Which type of cipher does RC4 belong to?

RC4 is classified as a stream cipher, which is a type of encryption algorithm that encrypts data one byte or bit at a time. Stream ciphers are particularly efficient for data streams where the size of the data is not known ahead of time, allowing for dynamic and flexible encryption.

RC4 operates by generating a pseudorandom stream of bits (the keystream) which is then combined with the plaintext data using the XOR bitwise operation. This characteristic allows RC4 to encrypt data continuously, making it suitable for applications such as secure communications and streaming media where data flows in a continuous stream rather than in fixed-size blocks.

In contrast, block ciphers encrypt data in fixed-size blocks, which can lead to inefficiencies when dealing with data of varying sizes. Hash functions are designed for creating a fixed-size hash value from input data and are not intended for encryption. Substitution ciphers change individual elements of plaintext into ciphertext but do not necessarily follow the operational principles or dynamic characteristics of stream ciphers like RC4. Thus, the classification of RC4 as a stream cipher accurately reflects its operational methodology and intended use in the field of cryptography.