mml2015: make key image extraction robuster
[gnus] / lisp / mml2015.el
index 65cf1a8..2c2187a 100644 (file)
@@ -1,7 +1,6 @@
 ;;; mml2015.el --- MIME Security with Pretty Good Privacy (PGP)
 
-;; Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
-;;   2008, 2009, 2010 Free Software Foundation, Inc.
+;; Copyright (C) 2000-2013 Free Software Foundation, Inc.
 
 ;; Author: Shenghuo Zhu <zsh@cs.rochester.edu>
 ;; Keywords: PGP MIME MML
 
 ;;; Code:
 
-;; For Emacs < 22.2.
 (eval-and-compile
-  (unless (fboundp 'declare-function) (defmacro declare-function (&rest r))))
+  ;; For Emacs <22.2 and XEmacs.
+  (unless (fboundp 'declare-function) (defmacro declare-function (&rest r)))
+
+  (if (locate-library "password-cache")
+      (require 'password-cache)
+    (require 'password)))
 
 (eval-when-compile (require 'cl))
 (require 'mm-decode)
@@ -44,6 +47,9 @@
                   (config &optional minimum-version))
 (declare-function epg-configuration "ext:epg-config" ())
 
+;; Maybe this should be in eg mml-sec.el (and have a different name).
+;; Then mml1991 would not need to require mml2015, and mml1991-use
+;; could be removed.
 (defvar mml2015-use (or
                     (condition-case nil
                         (progn
                           'epg)
                       (error))
                     (progn
-                      (ignore-errors
-                       ;; Avoid the "Recursive load suspected" error
-                       ;; in Emacs 21.1.
-                       (let ((recursive-load-depth-limit 100))
-                         (require 'pgg)))
-                      (and (fboundp 'pgg-sign-region)
-                           'pgg))
-                    (progn
-                      (ignore-errors
-                        (require 'gpg))
-                      (and (fboundp 'gpg-sign-detached)
-                           'gpg))
+                      (let ((abs-file (locate-library "pgg")))
+                        ;; Don't load PGG if it is marked as obsolete
+                        ;; (Emacs 24).
+                        (when (and abs-file
+                                   (not (string-match "/obsolete/[^/]*\\'"
+                                                      abs-file)))
+                          (ignore-errors (require 'pgg))
+                          (and (fboundp 'pgg-sign-region)
+                               'pgg))))
                     (progn (ignore-errors
                              (load "mc-toplev"))
                            (and (fboundp 'mc-encrypt-generic)
@@ -71,7 +74,7 @@
                                 (fboundp 'mc-cleanup-recipient-headers)
                                 'mailcrypt)))
   "The package used for PGP/MIME.
-Valid packages include `epg', `pgg', `gpg' and `mailcrypt'.")
+Valid packages include `epg', `pgg' and `mailcrypt'.")
 
 ;; Something is not RFC2015.
 (defvar mml2015-function-alist
@@ -81,24 +84,18 @@ Valid packages include `epg', `pgg', `gpg' and `mailcrypt'.")
               mml2015-mailcrypt-decrypt
               mml2015-mailcrypt-clear-verify
               mml2015-mailcrypt-clear-decrypt)
-    (gpg mml2015-gpg-sign
-        mml2015-gpg-encrypt
-        mml2015-gpg-verify
-        mml2015-gpg-decrypt
-        mml2015-gpg-clear-verify
-        mml2015-gpg-clear-decrypt)
-  (pgg mml2015-pgg-sign
-       mml2015-pgg-encrypt
-       mml2015-pgg-verify
-       mml2015-pgg-decrypt
-       mml2015-pgg-clear-verify
-       mml2015-pgg-clear-decrypt)
-  (epg mml2015-epg-sign
-       mml2015-epg-encrypt
-       mml2015-epg-verify
-       mml2015-epg-decrypt
-       mml2015-epg-clear-verify
-       mml2015-epg-clear-decrypt))
+    (pgg mml2015-pgg-sign
+        mml2015-pgg-encrypt
+        mml2015-pgg-verify
+        mml2015-pgg-decrypt
+        mml2015-pgg-clear-verify
+        mml2015-pgg-clear-decrypt)
+    (epg mml2015-epg-sign
+        mml2015-epg-encrypt
+        mml2015-epg-verify
+        mml2015-epg-decrypt
+        mml2015-epg-clear-verify
+        mml2015-epg-clear-decrypt))
   "Alist of PGP/MIME functions.")
 
 (defvar mml2015-result-buffer nil)
@@ -115,11 +112,6 @@ Valid packages include `epg', `pgg', `gpg' and `mailcrypt'.")
   :type '(repeat (cons (regexp :tag "GnuPG output regexp")
                       (boolean :tag "Trust key"))))
 
-(defcustom mml2015-verbose mml-secure-verbose
-  "If non-nil, ask the user about the current operation more verbosely."
-  :group 'mime-security
-  :type 'boolean)
-
 (defcustom mml2015-cache-passphrase mml-secure-cache-passphrase
   "If t, cache passphrase."
   :group 'mime-security
@@ -133,10 +125,17 @@ Whether the passphrase is cached at all is controlled by
   :type 'integer)
 
 (defcustom mml2015-signers nil
-  "A list of your own key ID which will be used to sign a message."
+  "A list of your own key ID(s) which will be used to sign a message.
+If set, it overrides the setting of `mml2015-sign-with-sender'."
   :group 'mime-security
   :type '(repeat (string :tag "Key ID")))
 
+(defcustom mml2015-sign-with-sender nil
+  "If t, use message sender so find a key to sign with."
+  :group 'mime-security
+  :type 'boolean
+  :version "24.1")
+
 (defcustom mml2015-encrypt-to-self nil
   "If t, add your own key ID to recipient list when encryption."
   :group 'mime-security
@@ -147,9 +146,15 @@ Whether the passphrase is cached at all is controlled by
   :group 'mime-security
   :type 'boolean)
 
+(defcustom mml2015-maximum-key-image-dimension 64
+  "The maximum dimension (width or height) of any key images."
+  :version "24.4"
+  :group 'mime-security
+  :type 'integer)
+
 ;; Extract plaintext from cleartext signature.  IMO, this kind of task
 ;; should be done by GnuPG rather than Elisp, but older PGP backends
-;; (such as Mailcrypt, PGG, and gpg.el) discard the output from GnuPG.
+;; (such as Mailcrypt, and PGG) discard the output from GnuPG.
 (defun mml2015-extract-cleartext-signature ()
   ;; Daiki Ueno in
   ;; <54a15d860801080142l70b95d7dkac4bf51a86196011@mail.gmail.com>: ``I still
@@ -189,9 +194,6 @@ Whether the passphrase is cached at all is controlled by
 (autoload 'mc-cleanup-recipient-headers "mc-toplev")
 (autoload 'mc-sign-generic "mc-toplev")
 
-(defvar mc-default-scheme)
-(defvar mc-schemes)
-
 (defvar mml2015-decrypt-function 'mailcrypt-decrypt)
 (defvar mml2015-verify-function 'mailcrypt-verify)
 
@@ -238,6 +240,58 @@ Whether the passphrase is cached at all is controlled by
          handles
        (list handles)))))
 
+(defun mml2015-gpg-pretty-print-fpr (fingerprint)
+  (let* ((result "")
+        (fpr-length (string-width fingerprint))
+        (n-slice 0)
+        slice)
+    (setq fingerprint (string-to-list fingerprint))
+    (while fingerprint
+      (setq fpr-length (- fpr-length 4))
+      (setq slice (butlast fingerprint fpr-length))
+      (setq fingerprint (nthcdr 4 fingerprint))
+      (setq n-slice (1+ n-slice))
+      (setq result
+           (concat
+            result
+            (case n-slice
+              (1  slice)
+              (otherwise (concat " " slice))))))
+    result))
+
+(defun mml2015-gpg-extract-signature-details ()
+  (goto-char (point-min))
+  (let* ((expired (re-search-forward
+                  "^\\[GNUPG:\\] SIGEXPIRED$"
+                  nil t))
+        (signer (and (re-search-forward
+                      "^\\[GNUPG:\\] GOODSIG \\([0-9A-Za-z]*\\) \\(.*\\)$"
+                      nil t)
+                     (cons (match-string 1) (match-string 2))))
+        (fprint (and (re-search-forward
+                      "^\\[GNUPG:\\] VALIDSIG \\([0-9a-zA-Z]*\\) "
+                      nil t)
+                     (match-string 1)))
+        (trust  (and (re-search-forward
+                      "^\\[GNUPG:\\] \\(TRUST_.*\\)$"
+                      nil t)
+                     (match-string 1)))
+        (trust-good-enough-p
+         (cdr (assoc trust mml2015-unabbrev-trust-alist))))
+    (cond ((and signer fprint)
+          (concat (cdr signer)
+                  (unless trust-good-enough-p
+                    (concat "\nUntrusted, Fingerprint: "
+                            (mml2015-gpg-pretty-print-fpr fprint)))
+                  (when expired
+                    (format "\nWARNING: Signature from expired key (%s)"
+                            (car signer)))))
+         ((re-search-forward
+           "^\\(gpg: \\)?Good signature from \"\\(.*\\)\"$" nil t)
+          (match-string 2))
+         (t
+          "From unknown user"))))
+
 (defun mml2015-mailcrypt-clear-decrypt ()
   (let (result)
     (setq result
@@ -450,279 +504,6 @@ Whether the passphrase is cached at all is controlled by
     (insert (format "--%s--\n" boundary))
     (goto-char (point-max))))
 
-;;; gpg wrapper
-
-(autoload 'gpg-decrypt "gpg")
-(autoload 'gpg-verify "gpg")
-(autoload 'gpg-verify-cleartext "gpg")
-(autoload 'gpg-sign-detached "gpg")
-(autoload 'gpg-sign-encrypt "gpg")
-(autoload 'gpg-encrypt "gpg")
-(autoload 'gpg-passphrase-read "gpg")
-
-(defun mml2015-gpg-passphrase ()
-  (or (message-options-get 'gpg-passphrase)
-      (message-options-set 'gpg-passphrase (gpg-passphrase-read))))
-
-(defun mml2015-gpg-decrypt-1 ()
-  (let ((cipher (current-buffer)) plain result)
-    (if (with-temp-buffer
-         (prog1
-             (gpg-decrypt cipher (setq plain (current-buffer))
-                          mml2015-result-buffer nil)
-           (mm-set-handle-multipart-parameter
-            mm-security-handle 'gnus-details
-            (with-current-buffer mml2015-result-buffer
-              (buffer-string)))
-           (set-buffer cipher)
-           (erase-buffer)
-           (insert-buffer-substring plain)
-           (goto-char (point-min))
-           (while (search-forward "\r\n" nil t)
-             (replace-match "\n" t t))))
-       '(t)
-      ;; Some wrong with the return value, check plain text buffer.
-      (if (> (point-max) (point-min))
-         '(t)
-       nil))))
-
-(defun mml2015-gpg-decrypt (handle ctl)
-  (let ((mml2015-decrypt-function 'mml2015-gpg-decrypt-1))
-    (mml2015-mailcrypt-decrypt handle ctl)))
-
-(defun mml2015-gpg-clear-decrypt ()
-  (let (result)
-    (setq result (mml2015-gpg-decrypt-1))
-    (if (car result)
-       (mm-set-handle-multipart-parameter
-        mm-security-handle 'gnus-info "OK")
-      (mm-set-handle-multipart-parameter
-       mm-security-handle 'gnus-info "Failed"))))
-
-(defun mml2015-gpg-pretty-print-fpr (fingerprint)
-  (let* ((result "")
-        (fpr-length (string-width fingerprint))
-        (n-slice 0)
-        slice)
-    (setq fingerprint (string-to-list fingerprint))
-    (while fingerprint
-      (setq fpr-length (- fpr-length 4))
-      (setq slice (butlast fingerprint fpr-length))
-      (setq fingerprint (nthcdr 4 fingerprint))
-      (setq n-slice (1+ n-slice))
-      (setq result
-           (concat
-            result
-            (case n-slice
-              (1  slice)
-              (otherwise (concat " " slice))))))
-    result))
-
-(defun mml2015-gpg-extract-signature-details ()
-  (goto-char (point-min))
-  (let* ((expired (re-search-forward
-                  "^\\[GNUPG:\\] SIGEXPIRED$"
-                  nil t))
-        (signer (and (re-search-forward
-                      "^\\[GNUPG:\\] GOODSIG \\([0-9A-Za-z]*\\) \\(.*\\)$"
-                      nil t)
-                     (cons (match-string 1) (match-string 2))))
-        (fprint (and (re-search-forward
-                      "^\\[GNUPG:\\] VALIDSIG \\([0-9a-zA-Z]*\\) "
-                      nil t)
-                     (match-string 1)))
-        (trust  (and (re-search-forward
-                      "^\\[GNUPG:\\] \\(TRUST_.*\\)$"
-                      nil t)
-                     (match-string 1)))
-        (trust-good-enough-p
-         (cdr (assoc trust mml2015-unabbrev-trust-alist))))
-    (cond ((and signer fprint)
-          (concat (cdr signer)
-                  (unless trust-good-enough-p
-                    (concat "\nUntrusted, Fingerprint: "
-                            (mml2015-gpg-pretty-print-fpr fprint)))
-                  (when expired
-                    (format "\nWARNING: Signature from expired key (%s)"
-                            (car signer)))))
-         ((re-search-forward
-           "^\\(gpg: \\)?Good signature from \"\\(.*\\)\"$" nil t)
-          (match-string 2))
-         (t
-          "From unknown user"))))
-
-(defun mml2015-gpg-verify (handle ctl)
-  (catch 'error
-    (let (part message signature info-is-set-p)
-      (unless (setq part (mm-find-raw-part-by-type
-                         ctl (or (mm-handle-multipart-ctl-parameter
-                                  ctl 'protocol)
-                                 "application/pgp-signature")
-                         t))
-       (mm-set-handle-multipart-parameter
-        mm-security-handle 'gnus-info "Corrupted")
-       (throw 'error handle))
-      (with-temp-buffer
-       (setq message (current-buffer))
-       (insert part)
-       ;; Convert <LF> to <CR><LF> in signed text.  If --textmode is
-       ;; specified when signing, the conversion is not necessary.
-       (goto-char (point-min))
-       (end-of-line)
-       (while (not (eobp))
-         (unless (eq (char-before) ?\r)
-           (insert "\r"))
-         (forward-line)
-         (end-of-line))
-       (with-temp-buffer
-         (setq signature (current-buffer))
-         (unless (setq part (mm-find-part-by-type
-                             (cdr handle) "application/pgp-signature" nil t))
-           (mm-set-handle-multipart-parameter
-            mm-security-handle 'gnus-info "Corrupted")
-           (throw 'error handle))
-         (mm-insert-part part)
-         (unless (condition-case err
-                     (prog1
-                         (gpg-verify message signature mml2015-result-buffer)
-                       (mm-set-handle-multipart-parameter
-                        mm-security-handle 'gnus-details
-                        (with-current-buffer mml2015-result-buffer
-                          (buffer-string))))
-                   (error
-                    (mm-set-handle-multipart-parameter
-                     mm-security-handle 'gnus-details (mml2015-format-error err))
-                    (mm-set-handle-multipart-parameter
-                     mm-security-handle 'gnus-info "Error.")
-                    (setq info-is-set-p t)
-                    nil)
-                   (quit
-                    (mm-set-handle-multipart-parameter
-                     mm-security-handle 'gnus-details "Quit.")
-                    (mm-set-handle-multipart-parameter
-                     mm-security-handle 'gnus-info "Quit.")
-                    (setq info-is-set-p t)
-                    nil))
-           (unless info-is-set-p
-             (mm-set-handle-multipart-parameter
-              mm-security-handle 'gnus-info "Failed"))
-           (throw 'error handle)))
-       (mm-set-handle-multipart-parameter
-        mm-security-handle 'gnus-info
-        (with-current-buffer mml2015-result-buffer
-          (mml2015-gpg-extract-signature-details))))
-      handle)))
-
-(defun mml2015-gpg-clear-verify ()
-  (if (condition-case err
-         (prog1
-             (gpg-verify-cleartext (current-buffer) mml2015-result-buffer)
-           (mm-set-handle-multipart-parameter
-            mm-security-handle 'gnus-details
-            (with-current-buffer mml2015-result-buffer
-              (buffer-string))))
-       (error
-        (mm-set-handle-multipart-parameter
-         mm-security-handle 'gnus-details (mml2015-format-error err))
-        nil)
-       (quit
-        (mm-set-handle-multipart-parameter
-         mm-security-handle 'gnus-details "Quit.")
-        nil))
-      (mm-set-handle-multipart-parameter
-       mm-security-handle 'gnus-info
-       (with-current-buffer mml2015-result-buffer
-        (mml2015-gpg-extract-signature-details)))
-    (mm-set-handle-multipart-parameter
-     mm-security-handle 'gnus-info "Failed"))
-  (mml2015-extract-cleartext-signature))
-
-(defun mml2015-gpg-sign (cont)
-  (let ((boundary (mml-compute-boundary cont))
-       (text (current-buffer)) signature)
-    (goto-char (point-max))
-    (unless (bolp)
-      (insert "\n"))
-    (with-temp-buffer
-      (unless (gpg-sign-detached text (setq signature (current-buffer))
-                                mml2015-result-buffer
-                                nil
-                                (message-options-get 'message-sender)
-                                t t) ; armor & textmode
-       (unless (> (point-max) (point-min))
-         (pop-to-buffer mml2015-result-buffer)
-         (error "Sign error")))
-      (goto-char (point-min))
-      (while (re-search-forward "\r+$" nil t)
-       (replace-match "" t t))
-      (set-buffer text)
-      (goto-char (point-min))
-      (insert (format "Content-Type: multipart/signed; boundary=\"%s\";\n"
-                     boundary))
-      ;;; FIXME: what is the micalg?
-      (insert "\tmicalg=pgp-sha1; protocol=\"application/pgp-signature\"\n")
-      (insert (format "\n--%s\n" boundary))
-      (goto-char (point-max))
-      (insert (format "\n--%s\n" boundary))
-      (insert "Content-Type: application/pgp-signature\n\n")
-      (insert-buffer-substring signature)
-      (goto-char (point-max))
-      (insert (format "--%s--\n" boundary))
-      (goto-char (point-max)))))
-
-(defun mml2015-gpg-encrypt (cont &optional sign)
-  (let ((boundary (mml-compute-boundary cont))
-       (text (current-buffer))
-       cipher)
-    (mm-with-unibyte-current-buffer
-      (with-temp-buffer
-       ;; set up a function to call the correct gpg encrypt routine
-       ;; with the right arguments. (FIXME: this should be done
-       ;; differently.)
-       (flet ((gpg-encrypt-func
-                (sign plaintext ciphertext result recipients &optional
-                      passphrase sign-with-key armor textmode)
-                (if sign
-                    (gpg-sign-encrypt
-                     plaintext ciphertext result recipients passphrase
-                     sign-with-key armor textmode)
-                  (gpg-encrypt
-                   plaintext ciphertext result recipients passphrase
-                   armor textmode))))
-         (unless (gpg-encrypt-func
-                   sign ; passed in when using signencrypt
-                   text (setq cipher (current-buffer))
-                   mml2015-result-buffer
-                   (split-string
-                    (or
-                     (message-options-get 'message-recipients)
-                     (message-options-set 'message-recipients
-                                          (read-string "Recipients: ")))
-                    "[ \f\t\n\r\v,]+")
-                   nil
-                   (message-options-get 'message-sender)
-                   t t) ; armor & textmode
-           (unless (> (point-max) (point-min))
-             (pop-to-buffer mml2015-result-buffer)
-             (error "Encrypt error"))))
-       (goto-char (point-min))
-       (while (re-search-forward "\r+$" nil t)
-         (replace-match "" t t))
-       (set-buffer text)
-       (delete-region (point-min) (point-max))
-       (insert (format "Content-Type: multipart/encrypted; boundary=\"%s\";\n"
-                       boundary))
-       (insert "\tprotocol=\"application/pgp-encrypted\"\n\n")
-       (insert (format "--%s\n" boundary))
-       (insert "Content-Type: application/pgp-encrypted\n\n")
-       (insert "Version: 1\n\n")
-       (insert (format "--%s\n" boundary))
-       (insert "Content-Type: application/octet-stream\n\n")
-       (insert-buffer-substring cipher)
-       (goto-char (point-max))
-       (insert (format "--%s--\n" boundary))
-       (goto-char (point-max))))))
-
 ;;; pgg wrapper
 
 (defvar pgg-default-user-id)
@@ -963,6 +744,7 @@ Whether the passphrase is cached at all is controlled by
 
 (defvar epg-user-id-alist)
 (defvar epg-digest-algorithm-alist)
+(defvar epg-gpg-program)
 (defvar inhibit-redisplay)
 
 (autoload 'epg-make-context "epg")
@@ -971,7 +753,6 @@ Whether the passphrase is cached at all is controlled by
 (autoload 'epg-context-set-signers "epg")
 (autoload 'epg-context-result-for "epg")
 (autoload 'epg-new-signature-digest-algorithm "epg")
-(autoload 'epg-verify-result-to-string "epg")
 (autoload 'epg-list-keys "epg")
 (autoload 'epg-decrypt-string "epg")
 (autoload 'epg-verify-string "epg")
@@ -982,12 +763,16 @@ Whether the passphrase is cached at all is controlled by
 (autoload 'epg-key-sub-key-list "epg")
 (autoload 'epg-sub-key-capability "epg")
 (autoload 'epg-sub-key-validity "epg")
+(autoload 'epg-sub-key-fingerprint "epg")
+(autoload 'epg-signature-key-id "epg")
+(autoload 'epg-signature-to-string "epg")
+(autoload 'epg-key-user-id-list "epg")
+(autoload 'epg-user-id-string "epg")
+(autoload 'epg-user-id-validity "epg")
 (autoload 'epg-configuration "epg-config")
 (autoload 'epg-expand-group "epg-config")
 (autoload 'epa-select-keys "epa")
 
-(defvar password-cache-expiry)
-
 (defvar mml2015-epg-secret-key-id-list nil)
 
 (defun mml2015-epg-passphrase-callback (context key-id ignore)
@@ -1013,17 +798,111 @@ Whether the passphrase is cached at all is controlled by
              (cons password-cache-key-id mml2015-epg-secret-key-id-list))
        (copy-sequence passphrase)))))
 
-(defun mml2015-epg-find-usable-key (keys usage)
-  (catch 'found
+(defun mml2015-epg-check-user-id (key recipient)
+  (let ((pointer (epg-key-user-id-list key))
+       result)
+    (while pointer
+      (if (and (equal (car (mail-header-parse-address
+                           (epg-user-id-string (car pointer))))
+                     (car (mail-header-parse-address
+                           recipient)))
+              (not (memq (epg-user-id-validity (car pointer))
+                         '(revoked expired))))
+         (setq result t
+               pointer nil)
+       (setq pointer (cdr pointer))))
+    result))
+
+(defun mml2015-epg-check-sub-key (key usage)
+  (let ((pointer (epg-key-sub-key-list key))
+       result)
+    ;; The primary key will be marked as disabled, when the entire
+    ;; key is disabled (see 12 Field, Format of colon listings, in
+    ;; gnupg/doc/DETAILS)
+    (unless (memq 'disabled (epg-sub-key-capability (car pointer)))
+      (while pointer
+       (if (and (memq usage (epg-sub-key-capability (car pointer)))
+                (not (memq (epg-sub-key-validity (car pointer))
+                           '(revoked expired))))
+           (setq result t
+                 pointer nil)
+         (setq pointer (cdr pointer)))))
+    result))
+
+(defun mml2015-epg-find-usable-key (context name usage
+                                           &optional name-is-key-id)
+  (let ((keys (epg-list-keys context name))
+       key)
     (while keys
-      (let ((pointer (epg-key-sub-key-list (car keys))))
-       (while pointer
-         (if (and (memq usage (epg-sub-key-capability (car pointer)))
-                  (not (memq (epg-sub-key-validity (car pointer))
-                             '(revoked expired))))
-             (throw 'found (car keys)))
-         (setq pointer (cdr pointer))))
-      (setq keys (cdr keys)))))
+      (if (and (or name-is-key-id
+                  ;; Non email user-id can be supplied through
+                  ;; mml2015-signers if mml2015-encrypt-to-self is set.
+                  ;; Treat it as valid, as it is user's intention.
+                  (not (string-match "\\`<" name))
+                  (mml2015-epg-check-user-id (car keys) name))
+              (mml2015-epg-check-sub-key (car keys) usage))
+         (setq key (car keys)
+               keys nil)
+       (setq keys (cdr keys))))
+    key))
+
+;; XXX: since gpg --list-secret-keys does not return validity of each
+;; key, `mml2015-epg-find-usable-key' defined above is not enough for
+;; secret keys.  The function `mml2015-epg-find-usable-secret-key'
+;; below looks at appropriate public keys to check usability.
+(defun mml2015-epg-find-usable-secret-key (context name usage)
+  (let ((secret-keys (epg-list-keys context name t))
+       secret-key)
+    (while (and (not secret-key) secret-keys)
+      (if (mml2015-epg-find-usable-key
+          context
+          (epg-sub-key-fingerprint
+           (car (epg-key-sub-key-list
+                 (car secret-keys))))
+          usage
+          t)
+         (setq secret-key (car secret-keys)
+               secret-keys nil)
+       (setq secret-keys (cdr secret-keys))))
+    secret-key))
+
+(defun mml2015-epg-key-image (key-id)
+  "Return the image of a key, if any"
+  (with-temp-buffer
+    (mm-set-buffer-multibyte nil)
+    (let* ((coding-system-for-write 'binary)
+           (coding-system-for-read 'binary)
+           (data (shell-command-to-string
+                  (format "%s --list-options no-show-photos --attribute-fd 3 --list-keys %s 3>&1 >/dev/null 2>&1"
+                          (shell-quote-argument epg-gpg-program) key-id))))
+      (when (> (length data) 0)
+        (insert (substring data 16))
+       (condition-case nil
+           (gnus-create-image (buffer-string) nil t)
+         (error))))))
+
+(autoload 'gnus-rescale-image "gnus-util")
+
+(defun mml2015-epg-key-image-to-string (key-id)
+  "Return a string with the image of a key, if any"
+  (let* ((result "")
+         (key-image (mml2015-epg-key-image key-id)))
+    (when key-image
+      (setq result "  ")
+      (put-text-property
+       1 2 'display
+       (gnus-rescale-image key-image
+                          (cons mml2015-maximum-key-image-dimension
+                                mml2015-maximum-key-image-dimension))
+       result))
+    result))
+
+(defun mml2015-epg-signature-to-string (signature)
+  (concat (epg-signature-to-string signature)
+         (mml2015-epg-key-image-to-string (epg-signature-key-id signature))))
+
+(defun mml2015-epg-verify-result-to-string (verify-result)
+  (mapconcat #'mml2015-epg-signature-to-string verify-result "\n"))
 
 (defun mml2015-epg-decrypt (handle ctl)
   (catch 'error
@@ -1067,7 +946,7 @@ Whether the passphrase is cached at all is controlled by
            (mm-set-handle-multipart-parameter
             mm-security-handle 'gnus-info
             (concat "OK\n"
-                    (epg-verify-result-to-string
+                    (mml2015-epg-verify-result-to-string
                      (epg-context-result-for context 'verify))))
          (mm-set-handle-multipart-parameter
           mm-security-handle 'gnus-info "OK"))
@@ -1115,7 +994,7 @@ Whether the passphrase is cached at all is controlled by
       (if (epg-context-result-for context 'verify)
          (mm-set-handle-multipart-parameter
           mm-security-handle 'gnus-details
-          (epg-verify-result-to-string
+          (mml2015-epg-verify-result-to-string
            (epg-context-result-for context 'verify)))))))
 
 (defun mml2015-epg-verify (handle ctl)
@@ -1133,7 +1012,7 @@ Whether the passphrase is cached at all is controlled by
        (mm-set-handle-multipart-parameter
         mm-security-handle 'gnus-info "Corrupted")
        (throw 'error handle))
-      (setq part (mm-replace-in-string part "\n" "\r\n" t)
+      (setq part (mm-replace-in-string part "\n" "\r\n")
            signature (mm-get-part signature)
            context (epg-make-context))
       (condition-case error
@@ -1149,7 +1028,8 @@ Whether the passphrase is cached at all is controlled by
         (throw 'error handle)))
       (mm-set-handle-multipart-parameter
        mm-security-handle 'gnus-info
-       (epg-verify-result-to-string (epg-context-result-for context 'verify)))
+       (mml2015-epg-verify-result-to-string
+       (epg-context-result-for context 'verify)))
       handle)))
 
 (defun mml2015-epg-clear-verify ()
@@ -1172,7 +1052,7 @@ Whether the passphrase is cached at all is controlled by
        (progn
          (mm-set-handle-multipart-parameter
           mm-security-handle 'gnus-info
-          (epg-verify-result-to-string
+          (mml2015-epg-verify-result-to-string
            (epg-context-result-for context 'verify)))
          (delete-region (point-min) (point-max))
          (insert (mm-decode-coding-string plain coding-system-for-read)))
@@ -1182,6 +1062,10 @@ Whether the passphrase is cached at all is controlled by
   (let* ((inhibit-redisplay t)
         (context (epg-make-context))
         (boundary (mml-compute-boundary cont))
+        (sender (message-options-get 'message-sender))
+        (signer-names (or mml2015-signers
+                          (if (and mml2015-sign-with-sender sender)
+                              (list (concat "<" sender ">")))))
         signer-key
         (signers
          (or (message-options-get 'mml2015-epg-signers)
@@ -1191,14 +1075,15 @@ Whether the passphrase is cached at all is controlled by
                   (epa-select-keys context "\
 Select keys for signing.
 If no one is selected, default secret key is used.  "
-                                   mml2015-signers t)
-                (if mml2015-signers
+                                   signer-names
+                                   t)
+                (if (or sender mml2015-signers)
                     (delq nil
                           (mapcar
                            (lambda (signer)
-                             (setq signer-key (mml2015-epg-find-usable-key
-                                               (epg-list-keys context signer t)
-                                               'sign))
+                             (setq signer-key
+                                   (mml2015-epg-find-usable-secret-key
+                                    context signer 'sign))
                              (unless (or signer-key
                                          (y-or-n-p
                                           (format
@@ -1206,7 +1091,7 @@ If no one is selected, default secret key is used.  "
                                            signer)))
                                (error "No secret key for %s" signer))
                              signer-key)
-                           mml2015-signers)))))))
+                           signer-names)))))))
         signature micalg)
     (epg-context-set-armor context t)
     (epg-context-set-textmode context t)
@@ -1215,6 +1100,10 @@ If no one is selected, default secret key is used.  "
        (epg-context-set-passphrase-callback
         context
         #'mml2015-epg-passphrase-callback))
+    ;; Signed data must end with a newline (RFC 3156, 5).
+    (goto-char (point-max))
+    (unless (bolp)
+      (insert "\n"))
     (condition-case error
        (setq signature (epg-sign-string context (buffer-string) t)
              mml2015-epg-secret-key-id-list nil)
@@ -1239,20 +1128,25 @@ If no one is selected, default secret key is used.  "
     (insert (format "\n--%s\n" boundary))
     (goto-char (point-max))
     (insert (format "\n--%s\n" boundary))
-    (insert "Content-Type: application/pgp-signature\n\n")
+    (insert "Content-Type: application/pgp-signature; name=\"signature.asc\"\n\n")
     (insert signature)
     (goto-char (point-max))
     (insert (format "--%s--\n" boundary))
     (goto-char (point-max))))
 
 (defun mml2015-epg-encrypt (cont &optional sign)
-  (let ((inhibit-redisplay t)
-       (context (epg-make-context))
-       (config (epg-configuration))
-       (recipients (message-options-get 'mml2015-epg-recipients))
-       cipher signers
-       (boundary (mml-compute-boundary cont))
-       recipient-key signer-key)
+  (let* ((inhibit-redisplay t)
+        (context (epg-make-context))
+        (boundary (mml-compute-boundary cont))
+        (config (epg-configuration))
+        (recipients (message-options-get 'mml2015-epg-recipients))
+        cipher
+        (sender (message-options-get 'message-sender))
+        (signer-names (or mml2015-signers
+                          (if (and mml2015-sign-with-sender sender)
+                              (list (concat "<" sender ">")))))
+        signers
+        recipient-key signer-key)
     (unless recipients
       (setq recipients
            (apply #'nconc
@@ -1266,9 +1160,9 @@ If no one is selected, default secret key is used.  "
                                              (read-string "Recipients: ")))
                     "[ \f\t\n\r\v,]+"))))
       (when mml2015-encrypt-to-self
-       (unless mml2015-signers
-         (error "mml2015-signers not set"))
-       (setq recipients (nconc recipients mml2015-signers)))
+       (unless signer-names
+         (error "Neither message sender nor mml2015-signers are set"))
+       (setq recipients (nconc recipients signer-names)))
       (if (eq mm-encrypt-option 'guided)
          (setq recipients
                (epa-select-keys context "\
@@ -1280,8 +1174,7 @@ If no one is selected, symmetric encryption will be performed.  "
                    (mapcar
                     (lambda (recipient)
                       (setq recipient-key (mml2015-epg-find-usable-key
-                                           (epg-list-keys context recipient)
-                                           'encrypt))
+                                           context recipient 'encrypt))
                       (unless (or recipient-key
                                   (y-or-n-p
                                    (format "No public key for %s; skip it? "
@@ -1301,14 +1194,15 @@ If no one is selected, symmetric encryption will be performed.  "
                     (epa-select-keys context "\
 Select keys for signing.
 If no one is selected, default secret key is used.  "
-                                     mml2015-signers t)
-                  (if mml2015-signers
+                                     signer-names
+                                     t)
+                  (if (or sender mml2015-signers)
                       (delq nil
                             (mapcar
                              (lambda (signer)
-                               (setq signer-key (mml2015-epg-find-usable-key
-                                                 (epg-list-keys context signer t)
-                                                 'sign))
+                               (setq signer-key
+                                     (mml2015-epg-find-usable-secret-key
+                                      context signer 'sign))
                                (unless (or signer-key
                                            (y-or-n-p
                                             (format
@@ -1316,7 +1210,7 @@ If no one is selected, default secret key is used.  "
                                              signer)))
                                  (error "No secret key for %s" signer))
                                signer-key)
-                             mml2015-signers)))))))
+                             signer-names)))))))
       (epg-context-set-signers context signers))
     (epg-context-set-armor context t)
     (epg-context-set-textmode context t)
@@ -1416,5 +1310,4 @@ If no one is selected, default secret key is used.  "
 
 (provide 'mml2015)
 
-;; arch-tag: b04701d5-0b09-44d8-bed8-de901bf435f2
 ;;; mml2015.el ends here