RC4 Decrypt

What is RC4?

RC4 (Rivest Cipher 4) is a stream cipher that was widely used. It's known for its simplicity and speed in encrypting data. However, due to security vulnerabilities discovered over time, RC4 is generally not recommended for new systems.

Key Features of RC4

• Stream Cipher: RC4 encrypts data one byte at a time.
• Variable Key Size: RC4 supports variable key sizes, typically ranging from 40 to 2048 bits.
• Simplicity: The algorithm is simple to implement in both hardware and software.

How RC4 Works

1. Key Scheduling Algorithm (KSA):

• The KSA initializes an array (S) with values from 0 to 255 and uses the key to shuffle the values in the array.

1. Pseudo-Random Generation Algorithm (PRGA):

• The PRGA generates a pseudo-random stream of bytes based on the shuffled array (S).
• Each byte of the plaintext is XORed with a byte from the pseudo-random stream to produce the ciphertext.

Security Concerns

RC4 has known vulnerabilities:

• Bias in Output: Biases exist in the generated pseudo-random stream, which can be exploited to recover the key.
• Key Recovery Attacks: Certain attacks can recover the key if RC4 is used improperly or with weak keys.

Alternatives

Due to the security vulnerabilities of RC4, modern cryptographic applications should use more secure algorithms such as:

• AES (Advanced Encryption Standard)
• ChaCha20