Encryption - Disappearing Cryptography - page 21

S-boxes
confuse data

KEY

Figure 2.1: A schematic view of one round of DES. 64 bits enter and
are split into two 32-bit halves. The left half is scrambled up with the
key using the S-boxes. This result is then mixed in with the right half
and the result of adding these two together becomes the new left half.
The new right half is just a copy of the old left half.

000000 → 1110 000001 → 0100 000010 → 1101 000011 → 0001

000100 → 0010 000101 → 1110 000110 → 1011 000111 → 1000

001000 → 0011 001001 → 1010 001010 → 0110 001011 → 1100

001100 → 0101 001101 → 1001 001110 → 0000 001111 → 0111

010000 → 0000 010001 → 1111 010010 → 0111 010011 → 0100

010100 → 1110 010101 → 0010 010110 → 1101 010111 → 0001

011000 → 1010 011001 → 0110 011010 → 1100 011011 → 1011

011100 → 1001 011101 → 0101 011110 → 0011 011111 → 1000

100000 → 0100 100001 → 0001 100010 → 1110 100011 → 1000

100100 → 1101 100101 → 0110 100110 → 0010 100111 → 1011

101000 → 1111 101001 → 1100 101010 → 1001 101011 → 0111

101100 → 0011 101101 → 1010 101110 → 0101 101111 → 0000

110000 → 1111 110001 → 1100 110010 → 1000 110011 → 0010

110100 → 0100 110101 → 1001 110110 → 0001 110111 → 0111

111000 → 0101 111001 → 1011 111010 → 0011 111011 → 1110

111100 → 1010 111101 → 0000 111110 → 0110 111111 → 1101

Figure 2.2: This table shows how the first DES S-box converts 6-bit
values into 4-bit ones. Note that a change in one input bit will gener-
ally change two output bits. The function is also nonlinear and diffi-
cult to approximate with linear functions.