Padding

For the ECB, CBC, and CFB modes, the plaintext must be a sequence of one or more

complete data blocks (or, for CFB mode, data segments). In other words, for these

three modes, the total number of bits in the plaintext must be a positive multiple of

the block (or segment) size. One common method of padding, if needed, consists of a

1 bit followed by as few zero 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

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