$.$ Recall that in a Feistel$-$network based block cipher, the round function F $($X$,$ Ki$)$ takes an

input X and a round key Ki$.$ Suppose that X is $32-$bits and the Feistel network has $4$ rounds.

Furthermore,suppose that all round keys are $32$ bits and the round function is defined as F $($X$,$ Ki$)=$ X

$$ Ki$,$ where $$ denotes bit XOR. We assume that the key for the entire cipher is a concatenation of the

$4$ round keys, i$.$e$.,$ the cipher key is $4*32=128$ bits long.