Now that we understand how block ciphers work, the second thing to do is to add the blocks together. block ciphers have different modes of operation. And when we see modes of operation, we mean the mechanism that allows the algorithm to add or to aggregate these cipher blocks together. Remember, block cipher encrypts chunks of the data 64 bits in the case of death 128 bits in a Aes 128. To understand how it is done, we need to understand another term and that is XOR x so are we will start with the bitstream. It doesn't matter if it is a plaintext an mp3 file or In image in any modern encryption scheme, we represent our symbols using binary digits.

The second part as we know is the key. It is also represented as a bit stream. To apply one to the other, we use different math operations. One that we will talk in this lesson is sore. The sole operator outputs a one whenever the inputs do not match. So if the first bit in our plaintext is zero, and the first bit in our key is zero, both inputs match.

So operation will get us as zero. If the second bit in our plaintext is one, and the second bit in our key is zero, that is both inputs don't match. So operation will get us a one. And if the third bit in our plaintext is one and the third bit in our key is one that is both inputs match source operation will get us as zero. We will see how we use sorry, in the difference block ciphers modes of operation in the next lesson