rotating vigenere decoder for adversary group

rotating_vigenere_decoder.py

from itertools import count
from string import ascii_letters

_cidx = dict(zip(ascii_letters, count(1)))

def decipher(key,enc,rot):
  """ 
  Deciphers Vigenere cipher with the given key and rotated alphabet

  Parameters: 
    key (str): Encryption key
    enc (str): Encrypted text
    rot (int): how many steps to rotate the alphabet
  
  Returns: 
    str: Decrypted text
  """

  i = 0
  ret = ''
  _dc = lambda c : ascii_letters[(_cidx[c] - _cidx[key[i%len(key)]] + rot)%26]
  _dc_case = lambda c : _dc(c) if c.islower() else _dc(c).upper()
  _dc_any = lambda c : c if not c.isalpha() else _dc_case(c)
  for c in enc:
    ret += _dc_any(c)
    if c.isalpha(): i += 1
  return ret

if __name__ == "__main__":
  encrypted = """
Tkz sedy icgjch uou omdw
hu mr jyzj bauerhgkhj tfdik'y xniddp uw eebu.
-Ymuggj Cxjwiqaa.
Qhat qpk pz ddacubd lp pt rgzgtfc uk olisg pwoxoezaks lpc.

Ofu euenf gvyktb dq jva.
Nexq hufw te qwzuittb mk iyw.
Mdsk dhh mfloz amqp.
Sagaa dzri urrx iw ounno xrlcb.
Kbqi iwfbwbz yhu, syovcbv ewv vte.
Jatlag ipl ez xrj dxin wiyy.
Ig uxkw nuh jt bxyg lyxy.
Szpzy og yty qcaw blvtjx.
Fe, Eys fei jhy hvpaq krpq?
"""

  key = "AdversaryGroup"

  for ln,encline in enumerate(encrypted.split("\n")):
    print ln,decipher(key,encline,ln-1)