kryptos_c1_decoder

#!/usr/bin/env python3
# Filename: kryptos_c1_decoder.py
# Author: Jeoi Reqi
# Decoder for The Kryptos Ciphers C1

# Define the alphabet and key
ALPHABET = "KRYPTOSABCDEFGHIJLMNQUVWXZ"
KEY = "PALIMPSEST"


# Function for the vigenere cryptography
def vigenere_decoder(ciphertext, key, alphabet):
    """
    Decrypt a Vigenere cipher using the specified key and alphabet.

    Parameters:
    ciphertext (str): The text to decrypt.
    key (str): The key to use for decryption.
    alphabet (str): The alphabet to use for decryption.

    Returns:
    str: The decrypted plaintext.
    """
    # Convert the key and ciphertext to uppercase
    key = key.upper()
    ciphertext = ciphertext.upper()

    # Calculate the length of the key and ciphertext
    key_length = len(key)
    ciphertext_length = len(ciphertext)

    # Generate the repeated key
    repeated_key = ""
    for i in range(ciphertext_length):
        repeated_key += key[i % key_length]

    # Decrypt the ciphertext using the repeated key
    plaintext = ""
    for i in range(ciphertext_length):
        ciphertext_char = ciphertext[i]
        key_char = repeated_key[i]
        # Find the position of the key and ciphertext characters in the alphabet
        key_pos = alphabet.find(key_char)
        ciphertext_pos = alphabet.find(ciphertext_char)
        # Subtract the key position from the ciphertext position to get the plaintext position
        plaintext_pos = (ciphertext_pos - key_pos) % len(alphabet)
        # Get the plaintext character from the alphabet
        plaintext_char = alphabet[plaintext_pos]
        plaintext += plaintext_char

    return plaintext

# Decrypt the ciphertext using the given key and alphabet
ciphertext = "EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJYQTQUXQBQVYUVLLTREVJYQTMKYRDMFD"
key = "PALIMPSEST"
alphabet = "KRYPTOSABCDEFGHIJLMNQUVWXZ"
plaintext = vigenere_decoder(ciphertext, key, alphabet)

# Print the decrypted plaintext
print(plaintext)