113 lines
5.4 KiB
Python
113 lines
5.4 KiB
Python
# Python Caeser Cipher Helper v1.0.1
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# Usage (encrypt): python3 caeser-cipher.py encrypt secretmessage
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# Usage (decrypt): python3 caeser-cipher.py decrypt secretmessage
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import re # Import Regex tools
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import string # Import string tools
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import collections # Import tools to sort letters.
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from sys import argv # Import tool to process command line arguments.
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#if action == "help": # If error, print help https://stackoverflow.com/questions/4042452/display-help-message-with-python-argparse-when-script-is-called-without-any-argu
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#print("\nUsage (encrypt): python3 caeser-cipher.py encrypt secretmessage")
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#print("Usage (decrypt): python3 caeser-cipher.py decrypt secretmessage\n")
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script, action, ciphertext = argv # Take command line input.
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#ciphertext = input("Please type in your cipher text:") # Set variable cipertext to the input from user.
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shiftNum = input("Please enter the shift used (Just hit enter if you don't know):") # Get input
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#action = input("Please enter encrypt or decrypt):") # Get input
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ciphertext = re.sub (r'([^a-zA-Z ]+?)', '', ciphertext) # Remove all non-letters.
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ciphertext = ciphertext.lower() # Make it all lowercase. https://www.geeksforgeeks.org/isupper-islower-lower-upper-python-applications/
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letters = list(string.ascii_lowercase) # Use a list of lowercase letters. https://stackoverflow.com/questions/43918437/how-to-iterate-through-the-alphabet
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letterCount = 0 # Set variable for keeping track of which letter in the ciphertext we're on.
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letterPos = 0 # Set variable for keeping track of the letter's position in the alphabet.
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answer = "" # The solution.
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commonletter = 0
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def encrypt():
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# Grab global variables.
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global ciphertext
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global shiftNum
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global letters
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global letterCount
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global letterPos
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global answer
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for c in ciphertext: # For every letter in the ciphertext
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while letterPos < 26: # While the letter's position in the alphabet is less than 26 (and thus valid), continue.
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if ciphertext[letterCount] == letters[letterPos]: # Match the letter in the ciphertext to a letter in the alphabet and once they match, continue.
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letter = int(letterPos) + int(shiftNum) # Take the position of the letter and the shift number and add them for the enciphered letter.
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if letter > 25: # If the enciphered letter's position is not valid because it is too high, fix it by rotating around the alphabet.
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letter = letter - 26
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if letter < 0:
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letter = letter + 26 # If the enciphered letter's position is not valid because it is too low, fix it by rotating around the alphabet.
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answer = answer + letters[letter] # Add letters together to get the enciphered text.
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letterPos = letterPos + 1 # Iterate through letter positions in the alphabet. (neccessary to find one that matches.)
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if letterPos > 25: # If the letter position is greater than 25, cycle back through the alphabet.
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letterPos = letterPos - 26
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letterCount = letterCount + 1 # Keep track of how many times we're doing this.
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print("\nYour enciphered text is: " + answer)
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def decrypt():
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# Grab global variables.
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global ciphertext
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global shiftNum
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global letters
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global letterCount
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global letterPos
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global answer
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global commonletter
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for c in ciphertext: # For every letter in the ciphertext
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while letterPos < 26: # While the letter's position in the alphabet is less than 26 (and thus valid), continue.
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if not commonletter == 0:
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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.
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shiftNum = letterPos - 4
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if ciphertext[letterCount] == letters[letterPos]: # Match the letter in the ciphertext to a letter in the alphabet and once they match, continue.
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letter = int(letterPos) - int(shiftNum) # Take the position of the letter and the shift number and add them for the enciphered letter.
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if letter > 25: # If the enciphered letter's position is not valid because it is too high, fix it by rotating around the alphabet.
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letter = letter - 26
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if letter < 0:
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letter = letter + 26 # If the enciphered letter's position is not valid because it is too low, fix it by rotating around the alphabet.
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answer = answer + letters[letter] # Add letters together to get the enciphered text.
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letterPos = letterPos + 1 # Iterate through letter positions in the alphabet. (neccessary to find one that matches.)
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if letterPos > 25: # If the letter position is greater than 25, cycle back through the alphabet.
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letterPos = letterPos - 26
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letterCount = letterCount + 1 # Keep track of how many times we're doing this.
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print("\nYour decrypted text is: " + answer)
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def freq():
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# Grab global variables.
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global ciphertext
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global commonletter
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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
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decrypt() # Decrypt using the frequency found in here.
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if action == "encrypt":
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encrypt()
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if action == "decrypt":
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if shiftNum == "":
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freq()
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else:
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decrypt()
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