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# Python Caeser Cipher Helper v1.0.2
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# Usage (encrypt): python3 caeser-cipher.py encrypt secretmessage
# Usage (decrypt): python3 caeser-cipher.py decrypt secretmessage
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import re # Import Regex tools
import string # Import string tools
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import collections # Import tools to sort letters.
from sys import argv # Import tool to process command line arguments.
#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
#print("\nUsage (encrypt): python3 caeser-cipher.py encrypt secretmessage")
#print("Usage (decrypt): python3 caeser-cipher.py decrypt secretmessage\n")
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 you would like to use (Just hit enter if you don ' t know the shift used): " ) # 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
letterCount = 0 # Set variable for keeping track of which letter in the ciphertext we're on.
letterPos = 0 # Set variable for keeping track of the letter's position in the alphabet.
answer = " " # The solution.
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commonletter = 0
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def encrypt ( ) :
# Grab global variables.
global ciphertext
global shiftNum
global letters
global letterCount
global letterPos
global answer
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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.
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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.
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.
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 ( " \n Your enciphered text is: " + answer )
def decrypt ( ) :
# Grab global variables.
global ciphertext
global shiftNum
global letters
global letterCount
global letterPos
global answer
global commonletter
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 ( " \n Your decrypted text is: " + answer )
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def freq ( ) :
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# Grab global variables.
global ciphertext
global commonletter
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global letterPos
global shiftNum
print ( shiftNum )
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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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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.)
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decrypt ( ) # Decrypt using the frequency found in here.
if action == " encrypt " :
encrypt ( )
if action == " decrypt " :
if shiftNum == " " :
freq ( )
else :
decrypt ( )