Question

In terms of cryptanalysis, what does it mean to break a cipher?

A finding a method to decrypt a message that is at least twice as efficient as brute force

B trying every possible key until you can decrypt the message

C deploying an algorithm that uses a 228 bit key

D finding any method to decrypt the message that is more efficient than brute force

Answer 1

Breaking a cipher means finding a method to decrypt a message that is more efficient than brute force. In the case of the Zimmerman Telegram, a transposition cipher was broken without trying all possible permutations.

Step-by-step explanation:

When we talk about breaking a cipher in the context of cryptanalysis, it means finding a method to decrypt a message that is more efficient than attempting every possible key until the message is decrypted, which is known as a brute force attack. Hence, the correct answer is D: finding any method to decrypt the message that is more efficient than brute force.

The Zimmerman Telegram is a historical example where a transposition cipher was used. In this type of cipher, plaintext letters are shuffled according to a specific rule. Typically, plaintext is divided into blocks, and a keyword may determine both the size of the blocks and the specific change applied to the order of the letters within each block. Breaking this cipher involves figuring out the rule and rearranging the letters back to their original order without having to try every possible permutation (which would be the brute force method).