updated for version 7.4.509
Problem:    Users are not aware their encryption is weak.
Solution:   Give a warning when prompting for the key.
diff --git a/src/fileio.c b/src/fileio.c
index 0843d04..a978ec2 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2958,6 +2958,7 @@
 		 * Happens when retrying to detect encoding. */
 		smsg((char_u *)_(need_key_msg), fname);
 		msg_scroll = TRUE;
+		crypt_check_method(method);
 		cryptkey = crypt_get_key(newfile, FALSE);
 		*did_ask = TRUE;