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[elisp/epg.git] / README

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 * 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:
+
+epa.el - EasyPG Assistant, a basic GUI of GnuPG
+epg.el - the EasyPG library which interacts with GnuPG
+
+NOTE: EasyPG is not a fork or a re-implementation of Gnus/PGG.
 
 * Requirements
 
-** GNU Emacs 21.4 or later
-** XEmacs 21.4 or later
+** GNU Emacs 21.4 or later, XEmacs 21.4 or later
+
 ** GnuPG 1.4.3 or later
 
 * Quick start
 
-(0) Put (require 'epg-file) in your ~/.emacs.el
+** Installation
 
-(1) Restart emacs
+$ ./configure
+$ sudo make install
 
-(2) C-x C-f ~/test.gpg
+Add the following line to your ~/.emacs
+
+(require 'epa-setup)
 
 * Advantages over other competitors
 
-** 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.
+
+** EasyPG avoides potential security flaws of Emacs
+
+See "Security consideration" section.
+
+** GnuPG features are directly accessible from Emacs
+
+Other competitors provide only specific features of GnuPG since they
+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.
 
-*** `call-process-region' writes data in region to a temporary file.
-PGG and gpg.el use `call-process-region' to communicate with a
-subprocess "gpg".  So, your passphrases may leak to the filesystem.
+** `(fillarray string 0)' is not enough to clear passphrases
 
-*** There is no way to clear strings safely.
-To prevent passphrases from been stealing from cores, `read-passwd'
-function clears passphrase strings by `(fillarray string 0)'.
-However, it is not enough.  Emacs does compaction of small strings in
-GC sweep phase.  If GC happens before `fillarray', passphrase strings
-may be copied elsewhere in the memory.  PGG and gpg.el enables
-passphrase caching by default.
+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.
 
-** Most GnuPG features can be accessible from Emacs
-As the name says, EasyPG is inspired by GPGME (GnuPG Made Easy), and
-the API is close to GPGME.
\ No newline at end of file
+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.