lisp/epa-file.el

   1 ;;; epa-file.el --- the EasyPG Assistant, transparent file encryption -*- lexical-binding: t -*-
   2 ;; Copyright (C) 2006-2014 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 gpg-agent which
  33 does the same job in a safer way.  See Info node `(epa) Caching
  34 Passphrases' for more information.
  35
  36 Note that this option has no effect if you use GnuPG 2.0."
  37   :type 'boolean
  38   :group 'epa-file)
  39
  40 (defcustom epa-file-select-keys nil
  41   "Control whether or not to pop up the key selection dialog.
  42
  43 If t, always asks user to select recipients.
  44 If nil, query user only when `epa-file-encrypt-to' is not set.
  45 If neither t nor nil, doesn't ask user.  In this case, symmetric
  46 encryption is used."
  47   :type '(choice (const :tag "Ask always" t)
  48                  (const :tag "Ask when recipients are not set" nil)
  49                  (const :tag "Don't ask" silent))
  50   :group 'epa-file)
  51
  52 (defvar epa-file-passphrase-alist nil)
  53
  54 (eval-and-compile
  55   (if (fboundp 'encode-coding-string)
  56       (defalias 'epa-file--encode-coding-string 'encode-coding-string)
  57     (defalias 'epa-file--encode-coding-string 'identity)))
  58
  59 (eval-and-compile
  60   (if (fboundp 'decode-coding-string)
  61       (defalias 'epa-file--decode-coding-string 'decode-coding-string)
  62     (defalias 'epa-file--decode-coding-string 'identity)))
  63
  64 (defun epa-file-passphrase-callback-function (context key-id file)
  65   (if (and epa-file-cache-passphrase-for-symmetric-encryption
  66            (eq key-id 'SYM))
  67       (progn
  68         (setq file (file-truename file))
  69         (let ((entry (assoc file epa-file-passphrase-alist))
  70               passphrase)
  71           (or (copy-sequence (cdr entry))
  72               (progn
  73                 (unless entry
  74                   (setq entry (list file)
  75                         epa-file-passphrase-alist
  76                         (cons entry
  77                               epa-file-passphrase-alist)))
  78                 (setq passphrase (epa-passphrase-callback-function context
  79                                                                    key-id
  80                                                                    file))
  81                 (setcdr entry (copy-sequence passphrase))
  82                 passphrase))))
  83     (epa-passphrase-callback-function context key-id file)))
  84
  85 ;;;###autoload
  86 (defun epa-file-handler (operation &rest args)
  87   (save-match-data
  88     (let ((op (get operation 'epa-file)))
  89       (if op
  90           (apply op args)
  91         (epa-file-run-real-handler operation args)))))
  92
  93 (defun epa-file-run-real-handler (operation args)
  94   (let ((inhibit-file-name-handlers
  95          (cons 'epa-file-handler
  96                (and (eq inhibit-file-name-operation operation)
  97                     inhibit-file-name-handlers)))
  98         (inhibit-file-name-operation operation))
  99     (apply operation args)))
 100
 101 (defun epa-file-decode-and-insert (string file visit beg end replace)
 102   (if (fboundp 'decode-coding-inserted-region)
 103       (save-restriction
 104         (narrow-to-region (point) (point))
 105         (insert (if enable-multibyte-characters
 106                     (string-to-multibyte string)
 107                   string))
 108           (decode-coding-inserted-region
 109            (point-min) (point-max)
 110            (substring file 0 (string-match epa-file-name-regexp file))
 111          visit beg end replace))
 112     (insert (epa-file--decode-coding-string string (or coding-system-for-read
 113                                                        'undecided)))))
 114
 115 (defvar epa-file-error nil)
 116 (defun epa-file--find-file-not-found-function ()
 117   (let ((error epa-file-error))
 118     (save-window-excursion
 119       (kill-buffer))
 120     (signal 'file-error
 121             (cons "Opening input file" (cdr error)))))
 122
 123 (defvar last-coding-system-used)
 124 (defun epa-file-insert-file-contents (file &optional visit beg end replace)
 125   (barf-if-buffer-read-only)
 126   (if (and visit (or beg end))
 127       (error "Attempt to visit less than an entire file"))
 128   (setq file (expand-file-name file))
 129   (let* ((local-copy
 130           (condition-case nil
 131               (epa-file-run-real-handler #'file-local-copy (list file))
 132             (error)))
 133          (local-file (or local-copy file))
 134          (context (epg-make-context))
 135          (buf (current-buffer))
 136          string length entry)
 137     (if visit
 138         (setq buffer-file-name file))
 139     (epg-context-set-passphrase-callback
 140      context
 141      (cons #'epa-file-passphrase-callback-function
 142            local-file))
 143     (epg-context-set-progress-callback
 144      context
 145      (cons #'epa-progress-callback-function
 146            (format "Decrypting %s" file)))
 147     (unwind-protect
 148         (progn
 149           (if replace
 150               (goto-char (point-min)))
 151           (condition-case error
 152               (setq string (epg-decrypt-file context local-file nil))
 153             (error
 154              (if (setq entry (assoc file epa-file-passphrase-alist))
 155                  (setcdr entry nil))
 156              ;; Hack to prevent find-file from opening empty buffer
 157              ;; when decryption failed (bug#6568).  See the place
 158              ;; where `find-file-not-found-functions' are called in
 159              ;; `find-file-noselect-1'.
 160              (when (file-exists-p local-file)
 161                (setq-local epa-file-error error)
 162                (add-hook 'find-file-not-found-functions
 163                          'epa-file--find-file-not-found-function
 164                          nil t))
 165              (signal 'file-error
 166                      (cons "Opening input file" (cdr error)))))
 167           (set-buffer buf) ;In case timer/filter changed/killed it (bug#16029)!
 168           (setq-local epa-file-encrypt-to
 169                       (mapcar #'car (epg-context-result-for
 170                                      context 'encrypted-to)))
 171           (if (or beg end)
 172               (setq string (substring string (or beg 0) end)))
 173           (save-excursion
 174             ;; If visiting, bind off buffer-file-name so that
 175             ;; file-locking will not ask whether we should
 176             ;; really edit the buffer.
 177             (let ((buffer-file-name
 178                    (if visit nil buffer-file-name)))
 179               (save-restriction
 180                 (narrow-to-region (point) (point))
 181                 (epa-file-decode-and-insert string file visit beg end replace)
 182                 (setq length (- (point-max) (point-min))))
 183               (if replace
 184                   (delete-region (point) (point-max))))
 185             (if visit
 186                 (set-visited-file-modtime))))
 187       (if (and local-copy
 188                (file-exists-p local-copy))
 189           (delete-file local-copy)))
 190     (list file length)))
 191 (put 'insert-file-contents 'epa-file 'epa-file-insert-file-contents)
 192
 193 (defun epa-file-write-region (start end file &optional append visit lockname
 194                                     mustbenew)
 195   (if append
 196       (error "Can't append to the file"))
 197   (setq file (expand-file-name file))
 198   (let* ((coding-system (or coding-system-for-write
 199                             (if (fboundp 'select-safe-coding-system)
 200                                 ;; This is needed since Emacs 22 has
 201                                 ;; no-conversion setting for *.gpg in
 202                                 ;; `auto-coding-alist'.
 203                                 (let ((buffer-file-name
 204                                        (file-name-sans-extension file)))
 205                                   (select-safe-coding-system
 206                                    (point-min) (point-max)))
 207                               buffer-file-coding-system)))
 208          (context (epg-make-context))
 209          (coding-system-for-write 'binary)
 210          string entry
 211          (recipients
 212           (cond
 213            ((listp epa-file-encrypt-to) epa-file-encrypt-to)
 214            ((stringp epa-file-encrypt-to) (list epa-file-encrypt-to))))
 215          buffer)
 216     (epg-context-set-passphrase-callback
 217      context
 218      (cons #'epa-file-passphrase-callback-function
 219            file))
 220     (epg-context-set-progress-callback
 221      context
 222      (cons #'epa-progress-callback-function
 223            (format "Encrypting %s" file)))
 224     (epg-context-set-armor context epa-armor)
 225     (condition-case error
 226         (setq string
 227               (epg-encrypt-string
 228                context
 229                (if (stringp start)
 230                    (epa-file--encode-coding-string start coding-system)
 231                  (unless start
 232                    (setq start (point-min)
 233                          end (point-max)))
 234                  (setq buffer (current-buffer))
 235                  (with-temp-buffer
 236                    (insert-buffer-substring buffer start end)
 237                    ;; Translate the region according to
 238                    ;; `buffer-file-format', as `write-region' would.
 239                    ;; We can't simply do `write-region' (into a
 240                    ;; temporary file) here, since it writes out
 241                    ;; decrypted contents.
 242                    (format-encode-buffer (with-current-buffer buffer
 243                                            buffer-file-format))
 244                    (epa-file--encode-coding-string (buffer-string)
 245                                                    coding-system)))
 246                (if (or (eq epa-file-select-keys t)
 247                        (and (null epa-file-select-keys)
 248                             (not (local-variable-p 'epa-file-encrypt-to
 249                                                    (current-buffer)))))
 250                    (epa-select-keys
 251                     context
 252                     "Select recipients for encryption.
 253 If no one is selected, symmetric encryption will be performed.  "
 254                     recipients)
 255                  (if epa-file-encrypt-to
 256                      (epg-list-keys context recipients)))))
 257       (error
 258        (if (setq entry (assoc file epa-file-passphrase-alist))
 259            (setcdr entry nil))
 260        (signal 'file-error (cons "Opening output file" (cdr error)))))
 261     (epa-file-run-real-handler
 262      #'write-region
 263      (list string nil file append visit lockname mustbenew))
 264     (if (boundp 'last-coding-system-used)
 265         (setq last-coding-system-used coding-system))
 266     (if (eq visit t)
 267         (progn
 268           (setq buffer-file-name file)
 269           (set-visited-file-modtime))
 270       (if (stringp visit)
 271           (progn
 272             (set-visited-file-modtime)
 273             (setq buffer-file-name visit))))
 274     (if (or (eq visit t)
 275             (eq visit nil)
 276             (stringp visit))
 277         (message "Wrote %s" buffer-file-name))))
 278 (put 'write-region 'epa-file 'epa-file-write-region)
 279
 280 (defun epa-file-select-keys ()
 281   "Select recipients for encryption."
 282   (interactive)
 283   (setq-local epa-file-encrypt-to
 284               (mapcar
 285                (lambda (key)
 286                  (epg-sub-key-id (car (epg-key-sub-key-list key))))
 287                (epa-select-keys
 288                 (epg-make-context)
 289                 "Select recipients for encryption.
 290 If no one is selected, symmetric encryption will be performed.  "))))
 291
 292 ;;;###autoload
 293 (defun epa-file-enable ()
 294   (interactive)
 295   (if (memq epa-file-handler file-name-handler-alist)
 296       (message "`epa-file' already enabled")
 297     (setq file-name-handler-alist
 298           (cons epa-file-handler file-name-handler-alist))
 299     (add-hook 'find-file-hook 'epa-file-find-file-hook)
 300     (setq auto-mode-alist (cons epa-file-auto-mode-alist-entry auto-mode-alist))
 301     (message "`epa-file' enabled")))
 302
 303 ;;;###autoload
 304 (defun epa-file-disable ()
 305   (interactive)
 306   (if (memq epa-file-handler file-name-handler-alist)
 307       (progn
 308         (setq file-name-handler-alist
 309               (delq epa-file-handler file-name-handler-alist))
 310         (remove-hook 'find-file-hook 'epa-file-find-file-hook)
 311         (setq auto-mode-alist (delq epa-file-auto-mode-alist-entry
 312                                     auto-mode-alist))
 313         (message "`epa-file' disabled"))
 314     (message "`epa-file' already disabled")))
 315
 316 (provide 'epa-file)
 317
 318 ;;; epa-file.el ends here