Question $1$

While tapping into the open channel which Alice and Bob are using to securely communicate, Eve intercepts the following ciphertext:

UMXWJIFWWPQWOMOLUQOSOMXWSPMFWBASQMXWFBQVRNRAFQMD

$($a$)$ Use the Kasiski method to determine the likely number of alphabets used in this poly$-$alphabetic cipher.

$(5$ marks$)$

$($b$)$ Which part of the ciphertext would you perform a frequency analysis on$,$ in order to find the first letter of the key? Explain your answer.

$(3$ marks$)$

$[$Total Marks $8]$