1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
|
* 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PGG is outdated PGP library used by old Gnus (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.
|
