Xit/lib_xit.py

#!/usr/bin/python3

import os, re, sys, random, hashlib
import sys
from utils import Sha1File

useUrandom = True

def xorIterable(data):
    """ Xors the iterable data, each element againts all the others """

    def xorList(data):
        """ Computes [var0^var1^var2^... for (var0,var1,var2,...) in zip(*data)]
        It's more effecient this way instead of

        xoredData = bytearray()
        for d in zip(*data):
            acc = 0
            for byte in d: acc ^= byte
            xoredData.append(acc)

        or this way:

        xoredData = bytearray([functools.reduce(operator.xor,d) for d in zip(*data)])
        """

        assert(len(data)>1)
        variables = ["var"+str(i) for i in range(len(data))]
        expressionGauche = "^".join(variables)
        expressionDroite = "("+",".join(variables)+")"
        expression = "["+expressionGauche + " for " + expressionDroite
        #XNOR: expression = "[~("+expressionGauche + ")%256 for " + expressionDroite
        expression += " in zip(*data)]"
        return eval(expression)

    assert(len(data))
    xoredData = data[0] if len(data)==1 else xorList(data) # len=1 => xor([data]) == data
    return bytearray(xoredData)


def resizeData(dataIterable, size=None):
    """ Expands dataIterable elements so they reach the maximum length, truncate to size

    Size can be either smaller than the smallest data or bigger than the bigest data

    """

    if type(size) is int and size > 0:
        for data in dataIterable:
            del data[size:]
    lenMax = max([len(data) for data in dataIterable]+[size if size else 0])
    for data in dataIterable:
        lenData = len(data)
        for i in range(lenData, lenMax):
            data.append(data[i%lenData])


def xorData(inData, count, size):
    """ returns count random xored data from inData

    Example: len(inData) == 3 and count == 4
    So:
    clear = inData[0] XOR inData[1] XOR inData[2]
    xored = rand1, rand2, rand3, rand1 XOR rand2 XOR rand3 XOR clear
    return shuffle(xored)

    """
    if type(inData) is not list: inData = [inData]

    # resize data, all of them of the same size 
    resizeData(inData, size if type(size) is int else None)

    # From this point:
    # if size is min, then fine, data will be truncated
    # if size is max, then the looping was just made
    # if size is even (default), then the size were successfuly checked

    # Xors the input data
    if len(inData):
        clearContent = xorIterable(inData)
    elif type(size) is int: # No input data, thus generating random file
        clearContent = bytearray(getRandomBytes(size))
    else:
        raise Exception("No input file specified, use --size with an integer to build a random file.")


    # If more than one outputs, adds random data, so that
    # All of it is random, except the last one with the data
    outData = [bytearray(getRandomBytes(len(clearContent))) for _ in range(count-1)] \
            + [clearContent]

    # Xor the random data and the clear data and replaces the last element
    # containing the clear data by the result
    outData[-1] = xorIterable(outData)

    # Until now, all outs are kind of "keys" and the last one is "encrypted"
    # With shuffle, one won't tell the difference
    random.shuffle(outData)

    # Test
    #assert(xorIterable(inData)==clearContent)
    #assert(xorIterable(outData)==clearContent)

    return outData


def getRandomBytes(size):
    """ Returns random bytes

    The non urandom way is slower and uses Python getrandbits().
    """
    if useUrandom:
        return os.urandom(size)
    else:
        return random.getrandbits(size<<2).to_bytes(size, sys.byteorder)