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

Question

6.7 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 motiva- tion for including a padding block when padding is not needed?

Explanation / Answer

The movtivation of adding paddings in the texts is to prevent the message from easily getting decoding during transmission. Adding simple plain texts in between the text and in the end helps and the attacker is not able to easily decrypt the encrypted message. Also padding helps as the length of the string increases from the actual message making it more difficult for the attacker to predict the actual plain text in the message.

Also sometimes padding is done to ensure that a minimum number of letters are reached for sending the message, This again adds a layer of protection for message sending and helps in protecting the information.

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