What is meet-in-the-middle attack

Question

Explain what is meet-in-the-middle attack?

Answer 1

Meet-in-the-middle attack was first explained in [DIFF77]. It is based upon the observation which says, if we have C=Ek2 [Ek1 [P]]

Then

X=Ek1 [P] =Dk2[C]

Provided a known pair, (P, C), attack proceeds as follows. First, encrypt P for all the 256 possible values of K1. Store these results within a table and then sort table through the values of X. Next, decrypt the C using all the 256 possible values of K2. Since every decryption is generated, check result against the table for the match. If a match happens, then test the two resulting keys against the new known plaintext-cipher text pair. If two keys generate the correct cipher text, accept them as correct keys.