$9.$ Which of the following statements on classical cryptography fundamentals are correct

A$)$ GSM system uses $11$ LSFRs coupled together in implementing a stream cipher in order to assure difficulty in breaking its security.

B$)$ Cryptanalysis can be divided into social engineering, implementation attacks $($including side$-$channel attacks$)$ and classical cryptanalysis $($further divided into analytical attacks and brute forces attacks$).$

C$)$ DES protocol uses $16$ subkeys and its effective key length is $56$ because it drops bits number $8,16,24,32,40,48,56$ and $64,$ because these bits serve as parity bits.

D$)$ In terms of basic algebraic structures fields generalize rings $($fields include division operation and have a multiplicative inverse for every element other than $0),$ while rings generalize groups $($rings include multiplication operation$).$

$10.$ Which of the following statements on classical cryptography fundamentals are correct

A$)$ The only really nondeterministic true random numbers generators $($TRNG$)$ are quantum random numbers generators $($QRNG$).$

B$)$ DES protocol was introduced to improve the security of the AES cryptosystem and successfully doing so became a world standard in practical encryption, later on improved by the $3$DES cryptosystem.

C$)$ The Feistel network iteratively runs multiple times a simple round function, which allows for easier hardware implementation of a block cipher cryptographic system.

D$)$ Pseudo random numbers generators recursively compute consecutive random numbers from a seed, which is an input random $($either truly or pseudo random$)$ number.

$11.$ Which of these statements are correct

A$)$ In general cryptographic encryption requires a key to encrypt messages $($encryption key$)$ and a key to decrypt messages $($decryption key$),$ which do not have to be identical, except for the symmetric$-$key cryptography.

B$)$ A pseudo random numbers generator, a hash function or a message authentication code $($MAC$)$ can be built from the block cipher.

C$)$ In the RSA cipher for Alice to encrypt the message to Bob, she needs to receive the public key of Bob, which must be sent to her by a reliable, however not necessarily secure$,$ communication channel.

D$)$ A block cipher can be easily turned into a stream cipher while the opposite is not the case.