11.$11.$ 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.