kryptos_c2_decoder

#!/usr/bin/env python3
# Filename: kryptos_c2_decoder.py
# Author: Jeoi Reqi
# Decoder for The Kryptos Ciphers C2

# Function for the vigenere cryptography
def vigenere_decoder(ciphertext, key, alphabet):
    plaintext = ''
    key_index = 0
    for c in ciphertext:
        if c not in alphabet:
            plaintext += c
            continue
        shift = alphabet.index(key[key_index])
        ciphertext_index = alphabet.index(c)
        plaintext_index = (ciphertext_index - shift) % len(alphabet)
        plaintext += alphabet[plaintext_index]
        key_index = (key_index + 1) % len(key)
    return plaintext

ciphertext = "VFPJUDEEHZWETZYVGWHKKQETGFQJNCEGGWHKKDQMCPFQZDQMMIAGPFXHQRLGTIMVMZJANQLVKQEDAGDVFRPJUNGEUNAQZGZLECGYUXUEENJTBJLBQCRTBJDFHRRYIZETKZEMVDUFKSJHKFWHKUWQLSZFTIHHDDDUVH?DWKBFUFPWNTDFIYCUQZEREEVLDKFEZMOQQJLTTUGSYQPFEUNLAVIDXFLGGTEZ?FKZBSFDQVGOGIPUFXHHDRKFFHQNTGPUAECNUVPDJMQCLQUMUNEDFQELZZVRRGKFFVOEEXBDMVPNFQXEZLGREDNQFMPNZGLFLPMRJQYALMGNUVPDXVKPDQUMEBEDMHDAFMJGZNUPLGEWJLLAETG"
key = "ABSCISSA"
alphabet = "KRYPTOSABCDEFGHIJLMNQUVWXZ"

plaintext = vigenere_decoder(ciphertext, key, alphabet)

# Print the decrypted plaintext
print(plaintext)