Cisco Certified Internetwork Expert (CCIE) Practice Test

Which three of these are properties of RC4?

1. It is used in AES

2. It is an asymmetric cipher

3. It is a stream cipher

4. It is a symmetric cipher

The correct answer is: It is a stream cipher

The identification of RC4 as a stream cipher underscores its functionality in cryptographic applications. As a stream cipher, RC4 processes data in a continuous stream, encrypting one byte at a time rather than operating on blocks of data. This characteristic allows it to be efficient in situations where data sizes are variable and real-time encryption is necessary, such as in secure communications over protocols like SSL/TLS. RC4 is also classified as a symmetric cipher, which means that the same key is used for both encryption and decryption. This dual use of the same key for both processes contrasts with asymmetric ciphers, which utilize a pair of keys—public and private. Although the question specifies three properties and lists symmetric cipher attributes, identifying RC4 predominantly as a stream cipher is critical in understanding its design and operational principles. In the context of the other options, RC4 is not used in AES (Advanced Encryption Standard), as AES employs a different algorithm based on block ciphers rather than stream ciphers. Therefore, knowing that RC4 is strictly associated with stream cipher functionality, while AES leverages different methodologies, helps clarify its unique role in the landscape of encryption techniques.