du dildlying is du valitage. 3. (20 points) (PRF or not?) Determine whether each of the following F' is a pseudorandom function. If yes, prove it; if not, describe and analyze a feasible distinguisher that has non-negligible advantage in the PRF game against F'. (a) (10 points) F (2):=G(2) Ok, where G is a PRG. (b) (10 points) F (1122) = F (11)|| F, (12), where is a PRF, and 21 = 1721. (Here ki, k are chosen uniformly and independently from the key space of F.) du dildlying is du valitage. 3. (20 points) (PRF or not?) Determine whether each of the following F' is a pseudorandom function. If yes, prove it; if not, describe and analyze a feasible distinguisher that has non-negligible advantage in the PRF game against F'. (a) (10 points) F (2):=G(2) Ok, where G is a PRG. (b) (10 points) F (1122) = F (11)|| F, (12), where is a PRF, and 21 = 1721. (Here ki, k are chosen uniformly and independently from the key space of F.)