Given n blocks of message, the ECB mode produces exactly n blocks of ciphertext.

However, the CBC mode produces $($n $+1)$ blocks, due to the use of IV$.$ Other modes

such as CFB$,$ OFB, and CTR also use an IV to encrypt messages. Show that secure

encryption of multiple blocks of plaintext necessarily requires the use of IV $($or some

other form of randomization in the encryption process$).$