Which of these statements are correct

$$ 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.

$$ 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.

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

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