from Crypto.Cipher import DES

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))