from Crypto.Cipher import DES
import binascii

IV = '13371337'

WEAK_KEYS = [
    '0101010101010101',
    'FEFEFEFEFEFEFEFE',
    'E0E0E0E0F1F1F1F1',
    '1F1F1F1F0E0E0E0E',
    '011F011F010E010E',
    '1F011F010E010E01',
    '01E001E001F101F1',
    'E001E001F101F101',
    '01FE01FE01FE01FE',
    'FE01FE01FE01FE01',
    '1FE01FE00EF10EF1',
    'E01FE01FF10EF10E',
    '1FFE1FFE0EFE0EFE',
    'FE1FFE1FFE0EFE0E',
    '01011F1F01010E0E',
    '1F1F01010E0E0101',
    'E0E01F1FF1F10E0E',
    '0101E0E00101F1F1',
    '1F1FE0E00E0EF1F1',
    'E0E0FEFEF1F1FEFE',
    '0101FEFE0101FEFE',
    '1F1FFEFE0E0EFEFE',
    'E0FE011FF1FE010E',
    '011F1F01010E0E01',
    '1FE001FE0EF101FE',
    'E0FE1F01F1FE0E01',
    '011FE0FE010EF1FE',
    '1FE0E01F0EF1F10E',
    'E0FEFEE0F1FEFEF1',
    '011FFEE0010EFEF1',
    '1FE0FE010EF1FE01',
    'FE0101FEFE0101FE',
    '01E01FFE01F10EFE',
    '1FFE01E00EFE01F1',
    'FE011FE0FE010EF1',
    'FE01E01FFE01F10E',
    '1FFEE0010EFEF101',
    'FE1F01E0FE0E01F1',
    '01E0E00101F1F101',
    '1FFEFE1F0EFEFE0E',
    'FE1FE001FE0EF101',
    '01E0FE1F01F1FE0E',
    'E00101E0F10101F1',
    'FE1F1FFEFE0E0EFE',
    '01FE1FE001FE0EF1',
    'E0011FFEF1010EFE',
    'FEE0011FFEF1010E',
    '01FEE01F01FEF10E',
    'E001FE1FF101FE0E',
    'FEE01F01FEF10E01',
    '01FEFE0101FEFE01',
    'E01F01FEF10E01FE',
    'FEE0E0FEFEF1F1FE',
    '1F01011F0E01010E',
    'E01F1FE0F10E0EF1',
    'FEFE0101FEFE0101',
    '1F01E0FE0E01F1FE',
    'E01FFE01F10EFE01',
    'FEFE1F1FFEFE0E0E',
    '1F01FEE00E01FEF1',
    'E0E00101F1F10101',
    'FEFEE0E0FEFEF1F1'
]
def getNibbleLength(offset):
    if str(offset)[0]=="9":
        return len(str(offset))+1
    return len(str(offset))

def duck(aChr):
    try:
        return int(aChr)
    except:
        return "abcdef".index(aChr)+11

def encodeText(plainText,offset):
    hexEncoded = plainText.encode("hex")
    nibbleLen = getNibbleLength(offset)
    output = ""
    for i in range(0,len(hexEncoded),2):
        hexByte = hexEncoded[i:i+2]
        try:
            output += str(duck(hexByte[0]) + offset).rjust(nibbleLen,"0")
            output += str(duck(hexByte[1]) + offset).rjust(nibbleLen,"0")
        except:
            continue
    return output

def decodeText(encoded,offset):
    nibbleLen = getNibbleLength(offset)
    output = ""
    for i in range(0, len(encoded), nibbleLen):
        chunk = encoded[i:i+nibbleLen]
        output += hex(int(chunk) - offset)[-1]
    return output.decode("hex")

def padInput(input):
    bS = len(input)/8
    if len(input)%8 != 0:
        return input.ljust((bS+1)*8,"_")
    return input

def desEncrypt(input,key):
    cipher = DES.new(key, DES.MODE_OFB, IV)
    msg = cipher.encrypt(padInput(input))
    return msg

def unpadInput(input):
    return input.rstrip('_')

def desDecrypt(input,key):
    cipher = DES.new(key, DES.MODE_OFB, IV)
    msg = cipher.decrypt(input)
    return unpadInput(msg)

def createKey(hex,fileName):
    with open(fileName, 'wb') as f:
        f.write(binascii.unhexlify(hex))

def createChallenge():
    createKey("INSERT_SOME_KEY","key1")
    createKey("SOME_OTHER_KEY","key2")

    plainText = open('FLAG.txt').read()
    key1 = open('key1').read()

    byte = desEncrypt(plainText,key1)
    key2 = open('key2').read()

    cipherText = desEncrypt(byte,key2)
    cipherText = encodeText(binascii.hexlify(cipherText),9133337)
    with open('FLAG.enc', 'w') as f:
        f.write(cipherText)

def findKeys(plaintext, ciphertext):
    for key1 in WEAK_KEYS:
        for key2 in WEAK_KEYS:
            if desDecrypt(desDecrypt(ciphertext, binascii.unhexlify(key1)), binascii.unhexlify(key2)) == plaintext:
                return [key1, key2]

key1, key2 = findKeys(open('DES2Bytes.txt').read(), binascii.unhexlify(decodeText(open('DES2Bytes.enc').read(),9133337)))
print desDecrypt(desDecrypt(binascii.unhexlify(decodeText(open('FLAG.enc').read(),9133337)), binascii.unhexlify(key1)), binascii.unhexlify(key2))