AES算法中xtime的理解

用python寫了個函數來加深一下理解，代碼如下：

#!/usr/bin/env python3
#coding:utf-8
#by spwpun

def xtime(hexstr):
	num = int(hexstr,16)
	bs1 = bin(num)[2:]
	if len(bs1)!=8:
		bs1 = '0'*(8-len(bs1))+bs1
	num = (num<<1)%2**8
	if bs1[0]=='1':
		num = num^int("1B",16)
	return hex(num)[2:]

print(xtime("AE"))