Question

Information Security

-Why are modes of operation needed for block ciphers like AES?

Answer 1

As taken the definition of the block cipher, it is stated that ->the plain text is divided into the blocks of the fixed particulate length and each block( which are at the same length) containing bits are encrypted very well. Simply means the whole block is encrypted at a time with the block cipher.

One of the limitation of the Block Cipher is that it allow the encrypt the message only limited to the block size , suppose your block size is 128 bits AND you want to encrypt the message above 128 bits (lets say 129 bits) then it does not allow block to encrypt that message, SO to overcome this problem , MODES OF OPERATION IS USED TO ENCRYPT THE message greater than block size

There are Several Modes of Operation Uses by block Cipher are as follows

1.Electronic Code Block

2.Cipher Block Chaining

3.Cipher Feedback Mode

etc.

that's why the modes of operation needed for block cipher like AES.