#1. What is the output of the first round of the DES algorithm when the plaintext and the key are both all zeros?
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Expert's answer
2016-11-19T06:04:10-0500
Let the input string is X = zeros(64). Let the input key is K = zeros(56). After the initial permutation of X we have L0 = zeros(32), R0 = zeros(32). After the fixed permutation of K we hawe the round-1 key K1 = zeros(48). The round-1 formula is R1 = L0 xor f(R0, K1) here f is Feistel function: 1) R0 expands to zeros(48) using a fixed permuted expansion rule. 2) The resulting string is xor with K1 and produces a zeros(48) 3) The result is splitted into 8 x zeros(6) chunks. Each chunk is mapped with correspondig S-boxes and becomes 1110 1111 1010 0111 0010 1100 0100 1101 4) At the permutattion stage the resulting 32-bit string is permutted according to the P-table to the following
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