Overview#Stream Cipher is a Symmetric Key cipher where plaintext digits are combined with a Pseudorandom Cipher digit stream (keystream).
Stream Cipher is also known as State Cipher.
Stream Cipher has 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.
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 Cipher represent a different approach to symmetric encryption from Block Ciphers.
Stream Cipher typically execute at a higher speed than Block Ciphers and have lower hardware complexity.
Stream Cipher can be susceptible to serious security problems if used incorrectly, in particular, the same starting state (seed) must never be used twice.