1 ;;; canlock.el --- functions for Cancel-Lock feature
3 ;; Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004
4 ;; Free Software Foundation, Inc.
6 ;; Author: Katsumi Yamaoka <yamaoka@jpl.org>
7 ;; Keywords: news, cancel-lock, hmac, sha1, rfc2104
9 ;; This program is free software; you can redistribute it and/or modify
10 ;; it under the terms of the GNU General Public License as published by
11 ;; the Free Software Foundation; either version 2, or (at your option)
14 ;; This program is distributed in the hope that it will be useful,
15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 ;; GNU General Public License for more details.
19 ;; You should have received a copy of the GNU General Public License
20 ;; along with this program; see the file COPYING. If not, write to the
21 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
22 ;; Boston, MA 02111-1307, USA.
26 ;; Canlock is a library for generating and verifying Cancel-Lock and/or
27 ;; Cancel-Key header in news articles. This is used to protect articles
28 ;; from rogue cancel, supersede or replace attacks. The method is based
29 ;; on draft-ietf-usefor-cancel-lock-01.txt which was released on November
30 ;; 3rd 1998. For instance, you can add Cancel-Lock (and possibly Cancel-
31 ;; Key) header in a news article by using a hook which will be evaluated
32 ;; just before sending an article as follows:
34 ;; (add-hook '*e**a*e-header-hook 'canlock-insert-header t)
36 ;; Verifying Cancel-Lock is mainly a function of news servers, however,
37 ;; you can verify your own article using the command `canlock-verify' in
38 ;; the (raw) article buffer. You will be prompted for the password for
39 ;; each time if the option `canlock-password' or `canlock-password-for-
40 ;; verify' is nil. Note that setting these options is a bit unsafe.
49 (defvar mail-header-separator
)
52 "The Cancel-Lock feature."
55 (defcustom canlock-password nil
56 "Password to use when signing a Cancel-Lock or a Cancel-Key header."
57 :type
'(radio (const :format
"Not specified " nil
)
58 (string :tag
"Password"))
61 (defcustom canlock-password-for-verify canlock-password
62 "Password to use when verifying a Cancel-Lock or a Cancel-Key header."
63 :type
'(radio (const :format
"Not specified " nil
)
64 (string :tag
"Password"))
67 (defcustom canlock-force-insert-header nil
68 "If non-nil, insert a Cancel-Lock or a Cancel-Key header even if the
69 buffer does not look like a news message."
74 (defmacro canlock-string-as-unibyte
(string)
75 "Return a unibyte string with the same individual bytes as STRING."
76 (if (fboundp 'string-as-unibyte
)
77 (list 'string-as-unibyte string
)
80 (defun canlock-sha1 (message)
81 "Make a SHA-1 digest of MESSAGE as a unibyte string of length 20 bytes."
82 (let (sha1-maximum-internal-length)
83 (sha1 message nil nil
'binary
)))
85 (defun canlock-make-cancel-key (message-id password
)
86 "Make a Cancel-Key header."
87 (when (> (length password
) 20)
88 (setq password
(canlock-sha1 password
)))
89 (setq password
(concat password
(make-string (- 64 (length password
)) 0)))
90 (let ((ipad (mapconcat (lambda (byte)
91 (char-to-string (logxor 54 byte
)))
93 (opad (mapconcat (lambda (byte)
94 (char-to-string (logxor 92 byte
)))
100 (concat ipad
(canlock-string-as-unibyte message-id
))))))))
102 (defun canlock-narrow-to-header ()
103 "Narrow the buffer to the head of the message."
104 (let (case-fold-search)
106 (goto-char (point-min))
107 (goto-char (if (re-search-forward
109 (regexp-quote mail-header-separator
))
114 (defun canlock-delete-headers ()
115 "Delete Cancel-Key or Cancel-Lock headers in the narrowed buffer."
116 (let ((case-fold-search t
))
117 (goto-char (point-min))
118 (while (re-search-forward "^Cancel-\\(Key\\|Lock\\):" nil t
)
119 (delete-region (match-beginning 0)
120 (if (re-search-forward "^[^\t ]" nil t
)
121 (goto-char (match-beginning 0))
124 (defun canlock-fetch-fields (&optional key
)
125 "Return a list of the values of Cancel-Lock header.
126 If KEY is non-nil, look for a Cancel-Key header instead. The buffer
127 is expected to be narrowed to just the headers of the message."
128 (let ((field (mail-fetch-field (if key
"Cancel-Key" "Cancel-Lock")))
130 (case-fold-search t
))
132 (setq fields
(split-string field
"[\t\n\r ,]+"))
134 (when (string-match "^sha1:" (setq field
(pop fields
)))
135 (push (substring field
5) rest
)))
138 (defun canlock-fetch-id-for-key ()
139 "Return a Message-ID in Cancel, Supersedes or Replaces header.
140 The buffer is expected to be narrowed to just the headers of the
142 (or (let ((cancel (mail-fetch-field "Control")))
144 (string-match "^cancel[\t ]+\\(<[^\t\n @<>]+@[^\t\n @<>]+>\\)"
146 (match-string 1 cancel
)))
147 (mail-fetch-field "Supersedes")
148 (mail-fetch-field "Replaces")))
151 (defun canlock-insert-header (&optional id-for-key id-for-lock password
)
152 "Insert a Cancel-Key and/or a Cancel-Lock header if possible."
153 (let (news control key-for-key key-for-lock
)
156 (canlock-narrow-to-header)
157 (when (setq news
(or canlock-force-insert-header
158 (mail-fetch-field "Newsgroups")))
160 (setq id-for-key
(canlock-fetch-id-for-key)))
161 (if (and (setq control
(mail-fetch-field "Control"))
162 (string-match "^cancel[\t ]+<[^\t\n @<>]+@[^\t\n @<>]+>"
164 (setq id-for-lock nil
)
166 (setq id-for-lock
(mail-fetch-field "Message-ID"))))
167 (canlock-delete-headers)
168 (goto-char (point-max))))
170 (if (not (or id-for-key id-for-lock
))
171 (message "There are no Message-ID(s)")
173 (setq password
(or canlock-password
175 "Password for Canlock: "))))
176 (if (or (not (stringp password
)) (zerop (length password
)))
177 (message "Password for Canlock is bad")
178 (setq key-for-key
(when id-for-key
179 (canlock-make-cancel-key
180 id-for-key password
))
181 key-for-lock
(when id-for-lock
182 (canlock-make-cancel-key
183 id-for-lock password
)))
184 (if (not (or key-for-key key-for-lock
))
185 (message "Couldn't insert Canlock header")
187 (insert "Cancel-Key: sha1:" key-for-key
"\n"))
189 (insert "Cancel-Lock: sha1:"
190 (base64-encode-string (canlock-sha1 key-for-lock
))
194 (defun canlock-verify (&optional buffer
)
195 "Verify Cancel-Lock or Cancel-Key in BUFFER.
196 If BUFFER is nil, the current buffer is assumed. Signal an error if
199 (let (keys locks errmsg id-for-key id-for-lock password
200 key-for-key key-for-lock match
)
206 (canlock-narrow-to-header)
207 (setq keys
(canlock-fetch-fields 'key
)
208 locks
(canlock-fetch-fields))
209 (if (not (or keys locks
))
211 "There are neither Cancel-Lock nor Cancel-Key headers")
212 (setq id-for-key
(canlock-fetch-id-for-key)
213 id-for-lock
(mail-fetch-field "Message-ID"))
214 (or id-for-key id-for-lock
215 (setq errmsg
"There are no Message-ID(s)")))))
218 (setq password
(or canlock-password-for-verify
219 (read-passwd "Password for Canlock: ")))
220 (if (or (not (stringp password
)) (zerop (length password
)))
221 (error "Password for Canlock is bad")
224 (setq key-for-key
(canlock-make-cancel-key id-for-key password
))
225 (while (and keys
(not match
))
226 (setq match
(string-equal key-for-key
(pop keys
)))))
227 (setq keys
(if match
"good" "bad")))
232 (base64-encode-string
233 (canlock-sha1 (canlock-make-cancel-key id-for-lock
235 (when (and locks
(not match
))
236 (setq match
(string-equal key-for-lock
(pop locks
)))))
237 (setq locks
(if match
"good" "bad")))
239 (when (member "bad" (list keys locks
))
241 (cond ((and keys locks
)
242 (message "Cancel-Key is %s, Cancel-Lock is %s" keys locks
))
244 (message "Cancel-Lock is %s" locks
))
246 (message "Cancel-Key is %s" keys
))))))))
250 ;;; arch-tag: 033c4f09-b9f1-459d-bd0d-254430283f78
251 ;;; canlock.el ends here