Implement `pad` function

tp/rsa/main.hs

@@ -9,3 +9,10 @@ stringToMessage = map ord
 
 messageToString::Message -> String
 messageToString = map chr
+
+pad::Int -> Message -> Message
+pad block msg = 
+	let msgSize = length msg in
+	let gap = mod msgSize block in
+	let padding = block - gap in
+	msg ++ [padding | _ <- [1..padding] ]