[Solved]514 Given Multiple Plaintext Ciphertext Pairs Objective Attack En Cryption Scheme Based Up Q37168290
5.14. Given multiple plaintext–ciphertext pairs, your objectiveis to attack an en- cryption scheme based upon multipleencryptions.
-
You want to break an encryption system E, which makes use oftriple AES-192 encryption (e.g. block length n = 128 bit, key sizeof k = 192 bit). How many tuples (xi , yi ) with yi = eK (xi ) doyou need to level down the probability of finding a key K, whichmatches the condition yi = eK(xi) for one particular i, but failsfor most other values of i (a so called false positive), to Pr(K′̸= K) = 2−20?
-
What is the maximum key size of a block cipher that you couldstill effectively attack with an error probability of at most Pr(K′̸= K) = 2−10 = 1/1024, if this cipher always uses double encryption(l = 2) and has a block length of n = 80 bit?
-
Estimate the success probability, if you are provided with fourplaintext–ciphertext blocks which are double encrypted usingAES-256 (n = 128 bits, k = 256 bits). Please justify yourresults.
Note that this is a purely theoretical problem. Key spaces ofsize 2128 and beyond can not be brute-forced.
Expert Answer
Answer to 5.14. Given multiple plaintext–ciphertext pairs, your objective is to attack an en- cryption scheme based upon multipl… . . .
OR
