$3$

Problem $4[20$ Points$]$: Use the Playfair cipher to encipher the message "Hello TSU". The secret key can be made by filling the first and part of the second row with the word "Computer" and filling the rest of the matrix with the rest of the alphabet in sequence. Please include the following results:

$[1]$ The key for this Playfair cipher $[8$ points$].$

$[2]$ The corresponding cipher text for each needed pair $[7$ points$]$; and then

$[3]$ The final result of the corresponding cipher text $[5$ points$].$

Problem $5[20$ Bonus$]$: Decipher the message UTZWZKZLZVGVBWB by using the Auto key cipher method with $15$ as the key. Please include the following results:

$[1]$ The values of the corresponding cipher text $[4$ points$].$

$[2]$ The value of the corresponding key stream $[6$ points$].$

$[3]$ The value of the corresponding plain text $[6$ points$]$; and then

$[4]$ The final result of the corresponding plain text $[4$ points$].$