(The problem of spam): Fix, reported by Cheng Gao

[gnus] / texi / pgg.texi

\input texinfo                  @c -*-texinfo-*-

@setfilename pgg

@set VERSION 0.1

@direntry
* PGG: (pgg).   Emacs interface to various PGP implementations.
@end direntry

@settitle PGG @value{VERSION}

@ifinfo
This file describes the PGG.

Copyright (C) 2003, 2004 Free Software Foundation, Inc.
Copyright (C) 2001 Daiki Ueno.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled "GNU
Free Documentation License".
@end ifinfo

@tex

@titlepage
@title PGG

@author by Daiki Ueno
@page

@vskip 0pt plus 1filll
Copyright @copyright{} 2001 Daiki Ueno.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled "GNU
Free Documentation License".
@end titlepage
@page

@end tex

@node Top
@top PGG
This manual describes 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.

@menu
* Overview::                    What PGG is.
* Prerequisites::               Complicated stuff you may have to do.
* How to use::                  Getting started quickly.
* Architecture::                
* Parsing OpenPGP packets::     
* Function Index::              
* Variable Index::              
@end menu

@node Overview
@chapter 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.

@node Prerequisites
@chapter 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, but Pretty Good Privacy version 2 or version
5 are also supported.  If you are new to such a system, I recommend that
you should look over the GNU Privacy Handbook (GPH) which is available
at @uref{http://www.gnupg.org/gph/}.

@node How to use
@chapter 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.

@lisp
(require 'pgg)
@end lisp

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

@lisp
(autoload 'pgg-encrypt-region "pgg"
  "Encrypt the current region." 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)
@end lisp

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

@node User Commands
@section 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 @code{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.

@deffn Command pgg-encrypt-region start end recipients &optional sign
Encrypt the current region between @var{start} and @var{end} for
@var{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 @var{sign} is non-nil, the function is request to
do a combined sign and encrypt.  This currently only work with GnuPG.
@end deffn

@deffn Command pgg-decrypt-region start end
Decrypt the current region between @var{start} and @var{end}.  If
decryption is successful, it replaces the current region contents (in
the accessible portion) with the resulting data.
@end deffn

@deffn Command pgg-sign-region start end &optional cleartext
Make the signature from text between @var{start} and @var{end}.  If the
optional third argument @var{cleartext} is non-@code{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.
@end deffn

@deffn Command pgg-verify-region start end &optional signature fetch
Verify the current region between @var{start} and @var{end}.  If the
optional third argument @var{signature} is non-@code{nil}, or the function
is called interactively, it is treated as the detached signature of the
current region.

If the optional 4th argument @var{fetch} is non-@code{nil}, or the
function is called interactively, we attempt to fetch the signer's
public key from the key server.
@end deffn

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

@deffn Command pgg-snarf-keys-region start end
Collect public keys in the current region between @var{start} and
@var{end}, and add them into the user's keyring.
@end deffn

@node Selecting an implementation
@section 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.

By default, if the variable @code{pgg-scheme} is not set, PGG searches the
registered scheme for an implementation of the requested service
associated with the named algorithm.  If there are no match, PGG uses
@code{pgg-default-scheme}.  In other words, there are two options to
control which command is used to process the incoming PGP armors.  One
is for encrypting and signing, the other is for decrypting and
verifying.

@defvar pgg-scheme
Force specify the scheme of PGP implementation for decrypting and verifying.
The value can be @code{gpg}, @code{pgp}, and @code{pgp5}.
@end defvar

@defvar pgg-default-scheme
Force specify the scheme of PGP implementation for encrypting and signing.
The value can be @code{gpg}, @code{pgp}, and @code{pgp5}.
@end defvar

@node Caching passphrase
@section Caching passphrase

PGG uses a simple passphrase caching mechanism, which is enabled by
default.

@defvar pgg-cache-passphrase
If non-@code{nil}, store passphrases.  The default value of this
variable is @code{t}.  If you were worry about security issue, however,
you could stop caching with setting it @code{nil}.
@end defvar

@defvar pgg-passphrase-cache-expiry
Elapsed time for expiration in seconds.
@end defvar

@node Default user identity
@section 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.

@defvar pgg-default-user-id
User ID of your default identity.  It defaults to the value returned
by @samp{(user-login-name)}.  You can customize this variable.
@end defvar

@defvar pgg-gpg-user-id
User ID of the GnuPG default identity.  It defaults to @samp{nil}.
This overrides @samp{pgg-default-user-id}.  You can customize this
variable.
@end defvar

@defvar pgg-pgp-user-id
User ID of the PGP 2.x/6.x default identity.  It defaults to
@samp{nil}.  This overrides @samp{pgg-default-user-id}.  You can
customize this variable.
@end defvar

@defvar pgg-pgp5-user-id
User ID of the PGP 5.x default identity.  It defaults to @samp{nil}.
This overrides @samp{pgg-default-user-id}.  You can customize this
variable.
@end defvar

@node Architecture
@chapter 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 backend.

@menu
* Initializing::                
* Backend methods::             
* Getting output::              
@end menu

@node Initializing
@section 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 @file{pgg-gpg.el}.  Once an
instance of @code{pgg-gpg} scheme is initialized, it's stored to the
variable @code{pgg-scheme-gpg-instance} and will be reused from now on.

@lisp
(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))))
@end lisp

The name of the function must follow the
regulation---@code{pgg-make-scheme-} follows the backend name.

@node Backend methods
@section Backend methods

In each backend, these methods must be present.  The output of these
methods is stored in special buffers (@ref{Getting output}), so that
these methods must tell the status of the execution.

@deffn Method pgg-scheme-lookup-key scheme string &optional type
Return keys associated with @var{string}.  If the optional third
argument @var{type} is non-@code{nil}, it searches from the secret
keyrings.
@end deffn

@deffn Method pgg-scheme-encrypt-region scheme start end recipients &optional sign
Encrypt the current region between @var{start} and @var{end} for
@var{recipients}.  If @var{sign} is non-nil, do a combined sign and
encrypt.  If encryption is successful, it returns @code{t}, otherwise
@code{nil}.
@end deffn

@deffn Method pgg-scheme-decrypt-region scheme start end
Decrypt the current region between @var{start} and @var{end}.  If
decryption is successful, it returns @code{t}, otherwise @code{nil}.
@end deffn

@deffn Method pgg-scheme-sign-region scheme start end &optional cleartext
Make the signature from text between @var{start} and @var{end}.  If the
optional third argument @var{cleartext} is non-@code{nil}, it does not
create a detached signature.  If signing is successful, it returns
@code{t}, otherwise @code{nil}.
@end deffn

@deffn Method pgg-scheme-verify-region scheme start end &optional signature
Verify the current region between @var{start} and @var{end}.  If the
optional third argument @var{signature} is non-@code{nil}, it is treated
as the detached signature of the current region.  If the signature is
successfully verified, it returns @code{t}, otherwise @code{nil}.
@end deffn

@deffn Method pgg-scheme-insert-key scheme
Retrieve the user's public key and insert it as ASCII-armored format.
On success, it returns @code{t}, otherwise @code{nil}.
@end deffn

@deffn Method pgg-scheme-snarf-keys-region scheme start end
Collect public keys in the current region between @var{start} and
@var{end}, and add them into the user's keyring.
On success, it returns @code{t}, otherwise @code{nil}.
@end deffn

@node Getting output
@section Getting output

The output of the backend methods (@ref{Backend methods}) is stored in
special buffers, so that these methods must tell the status of the
execution.

@defvar pgg-errors-buffer
The standard error output of the execution of the PGP command is stored
here.
@end defvar

@defvar pgg-output-buffer
The standard output of the execution of the PGP command is stored here.
@end defvar

@defvar pgg-status-buffer
The rest of status information of the execution of the PGP command is
stored here.
@end defvar

@node Parsing OpenPGP packets
@chapter 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.

@defun pgg-parse-armor string
List the sequence of packets in @var{string}.
@end defun

@defun pgg-parse-armor-region start end
List the sequence of packets in the current region between @var{start}
and @var{end}.
@end defun

@defvar pgg-ignore-packet-checksum
If non-@code{nil}, don't check the checksum of the packets.
@end defvar

@node Function Index
@chapter Function Index
@printindex fn

@node Variable Index
@chapter Variable Index
@printindex vr

@summarycontents
@contents
@bye

@c End: