* 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 an all-in-one 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).
+
+* Features
+
+The EasyPG Assistant provides the following features:
+
+- Keyring browser.
+- Cryptographic operations on regions.
+- Cryptographic operations on files.
+- Dired integration.
+- Encryption/decryption of *.gpg files.
+
+The EasyPG Library provides the following features:
+
+- The API covers most functions of GnuPG like GPGME.
+- S/MIME support using gpgsm.
+- Designed to avoid potential security pitfalls around Emacs
+
+* Requirements
+
+** GNU Emacs 21.4, XEmacs 21.4, or later
+
+** GnuPG 1.4.3 or later
+ If you are using earlier versions, you will need to specify
+ --disable-gpg-test when ./configure.
* 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)
+
+Restart emacs and type `M-x epa- TAB', and you will see a lot of
+commands available. For example,
+
+- To browse your keyring, type `M-x epa-list-keys'
+- To create a cleartext signature of the region, type `M-x epa-sign-region'
+
+You can also do some cryptographic operations from 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 uses EasyPG by default. To make sure of that,
+check mml2015-use set to 'epg. Other options which affect on the
+EasyPG 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+PGG is outdated PGP library used by old Gnus (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 using 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
+
+As I noted "PGG is outdated PGP library" above, PGG has several
+limitations. For example
+
+- PGG can't handle a message signed with multiple keys.
+- PGG can't prompt a user which key is being used.
+- PGG can't create a binary PGP messages.
+- PGG doesn't provide a way to select keys per cryptographic operation.
+- PGG ignores GnuPG's trust metrics.
+
+** 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.
-(1) Restart emacs
+** Passphrase may leak to a temporary file.
-(2) C-x C-f ~/test.gpg
+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.
-* Advantages over other competitors
+The EasyPG Library does not use call-process-region to communicate
+with a gpg subprocess.
-** EasyPG avoides potential security flaws of Emacs.
+** Passphrase may be stolen from a core file.
-*** `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) 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.
-*** 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.
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