path: root/README

	Sylpheed - lightweight and user-friendly e-mail client

   Copyright(C) 1999-2018 Hiroyuki Yamamoto <hiro-y@kcn.ne.jp>

   This program is free software; you can redistribute it and/or modify
   it 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.

   This program 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 this program; if not, write to the Free Software Foundation, 
   Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

   For more details see the file COPYING.


What's Sylpheed
===============

Sylpheed is an e-mail client based on GTK+ GUI toolkit.
Sylpheed runs on Unix-like systems such as Linux, BSD and Mac OS X, or
Microsoft Windows (XP or later).

Sylpheed is a free software distributed under the GNU GPL (the library part
LibSylph is GNU LGPL).

Sylpheed has the following features:

    * Simple, beautiful, and well-polished user interface
    * Comfortable operationality which is built in detail
    * Well-organized, easy-to-understand configuration
    * Lightweight operation
    * High reliability
    * Internationalization and Multilingualization support
    * High-level Japanese processing
    * Various protocols support
    * Multi-thread support
    * Security feature (GnuPG, SSL/TLSv1)
    * Powerful filtering and search
    * Junk mail control
    * Flexible cooperation with external commands
    * Plug-in faculty

The appearance and interface are similar to some popular e-mail clients for
Windows, such as Outlook or Becky!. Many commands are accessible with
the keyboard like the Emacs-based mailers such as Mew and Wanderlust.
So you will be able to migrate to Sylpheed without much discomfort, even if
you are accustomed to other mailers.

The messages are managed by MH format, and you will be able to use it together
with another mailer based on MH format (like Mew). It has less possibility
of losing mails on failures since one file corresponds to one mail. You can
import or export mbox and eml format messages. You can also utilize fetchmail
and/or procmail, and external programs on receiving (like inc or imget).

Currently implemented major features
====================================

Supported protocols

	o POP3
	o IMAP4rev1
	o SMTP
	o NNTP
	o SSL/TLSv1 (POP3, SMTP, IMAP4rev1, NNTP)
	o IPv6
	o SOCKS4/5

Features

	o multiple accounts
	o powerful filtering (POP3, IMAP4, local spool)
	o powerful search (query search, quick search, search folder)
	o Junk mail control
	o plug-in faculty
	o thread display
	o display and transfer of attachments by MIME
	o inline image display
	o News reader
	o SMTP AUTH support (PLAIN / LOGIN / CRAM-MD5)
	o CRAM-MD5 authentication (SMTP AUTH / IMAP4rev1)
	o APOP authentication (POP3)
	o PGP signature / encryption (requires GPGME)
	o spell checking (requires GtkSpell)
	o SOCKS4/5 proxy support
	o X-Face display
	o user-defined headers
	o mark / color label
	o Mew/Wanderlust compatible key bind
	o multiple MH folder support
	o mbox and eml import / export
	o action function to work with external commands
	o external editor
	o message queueing
	o automatic mail checking
	o draft message
	o template
	o line-wrapping
	o autosave
	o clickable URI
	o address book
	o newly arrived and unread message management
	o printing
	o POP3 remote mailbox
	o offline mode
	o tray icon (minimize to tray icon, new mail notification)
	o customization of toolbar
	o remote operation by command line
	o per-folder configuration
	o LDAP, vCard, and JPilot support in address book
	o CSV, LDIF file import in address book
	o auto-registration of recipient's addresses to address book
	o auto-completion of addresses
	o Drag & Drop
	o autoconf, automake support
	o internationalization of messages by gettext
	o m17n (multilingualization) support

and more.

Installation
============

See INSTALL for installation instructions.

Usage
=====

Preparation before running
--------------------------

If you are using a character encoding other than UTF-8 for filename,
you must set the following environmental variable (it will not work if
it is not specified):

(use locale-specific encoding)
% export G_FILENAME_ENCODING=@locale

or

(manually specifying encoding)
% export G_FILENAME_ENCODING=ISO-8859-1

If you want to display messages translated to your language,
you must specify some environmental variables related to locale.
For example:

% export LANG=de_DE.UTF-8

(replace de_DE.UTF-8 to the actual locale name)

If you don't want translated messages, set LC_MESSAGES to "C"
(and unset LC_ALL if specified).

How to run
----------

Input `sylpheed' on a command line, or double-click the icon in a file
manager to execute.

Initial startup
---------------

When Sylpheed is executed for the first time, it automatically creates the
configuration files under ~/.sylpheed-2.0/, and asks you the location of
mailbox. The default is ~/Mail. If some files, which are non-MH format,
already exist on the directory, you will have to specify another location.

If ~/.sylpheed-2.0/ doesn't exist, but the previous version of configuration
exists in ~/.sylpheed/, migration will be made automatically after the
confirmation.

If the locale encoding is not UTF-8 and the environmental variable
G_FILENAME_ENCODING is not set, an alert dialog will be displayed.

Required settings
-----------------

Initially, you have to create at least one account to send or receive
messages (you can read messages that already exist without creating
accounts). The configuration dialog will be shown by clicking
"Configuration -> Create new account..." in the menu, or "Account" on
the toolbar. Then, fill the required settings.

Refer to the manual supplied with this program for the general usage.

Hidden settings
---------------

You can configure most of the features in Sylpheed through the preferences
dialog, but there are a few parameters which don't have user interface
(you don't need to modify them in normal use). You must edit
~/.sylpheed-2.0/sylpheedrc by an editor while Sylpheed is not running.

allow_jisx0201_kana		allow JIS X 0201 Kana (half-width kana) on
				sending
				0: off  1: on   [default: 0]
translate_header		translate headers such as 'From:', 'To:' and
				'Subject:'
				0: off  1: on   [default: 1]
enable_rules_hint		enable alternating row colors for summary view
				0: off  1: on   [default: 1]
bold_unread			show unread messages using bold font in
				summary view
				0: off  1: on   [default: 1]
textview_cursor_visible		show cursor in the text view
				0: off  1: on   [default: 0]
mime_image_viewer		specify the command to open attached image
				files [default: none]
mime_audio_player		specify the command to open attached audio
				files [default: none]
mime_command			specify the command to open MIME attachments
				[default: none]
logwindow_line_limit		specify the limit of line numbers of log
				window
				0: unlimited  n (> 0): n lines [default: 1000]
mark_as_read_on_new_window	only mark messages as read when they are
				opened with new window
				0: off  1: on   [default: 0]

Unlike 1.0.x, this version doesn't allow direct modification of the menu
shortcuts by default. You can use the following methods to configure them:

1. Using GNOME 2.8 or later
   Run gconf-editor from 'Applications - System Tools - Configuration Editor'.
   Select 'desktop - gnome - interface' and check 'can-change-accels' in it.

2. Using GNOME before 2.8, or other environments
   Add gtk-can-change-accels = 1 to the file ~/.gtkrc-2.0 (or create a new
   one, if it doesn't exist).

3. When Sylpheed is not running, directly edit ~/.sylpheed-2.0/menurc with
   an editor.

Information
===========

You can check the newest version and information about Sylpheed at:

	http://sylpheed.sraoss.jp/

You can also download files from the SourceForce.JP project page:

	http://sourceforge.jp/projects/sylpheed/

The bug tracking system of Sylpheed is:

	http://sylpheed.sraoss.jp/redmine/projects/sylpheed

The Sylpheed documentation in English and several other languages can be
obtained from:

	http://sylpheeddoc.sourceforge.net/

Feedback
========

Comments, ideas and (most of all) bug reports (and especially patches) are
very welcome.

Subversion
==========

You can get the newest source code from the Subversion repository.

Move to an appropriate directory, and with the command:

	svn checkout svn://sylpheed.sraoss.jp/sylpheed/trunk

a source tree named 'trunk' is created under the current directory.

The subdirectory of sylpheed is divided as following:

    * trunk/     Main tree
    * branches/  Miscellaneous experimental branches
    * tags/      Release-tagged branches

To update to the newest source tree, run the command:

	svn update

at the target directory.

-- 
Hiroyuki Yamamoto <hiro-y@kcn.ne.jp>


Master password (by sgs)
========================

The master password feature is developed by
Simeon Simeonov (sgs - sgs@pichove.org) and is currently in an experimental
state.


Motivation
----------

Currently Sylpheed is storing passwords in palin-text. One can always refrain
from storing passwords and let Sylpheed prompt for them, but the more accounts
one has, the more annoying this becomes.

The goal is to have the passwords stored in a secure way and let Sylpheed only
prompt for the master password.


Security goals
--------------

- attacker (A) should not be able to derive the password from the digest

- A should not be able to derive the master password even if she has
  read and write access to the storage

- A should not be able to determine the length of the encrypted password
  even if she has read and write access to the storage

- A should not be able to craft an edited password without obtaining the
  master password

- a warning / prompt should be given if a user accidently types in a "wrong"
  master password before decryption is initiated


Usage in Sylpheed
-----------------

- backup your Sylpheed profile (often $HOME/.sylpheed-2.0)!

- start Sylpheed and open Configuration -> Common preferences...!

- select the "Master password" tab, enable "Use master password" and
  apply the changes!

- restart Sylpheed (exit and then start Sylpheed again)!

- you will be asked to type and verify a new master password.

Note:
Sylpheed will automatically convert existing stored passwords, but it will not
touch your backups. You will have to remove all remnants of plain-text
passwords manually.


Choice of cryptographic primitives
----------------------------------

The primary concern when selecting cryptographic primitives was portability.
The desire was to go for primitives that are both strong and available in all
supported production distributions of OpenSSL and LibreSSL.


Cipher
......

When it comes to implementation, there are several advantages in using stream
cipher or a block cipher that behaves like a stream cipher when used in a
certain mode of operation. One is avoiding to deal with padding.

AES-256 operating in CFB was selected for these reasons.
ChaCha20 should be considered as a replacement in the future.


Hash-function
.............

Hash-functions are used for:
- key derivation
- plain-text digest

Those operations do not have to use the same hash-function.
(See the "Encryption & decryption scheme" section for more details!)

Key-derivation:
Since AES-256 uses a 256 bits key, we need a hash-function with at least
the same digest size or bigger.
Since the digest (which is the key itself) is considered confidential and is
stored only in memory for only a limited amount of time, SHA-256 is considered
sufficiently strong for that purpose.

Size + plain-text + padding digest:
Since the digest is created of both the plain-text and the plain-text size,
as well as being encrypted, SHA-256 is considered sufficiently strong.
SHA-512 may increase security at the price of adding additional 32 bytes
to the encrypted password digest.

Stronger hash-functions like SHA-3 or BLAKE2b can be considered as a
replacement in the future.


Master password digest
......................

In order to be able to decide whether the user typed a "wrong" master password,
before attempting to decrypt, Sylpheed stores a digest of the master password
in 'master_password_hash' in sylpheedrc.
100000 iterations of PBKDF2_HMAC with SHA-512 and 16 bytes salt is used.
Note that this digest is useless as a key and even if a plain-text that
produces the same digest is found, it will most probably be useless as a
master-password.


Encryption & decryption scheme
------------------------------


Encryption
..........


Input:

- palin-text password to be encrypted (P)

- plain-text master-password used for key derivation (M)

- integer minimum password length (0 < L < 100)


Output:

- an encrypted password digest (base64) (B)


Operation:

- generate 16 bytes of random data to be used as a salt (S)

- derive the key (K): K = SHA_256(S + M)

- produce a 2 byte string (N) indicating the length of P

- if the length of P < L, produce L - P bytes of random data (R), N = "%02d"
  if the length of P >= L, N = "-1"

- produce a hash digest (H): H = SHA_256(N + P + R (if the length of P < L))

- encrypt (E): E = AES_256_CFB_ENCRYPT(H + N + P + R (if the length of P < L), K)

- B = mpes1:BASE64_ENCODE(S + E)
  example:
  mpes1:vo7lsIpD7i6byBA6+vlUoF4OVDfEe+aYRRk4FRtfJ2gMY8M43Kj6WfdfgbViIOl83bI4XEc96okhPW5Mla813aAR1gbPjDg0xmCyIbWOiUv/dg==


Decryption
..........


Input:

- encrypted password digest (base64) (B)

- plain-text master-password used for key derivation (M)


Output:

- palin-text password (P)


Operation:

- remove the prefix (mpes1:) and base64-decode the rest of the digest: B = BASE64_DECODE(B)

- fetch the first 16 bytes for the salt: S = B[0 : 15]

- derive the key (K): K = SHA_256(S + M)

- decrypt the rest of B (D): D = AES_256_CFB_DECRYPT(B[16 :], K)

- extract the first 16 bytes for the hash digest (H): H = D[0 : 15]

- in order to detect data-inconsistency, assert H == SHA_256(D[16 :])

- extract the next 2 bytes for the length of P (N): N = D[16 : 17]

- if N == "-1" the password is the remaining bytes of D: P = D[18 :]
  if N != "-1", extract the next N-bytes from D: P = D[18 : (18 + N)]


Limitations
-----------

- when Sylpheed starts, the master-password is loaded into memory and remains
  there as long as Sylpheed is running. Currently no strong mechanisms,
  preventing someone with access to the memory from snatching it,
  are implemented.
  "Unloading" the master-password immediately after
  account-processing (decryption) should be considered in the future.

- currently only the 'password' and 'smtp_password' keys in accountrc
  are encrypted.
  A machanism that allows for any key and even folders to be encrypted
  should be considered in the future.

- currently it is not possible to select alternative ciphers, hash-functions
  and modes of operation (without editing the source code).

- currently it is not possible to change your master password without having to
  set your passwords manually.

-- 
Simeon Simeonov <sgs [ATTT] pichove (DOT) org>