A keystream is a stream of random or pseudorandom characters that are combined with a plaintext message to produce an encrypted message (the ciphertext). The "characters" in the keystream can be bits, bytes, numbers or actual characters like A-Z depending on the usage case.
A keystream is a
|“||pseudorandom sequence of symbols, intended to be secret, used by the encryption and decryption algorithms of a stream cipher.||”|
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