Edit File: AllOrNothing.py
# # AllOrNothing.py : all-or-nothing package transformations # # Part of the Python Cryptography Toolkit # # Written by Andrew M. Kuchling and others # # =================================================================== # The contents of this file are dedicated to the public domain. To # the extent that dedication to the public domain is not available, # everyone is granted a worldwide, perpetual, royalty-free, # non-exclusive license to exercise all rights associated with the # contents of this file for any purpose whatsoever. # No rights are reserved. # # 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. # =================================================================== """This file implements all-or-nothing package transformations. An all-or-nothing package transformation is one in which some text is transformed into message blocks, such that all blocks must be obtained before the reverse transformation can be applied. Thus, if any blocks are corrupted or lost, the original message cannot be reproduced. An all-or-nothing package transformation is not encryption, although a block cipher algorithm is used. The encryption key is randomly generated and is extractable from the message blocks. This class implements the All-Or-Nothing package transformation algorithm described in: Ronald L. Rivest. "All-Or-Nothing Encryption and The Package Transform" http://theory.lcs.mit.edu/~rivest/fusion.pdf """ __revision__ = "$Id$" import operator import sys from Crypto.Util.number import bytes_to_long, long_to_bytes from Crypto.Util.py3compat import * from functools import reduce def isInt(x): test = 0 try: test += x except TypeError: return 0 return 1 class AllOrNothing: """Class implementing the All-or-Nothing package transform. Methods for subclassing: _inventkey(key_size): Returns a randomly generated key. Subclasses can use this to implement better random key generating algorithms. The default algorithm is probably not very cryptographically secure. """ def __init__(self, ciphermodule, mode=None, IV=None): """AllOrNothing(ciphermodule, mode=None, IV=None) ciphermodule is a module implementing the cipher algorithm to use. It must provide the PEP272 interface. Note that the encryption key is randomly generated automatically when needed. Optional arguments mode and IV are passed directly through to the ciphermodule.new() method; they are the feedback mode and initialization vector to use. All three arguments must be the same for the object used to create the digest, and to undigest'ify the message blocks. """ self.__ciphermodule = ciphermodule self.__mode = mode self.__IV = IV self.__key_size = ciphermodule.key_size if not isInt(self.__key_size) or self.__key_size==0: self.__key_size = 16 __K0digit = bchr(0x69) def digest(self, text): """digest(text:string) : [string] Perform the All-or-Nothing package transform on the given string. Output is a list of message blocks describing the transformed text, where each block is a string of bit length equal to the ciphermodule's block_size. """ # generate a random session key and K0, the key used to encrypt the # hash blocks. Rivest calls this a fixed, publically-known encryption # key, but says nothing about the security implications of this key or # how to choose it. key = self._inventkey(self.__key_size) K0 = self.__K0digit * self.__key_size # we need two cipher objects here, one that is used to encrypt the # message blocks and one that is used to encrypt the hashes. The # former uses the randomly generated key, while the latter uses the # well-known key. mcipher = self.__newcipher(key) hcipher = self.__newcipher(K0) # Pad the text so that its length is a multiple of the cipher's # block_size. Pad with trailing spaces, which will be eliminated in # the undigest() step. block_size = self.__ciphermodule.block_size padbytes = block_size - (len(text) % block_size) text = text + b(' ') * padbytes # Run through the algorithm: # s: number of message blocks (size of text / block_size) # input sequence: m1, m2, ... ms # random key K' (`key' in the code) # Compute output sequence: m'1, m'2, ... m's' for s' = s + 1 # Let m'i = mi ^ E(K', i) for i = 1, 2, 3, ..., s # Let m's' = K' ^ h1 ^ h2 ^ ... hs # where hi = E(K0, m'i ^ i) for i = 1, 2, ... s # # The one complication I add is that the last message block is hard # coded to the number of padbytes added, so that these can be stripped # during the undigest() step s = divmod(len(text), block_size)[0] blocks = [] hashes = [] for i in range(1, s+1): start = (i-1) * block_size end = start + block_size mi = text[start:end] assert len(mi) == block_size cipherblock = mcipher.encrypt(long_to_bytes(i, block_size)) mticki = bytes_to_long(mi) ^ bytes_to_long(cipherblock) blocks.append(mticki) # calculate the hash block for this block hi = hcipher.encrypt(long_to_bytes(mticki ^ i, block_size)) hashes.append(bytes_to_long(hi)) # Add the padbytes length as a message block i = i + 1 cipherblock = mcipher.encrypt(long_to_bytes(i, block_size)) mticki = padbytes ^ bytes_to_long(cipherblock) blocks.append(mticki) # calculate this block's hash hi = hcipher.encrypt(long_to_bytes(mticki ^ i, block_size)) hashes.append(bytes_to_long(hi)) # Now calculate the last message block of the sequence 1..s'. This # will contain the random session key XOR'd with all the hash blocks, # so that for undigest(), once all the hash blocks are calculated, the # session key can be trivially extracted. Calculating all the hash # blocks requires that all the message blocks be received, thus the # All-or-Nothing algorithm succeeds. mtick_stick = bytes_to_long(key) ^ reduce(operator.xor, hashes) blocks.append(mtick_stick) # we convert the blocks to strings since in Python, byte sequences are # always represented as strings. This is more consistent with the # model that encryption and hash algorithms always operate on strings. return [long_to_bytes(i,self.__ciphermodule.block_size) for i in blocks] def undigest(self, blocks): """undigest(blocks : [string]) : string Perform the reverse package transformation on a list of message blocks. Note that the ciphermodule used for both transformations must be the same. blocks is a list of strings of bit length equal to the ciphermodule's block_size. """ # better have at least 2 blocks, for the padbytes package and the hash # block accumulator if len(blocks) < 2: raise ValueError("List must be at least length 2.") # blocks is a list of strings. We need to deal with them as long # integers blocks = list(map(bytes_to_long, blocks)) # Calculate the well-known key, to which the hash blocks are # encrypted, and create the hash cipher. K0 = self.__K0digit * self.__key_size hcipher = self.__newcipher(K0) block_size = self.__ciphermodule.block_size # Since we have all the blocks (or this method would have been called # prematurely), we can calculate all the hash blocks. hashes = [] for i in range(1, len(blocks)): mticki = blocks[i-1] ^ i hi = hcipher.encrypt(long_to_bytes(mticki, block_size)) hashes.append(bytes_to_long(hi)) # now we can calculate K' (key). remember the last block contains # m's' which we don't include here key = blocks[-1] ^ reduce(operator.xor, hashes) # and now we can create the cipher object mcipher = self.__newcipher(long_to_bytes(key, self.__key_size)) # And we can now decode the original message blocks parts = [] for i in range(1, len(blocks)): cipherblock = mcipher.encrypt(long_to_bytes(i, block_size)) mi = blocks[i-1] ^ bytes_to_long(cipherblock) parts.append(mi) # The last message block contains the number of pad bytes appended to # the original text string, such that its length was an even multiple # of the cipher's block_size. This number should be small enough that # the conversion from long integer to integer should never overflow padbytes = int(parts[-1]) text = b('').join(map(long_to_bytes, parts[:-1])) return text[:-padbytes] def _inventkey(self, key_size): # Return key_size random bytes from Crypto import Random return Random.new().read(key_size) def __newcipher(self, key): if self.__mode is None and self.__IV is None: return self.__ciphermodule.new(key) elif self.__IV is None: return self.__ciphermodule.new(key, self.__mode) else: return self.__ciphermodule.new(key, self.__mode, self.__IV) if __name__ == '__main__': import sys import getopt import base64 usagemsg = '''\ Test module usage: %(program)s [-c cipher] [-l] [-h] Where: --cipher module -c module Cipher module to use. Default: %(ciphermodule)s --aslong -l Print the encoded message blocks as long integers instead of base64 encoded strings --help -h Print this help message ''' ciphermodule = 'AES' aslong = 0 def usage(code, msg=None): if msg: print(msg) print(usagemsg % {'program': sys.argv[0], 'ciphermodule': ciphermodule}) sys.exit(code) try: opts, args = getopt.getopt(sys.argv[1:], 'c:l', ['cipher=', 'aslong']) except getopt.error as msg: usage(1, msg) if args: usage(1, 'Too many arguments') for opt, arg in opts: if opt in ('-h', '--help'): usage(0) elif opt in ('-c', '--cipher'): ciphermodule = arg elif opt in ('-l', '--aslong'): aslong = 1 # ugly hack to force __import__ to give us the end-path module module = __import__('Crypto.Cipher.'+ciphermodule, None, None, ['new']) x = AllOrNothing(module) print('Original text:\n==========') print(__doc__) print('==========') msgblocks = x.digest(b(__doc__)) print('message blocks:') for i, blk in zip(list(range(len(msgblocks))), msgblocks): # base64 adds a trailing newline print(' %3d' % i, end=' ') if aslong: print(bytes_to_long(blk)) else: print(base64.encodestring(blk)[:-1]) # # get a new undigest-only object so there's no leakage y = AllOrNothing(module) text = y.undigest(msgblocks) if text == b(__doc__): print('They match!') else: print('They differ!')