Cryptography: Block Ciphers and the Data Encryption Standard

All answers must be in complete sentences or, if it is a problem, work must be shown.

1.What is the difference between diffusion and confusion?

2.Explain the avalanche effect.

3.Compute the bits number 1, 16, 33, and 48 at the output of the first round of the DES decryption, assuming that the ciphertext block is composed of all ones and the external key is composed of all ones.

4.Show that DES decryption is, in fact, the inverse of DES encryption.

5.Compare the initial permutation table (Table 3.2a) with the permuted choice one table (Table 3.4b). Are the structures similar? If so, describe the similarities. What conclusions can you draw from this analysis?

6.Show that in DES the first 24 bits of each subkey come from the same subset of 28 bits of the initial key and that the second 24 bits of each subkey come from a disjoint subset of 28 bits of the initial key.

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