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349 lines
13 KiB
EmacsLisp
349 lines
13 KiB
EmacsLisp
;;; org-crypt.el --- Public Key Encryption for Org Entries -*- lexical-binding: t; -*-
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;;
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;; Copyright (C) 2007-2024 Free Software Foundation, Inc.
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;; Author: John Wiegley <johnw@gnu.org>
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;; This file is part of GNU Emacs.
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;;
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; Right now this is just a set of functions to play with. It depends
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;; on the epg library. Here's how you would use it:
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;;
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;; 1. To mark an entry for encryption, tag the heading with "crypt".
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;; You can change the tag to any complex tag matching string by
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;; setting the `org-crypt-tag-matcher' variable.
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;;
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;; 2. Set the encryption key to use in the `org-crypt-key' variable,
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;; or use `M-x org-set-property' to set the property CRYPTKEY to
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;; any address in your public keyring. The text of the entry (but
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;; not its properties or headline) will be encrypted for this user.
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;; For them to read it, the corresponding secret key must be
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;; located in the secret key ring of the account where you try to
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;; decrypt it. This makes it possible to leave secure notes that
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;; only the intended recipient can read in a shared-org-mode-files
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;; scenario.
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;; If the key is not set, org-crypt will default to symmetric encryption.
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;;
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;; 3. To later decrypt an entry, use `org-decrypt-entries' or
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;; `org-decrypt-entry'. It might be useful to bind this to a key,
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;; like C-c C-/.
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;;
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;; 4. To automatically encrypt all necessary entries when saving a
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;; file, call `org-crypt-use-before-save-magic' after loading
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;; org-crypt.el.
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;;; Thanks:
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;; - Carsten Dominik
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;; - Vitaly Ostanin
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;;; Code:
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(require 'org-macs)
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(org-assert-version)
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(require 'org-macs)
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(require 'org-compat)
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(declare-function epg-decrypt-string "epg" (context cipher))
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(declare-function epg-list-keys "epg" (context &optional name mode))
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(declare-function epg-make-context "epg"
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(&optional protocol armor textmode include-certs
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cipher-algorithm digest-algorithm
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compress-algorithm))
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(declare-function epg-encrypt-string "epg"
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(context plain recipients &optional sign always-trust))
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(defvar epg-context)
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(declare-function org-back-over-empty-lines "org" ())
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(declare-function org-current-level "org" ())
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(declare-function org-back-to-heading "org" (&optional invisible-ok))
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(declare-function org-before-first-heading-p "org" ())
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(declare-function org-end-of-meta-data "org" (&optional full))
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(declare-function org-end-of-subtree "org" (&optional invisible-ok to-heading element))
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(declare-function org-entry-get "org" (pom property &optional inherit literal-nil))
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(declare-function org-fold-subtree "org-fold" (flag))
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(declare-function org-make-tags-matcher "org" (match &optional only-local-tags))
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(declare-function org-previous-visible-heading "org" (arg))
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(declare-function org-scan-tags "org" (action matcher todo-only &optional start-level))
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(declare-function org-set-property "org" (property value))
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(declare-function org-cycle-set-startup-visibility "org-cycle" ())
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(defgroup org-crypt nil
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"Org Crypt."
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:tag "Org Crypt"
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:group 'org)
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(defcustom org-crypt-tag-matcher "crypt"
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"The tag matcher used to find headings whose contents should be encrypted.
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See the \"Match syntax\" section of the org manual for more details."
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:type 'string
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:group 'org-crypt)
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(defcustom org-crypt-key ""
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"The default key to use when encrypting the contents of a heading.
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If this variable is nil, always use symmetric encryption, unconditionally.
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Otherwise, The string is matched against all keys in the key ring.
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In particular, the empty string matches no key. If no key is found,
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look for the `epa-file-encrypt-to' local variable. Ultimately fall back
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to symmetric encryption.
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This setting can be overridden in the CRYPTKEY property."
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:group 'org-crypt
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:type '(choice
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(string :tag "Public key(s) matching")
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(const :tag "Symmetric encryption" nil)))
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(defcustom org-crypt-disable-auto-save 'ask
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"What org-decrypt should do if `auto-save-mode' is enabled.
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t : Disable `auto-save-mode' for the current buffer
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prior to decrypting an entry.
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nil : Leave `auto-save-mode' enabled.
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This may cause data to be written to disk unencrypted!
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`ask' : Ask user whether or not to disable `auto-save-mode'
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for the current buffer.
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`encrypt': Leave `auto-save-mode' enabled for the current buffer,
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but automatically re-encrypt all decrypted entries
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*before* auto-saving.
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NOTE: This only works for entries which have a tag
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that matches `org-crypt-tag-matcher'."
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:group 'org-crypt
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:version "24.1"
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:type '(choice (const :tag "Always" t)
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(const :tag "Never" nil)
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(const :tag "Ask" ask)
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(const :tag "Encrypt" encrypt)))
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(defun org-crypt--encrypted-text (beg end)
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"Return encrypted text in between BEG and END."
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;; Ignore indentation.
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(replace-regexp-in-string
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"^[ \t]*" ""
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(buffer-substring-no-properties beg end)))
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(defun org-at-encrypted-entry-p ()
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"Is the current entry encrypted?
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When the entry is encrypted, return a pair (BEG . END) where BEG
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and END are buffer positions delimiting the encrypted area."
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(org-with-wide-buffer
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(unless (org-before-first-heading-p)
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(org-back-to-heading t)
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(org-end-of-meta-data 'standard)
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(let ((case-fold-search nil)
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(banner-start (rx (seq bol
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(zero-or-more (any "\t "))
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"-----BEGIN PGP MESSAGE-----"
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eol))))
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(when (looking-at banner-start)
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(let ((start (point))
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(banner-end (rx (seq bol
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(or (group (zero-or-more (any "\t "))
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"-----END PGP MESSAGE-----"
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eol)
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(seq (one-or-more "*") " "))))))
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(when (and (re-search-forward banner-end nil t) (match-string 1))
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(cons start (line-beginning-position 2)))))))))
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(defun org-crypt-check-auto-save ()
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"Check whether `auto-save-mode' is enabled for the current buffer.
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`auto-save-mode' may cause leakage when decrypting entries, so
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check whether it's enabled, and decide what to do about it.
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See `org-crypt-disable-auto-save'."
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(when buffer-auto-save-file-name
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(cond
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((or
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(eq org-crypt-disable-auto-save t)
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(and
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(eq org-crypt-disable-auto-save 'ask)
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(y-or-n-p "`org-decrypt': auto-save-mode may cause leakage. Disable it for current buffer? ")))
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(message "org-decrypt: Disabling auto-save-mode for %s"
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(or (buffer-file-name) (current-buffer)))
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;; The argument to auto-save-mode has to be "-1", since
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;; giving a "nil" argument toggles instead of disabling.
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(auto-save-mode -1))
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((eq org-crypt-disable-auto-save nil)
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(message "org-decrypt: Decrypting entry with auto-save-mode enabled. This may cause leakage."))
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((eq org-crypt-disable-auto-save 'encrypt)
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(message "org-decrypt: Enabling re-encryption on auto-save.")
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(add-hook 'auto-save-hook
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(lambda ()
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(message "org-crypt: Re-encrypting all decrypted entries due to auto-save.")
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(org-encrypt-entries))
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nil t))
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(t nil))))
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(defun org-crypt-key-for-heading ()
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"Return the encryption key(s) for the current heading.
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Assume `epg-context' is set."
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(and org-crypt-key
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(or (epg-list-keys epg-context
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(pcase (org-entry-get nil "CRYPTKEY" 'selective 'literal-nil)
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("nil" "")
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(key (or key org-crypt-key ""))))
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(bound-and-true-p epa-file-encrypt-to)
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(progn
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(message "No crypt key set, using symmetric encryption.")
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nil))))
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;;;###autoload
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(defun org-encrypt-entry ()
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"Encrypt the content of the current headline."
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(interactive)
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(unless (org-at-encrypted-entry-p)
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(require 'epg)
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(setq-local epg-context (epg-make-context nil t t))
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(org-with-wide-buffer
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(org-back-to-heading t)
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(let ((start-heading (point))
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(crypt-key (org-crypt-key-for-heading))
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(folded? (org-invisible-p (line-beginning-position))))
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(org-end-of-meta-data 'standard)
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(let ((beg (point))
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(folded-heading
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(and folded?
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(save-excursion
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(org-previous-visible-heading 1)
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(point)))))
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(goto-char start-heading)
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(org-end-of-subtree t t)
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(org-back-over-empty-lines)
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(let* ((contents (delete-and-extract-region beg (point)))
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(key (get-text-property 0 'org-crypt-key contents))
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(checksum (get-text-property 0 'org-crypt-checksum contents)))
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(condition-case err
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(insert
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;; Text and key have to be identical, otherwise we
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;; re-crypt.
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(if (and (equal crypt-key key)
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(string= checksum (sha1 contents)))
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(get-text-property 0 'org-crypt-text contents)
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(epg-encrypt-string epg-context contents crypt-key)))
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;; If encryption failed, make sure to insert back entry
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;; contents in the buffer.
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(error
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(insert contents)
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(error "%s" (error-message-string err)))))
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(when folded-heading
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(goto-char folded-heading)
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(org-fold-subtree t))
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nil)))))
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(defvar org-outline-regexp-bol)
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;;;###autoload
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(defun org-decrypt-entry ()
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"Decrypt the content of the current headline."
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(interactive)
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(pcase (org-at-encrypted-entry-p)
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(`(,beg . ,end)
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(require 'epg)
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(setq-local epg-context (epg-make-context nil t t))
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(org-with-point-at beg
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(org-crypt-check-auto-save)
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(let* ((folded-heading
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(and (org-invisible-p)
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(save-excursion
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(org-previous-visible-heading 1)
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(point))))
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(level (org-current-level))
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(encrypted-text (org-crypt--encrypted-text beg end))
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(decrypted-text
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(decode-coding-string
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(epg-decrypt-string epg-context encrypted-text)
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'utf-8))
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origin-marker)
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;; Delete region starting just before point, because the
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;; outline property starts at the \n of the heading.
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(delete-region (1- (point)) end)
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(setq origin-marker (point-marker))
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(if (string-match (org-headline-re level) decrypted-text)
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;; If decrypted text contains other headings with levels
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;; below LEVEL, adjust the subtree.
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(let ((start 0) (min-level level))
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(while (string-match (org-headline-re level) decrypted-text start)
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(setq min-level (min min-level (1- (length (match-string 0 decrypted-text))))
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start (match-end 0)))
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(insert "\n"
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(replace-regexp-in-string
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org-outline-regexp-bol
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(concat (make-string (1+ (- level min-level)) ?*) "\\&")
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decrypted-text)))
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;; Store a checksum of the decrypted and the encrypted text
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;; value. This allows reusing the same encrypted text if the
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;; text does not change, and therefore avoid a re-encryption
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;; process.
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(insert "\n"
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(propertize decrypted-text
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'org-crypt-checksum (sha1 decrypted-text)
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'org-crypt-key (org-crypt-key-for-heading)
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'org-crypt-text encrypted-text)))
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;; Apply initial visibility.
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(save-restriction
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(narrow-to-region origin-marker (point))
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(set-marker origin-marker nil)
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(org-cycle-set-startup-visibility))
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;; ... but keep the previous folded state.
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(when folded-heading
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(goto-char folded-heading)
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(org-fold-subtree t))
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nil)))
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(_ nil)))
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(defvar org--matcher-tags-todo-only)
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;;;###autoload
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(defun org-encrypt-entries ()
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"Encrypt all top-level entries in the current buffer."
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(interactive)
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(let ((org--matcher-tags-todo-only nil))
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(org-scan-tags
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'org-encrypt-entry
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(cdr (org-make-tags-matcher org-crypt-tag-matcher))
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org--matcher-tags-todo-only)))
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;;;###autoload
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(defun org-decrypt-entries ()
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"Decrypt all entries in the current buffer."
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(interactive)
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(let ((org--matcher-tags-todo-only nil))
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(org-scan-tags
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'org-decrypt-entry
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(cdr (org-make-tags-matcher org-crypt-tag-matcher))
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org--matcher-tags-todo-only)))
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;;;###autoload
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(defun org-crypt-use-before-save-magic ()
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"Add a hook to automatically encrypt entries before a file is saved to disk."
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(add-hook
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'org-mode-hook
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(lambda () (add-hook 'before-save-hook 'org-encrypt-entries nil t))))
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(add-hook 'org-fold-reveal-start-hook 'org-decrypt-entry)
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(provide 'org-crypt)
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;;; org-crypt.el ends here
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