xlentro.py

#!/usr/bin/python
import sys
import math
from sets import Set

# v 0.1

# Copyleft Thanat0s
# http://Thanat0s.trollprod.org
#
# Licence GNU GPL 


def shan(stin,pkey):
	fstList = list(stin) 
	falphabet = list(Set(fstList)) 
	ffreqList = []          
	for fsymbol in falphabet:
    		fctr = 0 
    		for fsym in fstList: 
        		if fsym == fsymbol: 
            			fctr += 1  
    		ffreqList.append(float(fctr) / len(fstList)) 
	fent = 0.0 
	for ffreq in ffreqList: 
    		fent = fent + ffreq * math.log(ffreq, 2) 
	fent = -fent  
	print 'KEYSIZE:', pkey,
	print 'BIT:',    
	print int(math.ceil(fent)),  
	print 'SE:',  
	print fent                       
	return fent

if len(sys.argv) != 2:
	print 'Find lenght of the xor key using shannon entropy'
	print 'To Use: '+ sys.argv[0]+  ' filename'
	sys.exit()
file = open(sys.argv[1], 'rb')
filename = sys.argv[1]
byteArr = bytearray(file.read())
file.close()
fileSize = len(byteArr)


maxkeylen=33
if fileSize < 33:
	maxkeylen=fileSize

for keylen in range (1,maxkeylen):
	index = 0
	st=''
	for byte in range( 0, fileSize / keylen ):
        	st = st + chr(byteArr[index]) 
		index = index + keylen	                   
	shan(st,keylen)