So when we use permutation in our bitstream, we are actually changing the mapping or the value of the bitstream. So if we have a bitstream in the plaintext, that looks like the possible eight options, that is 100 equals to 4110 equal to six. Now we can map each bit to another bit value. So for example, let's use different keys in key one, which is one out of 40,000. Remember, in key one, we have changed the bitstream that is equal to 410021 01 which is equal to five, so we are actually mapping the bit Ville value from four to five. In key number two if we choose key number two instead of key number one, we are mapping 010, which is equal to 22011, which is equal to three and that's we can use more than 40,000 permutation of the eight possible option as our keys.

We will look later on how do we use it in the algorithm itself.