Script for checking SHA256 hash of first N chars on a MAC byte...

scanmac.py

#!/usr/bin/env /usr/bin/python

# Quick script to map a MAC byte (0x00-0xFF) to the first n chars of a sha256 
# hash to look for collisions.  However, I do not understand why we bother 
# hashing a single byte when it is trivial to reverse the hash -- it
# can't be for privacy or anonymization reasons, so why?

import hashlib

itoh = {}
htoi = {}
DEBUG = False


def loopHash(ix, hx):
    for h, i in htoi.iteritems():
        if h == hx and DEBUG == True:
            print "Collision: new key '{}' & prev key '{}' have same hash '{}'".format(ix, i, h)


def loopAll(charcheck):
    countCollisions = 0
    for x in range(0xFF):
        # Check all variants of the hash
        numxx = "%.2x" % x
        numXX = "%.2X" % x
        numxX = numXX[0].lower()+numXX[1]
        numXx = numXX[0]+numXX[1].lower()
        numx = '\%.2x' % x
        #print "{} or {} ({} or {})".format(numxx, numXX, numxX, numXx)
        # Hash all the things
        hashedxx = hashlib.sha256(numxx).hexdigest()
        hashedXX = hashlib.sha256(numXX).hexdigest()
        hashedxX = hashlib.sha256(numxX).hexdigest()
        hashedXx = hashlib.sha256(numXx).hexdigest()
        hashedx = hashlib.sha256(numx).hexdigest()
        # Assuming the first n chars are unique (maybe true for such a small subset)
        hxx = str(hashedxx)[:charcheck]
        if htoi.get(hxx, False):
            # We've added this hash before...
            loopHash(numxx, hxx)
            countCollisions = countCollisions+1
        else:
            itoh[numxx] = hxx
            htoi[hxx] = numxx
        # Hash of all caps, but don't add if 00 == 00 kinda thing...
        hXX = str(hashedXX)[:charcheck]
        if numxx != numXX:
            if htoi.get(hXX, False):
                loopHash(numXX, hXX)
                countCollisions = countCollisions+1
            else:
                itoh[numXX] = hXX
                htoi[hXX] = numXX
        # Hash of first char not capitalized, but second yes - but don't add if already added
        hxX = str(hashedxX)[:charcheck]
        if numxx != numxX and numXX != numxX:
            if htoi.get(hxX, False):
                loopHash(numxX, hxX)
                countCollisions = countCollisions+1
            else:
                itoh[numxX] = hxX
                htoi[hxX] = numxX
        # Hash of second char not capitalized, but first yes - but don't add if already added
        hXx = str(hashedXx)[:charcheck]
        if numxx != numXx and numXX != numXx:
            if htoi.get(hXx, False):
                loopHash(numXx, hXx)
                countCollisions = countCollisions+1
            else:
                itoh[numXx] = hXx
                htoi[numxX] = hxX
        # Hash of the number as a number
        hx = str(hashedx)[:charcheck]
        if htoi.get(hx, False):
            loopHash(numx, hx)
            countCollisions = countCollisions+1
        else:
            itoh[numx] = hx
            htoi[hx] = numx
    return countCollisions


def main():
    for count in range(10):
        x = loopAll(count+1)
        print "{} Collisions using first {} chars of sha256".format(x, count+1)
    if DEBUG:
        for (key, val) in itoh.iteritems():
            print "{} :\t{}".format(key, val)

if __name__ == "__main__":
    main()

Just a mental exercise...