................................5
   3.    Data Element Formats....................................6
   3.1   Byte strings............................................6
   3.2   Whole number fields.....................................7
   3.3   Multiprecision fields...................................7
   3.4   String fields...........................................8
   3.5   Time fields.............................................8
   4.    Common Fields...........................................8
   4.1   Packet structure fields.................................8
   4.2   Number ID fields.......................................10
   4.3   Version fields.........................................10
   5.    Packets................................................10
   5.1   Overview...............................................10
   5.2   General Packet Structure...............................11
   5.2.1 Message component......................................11
   5.2.2 Signature component....................................11
   5.2.3 Session key component..................................11
   6.    PGP Packet Types.......................................12
   6.1   Literal data packets...................................12
   6.2   Signature packets......................................13
   6.2.1 Message-digest-related fields..........................14
   6.2.2 Public-key-related fields..............................15
   6.2.3 RSA signatures.........................................16

Atkins, et. al.              Informational                      [Page 1]
RFC 1991              PGP Message Exchange Formats           August 1996

   6.2.4 Miscellaneous fields...................................16
   6.3   Compressed data packets................................17
   6.4   Conventional-key-encrypted data packets................17
   6.4.1 Conventional-encryption type byte......................18
   6.5   Public-key-encrypted packets...........................18
   6.5.1 RSA-encrypted data encryption key (DEK)................19
   6.6   Public-key Packets.....................................19
   6.7   User ID packets........................................20
   7.    Transferable Public Keys...............................20
   8.    Acknowledgments........................................20
   9.    Security Considerations................................21
   10.   Authors' Addresses.....................................21

1. Introduction

   PGP (Pretty Good Privacy) uses a combination of public-key and
   conventional encryption to provide security services for electronic
   mail messages and data files.  These services include confidentiality
   and digital signature.  PGP is widely used throughout the global
   computer community.  This document describes the format of "PGP
   files", i.e., messages that have been encrypted and/or signed with
   PGP.

   PGP was created by Philip Zimmermann and first released, in Version
   1.0, in 1991. Subsequent versions have been designed and implemented
   by an all-volunteer collaborative effort under the design guidance of
   Philip Zimmermann.  PGP and Pretty Good Privacy are trademarks of
   Philip Zimmermann.

   This document describes versions 2.x of PGP.  Specifically, versions
   2.6 and 2.7 conform to this specification.  Version 2.3 conforms to
   this specification with minor differences.

   A new release of PGP, known as PGP 3.0, is anticipated in 1995. To
   the maximum extent possible, this version will be upwardly compatible
   with version 2.x. At a minimum, PGP 3.0 will be able to read messages
   and signatures produced by version 2.x.

2. PGP Services

   PGP provides four services related to the format of messages and data
   files: digital signature, confidentiality, compression, and radix-64