Add docstring.

[elisp/epg.git] / README

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 * What's this?
 
-EasyPG is yet another GnuPG interface for Emacs.  It consists of a
-transparent file encryption application and easy-to-use elisp library
-to interact with GnuPG.
+EasyPG is yet another GnuPG interface for Emacs.  It consists of two parts:
+
+- "The EasyPG Assistant" which provides basic GUI of GnuPG
+- "The EasyPG Library" which enables use of various features of GnuPG
+
+NOTE: EasyPG is neither a fork nor a re-implementation of Gnus/PGG.
+
+* Requirements
+
+** GNU Emacs 21.4 or XEmacs 21.4
+
+** GnuPG 1.4.3
 
 * Quick start
 
-(0) Put (require 'epg-file) in your ~/.emacs.el
+** Installation
+
+  $ ./configure
+  $ sudo make install
+
+Add the following line to your ~/.emacs
+
+  (require 'epa-setup)
+
+Then you can browse your keyring by `M-x epa-list-keys'.  In addition,
+you can do some cryptographic operations on dired.
+
+  M-x dired
+  (mark some files)
+  : e (or M-x epg-dired-do-encrypt)
+  (select recipients and click [OK])
 
-(1) Restart emacs
+* Security consideration
 
-(2) C-x C-f ~/test.gpg
+** `call-process-region' writes data in region to a temporary file
 
-* Advantages over other competitors
+`call-process-region' writes data in region to a temporary file.
+EasyPG does *not* use `call-process-region' to communicate with a gpg
+subprocess.
 
-** EasyPG avoides potential security flaws of Emacs.
+** `(fillarray string 0)' is not enough to clear passphrases
 
-*** `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.
+If Emacs crashes and dumps core, Lisp 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.  Therefore, passphrase
+caching in Elisp is generally a bad idea.
 
-*** 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.
+The EasyPG Library dares to disable passphrase caching.  Fortunately,
+there is more secure way to cache passphrases - use gpg-agent.  Elisp
+programs can set `epg-context-passphrase-callback' to cache user's
+passphrases, it is not recommended though.