lisp/epa-file.el

   1 ;;; epa-file.el --- the EasyPG Assistant, transparent file encryption
   2 ;; Copyright (C) 2006-2011 Free Software Foundation, Inc.
   3
   4 ;; Author: Daiki Ueno <ueno@unixuser.org>
   5 ;; Keywords: PGP, GnuPG
   6 ;; Package: epa
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  22
  23 ;;; Code:
  24
  25 (require 'epa)
  26 (require 'epa-hook)
  27
  28 (defcustom epa-file-cache-passphrase-for-symmetric-encryption nil
  29   "If non-nil, cache passphrase for symmetric encryption.
  30
  31 For security reasons, this option is turned off by default and
  32 not recommended to use.  Instead, consider using public-key
  33 encryption with gpg-agent which does the same job in a safer
  34 way."
  35   :type 'boolean
  36   :group 'epa-file)
  37
  38 (defcustom epa-file-select-keys 'silent
  39   "Control whether or not to pop up the key selection dialog.
  40
  41 If t, always asks user to select recipients.
  42 If nil, query user only when `epa-file-encrypt-to' is not set.
  43 If neither t nor nil, doesn't ask user.  In this case, symmetric
  44 encryption is used."
  45   :type '(choice (const :tag "Ask always" t)
  46                  (const :tag "Ask when recipients are not set" nil)
  47                  (const :tag "Don't ask" silent))
  48   :group 'epa-file)
  49
  50 (defvar epa-file-passphrase-alist nil)
  51
  52 (eval-and-compile
  53   (if (fboundp 'encode-coding-string)
  54       (defalias 'epa-file--encode-coding-string 'encode-coding-string)
  55     (defalias 'epa-file--encode-coding-string 'identity)))
  56
  57 (eval-and-compile
  58   (if (fboundp 'decode-coding-string)
  59       (defalias 'epa-file--decode-coding-string 'decode-coding-string)
  60     (defalias 'epa-file--decode-coding-string 'identity)))
  61
  62 (defun epa-file-passphrase-callback-function (context key-id file)
  63   (if (and epa-file-cache-passphrase-for-symmetric-encryption
  64            (eq key-id 'SYM))
  65       (progn
  66         (setq file (file-truename file))
  67         (let ((entry (assoc file epa-file-passphrase-alist))
  68               passphrase)
  69           (or (copy-sequence (cdr entry))
  70               (progn
  71                 (unless entry
  72                   (setq entry (list file)
  73                         epa-file-passphrase-alist
  74                         (cons entry
  75                               epa-file-passphrase-alist)))
  76                 (setq passphrase (epa-passphrase-callback-function context
  77                                                                    key-id
  78                                                                    file))
  79                 (setcdr entry (copy-sequence passphrase))
  80                 passphrase))))
  81     (epa-passphrase-callback-function context key-id file)))
  82
  83 ;;;###autoload
  84 (defun epa-file-handler (operation &rest args)
  85   (save-match-data
  86     (let ((op (get operation 'epa-file)))
  87       (if op
  88           (apply op args)
  89         (epa-file-run-real-handler operation args)))))
  90
  91 (defun epa-file-run-real-handler (operation args)
  92   (let ((inhibit-file-name-handlers
  93          (cons 'epa-file-handler
  94                (and (eq inhibit-file-name-operation operation)
  95                     inhibit-file-name-handlers)))
  96         (inhibit-file-name-operation operation))
  97     (apply operation args)))
  98
  99 (defun epa-file-decode-and-insert (string file visit beg end replace)
 100   (if (fboundp 'decode-coding-inserted-region)
 101       (save-restriction
 102         (narrow-to-region (point) (point))
 103         (insert (if enable-multibyte-characters
 104                     (string-to-multibyte string)
 105                   string))
 106           (decode-coding-inserted-region
 107            (point-min) (point-max)
 108            (substring file 0 (string-match epa-file-name-regexp file))
 109          visit beg end replace))
 110     (insert (epa-file--decode-coding-string string (or coding-system-for-read
 111                                                        'undecided)))))
 112
 113 (defvar epa-file-error nil)
 114 (defun epa-file--find-file-not-found-function ()
 115   (let ((error epa-file-error))
 116     (save-window-excursion
 117       (kill-buffer))
 118     (signal 'file-error
 119             (cons "Opening input file" (cdr error)))))
 120
 121 (defvar last-coding-system-used)
 122 (defun epa-file-insert-file-contents (file &optional visit beg end replace)
 123   (barf-if-buffer-read-only)
 124   (if (and visit (or beg end))
 125       (error "Attempt to visit less than an entire file"))
 126   (setq file (expand-file-name file))
 127   (let* ((local-copy
 128           (condition-case nil
 129               (epa-file-run-real-handler #'file-local-copy (list file))
 130             (error)))
 131          (local-file (or local-copy file))
 132          (context (epg-make-context))
 133          string length entry)
 134     (if visit
 135         (setq buffer-file-name file))
 136     (epg-context-set-passphrase-callback
 137      context
 138      (cons #'epa-file-passphrase-callback-function
 139            local-file))
 140     (epg-context-set-progress-callback context
 141                                        #'epa-progress-callback-function)
 142     (unwind-protect
 143         (progn
 144           (if replace
 145               (goto-char (point-min)))
 146           (condition-case error
 147               (setq string (epg-decrypt-file context local-file nil))
 148             (error
 149              (if (setq entry (assoc file epa-file-passphrase-alist))
 150                  (setcdr entry nil))
 151              ;; Hack to prevent find-file from opening empty buffer
 152              ;; when decryption failed (bug#6568).  See the place
 153              ;; where `find-file-not-found-functions' are called in
 154              ;; `find-file-noselect-1'.
 155              (when (file-exists-p local-file)
 156                (make-local-variable 'epa-file-error)
 157                (setq epa-file-error error)
 158                (add-hook 'find-file-not-found-functions
 159                          'epa-file--find-file-not-found-function
 160                          nil t))
 161              (signal 'file-error
 162                      (cons "Opening input file" (cdr error)))))
 163           (make-local-variable 'epa-file-encrypt-to)
 164           (setq epa-file-encrypt-to
 165                 (mapcar #'car (epg-context-result-for context 'encrypted-to)))
 166           (if (or beg end)
 167               (setq string (substring string (or beg 0) end)))
 168           (save-excursion
 169             ;; If visiting, bind off buffer-file-name so that
 170             ;; file-locking will not ask whether we should
 171             ;; really edit the buffer.
 172             (let ((buffer-file-name
 173                    (if visit nil buffer-file-name)))
 174               (save-restriction
 175                 (narrow-to-region (point) (point))
 176                 (epa-file-decode-and-insert string file visit beg end replace)
 177                 (setq length (- (point-max) (point-min))))
 178               (if replace
 179                   (delete-region (point) (point-max))))
 180             (if visit
 181                 (set-visited-file-modtime))))
 182       (if (and local-copy
 183                (file-exists-p local-copy))
 184           (delete-file local-copy)))
 185     (list file length)))
 186 (put 'insert-file-contents 'epa-file 'epa-file-insert-file-contents)
 187
 188 (defun epa-file-write-region (start end file &optional append visit lockname
 189                                     mustbenew)
 190   (if append
 191       (error "Can't append to the file"))
 192   (setq file (expand-file-name file))
 193   (let* ((coding-system (or coding-system-for-write
 194                             (if (fboundp 'select-safe-coding-system)
 195                                 ;; This is needed since Emacs 22 has
 196                                 ;; no-conversion setting for *.gpg in
 197                                 ;; `auto-coding-alist'.
 198                                 (let ((buffer-file-name
 199                                        (file-name-sans-extension file)))
 200                                   (select-safe-coding-system
 201                                    (point-min) (point-max)))
 202                               buffer-file-coding-system)))
 203          (context (epg-make-context))
 204          (coding-system-for-write 'binary)
 205          string entry
 206          (recipients
 207           (cond
 208            ((listp epa-file-encrypt-to) epa-file-encrypt-to)
 209            ((stringp epa-file-encrypt-to) (list epa-file-encrypt-to)))))
 210     (epg-context-set-passphrase-callback
 211      context
 212      (cons #'epa-file-passphrase-callback-function
 213            file))
 214     (epg-context-set-progress-callback context
 215                                        #'epa-progress-callback-function)
 216     (epg-context-set-armor context epa-armor)
 217     (condition-case error
 218         (setq string
 219               (epg-encrypt-string
 220                context
 221                (if (stringp start)
 222                    (epa-file--encode-coding-string start coding-system)
 223                  (unless start
 224                    (setq start (point-min)
 225                          end (point-max)))
 226                  (epa-file--encode-coding-string (buffer-substring start end)
 227                                                  coding-system))
 228                (if (or (eq epa-file-select-keys t)
 229                        (and (null epa-file-select-keys)
 230                             (not (local-variable-p 'epa-file-encrypt-to
 231                                                    (current-buffer)))))
 232                    (epa-select-keys
 233                     context
 234                     "Select recipents for encryption.
 235 If no one is selected, symmetric encryption will be performed.  "
 236                     recipients)
 237                  (if epa-file-encrypt-to
 238                      (epg-list-keys context recipients)))))
 239       (error
 240        (if (setq entry (assoc file epa-file-passphrase-alist))
 241            (setcdr entry nil))
 242        (signal 'file-error (cons "Opening output file" (cdr error)))))
 243     (epa-file-run-real-handler
 244      #'write-region
 245      (list string nil file append visit lockname mustbenew))
 246     (if (boundp 'last-coding-system-used)
 247         (setq last-coding-system-used coding-system))
 248     (if (eq visit t)
 249         (progn
 250           (setq buffer-file-name file)
 251           (set-visited-file-modtime))
 252       (if (stringp visit)
 253           (progn
 254             (set-visited-file-modtime)
 255             (setq buffer-file-name visit))))
 256     (if (or (eq visit t)
 257             (eq visit nil)
 258             (stringp visit))
 259         (message "Wrote %s" buffer-file-name))))
 260 (put 'write-region 'epa-file 'epa-file-write-region)
 261
 262 (defun epa-file-select-keys ()
 263   "Select recipients for encryption."
 264   (interactive)
 265   (make-local-variable 'epa-file-encrypt-to)
 266   (setq epa-file-encrypt-to
 267         (mapcar
 268          (lambda (key)
 269            (epg-sub-key-id (car (epg-key-sub-key-list key))))
 270         (epa-select-keys
 271          (epg-make-context)
 272          "Select recipents for encryption.
 273 If no one is selected, symmetric encryption will be performed.  "))))
 274
 275 ;;;###autoload
 276 (defun epa-file-enable ()
 277   (interactive)
 278   (if (memq epa-file-handler file-name-handler-alist)
 279       (message "`epa-file' already enabled")
 280     (setq file-name-handler-alist
 281           (cons epa-file-handler file-name-handler-alist))
 282     (add-hook 'find-file-hook 'epa-file-find-file-hook)
 283     (setq auto-mode-alist (cons epa-file-auto-mode-alist-entry auto-mode-alist))
 284     (message "`epa-file' enabled")))
 285
 286 ;;;###autoload
 287 (defun epa-file-disable ()
 288   (interactive)
 289   (if (memq epa-file-handler file-name-handler-alist)
 290       (progn
 291         (setq file-name-handler-alist
 292               (delq epa-file-handler file-name-handler-alist))
 293         (remove-hook 'find-file-hook 'epa-file-find-file-hook)
 294         (setq auto-mode-alist (delq epa-file-auto-mode-alist-entry
 295                                     auto-mode-alist))
 296         (message "`epa-file' disabled"))
 297     (message "`epa-file' already disabled")))
 298
 299 (provide 'epa-file)
 300
 301 ;;; epa-file.el ends here