test.py

import itertools
from hashlib import md5

vig = "ABCDEFGHIJKLMNOPQRSTUVWXYZ{}"
plaintext = "SECCON{???????????????????????????????????}"
md5text = "f528a6ab914c1ecf856a1d93103948fe"
cipher = "LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ"
k = ["?"]*12

def vir(x, y):
    k = vig.find(x) - vig.find(y)
    return vig[k if k>=0 else len(vig)  + k]

for i, p in enumerate(plaintext):
    if p != '?':
        k[i%len(k)] = vir(cipher[i], p)

k[7] = 'E'
key = "".join(k).replace('?', '')

for k in itertools.product(vig, repeat=12-len(key)):
    kk = key + "".join(k)
    tp = [ vir(c, kk[i%len(kk)]) for i, c in enumerate(cipher) ]
    if md5("".join(tp)).hexdigest() == md5text:
        print "".join(tp)
        exit()