COMPUTER ETHICS AND SECURITY
CRYPTOGRAPHY AND ENCRYPTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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14
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15
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16
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None of the mentioned
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Detailed explanation-1: -The fundamental building block of DES is a single combination of these techniques (a substitution followed by a permutation) on the text, based on the key. This is known as a round. DES has 16 rounds; it applies the same combination of techniques on the plaintext block 16 times (see Figure 12.1).
Detailed explanation-2: -These permutations are keyless straight permutations that are the opposite of each other. For instance, in the initial permutation, the 58th bit in the input develop into the first bit in the output. Likewise, in the final permutation, the first bit in the input develop into the 58th bit in the output.
Detailed explanation-3: -The final permutation is the inverse of the initial permutation; the table is interpreted similarly. That is, the output of the Final Permutation has bit 40 of the preoutput block as its first bit, bit 8 as its second bit, and so on, until bit 25 of the preoutput block is the last bit of the output.
Detailed explanation-4: -DES uses 16 rounds of the Feistel structure, using a different key for each round.