Cryptography Questions Medium
The Rivest Cipher, also known as RC4 (Ron's Code 4), is a symmetric stream cipher algorithm widely used in various cryptographic applications. It was developed by Ron Rivest in 1987 and gained popularity due to its simplicity and efficiency.
RC4 operates by generating a pseudorandom stream of bits, which is then combined with the plaintext using a bitwise XOR operation to produce the ciphertext. The key used for encryption and decryption is typically a variable-length key, ranging from 1 to 256 bytes.
The algorithm consists of two main components: key scheduling and pseudorandom generation. During the key scheduling phase, the key is expanded and used to initialize a permutation array of 256 bytes. This array is then shuffled based on the key, creating a unique state for each key.
In the pseudorandom generation phase, the permutation array is used to generate a keystream. The keystream is generated by repeatedly swapping elements of the array and producing a byte of the keystream. This process is performed for each byte of the plaintext, and the keystream is combined with the plaintext using XOR to produce the ciphertext.
RC4 is known for its simplicity and fast execution, making it suitable for applications with limited computational resources. However, it has been subject to several vulnerabilities and attacks over the years, leading to its decreased usage in modern cryptographic systems.