Which of the following statement $($s$)$ is $($are$)$ correct?

Cryptography does not mean only encryption and decryption.

Stream ciphers are often used as an encryption scheme on the fly.

RSA encryption can be broken by a side$-$channel attack.

In a digital signature scheme, the signer signs a message with the secret $($private$)$ public key.

a$.1$ and $4$

b$.$ All

c$.3$

d$.$ None of the options

e$.2$ and $4$