Explanation/Reference:
Explanation:
A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream. Since encryption of each digit is dependent on the current state of the cipher, so it is also known as state cipher. In practice, a digit is typically a bit and the combining operation an exclusive-or (XOR).
The pseudorandom keystream is typically generated serially from a random seed value using digital shift registers. The seed value serves as the cryptographic key for decrypting the ciphertext stream.
Stream ciphers typically execute at a higher speed than block ciphers and have lower hardware complexity. However, stream ciphers can be susceptible to serious security problems if used incorrectly; in particular, the same starting state (seed) must never be used twice.
Incorrect Answers:
A: A stream cipher is not a type of asymmetric encryption algorithm; it is a symmetric key cipher.
C: A stream cipher is not slower than a block cipher; it is faster.
D: Stream ciphers require a lot of randomness and encrypt individual bits at a time. This requires more processing power than block ciphers require, which is why stream ciphers are better suited to be implemented at the hardware level.
References:
https://en.wikipedia.org/wiki/Stream_cipher