Analysis of Standardized Algorithms for Streaming Cryptographic Convention, Defined in ISO/IEC 18033-4

The fourth part of the international standard ISO/IEC 18033 describes algorithms for streaming encryption. As defined in the standard, streaming encryption is understood to mean an encryption mechanism which uses a key stream to encrypt plaintext in a bit or block manner. There are two types of streaming conversion: a synchronous stream cipher in which a key stream is generated from a secret key (and initialization vector), and an asynchronous stream cipher (self-synchronizing) in which the key stream is generated only from the secret key and some previous ciphertexts (and the initialization vector). Under the keystream, according to ISO/IEC 180334, is understood as the PRS of secret symbols used by the encryption and decryption algorithms of the stream cipher. If part of the key stream is known to the attacker, then any information about the remainder of the key stream should be computationally invalidated by the attacker. These concepts and definitions are discussed in detail in the first chapter of this book. Consider the general models for the defined ciphers in ISO/IEC 18033-4, consisting of a combination of a key stream generator and an output function.