Q$4$: Consider the following table, which uses a Playfair cipher to encode the plaintext message "plaintext". The Playfair cipher is a digraph substitution cipher that uses a $5$x$5$ matrix filled with a keyword $($excluding repeated letters$)$ followed by the remaining letters of the alphabet. let's use the keyword "cipher" to create our Playfair matrix. Fill in the missing values in the table by encoding the plaintext message using the Playfair cipher and explain the process in detail for each step. $(5$Marks$)$