lisp/password-cache.el

   1 ;;; password-cache.el --- Read passwords, possibly using a password cache.
   2
   3 ;; Copyright (C) 1999-2000, 2003-2018 Free Software Foundation, Inc.
   4
   5 ;; Author: Simon Josefsson <simon@josefsson.org>
   6 ;; Created: 2003-12-21
   7 ;; Keywords: password cache passphrase key
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; Greatly influenced by pgg.el written by Daiki Ueno, with timer
  27 ;; fixes for XEmacs by Katsumi Yamaoka.  In fact, this is mostly just
  28 ;; a rip-off.
  29 ;;
  30 ;; (password-read "Password? " "test")
  31 ;; ;; Minibuffer prompt for password.
  32 ;;  => "foo"
  33 ;;
  34 ;; (password-cache-add "test" "foo")
  35 ;;  => nil
  36
  37 ;; (password-read "Password? " "test")
  38 ;; ;; No minibuffer prompt
  39 ;;  => "foo"
  40 ;;
  41 ;; (password-read "Password? " "test")
  42 ;; ;; No minibuffer prompt
  43 ;;  => "foo"
  44 ;;
  45 ;; ;; Wait `password-cache-expiry' seconds.
  46 ;;
  47 ;; (password-read "Password? " "test")
  48 ;; ;; Minibuffer prompt for password is back.
  49 ;;  => "foo"
  50
  51 ;;; Code:
  52
  53 ;; Options are autoloaded since they are used by eg mml-sec.el.
  54
  55 ;;;###autoload
  56 (defcustom password-cache t
  57   "Whether to cache passwords."
  58   :group 'password
  59   :type 'boolean)
  60
  61 ;;;###autoload
  62 (defcustom password-cache-expiry 16
  63   "How many seconds passwords are cached, or nil to disable expiring.
  64 Whether passwords are cached at all is controlled by `password-cache'."
  65   :group 'password
  66   :type '(choice (const :tag "Never" nil)
  67                  (integer :tag "Seconds")))
  68
  69 (defvar password-data (make-hash-table :test #'equal))
  70
  71 (defun password-read-from-cache (key)
  72   "Obtain passphrase for KEY from time-limited passphrase cache.
  73 Custom variables `password-cache' and `password-cache-expiry'
  74 regulate cache behavior."
  75   (and password-cache
  76        key
  77        (gethash key password-data)))
  78
  79 ;;;###autoload
  80 (defun password-in-cache-p (key)
  81   "Check if KEY is in the cache."
  82   (and password-cache
  83        key
  84        (gethash key password-data)))
  85
  86 (defun password-read (prompt &optional key)
  87   "Read password, for use with KEY, from user, or from cache if wanted.
  88 KEY indicate the purpose of the password, so the cache can
  89 separate passwords.  The cache is not used if KEY is nil.
  90 KEY is typically a string but can be anything (compared via `equal').
  91 The variable `password-cache' control whether the cache is used."
  92   (or (password-read-from-cache key)
  93       (read-passwd prompt)))
  94
  95 (defun password-read-and-add (prompt &optional key)
  96   "Read password, for use with KEY, from user, or from cache if wanted.
  97 Then store the password in the cache.  Uses `password-read' and
  98 `password-cache-add'.  Custom variables `password-cache' and
  99 `password-cache-expiry' regulate cache behavior.
 100
 101 Warning: the password is cached without checking that it is
 102 correct.  It is better to check the password before caching.  If
 103 you must use this function, take care to check passwords and
 104 remove incorrect ones from the cache."
 105   (declare (obsolete password-read "23.1"))
 106   (let ((password (password-read prompt key)))
 107     (when (and password key)
 108       (password-cache-add key password))
 109     password))
 110
 111 (defun password-cache-remove (key)
 112   "Remove password indexed by KEY from password cache.
 113 This is typically run by a timer setup from `password-cache-add',
 114 but can be invoked at any time to forcefully remove passwords
 115 from the cache.  This may be useful when it has been detected
 116 that a password is invalid, so that `password-read' query the
 117 user again."
 118   (let ((password (gethash key password-data)))
 119     (when (stringp password)
 120       (if (fboundp 'clear-string)
 121           (clear-string password)
 122         (fillarray password ?_)))
 123     (remhash key password-data)))
 124
 125 (defun password-cache-add (key password)
 126   "Add password to cache.
 127 The password is removed by a timer after `password-cache-expiry' seconds."
 128   (when (and password-cache-expiry (null (gethash key password-data)))
 129     (run-at-time password-cache-expiry nil
 130                  #'password-cache-remove
 131                  key))
 132   (puthash key password password-data)
 133   nil)
 134
 135 (defun password-reset ()
 136   "Clear the password cache."
 137   (interactive)
 138   (clrhash password-data))
 139
 140 (provide 'password-cache)
 141
 142 ;;; password-cache.el ends here