Certified Ethical Hacker (CEH) Practice Question

Stream ciphers are secure only when each plaintext is combined with a unique, never-repeated keystream. If the same key/IV pair is used twice, the keystream is identical in both encryptions. XORing two ciphertexts cancels out that keystream, leaving the XOR of the two plaintexts, which an attacker can "crib-drag" to recover each message. This is commonly called a two-time-pad or keystream-reuse attack and falls under ciphertext-only analysis because no plaintext must be known in advance. Linear cryptanalysis, differential cryptanalysis, and meet-in-the-middle require block ciphers and different data or assumptions; they do not rely on keystream reuse in stream ciphers.