lisp/org-crypt.el

   1 ;;; org-crypt.el --- Public key encryption for org-mode entries
   2
   3 ;; Copyright (C) 2007-2016 Free Software Foundation, Inc.
   4
   5 ;; Emacs Lisp Archive Entry
   6 ;; Filename: org-crypt.el
   7 ;; Keywords: org-mode
   8 ;; Author: John Wiegley <johnw@gnu.org>
   9 ;; Maintainer: Peter Jones <pjones@pmade.com>
  10 ;; Description: Adds public key encryption to org-mode buffers
  11 ;; URL: http://www.newartisans.com/software/emacs.html
  12 ;; Compatibility: Emacs22
  13
  14 ;; This file is part of GNU Emacs.
  15 ;;
  16 ;; GNU Emacs is free software: you can redistribute it and/or modify
  17 ;; it under the terms of the GNU General Public License as published by
  18 ;; the Free Software Foundation, either version 3 of the License, or
  19 ;; (at your option) any later version.
  20
  21 ;; GNU Emacs is distributed in the hope that it will be useful,
  22 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  23 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24 ;; GNU General Public License for more details.
  25
  26 ;; You should have received a copy of the GNU General Public License
  27 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  28
  29 ;;; Commentary:
  30
  31 ;; Right now this is just a set of functions to play with.  It depends
  32 ;; on the epg library.  Here's how you would use it:
  33 ;;
  34 ;; 1. To mark an entry for encryption, tag the heading with "crypt".
  35 ;;    You can change the tag to any complex tag matching string by
  36 ;;    setting the `org-crypt-tag-matcher' variable.
  37 ;;
  38 ;; 2. Set the encryption key to use in the `org-crypt-key' variable,
  39 ;;    or use `M-x org-set-property' to set the property CRYPTKEY to
  40 ;;    any address in your public keyring.  The text of the entry (but
  41 ;;    not its properties or headline) will be encrypted for this user.
  42 ;;    For them to read it, the corresponding secret key must be
  43 ;;    located in the secret key ring of the account where you try to
  44 ;;    decrypt it.  This makes it possible to leave secure notes that
  45 ;;    only the intended recipient can read in a shared-org-mode-files
  46 ;;    scenario.
  47 ;;    If the key is not set, org-crypt will default to symmetric encryption.
  48 ;;
  49 ;; 3. To later decrypt an entry, use `org-decrypt-entries' or
  50 ;;    `org-decrypt-entry'.  It might be useful to bind this to a key,
  51 ;;    like C-c C-/.  I hope that in the future, C-c C-r can be might
  52 ;;    overloaded to also decrypt an entry if it's encrypted, since
  53 ;;    that fits nicely with the meaning of "reveal".
  54 ;;
  55 ;; 4. To automatically encrypt all necessary entries when saving a
  56 ;;    file, call `org-crypt-use-before-save-magic' after loading
  57 ;;    org-crypt.el.
  58
  59 ;;; Thanks:
  60
  61 ;; - Carsten Dominik
  62 ;; - Vitaly Ostanin
  63
  64 (require 'org)
  65
  66 ;;; Code:
  67
  68 (declare-function epg-decrypt-string "epg" (context cipher))
  69 (declare-function epg-list-keys "epg" (context &optional name mode))
  70 (declare-function epg-make-context "epg"
  71                   (&optional protocol armor textmode include-certs
  72                              cipher-algorithm digest-algorithm
  73                              compress-algorithm))
  74 (declare-function epg-encrypt-string "epg"
  75                   (context plain recipients &optional sign always-trust))
  76 (defvar epg-context)
  77
  78
  79 (defgroup org-crypt nil
  80   "Org Crypt."
  81   :tag "Org Crypt"
  82   :group 'org)
  83
  84 (defcustom org-crypt-tag-matcher "crypt"
  85   "The tag matcher used to find headings whose contents should be encrypted.
  86
  87 See the \"Match syntax\" section of the org manual for more details."
  88   :type 'string
  89   :group 'org-crypt)
  90
  91 (defcustom org-crypt-key ""
  92   "The default key to use when encrypting the contents of a heading.
  93
  94 This setting can also be overridden in the CRYPTKEY property."
  95   :type 'string
  96   :group 'org-crypt)
  97
  98 (defcustom org-crypt-disable-auto-save 'ask
  99   "What org-decrypt should do if `auto-save-mode' is enabled.
 100
 101 t        : Disable auto-save-mode for the current buffer
 102            prior to decrypting an entry.
 103
 104 nil      : Leave auto-save-mode enabled.
 105            This may cause data to be written to disk unencrypted!
 106
 107 `ask'    : Ask user whether or not to disable auto-save-mode
 108            for the current buffer.
 109
 110 `encrypt': Leave auto-save-mode enabled for the current buffer,
 111            but automatically re-encrypt all decrypted entries
 112            *before* auto-saving.
 113            NOTE: This only works for entries which have a tag
 114            that matches `org-crypt-tag-matcher'."
 115   :group 'org-crypt
 116   :version "24.1"
 117   :type '(choice (const :tag "Always"  t)
 118                  (const :tag "Never"   nil)
 119                  (const :tag "Ask"     ask)
 120                  (const :tag "Encrypt" encrypt)))
 121
 122 (defun org-crypt-check-auto-save ()
 123   "Check whether auto-save-mode is enabled for the current buffer.
 124
 125 `auto-save-mode' may cause leakage when decrypting entries, so
 126 check whether it's enabled, and decide what to do about it.
 127
 128 See `org-crypt-disable-auto-save'."
 129   (when buffer-auto-save-file-name
 130     (cond
 131      ((or
 132        (eq org-crypt-disable-auto-save t)
 133        (and
 134         (eq org-crypt-disable-auto-save 'ask)
 135         (y-or-n-p "org-decrypt: auto-save-mode may cause leakage.  Disable it for current buffer? ")))
 136       (message "org-decrypt: Disabling auto-save-mode for %s"
 137                (or (buffer-file-name) (current-buffer)))
 138       ;; The argument to auto-save-mode has to be "-1", since
 139       ;; giving a "nil" argument toggles instead of disabling.
 140       (auto-save-mode -1))
 141      ((eq org-crypt-disable-auto-save nil)
 142       (message "org-decrypt: Decrypting entry with auto-save-mode enabled.  This may cause leakage."))
 143      ((eq org-crypt-disable-auto-save 'encrypt)
 144       (message "org-decrypt: Enabling re-encryption on auto-save.")
 145       (org-add-hook 'auto-save-hook
 146                     (lambda ()
 147                       (message "org-crypt: Re-encrypting all decrypted entries due to auto-save.")
 148                       (org-encrypt-entries))
 149                     nil t))
 150      (t nil))))
 151
 152 (defun org-crypt-key-for-heading ()
 153   "Return the encryption key for the current heading."
 154   (save-excursion
 155     (org-back-to-heading t)
 156     (or (org-entry-get nil "CRYPTKEY" 'selective)
 157         org-crypt-key
 158         (and (boundp 'epa-file-encrypt-to) epa-file-encrypt-to)
 159         (message "No crypt key set, using symmetric encryption."))))
 160
 161 (defun org-encrypt-string (str crypt-key)
 162   "Return STR encrypted with CRYPT-KEY."
 163   ;; Text and key have to be identical, otherwise we re-crypt.
 164   (if (and (string= crypt-key (get-text-property 0 'org-crypt-key str))
 165            (string= (sha1 str) (get-text-property 0 'org-crypt-checksum str)))
 166       (get-text-property 0 'org-crypt-text str)
 167     (set (make-local-variable 'epg-context) (epg-make-context nil t t))
 168     (epg-encrypt-string epg-context str (epg-list-keys epg-context crypt-key))))
 169
 170 (defun org-encrypt-entry ()
 171   "Encrypt the content of the current headline."
 172   (interactive)
 173   (require 'epg)
 174   (save-excursion
 175     (org-back-to-heading t)
 176     (set (make-local-variable 'epg-context) (epg-make-context nil t t))
 177     (let ((start-heading (point)))
 178       (forward-line)
 179       (when (not (looking-at "-----BEGIN PGP MESSAGE-----"))
 180         (let ((folded (outline-invisible-p))
 181               (crypt-key (org-crypt-key-for-heading))
 182               (beg (point))
 183               end encrypted-text)
 184           (goto-char start-heading)
 185           (org-end-of-subtree t t)
 186           (org-back-over-empty-lines)
 187           (setq end (point)
 188                 encrypted-text
 189                 (org-encrypt-string (buffer-substring beg end) crypt-key))
 190           (delete-region beg end)
 191           (insert encrypted-text)
 192           (when folded
 193             (goto-char start-heading)
 194             (outline-hide-subtree))
 195           nil)))))
 196
 197 (defun org-decrypt-entry ()
 198   "Decrypt the content of the current headline."
 199   (interactive)
 200   (require 'epg)
 201   (unless (org-before-first-heading-p)
 202     (save-excursion
 203       (org-back-to-heading t)
 204       (let ((heading-point (point))
 205             (heading-was-invisible-p
 206              (save-excursion
 207                (outline-end-of-heading)
 208                (outline-invisible-p))))
 209         (forward-line)
 210         (when (looking-at "-----BEGIN PGP MESSAGE-----")
 211           (org-crypt-check-auto-save)
 212           (set (make-local-variable 'epg-context) (epg-make-context nil t t))
 213           (let* ((end (save-excursion
 214                         (search-forward "-----END PGP MESSAGE-----")
 215                         (forward-line)
 216                         (point)))
 217                  (encrypted-text (buffer-substring-no-properties (point) end))
 218                  (decrypted-text
 219                   (decode-coding-string
 220                    (epg-decrypt-string
 221                     epg-context
 222                     encrypted-text)
 223                    'utf-8)))
 224             ;; Delete region starting just before point, because the
 225             ;; outline property starts at the \n of the heading.
 226             (delete-region (1- (point)) end)
 227             ;; Store a checksum of the decrypted and the encrypted
 228             ;; text value.  This allows reusing the same encrypted text
 229             ;; if the text does not change, and therefore avoid a
 230             ;; re-encryption process.
 231             (insert "\n" (propertize decrypted-text
 232                                      'org-crypt-checksum (sha1 decrypted-text)
 233                                      'org-crypt-key (org-crypt-key-for-heading)
 234                                      'org-crypt-text encrypted-text))
 235             (when heading-was-invisible-p
 236               (goto-char heading-point)
 237               (org-flag-subtree t))
 238             nil))))))
 239
 240 (defun org-encrypt-entries ()
 241   "Encrypt all top-level entries in the current buffer."
 242   (interactive)
 243   (let (todo-only)
 244     (org-scan-tags
 245      'org-encrypt-entry
 246      (cdr (org-make-tags-matcher org-crypt-tag-matcher))
 247      todo-only)))
 248
 249 (defun org-decrypt-entries ()
 250   "Decrypt all entries in the current buffer."
 251   (interactive)
 252   (let (todo-only)
 253     (org-scan-tags
 254      'org-decrypt-entry
 255      (cdr (org-make-tags-matcher org-crypt-tag-matcher))
 256      todo-only)))
 257
 258 (defun org-at-encrypted-entry-p ()
 259   "Is the current entry encrypted?"
 260   (unless (org-before-first-heading-p)
 261     (save-excursion
 262       (org-back-to-heading t)
 263       (search-forward "-----BEGIN PGP MESSAGE-----"
 264                       (save-excursion (outline-next-heading)) t))))
 265
 266 (defun org-crypt-use-before-save-magic ()
 267   "Add a hook to automatically encrypt entries before a file is saved to disk."
 268   (add-hook
 269    'org-mode-hook
 270    (lambda () (org-add-hook 'before-save-hook 'org-encrypt-entries nil t))))
 271
 272 (add-hook 'org-reveal-start-hook 'org-decrypt-entry)
 273
 274 (provide 'org-crypt)
 275
 276 ;;; org-crypt.el ends here