gnus/mml2015.el: Fix secret key validity check (Bug#7797).

* mml2015.el (epg-sub-key-fingerprint): Autoload.
(mml2015-epg-find-usable-secret-key): New function.
(mml2015-epg-sign): Use mml2015-epg-find-usable-secret-key instead of
mml2015-epg-find-usable-key (Bug#7797).
(mml2015-epg-encrypt): Ditto.

2 files changed, 33 insertions, 6 deletions

diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index 10d2cc4c663..abbddcc49cc 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,11 @@
+2011-01-07  Daiki Ueno  <ueno@unixuser.org>
+
+        * mml2015.el (epg-sub-key-fingerprint): Autoload.
+        (mml2015-epg-find-usable-secret-key): New function.
+        (mml2015-epg-sign): Use mml2015-epg-find-usable-secret-key instead of
+        mml2015-epg-find-usable-key (Bug#7797).
+        (mml2015-epg-encrypt): Ditto.
+
 2011-01-03  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * flow-fill.el (fill-flowed-encode): Do encoding citation-aware.
diff --git a/lisp/gnus/mml2015.el b/lisp/gnus/mml2015.el
index abcb0fda13e..9831b336190 100644
--- a/lisp/gnus/mml2015.el
+++ b/lisp/gnus/mml2015.el
@@ -742,6 +742,7 @@ 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-configuration "epg-config")
 (autoload 'epg-expand-group "epg-config")
 (autoload 'epa-select-keys "epa")
@@ -784,6 +785,24 @@ 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, `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
+           (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))
+
 (defun mml2015-epg-decrypt (handle ctl)
   (catch 'error
     (let ((inhibit-redisplay t)
@@ -960,9 +979,9 @@ If no one is selected, default secret key is used.  "
                      (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
@@ -1081,9 +1100,9 @@ If no one is selected, default secret key is used.  "
                        (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