Which of the following statements about a stream cipher are true? Each correct answer represents a complete solution. Choose three.

Question

Options

• AIt typically executes at a higher speed than a block cipher.
• BIt divides a message into blocks for processing.
• CIt typically executes at a slower speed than a block cipher.
• DIt divides a message into bits for processing.
• EIt is a symmetric key cipher.

• A
  92% (33)
• B
  6% (2)
• C
  3% (1)

Explanation

Stream ciphers are symmetric key ciphers (E) that encrypt data one bit at a time (D), generating a pseudorandom keystream that is XOR'd against the plaintext - this continuous, lightweight operation means they typically run faster than block ciphers (A), making them well-suited for real-time applications like streaming audio or secure communications.

Why the distractors fail:

• B is wrong because dividing a message into fixed-size blocks describes a block cipher (e.g., AES), not a stream cipher.
• C is the direct opposite of the truth - stream ciphers are faster precisely because they avoid the complex round-based transformations that block ciphers require.

Memory tip: Think of a stream cipher like a flowing river - it processes data in a continuous stream, bit by bit, fast and fluid. Block ciphers, by contrast, are like processing cargo in shipping containers (blocks) - more structure, more overhead, more time.

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