cipherdipher

ALPHABET = 'adbcefghijklmnopqrstuvwxyz0123456789!@#$%/.'


def caesar(message, key, mode):
  ciphertext = ''
  for character in message:

    index = ALPHABET.find(character)

    if index == -1:
      ciphertext += character
      continue

    if mode == 'encrypt':
      cipherIndex = (index + key) % len(ALPHABET)
    elif mode == 'decrypt':
      cipherIndex = (index - key) % len(ALPHABET)
    elif mode == 'alternate':
      mod = index % 2
      cipherIndex = (index - key[mod]) % len(ALPHABET)

    ciphertext += ALPHABET[cipherIndex]

  return ciphertext

#ciphertext = caesar('a plaintext message!', 30, 'encrypt')
#print(ciphertext)
# plaintext = caesar('Usw!s9 u07zw9 0! s @.7w 6x s !#t!@0@#@065 u07zw9 69 4656s37zstw@0u u07zw9 %zw9w w$w9. 3w@@w9 05 @zw 4w!!syw 0! 9w73suwv t. !64w 6@zw9 3w@@w9 x0/wv 5#4tw9 6x 76!0@065! v6%5 @zw s37zstw@r @zw 5#4tw9 6x !z0x@ 76!0@065! 0! @zw 2w.r', 18, 'decrypt')
plaintext = caesar('Usw!s9 u07zw9 0! s @.7w 6x s !#t!@0@#@065 u07zw9 69 4656s37zstw@0u u07zw9 %zw9w w$w9. 3w@@w9 05 @zw 4w!!syw 0! 9w73suwv t. !64w 6@zw9 3w@@w9 x0/wv 5#4tw9 6x 76!0@065! v6%5 @zw s37zstw@r @zw 5#4tw9 6x !z0x@ 76!0@065! 0! @zw 2w.r', [2, 3], 'alternate')
print(plaintext)