kryptos_c1_c2_decoder

#!/usr/bin/env python3
# Filename: kryptos_c1_c2_decoder.py
# Author: Jeoi Reqi
# Decoder for The Kryptos Ciphers C1 & C2


# 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.
    """
    plaintext = ''
    key_index = 0
    key_length = len(key)
    ciphertext_length = len(ciphertext)

    for i in range(ciphertext_length):
        if ciphertext[i] not in alphabet:
            plaintext += ciphertext[i]
            continue

        # Calculate the shift
        shift = alphabet.index(key[key_index])
        key_index = (key_index + 1) % key_length

        # Decrypt the character
        ciphertext_char = ciphertext[i]
        ciphertext_pos = alphabet.find(ciphertext_char)
        plaintext_pos = (ciphertext_pos - shift) % len(alphabet)
        plaintext += alphabet[plaintext_pos]

    return plaintext

# Test the combined function with the given ciphertexts and keys
ciphertext1 = "EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJYQTQUXQBQVYUVLLTREVJYQTMKYRDMFD"
key1 = "PALIMPSEST"
alphabet1 = "KRYPTOSABCDEFGHIJLMNQUVWXZ"
plaintext1 = vigenere_decoder(ciphertext1, key1, alphabet1)
print("Cipher 1:")
print(plaintext1)
print("\n\n")

ciphertext2 = "VFPJUDEEHZWETZYVGWHKKQETGFQJNCEGGWHKKDQMCPFQZDQMMIAGPFXHQRLGTIMVMZJANQLVKQEDAGDVFRPJUNGEUNAQZGZLECGYUXUEENJTBJLBQCRTBJDFHRRYIZETKZEMVDUFKSJHKFWHKUWQLSZFTIHHDDDUVH?DWKBFUFPWNTDFIYCUQZEREEVLDKFEZMOQQJLTTUGSYQPFEUNLAVIDXFLGGTEZ?FKZBSFDQVGOGIPUFXHHDRKFFHQNTGPUAECNUVPDJMQCLQUMUNEDFQELZZVRRGKFFVOEEXBDMVPNFQXEZLGREDNQFMPNZGLFLPMRJQYALMGNUVPDXVKPDQUMEBEDMHDAFMJGZNUPLGEWJLLAETG"
key2 = "ABSCISSA"
alphabet2 = "KRYPTOSABCDEFGHIJLMNQUVWXZ"
plaintext2 = vigenere_decoder(ciphertext2, key2, alphabet2)
print("Cipher 2:")

# Print the decrypted plaintext
print(plaintext2)
print("\n\n")