CAESAR'S CIPHER For Python

by jamied_uk 29th June 2016, 13:39

Code:: #!/usr/bin/env python # Usage: python cipher.py import sys #print(sys.version_info) # It should say major=3, minor=5 # if you get error use quotes like Enter your message : "testing" # or try python3 file.py # ---------- PROBLEM : CAESAR'S CIPHER ---------- # Receive a message and then encrypt it by shifting the # characters by a requested amount to the right # A becomes D, B becomes E for example # Also decrypt the message back again # A-Z have the numbers 65-90 in unicode # a-z have the numbers 97-122 # You get the unicode of a character with ord(yourLetter) # You convert from unicode to character with chr(yourNumber) # You should check if a character is a letter and if not # leave it as its default # Hints # Use isupper() to decided which unicodes to work with # Add the key (number of characters to shift) and if # bigger or smaller then the unicode for A, Z, a, or z # increase or decrease by 26 # Receive the message to encrypt and the number of characters to shift message = raw_input("Enter your message : ") key = int(input("How many characters should we shift (1 - 26)")) # Prepare your secret message secret_message = "" # Cycle through each character in the message for char in message: # If it isn't a letter then keep it as it is in the else below if char.isalpha(): # Get the character code and add the shift amount char_code = ord(char) char_code += key # If uppercase then compare to uppercase unicodes if char.isupper(): # If bigger than Z subtract 26 if char_code > ord('Z'): char_code -= 26 # If smaller than A add 26 elif char_code < ord('A'): char_code += 26 # Do the same for lowercase characters else: if char_code > ord('z'): char_code -= 26 elif char_code < ord('a'): char_code += 26 # Convert from code to letter and add to message secret_message += chr(char_code) # If not a letter leave the character as is else: secret_message += char print("Encrypted :", secret_message) # To decrypt the only thing that changes is the sign of the key key = -key orig_message = "" for char in secret_message: if char.isalpha(): char_code = ord(char) char_code += key if char.isupper(): if char_code > ord('Z'): char_code -= 26 elif char_code < ord('A'): char_code += 26 else: if char_code > ord('z'): char_code -= 26 elif char_code < ord('a'): char_code += 26 orig_message += chr(char_code) else: orig_message += char print("Decrypted :", orig_message)