lisp/gnus/mml-smime.el: Support signing by sender.

1 files changed, 46 insertions, 16 deletions

diff --git a/lisp/gnus/mml-smime.el b/lisp/gnus/mml-smime.el
index 3e769d396b0..e7f9de7980d 100644
--- a/lisp/gnus/mml-smime.el
+++ b/lisp/gnus/mml-smime.el
@@ -74,6 +74,11 @@ Whether the passphrase is cached at all is controlled by
   :group 'mime-security
   :type '(repeat (string :tag "Key ID")))
 
+(defcustom mml-smime-sign-with-sender nil
+  "If t, use message sender so find a key to sign with."
+  :group 'mime-security
+  :type 'boolean)
+
 (defun mml-smime-sign (cont)
   (let ((func (nth 1 (assq mml-smime-use mml-smime-function-alist))))
     (if func
@@ -366,6 +371,24 @@ Whether the passphrase is cached at all is controlled by
 	  (setq pointer (cdr pointer))))
       (setq keys (cdr keys)))))
 
+;; XXX: since gpg --list-secret-keys does not return validity of each
+;; key, `mml-smime-epg-find-usable-key' defined above is not enough for
+;; secret keys.  The function `mml-smime-epg-find-usable-secret-key'
+;; below looks at appropriate public keys to check usability.
+(defun mml-smime-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 (mml-smime-epg-find-usable-key
+	   (epg-list-keys context (epg-sub-key-fingerprint
+				   (car (epg-key-sub-key-list
+					 (car secret-keys)))))
+	   usage)
+	  (setq secret-key (car secret-keys)
+		secret-keys nil)
+	(setq secret-keys (cdr secret-keys))))
+    secret-key))
+
 (autoload 'mml-compute-boundary "mml")
 
 ;; We require mm-decode, which requires mm-bodies, which autoloads
@@ -376,29 +399,36 @@ Whether the passphrase is cached at all is controlled by
   (let* ((inhibit-redisplay t)
 	 (context (epg-make-context 'CMS))
 	 (boundary (mml-compute-boundary cont))
+	 (sender (message-options-get 'message-sender))
+	 (signer-names (or mml-smime-signers
+			   (if (and mml-smime-sign-with-sender sender)
+			       (list (concat "<" sender ">")))))
 	 signer-key
 	 (signers
 	  (or (message-options-get 'mml-smime-epg-signers)
 	      (message-options-set
-	      'mml-smime-epg-signers
-	      (if (eq mm-sign-option 'guided)
-		  (epa-select-keys context "\
+	       'mml-smime-epg-signers
+	       (if (eq mm-sign-option 'guided)
+		   (epa-select-keys context "\
 Select keys for signing.
 If no one is selected, default secret key is used.  "
-				   mml-smime-signers t)
-		(if mml-smime-signers
-		    (mapcar
-		     (lambda (signer)
-		       (setq signer-key (mml-smime-epg-find-usable-key
-					 (epg-list-keys context signer t)
-					 'sign))
-		       (unless (or signer-key
-				   (y-or-n-p
-				    (format "No secret key for %s; skip it? "
+				    signer-names
+				    t)
+		 (if (or sender mml-smime-signers)
+		     (delq nil
+			   (mapcar
+			    (lambda (signer)
+			      (setq signer-key
+				    (mml-smime-epg-find-usable-secret-key
+				     context signer 'sign))
+			      (unless (or signer-key
+					  (y-or-n-p
+					   (format
+					    "No secret key for %s; skip it? "
 					    signer)))
-			 (error "No secret key for %s" signer))
-		       signer-key)
-		     mml-smime-signers))))))
+				(error "No secret key for %s" signer))
+			      signer-key)
+			    signer-names)))))))
 	 signature micalg)
     (epg-context-set-signers context signers)
     (if mml-smime-cache-passphrase