<Dd> if this is the case then: </Dd> <P> Use the found combination of sub-keys (k f 1, k b 1, k f 2, k b 2) (\ displaystyle (k_ (f_ (1)), k_ (b_ (1)), k_ (f_ (2)), k_ (b_ (2)))) on another pair of plaintext / ciphertext to verify the correctness of the key . </P> <P> Time complexity of this attack without brute force, is </P> <Dl> <Dd> 2 k f 1 + 2 k b 2 + 2 s ⋅ (2 k b 1 + 2 k f 2) (\ displaystyle 2 ^ (k_ (f_ (1))) + 2 ^ (k_ (b_ (2))) + 2 ^ (s) \ cdot \ left (2 ^ (k_ (b_ (1))) + 2 ^ (k_ (f_ (2))) \ right)) </Dd> </Dl>

Difference between meet in the middle attack and man in the middle attack