# Python Caeser Cipher Helper v1.2.0 # Usage (encrypt): python3 caeser-cipher.py encrypt secretmessage # Usage (decrypt): python3 caeser-cipher.py decrypt secretmessage import re # Import Regex tools import string # Import string tools import collections # Import tools to sort letters. import argparse parser = argparse.ArgumentParser(usage="(encrypt): python3 caeser-cipher.py encrypt [secretmessage] [shift]\nusage: (decrypt): python3 caeser-cipher.py decrypt [secretmessage] [shift]\nusage: If you don't know the shift of encrypted text, use 0\nusage: For example: python3 caeser-cipher.py decrypt hhhhh 0") parser.add_argument("action") parser.add_argument("ciphertext") parser.add_argument("shiftNum") args = parser.parse_args() shiftNum = args.shiftNum ciphertext = re.sub (r'([^a-zA-Z]+?)', '', args.ciphertext) # Remove all non-letters. ciphertext = ciphertext.lower() # Make it all lowercase. https://www.geeksforgeeks.org/isupper-islower-lower-upper-python-applications/ letters = list(string.ascii_lowercase) # Use a list of lowercase letters. https://stackoverflow.com/questions/43918437/how-to-iterate-through-the-alphabet def encrypt(ciphertext, shiftNum, letters): # Grab parameters # Create local variables for this function. letterCount = 0 letterPos = 0 answer = "" for c in ciphertext: # For every letter in the ciphertext while letterPos < 26: # While the letter's position in the alphabet is less than 26 (and thus valid), continue. if ciphertext[letterCount] == letters[letterPos]: # Match the letter in the ciphertext to a letter in the alphabet and once they match, continue. letter = int(letterPos) + int(shiftNum) # Take the position of the letter and the shift number and add them for the enciphered letter. if letter > 25: # If the enciphered letter's position is not valid because it is too high, fix it by rotating around the alphabet. letter = letter - 26 if letter < 0: letter = letter + 26 # If the enciphered letter's position is not valid because it is too low, fix it by rotating around the alphabet. answer = answer + letters[letter] # Add letters together to get the enciphered text. letterPos = letterPos + 1 # Iterate through letter positions in the alphabet. (neccessary to find one that matches.) if letterPos > 25: # If the letter position is greater than 25, cycle back through the alphabet. letterPos = letterPos - 26 letterCount = letterCount + 1 # Keep track of how many times we're doing this. print("\nYour enciphered text is: " + answer) def decrypt(ciphertext, shiftNum, letters): # Grab parameters # Create local variables for this function. letterCount = 0 letterPos = 0 answer = "" for c in ciphertext: # For every letter in the ciphertext while letterPos < 26: # While the letter's position in the alphabet is less than 26 (and thus valid), continue. if ciphertext[letterCount] == letters[letterPos]: # Match the letter in the ciphertext to a letter in the alphabet and once they match, continue. letter = int(letterPos) - int(shiftNum) # Take the position of the letter and the shift number and add them for the enciphered letter. if letter > 25: # If the enciphered letter's position is not valid because it is too high, fix it by rotating around the alphabet. letter = letter - 26 if letter < 0: letter = letter + 26 # If the enciphered letter's position is not valid because it is too low, fix it by rotating around the alphabet. answer = answer + letters[letter] # Add letters together to get the enciphered text. letterPos = letterPos + 1 # Iterate through letter positions in the alphabet. (neccessary to find one that matches.) if letterPos > 25: # If the letter position is greater than 25, cycle back through the alphabet. letterPos = letterPos - 26 letterCount = letterCount + 1 # Keep track of how many times we're doing this. print("\nYour decrypted text is: " + answer) def freq(ciphertext): # Create local variables for this function. commonletter = 0 letterCount = 0 letterPos = 0 answer = "" commonletter = collections.Counter(ciphertext).most_common()[0][0] # Find most common letter and thus the shift https://stackoverflow.com/questions/47251934/how-to-count-the-most-frequent-letter-in-a-string for c in ciphertext: while letterPos < 26: if not commonletter == 0: if commonletter == letters[letterPos]: # If the most frequent letter matches the current letter, set the shift to that letter because that is the shift for the cipher. Forgot the double equals for comparison. shiftNum = letterPos - 4 if letterPos > 25: # If the letter position is greater than 25, cycle back through the alphabet. letterPos = letterPos - 26 letterPos = letterPos + 1 # Iterate through letter positions in the alphabet. (neccessary to find one that matches.) decrypt(ciphertext, shiftNum, letters) # Decrypt using the frequency found in here. if args.action == "encrypt": encrypt(ciphertext, shiftNum, letters) # Start the encrypt() function while passing 3 variables as parameters. if args.action == "decrypt": if shiftNum == "0": freq(ciphertext) else: decrypt(ciphertext, shiftNum, letters)