# =============================================================================
# Copyright (c) 2008 Christophe Oosterlynck <christophe.oosterlynck_AT_gmail.com>
# & NXP ( Philippe Teuwen <philippe.teuwen_AT_nxp.com> )
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
# =============================================================================
from . import util
from . import padding
import collections
import sys
MODE_ECB = 1
MODE_CBC = 2
MODE_CFB = 3
MODE_OFB = 5
MODE_CTR = 6
MODE_XTS = 7
MODE_CMAC = 8
class BlockCipher():
""" Base class for all blockciphers
"""
key_error_message = "Wrong key size" #should be overwritten in child classes
def __init__(self,key,mode,IV,counter,cipher_module,segment_size,args={}):
# Cipher classes inheriting from this one take care of:
# self.blocksize
# self.cipher
self.key = key
self.mode = mode
self.cache = ''
self.ed = None
if 'keylen_valid' in dir(self): #wrappers for pycrypto functions don't have this function
if not self.keylen_valid(key) and type(key) is not tuple:
raise ValueError(self.key_error_message)
if IV == None:
self.IV = '\x00'*self.blocksize
else:
self.IV = IV
if mode != MODE_XTS:
self.cipher = cipher_module(self.key,**args)
if mode == MODE_ECB:
self.chain = ECB(self.cipher, self.blocksize)
elif mode == MODE_CBC:
if len(self.IV) != self.blocksize:
raise Exception("the IV length should be %i bytes"%self.blocksize)
self.chain = CBC(self.cipher, self.blocksize,self.IV)
elif mode == MODE_CFB:
if len(self.IV) != self.blocksize:
raise Exception("the IV length should be %i bytes"%self.blocksize)
if segment_size == None:
raise ValueError("segment size must be defined explicitely for CFB mode")
if segment_size > self.blocksize*8 or segment_size%8 != 0:
# current CFB implementation doesn't support bit level acces => segment_size should be multiple of bytes
raise ValueError("segment size should be a multiple of 8 bits between 8 and %i"%(self.blocksize*8))
self.chain = CFB(self.cipher, self.blocksize,self.IV,segment_size)
elif mode == MODE_OFB:
if len(self.IV) != self.blocksize:
raise ValueError("the IV length should be %i bytes"%self.blocksize)
self.chain = OFB(self.cipher, self.blocksize,self.IV)
elif mode == MODE_CTR:
if (counter == None) or not isinstance(counter, collections.Callable):
raise Exception("Supply a valid counter object for the CTR mode")
self.chain = CTR(self.cipher,self.blocksize,counter)
elif mode == MODE_XTS:
if self.blocksize != 16:
raise Exception('XTS only works with blockcipher that have a 128-bit blocksize')
if not(type(key) == tuple and len(key) == 2):
raise Exception('Supply two keys as a tuple when using XTS')
if 'keylen_valid' in dir(self): #wrappers for pycrypto functions don't have this function
if not self.keylen_valid(key[0]) or not self.keylen_valid(key[1]):
raise ValueError(self.key_error_message)
self.cipher = cipher_module(self.key[0],**args)
self.cipher2 = cipher_module(self.key[1],**args)
self.chain = XTS(self.cipher, self.cipher2)
elif mode == MODE_CMAC:
if self.blocksize not in (8,16):
raise Exception('CMAC only works with blockcipher that have a 64 or 128-bit blocksize')
self.chain = CMAC(self.cipher,self.blocksize,self.IV)
else:
raise Exception("Unknown chaining mode!")
def encrypt(self,plaintext,n=''):
"""Encrypt some plaintext
plaintext = a string of binary data
n = the 'tweak' value when the chaining mode is XTS
The encrypt function will encrypt the supplied plaintext.
The behavior varies slightly depending on the chaining mode.
ECB, CBC:
---------
When the supplied plaintext is not a multiple of the blocksize
of the cipher, then the remaining plaintext will be cached.
The next time the encrypt function is called with some plaintext,
the new plaintext will be concatenated to the cache and then
cache+plaintext will be encrypted.
CFB, OFB, CTR:
--------------
When the chaining mode allows the cipher to act as a stream cipher,
the encrypt function will always encrypt all of the supplied
plaintext immediately. No cache will be kept.
XTS:
----
Because the handling of the last two blocks is linked,
it needs the whole block of plaintext to be supplied at once.
Every encrypt function called on a XTS cipher will output
an encrypted block based on the current supplied plaintext block.
CMAC:
-----
Everytime the function is called, the hash from the input data is calculated.
No finalizing needed.
The hashlength is equal to block size of the used block cipher.
"""
#self.ed = 'e' if chain is encrypting, 'd' if decrypting,
# None if nothing happened with the chain yet
#assert self.ed in ('e',None)
# makes sure you don't encrypt with a cipher that has started decrypting
self.ed = 'e'
if self.mode == MODE_XTS:
# data sequence number (or 'tweak') has to be provided when in XTS mode
return self.chain.update(plaintext,'e',n)
else:
return self.chain.update(plaintext,'e')
def decrypt(self,ciphertext,n=''):
"""Decrypt some ciphertext
ciphertext = a string of binary data
n = the 'tweak' value when the chaining mode is XTS
The decrypt function will decrypt the supplied ciphertext.
The behavior varies slightly depending on the chaining mode.
ECB, CBC:
---------
When the supplied ciphertext is not a multiple of the blocksize
of the cipher, then the remaining ciphertext will be cached.
The next time the decrypt function is called with some ciphertext,
the new ciphertext will be concatenated to the cache and then
cache+ciphertext will be decrypted.
CFB, OFB, CTR:
--------------
When the chaining mode allows the cipher to act as a stream cipher,
the decrypt function will always decrypt all of the supplied
ciphertext immediately. No cache will be kept.
XTS:
----
Because the handling of the last two blocks is linked,
it needs the whole block of ciphertext to be supplied at once.
Every decrypt function called on a XTS cipher will output
a decrypted block based on the current supplied ciphertext block.
CMAC:
-----
Mode not supported for decryption as this does not make sense.
"""
#self.ed = 'e' if chain is encrypting, 'd' if decrypting,
# None if nothing happened with the chain yet
#assert self.ed in ('d',None)
# makes sure you don't decrypt with a cipher that has started encrypting
self.ed = 'd'
if self.mode == MODE_XTS:
# data sequence number (or 'tweak') has to be provided when in XTS mode
return self.chain.update(ciphertext,'d',n)
else:
return self.chain.update(ciphertext,'d')
def final(self,padfct=padding.PKCS7):
# TODO: after calling final, reset the IV? so the cipher is as good as new?
"""Finalizes the encryption by padding the cache
padfct = padding function
import from CryptoPlus.Util.padding
For ECB, CBC: the remaining bytes in the cache will be padded and
encrypted.
For OFB,CFB, CTR: an encrypted padding will be returned, making the
total outputed bytes since construction of the cipher
a multiple of the blocksize of that cipher.
If the cipher has been used for decryption, the final function won't do
anything. You have to manually unpad if necessary.
After finalization, the chain can still be used but the IV, counter etc
aren't reset but just continue as they were after the last step (finalization step).
"""
assert self.mode not in (MODE_XTS, MODE_CMAC) # finalizing (=padding) doesn't make sense when in XTS or CMAC mode
if self.ed == 'e':
# when the chain is in encryption mode, finalizing will pad the cache and encrypt this last block
if self.mode in (MODE_OFB,MODE_CFB,MODE_CTR):
dummy = '0'*(self.chain.totalbytes%self.blocksize) # a dummy string that will be used to get a valid padding
else: #ECB, CBC
dummy = self.chain.cache
pad = padfct(dummy,padding.PAD,self.blocksize)[len(dummy):] # construct the padding necessary
return self.chain.update(pad,'e') # supply the padding to the update function => chain cache will be "cache+padding"
else:
# final function doesn't make sense when decrypting => padding should be removed manually
pass
class ECB:
"""ECB chaining mode
"""
def __init__(self, codebook, blocksize):
if sys.version_info.major > 2:
self.cache = b''
else:
self.cache = ''
self.codebook = codebook
self.blocksize = blocksize
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any length
ed: 'e' for encryption, 'd' for decryption
Output:
processed raw string block(s), if any
When the supplied data is not a multiple of the blocksize
of the cipher, then the remaining input data will be cached.
The next time the update function is called with some data,
the new data will be concatenated to the cache and then
cache+data will be processed and full blocks will be outputted.
"""
output_blocks = []
self.cache += data
if len(self.cache) < self.blocksize:
return ''
for i in range(0, len(self.cache)-self.blocksize+1, self.blocksize):
#the only difference between encryption/decryption in the chain is the cipher block
if ed == 'e':
output_blocks.append(self.codebook.encrypt( self.cache[i:i + self.blocksize] ))
else:
output_blocks.append(self.codebook.decrypt( self.cache[i:i + self.blocksize] ))
self.cache = self.cache[i+self.blocksize:]
if sys.version_info.major < 3:
return ''.join(output_blocks)
else:
return output_blocks[0]
class CBC:
"""CBC chaining mode
"""
def __init__(self, codebook, blocksize, IV):
self.IV = IV
self.cache = ''
self.codebook = codebook
self.blocksize = blocksize
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any length
ed: 'e' for encryption, 'd' for decryption
Output:
processed raw string block(s), if any
When the supplied data is not a multiple of the blocksize
of the cipher, then the remaining input data will be cached.
The next time the update function is called with some data,
the new data will be concatenated to the cache and then
cache+data will be processed and full blocks will be outputted.
"""
if ed == 'e':
encrypted_blocks = ''
self.cache += data
if len(self.cache) < self.blocksize:
return ''
for i in range(0, len(self.cache)-self.blocksize+1, self.blocksize):
self.IV = self.codebook.encrypt(util.xorstring(self.cache[i:i+self.blocksize],self.IV))
encrypted_blocks += self.IV
self.cache = self.cache[i+self.blocksize:]
return encrypted_blocks
else:
decrypted_blocks = ''
self.cache += data
if len(self.cache) < self.blocksize:
return ''
for i in range(0, len(self.cache)-self.blocksize+1, self.blocksize):
plaintext = util.xorstring(self.IV,self.codebook.decrypt(self.cache[i:i + self.blocksize]))
self.IV = self.cache[i:i + self.blocksize]
decrypted_blocks+=plaintext
self.cache = self.cache[i+self.blocksize:]
return decrypted_blocks
class CFB:
# TODO: bit access instead of only byte level access
"""CFB Chaining Mode
Can be accessed as a stream cipher.
"""
def __init__(self, codebook, blocksize, IV,segment_size):
self.codebook = codebook
self.IV = IV
self.blocksize = blocksize
self.segment_size = segment_size/8
self.keystream = []
self.totalbytes = 0
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any multiple of bytes
ed: 'e' for encryption, 'd' for decryption
Output:
processed raw string
The encrypt/decrypt functions will always process all of the supplied
input data immediately. No cache will be kept.
"""
output = list(data)
for i in range(len(data)):
if ed =='e':
if len(self.keystream) == 0:
block = self.codebook.encrypt(self.IV)
self.keystream = list(block)[:self.segment_size] # keystream consists of the s MSB's
self.IV = self.IV[self.segment_size:] # keeping (b-s) LSB's
output[i] = chr(ord(output[i]) ^ ord(self.keystream.pop(0)))
self.IV += output[i] # the IV for the next block in the chain is being built byte per byte as the ciphertext flows in
else:
if len(self.keystream) == 0:
block = self.codebook.encrypt(self.IV)
self.keystream = list(block)[:self.segment_size]
self.IV = self.IV[self.segment_size:]
self.IV += output[i]
output[i] = chr(ord(output[i]) ^ ord(self.keystream.pop(0)))
self.totalbytes += len(output)
return ''.join(output)
class OFB:
"""OFB Chaining Mode
Can be accessed as a stream cipher.
"""
def __init__(self, codebook, blocksize, IV):
self.codebook = codebook
self.IV = IV
self.blocksize = blocksize
self.keystream = []
self.totalbytes = 0
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any multiple of bytes
ed: 'e' for encryption, 'd' for decryption
Output:
processed raw string
The encrypt/decrypt functions will always process all of the supplied
input data immediately. No cache will be kept.
"""
#no difference between encryption and decryption mode
n = len(data)
blocksize = self.blocksize
output = list(data)
for i in range(n):
if len(self.keystream) == 0: #encrypt a new counter block when the current keystream is fully used
self.IV = self.codebook.encrypt(self.IV)
self.keystream = list(self.IV)
output[i] = chr(ord(output[i]) ^ ord(self.keystream.pop(0))) #as long as an encrypted counter value is available, the output is just "input XOR keystream"
self.totalbytes += len(output)
return ''.join(output)
class CTR:
"""CTR Chaining Mode
Can be accessed as a stream cipher.
"""
# initial counter value can be choosen, decryption always starts from beginning
# -> you can start from anywhere yourself: just feed the cipher encoded blocks and feed a counter with the corresponding value
def __init__(self, codebook, blocksize, counter):
self.codebook = codebook
self.counter = counter
self.blocksize = blocksize
self.keystream = [] #holds the output of the current encrypted counter value
self.totalbytes = 0
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any multiple of bytes
ed: 'e' for encryption, 'd' for decryption
Output:
processed raw string
The encrypt/decrypt functions will always process all of the supplied
input data immediately. No cache will be kept.
"""
# no need for the encryption/decryption distinction: both are the same
n = len(data)
blocksize = self.blocksize
output = list(data)
for i in range(n):
if len(self.keystream) == 0: #encrypt a new counter block when the current keystream is fully used
block = self.codebook.encrypt(self.counter())
self.keystream = list(block)
output[i] = chr(ord(output[i])^ord(self.keystream.pop(0))) #as long as an encrypted counter value is available, the output is just "input XOR keystream"
self.totalbytes += len(output)
return ''.join(output)
class XTS:
"""XTS Chaining Mode
Usable with blockciphers with a 16-byte blocksize
"""
# TODO: allow other blocksizes besides 16bytes?
def __init__(self,codebook1, codebook2):
self.cache = ''
self.codebook1 = codebook1
self.codebook2 = codebook2
def update(self, data, ed,tweak=''):
# supply n as a raw string
# tweak = data sequence number
"""Perform a XTS encrypt/decrypt operation.
Because the handling of the last two blocks is linked,
it needs the whole block of ciphertext to be supplied at once.
Every decrypt function called on a XTS cipher will output
a decrypted block based on the current supplied ciphertext block.
"""
output = ''
assert len(data) > 15, "At least one block of 128 bits needs to be supplied"
assert len(data) < 128*pow(2,20)
# initializing T
# e_k2_n = E_K2(tweak)
e_k2_n = self.codebook2.encrypt(tweak+ '\x00' * (16-len(tweak)))[::-1]
self.T = util.string2number(e_k2_n)
i=0
while i < ((len(data) // 16)-1): #Decrypt all the blocks but one last full block and opt one last partial block
# C = E_K1(P xor T) xor T
output += self.__xts_step(ed,data[i*16:(i+1)*16],self.T)
# T = E_K2(n) mul (a pow i)
self.__T_update()
i+=1
# Check if the data supplied is a multiple of 16 bytes -> one last full block and we're done
if len(data[i*16:]) == 16:
# C = E_K1(P xor T) xor T
output += self.__xts_step(ed,data[i*16:(i+1)*16],self.T)
# T = E_K2(n) mul (a pow i)
self.__T_update()
else:
T_temp = [self.T]
self.__T_update()
T_temp.append(self.T)
if ed=='d':
# Permutation of the last two indexes
T_temp.reverse()
# Decrypt/Encrypt the last two blocks when data is not a multiple of 16 bytes
Cm1 = data[i*16:(i+1)*16]
Cm = data[(i+1)*16:]
PP = self.__xts_step(ed,Cm1,T_temp[0])
Cp = PP[len(Cm):]
Pm = PP[:len(Cm)]
CC = Cm+Cp
Pm1 = self.__xts_step(ed,CC,T_temp[1])
output += Pm1 + Pm
return output
def __xts_step(self,ed,tocrypt,T):
T_string = util.number2string_N(T,16)[::-1]
# C = E_K1(P xor T) xor T
if ed == 'd':
return util.xorstring(T_string, self.codebook1.decrypt(util.xorstring(T_string, tocrypt)))
else:
return util.xorstring(T_string, self.codebook1.encrypt(util.xorstring(T_string, tocrypt)))
def __T_update(self):
# Used for calculating T for a certain step using the T value from the previous step
self.T = self.T << 1
# if (Cout)
if self.T >> (8*16):
#T[0] ^= GF_128_FDBK;
self.T = self.T ^ 0x100000000000000000000000000000087
class CMAC:
"""CMAC chaining mode
Supports every cipher with a blocksize available
in the list CMAC.supported_blocksizes.
The hashlength is equal to block size of the used block cipher.
Usable with blockciphers with a 8 or 16-byte blocksize
"""
# TODO: move to hash module?
# TODO: change update behaviour to .update() and .digest() as for all hash modules?
# -> other hash functions in pycrypto: calling update, concatenates current input with previous input and hashes everything
__Rb_dictionary = {64:0x000000000000001b,128:0x00000000000000000000000000000087}
supported_blocksizes = list(__Rb_dictionary.keys())
def __init__(self,codebook,blocksize,IV):
# Purpose of init: calculate Lu & Lu2
#blocksize (in bytes): to select the Rb constant in the dictionary
#Rb as a dictionary: adding support for other blocksizes is easy
self.cache=''
self.blocksize = blocksize
self.codebook = codebook
self.IV = IV
#Rb_dictionary: holds values for Rb for different blocksizes
# values for 64 and 128 bits found here: http://www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html
# explanation from: http://csrc.nist.gov/publications/nistpubs/800-38B/SP_800-38B.pdf
# Rb is a representation of a certain irreducible binary polynomial of degree b, namely,
# the lexicographically first among all such polynomials with the minimum possible number of
# nonzero terms. If this polynomial is expressed as ub+cb-1ub-1+...+c2u2+c1u+c0, where the
# coefficients cb-1, cb-2, ..., c2, c1, c0 are either 0 or 1, then Rb is the bit string cb-1cb-2...c2c1c0.
self.Rb = self.__Rb_dictionary[blocksize*8]
mask1 = int(('\xff'*blocksize).encode('hex'),16)
mask2 = int(('\x80' + '\x00'*(blocksize-1) ).encode('hex'),16)
L = int(self.codebook.encrypt('\x00'*blocksize).encode('hex'),16)
if L & mask2:
Lu = ((L << 1) & mask1) ^ self.Rb
else:
Lu = L << 1
Lu = Lu & mask1
if Lu & mask2:
Lu2 = ((Lu << 1) & mask1)^ self.Rb
else:
Lu2 = Lu << 1
Lu2 = Lu2 & mask1
self.Lu =util.number2string_N(Lu,self.blocksize)
self.Lu2=util.number2string_N(Lu2,self.blocksize)
def update(self, data, ed):
"""Processes the given ciphertext/plaintext
Inputs:
data: raw string of any length
ed: 'e' for encryption, 'd' for decryption
Output:
hashed data as raw string
This is not really an update function:
Everytime the function is called, the hash from the input data is calculated.
No finalizing needed.
"""
assert ed == 'e'
blocksize = self.blocksize
m = (len(data)+blocksize-1)/blocksize #m = amount of datablocks
i=0
for i in range(1,m):
self.IV = self.codebook.encrypt( util.xorstring(data[(i-1)*blocksize:(i)*blocksize],self.IV) )
if len(data[(i)*blocksize:])==blocksize:
X = util.xorstring(util.xorstring(data[(i)*blocksize:],self.IV),self.Lu)
else:
tmp = data[(i)*blocksize:] + '\x80' + '\x00'*(blocksize - len(data[(i)*blocksize:])-1)
X = util.xorstring(util.xorstring(tmp,self.IV),self.Lu2)
T = self.codebook.encrypt(X)
return T