root/trunk/lisp/gnus/canlock.el

;;; canlock.el --- functions for Cancel-Lock feature

;; Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004,
;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.

;; Author: Katsumi Yamaoka <yamaoka@jpl.org>
;; Keywords: news, cancel-lock, hmac, sha1, rfc2104

;; This program 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, or (at your option)
;; any later version.

;; This program 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 this program; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; 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)

;;; arch-tag: 033c4f09-b9f1-459d-bd0d-254430283f78
;;; canlock.el ends here