Which of these statements are correct

$$ Cryptography can be generally divided into symmetric $($public$-$key$)$ and asymmetric $($private$-$key$)$ cryptography.

$$ A linear feedback shift register $($LSFR$)$ has an input bit being a linear function of its previous state and can be easily implemented from flip$-$flops, however due to security issues it was not used in any practical cryptographic scenario.

$$ Permutation is an example of diffusion in a block cipher.

$$ Stream ciphers encrypt individual bits using public keys.