Computer Security and Cryptography

9.5 SAMPLE DES ENCIPHERMENT

A trace of DES is shown next in Table 9.19 including

• The initialization, including the user key k, the contents of the registers [C₀, D₀], the plaintext x, the result of the initial permutation IP[x], and the left and right data registers (L[0], R[0]);

TABLE 9.17 Weak DES Keys

TABLE 9.18 Semi-Weak DES Keys

• The transformations on rounds 1, 2, and 16 displaying

  – The entering contents of the left- and right-half-data registers (L[i − 1], R[i − 1]),

  – The entering contents of the registers [C_i−1, D_i−1],

  – The updated contents of the registers [C_i, D_i],

  – The key KEY[i] used on Round i,

  – The expanded right data block E[R[i − 1]],

  – The XOR of KEY[i] and E[R[i]],

  – The output of the S-boxes with input KEY[i] + E[R[i]],

  – The output of the P-box,

  – The entering left-half data register L[i − 1],

  – The XOR of the P-box output and the contents of L[i − 1],

  – The concatenation on the right of the P-BOX output + L[i − 1] with R[i − 1],

  – The updated (L[i], R[i]), and

• The output.