mirror of
https://github.com/Sneed-Group/Poodletooth-iLand
synced 2024-12-27 05:32:41 -06:00
245 lines
10 KiB
Python
245 lines
10 KiB
Python
#
|
|
# Chaffing.py : chaffing & winnowing support
|
|
#
|
|
# Part of the Python Cryptography Toolkit
|
|
#
|
|
# Written by Andrew M. Kuchling, Barry A. Warsaw, 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 the chaffing algorithm.
|
|
|
|
Winnowing and chaffing is a technique for enhancing privacy without requiring
|
|
strong encryption. In short, the technique takes a set of authenticated
|
|
message blocks (the wheat) and adds a number of chaff blocks which have
|
|
randomly chosen data and MAC fields. This means that to an adversary, the
|
|
chaff blocks look as valid as the wheat blocks, and so the authentication
|
|
would have to be performed on every block. By tailoring the number of chaff
|
|
blocks added to the message, the sender can make breaking the message
|
|
computationally infeasible. There are many other interesting properties of
|
|
the winnow/chaff technique.
|
|
|
|
For example, say Alice is sending a message to Bob. She packetizes the
|
|
message and performs an all-or-nothing transformation on the packets. Then
|
|
she authenticates each packet with a message authentication code (MAC). The
|
|
MAC is a hash of the data packet, and there is a secret key which she must
|
|
share with Bob (key distribution is an exercise left to the reader). She then
|
|
adds a serial number to each packet, and sends the packets to Bob.
|
|
|
|
Bob receives the packets, and using the shared secret authentication key,
|
|
authenticates the MACs for each packet. Those packets that have bad MACs are
|
|
simply discarded. The remainder are sorted by serial number, and passed
|
|
through the reverse all-or-nothing transform. The transform means that an
|
|
eavesdropper (say Eve) must acquire all the packets before any of the data can
|
|
be read. If even one packet is missing, the data is useless.
|
|
|
|
There's one twist: by adding chaff packets, Alice and Bob can make Eve's job
|
|
much harder, since Eve now has to break the shared secret key, or try every
|
|
combination of wheat and chaff packet to read any of the message. The cool
|
|
thing is that Bob doesn't need to add any additional code; the chaff packets
|
|
are already filtered out because their MACs don't match (in all likelihood --
|
|
since the data and MACs for the chaff packets are randomly chosen it is
|
|
possible, but very unlikely that a chaff MAC will match the chaff data). And
|
|
Alice need not even be the party adding the chaff! She could be completely
|
|
unaware that a third party, say Charles, is adding chaff packets to her
|
|
messages as they are transmitted.
|
|
|
|
For more information on winnowing and chaffing see this paper:
|
|
|
|
Ronald L. Rivest, "Chaffing and Winnowing: Confidentiality without Encryption"
|
|
http://theory.lcs.mit.edu/~rivest/chaffing.txt
|
|
|
|
"""
|
|
|
|
__revision__ = "$Id$"
|
|
|
|
from Crypto.Util.number import bytes_to_long
|
|
|
|
class Chaff:
|
|
"""Class implementing the chaff adding algorithm.
|
|
|
|
Methods for subclasses:
|
|
|
|
_randnum(size):
|
|
Returns a randomly generated number with a byte-length equal
|
|
to size. Subclasses can use this to implement better random
|
|
data and MAC generating algorithms. The default algorithm is
|
|
probably not very cryptographically secure. It is most
|
|
important that the chaff data does not contain any patterns
|
|
that can be used to discern it from wheat data without running
|
|
the MAC.
|
|
|
|
"""
|
|
|
|
def __init__(self, factor=1.0, blocksper=1):
|
|
"""Chaff(factor:float, blocksper:int)
|
|
|
|
factor is the number of message blocks to add chaff to,
|
|
expressed as a percentage between 0.0 and 1.0. blocksper is
|
|
the number of chaff blocks to include for each block being
|
|
chaffed. Thus the defaults add one chaff block to every
|
|
message block. By changing the defaults, you can adjust how
|
|
computationally difficult it could be for an adversary to
|
|
brute-force crack the message. The difficulty is expressed
|
|
as:
|
|
|
|
pow(blocksper, int(factor * number-of-blocks))
|
|
|
|
For ease of implementation, when factor < 1.0, only the first
|
|
int(factor*number-of-blocks) message blocks are chaffed.
|
|
"""
|
|
|
|
if not (0.0<=factor<=1.0):
|
|
raise ValueError, "'factor' must be between 0.0 and 1.0"
|
|
if blocksper < 0:
|
|
raise ValueError, "'blocksper' must be zero or more"
|
|
|
|
self.__factor = factor
|
|
self.__blocksper = blocksper
|
|
|
|
|
|
def chaff(self, blocks):
|
|
"""chaff( [(serial-number:int, data:string, MAC:string)] )
|
|
: [(int, string, string)]
|
|
|
|
Add chaff to message blocks. blocks is a list of 3-tuples of the
|
|
form (serial-number, data, MAC).
|
|
|
|
Chaff is created by choosing a random number of the same
|
|
byte-length as data, and another random number of the same
|
|
byte-length as MAC. The message block's serial number is
|
|
placed on the chaff block and all the packet's chaff blocks
|
|
are randomly interspersed with the single wheat block. This
|
|
method then returns a list of 3-tuples of the same form.
|
|
Chaffed blocks will contain multiple instances of 3-tuples
|
|
with the same serial number, but the only way to figure out
|
|
which blocks are wheat and which are chaff is to perform the
|
|
MAC hash and compare values.
|
|
"""
|
|
|
|
chaffedblocks = []
|
|
|
|
# count is the number of blocks to add chaff to. blocksper is the
|
|
# number of chaff blocks to add per message block that is being
|
|
# chaffed.
|
|
count = len(blocks) * self.__factor
|
|
blocksper = range(self.__blocksper)
|
|
for i, wheat in zip(range(len(blocks)), blocks):
|
|
# it shouldn't matter which of the n blocks we add chaff to, so for
|
|
# ease of implementation, we'll just add them to the first count
|
|
# blocks
|
|
if i < count:
|
|
serial, data, mac = wheat
|
|
datasize = len(data)
|
|
macsize = len(mac)
|
|
addwheat = 1
|
|
# add chaff to this block
|
|
for j in blocksper:
|
|
import sys
|
|
chaffdata = self._randnum(datasize)
|
|
chaffmac = self._randnum(macsize)
|
|
chaff = (serial, chaffdata, chaffmac)
|
|
# mix up the order, if the 5th bit is on then put the
|
|
# wheat on the list
|
|
if addwheat and bytes_to_long(self._randnum(16)) & 0x40:
|
|
chaffedblocks.append(wheat)
|
|
addwheat = 0
|
|
chaffedblocks.append(chaff)
|
|
if addwheat:
|
|
chaffedblocks.append(wheat)
|
|
else:
|
|
# just add the wheat
|
|
chaffedblocks.append(wheat)
|
|
return chaffedblocks
|
|
|
|
def _randnum(self, size):
|
|
from Crypto import Random
|
|
return Random.new().read(size)
|
|
|
|
|
|
if __name__ == '__main__':
|
|
text = """\
|
|
We hold these truths to be self-evident, that all men are created equal, that
|
|
they are endowed by their Creator with certain unalienable Rights, that among
|
|
these are Life, Liberty, and the pursuit of Happiness. That to secure these
|
|
rights, Governments are instituted among Men, deriving their just powers from
|
|
the consent of the governed. That whenever any Form of Government becomes
|
|
destructive of these ends, it is the Right of the People to alter or to
|
|
abolish it, and to institute new Government, laying its foundation on such
|
|
principles and organizing its powers in such form, as to them shall seem most
|
|
likely to effect their Safety and Happiness.
|
|
"""
|
|
print 'Original text:\n=========='
|
|
print text
|
|
print '=========='
|
|
|
|
# first transform the text into packets
|
|
blocks = [] ; size = 40
|
|
for i in range(0, len(text), size):
|
|
blocks.append( text[i:i+size] )
|
|
|
|
# now get MACs for all the text blocks. The key is obvious...
|
|
print 'Calculating MACs...'
|
|
from Crypto.Hash import HMAC, SHA
|
|
key = 'Jefferson'
|
|
macs = [HMAC.new(key, block, digestmod=SHA).digest()
|
|
for block in blocks]
|
|
|
|
assert len(blocks) == len(macs)
|
|
|
|
# put these into a form acceptable as input to the chaffing procedure
|
|
source = []
|
|
m = zip(range(len(blocks)), blocks, macs)
|
|
print m
|
|
for i, data, mac in m:
|
|
source.append((i, data, mac))
|
|
|
|
# now chaff these
|
|
print 'Adding chaff...'
|
|
c = Chaff(factor=0.5, blocksper=2)
|
|
chaffed = c.chaff(source)
|
|
|
|
from base64 import encodestring
|
|
|
|
# print the chaffed message blocks. meanwhile, separate the wheat from
|
|
# the chaff
|
|
|
|
wheat = []
|
|
print 'chaffed message blocks:'
|
|
for i, data, mac in chaffed:
|
|
# do the authentication
|
|
h = HMAC.new(key, data, digestmod=SHA)
|
|
pmac = h.digest()
|
|
if pmac == mac:
|
|
tag = '-->'
|
|
wheat.append(data)
|
|
else:
|
|
tag = ' '
|
|
# base64 adds a trailing newline
|
|
print tag, '%3d' % i, \
|
|
repr(data), encodestring(mac)[:-1]
|
|
|
|
# now decode the message packets and check it against the original text
|
|
print 'Undigesting wheat...'
|
|
# PY3K: This is meant to be text, do not change to bytes (data)
|
|
newtext = "".join(wheat)
|
|
if newtext == text:
|
|
print 'They match!'
|
|
else:
|
|
print 'They differ!'
|