$3.$True or False Questions $(20$ points$)$:$1)$True or False: AES encryption operates on variable$-$sized blocks of data$\mathrm{.}2)$True or False: Cryptanalysis is the process of converting ciphertext into plaintext$\mathrm{.}3)$True or False: AES encryption uses a substitution$-$permutation network $($SPN$)$ structure$\mathrm{.}4)$True or False: The Vigen$$re cipher is a type of substitution cipher$\mathrm{.}5)$True or False: The Caesar$/$shift cipher is vulnerable to frequency analysis$\mathrm{.}6)$True or False: Cryptography is primarily concerned with data compression techniques$\mathrm{.}7)$True or False: AES encryption always uses a $256-$bit key$\mathrm{.}8)$True or False: The Data Encryption Standard $($DES$)$ is still widely used in secure communications$\mathrm{.}9)$True or False: In the Caesar$/$shift cipher, the shift value can vary for each letter$\mathrm{.}10)$True or False: The Caesar$/$shift cipher can only encrypt letters; it cannot encrypt numbers or symbols.