The document describes a task involving the Caesar cipher, where a message 'halloween' must be encrypted using a key of 4, resulting in a specific ciphertext format. Additionally, it instructs on how to decrypt an intercepted message 'oqtpkpi' using a brute-force method to find the key and recover the plaintext. It provides hints on converting letters to numbers and searching for meaningful words or sentences.

1. 3. Caesar Cipher (1) You are given a message halloween and a key 4, please encrypt it with
Caesar Cipher and show the Ciphertext. Note: We normally use lower case letters to represent
plaintext and capital letters to represent ciphertext. (2) Suppose that you have intercepted a
message encrypted using Caesar cipher. The ciphertext is OQTPKPI. Please find the key using
the brute-force method, and show the plaintext.. Hint: You can convert the letters to the numbers
like A>1,B>2,Z>26, then try to subtract each number in the ciphertext by the key value ( k=1,2.).F
oreachresult, convert the numbers into letter and check whether it is a meaningful word or
sentence.