Vigenère Cipher (Python)

Vigenere CIpher in Python

Previously I looked at the Vigenère cipher, but I did not have a working Python example. After some thought and consideration I came to the realisation that the Vigenère cipher is pretty much just a Caesar cipher with a shift that changes each letter, which then allowed me to figure out how to make it in Python.

geektechstuff_vigenere_cipher_1
Vigenere Cipher (Python)
Vigenere Cipher (Python)
Vigenere Cipher (Python)
geektechstuff_vigenere_cipher_3
Vigenere Cipher (Python)

#!/usr/bin/python3
# GeekTechStuff
“””
To find out more about the Vigenère Cipher please visit: https://geektechstuff.com/2019/12/25/vigenere-cipher/
“””
def vigenere_enc():
alphabet = “abcdefghijklmnopqrstuvwxyz”
input_string = “”
enc_key = “”
enc_string = “”
# Takes encrpytion key from user
enc_key = input(“Please enter encryption key: “)
enc_key = enc_key.lower()
# Takes string from user
input_string = input(“Please enter a string of text: “)
input_string = input_string.lower()
# Lengths of input_string
string_length = len(input_string)
# Expands the encryption key to make it longer than the inputted string
expanded_key = enc_key
expanded_key_length = len(expanded_key)
while expanded_key_length < string_length:
# Adds another repetition of the encryption key
expanded_key = expanded_key + enc_key
expanded_key_length = len(expanded_key)
key_position = 0
for letter in input_string:
if letter in alphabet:
# cycles through each letter to find it’s numeric position in the alphabet
position = alphabet.find(letter)
# moves along key and finds the characters value
key_character = expanded_key[key_position]
key_character_position = alphabet.find(key_character)
key_position = key_position + 1
# changes the original of the input string character
new_position = position + key_character_position
if new_position > 26:
new_position = new_position – 26
new_character = alphabet[new_position]
enc_string = enc_string + new_character
else:
enc_string = enc_string + letter
return(enc_string)
def vigenere_dec():
alphabet = “abcdefghijklmnopqrstuvwxyz”
input_string = “”
dec_key = “”
dec_string = “”
# Takes encrpytion key from user
dec_key = input(“Please enter encryption key: “)
dec_key = dec_key.lower()
# Takes string from user
input_string = input(“Please enter a string of text: “)
input_string = input_string.lower()
# Lengths of input_string
string_length = len(input_string)
# Expands the encryption key to make it longer than the inputted string
expanded_key = dec_key
expanded_key_length = len(expanded_key)
while expanded_key_length < string_length:
# Adds another repetition of the encryption key
expanded_key = expanded_key + dec_key
expanded_key_length = len(expanded_key)
key_position = 0
for letter in input_string:
if letter in alphabet:
# cycles through each letter to find it’s numeric position in the alphabet
position = alphabet.find(letter)
# moves along key and finds the characters value
key_character = expanded_key[key_position]
key_character_position = alphabet.find(key_character)
key_position = key_position + 1
# changes the original of the input string character
new_position = position – key_character_position
if new_position > 26:
new_position = new_position + 26
new_character = alphabet[new_position]
dec_string = dec_string + new_character
else:
dec_string = dec_string + letter
return(dec_string)
# Testing
print(vigenere_enc())
print(vigenere_dec())

I’ve uploaded the full Python program into my Python Encryption GitHub repository: https://github.com/geektechdude/Python_Encryption with file directly at: https://github.com/geektechdude/Python_Encryption/blob/master/geektechstuff_vigenere_cipher.py

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