2 of 4
smaller value of 5

Decrypt the ciphertext with every possible key and store the result: $2^{56}$ decryptions. Now encrypt the (known) plaintext of the ciphertext with every possible key: $2^{56}$ encryptions. You have found the correct key pair if you find a result of the first list in the second list. All in all $2^{56} + 2^{56} = 2^{57}$ operations, not $2^{112}$. Just the normal Meet-in-the-middle attack.

Nova
  • 3.9k
  • 1
  • 16
  • 23