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man : pgg

File: pgg, Node: Top, Next: Overview, Up: (dir)

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::
* 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 backend.

* Menu:

* Initializing::
* Backend methods::
* Getting output::

File: pgg, Node: Initializing, Next: Backend 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 backend name.

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

4.2 Backend methods
===================

In each backend, 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: Backend methods, Up: Architecture

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

The output of the backend methods (*note Backend 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 1.2, November 2002

Everyone is permitted to copy and distribute verbatim copies
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0. PREAMBLE

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This License is a kind of "copyleft," which means that derivative
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It complements the GNU General Public License, which is a copyleft
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We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
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original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.

In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements," and any sections Entitled "Dedications." You
must delete all sections Entitled "Endorsements."

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.

You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.

If a section in the Document is Entitled "Acknowledgements,"
"Dedications," or "History," the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document
except as expressly provided for under this License. Any other
attempt to copy, modify, sublicense or distribute the Document is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation.

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 1.2
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: Backend methods. (line 29)
* pgg-scheme-encrypt-region: Backend methods. (line 16)
* pgg-scheme-encrypt-symmetric-region: Backend methods. (line 22)
* pgg-scheme-insert-key: Backend methods. (line 47)
* pgg-scheme-lookup-key: Backend methods. (line 11)
* pgg-scheme-sign-region: Backend methods. (line 34)
* pgg-scheme-snarf-keys-region: Backend methods. (line 51)
* pgg-scheme-verify-region: Backend 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)

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