Which of the following stream ciphers is both a block cipher and a product cipher?
A.
RC2
B.
AES
C.
DES
D.
RC4
Explanation:
The Data Encryption Standard (DES) is the most widely used encryption standard. The algorithm itself is referred to as Data Encryption Algorithm (DEA). It uses a 56-bit key to encrypt or decrypt data in 64-bit blocks. DES is both a block cipher and a product cipher. Answer option D is incorrect. RC4 is a stream cipher designed by Ron Rivest. It is used in many applications, including Transport Layer Security (TLS), Wired Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA), etc. RC4 is fast and simple. However, it has weaknesses that argue against its use in new systems. It is especially vulnerable when the beginning of the output keystream is not discarded, nonrandom or related keys are used, or a single keystream is used twice. Some ways of using RC4 can lead to veryinsecure cryptosystems such as WEP. It uses block cipher. Answer option A is incorrect. RC2 is a block cipher designed by Ron Rivest in 1987 and other ciphers designed by Rivest include RC4, RC5, and RC6. RC2 is a 64-bit block cipher with a variable size key. Its 18 rounds are arranged as a source-heavy Feistel network, with 16 rounds of one type punctuated by two rounds of another type. Answer option B is incorrect. The Advanced Encryption Standard (AES) is an encryption standard adopted by the U.S. government. The standard comprises three block ciphers, AES-128, AES-192, and AES-256. Each AES cipher has a 128-bit block size, with key sizes of 128, 192, and 256 bits, respectively. The AES ciphers have been analyzed extensively and are now used worldwide, as was the case with its predecessor, the Data Encryption Standard (DES). AES was announced by National Institute of Standards and Technology (NIST) as U.S. FIPS PUB 197 (FIPS 197) on November 26, 2001 after a 5-year standardization process in which fifteen competing designs were presented and evaluated before Rijndael was selected as the most suitable. It became effective as a standard on May 26, 2002. As of 2009, AES is one of the most popular algorithms used in symmetric key cryptography. It is available in many different encryption packages. AES is the first publicly accessible and open cipher approved by the NSA for top secret information.