Only 4.8

choose uniform r {01 1}n, compute and let the tag be r, t 4.8 Let F be a pseudorandom function. Show that the following MAC for messages of length 2n is insecure: Gen outputs a uniform k e 10,11n To authenticate a message milm2 with |mmn, compute the 4.9 Given any deterministic MAC (Mac, Vrfy), we may view Mac as a keyed function. In both Constructions 4.5 and 4.11, Mac is a pseudorandom function. Give a construction of a secure, deterministic MAC in which Mac is not a pseudorandom function choose uniform r {01 1}n, compute and let the tag be r, t 4.8 Let F be a pseudorandom function. Show that the following MAC for messages of length 2n is insecure: Gen outputs a uniform k e 10,11n To authenticate a message milm2 with |mmn, compute the 4.9 Given any deterministic MAC (Mac, Vrfy), we may view Mac as a keyed function. In both Constructions 4.5 and 4.11, Mac is a pseudorandom function. Give a construction of a secure, deterministic MAC in which Mac is not a pseudorandom function