Protecting Against Eavesdroppers with Symmetric Cryptography - Implementing SSL/TLS Using Cryptography and PKI - page 42

here as simple lookup tables in Listing 2-11. Note that each six-bit block has its
own unique s-box.
Listing 2-11: “des.c” s-boxes
static const int sbox[8][64] = {
{ 14, 0, 4, 15, 13, 7, 1, 4, 2, 14, 15, 2, 11, 13, 8, 1,
3, 10, 10, 6, 6, 12, 12, 11, 5, 9, 9, 5, 0, 3, 7, 8,
4, 15, 1, 12, 14, 8, 8, 2, 13, 4, 6, 9, 2, 1, 11, 7,
15, 5, 12, 11, 9, 3, 7, 14, 3, 10, 10, 0, 5, 6, 0, 13 },
{ 15, 3, 1, 13, 8, 4, 14, 7, 6, 15, 11, 2, 3, 8, 4, 14,
9, 12, 7, 0, 2, 1, 13, 10, 12, 6, 0, 9, 5, 11, 10, 5,
0, 13, 14, 8, 7, 10, 11, 1, 10, 3, 4, 15, 13, 4, 1, 2,
5, 11, 8, 6, 12, 7, 6, 12, 9, 0, 3, 5, 2, 14, 15, 9 },
{ 10, 13, 0, 7, 9, 0, 14, 9, 6, 3, 3, 4, 15, 6, 5, 10,
1, 2, 13, 8, 12, 5, 7, 14, 11, 12, 4, 11, 2, 15, 8, 1,
13, 1, 6, 10, 4, 13, 9, 0, 8, 6, 15, 9, 3, 8, 0, 7,
11, 4, 1, 15, 2, 14, 12, 3, 5, 11, 10, 5, 14, 2, 7, 12 },
{ 7, 13, 13, 8, 14, 11, 3, 5, 0, 6, 6, 15, 9, 0, 10, 3,
1, 4, 2, 7, 8, 2, 5, 12, 11, 1, 12, 10, 4, 14, 15, 9,
10, 3, 6, 15, 9, 0, 0, 6, 12, 10, 11, 1, 7, 13, 13, 8,
15, 9, 1, 4, 3, 5, 14, 11, 5, 12, 2, 7, 8, 2, 4, 14 },
{ 2, 14, 12, 11, 4, 2, 1, 12, 7, 4, 10, 7, 11, 13, 6, 1,
8, 5, 5, 0, 3, 15, 15, 10, 13, 3, 0, 9, 14, 8, 9, 6,
4, 11, 2, 8, 1, 12, 11, 7, 10, 1, 13, 14, 7, 2, 8, 13,
15, 6, 9, 15, 12, 0, 5, 9, 6, 10, 3, 4, 0, 5, 14, 3 },
{ 12, 10, 1, 15, 10, 4, 15, 2, 9, 7, 2, 12, 6, 9, 8, 5,
0, 6, 13, 1, 3, 13, 4, 14, 14, 0, 7, 11, 5, 3, 11, 8,
9, 4, 14, 3, 15, 2, 5, 12, 2, 9, 8, 5, 12, 15, 3, 10,
7, 11, 0, 14, 4, 1, 10, 7, 1, 6, 13, 0, 11, 8, 6, 13 },
{ 4, 13, 11, 0, 2, 11, 14, 7, 15, 4, 0, 9, 8, 1, 13, 10,
3, 14, 12, 3, 9, 5, 7, 12, 5, 2, 10, 15, 6, 8, 1, 6,
1, 6, 4, 11, 11, 13, 13, 8, 12, 1, 3, 4, 7, 10, 14, 7,
10, 9, 15, 5, 6, 0, 8, 15, 0, 14, 5, 2, 9, 3, 2, 12 },
{ 13, 1, 2, 15, 8, 13, 4, 8, 6, 10, 15, 3, 11, 7, 1, 4,
10, 12, 9, 5, 3, 6, 14, 11, 5, 0, 0, 14, 12, 9, 7, 2,
7, 2, 11, 1, 4, 14, 1, 7, 9, 4, 12, 10, 14, 8, 2, 13,
0, 15, 6, 12, 10, 9, 13, 0, 15, 3, 3, 5, 5, 6, 8, 11 }
};
Also note that I have taken the liberty to reorder these, as they're given
out-of-order in the specifi cation.
After substitution, the input block undergoes a fi nal permutation, shown in
Listing 2-12.
Listing 2-12: “des.c” fi nal input block permutation
static const int p_table[] = { 16, 7, 20, 21,
29, 12, 28, 17,
1, 15, 23, 26,
5, 18, 31, 10,