Fixed indentation.

[elisp/epg.git] / README

diff --git a/README b/README
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+++ b/README
@@ -1,58 +1,37 @@
 * What's this?
 
-EasyPG is yet another GnuPG interface for Emacs.  It consists of two
-parts: transparent file encryption utility and easy-to-use elisp
-library to interact with GnuPG.
+EasyPG is yet another GnuPG interface for Emacs.  It consists of two parts:
 
-* Requirements
+epa.el - EasyPG Assistant, a basic GUI of GnuPG
+epg.el - the EasyPG library which interacts with GnuPG
 
-** GNU Emacs 21.4 or later
+NOTE: EasyPG is not a fork or a re-implementation of Gnus/PGG.
 
-** XEmacs 21.4 or later
+* Requirements
 
-** GnuPG 1.4.3 or later
+** GNU Emacs 21.4 or later, XEmacs 21.4 or later
 
-** Gnus 5.10.8 or later (optional)
+** GnuPG 1.4.3 or later
 
 * Quick start
 
-** Transparent file encryption
-
-EasyPG provides transparent file encryption similar to crypt++,
-alpaca.el, hedgehog.  To enable this feature, put (require 'epg-file)
-in your ~/.emacs.el, C-x C-f ~/test.txt.gpg.
+** Installation
 
-** Using with Gnus/PGG
+$ ./configure
+$ sudo make install
 
-EasyPG provides an implementation of the backend interface of
-Gnus/PGG.  To use EasyPG instead of pgg-gpg, install pgg-epg.el and
-add the following line to your ~/.gnus
+Add the following line to your ~/.emacs
 
-(setq pgg-scheme 'epg)
+(require 'epa-setup)
 
 * Advantages over other competitors
 
-There are many competitors of EasyPG such as Mailcrypt, PGG, gpg.el,
-etc.  EasyPG has some advantages over them.
-
-** EasyPG avoides potential security flaws of Emacs.
+There are many competitors of EasyPG such as Mailcrypt, Gnus/PGG,
+gpg.el, etc.  EasyPG has some advantages over them.
 
-*** `call-process-region' writes data in region to temporary files.
+** EasyPG avoides potential security flaws of Emacs
 
-`call-process-region' writes data in region to temporary files.  PGG
-and gpg.el use `call-process-region' to communicate with a gpg
-subprocess.  Your passphrases leak to the filesystem!
-
-*** There is no way to clear strings safely.
-
-If Emacs crashed and dumps core, passphrase strings in memory are also
-dumped within the core file.  `read-passwd' function clears passphrase
-strings by `(fillarray string 0)'.  However, Emacs performs compaction
-in gc_sweep phase.  If GC happens before `fillarray', passphrase
-strings may be moved elsewhere in memory.  It is recommended that as
-soon as you are done with passphrase you should clear it manually.
-However, PGG and gpg.el can keep passphrase strings in cache for a
-while and this behavior is their default!
+See "Security consideration" section.
 
 ** GnuPG features are directly accessible from Emacs
 
@@ -61,3 +40,24 @@ still support PGP 2.*, 5.*, 6.*.  As the name indicates, EasyPG is
 inspired by GPGME (GnuPG Made Easy), and the library interface is
 close to GPGME.  With EasyPG you can benefit from a lot of features of
 GnuPG.
+
+* Security consideration
+
+** `call-process-region' writes data in region to a temporary file
+
+`call-process-region' writes data in region to a temporary file.
+EasyPG does *not* use `call-process-region' to communicate with a gpg
+subprocess.
+
+** `(fillarray string 0)' is not enough to clear passphrases
+
+If Emacs crashed and dumps core, passphrase strings in memory are also
+dumped within the core file.  `read-passwd' function clears passphrase
+strings by `(fillarray string 0)'.  However, Emacs performs compaction
+in gc_sweep phase.  If GC happens before `fillarray', passphrase
+strings may be moved elsewhere in memory.
+
+Fortunately, there is gpg-agent to cache passphrases in more secure
+way, so the EasyPG library dares *not* to cache passphrase by itself.
+Elisp programs can set `epg-context-passphrase-callback' to cache
+user's passphrases.