;;; epa-file.el --- the EasyPG Assistant, transparent file encryption -*- lexical-binding: t -*-
;; Copyright (C) 2006-2022 Free Software Foundation, Inc.
;; Author: Daiki Ueno <ueno@unixuser.org>
;; Keywords: PGP, GnuPG
;; Package: epa
;; 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 <https://www.gnu.org/licenses/>.
;;; Commentary:
;;; Code:
(require 'epa)
(require 'epa-hook)
(eval-when-compile (require 'subr-x))
;;; Options
(defcustom epa-file-cache-passphrase-for-symmetric-encryption nil
"If non-nil, cache passphrase for symmetric encryption.
For security reasons, this option is turned off by default and
not recommended to use. Instead, consider using gpg-agent which
does the same job in a safer way. See Info node `(epa) Caching
Passphrases' for more information.
Note that this option has no effect if you use GnuPG 2.0."
:type 'boolean
:group 'epa-file)
(defcustom epa-file-select-keys nil
"Control whether or not to pop up the key selection dialog.
If t, always ask user to select recipients.
If nil, query user only when `epa-file-encrypt-to' is not set.
If neither t nor nil, don't ask user. In this case, symmetric
encryption is used."
:type '(choice (const :tag "Ask always" t)
(const :tag "Ask when recipients are not set" nil)
(const :tag "Don't ask" silent))
:group 'epa-file)
;;; Other
(defvar epa-file-passphrase-alist nil)
(defun epa-file-passphrase-callback-function (context key-id file)
(if (and epa-file-cache-passphrase-for-symmetric-encryption
(eq key-id 'SYM))
(progn
(setq file (file-truename file))
(let ((entry (assoc file epa-file-passphrase-alist))
passphrase)
(or (copy-sequence (cdr entry))
(progn
(unless entry
(setq entry (list file))
(setq epa-file-passphrase-alist
(cons entry
epa-file-passphrase-alist)))
(setq passphrase (epa-passphrase-callback-function context
key-id
file))
(setcdr entry (copy-sequence passphrase))
passphrase))))
(epa-passphrase-callback-function context key-id file)))
;;; File Handler
(defvar epa-inhibit nil
"Non-nil means don't try to decrypt .gpg files when operating on them.")
;;;###autoload
(defun epa-file-handler (operation &rest args)
(save-match-data
(let ((op (get operation 'epa-file)))
(if (and op (not epa-inhibit))
(apply op args)
(epa-file-run-real-handler operation args)))))
(defun epa-file-run-real-handler (operation args)
(let ((inhibit-file-name-handlers
(cons 'epa-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))
(defun epa-file-decode-and-insert (string file visit beg end replace)
(save-restriction
(narrow-to-region (point) (point))
(insert string)
(decode-coding-inserted-region
(point-min) (point-max)
(substring file 0 (string-match epa-file-name-regexp file))
visit beg end replace)
(goto-char (point-max))
(- (point-max) (point-min))))
(defvar epa-file-error nil)
(defun epa-file--find-file-not-found-function ()
(let ((error epa-file-error))
(save-window-excursion
(kill-buffer))
(if (nth 3 error)
(user-error "Wrong passphrase: %s" (nth 3 error))
(signal 'file-missing
(cons "Opening input file" (cdr error))))))
(defun epa--wrong-password-p (context)
(let ((error-string (epg-context-error-output context)))
(and (string-match
"decryption failed: \\(Bad session key\\|No secret key\\)"
error-string)
(match-string 1 error-string))))
(defvar last-coding-system-used)
(defun epa-file-insert-file-contents (file &optional visit beg end replace)
(barf-if-buffer-read-only)
(if (and visit (or beg end))
(error "Attempt to visit less than an entire file"))
(setq file (expand-file-name file))
(let* ((local-copy
(condition-case nil
(epa-file-run-real-handler #'file-local-copy (list file))
(error)))
(local-file (or local-copy file))
(context (epg-make-context))
(buf (current-buffer))
string length entry)
(if visit
(setq buffer-file-name file))
(epg-context-set-passphrase-callback
context
(cons #'epa-file-passphrase-callback-function
local-file))
(epg-context-set-progress-callback
context
(cons #'epa-progress-callback-function
(format "Decrypting %s" file)))
(unwind-protect
(progn
(condition-case error
(setq string (epg-decrypt-file context local-file nil))
(error
(if (setq entry (assoc file epa-file-passphrase-alist))
(setcdr entry nil))
;; If the decryption program can't be found,
;; signal that as a non-file error
;; so that find-file-noselect-1 won't handle it.
;; Borrowed from jka-compr.el.
(if (and (memq 'file-error (get (car error) 'error-conditions))
(equal (cadr error) "Searching for program"))
(error "Decryption program `%s' not found"
(nth 3 error)))
(let ((exists (file-exists-p local-file)))
(when exists
(if-let ((wrong-password (epa--wrong-password-p context)))
;; Don't display the *error* buffer if we just
;; have a wrong password; let the later error
;; handler notify the user.
(setq error (append error (list wrong-password)))
(epa-display-error context))
;; When the .gpg file isn't an encrypted file (e.g.,
;; it's a keyring.gpg file instead), then gpg will
;; say "Unexpected exit" as the error message. In
;; that case, just display the bytes.
(if (equal (caddr error) "Unexpected; Exit")
(setq string (with-temp-buffer
(insert-file-contents-literally local-file)
(buffer-string)))
;; Hack to prevent find-file from opening empty buffer
;; when decryption failed (bug#6568). See the place
;; where `find-file-not-found-functions' are called in
;; `find-file-noselect-1'.
(setq-local epa-file-error error)
(add-hook 'find-file-not-found-functions
'epa-file--find-file-not-found-function
nil t)))
(signal (if exists 'file-error 'file-missing)
(cons "Opening input file" (cdr error))))))
(set-buffer buf) ;In case timer/filter changed/killed it (bug#16029)!
(setq-local epa-file-encrypt-to
(mapcar #'car (epg-context-result-for
context 'encrypted-to)))
(if (or beg end)
(setq string (substring string
(or beg 0)
(and end (min end (length string))))))
(save-excursion
;; If visiting, bind off buffer-file-name so that
;; file-locking will not ask whether we should
;; really edit the buffer.
(let ((buffer-file-name
(if visit nil buffer-file-name)))
(setq length
(if replace
(epa-file--replace-text string file visit beg end)
(epa-file-decode-and-insert
string file visit beg end replace))))
(if visit
(set-visited-file-modtime))))
(if (and local-copy
(file-exists-p local-copy))
(delete-file local-copy)))
(list file length)))
(put 'insert-file-contents 'epa-file 'epa-file-insert-file-contents)
(defun epa-file--replace-text (string file visit beg end)
;; The idea here is that we want to replace the text in the buffer
;; (for instance, for a `revert-buffer'), but we want to touch as
;; little of the text as possible. So we compare the new and the
;; old text and only starts replacing when the text changes.
(let ((orig-point (point))
new-start length)
(goto-char (point-max))
(setq new-start (point))
(setq length
(epa-file-decode-and-insert
string file visit beg end t))
(if (equal (buffer-substring (point-min) new-start)
(buffer-substring new-start (point-max)))
;; The new text is equal to the old, so just keep the old.
(delete-region new-start (point-max))
;; Compute the region the hard way.
(let ((p1 (point-min))
(p2 new-start))
(while (and (< p1 new-start)
(< p2 (point-max))
(eql (char-after p1) (char-after p2)))
(cl-incf p1)
(cl-incf p2))
(delete-region new-start p2)
(delete-region p1 new-start)))
;; Restore point, if possible.
(if (< orig-point (point-max))
(goto-char orig-point)
(goto-char (point-max)))
length))
(defun epa-file-write-region (start end file &optional append visit lockname
mustbenew)
(if append
(error "Can't append to the file"))
(setq file (expand-file-name file))
(let* ((coding-system (or coding-system-for-write
(if (fboundp 'select-safe-coding-system)
(let ((buffer-file-name file))
(select-safe-coding-system
(point-min) (point-max)))
buffer-file-coding-system)))
(context (epg-make-context))
(coding-system-for-write 'binary)
string entry
(recipients
(cond
((listp epa-file-encrypt-to) epa-file-encrypt-to)
((stringp epa-file-encrypt-to) (list epa-file-encrypt-to))))
buffer)
(epg-context-set-passphrase-callback
context
(cons #'epa-file-passphrase-callback-function
file))
(epg-context-set-progress-callback
context
(cons #'epa-progress-callback-function
(format "Encrypting %s" file)))
(setf (epg-context-armor context) epa-armor)
(condition-case error
(setq string
(epg-encrypt-string
context
(if (stringp start)
(encode-coding-string start coding-system)
(unless start
(setq start (point-min)
end (point-max)))
(setq buffer (current-buffer))
(with-temp-buffer
(insert-buffer-substring buffer start end)
;; Translate the region according to
;; `buffer-file-format', as `write-region' would.
;; We can't simply do `write-region' (into a
;; temporary file) here, since it writes out
;; decrypted contents.
(format-encode-buffer (with-current-buffer buffer
buffer-file-format))
(encode-coding-string (buffer-string)
coding-system)))
(if (or (eq epa-file-select-keys t)
(and (null epa-file-select-keys)
(not (local-variable-p 'epa-file-encrypt-to
(current-buffer)))))
(epa-select-keys
context
"Select recipients for encryption.
If no one is selected, symmetric encryption will be performed. "
recipients)
(if epa-file-encrypt-to
(epg--filter-revoked-keys
(epg-list-keys context recipients))))))
(error
(epa-display-error context)
(if (setq entry (assoc file epa-file-passphrase-alist))
(setcdr entry nil))
(signal 'file-error (cons "Opening output file" (cdr error)))))
(epa-file-run-real-handler
#'write-region
(list string nil file append visit lockname mustbenew))
(if (boundp 'last-coding-system-used)
(setq last-coding-system-used coding-system))
(if (eq visit t)
(progn
(setq buffer-file-name file)
(set-visited-file-modtime))
(if (stringp visit)
(progn
(set-visited-file-modtime)
(setq buffer-file-name visit))))
(if (or (eq visit t)
(eq visit nil)
(stringp visit))
(message "Wrote %s" buffer-file-name))))
(put 'write-region 'epa-file 'epa-file-write-region)
;;; Commands
(defun epa-file-select-keys ()
"Select recipients for encryption."
(interactive)
(setq-local epa-file-encrypt-to
(mapcar
(lambda (key)
(epg-sub-key-id (car (epg-key-sub-key-list key))))
(epa-select-keys
(epg-make-context)
"Select recipients for encryption.
If no one is selected, symmetric encryption will be performed. "))))
;;;###autoload
(defun epa-file-enable ()
(interactive)
(if (memq epa-file-handler file-name-handler-alist)
(message "`epa-file' already enabled")
(setq file-name-handler-alist
(cons epa-file-handler file-name-handler-alist))
(add-hook 'find-file-hook 'epa-file-find-file-hook)
(setq auto-mode-alist (cons epa-file-auto-mode-alist-entry auto-mode-alist))
(message "`epa-file' enabled")))
;;;###autoload
(defun epa-file-disable ()
(interactive)
(if (memq epa-file-handler file-name-handler-alist)
(progn
(setq file-name-handler-alist
(delq epa-file-handler file-name-handler-alist))
(remove-hook 'find-file-hook 'epa-file-find-file-hook)
(setq auto-mode-alist (delq epa-file-auto-mode-alist-entry
auto-mode-alist))
(message "`epa-file' disabled"))
(message "`epa-file' already disabled")))
(provide 'epa-file)
;;; epa-file.el ends here