Question

Problem 2: Caesar Cipher Decryption] Write a python 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. Reverse the operations performed by the encryption method to obtain the plaintext message.

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

Answer 1

Here our task is to create a python program which consist of a function called 'casesardecryption' which take 2 arguments which are a string type and an integer type.When we call the function with text and key it should return decrypted messege


ceaser cypher is a simple encription method in which cipher text is obatained by changing the letters to a new letter which is 'KEY' times infront of it in alphabetically.To decrypt the text select a letter which is key times before it in alphabetically

things to remeber before coding

• Create a function which have two arguments( data,key)
• create a new emptystring to store the deycrypted message
• iterate through each letter in data and check whether uppercase or lower
• according to if conditions decrement the ascii value of character by 'key' value
• append the decrypted character to the result string(deycrpt)

CODE

(Plaese read all commentss for better understanding of the program)

SAMPLE RUN

I am also attaching the text version of the code in case you need to copy paste

def ceaserdecryption(data,key): #defining the ceaserdecryption function
   decrypt = "" #craeting a empty string to store decrypt data

   for i in range(len(data)): #loop that iterate through each element in data
       c = data[i]   

       # Encrypt uppercase characters
       if (c.isupper()):
           decrypt += chr((ord(c) - key-65) % 26 + 65) #(ord () for convert to character to ASCII)

       # Encrypt lowercase characters
       else:
           decrypt += chr((ord(c) - key - 97) % 26 + 97) #(chr() for convert ASCII value to character)
  

  
   print(" INPUT data :",data) #print statement
   print(" Key :",key)
   print(" Decrypted message :",decrypt)

key=2 #defining key
data= "ETARVQITCRJA" #data
ceaserdecryption(data,key) #calling function