Question

Caesar Cipher Encryption] Write a method that takes two parameters: A parameter of type str and a parameter of type int. The first parameter is the plaintext message, and the second parameter is the encryption key. The method strictly does the following tasks:

a. Convert the string into a list (let us refer to it as lista). An element in the generated list is the position of the corresponding letter in the parameter string in the English alphabet. Example: ‘C’ or ‘c’ in the parameter string will be converted to the number

b in lista. Assume that the parameter string contains only alphabetic characters. 2. Encrypt the generated list (lista) using Caesar cipher using the provided encryption key. You do not need to create a new list, update the elements of the lista list.

c. Convert lista into a string again by converting the positional element in the list to a character in the ciphertext string. Assume that the plaintext is ‘WelcomeToCryptography’ and the shift key is 5.

Step Output 1

lista = [22, 4, 11, 2, 14, 12, 4, 19, 14, 2, 17, 24, 15, 19, 14, 6, 17, 0, 15, 7, 24] 2

lista = [1, 9, 16, 7, 19, 17, 9, 24, 19, 7, 22, 3, 20, 24, 19, 11, 22, 5, 20, 12, 3] 3

ciphertext = ‘BJQHTRJYTHWDUYTLWFUMD’

The method’s header is as follows: def casesarencryption(s, key):

Answer 1

Program:

#defining the function, where s is of type string
#and key of type int
def casesarencryption(s, key):
    
    #defining the list lista
    lista = []
    
    #converting all the characters in upper case
    #then we would not need to worry about
    #upper case or lower case character
    s = s.upper()
    
    #traversing plain text, s
    for i in s:
        
        #converting character to ASCII value
        #and subtracting 64 as ASCII value of 'A' is 65
        temp = ord(i)-65
        
        lista.append(temp)
        
    #printing Output 1
    print("Output 1")
    print("lista =",str(lista))
        
    #adding key to each element of the lista
    for i in range(len(lista)):
        lista[i] = (lista[i]+key)%26
    
    #printing Output 2
    print("\nOutput 2")
    print("lista =",str(lista))
    
    #converting the lista into cipher text
    cipher_text = ""
    
    for i in lista:
        #adding 65 as it is ASCII value of 'A'
        cipher_text += chr(i+65)
        
    #printing Output 3
    print("\nOutput 3")
    print("Cipher text ='{}'".format(cipher_text))

Output:

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