Question 1

A :

Alif sends a message to her friend Nadia. He encrypts his messages with a four-letter key (example of four letter key are home, fast, etc) that he shares with Nadia, and uses the key repeatedly to encrypt the message. You have intercepted the ciphertexts that represent four words, as follows:

A C L H K R Z X E C I V G Q K P A

What is the key and the message that Alif sent?

(Hint: When Sarah encrypts the word F O U R with the same key, the resulting ciphertexts will read H C L V)

B :

Retrieve the key and the whole plaintext when you received the following ciphertext:

w s w k b s f d b q u r w i b w t s f c t j n w s

By chance, you also obtained some hints as follows:

i. the sender uses simple substitution cipher to encrypt the plaintext.

ii. the ciphertext represents seven words of plaintexts.

iii. the key is of length 3 letters, and the second letter in the key is i that gives the last word in a plaintext as cat.

You also know that the encoder has removed the blanks between the ciphertext. The key and plaintext are meaningful English words/phrase.

Show every working steps until you reach to the answer