Make sure GPG keys are usable when composing non-MIME messages (bug#8955).

* mml1991.el (mml1991-epg-find-usable-key)
(mml1991-epg-find-usable-secret-key): New function.
(mml1991-epg-sign): Check if signing key is usable.
(mml1991-epg-encrypt): Check if encrypting key is usable (bug#8955).

2 files changed, 82 insertions, 19 deletions

diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index 9029ab8e6fd..b361760f511 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,10 @@
+2011-08-04  Daiki Ueno  <ueno@unixuser.org>
+
+        * mml1991.el (mml1991-epg-find-usable-key)
+        (mml1991-epg-find-usable-secret-key): New function.
+        (mml1991-epg-sign): Check if signing key is usable.
+        (mml1991-epg-encrypt): Check if encrypting key is usable (bug#8955).
+
 2011-08-03  Andrew Cohen  <cohen@andy.bu.edu>
 
         * nnir.el (nnir-read-server-parm): Add an argument to restrict to
diff --git a/lisp/gnus/mml1991.el b/lisp/gnus/mml1991.el
index a5d778845c1..ad9f95796fe 100644
--- a/lisp/gnus/mml1991.el
+++ b/lisp/gnus/mml1991.el
@@ -247,6 +247,10 @@ Whether the passphrase is cached at all is controlled by
 (autoload 'epg-context-set-textmode "epg")
 (autoload 'epg-context-set-signers "epg")
 (autoload 'epg-context-set-passphrase-callback "epg")
+(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-sign-string "epg")
 (autoload 'epg-encrypt-string "epg")
 (autoload 'epg-configuration "epg-config")
@@ -274,17 +278,59 @@ Whether the passphrase is cached at all is controlled by
               (cons key-id mml1991-epg-secret-key-id-list))
         (copy-sequence passphrase)))))
 
+(defun mml1991-epg-find-usable-key (keys usage)
+  (catch 'found
+    (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 'disabled (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)))))
+
+;; XXX: since gpg --list-secret-keys does not return validity of each
+;; key, `mml1991-epg-find-usable-key' defined above is not enough for
+;; secret keys.  The function `mml1991-epg-find-usable-secret-key'
+;; below looks at appropriate public keys to check usability.
+(defun mml1991-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 (mml1991-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 mml1991-epg-sign (cont)
   (let ((context (epg-make-context))
-        headers cte signers signature)
+        headers cte signer-key signers signature)
     (if (eq mm-sign-option 'guided)
         (setq signers (epa-select-keys context "Select keys for signing.
 If no one is selected, default secret key is used.  "
                                        mml1991-signers t))
       (if mml1991-signers
-          (setq signers (mapcar (lambda (name)
-                                  (car (epg-list-keys context name t)))
-                                mml1991-signers))))
+          (setq signers (delq nil
+                              (mapcar
+                               (lambda (name)
+                                 (setq signer-key
+                                       (mml1991-epg-find-usable-secret-key
+                                        context name 'sign))
+                                 (unless (or signer-key
+                                             (y-or-n-p
+                                              (format
+                                               "No secret key for %s; skip it? "
+                                               name)))
+                                   (error "No secret key for %s" name))
+                                 signer-key)
+                               mml1991-signers)))))
     (epg-context-set-armor context t)
     (epg-context-set-textmode context t)
     (epg-context-set-signers context signers)
@@ -344,7 +390,11 @@ If no one is selected, default secret key is used.  "
              (split-string
               (message-options-get 'message-recipients)
               "[ \f\t\n\r\v,]+")))
-        cipher signers config)
+        recipient-key signer-key cipher signers config)
+    (when mml1991-encrypt-to-self
+      (unless mml1991-signers
+        (error "mml1991-signers is not set"))
+      (setq recipients (nconc recipients mml1991-signers)))
     ;; We should remove this check if epg-0.0.6 is released.
     (if (and (condition-case nil
                  (require 'epg-config)
@@ -363,26 +413,32 @@ If no one is selected, default secret key is used.  "
 If no one is selected, symmetric encryption will be performed.  "
                                recipients))
       (setq recipients
-            (delq nil (mapcar (lambda (name)
-                                (car (epg-list-keys context name)))
-                              recipients))))
-    (if mml1991-encrypt-to-self
-        (if mml1991-signers
-            (setq recipients
-                  (nconc recipients
-                         (mapcar (lambda (name)
-                                   (car (epg-list-keys context name)))
-                                 mml1991-signers)))
-          (error "mml1991-signers not set")))
+            (delq nil (mapcar
+                       (lambda (name)
+                         (setq recipient-key (mml1991-epg-find-usable-key
+                                              (epg-list-keys context name)
+                                              'encrypt))
+                         (unless (or recipient-key
+                                   (y-or-n-p
+                                    (format "No public key for %s; skip it? "
+                                            name)))
+                           (error "No public key for %s" name))
+                         recipient-key)
+                       recipients)))
+      (unless recipients
+        (error "No recipient specified")))
     (when sign
       (if (eq mm-sign-option 'guided)
           (setq signers (epa-select-keys context "Select keys for signing.
 If no one is selected, default secret key is used.  "
                                          mml1991-signers t))
         (if mml1991-signers
-            (setq signers (mapcar (lambda (name)
-                                    (car (epg-list-keys context name t)))
-                                  mml1991-signers))))
+            (setq signers (delq nil
+                                (mapcar
+                                 (lambda (name)
+                                   (mml1991-epg-find-usable-secret-key
+                                    context name 'sign))
+                                 mml1991-signers)))))
       (epg-context-set-signers context signers))
     (epg-context-set-armor context t)
     (epg-context-set-textmode context t)