RC4 (Rivest Cipher 4) is a stream cipher that is simple and fast. While it has been widely used in protocols like SSL and WEP, it is no longer considered secure for most modern applications due to known vulnerabilities.

This tool is provided for educational purposes and for compatibility with legacy systems. For any new development requiring strong security, it is recommended to use more robust ciphers like AES.

How it works:

• Key Setup: A variable-length key (typically 40-256 bits) is used to initialize a 256-byte state table (S-box).
• Keystream Generation: A pseudorandom keystream is generated from the S-box.
• Encryption: The plaintext is XORed with the keystream to produce the ciphertext.

Security Considerations:

• Key Reuse: Never use the same key to encrypt two different messages. Doing so can allow an attacker to recover the plaintext.
• Weak Keys: Certain keys can lead to a non-random keystream, making the encryption easier to break.
• No Integrity Check: RC4 does not provide message authentication or integrity checks, making it vulnerable to bit-flipping attacks.