Which statement accurately describes the relationship between block ciphers and stream ciphers?

• A. Block ciphers require bit-by-bit encryption
• B. Block ciphers process data in fixed-size blocks; stream ciphers encrypt bit-by-bit or byte-by-byte
• C. Block ciphers are deprecated
• D. Stream ciphers have no padding

Answer: (B)

Block ciphers work by processing data in fixed-size blocks, such as 64 or 128 bits, and you need a mode of operation to handle longer messages—often with padding to fill the final block. Stream ciphers, by contrast, generate a keystream and encrypt the plaintext as a continuous flow, allowing bit-by-bit or byte-by-byte processing without needing to align to a block boundary. This fundamental distinction is what makes the statement describing their relationship accurate. Padding is a concern for block ciphers because of their fixed block size, whereas stream ciphers generally don’t require such padding. The other options misstate how block ciphers operate, claim deprecation, or imply padding is universally absent for stream ciphers, which does not define the core relationship.