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

@c tighten default spacing
@c @parskip 5pt plus 1 pt
@c @secheadingskip 10pt plus 6pt minus 3pt
@c @subsecheadingskip 8pt plus 6pt minus 3pt
@c @singlespace

@c %**start of header
@setfilename mailcrypt.info
@settitle @value{TITLE}
@setchapternewpage off
@c Entries for @command{install-info} to use
@dircategory Emacs
@direntry
* Mailcrypt: (mailcrypt).  An Emacs/PGP interface.
@end direntry
@c %**end of header

@syncodeindex ky cp
@syncodeindex vr cp
@syncodeindex fn cp

@set TITLE Mailcrypt
@set VERSION 3.5.8
@set UPDATED August 29, 1998

@ifinfo

This documentation describes Mailcrypt version @value{VERSION}.  This
documentation was last updated on @value{UPDATED}.

Copyright 1995 Patrick J. LoPresti
Copyright 1998 Leonard R. Budney
Copyright 2001 Brian Warner

The Mailcrypt program and this manual are published as free software.
You may redistribute and/or modify them under the terms of the GNU
General Public License as published by the Free Software Foundation;
either version 2, or (at your option) any later version.

Mailcrypt is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License along
with GNU Emacs; see the file COPYING.  If not, write to the Free
Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

@end ifinfo

@titlepage
@title Mailcrypt: An EMACS Interface to PGP
@subtitle Version @value{VERSION}
@subtitle @value{UPDATED}
@author Patrick J. LoPresti <patl@@lcs.mit.edu>
@author Leonard R. Budney <lbudney@@pobox.com>
@author Brian Warner <warner@@lothar.com>

@c Copyright page
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1995 Patrick J. LoPresti

Copyright @copyright{} 1998 Leonard R. Budney

Copyright @copyright{} 2001 Brian Warner

The Mailcrypt program and this documentation are published as free
software.  You may redistribute and/or modify them under the terms of
the GNU General Public License as published by the Free Software
Foundation; either version 2, or (at your option) any later version.

Mailcrypt is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License along
with GNU Emacs; see the file COPYING.  If not, write to the Free
Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

@end titlepage

@ifinfo
@node Top, Introduction, (dir), (dir)
@top Mailcrypt

Mailcrypt is an Emacs Lisp package which provides a simple but powerful
interface to cryptographic functions for mail and news.

This documentation describes Mailcrypt version @value{VERSION}.  The
documentation was last updated on @value{UPDATED}.

@end ifinfo

@menu
* Introduction::                Read this first.
* General Use::                 Everyday cryptographic functions.
* Remailer Support::            Interface to secure anonymous remailers.
* Passphrase Cache::            Letting Mailcrypt remember your passphrase
                                  for a while.
* Key Fetching::                Automatically retrieving public keys
                                  via finger or HTTP.
* Miscellaneous Configuration::  Random tweakables.
* Tips::                        Hints and tricks.
* Limitations::                 Things Mailcrypt does not do.
* References::                  Pointers to relevant information.
* Credits::                     Whom to blame.
* Index::                       Keys, variables, and functions.

 --- The Detailed Node Listing ---

Introduction

* Prerequisites::               Complicated stuff you may have to do.
* Installation::                Simple stuff you probably have to do.
* Command Overview::            A brief summary of the most common
                                  commands.

Installation

* Hooking into Rmail::          
* Hooking into VM::             
* Hooking into MH-E::           
* Hooking into Gnus::           
* Hooking into Mew::           

General Use

* Encrypting::                  Encrypting a message to one or more
                                  recipients.
* Signing::                     Clearsigning a message.
* Inserting Keys::              Extracting a key from your public key
                                  ring and inserting it.
* Decrypting::                  Decrypting a message to you.
* Verifying::                   Verifying the signature on a clearsigned
                                  message.
* Snarfing Keys::               Finding a key in the current message and
                                 adding it to your keyring.

Remailer Support

* Remailer Introduction::       A little about remailers in general.
* Remailer Quick Start::        Getting started quickly.
* Remailer Chains::             Creating custom chains of your very own.
* Response Blocks::             A way to let people reply to your
                                  anonymous messages.
* Pseudonyms::                  Who do you want to be today?
* Remailing Posts::             Posting to USENET anonymously or
                                  pseduonymously.
* Mixmaster Support::           Remailers for the truly paranoid.
* Remailer Security::           Caveats.
* Verifiable Pseudonyms::       Giving expression to the voices in your
                                  head.
* Remailer Tips::               Free advice.

Key Fetching

* Keyring Fetch::               Fetching from one or more other
                                  keyrings on the local system.
* Finger Fetch::                Fetching a key through finger.
* HTTP Fetch::                  Fetching a key off of the Web.
* GnuPG Fetch::                 Using GnuPG's internal keyserver interface.

Miscellaneous Configuration

* Alternate Keyring::           Specifying a different file to act
                                  like your public keyring.
* Comment Field::               Burma
                                  Shave
* Mode Line::                   Changing that "MC-w" and "MC-r" stuff
* Key Bindings::                Which keys cause which actions.
* Nonstandard Paths::           Useful if your PGP installation is weird.

References

* Online Resources::            Recreational reading with a purpose.
* Key Servers::                 Keepers of the Global Keyring.
* Mailing List::                Staying informed while pumping the
                                  authors' egos.
* Politics::                    Anarcho-foobarism.
@end menu

@node Introduction, General Use, Top, Top
@chapter Introduction

Mailcrypt is an Emacs Lisp package which provides a simple but powerful
interface to cryptographic functions for mail and news.  With Mailcrypt,
encryption becomes a seamlessly integrated part of your mail and news
handling environment.

This manual is long because it is complete.  All of the information you
need to get started is contained in this Introduction alone.

@menu
* Prerequisites::               Complicated stuff you may have to do.
* Installation::                Simple stuff you probably have to do.
* Command Overview::            A brief summary of the most common
                                  commands.
@end menu

@node Prerequisites, Installation, Introduction, Introduction
@section Prerequisites

Mailcrypt requires version 19 or higher of GNU Emacs.  Mailcrypt has
been tested on a variety of systems under both FSF Emacs and XEmacs.

Mailcrypt requires Pretty Good (tm) Privacy, usually known as PGP.  This
document assumes that you have already obtained and installed PGP and
that you are familiar with its basic functions.  The best way to become
familiar with these functions is to read the @cite{PGP User's Guide}, at
least Volume I.

For more information on obtaining and installing PGP, refer to the MIT
PGP home page at @file{http://web.mit.edu/network/pgp.html}.

Although Mailcrypt may be used to process data in arbitrary Emacs
buffers, it is most useful in conjunction with other Emacs packages for
handling mail and news.  Mailcrypt has specialized support for Rmail
(@pxref{Rmail, Rmail, Reading Mail with Rmail, emacs, The GNU Emacs
Manual}), VM (@pxref{Top, VM, Introduction, vm, The VM User's Manual}),
MH-E, and Gnus (@pxref{Top, Gnus, Overview, gnus, The Gnus Manual}).
Information on the general use of these packages is beyond the scope of
this manual.

@node Installation, Command Overview, Prerequisites, Introduction
@section Installation

If Mailcrypt is not installed on your system, obtain the latest version
from the Mailcrypt home page at @file{http://mailcrypt.sourceforge.net}
and follow the instructions in the file @file{INSTALL}.

Next, decide what version of PGP you are using.  Versions 3.5 and higher
of Mailcrypt support multiple versions of PGP.  To choose a version,
add the following lines to your @file{.emacs} file:

@lisp
(load-library "mailcrypt") ; provides "mc-setversion"
(mc-setversion "2.6")    ; for PGP 2.6 (default); also "5.0" and "gpg"
@end lisp

Next, teach your Emacs how and when to load the Mailcrypt functions and
install the Mailcrypt key bindings.  Almost all Emacs major modes
(including mail and news handling modes) have corresponding "hook"
variables which hold functions to be run when the mode is entered.  All
you have to do is add the Mailcrypt installer functions to the
appropriate hooks; then the installer functions will add the Mailcrypt
key bindings when the respective mode is entered.

Specifically, begin by placing the following lines into your
@file{.emacs} file (or the system-wide @file{default.el} file):

@lisp
(autoload 'mc-install-write-mode "mailcrypt" nil t)
(autoload 'mc-install-read-mode "mailcrypt" nil t)
(add-hook 'mail-mode-hook 'mc-install-write-mode)
@end lisp

Then add additional lines for your own mail and news packages as
described below.

@menu
* Hooking into Rmail::          
* Hooking into VM::             
* Hooking into MH-E::           
* Hooking into Gnus::           
* Hooking into Mew::           
@end menu

@node Hooking into Rmail, Hooking into VM, Installation, Installation
@subsection Hooking into Rmail

To hook Mailcrypt into Rmail, use the following lines:

@lisp
(add-hook 'rmail-mode-hook 'mc-install-read-mode)
(add-hook 'rmail-summary-mode-hook 'mc-install-read-mode)
@end lisp

Using Emacs version 20.3 or higher, you should use the following
lines instead:

@lisp
(add-hook 'rmail-show-message-hook 'mc-install-read-mode)
(add-hook 'rmail-summary-mode-hook 'mc-install-read-mode)
@end lisp

@node Hooking into VM, Hooking into MH-E, Hooking into Rmail, Installation
@subsection Hooking into VM

To hook Mailcrypt into VM, use the following lines:

@lisp
(add-hook 'vm-mode-hook 'mc-install-read-mode)
(add-hook 'vm-summary-mode-hook 'mc-install-read-mode)
(add-hook 'vm-virtual-mode-hook 'mc-install-read-mode)
(add-hook 'vm-mail-mode-hook 'mc-install-write-mode)
@end lisp

@node Hooking into MH-E, Hooking into Gnus, Hooking into VM, Installation
@subsection Hooking into MH-E

To hook Mailcrypt into MH-E, use the following lines:

@lisp
(add-hook 'mh-folder-mode-hook 'mc-install-read-mode)
(add-hook 'mh-letter-mode-hook 'mc-install-write-mode)
@end lisp

@node Hooking into Gnus, Hooking into Mew, Hooking into MH-E, Installation
@subsection Hooking into Gnus

To hook Mailcrypt into Gnus, use the following lines:

@lisp
(add-hook 'gnus-summary-mode-hook 'mc-install-read-mode)
(add-hook 'message-mode-hook 'mc-install-write-mode)
(add-hook 'news-reply-mode-hook 'mc-install-write-mode)
@end lisp

@node Hooking into Mew,  , Hooking into Gnus, Installation
@subsection Hooking into Mew

To hook Mailcrypt into Mew, use the following lines:

@lisp
(add-hook 'mew-message-mode-hook 'mc-install-read-mode)
(add-hook 'mew-summary-mode-hook 'mc-install-read-mode)
(add-hook 'mew-draft-mode-hook 'mc-install-write-mode)
@end lisp

Note that Mew already has extensive support for MIME-encoded encrypted
and/or signed messages (using the ``multipart/encrypted'' and
``application/pgp-encrypted'' formats specified by RFC3156). Using
MailCrypt within Mew is most useful for traditional ``inline'' armored
encrypted/signed messages.

@node Command Overview,  , Installation, Introduction
@section Command Overview

All Mailcrypt commands are (by default) activated by three-character key
sequences which begin with @kbd{C-c /}.  The most common operations are:

@table @emph

@item Encrypting a Message
@kbd{C-c / e} encrypts a message using the recipient's (or recipients')
public key(s).  @xref{Encrypting, , Encrypting a Message}.

@item Decrypting a Message
@kbd{C-c / d} decrypts a message using your secret key.
@xref{Decrypting, , Decrypting a Message}.

@item Signing a Message
@kbd{C-c / s} clearsigns a message using your secret key.
@xref{Signing, , Signing a Message}.

@item Verifying a Signature
@kbd{C-c / v} verifies the signature on a clearsigned message using the
sender's public key.  @xref{Verifying, , Verifying a Signature}.

@end table

These functions and others are documented in detail in the following
chapters.

Any time you are composing or reading mail or news, you can get a
summary of the available commands by typing @kbd{C-h m}.  If you are
running Emacs under X, an even easier way to see the available commands
is to access the @code{Mailcrypt} pull-down menu.

@node  General Use, Remailer Support, Introduction, Top
@chapter General Use

@findex mc-setversion
By default, Mailcrypt assumes you are using one of the PGP 2.6.x
versions.  This permits backward compatibility for the millions of
satisfied users of Mailcrypt 3.4 worldwide.  If you wish to specify a
different version of PGP, use this function. Its action is the same as
setting the variable @code{mc-default-scheme}. For a list of supported
versions, press the tab key. "2.6" means 2.6.x, the original (and default). 
"5.0" is pgp 5.0. "gpg" is GnuPG.

@findex mc-read-mode
@findex mc-write-mode
Mailcrypt works by providing two minor modes for interfacing with
cryptographic functions: @code{mc-read-mode} and @code{mc-write-mode}.
@code{mc-read-mode} provides key bindings for processing messages which
you have received; @code{mc-write-mode} provides key bindings for
processing messages which you are about to send.  These minor modes will
indicate when they are active by placing a characteristic string in the
mode line (@pxref{Mode Line}).  They will also add a @code{Mailcrypt}
pull-down menu to the menu bar.

@findex mc-install-read-mode
@findex mc-install-write-mode
The normal installation procedure (@pxref{Installation}) will arrange
for the appropriate mode to be active when you read and compose mail and
news.  But you may want to use Mailcrypt's functions at other times; to
do so, you can call @code{mc-install-read-mode} or
@code{mc-install-write-mode} directly.  For example, if you were editing
a file in Text mode and wanted to digitally sign it, you would type
@kbd{M-x mc-install-write-mode}, then @kbd{C-c / s} (@pxref{Signing}).

Once one of the Mailcrypt modes is active, you can get a summary of the
available functions by typing @kbd{C-h m} or by examining the
@code{Mailcrypt} pull-down menu.

The description of each function below includes which of the modes has a
binding for that function.

@menu
* Encrypting::                  Encrypting a message to one or more
                                  recipients.
* Signing::                     Clearsigning a message.
* Inserting Keys::              Extracting a key from your public key
                                  ring and inserting it.
* Decrypting::                  Decrypting a message to you.
* Verifying::                   Verifying the signature on a clearsigned
                                  message.
* Snarfing Keys::               Finding a key in the current message and
                                 adding it to your keyring.
@end menu

@node Encrypting, Signing, General Use, General Use
@section Encrypting a Message

@findex mc-encrypt
@kindex C-c / e
The function @code{mc-encrypt} will encrypt a message in the current
buffer.  @code{mc-write-mode} binds this function to @kbd{C-c / e} by
default.

When this function is called, Mailcrypt will prompt you for a
comma-separated list of recipients.  If called from a mail composition
buffer, the recipient list will default to the Email addresses in the
@samp{To}, @samp{CC}, and @samp{BCC} lines of the message.

@vindex mc-encrypt-for-me
If you want to be able to decrypt the message yourself, you need to add
yourself to the recipient list.  If you always want to do so, set the
variable @code{mc-encrypt-for-me} to @code{t}.  (Note that Mailcrypt
overrides the PGP "encrypttoself" flag; use this variable instead.)

If you provide an empty recipient list, Mailcrypt will ASCII-armor the
message without encrypting it.

@vindex mc-pgp-always-sign
Once you have edited the recipient list to your satisfaction, type
@kbd{@key{RET}} to accept it.  You will then be asked whether you want
to sign the message; answer @kbd{y} or @kbd{n}.  You can avoid this
question by setting the variable @code{mc-pgp-always-sign}:  A value of
@code{t} means "yes", a value of @code{'never} means "no".

If you elect to sign the message, Mailcrypt will prompt you for the
appropriate passphrase unless it is cached (@pxref{Passphrase Cache}).

@vindex mc-pre-encryption-hook
@vindex mc-post-encryption-hook
Mailcrypt will then pass the message to PGP for processing.  Mailcrypt
will call the functions listed in @code{mc-pre-encryption-hook} and
@code{mc-post-encryption-hook} immediately before and after processing,
respectively.  The encrypted message will then replace the original
message in the buffer.  You can undo the encryption with the normal
Emacs undo command @kbd{C-x u} (@pxref{Undo, Emacs Undo, Undoing
Changes, emacs, The GNU Emacs Manual}).

If an error occurs, Mailcrypt will display an appropriate diagnostic.
If you do not have the public key for one of the specified recipients,
Mailcrypt will offer to try to fetch it for you (@pxref{Key Fetching}).

@vindex mc-pgp-user-id
The default key for signing is the first one on the secret key ring
which matches the string @code{mc-pgp-user-id}; this defaults to
@code{(user-login-name)}.  Note that this differs from PGP's normal
default, which is to use the first of @emph{all} of the secret keys.  To
mimic PGP's behavior, set this variable to @code{""}. This variable is
specific to pgp 2.6.x; @code{mc-pgp50-user-id} and @code{mc-gpg-user-id} are
the corresponding variables for pgp 5.0 and GnuPG.

If you want to use a secret key other than your default for signing the
message, pass a prefix argument to @code{mc-encrypt}.  (That is, type
@kbd{C-u C-c / e}.)  Mailcrypt will prompt for a string and will sign with
the first key on your secret keyring which matches that string.  It will
be assumed that you want to sign the message, so you will not be
prompted.

@node Signing, Inserting Keys, Encrypting, General Use
@section Signing a Message

@findex mc-sign
@kindex C-c / s
The function @code{mc-sign} will clearsign a message in the current
buffer.  @code{mc-write-mode} binds this function to @kbd{C-c / s} by
default.

When this function is called, Mailcrypt will prompt you for the
appropriate passphrase unless it is cached (@pxref{Passphrase Cache}).

@vindex mc-pre-signature-hook
@vindex mc-post-signature-hook
Mailcrypt will then pass the message to PGP for processing.  Mailcrypt
will call the functions listed in @code{mc-pre-signature-hook} and
@code{mc-post-signature-hook} immediately before and after processing,
respectively.  The signed message will replace the original message in
the buffer.  @emph{Do not} edit the message further with the signature
attached, because the signature would then be incorrect.  If you
discover you need to edit a message after you have signed it, remove the
signature first with the normal Emacs undo command @kbd{C-x u}
(@pxref{Undo, Emacs Undo, Undoing Changes, emacs, The GNU Emacs
Manual}).

The variable @code{mc-pgp-user-id} controls which secret key is used for
signing; it is described in @ref{Encrypting, , Encrypting a Message}.
To use a different secret key, pass a prefix argument to @code{mc-sign}.
(That is, type @kbd{C-u C-c / s}.)  Mailcrypt will prompt for a string
and will sign with the first key on your secret keyring which matches
that string.

@node Inserting Keys, Decrypting, Signing, General Use
@section Inserting a Public Key Block

@findex mc-insert-public-key
@kindex C-c / x
The function @code{mc-insert-public-key} will extract a key from your
public keyring and insert it into the current buffer.
@code{mc-write-mode} binds this function to @kbd{C-c / x} by default.

This function is useful for sending your public key to someone else or
for uploading it to the key servers (@pxref{Key Servers}).  The inserted
key will be the first one on your public key ring which matches the
string @code{mc-pgp-user-id} (@pxref{Encrypting, , Encrypting a
Message}).

You may want to insert a different public key instead; for example, you
may have signed someone's key and want to send it back to them.  To do
so, pass a prefix argument to @code{mc-insert-public-key}.  (That is,
type @kbd{C-u C-c / x}.)  You will be prompted for a string; the first key
on your public key ring which matches that string will be inserted.

@node Decrypting, Verifying, Inserting Keys, General Use
@section Decrypting a message

@findex mc-decrypt
@kindex C-c / d
The function @code{mc-decrypt} will decrypt a message in the current
buffer.  @code{mc-read-mode} binds this function to @kbd{C-c / d} by
default.

When this function is called, Mailcrypt will prompt you for the
appropriate passphrase unless it is cached (@pxref{Passphrase Cache}).

The encrypted message will then be passed to PGP for processing.  If you
are not in a mail buffer, the decrypted message will replace the
encrypted form.  If you are in a mail buffer, you will be prompted
whether to do the replacement.

If you answer @kbd{n}, you will be placed in a new mail reading buffer
to view the decrypted message.  This new mail reading buffer will have
no corresponding disk file; its purpose is to provide you with all of
your usual reply and citation functions without requiring you to save
the message in decrypted form.  Type @kbd{q} to kill this buffer.

@vindex mc-always-replace
You can avoid the question of whether to replace the encrypted message
by setting the variable @code{mc-always-replace}.  A value of @code{t}
means "yes"; a value of @code{'never} means "no".

If the encrypted message is also signed, PGP will attempt to verify the
signature.  If the verification fails because you lack the necessary
public key, Mailcrypt will offer to fetch it for you (@pxref{Key
Fetching}).

Look in the @code{*MailCrypt*} buffer to see the result of the signature
verification.

@node Verifying, Snarfing Keys, Decrypting, General Use
@section Verifying a Signature

@findex mc-verify
@kindex C-c / v
The function @code{mc-verify} will verify the cleartext signature on a
message in the current buffer.  @code{mc-read-mode} binds this function
to @kbd{C-c / v} by default.

When this function is called, Mailcrypt will pass the message to PGP for
processing and report whether or not the signature verified.

If the signature failed to verify because you lack the necessary public
key, Mailcrypt will offer to fetch it for you (@pxref{Key Fetching}).

@node Snarfing Keys,  , Verifying, General Use
@section Snarfing a Key

@findex mc-snarf
@kindex C-c / a
The function @code{mc-snarf} will add to your keyring any keys in the
current buffer.  @code{mc-read-mode} binds this function to @kbd{C-c / a}
by default.

This function is useful when someone sends you a public key in an Email
message.

@node Remailer Support, Passphrase Cache, General Use, Top
@chapter Remailer Support
This is a long chapter describing an advanced feature; you
may want to skip it on first reading.

@menu
* Remailer Introduction::       A little about remailers in general.
* Remailer Quick Start::        Getting started quickly.
* Remailer Chains::             Creating custom chains of your very own.
* Response Blocks::             A way to let people reply to your
                                  anonymous messages.
* Pseudonyms::                  Who do you want to be today?
* Remailing Posts::             Posting to USENET anonymously or
                                  pseduonymously.
* Mixmaster Support::           Remailers for the truly paranoid.
* Remailer Security::           Caveats.
* Verifiable Pseudonyms::       Giving expression to the voices in your
                                  head.
* Remailer Tips::               Free advice.
@end menu

@node Remailer Introduction, Remailer Quick Start, Remailer Support, Remailer Support
@section Remailer Introduction
There are several anonymous remailer services running on the Internet.
These are programs that accept mail, strip off information that would
identify the origin of the message, and forward the mail to the
designated recipient.  This simple scheme alone, however, is insecure if
the anonymous remailer becomes compromised (or if the remailer was set
up by an untrustworthy party in the first place).  Whoever controls the
remailer will have access to the identities of senders and recipients.

One solution to this is to use @emph{chains} of remailers that send
encrypted messages.  For example, suppose Bill wishes to send a message
to Louis using a chain of remailers A, B, and C.  He writes the message
(possibly encrypting it for Louis), then encrypts the result (including
the fact that Louis is the recipient) using a public key supplied by
remailer C.  Then he encrypts this result using a public key supplied by
remailer B.  Then he encrypts this result using a public key supplied by
A and sends the message to A.

When A receives the message, it decrypts the message with its key to
produce something encrypted for B, learns that the next remailer in the
chain is B, strips off the information that the message came from Bill,
and sends the message on to B.  B then decrypts, learns that the next
remailer in the chain is C, strips off the information that the message
came from A, and sends the result to C.  C then decrypts, learns that
the destination is Louis, strips off the information that the message
came from B, and sends the result to Louis.  With this arrangement, only
A knows that the original message came from Bill, and only C knows that
the intended recipient is Louis.  In general, the sender and recipient
can both be known only to someone who has compromised all remailers in
the chain.

If Bill wishes, he can include an encrypted "response block" in his
message to Louis, which defines a remailer chain that Louis can use to
reply to Bill.  Louis can use this chain without knowing who Bill is --
only the last remailer in the chain need know the final recipient.  Bill
can also establish a @emph{pseudonym} for use in signing his anonymous
messages.

Mailcrypt includes facilities for sending messages via remailers, for
defining chains of remailers, for generating response blocks, and for
using pseudonyms.

@node Remailer Quick Start, Remailer Chains, Remailer Introduction, Remailer Support
@section Remailer Quick Start

To use Mailcrypt's remailing facilities, you need to configure them
first.  Begin with the following steps:

@enumerate

@item
Do @samp{finger rlist@@mixmaster.shinn.net > ~/.remailers}. This
will create a Levien-format list of remailers in the file
@file{.remailers} in your home directory (see the variable
@code{mc-levien-file-name}). Mailcrypt will parse this the first time
you access a remailer function. @samp{rlist@@noisebox.remailer.org} is
another good place to get this list.

@item
Look over the @file{.remailers} file and find the ones you want to use.

@item
Add their PGP public keys to your keyring. You can @code{finger
remailer-keys@@mixmaster.shinn.net} for an armored keyring full of
remailer public keys. Note that Mailcrypt @emph{requires} that you
have the public keys of all the remailers you want to use, and
therefore that the remailers support PGP encryption.

@end enumerate

@quotation
@emph{Note:} These steps need only be done once, although repeating them
from time to time is probably a good idea, since remailers come and go.
@end quotation

Now test the remailer functions.  First compose an outgoing Email
message (using @kbd{C-x m}, for example) addressed to yourself.  Type
@kbd{C-c / r}.  Choose a remailer; use @kbd{@key{TAB}} to get completion
on its name.  The buffer will be rewritten for anonymous mailing through
that remailer.

Note that you can only select a single remailer when you rewrite the
message. To send the message through multiple hops, either rewrite the
message multiple times, or define a @emph{chain} of remailers that can
be referred to like a single remailer. Remailer chains are described
in the next section.

The remailer list and keyrings can also be obtained via HTTP.
@file{http://anon.efga.org/Remailers/Settings} and
@file{http://mixmaster.shinn.net/stats/settings/index.html} have lists
of URLs from which these can be retrieved.


@node Remailer Chains, Response Blocks, Remailer Quick Start, Remailer Support
@section Remailer Chains

@findex mc-remailer-encrypt-for-chain
@kindex C-c / r
@code{mc-write-mode} binds the function
@code{mc-remailer-encrypt-for-chain} to the key @kbd{C-c / r}.  This
function rewrites the message for a remailer or chain.  The resulting
buffer is just a new Email message, so it can itself be rewritten for
another remailer; this is one way to manually construct a remailer
chain.

Mailcrypt also has powerful facilities for defining automatic chains.
We will start with an example.  Suppose you have put the following into
your @file{.emacs} file:

@vindex mc-remailer-user-chains
@lisp
(setq mc-remailer-user-chains
      '(("Foo" "alumni" "robo")
        ("Bar" (shuffle-vector ["replay" "flame" "spook"]))
        ("Baz" "Foo" "Bar" "rahul" "Bar")
        ("Quux" 4)))
@end lisp

This code defines four chains.  The first is named "Foo" and consists of
"alumni" and "robo", in that order.  The second is named "Bar" and
consists of "replay", "flame", and "spook" in some random order (a
different order will be chosen each time the chain is used).  The third
is named "Baz" and consists of 9 remailers: The two from "Foo", followed
by a permutation of the three from "Bar", followed by "rahul", followed
by another permutation of the three from "Bar".  Finally, the fourth is
named "Quux" and consists of a random permutation of the four best
remailers as ordered in the @file{~/.remailers} file.

Now whenever you are prompted for a "remailer or chain", the chains
"Foo", "Bar", "Baz", and "Quux" will be available, including
@kbd{@key{TAB}} completion on their names.  By capitalizing their names,
you guarantee they will show up near the top of the completion list if
you type @kbd{@key{TAB}} on an empty input.

Now for the gritty details.  @code{mc-remailer-user-chains} is a list of
chain definitions.  A chain definition is a list whose first element is
the name (a string) and whose remaining elements form a @dfn{remailer
list}.  Each element of a remailer list is one of the following:

@enumerate

@item
A raw remailer structure.  This is the base case, but you will probably
never want nor need to deal with these directly.

@item
A string naming another remailer chain to be spliced in at this point.

@item
A positive integer N representing a chain to be spliced in at this point
and consisting of a random permutation of the top N remailers as ordered
in the @file{~/.remailers} file.

@item
An arbitrary Emacs Lisp form, which should return another remailer
list which will be spliced in at this point and recursively
evaluated.  Mmmm, Lisp.

@end enumerate
So, in the example "Bar" above, @code{shuffle-vector} is actually a Lisp
primitive which returns a random permutation of the argument vector.
(Which brings up a side note: A remailer list can be a vector instead of
a list if you like.)

So where do the definitions for "replay" etc. come from?

@vindex mc-remailer-internal-chains
There is another variable, @code{mc-remailer-internal-chains}, which has
the same format as @code{mc-remailer-user-chains}.  In fact, the
concatenation of the two is always used internally when resolving chains
by name.  The "internal chains" are normally generated automatically
from a Levien-format remailer list, which lives in @file{~/.remailers}
by default and is parsed at startup time.  The parser creates several
chains, each containing a single remailer, and names each chain after
the respective remailer.

Thus "replay" (for example) is actually the name of a @emph{chain} whose
single element is the remailer at <remailer@@replay.com>.  So "replay"
is a valid name of a chain to include in the definition of another
chain, as was done above in the definition of "Bar".

@node Response Blocks, Pseudonyms, Remailer Chains, Remailer Support
@section Response Blocks

@kindex C-c / b
Mailcrypt can generate a response block for you.  Just type @kbd{C-c / b}
in an outgoing mail buffer.  That will prompt you for a chain to use,
and will insert the response block at point.  Note that you can use any
chain you want for your response block; it need not be related to the
chain you (later) use to remail the message.

If instead you type @kbd{C-u C-c / b}, you will be dropped into a
recursive edit of the innermost part of the response block.  This text
is what you will see at the top of the message when the response block
is used.  This text is the only way to identify the response block,
since it will be used to mail you through anonymous remailers.

You probably won't need to use the @kbd{C-u} feature, since by default
the response block contains the date, @samp{To} field, and @samp{From}
field of the message you are composing.  However, if you want your
response block to point to a USENET newsgroup instead of your Email
address, you may edit the innermost part of the response block to have a
@samp{Newsgroups} line instead of a @samp{To} line.

Inserting a response block also updates the @samp{Reply-to} hashmark
header field.  So, when your recipient replies to your message, the
reply will automatically be addressed properly.  This only works if the
last remailer in the chain used to encrypt the @emph{message} supports
hashmarks (the response block chain doesn't matter).  If the last
remailer does not support hashmarks, Mailcrypt will generate an error
when you try to use the chain.

Note that you should insert your response block before you encrypt the
message for remailing.  Also, see @ref{Remailer Security}.

@node Pseudonyms, Remailing Posts, Response Blocks, Remailer Support
@section Pseudonyms

@kindex C-c / p
Mailcrypt supports pseudonyms.  Type @kbd{C-c / p} in an outgoing message
buffer and you will be prompted for a pseudonym to use.  Your pseudonym
will show up in the @samp{From} line that the recipient sees.  Your
pseudonym may either be a complete @samp{From} line (including an Email
address), or just a full name (with no Email address).  In the latter
case, the Email address will automatically be set to <x@@x.x>, an invalid
address designed to prevent sendmail from going rewrite-happy.

If you have one or more pseudonyms which you normally use, and you
aren't afraid of revealing them if your account is compromised, you can
set up a default list of pseudonyms with lines like the following in
your @file{.emacs} file:

@vindex mc-remailer-pseudonyms
@lisp
(setq mc-remailer-pseudonyms
      '("Elvis Presley" "Vanna White" "Charles Manson"))
@end lisp

Then those names will be available for completion when you are
prompted for your pseudonym.

You should insert your pseudonym before you insert a response block, so
that the response block will contain the @samp{From} line as well as the
@samp{To} line.  That way you can tell who you were pretending to be
when you get a reply to your message.

Note: Many remailers do not support pseudonyms.  In addition, the Levien
format does not (yet) indicate which do and which do not, so Mailcrypt
can't warn you when your pseudonym isn't going to work.  The only way to
be sure is to send yourself a test message, and to try different
remailers until you find one or more which work.  On the bright side,
only the last remailer in the chain needs to provide such support; none
of the others matter.

@node Remailing Posts, Mixmaster Support, Pseudonyms, Remailer Support
@section Remailing Posts
Mailcrypt knows how to rewrite USENET posts for anonymous or
pseudonymous remailing.  Just compose your post or followup normally,
and use @kbd{C-c / r} to rewrite it for a remailer chain.  You don't
even need to start your newsreader to make a post; you can just compose
a message in mail mode and replace the @samp{To} line with a
@samp{Newsgroups} line before doing @kbd{C-c / r}.

@vindex mc-remailer-preserved-headers
Mailcrypt will generate an error if the last remailer in the chain does
not have both the @code{post} and @code{hash} (hashmarks) properties.
The hashmarks are used to preserve @samp{References} and similar
headers, so your anonymous or pseudonymous followups will thread
properly.  The variable @code{mc-remailer-preserved-headers} controls
which headers are preserved when rewriting a message, but you should not
need to change it since the default value is reasonable.

Before rewriting, you can use @kbd{C-c / p} to insert your pseudonym,
and @kbd{C-c / b} to insert your response block, just like when
composing mail.  In this case, the response block will include the
@samp{From} line and the @samp{Newsgroups} line (which is the news
analogue to the @samp{To} line).

@node Mixmaster Support, Remailer Security, Remailing Posts, Remailer Support
@section Mixmaster Support

@dfn{Mixmaster} is a new kind of remailer which provides excellent
security against traffic analysis and replay attacks.  (For more
information on these attacks and Mixmaster, see Lance Cottrell's home
page at @file{http://www.obscura.com/~loki/}.

If you do not use Mixmaster, you may skip this section entirely;
Mailcrypt's default configuration treats Mixmaster as if it did not
exist.

If you have the Mixmaster executable installed, you can tell Mailcrypt
to use it by placing lines like the following into your @file{.emacs}
file:

@vindex mc-mixmaster-path
@vindex mc-mixmaster-list-path
@lisp
(setq mc-mixmaster-path "mixmaster")
(setq mc-mixmaster-list-path "/foo/bar/baz/type2.list")
@end lisp

@code{mc-mixmaster-path} is a string representing the Mixmaster
executable.  @code{mc-mixmaster-list-path} is the complete path to the
@code{type2.list} file.

Once these variables are defined, Mailcrypt will automatically try to
use the Mixmaster executable whenever possible.  Specifically, when you
rewrite a message for a chain, Mailcrypt will find maximal length
sub-chains which have the @code{mix} property and will use the Mixmaster
executable to rewrite for those sub-chains.

This allows arbitrary intermingling of Mixmaster and normal (also called
@dfn{Type 1}) remailers, but you should note that this is @emph{not
recommended}.  The recommended procedure is to have a single Mixmaster
sub-chain which is most or all of the whole chain.

There are advantages and disadvantages to having the Mixmaster sub-chain
at the end of the whole chain.  The primary advantage is that Mixmaster
remailers support multiple recipients.  The primary disadvantages are
that they do not support pseudonyms nor posting.

So here, as always, it is the last element of the chain which needs to
support the special features you want.  In general, the remaining
elements do not matter, and the superior security of Mixmaster remailers
is a good argument for using them for the bulk of your chains.

@findex mc-demix
Mixmaster remailers also have a "Type 1 compatibility mode" which you
might want to invoke to use a pseudonym or make a post.  You can do this
with the function @code{mc-demix}.  Here is an example of its use:

@lisp
(setq mc-remailer-user-chains
      '(("Foo" "vishnu" "spook")
        ("Bar" "Foo" (mc-demix "replay"))))
@end lisp

This makes "Bar" a chain of three remailers, and guarantees that the
last one ("replay") will be used in compatibility mode.

Note that Mixmaster remailers cannot be used for response blocks.
Mailcrypt will ignore the @code{mix} property when generating a response
block.

@node Remailer Security, Verifiable Pseudonyms, Mixmaster Support, Remailer Support
@section Remailer Security

Keep in mind that there is only one person fully qualified to protect
your privacy: @emph{you}.  You are responsible for obtaining a list of
remailers and their public keys; you are responsible for choosing which
of them to use and in what order.  There are public lists of remailers
and keys (the Quick Start section above relies on them), but you pay for
the convenience by putting your trust in a single source.  This is one
reason Mailcrypt does not access these public lists automatically; you
need to get into the habit of watching what goes on behind the scenes.
You should also try to learn something about the remailers themselves,
since you are relying on them to help protect your privacy.

How many remailers should you include in your chain, and how should
you choose them?  That depends on whom you perceive as a threat.  If
the threat is your ex-spouse or your boss, even a single remailer is
probably adequate (more won't hurt, but will cost in latency).  If the
threat is the Church of Scientology, you probably want to use a fair
number of remailers across multiple continents.  If the threat is a
major world government, well, best of luck to you.

Also, there is a huge difference between chains suitable for regular
messages and chains suitable for response blocks.  Some remailers don't
even keep mail logs (at least, their operators claim they do not), so it
may be literally impossible to trace a message back to you after the
fact if you chain it through enough remailers.  Response blocks, on the
other hand, have your identity buried in there @emph{somewhere}.  In
principle, at least, it is possible to compromise the keys of all the
remailers in the chain and decrypt the response block.  So you should
either use very long and strong chains for your response blocks, avoid
using response blocks at all, or only use response blocks which
themselves ultimately point to a newsgroup.

@node Verifiable Pseudonyms, Remailer Tips, Remailer Security, Remailer Support
@section Verifiable Pseudonyms
Here is a plausible sequence of operations when using the remailer
support in Mailcrypt:

@enumerate

@item
You create a public/private PGP key pair.  You give it a User ID which
is your pseudonym.  You upload the public key to the key servers or
otherwise distribute it.  (Be aware that anyone who compromises your
account can read the IDs on your secret keyring, thus discovering your
verifiable pseudonyms.)
   
@item
You compose an Email message, Email reply, news post, or news followup.

@item
You insert your pseudonym with @kbd{C-c / p}.

@item
(Optional) You insert your response block with @kbd{C-c / b}.

@item
You type @kbd{C-c / s} to sign the message.  The @code{mc-sign} function
understands pseudonyms.

@item
You type @kbd{C-c / r} to rewrite the message for remailing.  (Or use
@kbd{C-u C-c / r} to view each step of the rewriting as it happens.)

@item
You type @kbd{C-c C-c} to send the message.

@end enumerate

Now the recipient(s), reading your message through mail or news, can
verify your pseudonymous signature; thus you have started to create a
verifiable pseudonymous identity.  If you use it consistently, it will
develop a reputation of its own.  With Mailcrypt, using a pseudonym is
almost as easy as using your real name (and your followups in news
will even thread properly).  Welcome to the new age of letters@dots{}

@node Remailer Tips,  , Verifiable Pseudonyms, Remailer Support
@section Remailer Tips

This is a collection of tips for using Mailcrypt's remailer support.

@itemize @bullet

@item
@vindex mc-levien-file-name
Read and understand the @file{.remailers} file.  Other sources for
this list include @file{http://www.chez.com/frogadmin/MyCypSta1.txt}
and @file{http://anon.efga.org/Remailers/rlist}.  If all of these
servers have gone away by the time you read this, track down a
comparable service elsewhere.  (Do a web search for ``anonymous
remailer list'', ask around in @file{news:alt.privacy.anon-server}, or,
as a last resort, @file{news:alt.security.pgp}.)  Check the
documentation (@kbd{C-h v}) for the variable
@code{mc-levien-file-name} for a description of Levien format.

@item
Mailcrypt needs to be able to encrypt a message to each remailer in
the chain, so it needs access to their public keys, in a keyring
usable by the currently selected backend.  Keyrings containing keys
for all the well-known remailers are usually available from the same
places as the remailer lists above:
@file{http://www.chez.com/frogadmin/Keys/dsskeys.asc},
@file{http://anon.efga.org/Remailers/TypeIList/pubring.asc}.

@c TODO: With the GPG backend, you can take one of the .pkr or .gpg -format
@c keyrings, save it to ~/remailer-pubring.pgp, and the remailer encryption
@c functions will automatically add that keyring to the set used when working
@c with remailers. This means you don't have to clutter your normal keyring
@c with the remailer keys.

@item
The relevant remailer properties are @code{pgp} (required), @code{hash}
(required if you use hashmark headers), and @code{post} (required for
posting to USENET).  Remailers which do not support PGP won't even show
up in the completion list.

@item
The only remailer which needs special properties (e.g., posting,
hashmarks, pseudonym support) is the last one in a chain.  Any remailer
can be used at the beginning or in the middle.  So if you find a few
remailers which support the feature(s) you require, and you always use
them at the end of your chains, then you can be confident that even the
longest chains will work.

@item
@findex mc-reread-levien-file
If you update your @file{~/.remailers} file, you can reread it with
@kbd{M-x mc-reread-levien-file}.

@item
Remember the natural order of operations.  First you compose your
message.  Then you insert your pseudonym with @kbd{C-c / p}.  Then you
insert your response block with @kbd{C-c / b}.  Then you sign (@kbd{C-c /
s}) or sign and encrypt (@kbd{C-c / e}) the message.  Then you rewrite it
for a remailer or chain (@kbd{C-c / r}).  Then you send it.  All but the
first and last two of these are optional.  (Well, strictly speaking,
they are all optional, but you get the idea.)

@item
Find and read some of the excellent remailer documentation available on
the Internet.  For some good starting points, see @ref{References}.

@end itemize

@node Passphrase Cache, Key Fetching, Remailer Support, Top
@chapter Passphrase Cache

@vindex mc-passwd-timeout
Mailcrypt can remember your passphrase so that you need not type it
repeatedly.  It will also "forget" your passphrase if it has not been
used in a while, thus trading some security for some convenience.  You
can tune this tradeoff with the variable @code{mc-passwd-timeout}, which
is a duration in seconds from the last time the passphrase was used
until Mailcrypt will forget it.  The default value is 60 seconds.

So, for example, to make Mailcrypt remember your passphrase for 10
minutes after each use, you would use the following line in your
@file{.emacs} file:

@lisp
(setq mc-passwd-timeout 600)
@end lisp

A value of @code{nil} or 0 will disable passphrase caching completely.
This provides some increase in security, but be aware that you are
already playing a dangerous game by typing your passphrase at a Lisp
interpreter.

Mailcrypt understands multiple secret keys with distinct passphrases.

@findex mc-deactivate-passwd
@kindex C-c / f
To manually force Mailcrypt to forget your passphrase(s), use the
function @code{mc-deactivate-passwd}.  Both @code{mc-read-mode} and
@code{mc-write-mode} bind this function to @kbd{C-c / f} by default.

@quotation
@strong{Warning:} Although Mailcrypt takes pains to overwrite your
passphrase when "forgetting", it cannot prevent the Emacs garbage
collector from possibly leaving copies elsewhere in memory.  Also, your
last 100 keystrokes can always be viewed with the function
@code{view-lossage}, normally bound to @kbd{C-h l}.  So be sure to type
at least 100 characters after typing your passphrase if you plan to
leave your terminal unattended.
@end quotation

@node Key Fetching, Miscellaneous Configuration, Passphrase Cache, Top
@chapter Key Fetching

@findex mc-pgp-fetch-key
@kindex C-c / k
Mailcrypt knows how to fetch PGP public keys from the key servers
(@pxref{Key Servers}).  The function @code{mc-pgp-fetch-key} is bound by
default to @kbd{C-c / k} in both @code{mc-read-mode} and
@code{mc-write-mode}.  Additionally, @code{mc-encrypt},
@code{mc-decrypt}, and @code{mc-verify} will offer to call this function
to automatically fetch a desired key.  If you call it manually, it will
prompt you for the User ID of the key to fetch.

@vindex mc-pgp-fetch-methods
The variable @code{mc-pgp-fetch-methods} is a list of ways to attempt to
fetch a key.  (More precisely, it is a list of functions to be called,
each of which will attempt to fetch the key.)  The methods will be tried
in the order listed.  The default list is:

@lisp
'(mc-pgp-fetch-from-keyrings
  mc-pgp-fetch-from-finger
  mc-pgp-fetch-from-http)
@end lisp

For a description of these functions, see the following sections.

If you are not directly on the Internet, you probably want to obtain a
copy of the global public key ring from the keyservers, install it
somewhere under the name @file{public-keys.pgp}, and do:

@lisp
(setq mc-pgp-fetch-methods '(mc-pgp-fetch-from-keyrings))
(setq mc-pgp-fetch-keyring-list '("/blah/blah/blah/public-keys.pgp"))
@end lisp

This will allow you to fetch keys from your local copy of the global key
ring instead of sending requests to the key servers directly
(@pxref{Keyring Fetch}).  Alternately, if your organization has a proxy
HTTP server, you can configure Mailcrypt to use that.  See @ref{HTTP
Fetch}.

If the key is found, you will be shown the result of running PGP on it
locally.  This allows you to inspect the signatures on the key
@emph{relative to your own keyring} before you consent to having it
added.  @strong{Inspect the signatures carefully!}  Key distribution is
often the Achilles' heel of public key protocols.  If you blindly use
keys obtained from the key servers, you are asking for trouble.

All of the methods use @code{mc-pgp-fetch-timeout} as a timeout in
seconds; the default value is 30.

@menu
* Keyring Fetch::               Fetching from one or more other
                                  keyrings on the local system.
* Finger Fetch::                Fetching a key through finger.
* HTTP Fetch::                  Fetching a key off of the Web.
* GnuPG Fetch::                 Using GnuPG's internal keyserver interface.
@end menu

@node Keyring Fetch, Finger Fetch, Key Fetching, Key Fetching
@section Keyring Fetch

@findex mc-pgp-fetch-from-keyrings
The function @code{mc-pgp-fetch-from-keyrings} will attempt to fetch a
key from a set of keyrings on the locally accessible filesystem.  This
is useful if your organization maintains a large common public keyring
whose entire contents you do not wish to duplicate on your own ring.  It
is also useful if you download a copy of the global public ring from the
key servers (@pxref{Key Servers}).

@vindex mc-pgp-fetch-keyring-list
The variable @code{mc-pgp-fetch-keyring-list} controls this behavior.
It is a list of file names of public keyrings which this function will
search, in order, when seeking a key.  The default value is @code{nil},
meaning this search will always fail.

@node Finger Fetch, HTTP Fetch, Keyring Fetch, Key Fetching
@section Finger Fetch

@findex mc-pgp-fetch-from-finger
The function @code{mc-pgp-fetch-from-finger} will attempt to fetch a key
by fingering an address and parsing the output for a PGP public key
block.

@node HTTP Fetch, GnuPG Fetch, Finger Fetch, Key Fetching
@section HTTP Fetch

@findex mc-pgp-fetch-from-http
The function @code{mc-pgp-fetch-from-http} will attempt to fetch a key
by connecting to a key server (@pxref{Key Servers}) which has a World
Wide Web interface.

@vindex mc-pgp-keyserver-address
@vindex mc-pgp-keyserver-port
@vindex mc-pgp-keyserver-url-template
The variables @code{mc-pgp-keyserver-address},
@code{mc-pgp-keyserver-port}, and @code{mc-pgp-keyserver-url-template}
control the fetching process.  The default is to use Brian LaMacchia's
key server at MIT.  If this default should stop working, or if you want
to help with network congestion and machine load, you can choose a
different server.  As of this writing, any of the following sequences of
Emacs Lisp in your @file{.emacs} file will work; choose one:

@lisp
;; Key server at MIT (Massachusetts, USA)
;; This is the default; these lines are only for reference
;(setq mc-pgp-keyserver-address "pgp.ai.mit.edu")
;(setq mc-pgp-keyserver-port 80)
;(setq mc-pgp-keyserver-url-template
;      "/htbin/pks-extract-key.pl?op=get&search=%s")
@end lisp

@lisp
;; Key server at UPC (Barcelona, Spain)
(setq mc-pgp-keyserver-address "goliat.upc.es")
(setq mc-pgp-keyserver-port 80)
(setq mc-pgp-keyserver-url-template
      "/cgi-bin/pks-extract-key.pl?op=get&search=%s")
@end lisp

@lisp
;; Key server at Cambridge University (Cambridge, England)
(setq mc-pgp-keyserver-address "www.cl.cam.ac.uk")
(setq mc-pgp-keyserver-port 80)
(setq mc-pgp-keyserver-url-template
      "/cgi-bin/pks-extract-key.pl?op=get&search=%s")
@end lisp

@lisp
;; Key server at UIT (Tromso, Norway)
(setq mc-pgp-keyserver-address "www.service.uit.no")
(setq mc-pgp-keyserver-port 80)
(setq mc-pgp-keyserver-url-template
      "/cgi-bin/pks-extract-key.pl?op=get&search=%s")
@end lisp

@lisp
;; Key server at CMU (Pennsylvania, USA)
(setq mc-pgp-keyserver-address "gs211.sp.cs.cmu.edu")
(setq mc-pgp-keyserver-port 80)
(setq mc-pgp-keyserver-url-template "/cgi-bin/pgp-key?pgpid=%s")
@end lisp

If your organization has a firewall, you might not be able to access the
World Wide Web directly.  Your organization may have a proxy HTTP server
set up, however.  In that case, you should place code like the following
in your @file{.emacs} file.  You can use any of the above key servers
instead of the one at MIT, of course.

@lisp
;; Mailcrypt configuration for accessing key server through HTTP proxy
(setq mc-pgp-keyserver-address "your.proxy.com")
(setq mc-pgp-keyserver-port 13013)  ; Your proxy's port
(setq mc-pgp-keyserver-url-template
      "http://pgp.ai.mit.edu/htbin/pks-extract-key.pl?op=get&search=%s")
@end lisp

Note that fetching from a key server can be somewhat slow, so be
patient.  (At least it beats the tar out of the Email interface.)

@node GnuPG Fetch,  , HTTP Fetch, Key Fetching
@section GnuPG Fetch

GnuPG happens to have a built-in HKP keyserver interface which is
completely independent from MailCrypt's own key fetching support.  If
your @file{.gnupg/options} file includes a line like:

@samp{keyserver wwwkeys.pgp.net}

then any operation that needs an otherwise-unavailable public key
(which generally means signature verification) will automatically
contact the keyserver and try to retrieve the key.  It sends the hex
keyid to the server, not a string, so it could only be used at
encryption time if you already know the keyid of your recipients.

You can also tell GPG to explicitly request a key (by hex keyid) with
@samp{--recv-keys}, or to send your own key with @samp{--send-keys}.
Check the GnuPG manual for details.


@node Miscellaneous Configuration, Tips, Key Fetching, Top
@chapter Miscellaneous Configuration

This chapter documents some additional Mailcrypt configuration options
which could not be naturally described elsewhere.

@menu
* Alternate Keyring::           Specifying a different file to act
                                  like your public keyring.
* Comment Field::               Burma
                                  Shave
* Mode Line::                   Changing that "MC-w" and "MC-r" stuff
* Key Bindings::                Which keys cause which actions.
* Nonstandard Paths::           Useful if your PGP installation is weird.
@end menu

@node Alternate Keyring, Comment Field, Miscellaneous Configuration, Miscellaneous Configuration
@section Alternate Keyring

By default, Mailcrypt will use the same public keyring that PGP would
use if executed from the shell.

@vindex mc-pgp-alternate-keyring
You can cause Mailcrypt to use a specific public keyring by setting the
variable @code{mc-pgp-alternate-keyring}.  If this variable is set,
Mailcrypt will use that keyring for all functions which would otherwise
have used the default.  This includes adding keys, extracting keys,
verifying signatures, and encrypting messages.

This feature might be useful if you maintain multiple keyrings; you can
switch between them by setting this variable.  Depending on your tastes,
you might want to configure fetching from a keyring as well
(@pxref{Keyring Fetch}).

@node Comment Field, Mode Line, Alternate Keyring, Miscellaneous Configuration
@section Comment Field

By default, Mailcrypt will supply a "comment" option to PGP, resulting
in output which looks something like this:

@example
----- BEGIN PGP FOOBAR -----
Version: 2.6.3
Comment: Processed by Mailcrypt @value{VERSION}, an Emacs/PGP interface

@dots{}
----- END PGP FOOBAR -----
@end example

@vindex mc-pgp-comment
@vindex mc-pgp50-comment
@vindex mc-gpg-comment
To change the comment to one of your own, set the variable
@code{mc-pgp-comment}. Set it to @code{nil} to use PGP's default, which
is probably either no comment or something defined in @file{config.txt}.
@code{mc-pgp50-comment} and @code{mc-gpg-comment} are the corresponding
variables for the other versions.

@node Mode Line, Key Bindings, Comment Field, Miscellaneous Configuration
@section Mode Line

@code{mc-read-mode} and @code{mc-write-mode} will each indicate they are
active by placing the string @samp{MC-r} or @samp{MC-w} in the mode
line, respectively.

@vindex mc-read-mode-string
@vindex mc-write-mode-string
You can change these strings by setting the variables
@code{mc-read-mode-string} and @code{mc-write-mode-string}.  So, for
example, to get rid of the mode indicators entirely, you might put the
following lines into your @file{.emacs} file:

@lisp
(setq mc-read-mode-string "")
(setq mc-write-mode-string "")
@end lisp

@node Key Bindings, Nonstandard Paths, Mode Line, Miscellaneous Configuration
@section Key Bindings

@vindex mc-read-mode-map
@vindex mc-write-mode-map
The Mailcrypt key bindings are defined by the keymaps
@code{mc-read-mode-map} and @code{mc-write-mode-map}.  To change the key
bindings, you just need to set these variables in your @file{.emacs}
file.

For example, if you wanted @kbd{C-c C-m} to be the Mailcrypt prefix
(instead of @kbd{C-c /}) in @code{mc-read-mode}, you would put the
following code in your @file{.emacs} file:

@lisp
(setq mc-read-mode-map (make-sparse-keymap))
(define-key mc-read-mode-map "\C-c\C-mf" 'mc-deactivate-passwd)
(define-key mc-read-mode-map "\C-c\C-md" 'mc-decrypt)
(define-key mc-read-mode-map "\C-c\C-mv" 'mc-verify)
(define-key mc-read-mode-map "\C-c\C-ma" 'mc-snarf)
(define-key mc-read-mode-map "\C-c\C-mk" 'mc-pgp-fetch-key)
@end lisp

For more information on Emacs key bindings, see @ref{Key Bindings, ,
Customizing Key Bindings, emacs, The GNU Emacs Manual}.

@node Nonstandard Paths,  , Key Bindings, Miscellaneous Configuration
@section Nonstandard Paths

The information in this section should be unnecessary, but is provided
"just in case".

@vindex mc-pgp-path
Mailcrypt will look for the PGP executable in your standard search path
under the name @file{pgp}.  To use a different name (or to provide a
complete path), set the variable @code{mc-pgp-path}.

@vindex mc-pgp50-pgpe-path
@vindex mc-pgp50-pgps-path
@vindex mc-pgp50-pgpv-path
@vindex mc-pgp50-pgpk-path
PGP 5.0 includes four separate executables, usually installed as "pgpe",
"pgps", "pgpv", and "pgpk". The variables @code{mc-pgp50-pgpe-path},
@code{mc-pgp50-pgps-path}, @code{mc-pgp50-pgpv-path}, and
@code{mc-pgp50-pgpk-path} tell Mailcrypt where to find them if they are
not on your search path.

@vindex mc-gpg-path
GnuPG is normally installed as "gpg". @code{mc-gpg-path} tells Mailcrypt
where to find the executable if it is not on your path.

In order to keep your identities straight, Mailcrypt needs to know where
your secret keyring resides.

Mailcrypt figures this out heuristically by assuming that the file
@file{secring.pgp} is in the same directory as your public key ring.  It
determines the location of the latter by doing a dry run of PGP with
@samp{+verbose=1} and parsing the output.

@vindex mc-pgp-keydir
If this heuristic is failing for you, you can manually tell Mailcrypt
where your secret key ring is by setting the variable
@code{mc-pgp-keydir}, like this:

@lisp
(setq mc-pgp-keydir "/users/patl/.pgp/")
@end lisp

Note that the trailing slash is @emph{required}.

If the heuristic fails, please report it as a bug (@pxref{Credits}).

Note that if you have changed the default location of your secret
keyring, Mailcrypt will be unable to locate it.  You can work around
this by either setting @code{mc-pgp-keydir}, or by making a symbolic
link to your secret keyring from @file{secring.pgp} in your default
public keyring directory.

@node Tips, Limitations, Miscellaneous Configuration, Top
@chapter Tips

Here are some random tips.

@itemize @bullet

@item
PGP provides quite good security when used correctly.  You are far more
likely to use it correctly if you have read the directions.  Read the
@cite{PGP User's Guide}!

@item
60 seconds is a relatively safe but somewhat inconvenient value for
@code{mc-passwd-timeout}.  If your paranoia permits, consider increasing
it to five or ten minutes (@pxref{Passphrase Cache}).

@item
If Mailcrypt ever does something you wish it had not, @emph{DON'T
PANIC}.  Just use the normal Emacs undo command, @kbd{M-x undo} or
@kbd{C-x u}, to restore your buffer (@pxref{Undo, Emacs Undo, Undoing
Changes, emacs, The GNU Emacs Manual}).  Mailcrypt keeps almost no state
except what you see in your buffer, so any action can be undone this
way.

@item
All Mailcrypt operations place PGP's output in the @code{*MailCrypt*}
buffer.  Check it occasionally for status and warning messages.

@item
Add yourself to the Mailcrypt announcements mailing list (@pxref{Mailing
List}).  That way you can find out about new versions of Mailcrypt
automatically, and we can enjoy the feeling that people are actually
using our package.

@end itemize

@node Limitations, References, Tips, Top
@chapter Limitations

Mailcrypt is a powerful program, but it is not a complete PGP interface.
Perhaps some future version will be; in the meantime, you will need to
use the command-line interface for some operations.  Things which the
current version does not support include:

@table @emph

@item Complete Key Management
Mailcrypt's key management support is limited to adding and extracting
keys from keyrings.  It does not support key generation, key removal,
key revocation, ID and trust parameter editing, or key signing.  It also
ignores PGP's warnings when you use a key which is not fully certified.
(Of course, you can see these warnings by viewing the @code{*MailCrypt*}
buffer; see @ref{Tips}.)

@item Encryption with Conventional Cryptography
Mailcrypt supports decryption but not encryption with "conventional"
(i.e., non-public key) cryptography.

@item Detached Signatures
Mailcrypt does not support the creation nor the verification of detached
signatures.

@item "For your eyes only" Decryption
Mailcrypt will be unable to decrypt a file which was encrypted with the
"for your eyes only" (@samp{-m}) option.  This is actually a bug in PGP,
which provides no portable way to avoid its paging behavior.

@end table

@node References, Credits, Limitations, Top
@chapter References

This chapter contains information and pointers to information about
topics related to PGP and Mailcrypt.

@menu
* Online Resources::            Recreational reading with a purpose.
* Key Servers::                 Keepers of the Global Keyring.
* Mailing List::                Staying informed while pumping the
                                  authors' egos.
* Politics::                    Anarcho-foobarism.
@end menu

@node Online Resources, Key Servers, References, References
@section Online Resources

@table @file

@item http://cag-www.lcs.mit.edu/mailcrypt/
"Mailcrypt: An Emacs/PGP Interface", by Pat LoPresti. This page has
been the Mailcrypt homepage since October 10, 1995.  It is still
the distribution site for version 3.4 of Mailcrypt--a rock-solid
version still to be recommended if you use only PGP 2.6.x.

@item http://world.std.com/~franl/crypto.html
"Cryptography, PGP, and Your Privacy", by Fran Litterio.  This page is
simply excellent.  It makes all the other References in this chapter
redundant, but we will include them anyway for redundancy.

@item http://web.mit.edu/network/pgp.html
MIT is the canonical distribution site for PGP; this is the announcement
page.

@item ftp://rtfm.mit.edu/pub/usenet/alt.security.pgp/
This is an archive site for the @file{alt.security.pgp} FAQ lists.

@item news:alt.security.pgp
The @file{alt.security.pgp} newsgroup is a good place to go for
discussion about PGP, as well as any topic which any fool anywhere ever
thinks is related to PGP.  It is also a good last resort for getting
answers to questions, but please read the FAQ lists first.

@item http://pgp.ai.mit.edu/~bal/pks-toplev.html
Brian LaMacchia (bal@@zurich.ai.mit.edu) has put together a World Wide
Web interface to the public key servers (@pxref{Key Servers}).
Mailcrypt uses this interface by default when attempting to fetch keys
via HTTP (@pxref{HTTP Fetch}); most people get to his interface through
this page.

@item ftp://ftp.csua.berkeley.edu/pub/cypherpunks/Home.html
The Cypherpunks are dedicated to taking proactive measures to ensure
privacy in the digital age.  They wrote the software for, and operate
many of, the anonymous remailers currently in existence.

@item http://www.cs.berkeley.edu/~raph/
Raph Levien actively maintains a remailer list which Mailcrypt knows how
to parse.  If you are impressed by how easy it is to configure
Mailcrypt's remailer functions, Raph is the one to thank.  Raph's page
also has many useful links.

@item http://www.obscura.com/~loki/
Lance Cottrell is the author of Mixmaster.  His home page is the
canonical source for information on Mixmaster and is a good source for
PGP pointers in general.

@item http://www.gnupg.org/
Homepage for the GNU Privacy Guard. This is a GPL-ed replacement for PGP.

@end table

@node Key Servers, Mailing List, Online Resources, References
@section Key Servers

@dfn{Key servers} are machines with a publicly accessible interface to
an enormous global public keyring.  Anyone may add keys to or query this
keyring.  Each key server holds a complete copy of the global keyring,
and they arrange to keep one another informed of additions they receive.

This means you can tell any key server to add your public key to the
global keyring, and all of the other servers will know about it within a
day or so.  Then anyone will be able to query any key server to obtain
your public key.

To add your key to the keyservers, send an Email message to
@code{pgp-public-keys@@pgp.ai.mit.edu} with a subject line of @samp{ADD}
and a body containing your public key block.  With Mailcrypt installed,
you can just type @kbd{C-c / x} to insert your public key block
(@pxref{Inserting Keys}) into the body of the message.

For help with the Email interface to the key servers, send a message
with a subject line of @samp{HELP}.  For a World Wide Web interface to
the key servers, see Brian LaMacchia's home page at
@file{http://www-swiss.ai.mit.edu/~bal/}.

Some other key servers include:

@itemize @bullet

@item
pgp-public-keys@@jpunix.com

@item
pgp-public-keys@@kub.nl

@item
pgp-public-keys@@uit.no

@item
pgp-public-keys@@pgp.ox.ac.uk

@end itemize

For a complete list, consult any good online repository of PGP
information (@pxref{Online Resources}).

It is strongly recommended that you submit your key to the key servers,
since many humans and programs (including Mailcrypt) may look for it
there.  Besides, it takes mere seconds and the pain passes quickly.

@node Mailing List, Politics, Key Servers, References
@section Mailing List
If you would like to automatically receive information about new
releases of Mailcrypt, send Email to
@samp{mc-announce-request@@cag.lcs.mit.edu} asking to be placed on the
@samp{mc-announce} mailing list.  The mailing list is maintained
manually, so please be patient.

The @samp{mc-announce} list is reserved for announcements of new
Mailcrypt versions, so it has extremely low volume.  We encourage you to
add yourself so we can get a rough idea of how many people are using
our package.

@node Politics,  , Mailing List, References
@section Politics

Cryptography in general, PGP in particular, and free software are
politically somewhat controversial topics.  Heck, in the U.S. Congress,
freedom of speech is a controversial topic.  Anyway, here are some
organizations you should definitely watch and preferably send lots of
money.

@table @emph

@item The Electronic Frontier Foundation
The EFF (@file{http://www.eff.org/}) works to protect civil liberties in
cyberspace.  They also maintain an impressive collection of on-line
resources.  If you like Mailcrypt so much that you wish you had paid for
it, this is the number one place we would want to see your money go.
The EFF newsgroups, @file{comp.org.eff.news} and
@file{comp.org.eff.talk}, are required reading for the well-informed.

@item The League for Programming Freedom
The LPF (@file{http://www.lpf.org/}) works to fight software patents,
which threaten to make free software like Mailcrypt impossible.

@item The Center for Democracy and Technology
The CDT (@file{http://www.cdt.org/}) has essentially the same goals as
the EFF, but is more of a lobbying group.

@end table

Mailcrypt's remailer support was inspired by the Communications Decency
Act of 1995 (see @file{http://www.cdt.org/cda.html}) and by the
International "Church" of Scientology (see
@file{http://www.mit.edu:8001/people/rnewman/scientology/}).

@node Credits, Index, References, Top
@chapter Credits
Mailcrypt was written by Jin Choi (jin@@atype.com) and Pat LoPresti
(patl@@lcs.mit.edu).  Please send us your bug reports and comments.
Also see @ref{Mailing List}.

This documentation was mostly written by Pat LoPresti, but borrows
heavily from an earlier version by Hal Abelson (hal@@mit.edu).

Mailcrypt would not be as robust nor as featureful if it were not for
our outstanding set of Beta testers:

@itemize @bullet

@item
Samuel Tardieu <sam@@inf.enst.fr>
@item
Richard Stanton <stanton@@haas.berkeley.edu>
@item
Peter Arius <arius@@immd2.informatik.uni-erlangen.de>
@item
Tomaz Borstnar <tomaz@@cmir.arnes.si>
@item
Barry Brumitt <belboz@@frc2.frc.ri.cmu.edu>
@item
Steffen Zahn <Steffen.Zahn%robinie@@sunserv.sie.siemens.co.at>
@item
Mike Campbell <mcampbel@@offenbach.sbi.com>
@item
Mark Baushke <mdb@@cisco.com>
@item
Mike Long <mike.long@@analog.com>

@end itemize

@page
@node Index,  , Credits, Top
@unnumbered Index

This index has an entry for every key sequence, function, and variable
documented in this manual.

@printindex cp

@contents
@bye

@c End:
