config: Introduce an enabled flag for S/MIME

This allows setups where there is no S/MIME. In some scenarios using just
GPG is fine and S/MIME might even be discouraged. Previously this required
to provide a dummy S/MIME key just to make remail happy. With this new flag
there is no need for that key if S/MIME is not required for the list.

Signed-off-by: Andreas Rammhold <andreas@rammhold.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/examples/conf/remail.yaml

@@ -13,6 +13,8 @@ use_smtp: True
 
 # S/MIME
 smime:
+ # Enable S/MIME
+ enabled:       True
  # Verify CA certs. Only disable for troubleshooting
  verify:        True
 

Documentation/man5/remail.config.rst

@@ -186,9 +186,14 @@ S/MIME options:
   .. code-block:: yaml
 
      smime:
+      enabled:             True
       verify:              True
       sign:                True
 
+  enabled:
+   Enable S/MIME processing. If this option is set to False then no attempts
+   are made to process S/MIME mails or keys.
+
   verify:
 
    When handling S/MIME encrypted mail then the validity of the senders key

remail/config.py

@@ -189,6 +189,7 @@ class archive_config(object):
             print('%*s%-40s: %s' % (indent, '', 'plain_list', self.m_list))
 
 smime_defaults = {
+    'enabled'    : True,
     'verify'     : True,
     'sign'       : True,
 }

remail/maillist.py

@@ -35,7 +35,9 @@ class maillist(object):
         self.enabled = listcfg.enabled
         self.use_smtp = use_smtp
 
-        self.smime = smime_crypt(self.config.smime, self.config.listaccount)
+        self.smime = None
+        if self.config.smime.enabled:
+            self.smime = smime_crypt(self.config.smime, self.config.listaccount)
         self.gpg = gpg_crypt(self.config.gpg, self.config.listaccount)
 
         self.tracking = account_tracking(self.config.tracking, logger)
@@ -72,7 +74,7 @@ class maillist(object):
         Encrypt plain text message for the account
         '''
         msg = msg_from_string(msg_plain.as_string())
-        if account.use_smime:
+        if self.smime and account.use_smime:
             self.smime.encrypt(msg, account)
         else:
             self.gpg.encrypt(msg, account)
@@ -143,7 +145,9 @@ class maillist(object):
         '''
         msg_sanitize_incoming(msg)
 
-        msg_plain = self.smime.decrypt(msg)
+        msg_plain = None
+        if self.smime:
+           msg_plain = self.smime.decrypt(msg)
         if not msg_plain:
             msg_plain = self.gpg.decrypt(msg)
         return msg_plain
@@ -303,10 +307,10 @@ class maillist(object):
         for account in self.config.subscribers.values():
             if not account.enabled:
                 continue
-            if not account.use_smime:
-                self.gpg.check_key(account)
-            else:
+            if account.use_smime and self.smime:
                 self.smime.check_cert(account)
+            else:
+                self.gpg.check_key(account)
 
 class maillist_checker(object):
     '''