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
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
|
;;; canlock.el --- functions for Cancel-Lock feature
;; Copyright (C) 1998-1999, 2001-2020 Free Software Foundation, Inc.
;; Author: Katsumi Yamaoka <yamaoka@jpl.org>
;; Keywords: news, cancel-lock, hmac, sha1, rfc2104
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Canlock is a library for generating and verifying Cancel-Lock and/or
;; Cancel-Key header in news articles. This is used to protect articles
;; from rogue cancel, supersede or replace attacks. The method is based
;; on draft-ietf-usefor-cancel-lock-01.txt which was released on November
;; 3rd 1998. For instance, you can add Cancel-Lock (and possibly Cancel-
;; Key) header in a news article by using a hook which will be evaluated
;; just before sending an article as follows:
;;
;; (add-hook '*e**a*e-header-hook 'canlock-insert-header t)
;;
;; Verifying Cancel-Lock is mainly a function of news servers, however,
;; you can verify your own article using the command `canlock-verify' in
;; the (raw) article buffer. You will be prompted for the password for
;; each time if the option `canlock-password' or
;; `canlock-password-for-verify' is nil. Note that setting these
;; options is a bit unsafe.
;;; Code:
(require 'sha1)
(defvar mail-header-separator)
(defgroup canlock nil
"The Cancel-Lock feature."
:group 'news)
(defcustom canlock-password nil
"Password to use when signing a Cancel-Lock or a Cancel-Key header."
:type '(radio (const :format "Not specified " nil)
(string :tag "Password"))
:group 'canlock)
(defcustom canlock-password-for-verify canlock-password
"Password to use when verifying a Cancel-Lock or a Cancel-Key header."
:type '(radio (const :format "Not specified " nil)
(string :tag "Password"))
:group 'canlock)
(defcustom canlock-force-insert-header nil
"If non-nil, insert a Cancel-Lock or a Cancel-Key header even if the
buffer does not look like a news message."
:type 'boolean
:group 'canlock)
(defun canlock-sha1 (message)
"Make a SHA-1 digest of MESSAGE as a unibyte string of length 20 bytes."
(sha1 message nil nil 'binary))
(defun canlock-make-cancel-key (message-id password)
"Make a Cancel-Key header."
(when (> (length password) 20)
(setq password (canlock-sha1 password)))
(setq password (concat password (make-string (- 64 (length password)) 0)))
(let ((ipad (mapconcat (lambda (byte)
(char-to-string (logxor 54 byte)))
password ""))
(opad (mapconcat (lambda (byte)
(char-to-string (logxor 92 byte)))
password "")))
(base64-encode-string
(canlock-sha1 (concat opad (canlock-sha1 (concat ipad message-id)))))))
(defun canlock-narrow-to-header ()
"Narrow the buffer to the head of the message."
(let (case-fold-search)
(narrow-to-region
(goto-char (point-min))
(goto-char (if (re-search-forward
(format "^$\\|^%s$"
(regexp-quote mail-header-separator))
nil t)
(match-beginning 0)
(point-max))))))
(defun canlock-delete-headers ()
"Delete Cancel-Key or Cancel-Lock headers in the narrowed buffer."
(let ((case-fold-search t))
(goto-char (point-min))
(while (re-search-forward "^Cancel-\\(Key\\|Lock\\):" nil t)
(delete-region (match-beginning 0)
(if (re-search-forward "^[^\t ]" nil t)
(goto-char (match-beginning 0))
(point-max))))))
(defun canlock-fetch-fields (&optional key)
"Return a list of the values of Cancel-Lock header.
If KEY is non-nil, look for a Cancel-Key header instead. The buffer
is expected to be narrowed to just the headers of the message."
(let ((field (mail-fetch-field (if key "Cancel-Key" "Cancel-Lock")))
fields rest
(case-fold-search t))
(when field
(setq fields (split-string field "[\t\n\r ,]+"))
(while fields
(when (string-match "^sha1:" (setq field (pop fields)))
(push (substring field 5) rest)))
(nreverse rest))))
(defun canlock-fetch-id-for-key ()
"Return a Message-ID in Cancel, Supersedes or Replaces header.
The buffer is expected to be narrowed to just the headers of the
message."
(or (let ((cancel (mail-fetch-field "Control")))
(and cancel
(string-match "^cancel[\t ]+\\(<[^\t\n @<>]+@[^\t\n @<>]+>\\)"
cancel)
(match-string 1 cancel)))
(mail-fetch-field "Supersedes")
(mail-fetch-field "Replaces")))
;;;###autoload
(defun canlock-insert-header (&optional id-for-key id-for-lock password)
"Insert a Cancel-Key and/or a Cancel-Lock header if possible."
(let (news control key-for-key key-for-lock)
(save-excursion
(save-restriction
(canlock-narrow-to-header)
(when (setq news (or canlock-force-insert-header
(mail-fetch-field "Newsgroups")))
(unless id-for-key
(setq id-for-key (canlock-fetch-id-for-key)))
(if (and (setq control (mail-fetch-field "Control"))
(string-match "^cancel[\t ]+<[^\t\n @<>]+@[^\t\n @<>]+>"
control))
(setq id-for-lock nil)
(unless id-for-lock
(setq id-for-lock (mail-fetch-field "Message-ID"))))
(canlock-delete-headers)
(goto-char (point-max))))
(when news
(if (not (or id-for-key id-for-lock))
(message "There are no Message-ID(s)")
(unless password
(setq password (or canlock-password
(read-passwd
"Password for Canlock: "))))
(if (or (not (stringp password)) (zerop (length password)))
(message "Password for Canlock is bad")
(setq key-for-key (when id-for-key
(canlock-make-cancel-key
id-for-key password))
key-for-lock (when id-for-lock
(canlock-make-cancel-key
id-for-lock password)))
(if (not (or key-for-key key-for-lock))
(message "Couldn't insert Canlock header")
(when key-for-key
(insert "Cancel-Key: sha1:" key-for-key "\n"))
(when key-for-lock
(insert "Cancel-Lock: sha1:"
(base64-encode-string (canlock-sha1 key-for-lock))
"\n")))))))))
;;;###autoload
(defun canlock-verify (&optional buffer)
"Verify Cancel-Lock or Cancel-Key in BUFFER.
If BUFFER is nil, the current buffer is assumed. Signal an error if
it fails."
(interactive)
(let (keys locks errmsg id-for-key id-for-lock password
key-for-key key-for-lock match)
(save-excursion
(when buffer
(set-buffer buffer))
(save-restriction
(widen)
(canlock-narrow-to-header)
(setq keys (canlock-fetch-fields 'key)
locks (canlock-fetch-fields))
(if (not (or keys locks))
(setq errmsg
"There are neither Cancel-Lock nor Cancel-Key headers")
(setq id-for-key (canlock-fetch-id-for-key)
id-for-lock (mail-fetch-field "Message-ID"))
(or id-for-key id-for-lock
(setq errmsg "There are no Message-ID(s)")))))
(if errmsg
(error "%s" errmsg)
(setq password (or canlock-password-for-verify
(read-passwd "Password for Canlock: ")))
(if (or (not (stringp password)) (zerop (length password)))
(error "Password for Canlock is bad")
(when keys
(when id-for-key
(setq key-for-key (canlock-make-cancel-key id-for-key password))
(while (and keys (not match))
(setq match (string-equal key-for-key (pop keys)))))
(setq keys (if match "good" "bad")))
(setq match nil)
(when locks
(when id-for-lock
(setq key-for-lock
(base64-encode-string
(canlock-sha1 (canlock-make-cancel-key id-for-lock
password))))
(when (and locks (not match))
(setq match (string-equal key-for-lock (pop locks)))))
(setq locks (if match "good" "bad")))
(prog1
(when (member "bad" (list keys locks))
"bad")
(cond ((and keys locks)
(message "Cancel-Key is %s, Cancel-Lock is %s" keys locks))
(locks
(message "Cancel-Lock is %s" locks))
(keys
(message "Cancel-Key is %s" keys))))))))
(provide 'canlock)
;;; canlock.el ends here
|
