path: root/lisp/epg-config.el

;;; epg-config.el --- configuration of the EasyPG Library  -*- lexical-binding: t -*-

;; Copyright (C) 2006-2021 Free Software Foundation, Inc.

;; Author: Daiki Ueno <ueno@unixuser.org>
;; Keywords: PGP, GnuPG
;; Package: epg

;; 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:
;;; Prelude

(eval-when-compile (require 'cl-lib))

(defconst epg-package-name "epg"
  "Name of this package.")

(defconst epg-version-number "1.0.0"
  "Version number of this package.")

(define-obsolete-variable-alias 'epg-bug-report-address
  'report-emacs-bug-address "27.1")

;;; Options

(defgroup epg ()
  "Interface to the GNU Privacy Guard (GnuPG)."
  :tag "EasyPG"
  :version "23.1"
  :group 'data
  :group 'external)

(defcustom epg-gpg-program (if (executable-find "gpg2")
                               "gpg2"
                             "gpg")
  "Say what gpg program to prefer (if it satisfies minimum requirements).

If this variable is \"gpg2\", but the version of gpg2 installed
is less than `epg-gpg2-minimum-version', then version 1 of
GnuPG (i.e., \"gpg\") will be used instead.  If the version of
version 1 is less than `epg-gpg-minimum-version', then that won't
be used either.

If you want to explicitly specify what gpg program to use, you
have to use \\[customize] instead (see the info node `Easy
Customization').  Setting this variable without \\[customize] has
no effect."
  :version "25.1"
  :type 'string)

(defcustom epg-gpgsm-program "gpgsm"
  "The `gpgsm' executable.
Setting this variable directly does not take effect;
instead use \\[customize] (see the info node `Easy Customization')."
  :type 'string)

(defcustom epg-gpgconf-program "gpgconf"
  "The `gpgconf' executable."
  :version "25.1"
  :type 'string)

(defcustom epg-gpg-home-directory nil
  "The directory which contains the configuration files of `epg-gpg-program'."
  :type '(choice (const :tag "Default" nil) directory))

(defcustom epg-passphrase-coding-system nil
  "Coding system to use with messages from `epg-gpg-program'."
  :type 'symbol)

(define-obsolete-variable-alias
  'epa-pinentry-mode 'epg-pinentry-mode "27.1")

;; In the doc string below, we say "symbol `error'" to avoid producing
;; a hyperlink for `error' the function.
(defcustom epg-pinentry-mode nil
  "The pinentry mode.

GnuPG 2.1 or later has an option to control the behavior of
Pinentry invocation.  The value should be the symbol `error',
`ask', `cancel', or `loopback'.  See the GnuPG manual for the
meanings.

A particularly useful mode is `loopback', which redirects all
Pinentry queries to the caller, so Emacs can query passphrase
through the minibuffer, instead of external Pinentry program."
  :type '(choice (const nil)
		 (const ask)
		 (const cancel)
		 (const error)
		 (const loopback))
  :version "27.1")

(defcustom epg-debug nil
  "If non-nil, debug output goes to the \" *epg-debug*\" buffer.
Note that the buffer name starts with a space."
  :type 'boolean)

;;; Constants

(defconst epg-gpg-minimum-version "1.4.3")
(defconst epg-gpg2-minimum-version "2.1.6")

(defconst epg-config--program-alist
  `((OpenPGP
     epg-gpg-program
     ("gpg2" . ,epg-gpg2-minimum-version)
     ("gpg" . ((,epg-gpg-minimum-version . "2.0")
               ,epg-gpg2-minimum-version)))
    (CMS
     epg-gpgsm-program
     ("gpgsm" . "2.0.4")))
  "Alist used to obtain the usable configuration of executables.
The first element of each entry is protocol symbol, which is
either `OpenPGP' or `CMS'.  The second element is a symbol where
the executable name is remembered.  The rest of the entry is an
alist mapping executable names to the minimum required version
suitable for the use with Emacs.")

(defconst epg-config--configuration-constructor-alist
  '((OpenPGP . epg-config--make-gpg-configuration)
    (CMS . epg-config--make-gpgsm-configuration))
  "Alist used to obtain the usable configuration of executables.
The first element of each entry is protocol symbol, which is
either `OpenPGP' or `CMS'.  The second element is a function
which constructs a configuration object (actually a plist).")

;;; "Configuration"

(defvar epg--configurations nil)

;;;###autoload
(defun epg-find-configuration (protocol &optional no-cache program-alist)
  "Find or create a usable configuration to handle PROTOCOL.
This function first looks at the existing configuration found by
the previous invocation of this function, unless NO-CACHE is non-nil.

Then it walks through PROGRAM-ALIST or
`epg-config--program-alist'.  If `epg-gpg-program' or
`epg-gpgsm-program' is already set with custom, use it.
Otherwise, it tries the programs listed in the entry until the
version requirement is met."
  (unless program-alist
    (setq program-alist epg-config--program-alist))
  (let ((entry (assq protocol program-alist)))
    (unless entry
      (error "Unknown protocol `%S'" protocol))
    (cl-destructuring-bind (symbol . alist)
        (cdr entry)
      (let ((constructor
             (alist-get protocol epg-config--configuration-constructor-alist)))
        (or (and (not no-cache) (alist-get protocol epg--configurations))
            ;; If the executable value is already set with M-x
            ;; customize, use it without checking.
            (if (and symbol (or (get symbol 'saved-value)
                                (get symbol 'customized-value)))
                (let ((configuration
                       (funcall constructor (symbol-value symbol))))
                  (push (cons protocol configuration) epg--configurations)
                  configuration)
              (catch 'found
                (dolist (program-version alist)
                  (let ((executable (executable-find (car program-version))))
                    (when executable
                      (let ((configuration
                             (funcall constructor executable)))
                        (when (ignore-errors
                                (epg-check-configuration configuration
                                                         (cdr program-version))
                                t)
                          (unless no-cache
                            (push (cons protocol configuration)
                                  epg--configurations))
                          (throw 'found configuration)))))))))))))

;; Create an `epg-configuration' object for `gpg', using PROGRAM.
(defun epg-config--make-gpg-configuration (program)
  (let (config groups type args)
    (with-temp-buffer
      ;; The caller might have bound coding-system-for-* to something
      ;; like 'no-conversion, but the below needs to call PROGRAM
      ;; expecting human-readable text in both directions (since we
      ;; are going to parse the output as text), so let Emacs guess
      ;; the encoding of that text by its usual encoding-detection
      ;; machinery.
      (let ((coding-system-for-read 'undecided)
            (coding-system-for-write 'undecided))
        (apply #'call-process program nil (list t nil) nil
	       (append (if epg-gpg-home-directory
			   (list "--homedir" epg-gpg-home-directory))
		       '("--with-colons" "--list-config"))))
      (goto-char (point-min))
      (while (re-search-forward "^cfg:\\([^:]+\\):\\(.*\\)" nil t)
	(setq type (intern (match-string 1))
	      args (match-string 2))
	(cond
	 ((eq type 'group)
	  (if (string-match "\\`\\([^:]+\\):" args)
	      (setq groups
		    (cons (cons (downcase (match-string 1 args))
				(delete "" (split-string
					    (substring args
						       (match-end 0))
					    ";")))
			  groups))
	    (if epg-debug
		(message "Invalid group configuration: %S" args))))
	 ((memq type '(pubkey cipher digest compress))
	  (if (string-match "\\`\\([0-9]+\\)\\(;[0-9]+\\)*" args)
	      (setq config
		    (cons (cons type
				(mapcar #'string-to-number
					(delete "" (split-string args ";"))))
			  config))
	    (if epg-debug
		(message "Invalid %S algorithm configuration: %S"
			 type args))))
	 (t
	  (setq config (cons (cons type args) config))))))
    (push (cons 'program program) config)
    (if groups
	(cons (cons 'groups groups) config)
      config)))

;; Create an `epg-configuration' object for `gpgsm', using PROGRAM.
(defun epg-config--make-gpgsm-configuration (program)
  (with-temp-buffer
    (call-process program nil (list t nil) nil "--version")
    (goto-char (point-min))
    (when (looking-at "\\S-+ (")
      (goto-char (match-end 0))
      (backward-char)
      (forward-sexp)
      (skip-syntax-forward "-" (point-at-eol))
      (list (cons 'program program)
            (cons 'version (buffer-substring (point) (point-at-eol)))))))

;;;###autoload
(defun epg-configuration ()
  "Return a list of internal configuration parameters of `epg-gpg-program'."
  (declare (obsolete epg-find-configuration "25.1"))
  (epg-config--make-gpg-configuration epg-gpg-program))

;;;###autoload
(defun epg-check-configuration (config &optional req-versions)
  "Verify that a sufficient version of GnuPG is installed.
CONFIG should be a `epg-configuration' object (a plist).
REQ-VERSIONS should be a list with elements of the form (MIN
. MAX) where MIN and MAX are version strings indicating a
semi-open range of acceptable versions.  REQ-VERSIONS may also be
a single minimum version string."
  (let ((version (alist-get 'version config)))
    (unless (stringp version)
      (error "Undetermined version: %S" version))
    (catch 'version-ok
      (pcase-dolist ((or `(,min . ,max)
                         (and min (let max nil)))
                     (if (listp req-versions) req-versions
                       (list req-versions)))
        (when (and (version<= (or min epg-gpg-minimum-version)
                              version)
                   (or (null max)
                       (version< version max)))
          (throw 'version-ok t)))
      (error "Unsupported version: %s" version))))

(defun epg-required-version-p (protocol required-version)
  "Verify a sufficient version of GnuPG for specific protocol.
PROTOCOL is symbol, either `OpenPGP' or `CMS'.  REQUIRED-VERSION
is a string containing the required version number.  Return
non-nil if that version or higher is installed."
  (let ((version (cdr (assq 'version (epg-find-configuration protocol)))))
    (and (stringp version)
         (version<= required-version version))))

;;;###autoload
(defun epg-expand-group (config group)
  "Look at CONFIG and try to expand GROUP."
  (let ((entry (assq 'groups config)))
    (if (and entry
	     (setq entry (assoc (downcase group) (cdr entry))))
	(cdr entry))))

(provide 'epg-config)

;;; epg-config.el ends here