Symmetric Encryption, meet in the middle attack, effective key length
I believe I have settled it, please comment below if I have inaccuracies or am missing something:
c=Ek5(Ek4(Ek3(Ek2(Ek1(m))))
We can also represent these as the following: (by applying the appropriate decryptions to either side)
Dk4(Dk5(c)) = Ek3(Ek2(Ek1(m))) _____ OR ______  Dk3(Dk4(Dk5(c)))=Ek2(Ek1(m))
Effective key length: with the mitm attacker, it would take 2^192 operations on one side of the equation to find the &quot;collisions&quot; in the stored lists and determine a set of proper keys by brute force, and 2^128 operations on the other side.
Stated more abstractly, approximately ~|K|^3 + ~|K|^2, but in big O notation O(|K|^3)