Problem 2: If I can encrypt or decrypt 10^13 AES blocks per second (each with different keys), how many years would it take me to find a key that decrypts a block of ciphertext given known plaintext(using 128 bit keys)? Is the 10^13 encryptions per second reasonable for an attacker? 2.1 Let's now assume that AES is broken in the sense that we can exclude 2^40 of the keys from our search. How many years are required? Is this a practical break of the algorithm or not?