$16.$ Which of the statements below are correct$$ The output feedback $($OFB$)$ mode of operation of the block cipher can be used as a keystream generator.$$ In cryptography an initialization vector $($IV$)$ does not always have to be random and can be a nonce $($i$.$e$.$ a number used only once, fulfilling the non$-$repeating property$).$ In the RSA cipher the public key has one part, while the private key has two parts used in modular algebra computations.$$