Consider a k-bit hash function H(x) (i.e., it outputs k-bit hash values). It is preimage resistant and collision resistant. Now construct a (k+1)-bit hash function H(x) as follows: - If x is exactly k bits long, then output 0x (a single 0 bit followed by x ); - Otherwise, output 1H(x) (a single 1 bit followed by H(x) ). a) (4 marks) Is H(x) preimage resistant? Justify your answer. b) ( 6 marks) Is H(x) second preimage resistant? Justify your