Which statement about stream ciphers is true?

Which statement about stream ciphers is true?

• A. A stream cipher encrypts one bit or byte at a time.
• B. A stream cipher encrypts data in fixed-size blocks.
• C. A stream cipher uses no keys.
• D. A stream cipher is always faster than a block cipher.

Answer: (A)

Stream ciphers work by generating a keystream from a secret key (often with an IV) and combining it with the plaintext bit by bit or byte by byte, typically using XOR. That continuous, bit- or byte-level processing is what makes them different from block ciphers, which operate on fixed-size blocks of data at a time. So the statement is true because a defining feature of stream ciphers is precisely encrypting data one bit or one byte at a time as it flows through the system. Keep in mind that stream ciphers do use a key to drive the keystream, and they can be highly efficient for real-time or variable-length data. They are not always faster than block ciphers, though—their performance depends on the specific algorithm and the hardware or software implementation. Also, a keystream must never be reused with different messages, or security is severely compromised.

Stream ciphers work by generating a keystream from a secret key (often with an IV) and combining it with the plaintext bit by bit or byte by byte, typically using XOR. That continuous, bit- or byte-level processing is what makes them different from block ciphers, which operate on fixed-size blocks of data at a time. So the statement is true because a defining feature of stream ciphers is precisely encrypting data one bit or one byte at a time as it flows through the system.

Keep in mind that stream ciphers do use a key to drive the keystream, and they can be highly efficient for real-time or variable-length data. They are not always faster than block ciphers, though—their performance depends on the specific algorithm and the hardware or software implementation. Also, a keystream must never be reused with different messages, or security is severely compromised.