We now analyze the security of DES double encryption (2DES) by doing a cost-estimate: 2DES(x) = DESK₂ (DESK₁ (x))

2. Let us now consider the meet-in-the-middle (or time-memory tradeoff) attack, in which we can use memory. Answer the following questions:

a. How many entries have to be stored?

b. How many bytes (not bits!) have to be stored for each entry?

c. How costly is a key search in one week? Please note that the key space has to be searched before filling up the memory completely. Then we can begin to search the key space of the second key. Assume the same hardware for both key spaces.