Implement `ungroupBytes`

tp/rsa/main.hs

@@ -39,3 +39,7 @@ groupBytes = subgroupBytes 1 0
 subgroupBytes::Int -> Int -> Message -> Int
 subgroupBytes _ acc [] = acc
 subgroupBytes pow acc (c:msg) = subgroupBytes (pow * 256) (acc + c * pow) msg
+
+ungroupBytes::Int -> Message
+ungroupBytes 0 = []
+ungroupBytes n = (mod n 256):ungroupBytes (div n 256)