What does the DES key look like?
It is a 64-bit key. But only 56 bits are used. There are 8 bits used to as parity checks for each 7-bit value of the key. The organization is that for every 7 bit quantity, a bit of check bit follows. This setup repeats itself for 8 times for a total of 64 bits. What is this 8th bit? It is an odd parity bit, meaning that the value of it depends on the 7-bits it is following. If the number of 1’s (in binary notation) is odd, then the parity bit is 0; if the number of 1’s is even, then the parity bit is 1. The parity bit makes the number of total 1’s in each 8-bit quantity part of the key odd, hence Odd Parity. The parity key is the least significant bit here. Example: 11010110 (parity bit in yellow.
