Exam CISSP Topic 2 Question 1597 Discussion

The question stem describes one round of a Feistel cipher. This algorithm was developed by an IBM team led by Horst Feistel. (h. Feistel, Cryptography and Computer Privacy, Scientific American, v.228, n.5, May 1973) The algorithm was called Lucifer and was the basis for the Data Encryption Standard (DES). In answer a, RC4 is a variable keysize stream cipher developed by Ronald Rivest. In this type of cipher, a sequence of bits that are the key is bit-wise XORed with the plaintext.
* Diffie-Hellman describes the first public key algorithm and is based on the difficulty of calculating discrete logarithms in a finite field. (W. Diffie and M.e. Hellman, New Directions in Cryptography, IEEE Transactions on Information Theory, v. IT-22, n. 6, Nov 1976). It is used for exchanging keys. RC6, in answer c, is a fast block cipher designed by Rivest, Sidney and Yin. In RC6, the block size, the key size and the number of rounds are variable. The key size can be no larger than 2040 bits. RC6 was one of the five finalists in the Advanced Encryption Standard (AES) competition.