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What Is RC4 Encryption?

Designed with simplicity yet renowned for speed, the symmetric key algorithm known as RC4 has marked its presence in the realm of secure data transmission. Despite the straightforward design, the significant role it plays in various protocols such as Wireless Encryption Protocol for wireless network security and Secure Sockets Layer(SSL)/Transport Layer Security(TLS) for internet security, is noteworthy.

What is RC4?

RC4 is a stream cipher symmetric key algorithm, widely recognized for its simplicity and speed. Ronald Rivest of RSA Security first designed this algorithm. Despite its simplicity, RC4 has been instrumental in several protocols, including WEP for wireless network encryption and SSL/TLS for internet security.

How does RC4 work

The working mechanism of RC4 involves the generation of a pseudorandom keystream, which is then XORed with the plaintext to deliver the ciphertext. It initiates with a variable-length key, ranging from 1 to 256 bytes, to initialize a 256-byte state table. The table undergoes permutations based on the key, leading to the production of the keystream.

The importance of RC4 encryption

RC4 encryption plays a crucial role in maintaining information confidentiality. Its ability to generate a unique keystream for each encryption makes it difficult for unauthorized entities to decipher the encrypted data. Hence, RC4 helps secure sensitive information during transmission over insecure networks.

Is RC4 secure?

While RC4 was once deemed secure, vulnerabilities have been discovered over time. These include biases in the output stream that make it susceptible to attacks, such as the Fluhrer, Mantin, and Shamir (FMS) attack or the Royal Holloway attack. Consequently, many organizations have moved away from RC4 to more secure encryption algorithms.

Types of RC4


Spritz is an RC4 variant that offers enhanced security features. Unlike RC4, which generates one output per iteration, Spritz can produce multiple outputs, adding complexity and making it more resistant to attacks.


RC4A is another variant of RC4. It introduces an additional permutation in the algorithm, which significantly improves the security compared to the original RC4.


VMPC (Variable Modified Permutation Cipher) is a further development of the RC4 algorithm. It introduces a different method of generating the pseudo random stream and changing the state array, thus offering better security.


RC4A+ is an enhanced version of RC4A, which provides stronger security by incorporating additional steps in the key-scheduling algorithm. It has been designed to resist known vulnerabilities in the RC4 and RC4A algorithms.

The relevance of RC4 today

Despite its vulnerabilities, RC4 still finds application in systems where high speed and simplicity are crucial. However, the cybersecurity community recommends its use with caution, considering the known vulnerabilities. RC4’s variants, like Spritz, RC4A, VMPC, and RC4A+, offer improved security, thus extending the relevance of this algorithm in today’s digital era.

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