--- /dev/null
+;;; canlock.el --- functions for Cancel-Lock feature
+
+;; Copyright (C) 1998-1999, 2001-2016 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 <http://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:
+
+(eval-when-compile
+ (require 'cl))
+
+(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)
+
+(eval-when-compile
+ (defmacro canlock-string-as-unibyte (string)
+ "Return a unibyte string with the same individual bytes as STRING."
+ (if (fboundp 'string-as-unibyte)
+ (list 'string-as-unibyte string)
+ string)))
+
+(defun canlock-sha1 (message)
+ "Make a SHA-1 digest of MESSAGE as a unibyte string of length 20 bytes."
+ (let (sha1-maximum-internal-length)
+ (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 (canlock-string-as-unibyte 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
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