updated for version 7.4.509

Problem:    Users are not aware their encryption is weak.
Solution:   Give a warning when prompting for the key.

src/crypt.c

@@ -503,6 +503,26 @@ crypt_free_key(key)
     }
 }
 
+/*
+ * Check the crypt method and give a warning if it's outdated.
+ */
+    void
+crypt_check_method(method)
+    int method;
+{
+    if (method < CRYPT_M_BF2)
+    {
+	msg_scroll = TRUE;
+	MSG(_("Warning: Using a weak encryption method; see :help 'cm'"));
+    }
+}
+
+    void
+crypt_check_current_method()
+{
+    crypt_check_method(crypt_get_method_nr(curbuf));
+}
+
 /*
  * Ask the user for a crypt key.
  * When "store" is TRUE, the new key is stored in the 'key' option, and the