Sometimes, the length of the plaintext will be a multiple of the block size (as in the example on the previous slide. However, this isn't always the case! This means that the last block will, usually, be smaller than the others. To be able to apply a block cipher, we will pad the last block with 0s (or another distinguishable character.)
Padding the last block. Miriam Briskman, CC BY-NC 4.0