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@volpino volpino/decrypt.py
Created Apr 20, 2015

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import struct
import xtea
ciphertext = open("./ciphertext.bin").read()
def dec(word):
return struct.unpack("<I", word)[0]
def chunks(l, n):
for i in xrange(0, len(l), n):
yield l[i:i+n]
key = '#\x0f\xc7d^\x1c~\x02\xca\xe2^(\x9fB])'
rev_key = ""
for chunk in chunks(key, 4):
rev_key += chunk[::-1]
key = rev_key
iv = "796287ab2d7fef4f".decode('hex')
rev_ciphertext = ""
for chunk in chunks(ciphertext, 4):
rev_ciphertext += chunk[::-1]
c = xtea.new(key, mode=xtea.MODE_CBC, IV=iv)
plain = c.decrypt(rev_ciphertext)
rev_plain = ""
for chunk in chunks(plain, 4):
rev_plain += chunk[::-1]
print rev_plain
"""
XTEA-Cipher in Python (eXtended Tiny Encryption Algorithm)
XTEA is a blockcipher with 8 bytes blocksize and 16 bytes Keysize (128-Bit).
The algorithm is secure at 2014 with the recommend 64 rounds (32 cycles). This
implementation supports following modes of operation:
ECB, CBC, CFB, OFB, CTR
Example:
>>> from xtea import *
>>> key = " "*16 # Never use this
>>> text = "This is a text. "*8
>>> x = new(key, mode=MODE_OFB, IV="12345678")
>>> c = x.encrypt(text)
>>> c.encode("hex")
'fa66ec11b82e38bc77c14be093bb8aa0d7fe0fb9e6ec015
7a22d254fee43aea9a64c8dbb2c2b899f66800f264419c8e
8796ad8f94c7758b916428019d10573943324a9dcf60f883
1f0f925cd7215e5dd4f1334d9ee242d41ac02d0a64c49663
e5897bfd2450982379267e6cd7405b477ccc19d6c0d32e2f
887b76fe01d621a8d'
>>> text == x.decrypt(c)
True
"""
import struct
import binascii
import sys
import warnings
import types
MODE_ECB = 1
MODE_CBC = 2
MODE_CFB = 3
MODE_PGP = 4
MODE_OFB = 5
MODE_CTR = 6
MODE_CCM = 8 # Unofficial
block_size = 64
key_size = 128
def new(key, **kwargs):
"""Create an cipher object.
Keyword arguments
key -- the key for encrypting (and decrypting)
Other arguments:
mode -- Block cipher mode of operation (default MODE_ECB)
IV -- Initialisation vector (needed with CBC/CFB)
counter -- a callable counter (needed with CTR)
endian -- how to use struct (default "!" (big endian/network)) """
return XTEACipher(key, **kwargs)
################ XTEACipher class
class XTEACipher(object):
"""The cipher class
Functions:
encrypt -- encrypt data
decrypt -- decrypt data
_block -- splits the data in blocks (you may need padding)
Constants:
block_size = 8
Variables:
IV -- the initialisation vector (default None or "\00"*8)
conuter -- counter for CTR (default None)
"""
block_size = 8
IV = None
counter = None
def __init__(self, key, **kwargs):
"""Initiate the cipher
same arguments as for new."""
self.key = key
if len(key) != key_size/8: # Check key len
raise ValueError("Key must be 128 bit long")
keys = kwargs.keys() # arguments
if "mode" in keys: # check for mode
self.mode = kwargs["mode"] # read mode
else:
self.mode = MODE_ECB # if not given
if self.mode == MODE_PGP:
raise NotImplementedError("PGP-CFB is not implemented")
if "IV" in keys: # get iv
self.IV = kwargs["IV"]
if len(self.IV) != self.block_size: # iv len = blocksize
raise ValueError("IV must be 8 bytes long")
elif self.mode == MODE_CBC or self.mode == MODE_CFB: # cfb & cbc need iv
raise ValueError("CBC, CFB need an IV")
elif self.mode == MODE_OFB: # ofb nocne if not given = "\x00" * 16
self.IV = '\00\00\00\00\00\00\00\00'
if "counter" in keys: # ctr needs counter
self.counter = kwargs["counter"]
elif self.mode == MODE_CTR: # if ctr and counter not given
raise ValueError("CTR needs a counter")
if "rounds" in keys: # rounds to operate
self.rounds = kwargs["rounds"]
else:
self.rounds = 128
if "endian" in keys: # endian for struct str -> int -> str (byte order)
self.endian = kwargs["endian"]
else:
self.endian = "!" # default network/big endian
def encrypt(self, data):
"""Encrypt data.
Keyword arguments:
data -- the data (plaintext) to encrypt
On OFB, encrypt and decrypt is the same.
"""
#ECB
if self.mode == MODE_ECB:
if not len(data) % (self.block_size):
out = []
blocks=self._block(data)
for block in blocks:
out.append(_encrypt(self.key, block, self.rounds/2, self.endian))
return "".join(out)
else:
raise ValueError("Input string must be a multiple of blocksize in length")
#CBC
elif self.mode == MODE_CBC:
if not len(data) % (self.block_size):
out = [self.IV]
blocks=self._block(data)
for i in range(0, len(blocks)):
xored = xor_strings(blocks[i], out[i])
out.append(_encrypt(self.key,xored,self.rounds/2,self.endian))
return "".join(out[1:])
else:
raise ValueError("Input string must be a multiple of blocksize in length")
#OFB
elif self.mode == MODE_OFB:
return _crypt_ofb(self.key, data, self.IV, self.rounds/2)
#CFB
elif self.mode == MODE_CFB:
if not len(data) % self.block_size:
blocks = self._block(data)
out = []
fb = self.IV
for bn in blocks:
tx = _encrypt(self.key, fb, self.rounds/2, self.endian)
fb = xor_strings(bn, tx)
out.append(fb)
return "".join(out)
else:
raise ValueError("Input string must be a multiple of blocksize in length")
#CTR
elif self.mode == MODE_CTR:
l = (types.IntType, types.LongType, types.FloatType) # Typelist
blocks = self._block(data)
out = []
for block in blocks:
c = self.counter()
if type(c) in l:
warnings.warn(
"Numbers as counter-value is buggy and deprecated!",
DeprecationWarning)
n = stringToLong(block)
out.append(
_encrypt(
self.key,struct.pack(self.endian+'Q', n^c),
self.rounds/2, self.endian))
else:
n = block
out.append(
_encrypt(
self.key,
xor_strings(n, c),
self.rounds/2,
self.endian)
)
return "".join(out)
def decrypt(self, data):
"""Decrypt data.
Keyword arguments:
data -- the data (ciphertext) to decrypt.
On OFB, encrypt and decrypt is the same.
"""
#ECB
if self.mode == MODE_ECB:
if not (len(data) % self.block_size):
out = []
blocks=self._block(data)
for block in blocks:
out.append(_decrypt(self.key, block, self.rounds/2, self.endian))
return "".join(out)
else:
raise ValueError("Input string must be a multiple of blocksize in length")
#CBC
elif self.mode == MODE_CBC:
if not (len(data) % self.block_size):
out = []
blocks = self._block(data)
blocks = [self.IV]+blocks
for i in range(1, len(blocks)):
out.append(
xor_strings(
_decrypt(
self.key,blocks[i]
,self.rounds/2,
self.endian),
blocks[i-1])
)
return "".join(out)
#OFB
elif self.mode == MODE_OFB:
return _crypt_ofb(self.key, data, self.IV, self.rounds/2)
#CFB
elif self.mode == MODE_CFB:
if not len(data) % self.block_size:
blocks = self._block(data)
out = []
fb = self.IV
for block in blocks:
tx = _encrypt(self.key, fb, self.rounds/2, self.endian)
fb = block[:]
out.append(xor_strings(block,tx))
return "".join(out)
else:
raise ValueError("Input string must be a multiple of blocksize in length")
#CTR
elif self.mode == MODE_CTR:
l = (types.IntType, types.LongType, types.FloatType)
blocks = self._block(data)
out = []
for block in blocks:
c = self.counter()
if type(c) in l:
warnings.warn(
"Numbers as counter-value are buggy and deprecated!",
DeprecationWarning)
nc = struct.unpack(self.endian+"Q",_decrypt(self.key, block, self.rounds/2, self.endian))
try:
out.append(longToString(nc[0]^c))
except:
warnings.warn(
"Unable to decrypt this block, block is lost",
RuntimeWarning)
out.append("\00"*8)
else:
nc = _decrypt(self.key, block, self.rounds/2, self.endian)
out.append(xor_strings(nc, c))
return "".join(out)
def _block(self, s):
l = []
rest_size = len(s) % self.block_size
for i in range(len(s)/self.block_size):
l.append(s[i*self.block_size:((i+1)*self.block_size)])
if rest_size:
raise ValueError()
return l
################ CBCMAC class
class CBCMAC(object):
name = "xtea-cbcmac"
block_size = 64
digest_size = 8
"""Just a small implementation of the CBCMAC algorithm, based on XTEA."""
def __init__(self, key, string="", endian="!"):
warnings.warn("This is experimental!")
self.cipher = new(key, mode=MODE_CBC, IV="\00"*8, endian=endian)
self.text = string
self.key = key
@staticmethod
def new(key, string="", endian="!"):
return CBCMAC(key, string, endian)
def update(self, string):
self.text += string
def copy(self):
return CBCMAC.new(self.key, self.text, self.cipher.endian)
def digest(self):
return self.cipher.encrypt(self.text)[-8:]
def hexdigest(self):
return binascii.hexlify(self.digest())
################ Util functions: basic encrypt/decrypt, OFB, xor, stringToLong
"""
This are utilities only, use them only if you know what you do.
Functions:
_crypt_ofb -- Encrypt or decrypt data in OFB mode.
_encrypt -- Encrypt one single block of data.
_decrypt -- Decrypt one single block of data.
xor_strings -- xor to strings together.
stringToLong -- Convert any string to a number.
longToString --Convert some longs to string.
"""
def _crypt_ofb(key,data,iv='\00\00\00\00\00\00\00\00',n=64):
"""Encrypt or decrypt data in OFB mode.
Only use if you know what you do.
Keyword arguments:
key -- the key for encrypting (and decrypting)
data -- plain / ciphertext
iv -- initialisation vector (default "\x00"*8)
n -- cycles, more cycles -> more security (default 32)
"""
def keygen(key,iv,n):
while True:
iv = _encrypt(key,iv,n)
for k in iv:
yield ord(k)
xor = [ chr(x^y) for (x,y) in zip(map(ord,data),keygen(key,iv,n)) ]
return "".join(xor)
def _encrypt(key,block,n=64,endian="!"):
"""Encrypt one single block of data.
Only use if you know what to do.
Keyword arguments:
key -- the key for encrypting (and decrypting)
block -- one block plaintext
n -- cycles, one cycle is two rounds, more cycles
-> more security and slowness (default 32)
endian -- how struct will handle data (default "!" (big endian/network))
"""
v0,v1 = struct.unpack(endian+"2L",block)
k = struct.unpack(endian+"4L",key)
sum,delta,mask = 0L,0x9e3779b9L,0xffffffffL
for round in range(n):
v0 = (v0 + (((v1<<4 ^ v1>>5) + v1) ^ (sum + k[sum & 3]))) & mask
sum = (sum + delta) & mask
v1 = (v1 + (((v0<<4 ^ v0>>5) + v0) ^ (sum + k[sum>>11 & 3]))) & mask
return struct.pack(endian+"2L",v0,v1)
def _decrypt(key,block,n=64,endian="!"):
"""Decrypt one single block of data.
Only use if you know what to do.
Keyword arguments:
key -- the key for encrypting (and decrypting)
block -- one block ciphertext
n -- cycles, one cycle is two rounds, more cycles =
-> more security and slowness (default 32)
endian -- how struct will handle data (default "!" (big endian/network))
"""
v0,v1 = struct.unpack(endian+"2L",block)
k = struct.unpack(endian+"4L",key)
delta,mask = 0x9e3779b9L,0xffffffffL
sum = (delta * n) & mask
for round in range(n):
v1 = (v1 - (((v0<<4 ^ v0>>5) + v0) ^ (sum + k[sum>>11 & 3]))) & mask
sum = (sum - delta) & mask
v0 = (v0 - (((v1<<4 ^ v1>>5) + v1) ^ (sum + k[sum & 3]))) & mask
return struct.pack(endian+"2L",v0,v1)
def xor_strings(s,t):
"""xor to strings together.
Keyword arguments:
s -- string one
t -- string two
"""
return "".join(chr(ord(a)^ord(b)) for a,b in zip(s,t))
def stringToLong(s):
"""Convert any string to a number."""
return long(binascii.hexlify(s),16)
def longToString(n):
"""Convert some longs to string."""
return binascii.unhexlify("%x" % n)
c = 0 # Test (double global)
def _test():
global c
import os
from time import clock
print "Starting test..."
print "Testing ECB"
fails_ecb = 0
start = clock()
for i in range(250):
try:
plain = os.urandom(56)*8
e = new(os.urandom(16))
encrypted = e.encrypt(plain)
decrypted = e.decrypt(encrypted)
if decrypted != plain: fails_ecb += 1
except:
print >> sys.stderr, "Fail with Error..."
fails_ecb+=1
end = clock()
time_ecb = end - start
print "Testing CBC"
fails_cbc = 0
start = clock()
for i in range(250):
try:
key = os.urandom(16)
iv = os.urandom(8)
c1 = new(key, mode=MODE_CBC, IV=iv)
c2 = new(key, mode=MODE_CBC, IV=iv)
plain = os.urandom(56)*8
encrypted = c1.encrypt(plain)
decrypted = c2.decrypt(encrypted)
if decrypted != plain: fails_cbc+=1
except:
print >> sys.stderr, "Fail with Error..."
fails_cbc+=1
end = clock()
time_cbc = end - start
print "Testing CFB"
fails_cfb = 0
start = clock()
for i in range(250):
try:
key = os.urandom(16)
iv = os.urandom(8)
c1 = new(key, mode=MODE_CFB, IV=iv)
c2 = new(key, mode=MODE_CFB, IV=iv)
plain = os.urandom(56)*8
encrypted = c1.encrypt(plain)
decrypted = c2.decrypt(encrypted)
if decrypted != plain: fails_cfb+=1
except:
print >> sys.stderr, "Fail with Error..."
fails_cfb+=1
end = clock()
time_cfb = end - start
print "Testing OFB (function)"
fails_ofb = 0
start = clock()
for i in range(250):
try:
key = os.urandom(16)
plain = os.urandom(56)*8
encrypted = _crypt_ofb(key, plain)
decrypted = _crypt_ofb(key, encrypted)
if decrypted != plain:
fails_ofb+=1
except:
print >> sys.stderr, "Fail with Error..."
fails_ofb+=1
end = clock()
time_ofb = end - start
print "Testing CTR (old number-counter)"
fails_ctr = 0
def count():
global c
c += 1
return c
start = clock()
for i in range(250):
try:
key = os.urandom(16)
c_b = stringToLong(os.urandom(6))
c=c_b
cf = new(key, mode=MODE_CTR, counter=count)
plain = os.urandom(56)*8
encrypted = cf.encrypt(plain)
c=c_b
decrypted = cf.decrypt(encrypted)
if decrypted != plain:
fails_ctr+=1
except Warning:
pass
except DeprecationWarning:
print "Outdated test function..."
except Exception:
print >> sys.stderr, "Fail with Error..."
fails_ctr += 1
end = clock()
time_ctr = end - start
print
print
print "Result"
print "="*15
print
print
print "Fails:"
print
print "|ECB|CBC|CFB|OFB|CTR|"
print "|---|---|---|---|---|"
print "|%s|%s|%s|%s|%s|" % (
str(fails_ecb).rjust(3,"0"),
str(fails_cbc).rjust(3,"0"),
str(fails_cfb).rjust(3,"0"),
str(fails_ofb).rjust(3,"0"),
str(fails_ctr).rjust(3,"0"))
print
print "Time:"
print
print "ECB: %s\nCBC: %s\nCFB: %s\nOFB: %s\nCTR: %s\n" % (
str(time_ecb),
str(time_cbc),
str(time_cfb),
str(time_ofb),
str(time_ctr))
if __name__ == "__main__":
_test()
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