A mail gateway hands a plaintext message, together with a shared secret, to the one component of the scheme that actually does the scrambling — mixing and rearranging the bits until the output is unintelligible. Which of the five ingredients has it just invoked?
A mail gateway hands a plaintext message, together with a shared secret, to the one component of the scheme that actually does the scrambling — mixing and rearranging the bits until the output is unintelligible. Which of the five ingredients has it just invoked?
Answer
The encryption algorithm
Options - A. The encryption algorithm - B. The cipher - C. The codebook - D. The keystream - E. The secret key Why - A. Correct — the encryption algorithm is the machinery that does the mixing and rearranging; the key only selects which particular mixing is applied. - B. A cipher is the whole scheme (all five ingredients together), not the component that does the scrambling. - C. A codebook is the mental model for ECB mode — one ciphertext per plaintext block per key — not a component of the scheme. - D. A keystream is what a stream cipher generates and XORs with the plaintext; it is an intermediate value, not the transforming component. - E. The key is supplied to the algorithm and is independent of the plaintext. It chooses the transformation; it does not perform it.
SB5e ch2 §2.1; ch20 §20.1