* What's this?

EasyPG is a GnuPG interface for Emacs.  It has two aspects: convenient
tools which allow to use GnuPG from Emacs (EasyPG Assistant), and a
fully functional interface library to GnuPG (EasyPG Library.)

* Requirements

** GNU Emacs 21.4 or XEmacs 21.4

** GnuPG 1.4.3

* Quick start

** 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 epa-dired-do-encrypt)
  (select recipients by 'm' and click [OK])

* MUA Integration

The EasyPG Library can be used in combination with various MUA (Mail
User Agents.)

** CVS version of Gnus

CVS version of Gnus supports EasyPG natively.  To use, simply put the
following line into your ~/.emacs.

  (setq mml2015-use 'epg)

Other options which affect on the binding are

  mml2015-signers
  mml2015-encrypt-to-self
  mml2015-cache-passphrase
  mml2015-passphrase-cache-expiry
  mml2015-verbose

NOTE: You don't need pgg-epg.el in this case.

** PGG based MUA

PGG is outdated PGP library used by old Gnus (<= v5.11), MH-E, etc.

There is a PGG backend written EasyPG called pgg-epg.el.  However,
EasyPG API is a superset of PGG and pgg-epg.el provides nothing but
compatibility with PGG.

Limitations of PGG

- PGG doesn't have a user interface to select keys for typical
  cryptographic operations
- PGG can't handle messages signed with multiple keys correctly
- PGG trusts any keys for encryption

** SEMI based MUA

SEMI is the MIME library used by Wanderlust, cmail, T-gnus, etc.

There is an EasyPG capable SEMI library called EMIKO-EasyPG.  It can
be downloaded from the same site of the EasyPG distribution point.

* Security

There are security pitfalls around Emacs.  EasyPG is written with
avoiding them.

** Passphrase may leak to a temporary file.

The function call-process-region writes data in region to a temporary
file. If your PGP library used this function, your passphrases would
leak to the filesystem.

The EasyPG Library does not use call-process-region to communicate
with a gpg subprocess.

** Passphrase may be stolen from a core file.

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) to avoid this risk. 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.

The EasyPG Library dares to disable passphrase caching. Fortunately,
there is more secure way to cache passphrases - use gpg-agent.