Breaks a message encrypted with Cape

break.py

enc = open('enc').read().split(',')
for i in xrange(len(enc)):
  enc[i] = int(enc[i][2:],16)
length = len(enc)-1

ALPHABET = '0.123456789[],\'positions:{}\n '

def all_choices_for(x):
  if len(x)>1:
    for i in x[0]:
      for j in list(all_choices_for(x[1:])):
        yield [i] + j
  elif len(x) ==1:
    for i in x[0]:
      yield [i]

for key_length in xrange(1,20):
  print "Trying key length",key_length
  for srk in xrange(256):
    key_options = []
    for i in xrange(key_length):
      key_options.append([])
      for option in xrange(256):
        if i == (length ^ srk) % key_length:
          if option != length ^ enc[-1]:
            continue
        good = True
        for j in xrange(length):
          if i == (srk^j) % key_length:
            dec = enc[j] ^ j ^ option
            if chr(dec) not in ALPHABET:
              good = False
        if not good:
          continue
        key_options[-1].append(chr(option))
      if key_options[-1] == []: break
    if 0 in map(len,key_options):
      continue
    if all(map(lambda x: len(x)<=2, key_options)):
      for key in all_choices_for(key_options):
        message= ''
        for i in xrange(length):
          message += chr(enc[i] ^ i ^ ord(key[(srk^i)%key_length]))
        print "Possible message:"
        print message