For the ECB and CBC modes, the plaintext must be a sequence of one or more complete data blocks. In other words, the total number of bits in the plaintext must be a positive multiple of the block size. One common method of padding, if needed, consists of a 1 but followed by as few O bits, possibly none, as are necessary to complete the final block. It is considered good practice for the sender to pad every message, including messages in which the final message block is already complete. What is the motivation for including a padding block when padding is not needed