- What's this?
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
Earlier versions are supported but not recommended.
- Quick start
** 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PGG is outdated PGP library used by old Gnus (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As I noted "PGG is outdated PGP library" above, PGG has several limitations.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.
** 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.