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PGG
***

PGG is an interface library between Emacs and various tools for secure
communication.  PGG also provides a simple user interface to encrypt,
decrypt, sign, and verify MIME messages.

   This file describes PGG 0.1, an Emacs interface to various PGP
implementations.

   Copyright (C) 2001, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free
Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with the Front-Cover texts
     being "A GNU Manual," and with the Back-Cover Texts as in (a)
     below.  A copy of the license is included in the section entitled
     "GNU Free Documentation License."

     (a) The FSF's Back-Cover Text is: "You have the freedom to copy and
     modify this GNU manual.  Buying copies from the FSF supports it in
     developing GNU and promoting software freedom."

* Menu:

* Overview::                    What PGG is.
* Prerequisites::               Complicated stuff you may have to do.
* How to use::                  Getting started quickly.
* Architecture::
* Parsing OpenPGP packets::
* GNU Free Documentation License:: The license for this documentation.
* Function Index::
* Variable Index::

File: pgg,  Node: Overview,  Next: Prerequisites,  Prev: Top,  Up: Top

1 Overview
**********

PGG is an interface library between Emacs and various tools for secure
communication.  Even though Mailcrypt has similar feature, it does not
deal with detached PGP messages, normally used in PGP/MIME
infrastructure.  This was the main reason why I wrote the new library.

   PGP/MIME is an application of MIME Object Security Services
(RFC1848).  The standard is documented in RFC2015.

File: pgg,  Node: Prerequisites,  Next: How to use,  Prev: Overview,  Up: Top

2 Prerequisites
***************

PGG requires at least one implementation of privacy guard system.  This
document assumes that you have already obtained and installed them and
that you are familiar with its basic functions.

   By default, PGG uses GnuPG.  If you are new to such a system, I
recommend that you should look over the GNU Privacy Handbook (GPH)
which is available at `http://www.gnupg.org/documentation/'.

   When using GnuPG, we recommend the use of the `gpg-agent' program,
which is distributed with versions 2.0 and later of GnuPG.  This is a
daemon to manage private keys independently from any protocol, and
provides the most secure way to input and cache your passphrases (*note
Caching passphrase::).  By default, PGG will attempt to use `gpg-agent'
if it is running.  *Note Invoking GPG-AGENT: (gnupg)Invoking GPG-AGENT.

   PGG also supports Pretty Good Privacy version 2 or version 5.

File: pgg,  Node: How to use,  Next: Architecture,  Prev: Prerequisites,  Up: Top

3 How to use
************

The toplevel interface of this library is quite simple, and only
intended to use with public-key cryptographic operation.

   To use PGG, evaluate following expression at the beginning of your
application program.

     (require 'pgg)

   If you want to check existence of pgg.el at runtime, instead you can
list autoload setting for desired functions as follows.

     (autoload 'pgg-encrypt-region "pgg"
       "Encrypt the current region." t)
     (autoload 'pgg-encrypt-symmetric-region "pgg"
       "Encrypt the current region with symmetric algorithm." t)
     (autoload 'pgg-decrypt-region "pgg"
       "Decrypt the current region." t)
     (autoload 'pgg-sign-region "pgg"
       "Sign the current region." t)
     (autoload 'pgg-verify-region "pgg"
       "Verify the current region." t)
     (autoload 'pgg-insert-key "pgg"
       "Insert the ASCII armored public key." t)
     (autoload 'pgg-snarf-keys-region "pgg"
       "Import public keys in the current region." t)

* Menu:

* User Commands::
* Selecting an implementation::
* Caching passphrase::
* Default user identity::

File: pgg,  Node: User Commands,  Next: Selecting an implementation,  Up: How to use

3.1 User Commands
=================

At this time you can use some cryptographic commands.  The behavior of
these commands relies on a fashion of invocation because they are also
intended to be used as library functions.  In case you don't have the
signer's public key, for example, the function `pgg-verify-region'
fails immediately, but if the function had been called interactively, it
would ask you to retrieve the signer's public key from the server.

 -- Command: pgg-encrypt-region start end recipients &optional sign
          passphrase
     Encrypt the current region between START and END for RECIPIENTS.
     When the function were called interactively, you would be asked
     about the recipients.

     If encryption is successful, it replaces the current region
     contents (in the accessible portion) with the resulting data.

     If optional argument SIGN is non-`nil', the function is request to
     do a combined sign and encrypt.  This currently is confirmed to
     work with GnuPG, but might not work with PGP or PGP5.

     If optional PASSPHRASE is `nil', the passphrase will be obtained
     from the passphrase cache or user.

 -- Command: pgg-encrypt-symmetric-region &optional start end passphrase
     Encrypt the current region between START and END using a symmetric
     cipher.  After invocation you are asked for a passphrase.

     If optional PASSPHRASE is `nil', the passphrase will be obtained
     from the passphrase cache or user.

     symmetric-cipher encryption is currently only implemented for
     GnuPG.

 -- Command: pgg-decrypt-region start end &optional passphrase
     Decrypt the current region between START and END.  If decryption
     is successful, it replaces the current region contents (in the
     accessible portion) with the resulting data.

     If optional PASSPHRASE is `nil', the passphrase will be obtained
     from the passphrase cache or user.

 -- Command: pgg-sign-region start end &optional cleartext passphrase
     Make the signature from text between START and END.  If the
     optional third argument CLEARTEXT is non-`nil', or the function is
     called interactively, it does not create a detached signature.  In
     such a case, it replaces the current region contents (in the
     accessible portion) with the resulting data.

     If optional PASSPHRASE is `nil', the passphrase will be obtained
     from the passphrase cache or user.

 -- Command: pgg-verify-region start end &optional signature fetch
     Verify the current region between START and END.  If the optional
     third argument SIGNATURE is non-`nil', it is treated as the
     detached signature file of the current region.

     If the optional 4th argument FETCH is non-`nil', or the function
     is called interactively, we attempt to fetch the signer's public
     key from the key server.

 -- Command: pgg-insert-key
     Retrieve the user's public key and insert it as ASCII-armored
     format.

 -- Command: pgg-snarf-keys-region start end
     Collect public keys in the current region between START and END,
     and add them into the user's keyring.

File: pgg,  Node: Selecting an implementation,  Next: Caching passphrase,  Prev: User Commands,  Up: How to use

3.2 Selecting an implementation
===============================

Since PGP has a long history and there are a number of PGP
implementations available today, the function which each one has differs
considerably.  For example, if you are using GnuPG, you know you can
select cipher algorithm from 3DES, CAST5, BLOWFISH, and so on, but on
the other hand the version 2 of PGP only supports IDEA.

   Which implementation is used is controlled by the `pgg-scheme'
variable.  If it is `nil' (the default), the value of the
`pgg-default-scheme' variable will be used instead.

 -- Variable: pgg-scheme
     Force specify the scheme of PGP implementation.  The value can be
     set to `gpg', `pgp', and `pgp5'.  The default is `nil'.

 -- Variable: pgg-default-scheme
     The default scheme of PGP implementation.  The value should be one
     of `gpg', `pgp', and `pgp5'.  The default is `gpg'.

File: pgg,  Node: Caching passphrase,  Next: Default user identity,  Prev: Selecting an implementation,  Up: How to use

3.3 Caching passphrase
======================

When using GnuPG (gpg) as the PGP scheme, we recommend using a program
called `gpg-agent' for entering and caching passphrases(1).

 -- Variable: pgg-gpg-use-agent
     If non-`nil', attempt to use `gpg-agent' whenever possible.  The
     default is `t'.  If `gpg-agent' is not running, or GnuPG is not
     the current PGP scheme, PGG's own passphrase-caching mechanism is
     used (see below).

   To use `gpg-agent' with PGG, you must first ensure that `gpg-agent'
is running.  For example, if you are running in the X Window System,
you can do this by putting the following line in your `.xsession' file:

     eval "$(gpg-agent --daemon)"

   For more details on invoking `gpg-agent', *Note Invoking GPG-AGENT:
(gnupg)Invoking GPG-AGENT.

   Whenever you perform a PGG operation that requires a GnuPG
passphrase, GnuPG will contact `gpg-agent', which prompts you for the
passphrase.  Furthermore, `gpg-agent' "caches" the result, so that
subsequent uses will not require you to enter the passphrase again.
(This cache usually expires after a certain time has passed; you can
change this using the `--default-cache-ttl' option when invoking
`gpg-agent'.)

   If you are running in a X Window System environment, `gpg-agent'
prompts for a passphrase by opening a graphical window.  However, if
you are running Emacs on a text terminal, `gpg-agent' has trouble
receiving input from the terminal, since it is being sent to Emacs.
One workaround for this problem is to run `gpg-agent' on a different
terminal from Emacs, with the `--keep-tty' option; this tells
`gpg-agent' use its own terminal to prompt for passphrases.

   When `gpg-agent' is not being used, PGG prompts for a passphrase
through Emacs.  It also has its own passphrase caching mechanism, which
is controlled by the variable `pgg-cache-passphrase' (see below).

   There is a security risk in handling passphrases through PGG rather
than `gpg-agent'.  When you enter your passphrase into an Emacs prompt,
it is temporarily stored as a cleartext string in the memory of the
Emacs executable.  If the executable memory is swapped to disk, the
root user can, in theory, extract the passphrase from the swapfile.
Furthermore, the swapfile containing the cleartext passphrase might
remain on the disk after the system is discarded or stolen.
`gpg-agent' avoids this problem by using certain tricks, such as memory
locking, which have not been implemented in Emacs.

 -- Variable: pgg-cache-passphrase
     If non-`nil', store passphrases.  The default value of this
     variable is `t'.  If you are worried about security issues,
     however, you could stop the caching of passphrases by setting this
     variable to `nil'.

 -- Variable: pgg-passphrase-cache-expiry
     Elapsed time for expiration in seconds.

   If your passphrase contains non-ASCII characters, you might need to
specify the coding system to be used to encode your passphrases, since
GnuPG treats them as a byte sequence, not as a character sequence.

 -- Variable: pgg-passphrase-coding-system
     Coding system used to encode passphrase.

   ---------- Footnotes ----------

   (1) Actually, `gpg-agent' does not cache passphrases but private
keys.  On the other hand, from a user's point of view, this technical
difference isn't visible.

File: pgg,  Node: Default user identity,  Prev: Caching passphrase,  Up: How to use

3.4 Default user identity
=========================

The PGP implementation is usually able to select the proper key to use
for signing and decryption, but if you have more than one key, you may
need to specify the key id to use.

 -- Variable: pgg-default-user-id
     User ID of your default identity.  It defaults to the value
     returned by `(user-login-name)'.  You can customize this variable.

 -- Variable: pgg-gpg-user-id
     User ID of the GnuPG default identity.  It defaults to `nil'.
     This overrides `pgg-default-user-id'.  You can customize this
     variable.

 -- Variable: pgg-pgp-user-id
     User ID of the PGP 2.x/6.x default identity.  It defaults to
     `nil'.  This overrides `pgg-default-user-id'.  You can customize
     this variable.

 -- Variable: pgg-pgp5-user-id
     User ID of the PGP 5.x default identity.  It defaults to `nil'.
     This overrides `pgg-default-user-id'.  You can customize this
     variable.

File: pgg,  Node: Architecture,  Next: Parsing OpenPGP packets,  Prev: How to use,  Up: Top

4 Architecture
**************

PGG introduces the notion of a "scheme of PGP implementation" (used
interchangeably with "scheme" in this document).  This term refers to a
singleton object wrapped with the luna object system.

   Since PGG was designed for accessing and developing PGP
functionality, the architecture had to be designed not just for
interoperability but also for extensiblity.  In this chapter we explore
the architecture while finding out how to write the PGG back end.

* Menu:

* Initializing::
* Back end methods::
* Getting output::

File: pgg,  Node: Initializing,  Next: Back end methods,  Up: Architecture

4.1 Initializing
================

A scheme must be initialized before it is used.  It had better
guarantee to keep only one instance of a scheme.

   The following code is snipped out of `pgg-gpg.el'.  Once an instance
of `pgg-gpg' scheme is initialized, it's stored to the variable
`pgg-scheme-gpg-instance' and will be reused from now on.

     (defvar pgg-scheme-gpg-instance nil)

     (defun pgg-make-scheme-gpg ()
       (or pgg-scheme-gpg-instance
           (setq pgg-scheme-gpg-instance
     	    (luna-make-entity 'pgg-scheme-gpg))))

   The name of the function must follow the
regulation--`pgg-make-scheme-' follows the back end name.

File: pgg,  Node: Back end methods,  Next: Getting output,  Prev: Initializing,  Up: Architecture

4.2 Back end methods
====================

In each back end, these methods must be present.  The output of these
methods is stored in special buffers (*note Getting output::), so that
these methods must tell the status of the execution.

 -- Method: pgg-scheme-lookup-key scheme string &optional type
     Return keys associated with STRING.  If the optional third
     argument TYPE is non-`nil', it searches from the secret keyrings.

 -- Method: pgg-scheme-encrypt-region scheme start end recipients
          &optional sign passphrase
     Encrypt the current region between START and END for RECIPIENTS.
     If SIGN is non-`nil', do a combined sign and encrypt.  If
     encryption is successful, it returns `t', otherwise `nil'.

 -- Method: pgg-scheme-encrypt-symmetric-region scheme start end
          &optional passphrase
     Encrypt the current region between START and END using a symmetric
     cipher and a passphrases.  If encryption is successful, it returns
     `t', otherwise `nil'.  This function is currently only implemented
     for GnuPG.

 -- Method: pgg-scheme-decrypt-region scheme start end &optional
          passphrase
     Decrypt the current region between START and END.  If decryption
     is successful, it returns `t', otherwise `nil'.

 -- Method: pgg-scheme-sign-region scheme start end &optional cleartext
          passphrase
     Make the signature from text between START and END.  If the
     optional third argument CLEARTEXT is non-`nil', it does not create
     a detached signature.  If signing is successful, it returns `t',
     otherwise `nil'.

 -- Method: pgg-scheme-verify-region scheme start end &optional
          signature
     Verify the current region between START and END.  If the optional
     third argument SIGNATURE is non-`nil', it is treated as the
     detached signature of the current region.  If the signature is
     successfully verified, it returns `t', otherwise `nil'.

 -- Method: pgg-scheme-insert-key scheme
     Retrieve the user's public key and insert it as ASCII-armored
     format.  On success, it returns `t', otherwise `nil'.

 -- Method: pgg-scheme-snarf-keys-region scheme start end
     Collect public keys in the current region between START and END,
     and add them into the user's keyring.  On success, it returns `t',
     otherwise `nil'.

File: pgg,  Node: Getting output,  Prev: Back end methods,  Up: Architecture

4.3 Getting output
==================

The output of the back end methods (*note Back end methods::) is stored
in special buffers, so that these methods must tell the status of the
execution.

 -- Variable: pgg-errors-buffer
     The standard error output of the execution of the PGP command is
     stored here.

 -- Variable: pgg-output-buffer
     The standard output of the execution of the PGP command is stored
     here.

 -- Variable: pgg-status-buffer
     The rest of status information of the execution of the PGP command
     is stored here.

File: pgg,  Node: Parsing OpenPGP packets,  Next: GNU Free Documentation License,  Prev: Architecture,  Up: Top

5 Parsing OpenPGP packets
*************************

The format of OpenPGP messages is maintained in order to publish all
necessary information needed to develop interoperable applications.
The standard is documented in RFC 2440.

   PGG has its own parser for the OpenPGP packets.

 -- Function: pgg-parse-armor string
     List the sequence of packets in STRING.

 -- Function: pgg-parse-armor-region start end
     List the sequence of packets in the current region between START
     and END.

 -- Variable: pgg-ignore-packet-checksum
     If non-`nil', don't check the checksum of the packets.

File: pgg,  Node: GNU Free Documentation License,  Next: Function Index,  Prev: Parsing OpenPGP packets,  Up: Top

Appendix A GNU Free Documentation License
*****************************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008, 2009 Free Software Foundation, Inc.
     `http://fsf.org/'

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     This License is a kind of "copyleft", which means that derivative
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     We have designed this License in order to use it for manuals for
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       K. For any section Entitled "Acknowledgements" or "Dedications",
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       L. Preserve all the Invariant Sections of the Document,
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       M. Delete any section Entitled "Endorsements".  Such a section
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       N. Do not retitle any existing section to be Entitled
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       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
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     You may add a section Entitled "Endorsements", provided it contains
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     You may add a passage of up to five words as a Front-Cover Text,
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     The author(s) and publisher(s) of the Document do not by this
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  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
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     In the combination, you must combine any sections Entitled
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  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
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     this License in all other respects regarding verbatim copying of
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  7. AGGREGATION WITH INDEPENDENT WORKS

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     Preserve its Title (section 1) will typically require changing the
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  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
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     the same material does not give you any rights to use it.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
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     versions will be similar in spirit to the present version, but may
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 11. RELICENSING

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     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
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     "Incorporate" means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is "eligible for relicensing" if it is licensed under this
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     The operator of an MMC Site may republish an MMC contained in the
     site under CC-BY-SA on the same site at any time before August 1,
     2009, provided the MMC is eligible for relicensing.


ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.

File: pgg,  Node: Function Index,  Next: Variable Index,  Prev: GNU Free Documentation License,  Up: Top

Function Index
**************

[index]
* Menu:

* pgg-decrypt-region:                    User Commands.        (line 40)
* pgg-encrypt-region:                    User Commands.        (line 15)
* pgg-encrypt-symmetric-region:          User Commands.        (line 30)
* pgg-insert-key:                        User Commands.        (line 67)
* pgg-parse-armor:                       Parsing OpenPGP packets.
                                                               (line 13)
* pgg-parse-armor-region:                Parsing OpenPGP packets.
                                                               (line 16)
* pgg-scheme-decrypt-region:             Back end methods.     (line 29)
* pgg-scheme-encrypt-region:             Back end methods.     (line 16)
* pgg-scheme-encrypt-symmetric-region:   Back end methods.     (line 22)
* pgg-scheme-insert-key:                 Back end methods.     (line 47)
* pgg-scheme-lookup-key:                 Back end methods.     (line 11)
* pgg-scheme-sign-region:                Back end methods.     (line 34)
* pgg-scheme-snarf-keys-region:          Back end methods.     (line 51)
* pgg-scheme-verify-region:              Back end methods.     (line 41)
* pgg-sign-region:                       User Commands.        (line 48)
* pgg-snarf-keys-region:                 User Commands.        (line 71)
* pgg-verify-region:                     User Commands.        (line 58)

File: pgg,  Node: Variable Index,  Prev: Function Index,  Up: Top

Variable Index
**************

[index]
* Menu:

* pgg-cache-passphrase:                  Caching passphrase.   (line 55)
* pgg-default-scheme:                    Selecting an implementation.
                                                               (line 21)
* pgg-default-user-id:                   Default user identity.
                                                               (line 11)
* pgg-errors-buffer:                     Getting output.       (line 11)
* pgg-gpg-use-agent:                     Caching passphrase.   (line 10)
* pgg-gpg-user-id:                       Default user identity.
                                                               (line 15)
* pgg-ignore-packet-checksum:            Parsing OpenPGP packets.
                                                               (line 20)
* pgg-output-buffer:                     Getting output.       (line 15)
* pgg-passphrase-cache-expiry:           Caching passphrase.   (line 61)
* pgg-passphrase-coding-system:          Caching passphrase.   (line 68)
* pgg-pgp-user-id:                       Default user identity.
                                                               (line 20)
* pgg-pgp5-user-id:                      Default user identity.
                                                               (line 25)
* pgg-scheme:                            Selecting an implementation.
                                                               (line 17)
* pgg-status-buffer:                     Getting output.       (line 19)