For any block cipher, the fact that it is a nonlinear function is crucial to its security. To see this, suppose that we have a linear block cipher EnLinear that encrypts $256-$bit blocks of plaintext into $256-$bit blocks of ciphertext. Let $(,)$ denote the encryption of a $256-$bit message m under a key $($the actual bit length of $$ is irrelevant$).$ Thus,

$(,[12])=(,1)(,2)$ for all $128-$bit patterns $1,2.$

Describe how, with $256$ chosen ciphertexts, an adversary can decrypt any ciphertext without knowledge of the secret key $.($A $$chosen ciphertext$$ means that an adversary has the ability to choose a ciphertext and then obtain its decryption. Here, you have $256$ plaintext$/$ciphertext pairs to work with, and you have the ability to choose the value of the ciphertexts.