;;; org-crypt.el --- Public key encryption for org-mode entries
;; Copyright (C) 2007, 2009-2012 Free Software Foundation, Inc.
;; Emacs Lisp Archive Entry
;; Filename: org-crypt.el
;; Keywords: org-mode
;; Author: John Wiegley <johnw@gnu.org>
;; Maintainer: Peter Jones <pjones@pmade.com>
;; Description: Adds public key encryption to org-mode buffers
;; URL: http://www.newartisans.com/software/emacs.html
;; Compatibility: Emacs22
;; 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:
;; Right now this is just a set of functions to play with. It depends
;; on the epg library. Here's how you would use it:
;;
;; 1. To mark an entry for encryption, tag the heading with "crypt".
;; You can change the tag to any complex tag matching string by
;; setting the `org-crypt-tag-matcher' variable.
;;
;; 2. Set the encryption key to use in the `org-crypt-key' variable,
;; or use `M-x org-set-property' to set the property CRYPTKEY to
;; any address in your public keyring. The text of the entry (but
;; not its properties or headline) will be encrypted for this user.
;; For them to read it, the corresponding secret key must be
;; located in the secret key ring of the account where you try to
;; decrypt it. This makes it possible to leave secure notes that
;; only the intended recipient can read in a shared-org-mode-files
;; scenario.
;; If the key is not set, org-crypt will default to symmetric encryption.
;;
;; 3. To later decrypt an entry, use `org-decrypt-entries' or
;; `org-decrypt-entry'. It might be useful to bind this to a key,
;; like C-c C-/. I hope that in the future, C-c C-r can be might
;; overloaded to also decrypt an entry if it's encrypted, since
;; that fits nicely with the meaning of "reveal".
;;
;; 4. To automatically encrypt all necessary entries when saving a
;; file, call `org-crypt-use-before-save-magic' after loading
;; org-crypt.el.
;;; Thanks:
;; - Carsten Dominik
;; - Vitaly Ostanin
(require 'org)
;;; Code:
(declare-function epg-decrypt-string "epg" (context cipher))
(declare-function epg-list-keys "epg" (context &optional name mode))
(declare-function epg-make-context "epg"
(&optional protocol armor textmode include-certs
cipher-algorithm digest-algorithm
compress-algorithm))
(declare-function epg-encrypt-string "epg"
(context plain recipients &optional sign always-trust))
(defgroup org-crypt nil
"Org Crypt."
:tag "Org Crypt"
:group 'org)
(defcustom org-crypt-tag-matcher "crypt"
"The tag matcher used to find headings whose contents should be encrypted.
See the \"Match syntax\" section of the org manual for more details."
:type 'string
:group 'org-crypt)
(defcustom org-crypt-key ""
"The default key to use when encrypting the contents of a heading.
This setting can also be overridden in the CRYPTKEY property."
:type 'string
:group 'org-crypt)
(defcustom org-crypt-disable-auto-save 'ask
"What org-decrypt should do if `auto-save-mode' is enabled.
t : Disable auto-save-mode for the current buffer
prior to decrypting an entry.
nil : Leave auto-save-mode enabled.
This may cause data to be written to disk unencrypted!
'ask : Ask user whether or not to disable auto-save-mode
for the current buffer.
'encrypt : Leave auto-save-mode enabled for the current buffer,
but automatically re-encrypt all decrypted entries
*before* auto-saving.
NOTE: This only works for entries which have a tag
that matches `org-crypt-tag-matcher'."
:group 'org-crypt
:version "24.1"
:type '(choice (const :tag "Always" t)
(const :tag "Never" nil)
(const :tag "Ask" ask)
(const :tag "Encrypt" encrypt)))
(defun org-crypt-check-auto-save ()
"Check whether auto-save-mode is enabled for the current buffer.
`auto-save-mode' may cause leakage when decrypting entries, so
check whether it's enabled, and decide what to do about it.
See `org-crypt-disable-auto-save'."
(when buffer-auto-save-file-name
(cond
((or
(eq org-crypt-disable-auto-save t)
(and
(eq org-crypt-disable-auto-save 'ask)
(y-or-n-p "org-decrypt: auto-save-mode may cause leakage. Disable it for current buffer? ")))
(message (concat "org-decrypt: Disabling auto-save-mode for " (or (buffer-file-name) (current-buffer))))
; The argument to auto-save-mode has to be "-1", since
; giving a "nil" argument toggles instead of disabling.
(auto-save-mode -1))
((eq org-crypt-disable-auto-save nil)
(message "org-decrypt: Decrypting entry with auto-save-mode enabled. This may cause leakage."))
((eq org-crypt-disable-auto-save 'encrypt)
(message "org-decrypt: Enabling re-encryption on auto-save.")
(add-hook 'auto-save-hook
(lambda ()
(message "org-crypt: Re-encrypting all decrypted entries due to auto-save.")
(org-encrypt-entries))
nil t))
(t nil))))
(defun org-crypt-key-for-heading ()
"Return the encryption key for the current heading."
(save-excursion
(org-back-to-heading t)
(or (org-entry-get nil "CRYPTKEY" 'selective)
org-crypt-key
(and (boundp 'epa-file-encrypt-to) epa-file-encrypt-to)
(message "No crypt key set, using symmetric encryption."))))
(defun org-encrypt-string (str crypt-key)
"Return STR encrypted with CRYPT-KEY."
;; Text and key have to be identical, otherwise we re-crypt.
(if (and (string= crypt-key (get-text-property 0 'org-crypt-key str))
(string= (sha1 str) (get-text-property 0 'org-crypt-checksum str)))
(get-text-property 0 'org-crypt-text str)
(let ((epg-context (epg-make-context nil t t)))
(epg-encrypt-string epg-context str (epg-list-keys epg-context crypt-key)))))
(defun org-encrypt-entry ()
"Encrypt the content of the current headline."
(interactive)
(require 'epg)
(save-excursion
(org-back-to-heading t)
(let ((start-heading (point)))
(forward-line)
(when (not (looking-at "-----BEGIN PGP MESSAGE-----"))
(let ((folded (outline-invisible-p))
(epg-context (epg-make-context nil t t))
(crypt-key (org-crypt-key-for-heading))
(beg (point))
end encrypted-text)
(goto-char start-heading)
(org-end-of-subtree t t)
(org-back-over-empty-lines)
(setq end (point)
encrypted-text
(org-encrypt-string (buffer-substring beg end) crypt-key))
(delete-region beg end)
(insert encrypted-text)
(when folded
(goto-char start-heading)
(hide-subtree))
nil)))))
(defun org-decrypt-entry ()
"Decrypt the content of the current headline."
(interactive)
(require 'epg)
(unless (org-before-first-heading-p)
(save-excursion
(org-back-to-heading t)
(let ((heading-point (point))
(heading-was-invisible-p
(save-excursion
(outline-end-of-heading)
(outline-invisible-p))))
(forward-line)
(when (looking-at "-----BEGIN PGP MESSAGE-----")
(org-crypt-check-auto-save)
(let* ((end (save-excursion
(search-forward "-----END PGP MESSAGE-----")
(forward-line)
(point)))
(epg-context (epg-make-context nil t t))
(encrypted-text (buffer-substring-no-properties (point) end))
(decrypted-text
(decode-coding-string
(epg-decrypt-string
epg-context
encrypted-text)
'utf-8)))
;; Delete region starting just before point, because the
;; outline property starts at the \n of the heading.
(delete-region (1- (point)) end)
;; Store a checksum of the decrypted and the encrypted
;; text value. This allow to reuse the same encrypted text
;; if the text does not change, and therefore avoid a
;; re-encryption process.
(insert "\n" (propertize decrypted-text
'org-crypt-checksum (sha1 decrypted-text)
'org-crypt-key (org-crypt-key-for-heading)
'org-crypt-text encrypted-text))
(when heading-was-invisible-p
(goto-char heading-point)
(org-flag-subtree t))
nil))))))
(defun org-encrypt-entries ()
"Encrypt all top-level entries in the current buffer."
(interactive)
(let (todo-only)
(org-scan-tags
'org-encrypt-entry
(cdr (org-make-tags-matcher org-crypt-tag-matcher))
todo-only)))
(defun org-decrypt-entries ()
"Decrypt all entries in the current buffer."
(interactive)
(let (todo-only)
(org-scan-tags
'org-decrypt-entry
(cdr (org-make-tags-matcher org-crypt-tag-matcher))
todo-only)))
(defun org-crypt-use-before-save-magic ()
"Add a hook to automatically encrypt entries before a file is saved to disk."
(add-hook
'org-mode-hook
(lambda () (add-hook 'before-save-hook 'org-encrypt-entries nil t))))
(add-hook 'org-reveal-start-hook 'org-decrypt-entry)
(provide 'org-crypt)
;;; org-crypt.el ends here