The Data Encryption Standard (DES) was developed in the 1970s by IBM and adopted as a standard by NIST by 1976. The DES algorithm itself has since then been declared insecure by NIST; however, it is believed to be reasonably secure in the form of Triple DES.

The DES algorithm consists of 16 rounds of data manipulation preceded by an initial permutation and followed by the inverse of the initial permutation. Figure 4-9 has a visual description of the algorithm structure. After the initial permutation, the data block is split in half into left and right blocks. The right block is sent through a function block with a round key and then is used as the left block for the next round. The left block is XORed with the result of the function block, the result of which is used as the right block in the next round. This is continued until the last round where the left and right blocks do not switch sides. At this point, the data is put through the inverse of the initial permutation resulting in the wanted cipher text.