Which of the following is the best method to thwart exhaustive searches by cryptanalysts?

• A. To use codes
• B. To make the key very long
• C. Randomize the key thoroughly
• D. All of the above

Answer: (D)

The strongest way to push brute-force attacks into impractical territory is to maximize the secrecy and randomness of the overall encryption. A very long key makes the space of possible keys astronomically large, so trying every option becomes almost impossible. When that key is also random and high-entropy, there are no predictable patterns for an attacker to exploit, so shortcuts or educated guesses don’t help much and the effort remains immense. Adding codes introduces an additional layer of secret mappings or a large codebook, which further expands the possibilities an attacker would have to consider if the codebook isn’t known. Put together, these methods multiply the barriers against exhaustive searching, making all of the above approaches collectively the most effective defense.