Which following statements are correct

Substitution cipher is an example of a historical cypher in which every plaintext letter is replaced by another fixed letter, hence it is an example of an asymmetric cipher.

In cryptography key space refers to possible keys used by a certain cryptographic protocol.

In modular arithmetic under a mod $5$ operation the numbers $7$ and $12$ are equivalent.

A block cipher according to Shannon should comprise two atomic operations, i$.$e$.$ confusion $($obscuring relationship between plaintext and ciphertext$)$ and diffusion $($single bits of ciphertext influenced by many bits of plaintext$).$