What is RC4? Is RC4 secure?

RC4, also known as Rivest Cipher 4, is a symmetric key stream cipher designed by Ron Rivest in 1987.  The National Institute of Standards and Technology (NIST) has discouraged the use of RC4 in favor of more secure cryptographic algorithms. NIST has published guidelines and recommendations for cryptographic algorithms, and RC4 is generally considered insecure for applications requiring strong security. 

A stream cipher is a type of cipher that operates on data a byte at a time to encrypt that data. RC4 is one of the most commonly used stream ciphers, having been used in Secure Socket Layer (SSL)/ Transport Layer Security (TLS) protocols, IEEE 802.11 wireless LAN standard, and the Wi-Fi Security Protocol WEP (Wireless Equivalent Protocol). RC4 owes its popularity, relating to stream ciphers, to its ease of use and performance speed. Now, significant flaws mean RC4 is not used nearly as often as before.

Vulnerabilities of RC4

RC4 is not recommended for use in modern cryptographic applications due to various vulnerabilities: – 

• Key Biases

  RC4 suffers from biases in its key scheduling algorithm, which can lead to statistical biases in the generated keystream. An attacker can exploit these biases to deduce information about the key and potentially recover parts of the plaintext.

• Weaknesses in the Initial Keystream Bytes

  The initial bytes generated by RC4 are particularly weak. The first few bytes exhibit biases that can be exploited to predict or guess plaintext portions.

• Fluhrer, Mantin, and Shamir (FMS) Attack

  The FMS attack is a specific type of attack against RC4 that focuses on the vulnerabilities in the initial keystream bytes. This attack can recover parts of the key by analyzing the biases in the generated keystream.

• Bar Mitzvah Attack

  This attack exploits vulnerabilities in the RC4 algorithm, allowing an attacker to recover portions of the plaintext. It is related to biases in the keystream, particularly when RC4 is used in certain protocols and configurations.

• Vulnerability to Cryptanalysis

  RC4 is vulnerable to various cryptanalytic techniques, and its security degrades with time as more vulnerabilities are discovered. As cryptanalysis techniques advance, the likelihood of successful attacks against RC4 increases.

Advantages and Disadvantages