What is RC4 Encryption? (Working, Usage, Advantages & Disadvantages)

Anti VirusCyber SecuritySafe & Security

What is RC4?

RC4 stands for Rivest Cipher 4. Ron Rivest invented RC4 in 1987, and it is a stream cipher. Because RC4 is a stream cipher, it encrypts data bytes by bits. Because of its speed and simplicity, RC4 is the most extensively used stream cipher of all the stream ciphers.

While RC4 is known for its ease of use and speed in software, it has been found to have several weaknesses, making it insecure. When the beginning of the output keystream isn't destroyed, or when non-random or linked keys are utilized, it's highly vulnerable. The usage of RC4, in particular, has resulted in relatively insecure protocols such as WEP.

As of 2015, several state cryptologic agencies were suspected of being able to break RC4 when it was employed in the TLS protocol. RFC 7465, published by the Internet Engineering Task Force, prohibits the use of RC4 in TLS, and Mozilla and Microsoft have issued similar recommendations.

Working of RC4

RC4 creates a pseudo-random bit stream (a keystream). These, like any other stream cipher, can be used for encryption by utilizing bit-wise exclusive or to combine it with the plaintext. The same procedure is used for decryption (since exclusive-OR is a symmetric operation).

The cipher uses a secret internal state that is divided into two sections to generate the keystream −

  • Each of the 256 available bytes is permuted.

  • Two index pointers (8 bits each).

The key-scheduling algorithm is known to initialize the permutation using a variable-length key, typically between 40 and 256 bits (KSA). A pseudo-random generating technique then generates the stream of bits.

For encryption −

  • The user enters the Plaintext and a secret key.

  • For the secret key entered, the encryption engine creates the keystream using the KSA and PRGA algorithms.

  • Plaintext is XORed with the generated keystream. Because RC4 is a stream cipher, byte-by-byte XORing is used to generate the encrypted text.

  • This encrypted text is now sent in encrypted form to the intended recipient.

For Decryption −

  • The same byte-wise X-OR technique is used on the ciphertext to decrypt it.

Usage of RC4

Over the years, RC4 has grown in popularity and has become a standard in commercial applications. It has a reputation for being a simple, quick, and inexpensive encryption technology.

The key benefits of RC4 are its ease of implementation and use, as well as its speed of operation and deployment. It enables efficient and quick processing of large data streams. In terms of memory usage, RC4 stream ciphers are also efficient.

However, due to proof of flaws and cyberattacks in recent years, there have been calls to stop using RC4 encryption algorithms. Other drawbacks were identified, such as the inability to operate with small data streams and the need for additional investigation prior to implementing new systems.

The Internet Engineering Task Force (IETF) banned the usage of RC4 in TLS protocols in 2015. Because of threat vulnerabilities, Microsoft and Mozilla have also issued recommendations to limit the use of RC4. There are many RC4 based ecosystems such as WEP, WPA, BitTorrent protocol encryption, Microsoft Point-to-Point Encryption, etc.

 RC4A is a more powerful variation of RC4. RC4A+ is a modified version of RC4 with a more complex 3-phase key schedule that is 1.7 times longer than the basic RC4.

Advantages and Disadvantages of Using RC4 Encryption

Following are the advantages of using RC4 Encryption −

  • It is easy to use RC4 stream ciphers.

  • In comparison to other ciphers, RC4 has a quick operation speed.

  • RC4 stream ciphers have a high coding strength and are simple to construct.

  • RC4 stream ciphers do not require additional memory.

Following are the disadvantages of using RC4 Encryption −

  • Encryption is vulnerable to a bit-flipping attack if RC4 is not used with a robust MAC.

  • Authentication is not possible using RC4 stream ciphers.

  • Before adding new systems to the RC4 algorithm, more research is needed.

  • RC4 stream ciphers can't be used with tiny data streams.

Updated on 22-Jun-2022 14:26:43