Explain how to encrypt the final two blocks of a message, using ECB mode, so that the ciphertext is the same number of bits as the plaintext, even though the plaintext is not an integral number of encryption blocks. Write out the steps. Assume blocks are $128$ bits long, except for block n $($the last one$),$ which is $40$ bits. How would you obtain the final plaintext block $($block n$)$ when decrypting? How would you obtain plaintext block n$-1?$ Again, write out the steps.