Which type of cipher encrypts plaintext one byte or one bit at a time?

Which type of cipher encrypts plaintext one byte or one bit at a time?

• A. Block cipher
• B. Transposition cipher
• C. Stream cipher
• D. Public-key cipher

Answer: (C)

Stream ciphers encrypt data as a continuous stream, processing one bit or one byte at a time. They generate a keystream and combine it with the plaintext, usually by XOR, so the encryption can proceed from start to finish without waiting for fixed-size blocks. This makes them well-suited for streaming data and will handle data of any length directly. Block ciphers, on the other hand, operate on fixed-size chunks (blocks) at a time, so they don’t inherently encrypt a single bit or byte in isolation. Transposition ciphers only permute the order of characters and don’t provide the same kind of bit-level encryption. Public-key ciphers are asymmetric algorithms used mainly for key exchange and encrypting small data, not for stream-like bit-by-bit or byte-by-byte processing.

Stream ciphers encrypt data as a continuous stream, processing one bit or one byte at a time. They generate a keystream and combine it with the plaintext, usually by XOR, so the encryption can proceed from start to finish without waiting for fixed-size blocks. This makes them well-suited for streaming data and will handle data of any length directly.

Block ciphers, on the other hand, operate on fixed-size chunks (blocks) at a time, so they don’t inherently encrypt a single bit or byte in isolation. Transposition ciphers only permute the order of characters and don’t provide the same kind of bit-level encryption. Public-key ciphers are asymmetric algorithms used mainly for key exchange and encrypting small data, not for stream-like bit-by-bit or byte-by-byte processing.