RC4 is described as a variable key-size symmetric-key stream cipher with byte-oriented operations based on a random permutation. Which statement best describes RC4?

RC4 is described as a variable key-size symmetric-key stream cipher with byte-oriented operations based on a random permutation. Which statement best describes RC4?

• A. A variable key-size symmetric-key stream cipher with byte-oriented operations based on a random permutation
• B. A block cipher with fixed key
• C. A public-key algorithm
• D. A hash function

Answer: (A)

RC4 is a symmetric-key stream cipher. It generates a keystream byte by byte and XORs that stream with the plaintext to produce ciphertext (and the same process to recover the plaintext during decryption). The keystream comes from a 256-byte state array that starts as a permutation of 0 through 255 and is shuffled using a key-dependent algorithm. Because the key can have varying lengths, RC4 supports variable key sizes. The operations are performed one byte at a time, which is why it’s described as byte-oriented rather than block-oriented. This description fits RC4 precisely: a variable-length key used in a symmetric, stream-cipher mode, producing and using a keystream derived from a random permutation of 256 values. It isn’t a block cipher (no fixed-size blocks), nor a public-key algorithm, nor a hash function, which is why those options don’t describe RC4.

RC4 is a symmetric-key stream cipher. It generates a keystream byte by byte and XORs that stream with the plaintext to produce ciphertext (and the same process to recover the plaintext during decryption). The keystream comes from a 256-byte state array that starts as a permutation of 0 through 255 and is shuffled using a key-dependent algorithm. Because the key can have varying lengths, RC4 supports variable key sizes. The operations are performed one byte at a time, which is why it’s described as byte-oriented rather than block-oriented.

This description fits RC4 precisely: a variable-length key used in a symmetric, stream-cipher mode, producing and using a keystream derived from a random permutation of 256 values. It isn’t a block cipher (no fixed-size blocks), nor a public-key algorithm, nor a hash function, which is why those options don’t describe RC4.