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Diffstat (limited to 'frozen_deps/Crypto/Protocol/Chaffing.py')
| -rw-r--r-- | frozen_deps/Crypto/Protocol/Chaffing.py | 245 |
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diff --git a/frozen_deps/Crypto/Protocol/Chaffing.py b/frozen_deps/Crypto/Protocol/Chaffing.py deleted file mode 100644 index bbfcbda..0000000 --- a/frozen_deps/Crypto/Protocol/Chaffing.py +++ /dev/null @@ -1,245 +0,0 @@ -# -# 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 = list(range(self.__blocksper)) - for i, wheat in zip(list(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 = list(zip(list(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!') |